PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3445, 36 pp., 16 ®gures June 2, 2004

A New Crocodyliform from Zos Canyon, Mongolia

DIEGO POL1 AND MARK A. NORELL2

ABSTRACT Here we report on a new fossil crocodyliform from Cretaceous Redbeds in the Zos Canyon, Gobi Desert, Mongolia. This new taxon, Zosuchus davidsoni, is described based on the infor- mation provided by ®ve specimens collected during expeditions of the Mongolian Academy of Sciences±American Museum of Natural History. Zosuchus davidsoni is identi®able by nu- merous characters, including a posteriorly extensive secondary palate that opens through a secondary choana bordered by the palatines and pterygoids near the posterior edge of the skull, and a lacrimal±premaxillary contact on the dorsal surface of the snout. The phylogenetic relationships of Zosuchus davidsoni are shown through a parsimony analysis in the context of Crocodyliformes. This new form is found to be a late-appearing basal crocodyliform, forming a monophyletic group with two other taxa from the Early Cretaceous of China. Because of the basal position of Zosuchus within Crocodyliformes, the marked posterior extension of the secondary palate is most parsimoniously interpreted as a convergence with the derived con- dition of neosuchian crocodyliforms.

INTRODUCTION lizards) are very common, crocodyliform During the last decade, expeditions from specimens are rare. Other expeditions have the Mongolian Academy of Sciences and the noticed this as well, and only a few crocod- American Museum of Natural History have yliform specimens have been collected in developed large collections of fossil verte- these beds (OsmoÂlska, 1972; Storrs and E®- brates from Djadokhta and Djadokhta-like mov, 2000; Mook, 1924; E®mov, 1983, rocks in the Gobi Desert (Dashzeveg et al., 1988; OsmoÂlska et al., 1997). However, at 1995; Novacek, 1996, 2002). Although re- one locality, Zos Canyon, multiple corocod- mains of reptiles (especially dinosaurs and ilian specimens have been collected. Re-

1 Division of Paleontology, American Museum of Natural History ([email protected]). 2 Division of Paleontology, American Museum of Natural History ([email protected]).

Copyright ᭧ American Museum of Natural History 2004 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3445 mains of three taxa have been recovered, SAM-K South African Museum, Cape Town, which are known from seven specimens. One South Africa of these taxa, Zosuchus davidsoni, n.gen. and SMNS Staatliches Museum fuÈr Naturkunde n.sp., is surprisingly primitive for a Late Cre- Stuttgart, Stuttgart, Germany taceous crocodyliform. UA University of Antananarivo, Mada- In the following report we describe the gascar UCMP Museum of Paleontology, Universi- anatomy of this new form from the Zos Can- ty of California, Berkeley yon locality and analyze the phylogenetic re- ZPAL Instytut Paleobiologii PAN, Warsza- lationships within the context of Crocodyli- wa, Poland formes. This new taxa is depicted as a basal crocodyliform, forming a clade with two forms from the Early Cretaceous of China. HORIZON AND LOCALITY The following institutional abbreviations The Zos Canyon locality (®gs. 1, 2) was are used throughout the text: ®rst visited by Mongolian Academy of Sci- AMNH American Museum of Natural His- ences±American Museum of Natural History tory, New York ®eld parties in 1992. It had previously been BSP Bayerische Staatssammlung fuÈr Pa- visited by Mongolian and Russian paleontol- laÈontologie und Geologie, MuÈnich, ogists (Dashzeveg, personal commun.); how- Germany ever, according to Dashzeveg, little was CNM Chongqing Natural Museum, Sich- found and nothing about this locality was uan, People's Republic of China ever published. The locality has also been DGM Departamento de ProducËaÄo Mineral, Rio de Janeiro, Brazil referred to informally as Kholbot (Dashzev- GPIT Institut und Museum fuÈr Geologie eg, personal commun.). und PalaÈontologie, Universitat TuÈ- The locality lies on the southern ¯ank of bingen, TuÈbingen, Germany the Gilvent Ul, about 6 km northwest of the GWU George Washington University, main locality at Ukhaa Tolgod (®g. 1). The Washington, DC canyon is at the mouth of a large north±south IGM Mongolian Institute of Geology, pass that transects the Gilbent Ul. Although Ulaan Bataar, Mongolia topographically higher than the exposures at IVPP Institute of Vertebrate Paleontology Ukhaa Tolgod, the rocks at the Zos locality and Paleoanthropology, Beijing, People's Republic of China are stratigraphically lower, as the beds dip to LACM Los Angeles County Museum, Los the south underneath the Ukhaa Tolgod beds. Angeles No geochronologic work has commenced at MACN Museo Argentino de Ciencias Na- Zos Canyon; however, Protoceratops sp. re- turales, Buenos Aires, Argentina mains are common throughout the exposures. MAL Malawi Department of Antiquities, Interestingly, the mammalian fauna seems to Malawi be distinct as taxa unknown at other Mon- MB Institut fuÈr Palaontologie, Museum golian Djadokhta and Djadokhta-like beds fuÈr Naturkunde, Humbolt-Universi- have been recovered (e.g., ``zhelestids'' tat, Berlin, Germany MCZ Museum of Comparative Zoology, [Novacek et al., 2000]). Harvard University, Cambridge, At Zos Canyon three distinct levels are MA preserved (®g. 2). The uppermost of these MLP Museo de La Plata, La Plata, Argen- (the Red Rum locality) is where the zhelestid tina material is from. Also occurring at this lo- MOZ Museo Profesor J. Olsacher, Zapala, cality are lizards, protoceratopsians, and di- Argentina nosaur eggs. Sediments at Red Rum are MUC-PV Museo de GeologõÂa y PaleontologõÂa, bright red and very similar to classic Dja- Universidad Nacional del Comahue, dokhta rocks. Below this is a series of white NeuqueÂn, Argentina PVL Instituto Miguel Lillo, TucumaÂn, beds (Zos Canyon White beds); these rocks Argentina are much more similar to sediments of the RCL Museo de Ciencias Naturales, Pon- Nemegt Formation than they are to other ti®cia Universidade Catolica de Mi- Djadokhta sediments. The beds are white, nas Gerais, Brazil poorly sorted, and represent a series of 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 3

Fig. 1. Satellite photo of the Zos and Ukhaa Tolgod localities. stream channels preserved as indurated sands REFERRED SPECIMENS: IGM 100/1304, 100/ and gravels. Fossils in these beds are not 1306, 100/1307, and 100/1308. common, and when found include large di- ETYMOLOGY: Zos, from the type locality; nosaurs (ornithischans such as hadrosaurs, suchus, Greek for crocodile; anddavidsoni, sauropods, large theropods), turtle pieces, for Amy Davidson who prepared several of and occasional pieces of petri®ed wood. Be- these specimens and has been so instrumen- low these white beds a layer of red beds sim- tal in the exquisite preparation of Mongolian ilar to, but more ¯uvial than, classic Djadokhta specimens allowing the success of our work. beds lies atop the Paleozoic basement. The DIAGNOSIS: Small and extremely short- rocks have produced several poorly preserved snouted crocodyliform with an extensive an- dinosaur skeletons (dromaeosaurids and pro- toceratopsians) and lizards. It is in these beds terodorsal lacrimal process wedging between that all the specimens of Zosuchus davidsoni the nasal and maxilla, contacting anteriorly were collected. the posterodorsal process of premaxilla. Pal- atines forming a posteriorly extended sec- SYSTEMATIC PALEONTOLOGY ondary palate, almost reaching the posterior CROCODYLOMORPHA WALKER, 1970 edge of the pterygoid ¯anges where the sec- CROCODYLIFORMES HAY, 1930 (SENSU CLARK, ondary choana is located. Posttemporal re- 1986) gion of the parietal extremely narrow, wedg- Zosuchus davidsoni, n.gen. and n.sp. ing between the squamosals (paralleled in HOLOTYPE: IGM 100/1305, isloated skull Gobiosuchus). Reduced upper dentition, pre- and lower jaws. maxilla with three teeth and maxilla with ®ve 4 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 2. Exposures of the Zos Canyon and overlying beds. Photo: G.W. Rougier. teeth (paralleled in some mesoeucrocodyli- here as a product of ontogenetic change. ans). Similar ontogenetic changes in supratempor- al fenestra shape have been noted in extant DESCRIPTION crocodyliforms (Mook, 1921; KaÈlin, 1933). The skull of IGM 100/1305 has most of Moreover, this variation is congruent with its elements preserved except for the palatine other differences in IGM 100/1304 that are shelves, supraoccipital, and left side of the also subject to ontogenetic change (see be- rostrum (®gs. 3±5). However, most of these low). The infratemporal fenestra is not com- elements are nicely preserved in IGM 100/ pletely preserved in any of the specimens 1304, 100/1306, 100/1307, and 100/1308. studied here, although it probably was small The snout is extremely short, high, and due to the broadness of the dorsal process of moderately broad (i.e., oreinirostral, sensu the quadratojugal. The external surface of the Busbey, 1994). The external nares are con- skull is ornamentated with a slight pitted pat- ¯uent and face anteriorly. The antorbital fe- tern as in most members of Crocodyliformes. nestrae are markedly reduced and located This sculpture is missing in the smaller spec- just anterior to the orbital margin. Zosuchus imen (IGM 100/1304). davidsoni has extremely large and laterodor- The premaxilla is a short element, yet its sally facing orbits occupying 33% of the total ventral edge occupies the anterior third of the skull length (IGM 100/1305). The supratem- anteroposterior extension of the snout. It poral fenestrae are extremely reduced and forms the ventral, lateral, and dorsolateral oriented oblique to the longitudinal axis of margin of the external nares. It possesses an the skull with their anterior ends pointing an- extremely well-developed posterodorsal pro- terolaterally. One of the specimens (IGM cess that wedges between the maxilla and na- 100/1304) shows minor differences in the sal bones on the dorsal surface of the snout shape and size of the supratemporal fenestra (®g. 3). The suture between these two bones (®g. 6). IGM 100/1304 (®g. 7) is the smallest does not seem to overlap, although it is not specimen, and this variation is interpreted interdigitated. A large vertically oriented 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 5

Fig. 3. Skull of the holotype of Zosuchus davidsoni IGM 100/1305 in dorsal view. 6 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 4. Skull of the holotype of Zosuchus davidsoni IGM 100/1305 in ventral view. 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 7

Fig. 5. Skull of the holotype of Zosuchus davidsoni IGM 100/1305 in lateral view. notch which ®ts the canineform dentary served. The suture with the palatal branch of tooth lies at the suture between the premaxila the maxilla extends anteromedially (®g. 4) and the maxilla (®g. 5). A small neurovas- rather than medially as in most Crocodyli- cular foramina is located on the premaxillary formes. wall that forms the anterior edge of the pre- The premaxillary dentition is well pre- maxillary-maxillary notch. The palatal served in the right premaxilla of IGM 100/ branches of the premaxillae extend medially, 1305 and consists of only three slender con- presumably contacting each other at the mid- ical teeth. None of these elements has ser- line, although this contact has not been pre- rations on anterior or posterior edges. The

Fig. 6. Skull of specimen IGM 100/1304 in dorsal (A) and ventral (B) views. 8 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 7. Skull of specimen IGM 100/1304 in left (A) and right (B) lateral views.

