A new species of Maomingosuchus from the Eocene of the Na Duong Basin (northern Vietnam) sheds new light on the phylogenetic relationship of tomistomine crocodylians and their dispersal from Europe to Asia

Maomingosuchus acutirostris sp. nov. is a new tomistomine crocodile from the middle–upper Eocene deposits (late Bartonian–Priabonian age, 39–35 Ma) of the Na Duong Basin in northern Vietnam. M. acutirostris can be differentiated from the type species Maomingosuchus petrolicus by having an acute anterior tip of the premaxilla. Both species differ from another Maomingosuchus from Krabi (Thailand) by differences in the surangular–dentary suture and maxillary alveoli. According to our phylogenetic results, M. acutirostris seems to be the sister species to the group M. petrolicus + Krabi-Maomingosuchus. The close relationship between those three tomistomines is supported in the present phylogenetic analysis by three synapomorphies. In our phylogenetic analysis, Maomingosuchus was retrieved in a basal position forming the sister group to Paratomistoma + Gavialosuchus + Melitosaurus + Tomistoma, including the extant Tomistoma schlegelii. This phylogeny indicates three different dispersal events of Tomistominae from Europe towards eastern Asia: 1) for the stem lineage of Maomingosuchus, no later than the late Eocene; 2) for the stem lineage of Penghusuchus pani + Toyotamaphimeia machikanensis, no later than the early–middle Miocene; and (3) for the stem lineage of T. schlegelii, during the Neogene. http://zoobank.org/urn:lsid:zoobank.org:pub:19B27C1E-0A3F-4425-AA8C-F904277DF327

Maomingosuchus petrolicus (Yeh, 1958) was described based on a fragmentary skull. Later, a partially preserved individual was described by Li (1975), based on new material from the Youganwo Formation of the Maoming Basin; Shan et al. (2017) later provided a re-description of this material. Recently, another Maomingosuchus from Wai-Lek, Krabi Province, Thailand was described by Martin et al. (2019). Unfortunately, this specimen is poorly preserved and was provisionally referred to as Krabi-Maomingosuchus sp., but it might represent a distinct species.
In this study, we describe a new almost complete species of Maomingosuchus, which was excavated in the Na Duong Basin in northern Vietnam in 2011 (B€ ohme et al. 2013) and prepared at the laboratory of the Geological-Palaeontological Institute of the Eberhard Karls University of T€ ubingen (GPIT). The new species allows novel insights into the anatomy of Maomingosuchus. We incorporated these new data in an expanded phylogenetic analysis of Tomistominae, retrieving a more basal position for Maomingosuchus than previously suggested (Shan et al. 2017;Iijima et al. 2018;Martin et al. 2019;Nicholl et al. 2020).

Geological setting
The Na Duong Basin is located in northern Vietnam near the Chinese border (Fig. 1). It represents one of the few areas in eastern and south-eastern Asia with a complete sequence of continental sediments from the middle Eocene-lower Oligocene (B€ ohme et al. 2013). The basin is part of the Cao Bang-Tien Yen fault system and covers an area of 45 km 2 . The middle-upper Eocene (late Bartonian-Priabonian, 39-35 Ma) Na Duong Formation is 240 m thick with the upper 140 m of the section being exposed in the Na Duong open cast coal mine.
The tomistomine remains described in this study were found within the transition zone between the coaly shale of the main seam and the underlying dark-brown claystone (layer 80).
The sediments of layer 80 are lacustrine lignitic shales and were deposited during a time of tropical to warm sub-tropical climate. During this time, this region was in a transitional stage from an environment characterized by shallow ponds to a large anoxic lake environment (B€ ohme et al. 2013;Garbin et al. 2019). The ecosystem yielded both aquatic and terrestrial faunal elements. The new tomistomine Maomingosuchus acutirostris occurred sympatrically with Orientalosuchus naduongensis Massonne, Vasilyan, Rabi & B€ ohme, 2019, members of Cetartiodactyla and Perissodactyla, many fish and two turtle species (B€ ohme et al. 2013;Garbin et al. 2019). While the majority of aquatic specimens were found articulated, the terrestrial mammals were preserved disarticulated (Garbin et al. 2019).

Materials and methods
All of the herein described material belongs to one individual GPIT-PV-31657, which was found at the base of layer 80 (sensu B€ ohme et al. 2011) in the Na Duong coal mine. The bones were disarticulated and dispersed over a small area of around 4 m 2 . Since all of the bones were found in close proximity, and are of the same general size with no duplication of elements, it is clear that GPIT-PV-31657 represents a single individual. The material consists of a skull with articulated mandibles as well as the almost complete disarticulated postcranial material. The skull is dorsolaterally compressed, so the ventral and occipital regions are poorly preserved. The disarticulated vertebral column consists of the proatlas, seven cervical, 12 dorsal, two sacral and 15 caudal vertebrae, as well as multiple chevrons. Of the ribs, a single atlantal rib, seven cervical ribs and nine dorsal ribs are preserved. Both scapulae and coracoids are also preserved as well as both humeri and a single ulna, while the radius, the metacarpals and the manual phalanges are missing. Also preserved are both ilia, ischia and pubes, both femora, a single tibia and fibula, as well as four metatarsals, whereas all pedal phalanges are missing. Osteoderms from the dorsal and lateral body sections were found in large numbers.
For our phylogenetic analysis we used the dataset of Nicholl et al. (2020) (see Supplemental material S1), which was the most recent dataset focusing mainly on the relationships of tomistomines. Their dataset is mainly based on Jouve (2016), which is derived from multiple previous datasets including Brochu (1999) and Jouve et al. (2015). The focus of our updated phylogeny is to clarify the relationships of Maomingosuchus within the family Tomistominae. The species Maomingosuchus acutirostris sp. nov. as well as the Krabi-Maomingosuchus (Martin et al. 2019) were added to the dataset that now consists of 72 taxa and 244 characters. Bernissartia fagesii Dollo, 1883 was used as the outgroup taxon. For the analysis, we followed Nicholl et al. (2020) and retained the 31 ordered characters from that analysis (characters 7, 30, 37, 62, 64, 75, 78, 81, 87, 91, 95, 103, 124, 131, 145, 151, 152, 153, 156, 161, 169, 171, 173, 174, 176, 177, 179, 194, 195, 206, 238). For M. acutirostris we scored 111 characters (see dataset in Supplemental material S1). Character scorings were modified for Maomingosuchus petrolicus and the Krabi-Maomingosuchus (a complete list of changes and the list of specimens are in Supplemental material S2, while the list of characters is in Supplemental material S3).
We conducted a maximum parsimony analysis as a 'traditional' search in TNT v. 1.5 standard version updated on 31 March 2021 (Goloboff & Catalano 2016). We treated the multistate characters as ordered (see above) and equally weighted; set the maximum of trees to 99,999 and the tree replications to 1000. For the branch swapping algorithm, we used tree bisection reconnection with 10 trees saved per replication. A first run of heuristic search tree-bisection-reconnection failed to find all the most parsimonious trees (MPT) and, therefore, the heuristic search was repeated until the MPTs were found 50 times during each replicate (using the command 'xmult ¼ hits 50;'), as in Massonne et al. (2019). The trees retained in the memory were exposed to a second round of tree-bisection-reconnection.
We also conducted a 'New Technology' search due to the large dataset (Goloboff et al. 2008). The random addition sequence was set to 1000. For the search algorithm, sectorial search, ratchet and tree fusing were used. For sectorial search in the RSS settings, the maximal sector size was set to 36, representing half of the taxa in the dataset, in the CSS settings the rounds were set to 100 and the minimal sector size to five, and for the XSS settings the number of rounds was set to 10. In the ratchet settings the total number of iterations was set to 100, for tree fusing the rounds were set to 100. All other options were left as default. After the first round, we conducted a second round of new technology search with the trees saved from ram. Sectoral search was disabled, and we changed the number of iterations in the ratchet settings to 1000 and the tree fusing to 1000 rounds. The result was filtered for sub-optimal trees and the analysis was run again until the number of found trees did not change further. Emended genus diagnosis. Maomingosuchus is diagnosed by the unique combination of the following characters: 1) distinct dorsoventrally extending ridges on the lateral and mesial surfaces of the anterior teeth (shared with an indeterminate tomistomine from the Ikovo locality and some non-tomistomine taxa); 2) presence of a frontal fossa between the orbits, close to the posterior end of the prefrontals (shared with 'Crocodylus' affinis Marsh, 1871 and Prodiplocynodon langi Mook, 1941); 3) a flat frontal margin between the orbits (shared with Dollosuchoides). Only preserved in Maomingosuchus acutirostris and Maomingosuchus petrolicus are: 4) perforations for the first dentary tooth anterior to the external naris (shared with Kentisuchus spenceri [Buckland, 1836]); 5) 15 maxillary teeth in total (shared with Dollosuchoides); and (6) exoccipital with ventrally projecting lamina hiding the entrance to the cranio-quadrate passage (shared with gharials and basal eusuchians).