®rst premaxillary tooth is small and located between the nasal and the maxilla reaching below the lateral edge of the external nares. the posteromedial edge of the posterodorsal The second tooth is more than twice the size process of the premaxilla (®g. 8). Thus, the of the more anterior teeth, causing the pre- maxilla does not contact the nasals, a unique maxilla to bulge at this point. The third pre- condition among Crocodylomorpha. maxillary tooth is extremely reduced and is The maxilla borders the anterior edge of a located just before the anterior edge of the reduced antorbital fenestra located just ante- premaxillary-maxillary notch. rior to the anterior orbital edge (®g. 5). The The maxilla has a limited exposure on the maxilla and lacrimal are not depressed lateral surface of the snout due to the exten- around the antorbital fenestra in contrast to sion of the premaxillary-maxillary notch. most non-neosuchian crocodyliforms that Dorsal to this notch the maxilla borders the have a marked antorbital fossa surrounding premaxillary posterodorsal process. At the the antorbital fenestra (e.g., Protosuchus ri- posterior edge of the posterodorsal premax- chardsoni MCZ 6727, Gobiosuchus kielanae illary process, the maxilla contacts the anter- ZPAL MgR-II/70, Notosuchus terrestris odorsal process of the lacrimal which wedges MACN-RN 1037). Posteriorly, the maxilla 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 9

Fig. 8. Skull of specimen IGM 100/1307 in dorsal view. borders the anteroventral margin of the en- maxillary teeth are preserved on the left side larged orbit and contacts the jugal before the of IGM 100/1304, although these elementes midpoint of the orbit. are poorly preseved (®g. 6). The four poste- The ventral edge of the maxilla is straight riormost maxillary teeth are nicely preserved and increases its ventral extension posterior in IGM 100/1305 and have no serrations to the premaxillary-maxillary notch. Five along their anterior or posterior edges. All of 10 AMERICAN MUSEUM NOVITATES NO. 3445 them are conical and subequal in size, except slightly along their contact with the lacrimal for the third tooth, which is approximately and prefrontal (®g. 8). The posterior edge of twice the size of the other maxillary teeth the nasals contacts with the frontal in an in- (®g. 5). In contrast to neosuchian crocodyli- terdigitated transverse suture. forms, the tooth size variation of Zosuchus The lacrimal is poorly preserved in most davidsoni is not matched by a sinusoidal specimens. This element forms the posterior ventral edge of the maxilla. and dorsal margins of the antorbital fenestra The palatal branch of the left maxilla of and the dorsal half of the anterior orbital IGM 100/1305 extends posteromedially to margin. Posterior to the antorbital fenestra, the premaxilla-maxilla palatal contact (®g. the lacrimal is a thin columnar bar, slightly 4). Specimen IGM 100/1306 shows the pos- exposed on the lateral surface of the snout terior region of both palatal shelves exposed (®g. 5). Therefore, the posterior edge of the in dorsal view. These contact each other, antorbital fenestra is very close to the ante- forming a brief and anteriorly located sec- rior orbital margin. Dorsal to the antorbital ondary palate as well as the anterior and lat- fenestra, the lacrimal extends anteromedially eral edges of the anterior (primary) choanal on the dorsal surface of the snout. As de- opening (®g. 11). scribed above, this well-developed process This condition clearly resembles the mor- wedges between the nasal and maxilla, phology present in basal crocodyliforms reaching the posterodorsal end of the pre- (e.g., Gobiosuchus ZPAL MgR-II/67, Fruita maxilla anteriorly. A similar, anteriorly ex- form LACM 120455a) that lack the posteri- tended process is also present in other short- orly extended maxillary secondary palate snouted crocodyliforms such as Simosuchus present in mesoeucrocodylians, in which the clarki (UA 8679) or Navajosuchus mooki (ϭ maxillary palatal branches contact each other ''Allognathosuchus'' mooki (Brochu, 1999); medially along their entire length. Lateral to AMNH 6780), although in these forms the this opening, the palatal branch of the max- anterior process of the lacrimal does not illa forms the anterior and medial edges of a reach the posterodorsal process of the pre- large suborbital fenestra. maxilla. Furthermore, the derived similarities The nasals form most of the the dorsal between these taxa and Zosuchus are limited margin of the con¯uent external nares. Their to this character and the extremely short- dorsal surfaces have different degrees of or- snouted condition. namentation in the three specimens in which The prefrontals are elongate, longitudinal- this region was preserved (IGM 100/1304, ly oriented bones that form the anteromedial 100/1305, and 100/1307). The nasals of IGM edge of the orbits. The medial edge of the 100/1304 are smooth, whereas those of the prefrontal contacts the frontal and nasals. IGM 100/1307 are the most heavily orna- Anteriorly, the prefrontal is sutured to the mented (showing a pattern of small and well- lacrimal on the dorsal surface of the snout. spaced pits). This difference in ornamenta- They are overlapped by a large anterior pal- tion is interpreted as ontogenetic differences, pebral preserved in IGM 100/1304 (®g. 6). which is also expressed in differences in the The descending process of the prefrontal is ornamentation of other bones, the degree of not preserved in any of the specimens, and interdigitation of sutures, and skull size therefore it cannot be determined if they con- among the specimens studied here. The an- tact the palate as in mesoeucrocodylians terior region of the lateral edges of the nasals (Clark, 1994). is straight (IGM 100/2 and 100/1307) or Two large palpebrals are preserved above slightly concave (IGM 100/1304). In this re- the orbit of specimen IGM 100/1304. The gion the lateral edges of the nasals diverge anterior palpebral is triangular and extends slightly posteriorly along their contact with posterolaterally from the anteromedial mar- the posterodorsal process of the premaxilla. gin of the orbit. Its anterior end overlaps the Posterior to this area, the nasal contacts the prefrontal and probably the lacrimal at its anterodorsal process of the lacrimal that contact with the skull. In contrast with most wedges between the maxilla and the nasals. crocodyliforms, the posterior palpebral is ex- The lateral edges of the nasals converge tremely large, being subequal to the anterior 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 11 element. This particular condition is also pressed region of the parietal dorsal surface, found in Sichuanosuchus (IVPP V 10594). medially bounded by an oblique ridge par- The frontals are fused along the midline allel to the parietal-squamosal suture (®g. 3). and have a smooth and ¯at dorsal surface The diminutive posterior edge of the parie- (®g. 3). The frontals are moderately narrow tals brie¯y contacts the anteriormost edge of anteriorly and across the interorbital region the supraoccipital surface on the skull roof. (subequal to the width of the nasals). They The squamosals form most of the ¯at skull expand at the posterior end of the orbits roof characteristic of Crocodyliformes. These where they contact the postorbitals laterally are distinctive elements of Zosuchus david- and the parietals posteriorly. The suture with soni due to the presence of an extremely en- the postorbital on the skull roof shows that larged surface which extends posteriorly and the frontals formed, at least, the anteromedial posterolaterally to the supratemporal fenes- margin of the supratemporal fossa. The lat- tra. Like other bones of the skull roof, the eral edges of the frontals delimiting the orbits squamosal shows variation in the ornamen- are elevated with respect to the dorsal surface tation among the specimens studied here. In of this bone, forming small supraorbital ridg- IGM 100/1307, the squamosal is densely or- es. At the midpoint of the orbital margin, the namented with a pitted pattern on its dorsal frontals contact elongate posterior processes surface. Its contact with the postorbital in the of the prefrontals. The anterior contact of the anterolateral region of the squamosal cannot frontals with the nasals is oriented trans- be precisely located in any of the specimens versely, is slightly concave posteriorly, and studied here due to poor preservation. The is interdigitated (®g. 8). lateral region of the squamosal overhangs the The parietals are fused and wide between otic recess and bears a smooth and slightly the supratemporal fenestrae to form a skull developed groove on its lateral edge, presum- table with the frontal postorbital and squa- ably for the insertion of a muscular ear ¯ap. mosal. This surface is ¯at, lacks a medial Medially, the squamosal borders the supra- ridge, and has varying degrees of ornamen- temporal fossa and contributes to the exten- tation in the different specimens. In IGM sive smooth ¯oor of this fossa. The squa- 100/1304, this area is almost completely un- mosal extends posteromedially to border the ornamented, while in IGM 100/1307 this re- supratemporal fossa, where it contacts the gion has a marked ornamentation composed of small pits and slightly marked grooves. parietal at the anterior opening of the tempo- The parietal table's anterior edge contacts orbital passage. The contact with the parietal the frontal through an interdigitated transver- is located more medially than in most cro- sal suture (IGM 100/1305). Posteriorly to codyliforms, since it originates on the pos- this, it forms the medial and posteromedial teromedial corner of the supratemporal fe- edges of the supratemporal fossae where it nestra and extends posteromedially toward contacts the squamosals, forming the roof of the dorsal surface of the supraoccipital (®g. the anterior opening of the tempo-orbital pas- 3). sage. Lateral to these edges, and more ven- Posterior to the occipital edge of the skull trally located, the parietal extends as a ¯at roof, a ¯ange of the squamosal extends pos- and smooth ¯ange, forming more than half teroventrally to border the lateral edge of the the ¯oor of the supratemporal fossa. This occipital surface of the supraoccipital. The ¯oor is also formed by the quadrate and the lateral region of this surface of the squamosal squamosal and occupies the posterior half of contacts the dorsal edge of the paroccipital the supratemporal fossa, leaving a rather process. As in most basal crocodyliforms small supratemporal fenestra located anteri- (e.g., Protosuchus UCMP 131827, Shantun- orly to it (®g. 3). Posterior to the supratem- gosuchus (Wu et al., 1994a), Gobiosuchus poral fossa, the parietal narrows markedly ZPAL MgR-II/67), the occipital ¯ange of the along an intedigitated suture with the squa- squamosal extends laterally beyond the lat- mosal (similar to the condition present in Go- eral edge of the paroccipital process. This biosuchus ZPAL MgR-II/68). Interestingly, contrasts with the condition of most mesoeu- this contact is located along a slightly de- crocodylians, in which the paroccipital pro- 12 AMERICAN MUSEUM NOVITATES NO. 3445 cess reaches the lateral edge of the occipital namented in IGM 100/1305. Along this re- ¯ange of the squamosal. gion, a slightly marked and extremely narrow The occipital ¯ange of the squamosal is groove is oriented longitudinally. Dorsal to bordered dorsolaterally by a moderately this groove, the jugal has a rounded dorsal long, acute, and descending posterodorsal surface, while ventral to it, the jugal's surface process of the squamosal that is ornamented is slightly concave and faces lateroventrally. in IGM 100/1307 but smooth in all the other The base of the postorbital process is pre- specimens (probably because of preserva- served on the right jugal of IGM 100/1304 tional and/or ontogenetic reasons). The distal and 100/1305. As in basal crocodyliforms, extremity of the posterolateral process con- this region is wide, somewhat ¯attened, dor- tacts the occipital surface of the quadrate as sally oriented, and continuous with the lateral well as the distal end of the paroccipital pro- surface of the jugal. The jugal bar below the cess. Interestingly, a descending and acute infratemporal fenestra is also moderately nar- posterodorsal process of the squamosal is ab- row and forms part of the ventral edge of the sent in the most basal crocodyliforms (Pro- infratemporal fenestra. The infratemporal re- tosuchus AMNH 3024, Orthosuchus SAM-K gion of the jugal is dorsoventrally ¯attened 409, Hemiprotosuchus PVL 3829), but is as in Sichuanosuchus IVPP V 10594, al- present in Gobiosuchus ZPAL MgR-II/67, though this might be accentuated as a pres- Shantungosuchus (Wu et al., 1994a), Sichu- ervational artifact. Both the posterior end and anosuchus IVPP V 10594, and most basal the jugal's contact with the quadratojugal are mesoeucrocodylians. not preserved. The postorbital is best preserved on the The quadratojugal is best preserved in right side of IGM 100/1304. On its dorsal IGM 100/1305 and 100/1306. The quadrato- surface, the postorbital contacts the frontal jugal extends posterior to the infratemporal medially on the skull roof and extends lat- fenestra and has a wide and smooth surface erally as a thin cylindrical bar between the that nearly reaches the posterior edge of the supratemporal fenestra and the orbit (®g. 6). quadrate, as in basal crocodyliforms. The The anterolateral corner of the postorbital posterior region of the quadratojugal has a bears a small anterolateraly pointed process. sinusoidal ventral margin that ends in a wide This process is continuous with the dorsal and round posterior edge (®g. 9), similar to surface of this bone instead of being located the ``fan-shaped'' process described for ventrally, as in most non-neosuchian crocod- Shantungosuchus IVPP V 10594 and Sichu- yliforms (e.g., Notosuchus MACN-RN 1037, anosuchus (Wu et al., 1994b). A unique char- Araripesuchus AMNH 24450, Baurusuchus acteristic of this posterior quadratojugal fan- DGM 299-R) and dyrosaurids (Buffetaut, shaped process is that it forms a small lat- 1976). The lateral edge of the postorbital erally projected shelf, which slightly over- continues posteriorly to the pointed process, hangs the lateral surface of the quadrate (®g. thus lacking the anteroventrally exposed 10). In other crocodyliforms, instead, this postorbital edge that characterizes basal me- process is absent and therefore the lateral soeucrocodylians (Clark, 1994). A poorly surface of the quadratojugal and quadrate is preserved descending process of the postor- continuous. bital is present only in IGM 100/1305. This The dorsal process of the quadratojugal process forms the dorsal half of a somewhat extends anterodorsally as a broad sheet, as in ¯attened and smooth postorbital bar. Dorsal- basal crocodyliforms. This process is bor- ly, the postorbital bar expands abruptly to dered posteriorly by the quadrate and has a form the dorsal surface of the postorbital. moderately developed ridge running parallel The jugal delimits the ventral margin of to the dorsal half of the quadrate-quadrato- the enlarged orbits and, as in basal croco- jugal suture (resembling the condition pre- dyliforms, is not dorsoventrally expanded sent in Gobiosuchus kielanae [OsmoÂlska et with respect to the postorbital region. The al., 1997; ZPAL MgR-II/68]). The anterior jugal's anterior end does not reach the ante- edge of the quadratojugal dorsal process pre- rior edge of the orbit (®gs. 5, 6). The lateral sumably forms the posterior edge of the in- surface of the suborbital process is poorly or- fratemporal fenestra, although it is not clear 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 13

Fig. 9. Posterior region of skull of specimen IGM 100/1306 in lateral view. if this edge was preserved in any of the spec- basal crocodyliforms from the Jurassic of imens studied here. Dorsally, this process ar- North America (Fruita form; Clark, 1985) ticulates extensively with the postorbital de- and Mongolia (Nominosuchus and Adzhosu- scending process. chus; E®mov, 1996; E®mov et al., 2000). The lateral process of the ectopterygoid is Unfortunately, the maxillopalatine suture is only preserved in IGM 100/1304. This ele- not well de®ned in this area but was probably ment is a delicate cylindrical bar which ex- located on the posterolateral edges of the an- pands slightly at its contact with the infra- terior (primary) choana. orbital jugal bar. The medial branch of the The posterior region of the palatines is ectopterygoid has not been preserved in any preserved in IGM 100/1306, showing an of the specimens studied here. overlapping articulation with the pterygoids The anterior processes of the palatines over a depressed area on the lateral edges of have not been preserved in IGM 100/1305, the choanal groove (clearly seen in IGM 100/ although they are present but poorly pre- 1305; ®g 4). The palatines of Zosuchus dav- served in IGM 100/1304 and 100/1306. IGM idsoni extend posteriorly to contact each oth- 100/1306 is particularly interesting since it er medially (®g. 12), forming a posteriorly has preserved both the anterior and posterior located palatine secondary palate that closes edges of the palatines, although the midre- the choanal groove (ventrally opened in basal gion of them has not been preserved. crocodyliforms). The palatines of Zosuchus The anterior edge of the palatine shelves davidsoni are unique since they extend pos- extends medially to contact each other me- teriorly much more than in any other basal dially and form the posterior border of the crocodyliform, almost reaching the posterior anterior (primary) choana (®gs. 11, 12), margin of the pterygoid ¯anges (®gs. 12, 13). which is bordered anteriorly by the palatal At their posterior end, the palatines form the branches of the maxillae. A similar anterior anterior edge of a posterior (secondary) cho- palatal morphology was reported on some anal opening. This resembles the choanal 14 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 10. Skull of specimen IGM 100/1306 in occipital view. opening of basal mesoeucrocodylians which although it differs structurally from these is enclosed between the palatines and the taxa since the posterior (secondary) choana pterygoids. Interestingly, the palate of Zo- of Zosuchus is anteriorly closed by the pal- suchus davidsoni is projected dramatically atines rather than being enclosed within the posteriorly, leaving the small posterior (sec- pterygoids as in eusuchians (®g. 12). Addi- ondary) choanal opening close to the poste- tionally, the posterior (secondary) choana of rior edge of the pterygoid ¯anges. A similar Zosuchus davidsoni opens posteriorly near condition is present in derived neosuchians, the pterygoid-basisphenoid contact, while the

Fig. 11. Palatal region specimen of IGM 100/1306 in posterodorsal view. 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 15