Maomingosuchus acutirostris sp. nov. (Figs 2-14)
Diagnosis. M. acutirostris is a medium-sized tomistomine with a skull length (premaxilla-supraoccipital) of 546 mm and an estimated total length of around 3.5 m based on the skull to body length ratio of extant Tomistoma schlegelii (1:6.4 according to Whitaker & Whitaker 2008), which presumably has similar body proportions. It can be diagnosed by the combination of the following characters: 1) relatively robust teeth, especially the 5th maxillary tooth and the 11th or 12th dentary teeth (similar to Maroccosuchus); 2) anterior part of the prefrontal on the same level as anterior part of the frontal (shared with the Krabi-Maomingosuchus, some individuals of Maomingosuchus petrolicus and Gavialosuchus eggenburgensis [Toula & Kail, 1885]); 3) supraoccipital visible on dorsal skull table (shared with 'Tomistoma' cairense, 'Tomistoma' coppense, Paratomistoma and M. petrolicus); 4) atlantal rib with process on dorsal margin (shared with Toyotamaphimeia and some non-tomistomines); and 5) ilium with a prominent anterior process (shared with Penghusuchus and Toyotamaphimeia).
Beside the characters mentioned above, M. acutirostris can be further differentiated from M. petrolicus by: having an elongated premaxilla, anterior to the external naris; a ratio of the mediolateral width of the supratemporal fenestral bar to the width of the skull table at the same level of 0.100-0.175, and a ratio of the anteroposterior length of supratemporal fenestra to the anteroposterior length of the orbit >0.75.
Both M. acutirostris and M. petrolicus can be differentiated from the Krabi-Maomingosuchus by: having the first five maxillary teeth getting continuously larger posteriorly; the 7th and 8th maxillary teeth more widely spaced than other teeth; a ratio of the anteroposterior length of the supratemporal fenestra to the anteroposterior length of the orbit >0.75 and a surangular-dentary suture intersecting the external mandibular fenestra anterior to its posterior corner.
Etymology. The species name derives from the Latin word acutus for 'acute' and rostrum for 'snout' and refers to the elongated acute premaxilla anterior to the external naris, which stands in a marked contrast to the short and rounded premaxilla of M. petrolicus.
Holotype. GPIT-PV-31657, partial skeleton consisting of the complete skull, lower jaw and incomplete postcranial material (see Supplemental material S4 for a complete list of the material).
Type locality and horizon. The fossil was recovered from layer 80 of the Na Duong coal mine (B€ ohme et al. 2013)  closely related to M. petrolicus, but with three autapomorphies distinguishing it from the other maomingosuchids: 1) a surangular-dentary suture that intersects the external mandibular fenestra at its posterior corner (character [ch.] 65-1); 2) from the 1st to the 10th maxillary alveolus only one tooth larger, the others being of nearly same size (ch. 203-1); and 3) maxillary teeth widely spaced and the 7th and 8th teeth not more widely spaced than other teeth (ch. 235-1). We therefore treat the Krabi-Maomingosuchus as a provisionally valid but unnamed species of Maomingosuchus (see Discussion, below).
For measurements of the cranial and postcranial material see Supplemental material S4.

Cranial bones
General shape and taphonomic remarks. The skull is relatively robust, with the snout (measured from the snout tip to the anterior margin of orbit) making up around 72% of total skull length. The snout is overall Figure 3. Maomingosuchus acutirostris, holotype GPIT-PV-31657, Na Duong Formation, middle to upper Eocene, Vietnam. Skull in A, B, ventrolateral view and C, a sketch with the visible bones and characteristics. Abbreviations: an, angular; ar, articular; co, coronoid; d, dentary; d4, dentary tooth 4; ect, ectopterygoid; fr, fragment; j, jugal; ls, laterosphenoid; ma, matrix; mx, maxilla; mx5, maxillary tooth 5; mx15, maxillary tooth 15; nos, nuchal osteoderm; os, osteoderm; pmx, premaxilla, pt, pterygoid; q, quadrate; qj, quadratojugal; r, rib; sa, surangular; sc, scapula; sof, suborbital fenestra; sp, splenial; stf, supratemporal fenestra; v, vertebra. Scale bar ¼ 10 cm. narrow but widens at the level of the 5th maxillary tooth. The skull table is solid with relatively small supratemporal fenestrae and a wide frontal region between the orbits. The postorbital bar is very robust. The skull is highly pyritized and cracked in multiple regions; for example, posterior to the external naris, the region of the skull table and the otic region. The skull is articulated with the lower jaw and dorsolaterally compressed, so that most of its ventral surface is obscured. The occiput is partly embedded in matrix together with some postcranial elements. Most cranial features described below can be seen in Figures 2 and 3.
Cranial openings. The external naris (Fig. 2) is a large singular opening in the anterior region of the snout and formed exclusively by the premaxillae. Due to mediolateral compression of the skull the exact shape of the external naris is difficult to assess, but it seems to be trapezoidal and broader anteriorly than posteriorly. Both orbits ( Fig. 2) are preserved, but only the right one is well exposed and is oriented dorsolateral and almost oval, but slightly lateromedially compressed. Its margins are formed by the lacrimal, prefrontal, frontal, postorbital and jugal. Both supratemporal fenestrae (Fig. 2) are visible, lie on the skull table, and are small for a tomistomine. The outlines of the fenestrae are difficult to determine due to some broken areas and compression but they seem to be rounded and slightly longer than broad. Their medial walls are smooth without any visible foramina, and their margins are formed by the postorbitals, squamosals and parietals. Only the right infratemporal fenestra (Fig. 2) is visible posterior to the orbits. It is triangular in shape and enclosed by the postorbital, jugal and quadratojugal. Only the left suborbital fenestra (Fig. 3) is exposed in ventral view, bordered by the ectopterygoid and pterygoid so far as visible. Both external mandibular fenestrae (Figs 2, 3) are preserved and lie in the posterolateral region of the lower jaw. They are oval and anteroposteriorly elongated. Their margins are formed by the dentaries, angulars and surangulars. The incisive foramen, posttemporal foramen, foramen magnum, eustachian opening, choana and the foramen intermandibularis caudalis are not exposed.
Premaxilla. The right premaxilla is better preserved than the left. The premaxillae form the anterior part of the snout and entirely surround the external naris. Their surface is weakly ornamented. Close to the tooth row, small, rounded foramina for the receptor canals are exposed. The premaxilla projects anterior to the external naris for around half of narial length and forms the acute tip of the snout. In front of the external naris a perforation for the first dentary tooth is visible. The premaxilla extends posterior to the level of the 3rd maxillary tooth, presumably reaching the level of the posterior border of the 4th maxillary tooth parasagitally. Both premaxillae meet each other anterior to as well as posterior to the external naris. The premaxillary-maxillary suture extends as a sinusoidal line from the notch for the 4th dentary tooth posteromedially. The premaxilla contacts the nasal behind the external naris. Only one large tooth is visible, which can be identified as the 4th premaxillary tooth, based on comparisons with other tomistomines. Taking the length of the premaxilla into account a total of five premaxillary teeth is estimated.
Maxilla. The maxilla forms the posterolateral part of the snout, most of the tooth row and terminates about 15 mm posterior to the last tooth. It is weakly ornamented with a higher density of pits and grooves on the level between the 3rd and 5th maxillary tooth. Along the tooth row, openings for the receptor canals can be observed. These foramina are rounded anteriorly and get more elongated posteriorly. In dorsal view, the maxilla broadens slightly from the notch for the 4th dentary tooth towards the level of the 5th maxillary tooth, narrowing again at level of the 7th to 8th maxillary tooth, before bending posterolaterally. The maxilla sutures with the nasal medially, the lacrimal posteromedially, the jugal posteriorly and the ectopterygoid posteroventrally. The maxilla has a total of 15 alveoli. The 1st maxillary alveolus is the smallest. The teeth then increase in diameter until the 5th maxillary tooth, which is the largest in the series. The teeth become slightly smaller posteriorly, but stay relatively large, except for the last four which are significantly smaller than the previous ones. The alveoli are widely spaced (Fig. 2), especially among the smaller anterior teeth, whereas the larger posterior teeth are closer together. Between the 7th and 8th maxillary teeth there is a wider gap.
Nasal. The nasals are thin, elongate bones forming the medial part of the snout. Their anterior-most part is not clearly visible but it is definitely excluded from the external naris. The nasal surface is only weakly ornamented anteriorly, but more strongly so posteriorly with rounded and elongated pits. The nasal contacts the premaxilla anteriorly, the maxilla laterally and the lacrimal posterolaterally. Posteriorly, the nasal sutures with the prefrontal for a short distance (only 20 mm), whereas posteromedially they are separated by a 15 mm long anterior process of the frontal.
Lacrimal. Only the right lacrimal is well preserved. The bone is elongated anteroposteriorly, slightly bowed medially and forms the anterolateral margin of the orbit. The bone is almost double the size of the prefrontal and projects far anteriorly between the nasal and maxilla. Its surface is heavily ornamented with large rounded pits. The opening for the ductus nasolacrimalis is not exposed. The lacrimal contacts the maxilla anterolaterally, the jugal laterally, the prefrontal medially and the nasal anteromedially.
Prefrontal. The prefrontal forms the anteromedial margin of the orbit. The bone is almost rectangular and does not project further anteriorly than the anterior end of the frontal and is approximately as broad as the lacrimal. The orbital margin has a small bulge extending medially onto the frontal fossa. The surface of the prefrontal is weakly ornamented with a few deeper pits posteriorly. Due to crushing of the skull, neither prefrontal pillars is preserved. The prefrontal contacts the nasal anteriorly, the lacrimal laterally and the frontal medially.
Frontal. The frontals are fused and form the anterior part of the skull table. The bone is almost square-shaped with an elongate anterior wedge-shaped process, which projects with its anterior-most extension between the nasals. The whole process has nearly the same length as the broad part between the orbits and the skull table. The frontal does not reach the supratemporal fenestra posteriorly. The region between the orbits is flat, not upturned, very broad and around three times wider than the supratemporal bridge. The region between the broader part of the frontal and the narrow region of the anterior process is marked by a lateromedially oriented frontal fossa forming a ledge between the skull table and the snout. This fossa extends anterolaterally onto the prefrontal. The frontal is weakly ornamented anteriorly, but heavily ornamented with deep rounded pits posterior to the ledge. Anteromedially, the frontal contacts the nasal and anterolaterally, the prefrontal. On the skull table, the frontal contacts the postorbital laterally and the parietal posteriorly. The suture with the latter seems to project relatively straight lateromedially, but a slight posteromedial convexity is visible.
Postorbital. The right postorbital is the better preserved and forms the anterolateral part of the skull table, the posterolateral margin of the orbit, the anterolateral margin of the supratemporal fenestra and the anterior margin of the infratemporal fenestra. The skull table is damaged and therefore the postorbital is somewhat distorted with its surface partially broken off. The preserved part is ornamented with large rounded pits, especially posteriorly. In dorsal view, the postorbital contacts the frontal anteromedially, the parietal posteromedially and the squamosal posteriorly. In lateral view, the postorbital is indented by an anterior process of the squamosal. The postorbital bar is slightly inset from the margin of the skull table, very robust and is at least 50% the size of the infratemporal fenestra. The sutural contact with the jugal is not visible.
Parietal. The flat, dumbbell-shaped parietals are fused at midline and form most of the posteromedial part of the skull table as well as the medial margin of the supratemporal fenestra. The region posterior to the supratemporal fenestra is very broad. The supratemporal bar is narrow, but quite broad for a tomistomine. The parietal surface is ornamented with deep rounded pits. The parietal contacts the frontal anteriorly, the postorbital anterolaterally and the squamosal posterolaterally. The parietal encompasses the supraoccipital in the posterior part of the skull table, so that the parietal does not form the entire skull table. Inside the supratemporal fenestra, the parietal contacts the quadrate along its posterior wall, but the suture is difficult to see.
Squamosal. The squamosal is better preserved on the right side, and forms the posterolateral part of the skull table and the posterolateral margin of the supratemporal fenestra. The squamosal prongs extend posterolaterally, away from the skull table. The dorsal and ventral rims of the squamosal groove for the external ear valve musculature are parallel. The squamosal surface is ornamented with rounded pits only in the skull table region. Due to compression, the squamosal completely covers the auditory meatus. On the skull table, the squamosal contacts the postorbital anteriorly, the parietal posterolaterally and the quadrate on the lateral wall of the supratemporal fenestra. In lateral view, the squamosal projects anteriorly into the postorbital and contacts the quadrate posterolaterally on the squamosal prongs. The suture with the exoccipital is poorly preserved, but it is clear that the squamosal does not cover the paroccipital process.
Jugal. The right jugal is better preserved than the left and forms the lateral part of the skull as well as the ventrolateral margins of the orbit and the infratemporal fenestra. Anteriorly, a process extends far anteriorly to the level of the anterior extension of the frontal. The jugal is narrowest at level of the postorbital bar. The postorbital bar is set inwards from the lateral part of the skull and separated from it by a deep groove. The entire surface of the jugal is heavily ornamented. The jugal contacts the maxilla anteriorly, the lacrimal medially and the ectopterygoid ventrally. The jugal-quadratojugal suture is somewhat damaged posteriorly and its interaction with the posterior margin of the infratemporal fenestra is unclear. The jugal-postorbital suture on the postorbital bar is not visible.
Quadratojugal. The right quadratojugal is the best preserved. The bone is small, situated at the posterolateral part of the skull and forms the posterior margin of the infratemporal fenestra. The quadratojugal extends to the posterior end of the skull, surpassed only by the quadrate condyles. No surface ornamentation is observable. The quadratojugal contacts the jugal anteriorly and the quadrate posteromedially. A potential contact with the postorbital and squamosal at the superior margin of the infratemporal fenestra is not exposed.
Quadrate. The right quadrate is visible in dorsal and posterior views, while the left quadrate is exposed in ventral view only. It forms the posterior-most part of the skull, the inner posterior part of the supratemporal fenestra as well as the articulation with the articular of the lower jaw and most of the margin of the auditory meatus, which is not exposed. The articular surface of the quadrate is formed by two condyles, of which the lateral one is more expanded lateromedially than the medial one. The surface of the bone is unornamented. The quadrate foramen aerum is located in the dorsomedial corner of the bone. The quadrate is broad at the level of the condyles and narrows anteriorly close to the quadratojugal. The ventral surface of the quadrate is generally smooth with a moderate ridge for the insertion of the posterior mandibular adductor muscle. In dorsolateral view, the quadrate contacts the quadratojugal anteriorly, the squamosal medially and the exoccipital posteromedially. Inside the supratemporal fenestra, the quadrate contacts the parietal posteromedially and the squamosal posterolaterally, but this region is poorly preserved. In occipital view, the quadrate contacts the exoccipital dorsally.
Pterygoid. The pterygoid is only visible in ventral view where it forms the posterior part of the palate and the posterior margin of the suborbital fenestra. Due to dorsolateral compression, it is poorly preserved and only the left wing of the pterygoid is exposed (Fig. 3). The region around the choana is damaged. The pterygoid contacts the ectopterygoid anterolaterally. Unfortunately, no other sutural contacts are visible.
Ectopterygoid. Only the left ectopterygoid is exposed in ventral view. It forms the posterolateral part of the palate and forms the posterolateral margin of the suborbital fenestra. The ectopterygoid is poorly preserved and distorted, but its posterior extension contacts the pterygoid and ends anterior to the posterior tip of the latter. It further contacts the maxilla anteriorly and the jugal dorsally.
Supraoccipital. The supraoccipital is an unpaired bone and forms a small part of the skull roof and the central dorsal part of the occiput. On the skull table, it is a small triangular element that is pinched between the parietals. Its surface is somewhat weathered but no surface ornamentation is visible. The occipital part of the bone is damaged due to dorsolateral compression.
Exoccipital. The right exoccipital is exposed in occipital view but only its posterolateral-most parts are preserved. It forms most of the posterolateral region of the skull and the paroccipital process is visible in lateral view. The opening for the cranioquadrate passage is not directly visible, but the exoccipital shows a ventrally projecting convexity at the level of the foramen. The exoccipital contacts the squamosal dorsal and the quadrate ventrally. No other sutural contacts are visible.
Laterosphenoid. Only the left laterosphenoid is partly exposed and situated on the anteroventral part of the skull table, posteromedial to the orbit. It forms the anterolateral braincase wall and the inner anteromedial wall of the supratemporal fenestra. Sutural contacts with other bones are not discernible.
Dentary. Both dentaries are well-preserved in lateral view. The bone covers the anterolateral part of the lower jaw and reaches the anterodorsal and anteroventral part of the external mandibular fenestra. The dentary symphysis is relatively short for a tomistomine and seems to extend back to the level of the 6th to 8th dentary alveolus, although its exact length is difficult to determine due to poor preservation. The surface of the dentary is slightly ornamented with rounded pits anteriorly and elongated grooves ventrally, while its posterodorsal part is almost smooth. The tooth row is almost straight and, close to it, openings for receptor canals are visible. The slight curvature of the dentary, observable on the right side in lateral view (Fig. 2) is most likely a compressional artefact, as it is not present on the left side (Fig.  3). The dentary contacts the surangular posterodorsally, the angular posteroventrally and the splenial posteromedially. The total tooth number is unclear. The 1st dentary tooth perforates the premaxilla immediately anterior to the external naris. The 4th dentary tooth is the largest tooth in the anterior half of the lower jaw and its alveolus is slightly elevated. Posteriorly, the teeth are smaller but the 11th or 12th tooth (estimated based on the distance between the anterior teeth) is very broad and slightly larger than the 4th. Posteriorly, the tooth row is not exposed.