Fig. 12. Posterior region of skull of specimen IGM 100/1306 in ventral view. 16 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 13. Lower jaws of the holotype of Zosuchus davidsoni IGM 100/1305 in dorsal (A) and ventral (B) views. secondary choana of eusuchians is posteri- braincase (®gs. 4, 12), as in basal croco- orly closed by a posterior wall of the ptery- dyliforms. The anterior margin of the basi- goids (®g. 12). sphenoid is transversally oriented, lacking The pterygoids are almost completely pre- the acute anterior process that wedges be- served in IGM 100/1305 and 100/1306. As tween the pterygoids in most basal crocod- in most basal crocodyliforms, the pterygoid yliforms (Protosuchus UCMP 131827, Go- wings are reduced, directed laterally on a biosuchus ZPAL MgR-II/67, Shantungosu- transverse plane, dorsoventrally thick, and chus [Wu et al., 1994b]). The basisphenoid ®lled with pneumatic spaces (®g. 10). The has two well-developed longitudinal ridges ventral surface of the pterygoids is ¯at and located medially on its ventral surface (®gs. smooth, except for the medial region, which 4, 12). Anteriorly, at the pterygoid-basisphe- is markedly depressed, forming a narrow and noid contact, these ridges approach one an- longitudinally oriented trough-shaped groove other (separated by 1.3 mm) and are contin- that narrows posteriorly to the pterygoid uous with the lateral edges of the choanal ¯anges toward the basisphenoid-pterygoid groove of the pterygoids. The basisphenoidal contact (®g. 4). The pterygoids contact each ridges diverge posteriorly and dissapear at other along this depression and are appar- the basisphenoid-basioccipital contact, be- ently fused posteriorly. The posterior half of tween the foramen intertympanicum and the the pterygoideal groove bears a longitudinal lateral eustachian foramina (®g. 10). At this ridge that forms an incipient septum in the point, these ridges are separated by 3.3 mm. posterior (secondary) choanal opening (®g. Several basal crocodyliforms have paired 12). This ridge extends posteriorly to the ridges on the ventral surface of the basisphe- pterygoid wings, reaching the anterior edge noid (e.g., Protosuchus richardsoni UCMP of the basisphenoid. The base of the quadrate 130860); however, in these forms, the ridges processes of the pterygoids is lateromedially are usually located laterally on the ventral wide and faces posteroventrally (®g. 4), as in surface of the basisphenoid, at the lateral most basal crocodyliforms. These processes edges of this element. Paired basisphenoidal are sutured strongly to the basisphenoid and ridges located medially on the ventral surface quadrates. of the basisphenoid similar to those of Zo- The basisphenoid is semicircular and suchus are present in Sichuanosuchus (IVPP widely exposed on the ventral surface of the V 10594) and Shantungosuchus (Wu et al., 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 17

1994b). The lateral eustachian foramina and Unfortunately, none of the specimens of Zo- the foramen intertympanicum are located on suchus davidsoni has preserved details on the the basisphenoid posterior edge, at its contact cranial nerve and vascular foramina which with the basioccipital. open on the occiput. The dorsal planes of the The basioccipital is best preserved in IGM otoccipitals contact each other medially 100/1306. This bone is exposed posteroven- through a vertical suture. Dorsal to the trans- trally on the occipital surface of the skull verse ridge, the otoccipitals are exposed pos- (®gs. 10, 12). Anteriorly, it contacts the ba- terodorsally. Their dorsomedial edges con- sisphenoid in a wide U-shaped suture that de- tact the supraoccipital along an interdigitated limits the posterior edge of the foramen in- suture directed dorsolaterally. At this point tertympanicum and the lateral eustachian fo- the otoccipitals extend laterally to form a ramina. The basioccipital surface is elevated rather narrow and short paroccipital process at this point, forming a marked ridge along (®g. 10). Dorsally, the paroccipital process is the basisphenoidal suture. The lateral ends of bounded by a ventrolaterally directed suture this ridge are slightly more elevated, forming along a large occipital ¯ange of the squa- small and delicate basioccipital tubera. Pos- mosal. The paroccipital process is dorsoven- terior to the foramen intertympanicum, the trally narrow and curves slightly posteriorly basioccipital bears a medially located longi- at its lateral end. In this region, the paroccip- tudinal ridge which extends onto the ventral ital process overhangs the ventral region of half of this bone (®g. 10). The remainder of the otoccipital (®g. 10), forming a notch sim- the basioccipital surface is ¯at or slightly ilar to the cranioquadrate passage of Croco- concave. The basioccipital forms only the dylia. The identi®cation of this structure as ventral half of the occipital condyle (®g. 10), the cranioquadrate passage cannot be deter- in contrast to the condition seen in most cro- mined since it is dependent on the identi®- codyliforms where the basioccipital forms cation of the other nerve and vascular open- nearly all of the occipital condyle. The ba- ings of the occipital region (see Clark, 1986). sioccipital-otoccipital contact is not well de- The supraoccipital is well preserved in ®ned except for sutures at the occipital con- IGM 100/1305, 100/1306, and 100/1308. It dyle. is exposed both on the occipital and dorsal The otoccipitals are also best preserved in surfaces of the skull. The occipital region is IGM 100/1306. These are exposed widely on best preserved in IGM 100/1308 where it is the occipital surface of the skull and, in con- triangular-shaped and exposed posterodorsal- trast to the typical crocodyliform condition, ly. Its surface is smooth and ¯at and bears a they form the dorsal half of the lateral region medial sagittal ridge, as in several other cro- of the occipital condyle (®g. 10). Dorsal to codyliforms. The dorsal surface of the supra- the condyle, the otoccipitals form the lateral occipital is best preserved in IGM 100/1305. and dorsal margins of the foramen magnum, The supraoccipital region is smaller than the contacting each other medially (excluding occipital surface, semicircular-shaped, and the supraoccipital from the dorsal margin of slightly ornamented (®g. 4). The posttem- the foramen magnum). Lateral to this region poral fenestra cannot be observed in any the otoccipitals are exposed along two dif- specimen due to poor preservation. ferent planes, separated by a transverse ridge The quadrate of Zosuchus davidsoni is that runs from the dorsal margin of the fo- best preserved in IGM 100/1305 and 100/ ramen magnum to the ventrolateral edge of 1306. Its anterodorsal region is clearly ex- the paroccipital process (®g. 10). Ventral to posed on the left quadrate of IGM 100/1305. this ridge the otoccipitals are slightly ex- The otic recess is very deep and roofed by a posed posteroventrally and lack the enlarged large lateral ¯ange of the squamosal (®gs. 5, ventrolateral process that characterizes most 9). On its posterodorsal surface, the quad- basal crocodyliforms (e.g., Protosuchus rate's anterior edge contacts the quadratoju- UCMP 131827; Clark, 1986). Along the lat- gal along an overlapping suture that is slight- eral edge of this region the otoccipitals ex- ly concave posteriorly. Posterior to this su- tensively contact the quadrates in an inter- ture the quadrate surface is perforated by digitated suture that extends dorsolaterally. several foramina (®g. 5), as is commonly 18 AMERICAN MUSEUM NOVITATES NO. 3445 found in basal crocodyliforms (e.g., Proto- in these taxa is much less extensive than in suchus AMNH 3024, Orthosuchus SAM-K most mesoeucrocodylians. The distal body of 409, Gobiosuchus ZPAL MgR-II/67, Shan- the quadrate is posteroventrally directed and tungosuchus [Wu et al., 1994b]). Hecht and is about as wide as long (®g. 9). Tarsitano (1983) and Nash (1975) described The posterior surface of the quadrate body these fenestrae in Protosuchus richardsoni has a vertical ridge that divides this surface and Orthosuchus stormbergi and they were (®g. 10). The articular condyles face postero- later found to be present in other basal croco- ventrally and are horizontally aligned. The dyliforms (Busbey and Gow, 1984; Clark, medial condyle is narrower and sharper than 1985, 1986). In Zosuchus davidsoni (IGM the rounded lateral condyle. 100/1305) only three fenestra can be identi- The anteroventral surface of the quadrate ®ed, closely resembling the condition de- of Zosuchus davidsoni (IGM 100/1305) is scribed for Shantungosuchus (Wu et al., convex rather than ¯at as in most crocody- 1994b). The most distal fenestra is very elon- liforms. A single, oblique crest runs from the gate, extending anterodorsally on the postero- lateral condyle to the midpoint of the antero- dorsal surface of the quadrate (®g. 5). Within ventral surface of the quadrate. Anteroven- this fenestra lie several delicate bony struts. trally, the quadrate is tightly joined to the This fenestra could be homologized with fe- quadrate process of the pterygoids via an in- nestra A of Protosuchus, due to its location, terdigitated suture. Dorsal to this suture the shape, and the presence of numerous internal quadrate contacts the laterosphenoid to form bony struts, although in most forms this fe- the posterior edge of the trigeminal foramen nestra is not as elongated as in Zosuchus dav- (at this point the quadrate probably contacted idsoni. Notably, Shantungosuchus presents a the prootic on its medial surface, although fenestra A that is remarkably similar to that this contact is not exposed). The quadrate ex- of Zosuchus davidsoni. Anterodorsal to this tends dorsally to wedge between the parietal large fenestra are two well-de®ned and and squamosal on the ¯oor of the supratem- rounded fenestrae. The ®rst contains an poral fossa, reaching the posterior edge of oblique bony strut while the second one does the supratemporal fossa. not seem to be subdivided (®g. 5). Again, the The laterosphenoid is partially preserved number and shape of these fenestrae are re- in IGM 100/1305, 100/1306, and 100/1308. markably similar to those of Shantungosu- Posteriorly, it contacts the quadrate enclosing chus, in contrast to the condition of other the trigeminal foramen (it probably also con- basal crocodyliforms that have four distinct tacted the prootic at this region, although this fenestrae in addition to fenestra A. Posterior element is not exposed). At the ventral edge to this area the quadrate is poorly preserved, of the trigeminal foramen, the laterosphenoid and therefore it is not possible to determine brie¯y contacts the ascending process of the the morphology of the otic notch and con®rm pterygoid at an interdigitated suture located the presence of a posteriorly closed otic me- on the lateral surface of the braincase wall. atus. The sutures with the squamosal and Anterior to this region the laterosphenoid's postorbital are not preserved on any of the lateral surface curves medially and bears a specimens. slightly developed ventral notch (which ex- The distal region of the quadrate is best tends ventrally onto the pterygoids, lateral to preserved in IGM 100/1306. The distal body the area occupied by the basisphenoid cultri- of the quadrate extends ventral to its contact form process in Crocodylia). Although the with the posterolateral process of the squa- anteriormost surface of the laterosphenoid is mosal on the occipital surface of the skull not exposed, it seems that the external sur- (®gs. 9, 10). Most basal crocodyliforms do face of the laterosphenoid of Zosuchus da- not have a differentiated distal body of the vidsoni is convex, lacking the large ridge that quadrate, which contrasts with the incipient separates the lateral and anterior laterosphen- development of this process in Zosuchus oid surfaces as in Crocodylia. No details on davidsoni. A similar morphology is also pre- the notches and foramina for the passage of sent in Sichuanosuchus IVPP V 10594, al- nerves II, III, and IV are preserved in any of though the development of the quadrate body these specimens. Dorsally, the anteromedial 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 19

Fig. 14. Lower jaws of the holotype of Zosuchus davidsoni IGM 100/1305 in lateral view.