Splenial. The left splenial is the best preserved but is somewhat distorted. It forms the posteromedial part of the mandibular symphysis with a length that is less than the distance between five alveoli. An anterior foramen for cranial nerve V is not visible, but this could be a preservational artefact. There is no surface ornamentation. The splenial contacts the dentary laterally, the coronoid posterodorsally and the angular posteroventrally.
Coronoid. The left coronoid is exposed medially but is poorly preserved, and only its crescent-shaped anterior part is visible. Its surface is smooth, with no visible foramina, but this could be an artefact. The coronoid contacts the splenial anteriorly and the angular ventrally. The contact with the surangular is not exposed.
Surangular. Both surangulars are preserved in lateral view only. The surangular forms the posterodorsal part of the lower jaw, the posterodorsal margin of the external mandibular fenestra, contributes laterally to the posterior-most end of the retroarticular process, and reaches the dorsal tip of the lateral wall of the glenoid fossa. Anteriorly, the bone has two processes, a longer dorsal one, presumably reaching the tooth row, and a shorter ventral one, extending anteriorly to the external mandibular fenestra for around half of the fenestral length. The surangular is strongly ornamented with deep elongated pits posterior to the external mandibular fenestra. It contacts the dentary anteriorly, the angular ventrally and the articular dorsomedially.
Angular. Both angulars are preserved in lateral view and the right one is partially visible in medial view. The angular forms the posteroventral part of the mandible and the posteroventral margin of the external mandibular fenestra. Anteroventrally, the bone forms a process projecting between the dentary and splenial while extending posteriorly alongside the surangular on the lateral wall of the retroarticular process until its posterior-most end. The angular is strongly ornamented on its lateral part with deep and elongated pits, as well as with a few rounded pits posteroventral to the external mandibular fenestra. On its posteroventral part, a small nutritional foramen is visible in ventral view. In lateral view, the angular contacts the dentary anteriorly and the surangular dorsally. In medial view, the angular contacts the splenial anteriorly, the coracoid anterodorsally and the articular posterodorsally. A contact with the surangular in medial view is not exposed.
Articular. Both articulars are preserved in dorsolateral view and the right one is partially visible in medial view. The articular forms the posteromedial part of the mandible, the articulation surface with the quadrate, most of the retroarticular process and is slightly visible in lateral view. The retroarticular process projects posterodorsally. The glenoid fossa and the foramen aerum are not exposed. In lateral view, the articular contacts the surangular ventrolaterally and, in medial view, the angular ventrally.
Hyoid. Both hyoids (Fig. 4) are preserved and have a recumbent 'L'-shaped outline with a longer ventral than dorsal branch of the cornu. The dorsal branch is flattened and the ventral one is broadened anteriorly. The lateral part of the ventral branch of the cornu is slightly bowed medially, whereas its medial part is nearly straight and dorsoventrally oriented. The anterior-most extension is rounded and has a rough surface. Posterior to this surface there are multiple shallow pits of different sizes. The dorsal surface of the ventral cornual branch has a shallow anteroposteriorly oriented groove. The dorsal branch of the cornu is lateromedially flattened with parallel sides. Its dorsal-most part is slightly posteriorly shifted and has a rugose surface.
Dentition. The teeth of M. acutirostris are circular in cross-section and differ in size. The premaxillary, anterior maxillary (to the 5th tooth position) and anterior dentary teeth (to the 4th tooth position) have multiple dorsoventrally oriented ridges on their lateral and medial surfaces, and sharp but unserrated edges. In the premaxilla, the 4th tooth is the largest one. In the maxilla, the 1st tooth is small and the following teeth are gradually larger until the 5th maxillary tooth, the largest tooth in the tooth row. Posteriorly, the teeth become gradually smaller, but are still much larger overall than the first four maxillary teeth. The posterior-most four teeth are reduced in size and the smallest in the series. In the mandible, the 4th dentary tooth is the largest one in the anterior half of the lower jaw and projects into a notch between the premaxilla and maxilla. The other anterior dentary teeth are small until reaching the presumably 11th or 12th tooth, which is very broad and even slightly larger than the 4th one. Further posteriorly, the teeth seem to get smaller, but due to the occlusion of the jaws this region is not exposed. The dentary teeth are in line with the maxillary tooth row and the teeth are more widely spaced anteriorly, but closer together posteriorly due to their larger size. An enlarged gap can be found between the 7th and 8th maxillary teeth for the enlarged 11th or 12th tooth.

Postcranial bones
Axial skeleton. The vertebral column (Figs 5-8) is nearly complete and in total, the proatlas, seven cervical, 12 dorsal, two sacral and 15 caudal vertebrae are preserved.
Proatlas. The proatlas (Fig. 5A-D) is boomerangshaped with a posterolateral process on each side. The anterior part is slightly offset from the main body without forming a distinct process. The ventral tubercle is not clearly discernible, but based on the general morphology it is relatively large and at least half the width of the dorsal crest. Sagittally, a well-developed median keel is present that has a slightly rounded dorsal surface and slopes strongly posteriorly.
Cervical vertebrae. The best-preserved cervical vertebra ( Fig. 5E-J) is from the anterior region, but its exact position is unknown. Because the cervical vertebrae are rather uniform in morphology, we only describe the best-preserved in detail. The centrum is longer than wide but its height and width are similar. The centrum is constricted between the parapophysis and diapophysis and is ventrally convex in lateral view. The surface is smooth but bears small nutritional foramina below the diapophysis. The anterior articular surface is rounded and slightly more expanded dorsoventrally than the centrum. The posterior condylus is rounded. The hypapophysis is short and does not reach the middle of the centrum. Posteroventrally, a short shallow ridge is discernible. The articular surface of the parapophysis is oval and projects mostly laterally. The slightly damaged diapophysis is lateroventrally oriented and its articular surface is oval and smaller than the articular surface of the parapophysis. The prezygapophysis is oval-shaped and larger than the postzygapophysis. It projects dorsally, whereas the oval-shaped postzygapophysis turns ventrally, both at a 45 angle. The neural spine is nearly as high as the ventral part of the vertebra, is anteroposteriorly broad and slightly rounded dorsally.
Dorsal vertebrae. The best-preserved dorsal vertebra (Fig. 6) is from the anterior region, but its exact position is unknown. Because the dorsal vertebrae, like the cervical vertebrae (see above), are rather uniform in morphology, we only describe the best-preserved dorsal vertebra in detail. The centrum is nearly as long as wide but damaged by deep cracks. The anterior articular surface is round and wider than the centrum, while the posterior condylus seems to be nearly equal in size to the centrum. Ventrally, the centrum is slightly convex in lateral view. Its surface is smooth without visible foramina. The hypapophysis is narrow and anteriorly oriented, and does not reach the central part of the centrum. The transverse process is relatively slender and projects horizontally at an angle of 90 from the centrum. The parapophysis is located anteroventrally at mid-length and the diapophysis is positioned on the distal end of the transverse process. The prezygapophysis projects dorsally and seems to be larger than the postzygapophysis. The latter faces ventrally with an oval articular surface. A deep groove is present between the postzygapophyses. The neural spine is long and relatively low. Its dorsal tip is generally wide but broader anteriorly than posteriorly.
Sacral vertebra. Both sacral vertebrae (Fig. 7) are preserved. In the first sacral vertebra, the lateral extensions of the sacral ribs are covered by osteoderm fragments, the neural spine is broken into two pieces and the neural canal is damaged due to dorsoventral compression. The second sacral vertebra is also covered by osteoderms and its neural spine is broken but the neural canal is intact.
The centrum of the first sacral vertebra (Fig. 7A-F) is nearly as broad as long, and anteriorly and posteriorly slightly ventrally curved and posteriorly sloped. The surface of the centrum is smooth without discernible foramina. On the ventral part of the centrum there is a sulcus reaching from near its posterior end to the middle of the centrum. The anterior articular surface is concave, lateromedially expanded and deep, whereas the posterior articular surface is also expanded but nearly flat with only a very slight concavity. The sacral rib is dorsoventrally compressed. The anterior extension of the articular surface for the ilium reaches further laterally than the posterior one. The prezygapophysis is one-quarter larger than the postzygapophysis and its articular surface is rectangular. The prezygapophysis projects dorsally, whereas the postzygapophysis turns ventrally. The neural spine is long and reaches two-thirds of the dorsoventral length of the centrum. Its dorsal-most extension is damaged but seems to be slightly broader anteriorly than posteriorly.