¯ange of the laterosphenoid is tightly sutured izes neosuchian crocodyliforms. The dentar- to the frontals and presumably the parietals ies have well-developed posterodorsal and (IGM 100/1305). The capitate process of the posteroventral processes that extend above laterosphenoid and its contact with the post- and below the mandibular fenestra (®g. 6). orbital is not preserved in any of the speci- The lower dentition is best preserved in mens. IGM 100/1305. All preserved teeth are thin, The dentaries are very low and broad at conical, and apparently unserrated. The an- the symphyseal region (®gs. 13, 14). The terior tip of the dentaries lack preserved mandibular symphysis is elongate, extending teeth, although in IGM 100/1305 there are posteriorly to the level of the enlarged max- two poorly preserved cavities that are prob- illary teeth and anterior edge of the orbit. ably the anteriormost alveoli. Posterior to The dorsal surface of the mandibular sym- this region, the dentary has a small diastema physis is wide, ¯at, and horizontally exposed of 2.0 mm. This edentulous region extends (®g. 13). Several neurovascular foramina are to the next dentary tooth that precedes the located on this surface, close to the lateral lower caniniform tooth (®g. 13). This tooth edges of the dentaries. These edges bulge at is small judging from the alveolar dimen- the midpoint of the symphysis where the sions in IGM 100/1305 and from the base of lower caniniform tooth is located (®g. 13). a small crown poorly preserved in IGM 100/ At this region the ventral surface is ¯at and 1307. The next dentary tooth is the lower slightly ornamented with well-spaced small caniniform, which is well preserved in IGM pits (IGM 100/1304 and 100/1307). Posterior 100/1304 (®g. 6). This enlarged tooth is ap- to the mandibular symphysis, the dentaries proximately twice the size of the other den- increase in dorsoventral height and have a tary teeth. The ®rst postcaninform dentary convex lateral surface. In this region the den- tooth is small and conical as preserved in the taries are smooth (IGM 100/1304) or slightly left dentary of IGM 100/1305. Posterior to ornamented (IGM 100/1305). The dorsal this tooth, the dentaries have a short posterior edge of the dentary is slightly elevated at the diastema (1.6 mm) that is present in both lower caniniform tooth (®g. 14). Posterior to dentaries of IGM 100/1305 (®g. 13). This re- this area, the dorsal edge is slightly concave, gion accommodated the enlarged maxillary lacking the sinusoidal margin that character- tooth. Posterior to the second diastema, the 20 AMERICAN MUSEUM NOVITATES NO. 3445 dentary bears several alveoli showing a sin- PHYLOGENETIC RELATIONSHIPS gle wave of size variation. The dimensions of these teeth increase along the ®rst three A dataset of 183 characters with the ad- alveoli and decrease posteriorly (®g. 13). The dition of seven new characters was gathered ®rst three alveoli are partially divided by sep- from previous studies (Clark, 1994; Wu and ta located ventral to the lateral and medial Sues, 1996; Gomani, 1997; Wu et al., 1997; edges of the toothrow. Therefore, these al- Buckley et al., 2000; Ortega et al., 2000; Pol, veoli are super®cially continuous, resem- in press). These characters were scored bling the tooth groove present in some basal across 44 taxa. The taxon-sampling regime mesoeucrocodylians (e.g., Notosuchus focused on non-neosuchian crocodyliforms, MACN-RN 1040). The posterior half of the although 15 representatives of the neosuchi- toothrow lacks internal septa between the an clade were included. This dataset was an- tooth sockets (®g. 13). The precise number alyzed under equal-weighted parsimony us- of postcaniniform dentary teeth is dif®cult to ing Nona (Goloboff, 1993). A heuristic tree determine because none of the specimens search was performed consisting of 1000 preserves the entire toothrow; however, this replicates of RAS ϩ TBR with a ®nal round number probably was either seven or eight. of TBR (mult*1000; max*;), holding 20 The splenials do not form part of the man- trees per replication (hold/20;). Zero-length dibular symphysis (at least as can be deter- branches were collapsed using the strictest mined from the ventral surface). Posterior to criterion (i.e., when any possible states are this area, they overlap the ventral surface of shared between the ancestor and descendant the dentaries medially and are only slightly node; amb-). Six most parsimonious trees of exposed in ventral view. The medial surface 615 steps (CI ϭ 0.36, CIinf ϭ 0.35, RI ϭ of the splenials is thin and very convex (IGM 0.67) were found in 863 of 1000 replications. 100/1304 and 100/1305). Further searches employing 10,000 iterations The angular forms most of the ventral bor- of the Parsimony Ratchet (Nixon, 1999) im- der of the mandibular fenestra (®g. 6). This plemented in Nona resulted in the same set element extends anteriorly beyond the man- of topologies (hitting the best length in 9351 dibular fenestra and ventrally borders the times). posteroventral process of the dentary. The In all most parsimonious hypotheses, Zo- angular forms the ventral edge of the poste- suchus is depicted as the sister taxon of a rior half of the mandibular ramus, which de- clade composed by Sichuanosuchus and ¯ects dorsally only slightly posterior to the Shantungosuchus, both from the Early Cre- mandibular fenestra. In this region, the lateral taceous of China (®g. 15). This Cretaceous extension of the angular is extremely reduced Asian clade is located basally within the cro- and, thus, the surangular forms most of the codyliform clade and is diagnosed by four lateral surface of the mandible (®g. 6). This unambiguous synapomorphies (quadratoju- condition is also present in Sichuanosuchus gal posterior end not reaching the quadrate and Shantungosuchus (Wu et al., 1994b, condyles [char. 141]; angular shifted to the 1997). ventral surface mandibular rami posterior to The surangular anteriorly contacts the pos- the mandibular fenestra [char. 171]; paired terodorsal process of the dentary above the basisphenoid ridges located medially on the mandibular fenestra. It posteriorly forms the ventral surface of basisphenoid [char. 179]; dorsal edge of the this fenestra, where it is ``fan-shaped'' posterior process of the quad- slightly arched (®g. 6). As noted, posterior to ratojugal [char. 180]). the mandibular fenestra, the surangular ex- Zosuchus is depicted as the sister taxon of tends ventrolaterally much more than in any the Sichuanosuchus-Shantungosuchus clade other crocodyliform (except Shantungosu- since these taxa share the presence of a ven- chus and Sichuanosuchus), reaching the ven- trally de¯ected posterior region of the man- tral surface of the posteriormost region of the dibular rami (char. 172): Other characters, mandibular ramus, where it contacts the an- such as the palatines excluded from the mar- gular (®g. 6). gins of the suborbital fenestra (char. 170), 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 21

Fig. 15. Strict consensus of the six most parsimonious hypotheses obtained with Nona. may diagnose this clade but are unknown in all these basal forms (traditionally referred as Zosuchus. ``Protosuchia'') is only two steps longer than The clade composed by Zosuchus, Sichu- the most parsimonious hypotheses. anosuchus, and Shantungosuchus is support- ed to be more closely related to derived me- DISCUSSION soeucrocodylians than Gobiosuchus and pro- tosuchids by ®ve synapormorphies (presence Zosuchus davidsoni is depicted as a late- of palatine shelves extended below narial appearing basal crocodyliform in the out- passage [char. 37]; choana opens posteriorly come of the phylogenetic analysis. Note that into a midline depression (choanal groove) the presence of this new taxon in Late Cre- [char. 39]; fusion of pterygoids posterior to taceous sediments provides another case of a choana [char. 41]; presence of one enlarged Mongolian basal crocodyliform registered maxillary tooth [char. 79]; presence of a unusually late in the stratigraphic record (E®- well-developed posterodorsal process of pre- mov et al., 2000; Storrs and E®mov, 2000). maxilla [char. 125]). Gobiosuchus kielanae (OsmoÂlska, 1972; Os- All the most parsimonious hypotheses de- moÂlska et al., 1997) is also known from the pict Gobiosuchus, the Fruita form, and the Late Cretaceous of Mongolia (Bayn Dzak lo- Zosuchus clade as more closely related to de- cality) and, although it is not closely related rived crocodyliforms than to protosuchids. to Zosuchus, it also shows a basal position However, the best tree that supports a mono- among crocodyliforms (®g. 15). A related phyletic clade formed by protosuchids and taxon, Gobiosuchus parvus, was also de- 22 AMERICAN MUSEUM NOVITATES NO. 3445

Fig. 16. Artzosuchus brachycephalus GIN PST 10/23, taken from E®mov (1983). scribed from the Late Cretaceous beds of Zosuchus davidsoni also provides interest- Mongolia (E®mov, 1983), although there are ing information on the evolutionary history some doubts on the validity of this species of the secondary palate of Crocodyliformes. (OsmoÂlska et al., 1997; Storrs and E®mov, Since Victorian times the position of the cho- 2000). E®mov (1983) also described Artzo- ana in crocodilians has been used as an im- suchus brachycephalus (®g. 16), another cro- portant character in classifying the group. codyliform from the Udan Sair locality that The posterior migration of the palate has differs from Gobiosuchus in numerous char- been considered a specialization for aquatic acters. According to the information provid- existence and/or a structural requirement of ed by E®mov (1983), Artzosuchus also dif- the feeding behavior present in modern croc- fers from Zosuchus in several characters odiles (Busbey, 1994). In extant forms the (e.g., inset postorbital bar, angular exposed secondary palate is posteriorly extensive, the on the lateral surface of the mandibular ra- choanal opening is located near the glottis, mus, absence of posterodorsal and postero- and therefore the oral cavity can be closed ventral processes of the dentaries extending by the palatal valve, allowing the animal to above and below the mandibular fenestra, breath while the mouth cavity is full of water posterolaterally directed processes on the or to breath while eating. posterior squamosal corners). Unfortunately, In Eusuchia the posterior region of the sec- Artzosuchus was brie¯y described from an ondary palate is composed both of the pala- incomplete and unprepared skull (E®mov, tines and the pterygoids (the vomers also 1983; Storrs and E®mov, 2000), and its phy- form part of the palate but they are rarely logenetic af®nities are not clear at present. exposed externally), while in more basal taxa 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 23