The second sacral vertebra ( Fig. 7G-L) has a similar morphology to the first, but the sacral ribs are anteroposteriorly compressed. The centrum has small nutritional foramina anterolaterally and the sulcus on the ventral surface is less pronounced than in the first sacral. The centrum is nearly straight in lateral view with only a slight ventral projection at its anterior and posterior ends. The anterior articular surface with the first sacral vertebra is wide and flat with a slight concavity. The posterior articular surface is also wide but with a deep concavity for the anterior condylus of the first caudal vertebra. The lateral articular surface of the sacral rib with the ilium is boomerang-shaped with a posterodorsal extension contacting the posterior part of the iliac blade. The prezygapophysis is larger than the postzygapophysis and projects dorsally, whereas the postzygapophysis turns ventrally, and both have a lateromedially shifted angle of 45 . The neural spine is broken but its height is around two-thirds of the dorsoventral length of the centrum.
Caudal vertebrae. The first caudal vertebra (Fig.  8A-F) differs significantly from the more posterior caudal vertebrae and is described separately. The first caudal vertebra is biconvex and its centrum is similar to the centrum of the sacral vertebra in being as wide as it is long. The surface of the centrum is mostly smooth and no sulcus is present, but the ventral part slightly posterior to the anterior condylus has a rugose surface. In lateral view, the centrum is concave with a strong ventral shift posteriorly. Both condyles are similarly sized with the anterior condylus being slightly broader, whereas the posterior condylus is more rounded. The transverse process is incomplete but its lateral-most part shifts slightly posteriorly. The prezygapophysis is larger than the postzygapophysis and its articular surface is oval. The neural spine is elongated but narrower than the neural spines of the sacral vertebrae.
More posteriorly positioned caudal vertebrae ( Fig.  8G-L) have a slenderer morphology than the first caudal vertebra and the centrum is elongated, mediolaterally narrow and slightly convex in lateral view. The centrum tapers towards its middle part and a deep sulcus extends over the whole length of the centrum on its ventral surface. The anterior articular surface is rounded and concave, whereas the posterior articular surface has a round condylus. The transverse process is incomplete and projects straight from the centrum at almost 90 . The articular surface of the prezygapophysis is oval and projects dorsally, whereas the articular surface of the postzygapophysis turns ventrally. The neural spine is posteriorly shifted. In the anterior caudal vertebrae, the spine is elongated and flares towards the postzygapophyses. In the posterior caudal vertebrae, the spine tapers into a rod-like morphology and is shifted even more posteriorly and transverse processes are lost.
Chevron. The articular surface of the chevron ( Fig.  8M-P) for the caudal vertebra is dumbbell-shaped and the haemal canal is rectangular and slightly ventrally tapered. The haemal arch is narrow in anteroposterior view but expanded in lateral view. The haemal spine Abbreviations: ce, centrum; dp, diapophysis; hp, hypapophysis; na, neural arch; nc, neural canal; ns, neural spine; pcd, posterior condylus; pp, parapophysis; prz, prezygapophysis; pz, postzygapophysis. Scale bar ¼ 1 cm. comprises around two-thirds of the total chevron length and is slightly thickened at its ventral-most part.
Atlantal rib. The atlantal rib (Fig. 9A-D) is elongated and flat. The articular surface with the atlas is kidney-shaped and the anterior part of the rib has parallel sides. Neither a large articular facet for the other atlantal rib nor a thin medial lamina are present. The medial part is slightly concave, whereas the lateral part is slightly convex. From the middle part onwards, the rib expands and   forms a dorsal process, which tapers rapidly posteriorly. The ventral part expands only slightly before projecting straight posteriorly.
Cervical ribs. The best-preserved cervical rib is from the anterior region ( Fig. 9E-J), but its exact position is unclear. The dorsal part consists of two columnar processes, the medial capitulum and the lateral tuberculum. The capitulum contacts the parapophysis of the cervical vertebra, whereas the tuberculum contacts the diapophysis. The capitulum is shorter than the tuberculum, but its articular surface is broader and rounded, while that of the tuberculum is more elongate. The anterior region of the ventral part of the bone is shorter than the posterior extension and steep, whereas the posterior part is flat with a deep medial concavity.
A posterior left cervical rib (Fig. 9K-N) is preserved and likely contacted the 6th cervical vertebra. The capitulum is elongated and much longer than the tuberculum. The articular surface of the capitulum is small and rounded, while that of the tuberculum is nearly double the size and broad. A lateral projecting lamina was folded due to compression, but would normally project perpendicular to the shaft. The posteroventrally projecting shaft tapers slightly distally and has a lateral ridge contacting the lamina and reaches the posterior third of the bone. The medial part of the shaft is flat.
Dorsal rib. The dorsal ribs are incomplete, but their general morphology does not seem to differ from other tomistomines.
Scapula. Both scapulae (Fig. 10A, B, E, F) are present, but only the right one is well preserved. The scapular blade expands dorsally, with a relatively straight anterior edge. The deltoid crest is partially covered by a dorsal rib, but the bulge of the crest is relatively narrow. The articular surface for the coracoid is elongate, but lateromedially flattened due to compression. Anterior to the deltoid crest and anterodorsal to the articulation surface, the scapula is elongated and rectangular. The glenoid fossa is ventrolaterally oriented and oval.
Coracoid. The left coracoid (Fig. 10C, D, G, H) is better-preserved, but lateromedially compressed. The shaft is slightly bowed and the coracoid blade expands ventrally, but is narrow compared to the scapular blade. Anteroventrally, the blade has a small process projecting anteriorly. The articular surface for the scapula is elongate, but lateromedially flattened due to compression. Anterior to the articular surface with the scapula, the coracoid is elongated and rectangular. The glenoid fossa has an oval outline and the coracoid foramen is small and situated well anterior to the glenoid fossa.
Humerus. The right humerus (Fig. 11A-H) is better preserved than the left. The bone is relatively slender and its surface is mostly smooth with rugose areas ventral to the proximal and dorsal to the distal articulation surfaces. The humeral head is divided in an anterior and a posterior tubercle. The anterior tubercle forms the proximal-most point of the humerus, whereas the posterior tubercle is posterodistally shifted. The deltopectoral crest has a concave surface and projects nearly perpendicular to the shaft. Close to its distal end, the humerus has a visible central concavity on its dorsal and ventral part. Distally, the medial and lateral condyles form the articular surfaces for the radius and ulna. Both condyles are rounded with the lateral condylus being slightly larger. Scars for the musculature are not visible.
Ulna. Only the left ulna ( Fig. 11I-L) is preserved. It is sigmoidal and proximally expanded. The articular surfaces are compressed. The small olecranon process forms its proximal-most point and the proximal articular surface slopes anteriorly. The distal articular surface is kidney-shaped.
Ilium. The right ilium (Fig. 12A-D) is better preserved, but deformed with its posterodorsal end shifted, whereas the left ilium is less deformed but fused to the left ischium. The dorsal part of the bone has a rugose surface, is slightly sigmoidal with a shallow indentation posteriorly and a small anterior process. The iliac blade in general is narrow but posteroventrally slightly broadened. In medial view, the bone has two prominent scars for articulation with the first and second sacral ribs. The anterior scar is oval, whereas the posterior scar is elongated and reaches the ventral part of the iliac blade. In lateral view, the supraacetabular crest is narrow with a rounded outline and the acetabulum forms a broadly rounded depression. The ventral part of the ilium forms the articular surfaces for the ischium. The posterior articular surface is boomerang-shaped, whereas the anterior one is elongate and kidney-shaped. The acetabulum foramen is visible between the two surfaces.
Ischium. The right ischium (Fig. 12E-H) is better preserved, but has a deformed posteroventral part, whereas the left ischium is less deformed but fused to the left ilium. The ventral part is formed by the ventromedially bowed ischium blade and the anteroventral part of the blade is nearly rectangular, whereas the posterior part extends far posteriorly. The dorsal part of the bone can be divided into two processes. The posterior process forms the articular surface with the posterior part of the ilium. This surface is triangular with a small elongate anterior process. The anterior process is slenderer and has two separated articular surfaces. The dorsal one contacts the anterior articular surface of the ilium, whereas the anteroventrally projecting one contacts the pubis. The articular surface with the ilium is lateromedially elongate and the articular surface with the pubis is oval. Between the anterior and posterior process, the acetabulum foramen is present.
Pubis. The left pubis (Fig. 12I-L) is well-preserved. Its ventral blade flares nearly symmetrically with a rounded ventral edge. The posteroventral part of this edge is vertical for a short distance. The blade is lateromedially flattened and the shaft is oval in cross-section. The dorsal articular surface is oval and slightly shifted posteriorly. It contacts the anteroventral articular surface of the anterior process of the ischium.
Femur. The left femur (Fig. 13A-H) is better preserved, relatively slender, larger than the humerus and has a sigmoidal outline with a slight torsion. The femoral head is compressed and therefore appears to be oval. Directly ventral to the femoral head, the bone surface is rugose, with small openings, most likely representing nutritional foramina. Proximocaudally, the insertion scar for the M. puboischiofemoralis externus is visible. The 4th trochanter is prominent and positioned on the proximal onethird of the bone. The distal end of the femur is divided into two condyles: a lateral condylus and a slightly smaller medial condylus. In dorsal view, a small groove between the two condyles is present, whereas a deeper depression can be seen in ventral view.