(i.e., noneusuchian mesoeucrocodylians or (MNUFRJ), S. Cocca (MOZ), J.O. Calvo and ``mesosuchians'') the choana lies in a more L. Salgado (MUC-PV), J. Powell (PVL), C. anterior position on the border between the Cartelle (RCL), A. Chinsamy (SAM), R. palatines and the pterygoids. It is doubtful Wild (SMNS), D. Krause and G. Buckley that this more anterior position would have (UA), A. Buscalioni and F. Ortega (UAM), rendered a modern type palatal valve func- I.S. Carvalho (UFRJ), and H. OlsmoÂlska tional (Busbey, 1994). (ZPAL). Curiously, Zosuchus davidsoni mimics the eusuchian condition. Yet instead of a second- REFERENCES ary palate formed posteriorly by the ptery- Antunes, M.T. 1975. Iberosuchus, crocodile Se- goids, Zosuchus exhibits a drastically long becosuchien nouveau, l'Eocene iberique au posterior region of the palate exclusively Nord de la Chaine Centrale, et l'origine du can- formed by the palatines. While in no way yon de Nazare. ComunicacËoes dos ServicËos homologous to the condition in Eusuchia, GeoloÂgicos de Portugal 59: 285±330. this posterior extension of the palatines Bonaparte, J.F. 1971. Los tetraÂpodos del sector su- yields the posterior (secondary) choanal perior de la FormacioÂn Los Colorados, La Rio- opening close to the posterior edge of the ja, Argentina. Opera Lilloana 22: 1±183. pterygoid ¯anges as in eushuchians. Inter- Bonaparte, J.F. 1991. Los vertebrados foÂsiles de la formacioÂn RõÂo Colorado, de la ciudad de Ne- estingly, another case of convergent exten- uqueÂn y sus cercanõÂas, CretaÂcico superior, Ar- sion of the secondary palate was also noted gentina. Revista del Museo Argentino de Cien- in a clade of noneusuchian mesoeucrocody- cias Naturales ``Bernardino Rivadavia'' Paleon- lians (e.g., Bretesuchus, Iberosuchus; Gas- tologõÂa 4: 17±123. parini et al., 1993; Ortega et al., 2000; see Brochu, C.A. 1997a. Fossils, morphology, diver- ®g. 15). gence timing, and the phylogenetic relation- Considering the new information present- ships of Gavialis. Systematic Biology 46: 479± ed here and the phylogenetic position of Zo- 522. suchus, it seems clear that the posterior ex- Brochu, C.A. 1997b. A review of ''Leidyo- tension of the secondary palate has an evo- suchus'' (Crocodyliformes, Eusuchia) from the Cretaceous through Eocene of North America. lutionary history much more complex than Journal of Vertebrate Paleontology 17: 679± previously thought. 697. Brochu, C.A. 1999. Phylogenetics, taxonomy, and ACKNOWLEDGMENTS historical biogeography of Alligatoroidea. Jour- nal of Vertebrate Paleontology Memoir 6: 9± We thank Amy Davidson for the skillful 100. preparation of several specimens described Buckley, G.A., C.A. Brochu, D.W. Krause, and D. here (IGM 100/2, 100/3, 100/5). We also Pol. 2000. A pug-nosed crocodyliform from the thank Jane Shumsky for the preparation of Late Cretaceous of Madagascar. Nature 405: IGM 100/1. Mick Ellison masterfully pre- 941±944. Buffetaut, E. 1976. Une nouvelle de®nition de la pared the illustrations and ®gures. Our thanks famille des Dyrosauridae De Stefano, 1903 are extensive to the Mongolian Academy of (Crocodylia, Mesosuchia) et ses consequences: Sciences±American Museum of Natural His- inclusion des genres Hyposaurus et Sokotosu- tory ®eld crews that collected the specimens chus dans les Dyrosauridae. Geobios 9: 333± reported here. Financial support to D.P. was 336. provided by the Department of Earth and En- Buffetaut, E. 1978. Les Dyrosauridae (Crocodylia, vironmental Sciences of Columbia Univer- Mesosuchia) des phosphates de l'Eocene infer- sity and the American Museum of Natural ieur de Tunisie: Dyrosaurus, Rhabdognathus, History. Access to collections was possible Phosphatosaurus. Geologie MeÂditerraneÂenne 5: thanks to:) M. Moser (BSP), M. Maisch 237±256. Buffetaut, E. 1982. Radiation evolutive, paleoe- (GPIT), X. Xing (IVPP), J.M. Clark (GWU), cologie et biogeographie des crocodiliens me- J.F. Bonaparte (AMNH), E. Gomani (MAL), sosuchiens. Memoires de la SocieÂte Geologique D. Unwin (MB), L.E. Ruigomez and R. Cu- de France 60: 1±88. neo (MEF), Z.B. Gasparini and M. Reguero Busbey, A.B., III. 1994. Structural consequences (MLP), F.L. de Broin (MNHN), A. Kellner of skull ¯attening in crocodilians. In J. Tho- 24 AMERICAN MUSEUM NOVITATES NO. 3445

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APPENDIX 1

CHARACTER LIST CORRESPONDING TO DATA Character 4 (Clark, 1994: char. 4): Premaxilla MATRIX USED IN PHYLOGENETIC ANALYSIS participation in internarial bar: forming at least the ventral half (0), or with little participation (1). Character de®nitions 1±101 were taken from Character 5 (Clark, 1994: char. 5): Premaxilla Clark (1994) and have the same numeration as in anterior to nares: narrow (0), or broad (1). the original publication. Character 5 was excluded Character 6 (modi®ed from Clark, 1994: char. from the analysis (due to dependence with the 6): ϩ External nares facing: anterolaterally or an- modi®ed de®nition of character 6); however, its teriorly (0), dorsally not separated by premaxil- inclusion does not affect the outcome of the anal- lary bar from anterior edge of rostrum (1), or dor- ysis (except for the tree length). The additional sally separated by premaxillary bar (2). characters are also listed here and their respective Character 7 (Clark, 1994: char. 7): Palatal parts sources are cited along with the character num- of premaxillae: do not meet posterior to incisive bers of the original publication. Characters 1, 3, 6, 37, 45, 49, 65, 67, 69, 73, 77, 79, 83, 90, 91, foramen (0), or meet posteriorly along contact 97, 103, 104, 105, 121, 126, 139, 143, 150, and with maxillae (1). 167 were set as ordered characters (also marked Character 8 (Clark, 1994: char. 8): Premaxilla- ``ϩ'' in this list). maxilla contact: premaxilla loosely overlies max- Character 1 (modi®ed from Clark, 1994: char. illa (0), or sutured together along a butt joint (1). 1): ϩ External surface of dorsal cranial bones: Character 9 (modi®ed from Clark, 1994: char. smooth (0), slightly grooved (1), or heavily or- 9): Ventrally opened notch on ventral edge of ros- namented with deep pits and grooves (2). trum at premaxilla-maxilla contact: absent (0), Character 2 (modi®ed from Clark, 1994: char. present as a notch (1), or present as a large fe- 2): Skull expansion at orbits: gradually (0), or nestra (2). abruptly (1). Character 10 (Clark, 1994: char. 10): Posterior Character 3 (modi®ed from Clark, 1994: char. ends of palatal branches of maxillae anterior to 3): ϩ Rostrum proportions: narrow oreinirostral palatines: do not meet (0), or meet (1). (0), broad oreinirostral (1), nearly tubular (2), or Character 11 (Clark, 1994: char. 11): Nasal-lac- platyrostral (3). rimal contact: contact (0), or do not contact (1). 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 27