Tibia. The left tibia (Fig. 13I-L) is poorly preserved and its shaft is damaged. The proximal part is divided into a medial and lateral condylus. The medial condylus is oval and separated from the larger lateral one by a groove. The distal articular surface is crescent-shaped with an anterior and a posterior condylus, which are separated from each other by a shallow groove.
Fibula. The left fibula ( Fig. 13M-P) is poorly preserved, with a proximal articular surface that has been nearly completely lost. The shaft is oval in cross-section. The distal articular surface is bean-shaped and slightly shifted posteriorly.
Metatarsals. The left metatarsal II (Fig. 13Q-T) is the best preserved and its proximal articular surface is flat and elongate. The shaft is flattened proximally, but is slightly oval in cross-section distally. The distal articular surface is broad with a nearly rectangular outline. The two condyles are very low with only a very shallow groove separating them. In ventral view, a deep depression is visible directly proximal to the distal articular surface.
Osteoderms. Several dorsal osteoderms (Fig. 14A, B), some putative lateral osteoderms (Fig. 14C, D) and many osteoderm fragments are preservedmost of them occurring isolated. The osteoderm central surface is strongly ornamented with a pattern of deep oval and Abbreviations: acd, anterior condylus; atb, anterior tubercle; dpc, deltopectoral crest; hh, humeral head; lcd, lateral condylus; mcd, medial condylus; op, olecranon process; pcd, posterior condylus; ptb; posterior tubercle. Scale bar ¼ 5 cm. round pits. Towards the edges, the surface is smooth. The dorsal osteoderms are rectangular with a broad facet to contact the anteriorly positioned osteoderm. A welldeveloped dorsal keel is present, projecting from slightly posterior of the anterior facet to the posterior end of the osteoderm. The putative lateral osteoderms have a more oval outline and are slightly curved, but show a welldeveloped dorsal keel also. A contact surface is not visible but the edges seem to be damaged.  Martin et al. 2019]). The snout length is also very similar within Maomingosuchus with a snout-to-skull length ratio ranging between 0.71 and 0.72, but the snout shape differs slightly: in M. petrolicus and Krabi-Maomingosuchus it is narrow, with only a slight broadening at the level of the 5th maxillary tooth, while the snout of M. acutirostris is much broader at this level with a strongly enlarged 5th maxillary tooth.
M. acutirostris and M. petrolicus are large and broader anteriorly than posteriorly (unknown in the Krabi specimen), but the premaxillary process reaching into the external naris described for M. petrolicus (Shan et al. 2017, p. 675), is not visible in M. acutirostris. The orbit of M. acutirostris is more elongated than the rounded one of M. petrolicus whereas the supratemporal fenestra is smaller than in the latter, resulting in a different ratio of the supratemporal fenestral length to orbit length (0.57 in M. acutirostris; 0.83 in M. petrolicus; and 0.76 for Krabi-Maomingosuchus).
The supratemporal bar in M. petrolicus is thin compared to skull table width (Shan et al. 2017, fig. 2). Its ratio is only around 0.07, while it is 0.11 in M. acutirostris. In Krabi-Maomingosuchus this ratio is difficult to determine, but the bar seems to be relatively broad (Martin et al. 2019, fig. 1), and the ratio appears to be closer to the ratio seen in M. acutirostris.
Skull bones. In general, the shapes of the individual skull bones and their sutures are similar in all Maomingosuchus specimens.
The premaxilla is only known for M. acutirostris and M. petrolicus, but in both species the anterior-most part differs, with a short and rounded anterior snout in M. petrolicus (Shan et al. 2017, figs 2, 4) and an elongated and acute one in M. acutirostris.
The anterior part of the prefrontal lies at the same level as the anterior part of the frontal in M. acutirostris and Krabi-Maomingosuchus. According to Shan et al. (2017), this condition is variable in M. petrolicus, as in some specimen (e.g. NMNS005146-F041793) the frontal is shorter than the prefrontal.
In M. petrolicus and Krabi-Maomingosuchus the prefrontal slightly overhangs the orbital margin (Martin et al. 2019). This is not the case in M. acutirostris but this could be a compressional artefact.
The supraoccipital is largely exposed on the skull table in M. acutirostris and M. petrolicus. In M. petrolicus, the exposure and shape of the supraoccipital is variable and either more rectangular, as in DM-F0001, or more triangular, as in NMNS002060-F027511 (Shan et al. 2017, fig . 3). In M. acutirostris, it is more triangular, whereas in Krabi-Maomingosuchus the condition is unknown.
Krabi-Maomingosuchus differs from M. acutirostris and M. petrolicus in the position of the surangular-dentary suture in the external mandibular fenestra. Only in Krabi-Maomingosuchus does the suture reach the posterior-most corner (Martin et al. 2019, fig. 2), whereas the suture intersects the fenestra anterior to its posterior margin in M. acutirostris and M. petrolicus.
Teeth. In general, the tooth rows and teeth of Maomingosuchus specimens are similar but there are some noteworthy differences. In total, there are 15 maxillary teeth in M. acutirostris and M. petrolicus. In Krabi-Maomingosuchus the tooth number is difficult to assess, but at least 14 maxillary alveoli are visible (Martin et al. 2019, fig. 1). The 1st dentary tooth perforates the premaxilla anterior to the external naris in M. acutirostris and M. petrolicus, which is a rare character among tomistomines (see below). Due to the missing tip of the snout this condition is unknown in Krabi-Maomingosuchus. In Maomingosuchus, the premaxillary, anterior maxillary and anterior dentary teeth have clearly visible dorsoventrally projecting ridges on their lateral and mesial surfaces and the teeth have sharp outer edges (Shan et al. 2017, fig. 4;Martin et al. 2019, fig. 3).
Differences between the Maomingosuchus specimens occur in tooth size. In M. acutirostris, the 5th maxillary tooth and the 11th or 12th dentary tooth are enlarged, whereas in M. petrolicus (Shan et al. 2017, fig. 2) and Krabi-Maomingosuchus (Martin et al. 2019, fig. 1), the 5th maxillary tooth is also enlarged but smaller overall. In M. acutirostris and M. petrolicus the anterior alveoli increase in size towards the 5th maxillary tooth, whereas there is no size difference in Krabi-Maomingosuchus, with the 5th maxillary tooth being only slightly larger (Martin et al. 2019, fig. 1).
The spacing of the teeth posterior to the 5th maxillary alveolus also differs within Maomingosuchus. A wider distance between the 7th and 8th maxillary alveoli for the enlarged 11th or 12th dentary tooth is only present in M. acutirostris and to a smaller degree in M. petrolicus (Shan et al. 2017, fig. 4c, e). In Krabi-Maomingosuchus there are no enlarged dentary teeth and therefore no enlarged maxillary distance is present (Martin et al. 2019, fig. 2).
Postcranial skeleton. Two differences between M. acutirostris and M. petrolicus are present in the postcranial skeleton but not preserved for Krabi-Maomingosuchus. On the atlantal rib, there is a process on the dorsal margin in M. acutirostris, while this region seems to be smooth in M. petrolicus (described as similar to T. schlegelii by Shan et al. [2017]). The ilium of M. acutirostris has a prominent anterior process. This region is poorly preserved in M. petrolicus (Shan et al. 2017, fig.  10), but the anterior iliac border does not seem to lead into a process comparable to the one in M. acutirostris.

Comparisons with other taxa
Skulls. Maomingosuchus is a medium-sized tomistomine genus with a skull reaching slightly more than 500 mm (see above). Tomistomines in general have a broad size range, from around 430 mm in Kentisuchus spenceri and Dollosuchoides to over 1 m in the giant species Toyotamaphimeia. The extant Tomistoma schlegelii exhibits remarkable size variation with a typical skull length of around 500 mm to a maximum of over 800 mm (Whitaker & Whitaker 2008). By contrast, the skull to snout ratio in Tomistominae remains relatively constant and ranges from around 0.7 to 0.8. With a skull to snout ratio between 0.71 and 0.72, Maomingosuchus is one of the shortest-snouted taxa, comparable to Maroccosuchus and K. spenceri. This is shorter than extant T. schlegelii (with a ratio of 0.74) and much shorter than long snouted Miocene taxa like Gavialosuchus (with a ratio of 0.79).

Cranial openings. The external naris in all known
Maomingosuchus specimens with a preserved snout is large and anteriorly wider than posteriorly, with a nearly straight lateromedially projecting anterior margin, which is unique among tomistomines. In species like T. schlegelii or Melitosaurus champsoides Owen, 1849 (Nicholl et al. 2020, fig. 2) the external naris is smaller and oval. In species like K. spenceri (Brochu 2007, fig. 2), the external naris is relatively large and oval. A more rectangular shape with a straighter anterior margin similar to Maomingosuchus can be seen in Maroccosuchus (Jouve et al. 2015, figs 3, 7) and Dollosuchoides (Brochu 2007, fig. 3).
The size of the supratemporal fenestrae also affects the shape of the interfenestral bar, which is usually wider in taxa with smaller fenestrae. The broadest bar is found in Paratomistoma (Brochu & Gingerich 2000, fig. 2) which also has the smallest fenestrae. The interfenestral bar is relatively broad in Maroccosuchus despite its medium-sized fenestrae (Jouve et al. 2015, figs 3, 8, 11).
The external mandibular fenestra of Maomingosuchus is medium-to large-sized for a tomistomine. In T.
The frontal in Maomingosuchus is wide and flat between the orbits, and the edges are not upturned, which is otherwise only known for Dollosuchoides. The postorbital bar in Maomingosuchus is anteroposteriorly expanded, whereas in most tomistomines the bar is massive but slenderer (e.g. T. schlegelii). Otherwise, a broad bar is only found in some basal eusuchians and gharials. The supraoccipital is only slightly exposed on the skull table and barely visible in most tomistomines, but this is pronounced in Maomingosuchus, 'T.' cairense and 'Tomistoma' coppensi Pickford, 1994. In Maomingosuchus, there is a ventrally projecting lamina on the exoccipital covering the entrance to the cranio-quadrate passage. The character is otherwise only known for basal eusuchians like Allodaposuchus precedens Nopcsa, 1928(Delfino et al. 2008 fig. 3) or Hylaeochampsa vectiana Owen, 1874(Clark & Norell 1992) and among crocodilians only for gharials and thoracosaurs. A similar structure is present in Penghusuchus, but here the lamina is more medially oriented.
Teeth. The total tooth count in tomistomines is variable between species. Maroccosuchus, Thecachampsa carolinensis and 'T.' gaudense have 14 teeth in the maxilla, Dollosuchoides and Maomingosuchus have a maximum of 15 teeth, T. schlegelii and Toyotamaphimeia have 16 and Penghusuchus 17 teeth.
In Maomingosuchus, the 1st dentary tooth perforates the premaxilla anterior to the external naris. In tomistomines, this is only known for K. spenceri (Brochu 2007, fig. 2) and some specimens of T. schlegelii (C. Brochu, pers. comm.). In Toyotamaphimeia, the premaxilla is also perforated by the 1st dentary tooth, but the openings are situated inside the external naris (Kobayashi et al. 2006, figs 7, 15). In other taxa, such as Dollosuchoides (Brochu 2007, fig. 3) or most T. schlegelii, the 1st dentary tooth projects into an anterolateral notch of the premaxilla. In Maroccosuchus, there is no lateral notch or perforation for the 1st dentary tooth visible in dorsal view (Jouve et al. 2015, figs 7, 8), implying that the 1st dentary tooth is small. A perforated premaxilla is rare among tomistomines, but frequently present in members of Crocodylinae, such as Crocodylus niloticus Laurenti, 1768, in which the perforations are positioned further anteriorly.
In M. acutirostris, the difference in tooth sizes resembles the condition found in Maroccosuchus, but the gaps between the teeth are distinctly smaller and the dentary is only slightly bent in lateral view, but more curved in Maroccosuchus (Jouve et al. 2015, figs 2, 4, 15). The teeth of Megadontosuchus are all enlarged and represent an apomorphic morphology for a tomistomine (Piras et al. 2007, fig. 2). The dentition of T. schlegelii is homodont with only the 5th maxillary tooth being larger, and almost constant spacing along the tooth row. Similar morphology is also found in Gavialosuchus (Toula & Kail 1885, pl. 2), 'T.' calaritanum (Nicholl et al. 2020, fig. 14) and 'T.' gaudense (Nicholl et al. 2020, fig. 8).
The proatlas of M. acutirostris is boomerang-shaped and resembles that of Penghusuchus and Toyotamaphimeia, but it has a more elongated posterior process and a much higher medial keel. In the other species, like T. schlegelii, the proatlas is more block-like. An atlantal rib with a dorsal projection is known only in Maomingosuchus and Toyotamaphimeia.
In M. acutirostris, Thecachampsa carolinensis and T. schlegelii, the scapular blade is broad, whereas it is narrower in Toyotamaphimeia and even wider in Penghusuchus. The coracoid foramen in M. acutirostris is much smaller than that of Toyotamaphimeia, Thecachampsa carolinensis and T. schlegelii. The iliac blade of M. acutirostris is slightly distorted, but relatively broad with a shallow dorsal indentation, similar to T. schlegelii. Toyotamaphimeia has a narrower iliac blade and a shallower dorsal indentation. In Penghusuchus the dorsal indentation is very small, and in Thecachampsa carolinensis the posterior part of the blade seems to be sloped. Anteriorly, a prominent process is visible on the ilium of M. acutirostris. The process is visible, but smaller than in Toyotamaphimeia and Penghusuchus. No such process is visible in T. schlegelii or Thecachampsa carolinensis. Besides M. acutirostris, Toyotamaphimeia and Penghusuchus, such a process is known in gharials.
The dorsal osteoderms of M. acutirostris, T. schlegelii and Toyotamaphimeia have a prominent dorsal keel, whereas no keel is present in Penghusuchus or Thecachampsa carolinensis.

Comparative discussion
Maomingosuchus differs from other tomistomines in general snout shape, but the sizes and snout-to-skull ratios are almost similar. Only in Maomingosuchus acutirostris is the snout much broader at the level of the 5th maxillary tooth and similar to Maroccosuchus. Both of these species also have large teeth (see below) that could indicate a more generalist lifestyle.
The size ratio between the supratemporal fenestra and the orbit differs between M. acutirostris and other Maomingosuchus specimens. However, the size difference in the supratemporal fenestrae between Maomingosuchus specimens is not large, but represents the only synapomorphy in the phylogenetic analysis that unites Maomingosuchus petrolicus þ Krabi-Maomingosuchus. This ratio seems to be variable between other tomistomine taxa. For ch. 244 (ratio of the anteroposterior length of the supratemporal fenestra to the anteroposterior length of the orbit: <0.5 [0], 0.5-0.75 [1] or >0.75 [2]); half of the tomistomine taxa were scored with state (1) whereas the other half were scored with state (2). The variability of this character within Tomistominae challenges the synapomorphy of M. petrolicus þ Krabi-Maomingosuchus.
In most tomistomines, the intersupratemporal bar is very narrow in comparison with the width of the skull table. In M. acutirostris the ratio is slightly different and the bar is broader compared to other Maomingosuchus specimens, but the difference is not that large (for more information see Supplemental material S2).
In M. acutirostris and M. petrolicus the 1st dentary tooth perforates the premaxilla anterior to the external naris (unknown for Krabi-Maomingosuchus) and this could either be autapomorphic for Maomingosuchus or synapomorphic for M. acutirostris þ M. petrolicus.
In M. petrolicus and Krabi-Maomingosuchus overall tooth size is uniform and the teeth are slender and pointed, as in most tomistomines, but some teeth are more robust and blunter in M. acutirostris similar to Maroccosuchus. This may indicate a somewhat different lifestyle for M. acutirostris with a less exclusive piscivorous diet.
M. acutirostris and M. petrolicus have a thin lamina of the exoccipital projecting ventrally to cover the entrance of the cranio-quadrate passage on the exoccipital, similar to Gavialis gangeticus (Gmelin, 1789). This lamina could either be a synapomorphy uniting M. acutirostris with M. petrolicus or it could be an autapomorphy for the whole genus, depending on the condition in Krabi-Maomingosuchus. Determination of the condition in Penghusuchus is needed to check if the structure present there is homologous to the condition in Maomingosuchus.

Phylogenetic analysis Results
For the maximum parsimony analysis of the traditional search, a total of 17,496 equally optimal trees with lengths of 1017 steps, a consistency index (CI) of 0.317 and a retention index (RI) of 0.690 were recovered (Figs 15, 16). For the New Technology search analysis, a total of 864 equally optimal trees with the same lengths and same consistency and retention indices were found, and there are no differences in the tree topologies between the results of the traditional and the New Technology search approaches.
Two taxa (Kentisuchus astrei Jouve, 2016 and Melitosaurus) were pruned from the strict consensus tree after the analysis, because of their unstable positions in the tree. Their potential positions are indicated by the letters 'a' or '> a' for K. astrei and '> b' for Melitosaurus (Fig. 16): 'a' indicates that the taxa, if included on the tree, would be sister taxon to a single other taxon, whereas '> a' and '> b' mean that those taxa would be in a polytomy. If K. astrei is not pruned from the tree, the resolution is reduced at the base of Tomistominae, whereas the inclusion of Melitosaurus leads to a significant loss of resolution among more derived taxa. A complete tree with all of the taxa included can be found in Supplemental material S2.
Maomingosuchus is monophyletic with M. petrolicus from Maoming and Krabi-Maomingosuchus forming the sister group to M. acutirostris. Maomingosuchus was recovered in a basal position within Tomistominae as the sister clade to Tomistoma þ Paratomistoma þ Gavialosuchus þ Melitosaurus. A list of synapomorphies can be found in Supplemental material S2.