Character 12 (Clark, 1994: char. 12): Lacrimal Character 29 (Clark, 1994: char. 29): Dorsal contacts nasal along: medial edge only (0), or me- part of the postorbital: with anterior and lateral dial and anterior edges (1). edges only (0), or with anterolaterally facing edge Character 13 (Clark, 1994: char. 13): Nasal (1). contribution to narial border: yes (0), or no (1). Character 30 (Clark, 1994: char. 30): Dorsal Character 14 (Clark, 1994: char. 14): Nasal-pre- end of the postorbital bar broadens dorsally, con- maxilla contact: present (0), or absent (1). tinuous with dorsal part of postorbital (0), or dor- Character 15 (modi®ed from Clark, 1994: char. sal part of the postorbital bar constricted, distinct 15): Descending process of prefrontal: does not from the dorsal part of the postorbital (1). contact palate (0), or contacts palate (1). Character 31 (Clark, 1994: char. 31): Bar be- Character 16 (Clark, 1994: char. 16): Postorbit- tween orbit and supratemporal fossa broad and al-jugal contact: postorbital anterior to jugal, or solid, with broadly sculpted dorsal surface (0), or postorbital medial to jugal (1), or postorbital lat- bar narrow, sculpting restricted to anterior surface eral to jugal (2). (1). Character 17 (Clark, 1994: char. 17): Anterior Character 32 (modi®ed from Clark, 1994: char. part of the jugal with respect to posterior part: as 32): Parietal: with broad occipital portion (0), or broad (0), or twice as broad (1). without broad occipital portion (1). Character 18 (Clark, 1994: char. 18): Jugal bar Character 33 (Clark, 1994: char. 33): Parietal: beneath infratemporal fenestra: ¯attened (0), or with broad sculpted region separating fossae (0), rod-shaped (1). or with sagittal crest between supratemporal fos- Character 19 (Clark, 1994: char. 19): Quadra- sae (1). tojugal dorsal process: narrow, contacting only a Character 34 (Clark, 1994: char. 34): Postpar- small part of postorbital (0), or broad, extensively ietal (dermosupraoccipital): a distinct element (0), contacting the postorbital (1). or not distinct (fused with parietal?) (1). Character 20 (Clark, 1994: char. 20): Frontal Character 35 (Clark, 1994: char. 35): Postero- width between orbits: narrow, as broad as nasals dorsal corner of the squamosal: squared off, lack- (0), or broad, twice as broad as nasals (1). ing extra ``lobe'' (0), or with unsculptured lobe Character 21 (Clark, 1994: char. 21): Frontals: (1). paired (0), unpaired (1). Character 36 (modi®ed from Clark, 1994: char. Character 22 (Clark, 1994: char. 22): Dorsal 36): Posterior edge of the squamosal: nearly ¯at surface of frontal and parietal: ¯at (0), or with (0), or with elongated and posteriorly directed midline ridge (1). process (1). Character 23 (modi®ed from Clark, 1994: char. Character 37 (Clark, 1994: char. 37): ϩ Pala- 23 by Buckley and Brochu, 1999: char. 81): ϩ tines: do not meet on palate below the narial pas- Parieto-postorbital suture: absent from dorsal sur- sage (0), form palatal shelves that do not meet (1), face of skull roof and supratemporal fossa (0), or meet ventrally to the narial passage, forming absent from dorsal surface of skull roof but broad- part of secondary palate (2). ly present within supratemporal fossa (1), or pre- Character 38 (Clark, 1994: char. 38): Pterygoid: sent within supratemporal fossa and on dorsal sur- restricted to palate and suspensorium, joints with face of skull roof (2). quadrate and basisphenoid overlapping (0), or Character 24 (Clark, 1994: char. 24): Supratem- pterygoid extends dorsally to contact laterosphen- poral roof dorsal surface: complex (0), or dorsally oid and form ventrolateral edge of the trigeminal ¯at ``skull table'' developed, with postorbital and foramen, strongly sutured to quadrate and later- squamosal with ¯at shelves extending laterally be- osphenoid (1). yond quadrate contact (1). Character 39 (modi®ed from Clark, 1994: char. Character 25 (modi®ed from Clark, 1994: char. 39): Choanal opening: continuous with pterygoid 25): Postorbital bar: sculpted (if skull sculpted) ventral surface except for anterior and anterolat- (0), or unsculpted (1). eral borders (0), or opens into palate through a Character 26 (modi®ed from Clark, 1994: char. deep midline depression (choanal groove) (1). 26): Postorbital bar: transversely ¯attened (0), or Character 40 (Clark, 1994: char. 40): Palatal cylindrical (1). surface of pterygoids: smooth (0), or sculpted (1). Character 27 (Clark, 1994: char. 27): Vascular Character 41 (Clark, 1994: char. 41): Ptery- opening in dorsal surface of postorbital bar: ab- goids posterior to choanae: separated (0), or fused sent (0), present (1). (1). Character 28 (modi®ed from Clark, 1994: char. Character 42 (modi®ed from Clark, 1994: char. 28): Postorbital anterolateral process: absent or 42 by Ortega et al., 2000: char 139): Depression poorly developed (0), or well developed, long, on primary pterygoidean palate posterior to cho- and acute (1). ana: absent or moderate in size being narrower 28 AMERICAN MUSEUM NOVITATES NO. 3445 than palatine bar (0), or wider then palatine bar Character 57 (Clark, 1994: char. 57): Basioc- (1). cipital: without well-developed biltaeral tuberosi- Character 43 (Clark, 1994: char. 43): Ptery- ties (0), or with large pendulous tubera (1). goids: do not enclose choana (0), or enclose cho- Character 58 (Clark, 1994: char. 58): Otoccip- ana (1). ital: without laterally concave descending ¯ange Character 44 (modi®ed from Clark, 1994: char. ventral to subcapsular process (0), or with ¯ange 44): Anterior edge of choanae situated near pos- (1). terior edge of suborbital fenestra (or anteriorly) Character 59 (Clark, 1994: char. 59): Cranial (0), or near posterior edge of pterygoid ¯anges nerves IX±XI: pass through common large fora- (1). men vagi in otoccipital (0), or cranial nerve IX Character 45 (Clark, 1994: char. 45): ϩ Quad- pass medial to nerves X and XI in separate pas- rate: without fenestrae (0), with single fenestrae sage (1). (1), or with three or more fenestrae on dorsal and Character 60 (Clark, 1994: char. 60): Otoccip- posteromedial surfaces (2). ital: without large ventrolateral part ventral to par- Character 46 (Clark, 1994: char. 46): Posterior occipital process (0), or with large ventrolateral edge of quadrate: broad medial to tympanum, part (1). gently concave (0), or posterior edge narrow dor- Character 61 (Clark, 1994: char. 61): Crista in- sal to otoccipital contact, strongly concave (1). terfenestralis between fenestrae pseudorotunda Character 47 (Clark, 1994: char. 47): Dorsal, and ovalis nearly vertical (0), or horizontal (1). primary head of quadrate articulates with: squa- Character 62 (Clark, 1994: char. 62): Supraoc- mosal, otoccipital, and prootic (0), or with prootic cipital: forms dorsal edge of the foramen magnum and laterosphenoid (1). (0), or otoccipitals broadly meet dorsal to the fo- Character 48 (Clark, 1994: char. 48): Ventro- ramen magnum, separating supraoccipital from lateral contact of otoccipital with quadrate: very foramen (1). narrow (0), or broad (1). Character 63 (Clark, 1994: char. 63): Mastoid Character 49 (Clark, 1994: char. 49): ϩ Quad- antrum: does not extend into supraoccipital (0), or rate, squamosal, and otoccipital: do not meet to extends through transverse canal in supraoccipital enclose cranioquadrate passage (0), enclose pas- to connect middle-ear regions (1). sage near lateral edge of skull (1), or meet broadly Character 64 (Clark, 1994: char. 64): Posterior lateral to the passage (2). surface of supraoccipital: nearly ¯at (0), or with Character 50 (Clark, 1994: char. 50): Pterygoid bilateral posterior prominences (1). ramus of quadrate: with ¯at ventral edge (0), or Character 65 (modi®ed from Clark, 1994: char. with deep groove along ventral edge (1). 65): ϩ One small palpebral present in orbit (0), Character 51 (Clark, 1994: char. 51): Ventro- one large palpebral (1), or two large palpebrals medial part of quadrate: does not contact otoccip- (2). ital (0), or contacts otoccipital to enclose carotid Character 66 (Clark, 1994: char. 66): External artery and form passage for cranial nerves IX±XI nares: divided by a septum (0), or con¯uent (1). (1). Character 67 (Clark, 1994: char. 67): ϩ Antor- Character 52 (Clark, 1994: char. 52): Eustachi- bital fenestra: as large as orbit (0), about half the an tubes: not enclosed between basioccipital and diameter of the orbit (1), much smaller than the basisphenoid (0), or entirely enclosed (1). orbit (2), or absent (3). Character 53 (Clark, 1994: char. 53): Basisphe- Character 68 (modi®ed from Clark, 1994: char. noid rostrum (cultriform process): slender (0), or 68 by Ortega et al., 2000: char. 41): Supratem- dorsoventrally expanded (1). poral fenestrae extension: relatively large, cover- Character 54 (Clark, 1994: char. 54): Basipter- ing most of surface of skull roof (0), or relatively ygoid process: prominent, forming movable joint short, fenestrae surrounded by a ¯at and extended with pterygoid (0), or basipterygoid process small skull roof (1). or absent, with basisphenoid joint suturally closed Character 69 (modi®ed from Clark, 1994: char. (1). 69): ϩ Choanal groove: undivided (0), partially Character 55 (modi®ed from Clark, 1994: char. septated (1), or completely septated (2). 55 by Ortega et al., 2000: char. 68): Basisphenoid Character 70 (Clark, 1994; character 70): Den- ventral surface: shorter than the basioccipital (0), tary: extends posteriorly beneath mandibular fe- or wide and similar to, or longer in length than, nestra (0), or does not extend beneath fenestra (1). basioccipital (1). Character 71 (modi®ed from Clark, 1994: char. Character 56 (Clark, 1994: char. 56): Basisphe- 71): Retroarticular process: absent or extremely noid: exposed on ventral surface of braincase (0), reduced (0), very short, broad, and robust (1), or virtually excluded from ventral surface by pter- with an extensive rounded, wide, and ¯at (or ygoid and basioccipital (1). slightly concave) surface projected posteroven- 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 29 trally and facing dorsomedially (2), posteriorly Character 86 (Clark, 1994: char. 86): Pubis: elongated, triangular-shaped and facing dorsally forms anterior half of ventral edge of acetabulum (3), or posteroventrally projecting and paddle- (0), or pubis at least partially excluded from the shaped (4). acetabulum by the anterior process of the ischium Character 72 (Clark, 1994: char. 72): Prearti- (1). cular: present (0), or absent (1). Character 87 (Clark, 1994: char. 87): Distal end Character 73 (modi®ed from Clark, 1994: char. of femur: with large lateral facet for the ®bula (0), 73): ϩ Articular without medial process (0), with or with very small facet (1). short process not contacting braincase (1), or with Character 88 (Clark, 1994: char. 88): Fifth ped- process articulating with otoccipital and basisphe- al digit: with phalanges (0), or without phalanges noid (2). (1). Character 74 (Clark, 1994; character 74): Dor- Character 89 (Clark, 1994: char. 89): Atlas in- sal edge of surangular: ¯at (0), or arched dorsally tercentrum: broader than long (0), or as long as (1). broad (1). Character 75 (Clark, 1994: char. 75): Mandib- Character 90 (modi®ed from Clark, 1994: char. ular fenestra: present (0), or absent (1). 