Bremer support and bootstrap values on the tree are generally low. The Bremer support for Tomistominae is 1. This is also the case for Maomingosuchus and M.

Phylogenetic discussion
Outside Tomistominae, the tree is mostly consistent with previous analyses based on morphological data alone (e.g. Brochu 1999Brochu , 2011Jouve et al. 2015;Shan et al. 2017;Martin et al. 2019;Massonne et al. 2019;Nicholl et al. 2020), but lacks resolution at some nodes (Gavialoidea, Borealosuchus spp. and Crocodyloidea) as is also the case in Nicholl et al. (2020). This is different in Shan et al. (2017) and Iijima et al. (2018), most likely due to our ordering of characters (see Materials and methods, above). This ordering also affects tomistomines, in that Dollosuchoides is considered to be the sister taxon to Thecachampsa antiqua þ Thecachampsa carolinensis þ Penghusuchus þ Toyotamaphimeia instead of being placed in a more basal position on the tree.
Our analysis yields a polytomy at the base of Tomistominae including Maroccosuchus, Kentisuchus astrei, Kentisuchus spenceri and Megadontosuchus or a polytomy between Maroccosuchus and K. spenceri if K. astrei is pruned from the tree.
Maomingosuchus consists of Maomingosuchus acutirostris, Maomingosuchus petrolicus and the Krabi-Maomingosuchus and is supported by three autapomorphies, a flush margin of the orbit with the skull surface (103-0), a ventral border of the exoccipital convex and ventrally projected (166-0) and a frontal ending at the same level as the anterior extension of the prefrontal (171-1).
The monophyly of Maomingosuchus is the most parsimonious hypothesis and found in all trees, despite the weak Bremer support.
In previous analyses (Shan et al. 2017;Iijima et al. 2018;Nicholl et al. 2020), M. petrolicus was found in varying positions among tomistomines, but usually in a more derived position than in our current analysis. Only Our rescoring of some characters for M. petrolicus and Krabi-Maomingosuchus (Supplemental material S2), as well as the incorporation of M. acutirostris, results in a more basal position of Maomingosuchus that is more congruent with its upper Eocene-lower Oligocene age.
It is noteworthy that the position of Maomingosuchus is generally stable on the tree. The genus always forms the sister clade to a group consisting of 'Tomistoma' cairense þ 'Tomistoma' coppensi þ Paratomistoma þ Tomistoma schlegelii þ 'Tomistoma' lusitanica þ Gavialosuchus þ 'Tomistoma' gaudense þ 'Tomistoma' calaritanum þ Melitosaurus, regardless of whether K. astrei or Melitosaurus are pruned from the tree or not. A new phylogenetic analysis by Rio & Mannion (2021) recovered Gavialis as more closely related to Tomistoma than to other extant crocodylians, based solely on morphological data. This further suggests paraphyly of the classical subfamily Tomistominae. However, the more basal position of M. petrolicus is also supported in this analysis, indicating that Maomingosuchus belongs to a stem group leading to recent Tomistoma and Gavialis. Further analyses that include M. acutirostris and Krabi-Maomingosuchus are necessary to get better insights into the relationships between Maomingosuchus and other gavialoids.

Palaeobiogeographical implications
Based on our analysis and previous phylogenies most basal tomistomine taxa are from the western Tethyan region. It is therefore most parsimonious to assume that they originated in that area before the early Eocene (as already proposed by Jouve et al. 2015;Jouve 2016;Shan et al. 2017;Iijima et al. 2018;Nicholl et al. 2020). Moreover, based on our analysis, we conclude that dispersals towards eastern Asia must have happened multiple times independently. Accordingly, the first dispersal occurred no later than the late Eocene for the stem lineage of Maomingosuchus, while a second dispersal occurred no later than the early-middle Miocene for the stem lineage of Penghusuchus þ Toyotamaphimeia, and a third one took place for the stem lineage of the extant Tomistoma schlegelii during the Neogene. For better clarification, we mapped the ages of the respective fossils based on available data from the literature onto our phylogenetic tree (Fig. 17).
Based on palaeogeographical reconstructions, two different dispersal routes for the stem lineage of Maomingosuchus seem possible: an eastern route from Europe via coastal dispersal along the Neotethys to south-eastern Asia (consistent with Jouve et al. 2015, fig. 18) and a western route from Europe via North America and Beringia to south-eastern Asia. The latter one as suggested for Orientalosuchina (Massonne et al. 2019) seems rather unlikely, due to the absence of suitable fossils in North America at that time.
A potential key to solve this problem are the tomistomine species from the middle Eocene of central and south Asia, but their tomistomine affinities have been questioned (Jouve 2004;Jouve et al. 2015). 'Tomistoma' borisovi Efimov, 1988 and Dollosuchus zajsanicus (Efimov, 1982) are only fragmentary and difficult to diagnose (Piras et al. 2007;Jouve et al. 2015;Kuzmin & Zvonok 2021). 'Tomistoma' tandoni Sahni & Mishra, 1975 is known only from a mandible and Ferganosuchus planus Efimov, 1982 from a skull table and some postcranial material. Further crocodilian remains are known from the middle Eocene Pondaung Formation of central Myanmar (Tsubamoto et al. 2006a, b), including two different crocodilian teeth figured by Tsubamoto et al. (2006b, fig. 12) of which the larger one resembles the larger teeth of Maomingosuchus acutirostris in exhibiting a well-developed lateral edge. According to Tsubamoto et al. (2006a), there are more teeth and bone fragments from the same locality, but they remain unpublished.
The results of the current phylogenetic analysis, together with previous analyses (Martin & Lauprasert 2010;Skutschas et al. 2014;Shan et al. 2017Shan et al. , 2021Martin et  Dispersal towards eastern Asia, however, probably differed for both groups. While Orientalosuchina were already present in the region during the Late Cretaceous (Li et al. 2019) and most likely originated in North America (Massonne et al. 2019), the stem lineage of Maomingosuchus probably arrived in eastern Asia from Europe sometime before the upper Eocene (e.g. Jouve et al. 2015;Shan et al. 2017;Martin et al. 2019).
The crocodilian faunas of the three localities (Na Duong, Maoming and Krabi) are very similar, but show distinct species, which could be explained by either climatic and/or geographical barriers. Climatic barriers between the Na Duong and Maoming basins seem unlikely, since both basins are close to each other ($400 km apart) and at the same latitude (Fig. 1). This distribution recalls a similar case in the turtle fauna with Banhxeochelys trani Garbin, B€ ohme & Joyce, 2019 from Na Duong being closely related to Isometremys lacuna Chow & Yeh, 1962 and Guangdongemys pingi Claude, Zhang, Li, Mo, Kuang & Tong, 2012 from Maoming (Garbin et al. 2019). Based on the presence of closely related crocodile and turtle faunas in Na Duong, Maoming and Krabi, it seems likely that other middle-upper Eocene deposits in eastern and south-eastern Asia (e.g. the Pondaung Formation in Myanmar) will yield species of Maomingosuchus and orientalosuchines. Further investigations on those fossil sites are needed to obtain more information of the faunas and palaeobiogeography of eastern and south-eastern Asia during the upper Eocene-lower Oligocene.

Conclusions
Maomingosuchus acutirostris sp. nov. is a new tomistomine species from the middle-upper Eocene deposits (late Bartonian-Priabonian age, 39-35 Ma) of the Na Duong Basin in Vietnam. M. acutirostris is a mediumsized tomistomine with a relatively robust snout and multiple enlarged teeth, similar to Maroccosuchus, potentially indicating a less piscivorous diet than the extant Tomistoma schlegelii.
Our phylogenetic analysis recovers M. acutirostris as the sister taxon to a monophyletic group consisting of M. petrolicus from the upper Eocene of the Maoming Basin of south-eastern China and Krabi-Maomingosuchus from the upper Eocene-lower Oligocene of Wai-Lek from Krabi Province, Thailand. The basal position of Maomingosuchus is generally stable on the tree, being congruent with the upper Eocene-lower Oligocene age of Maomingosuchus.
The phylogenetic analysis supports a western Tethyan origin for tomistomines with three independent dispersal events from Europe to eastern Asia. One for the stem lineage of Maomingosuchus, another for the stem lineage of Pengusuchus þ Toyotamaphimeia and a third for the stem lineage of the extant T. schlegelii.
The similarities between the crocodile faunas of Na Duong, Maoming and Krabi are noteworthy. More material from other upper Eocene-lower Oligocene sites in eastern Asia could show if representatives of Maomingosuchus and orientalosuchines were more widely spread across east Asia than currently known and could shed new light on the palaeobiogeographical and faunal connections between these different Eocene-Oligocene localities in eastern Asia. 2012: Nguyẽn Viê : t Hung, La Thẽ Ph uc, -D a : ng Ng _ oc