90): ϩ Cervical neural spines: all anteroposteri- Character 76 (Clark, 1994: char. 76): Insertion orly large (0), only posterior ones rodlike (1), or area for M. pterygoideous posterior: does not ex- all spines rodlike (2). tend onto lateral surface of angular (0), or extends Character 91 (modi®ed from Clark, 1994: char. onto lateral surface of angular (1). 91 by Buscalioni and Sanz, 1988: char. 37 and by Character 77 (modi®ed from Clark, 1994: char. Brochu, 1997a: char. 7): ϩ Hypapophyses in cer- 77): ϩ Splenial involvement in symphysis in ven- vicodorsal vertebrae: absent (0), present only in tral view: not involved (0), involved slightly in cervical vertebrae (1), present in cervical and the symphysis (1), or extensively involved (2). ®rst two dorsal vertebrae (2), present up to the Character 78 (Clark, 1994: char. 78): Posterior third dorsal vertebra (3), or up to the fourth dorsal premaxillary teeth: similar in size to anterior teeth vertebrae (4). (0), or much longer (1). Character 92 (Clark, 1994: char. 92): Cervical Character 79 (modi®ed from Clark, 1994: char. vertebrae: amphicoelous or amphyplatian (0), or 79): ϩ Maxillary teeth waves: absent, no tooth procoelous (1). size variation (0), one wave of teeth enlarged (1), Character 93 (Clark, 1994: char. 93): Trunk ver- or enlarged maxillary teeth curved in two waves tebrae: amphicoelous or amphyplatian (0), or pro- (``festooned'') (2). coelous (1). Character 80 (Clark, 1994: char. 80): Anterior Character 94 (Clark, 1994: char. 94): All caudal dentary teeth opposite premaxilla-maxilla contact: vertebrae: amphicoelous or amphyplatian (0), ®rst no more than twice the length of other dentary caudal biconvex with other procoelous (1), or pro- teeth (0), or more than twice the length (1). coelous (2). Character 81 (modi®ed from Clark, 1994: char. Character 95 (Clark, 1994: char. 95): Dorsal os- 81): Dentary teeth posterior to tooth opposite pre- teoderms: rounded or ovate (0), rectangular, maxilla-maxilla contact: equal in size (0), or en- broader than long (1), or square (2). larged dentary teeth opposite to smaller teeth in Character 96 (modi®ed from Clark, 1994: char. maxillary toothrow (1). 96 and Brochu, 1997: char. 40): ϩ Dorsal osteo- Character 82 (modi®ed from Clark, 1994: char. derms without articular anterior process (0), with 82 by Ortega et al., 2000: char. 120): Anterior and a discrete convexity on anterior margin (1), or posterior scapular edges: symmetrical in lateral with a well-developed process located anterolat- view (0), anterior edge more strongly concave erally in dorsal parasagittal osteoderms (2). than posterior edge (1), or dorsally narrow with Character 97 (modi®ed from Clark, 1994: char. straight edges (2). 97 by Ortega et al., 2000: chars. 107, 108): ϩ Character 83 (modi®ed from Clark, 1994: char. Rows of dorsal osteoderms: two parallel rows (0), 83 by Ortega et al., 2000: char. 121): Coracoid more than two (1), or more than four with ``ac- length: up to two-thirds of the scapular length (0), cessory ranges of osteoderms'' (sensu Frey, 1988) or subequal in length to scapula (1). (2). Character 84 (Clark, 1994: char. 84): Anterior Character 98 (Clark, 1994: char. 98): Osteo- process of ilium: similar in length to posterior derms: Some or all imbricated (0), or sutured to process (0), or one-quarter or less the length of one another (1). the posterior process (1). Character 99 (Clark, 1994: char. 99): Tail os- Character 85 (Clark, 1994: char. 85): Pubis: teoderms: dorsal only (0), or completely sur- rodlike without expanded distal end (0), or with rounded by osteoderms (1). expanded distal end (1). Character 100 (Clark, 1994: char. 100): Trunk 30 AMERICAN MUSEUM NOVITATES NO. 3445 osteoderms: absent from ventral part of the trunk Character 115 (Buscalioni and Sanz, 1988: (0), or present (1). char. 44): Number of sacral vertebrae: two (0), or Character 101 (Clark, 1994: char. 101): Osteo- more than two (1). derms: with longitudinal keels on dorsal surfaces Character 116 (Buscalioni and Sanz, 1988: (0), or without longitudinal keels (1). char. 49): Supra-acetabular crest: present (0), or Character 102 (Wu and Sues, 1996: char. 14): absent (1). Jugal: participating in margin of antorbital fossa Character 117 (Buscalioni and Sanz, 1988: (0), or separated from it (1). char. 54): Proximal end of radiale expanded sym- Character 103 (modi®ed from Wu and Sues, metrically, similarly to the distal end (0), or more 1996: char. 23): ϩ Articular facet for quadrate expanded proximomedially than proximolaterally condyle: equal in length to the quadrate condyles (1). (0), slightly longer (1), or close to three times the Character 118 (Ortega et al., 1996: char. 5): length of the quadrate condyles (2). Lateral surface of the dentary: without a longitu- Character 104 (modi®ed from Wu and Sues, dinal depression (0), or with a longitudinal de- 1996: char. 24 and Wu et al., 1997: char. 124): ϩ pression (1). Jaw joint: placed at level with basioccipital con- Character 119 (Ortega et al., 1996: char. 9): dyle (0), below basioccipital condyle about above Ventral exposure of splenials: absent (0), or pre- level of lower toothrow (1), or below level of sent (1). toothrow (2). Character 120 (Ortega et al., 1996: char. 11, Character 105 (modi®ed from Wu and Sues, 2000: char. 100): Tooth margins: with denticulate 1996: char. 27 and Ortega et al., 2000: char. 133): carinae (0), or without carinae or with smooth or ϩ Premaxillary teeth: ®ve (0), four (1), three (2), crenulated carinae (1). or two (3). Character 121 (modi®ed from Pol, 1999a: char. Character 106 (modi®ed from Wu and Sues, 133 and Ortega et al., 2000: char. 145): Lateral 1996: char. 29): Unsculptured region along alve- surface of anterior process of jugal: ¯at or convex olar margin on lateral surface of maxilla: absent (0), or with broad shelf below the orbit with tri- (0), or present (1). angular depression underneath it (1). Character 107 (Wu and Sues, 1996: char. 30): Character 122 (Pol, 1999a: char. 134): Jugal: Maxilla: with eight or more teeth (0), or seven or does not exceed the anterior margin of orbit (0), fewer teeth (1). or exceeds margin (1). Character 108 (Wu and Sues, 1996: char. 33): Coracoid: without posteromedial or ventromedial Character 123 (Pol, 1999a: char. 135): Notch in process (0), with elongate posteromedial process premaxilla on lateral edge of external nares: ab- (1), or distally expanded ventromedial process (2). sent (0), or present on the dorsal half of the ex- Character 109 (Wu and Sues, 1996: char. 40): ternal nares lateral margin (1). Radiale and ulnare: short and massive (0), or Character 124 (Pol, 1999a: char. 136): Dorsal elongate (1). border of external nares: formed mostly by the Character 110 (Wu and Sues, 1996: char. 41): nasals (0), or by both the nasals and premaxilla Postacetabular process: directed posteroventrally (1). or posteriorly (0), or directed posterodorsally and Character 125 (Pol, 1999a: char. 138): Poster- much higher in position than preacetabular pro- odorsal process of premaxilla: absent (0), or pre- cess (1). sent extending posteriorly wedging between max- Character 111 (modi®ed from Gomani, 1997: illa and nasals (1). char. 4): Prefrontals anterior to orbits: elongated, Character 126 (Pol, 1999a: char. 139 and Or- oriented parallel to anteroposterior axis of the tega et al., 2000: char. 9): ϩ Premaxilla-maxilla skull (0), or short and broad, oriented postero- suture in palatal view: projected markedly for- medially±anterolaterally (1). ward (0), projected slightly anteriorly (1), or pro- Character 112 (modi®ed from Gomani, 1997: jected posteriorly (2). char. 32): Basioccipital and ventral part of otoc- Character 127 (Pol, 1999a: char. 140): Nasal cipital: facing posteriorly (0), or posteroventrally lateral border posterior to external nares: laterally (1). concave (0), or straight (1). Character 113 (Buscalioni and Sanz, 1988: Character 128 (Pol, 1999a: char. 141): Nasal char. 35): Vertebral centra: cylindrical (0), or lateral edges: nearly parallel (0), parallel but the spool-shaped (1). anterior end oblique to each other (1), or entirely Character 114 (modi®ed from Buscalioni and oblique to each other (2). Sanz, 1988: char. 39): Transverse process of pos- Character 129 (Pol, 1999a: char. 143): Palatine terior dorsal vertebrae: dorsoventrally low and anteromedial margin: exceeding the anterior mar- laminar (0), or dorsoventrally high (1). gin of the palatal fenestrae wedging between the 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 31 maxillae (0), or not exceeding the anterior margin ratojugal: not ornamented (0), or ornamented in of palatal fenestrae (1). the base (1). Character 130 (Pol, 1999a: char. 144): Dorso- Character 146 (Pol, 1999a: char. 162): Prefron- ventral height of jugal antorbital region respect to tal-maxillary contact in the inner anteromedial re- infraorbital region: equal or lower (0), or antor- gion of orbit: absent (0), or present (1). bital region more expanded than infraorbital re- Character 147 (Pol, 1999a: char. 163): Basi- gion of jugal (1). sphenoid: without lateral exposure (0), or with lat- Character 131 (Pol, 1999a: char. 145): Maxilla- eral exposure on the braincase (1). lacrimal contact: partially included in antorbital Character 148 (Pol, 1999a: char. 164): Posteri- fossa (0), or completely included (1). orly facing notch between the base of pterygoid Character 132 (Pol, 1999a: char. 146): Lateral wing: absent (0), or present (1). eustachian tube openings: located posteriorly to Character 149 (Pol, 1999a: char. 165): Quadrate the medial opening (0), or aligned anteroposteri- process of pterygoids: well developed (0), or orly and dorsoventrally (1). poorly developed (1). Character 133 (Pol, 1999a: char. 147): Anterior Character 150 (modi®ed from Pol, 1999a: char. process of ectopterygoid: developed (0), or re- 166 and Ortega et al., 2000: char. 44): ϩ Quadrate duced±absent (1). major axis directed: posteroventrally (0), ventrally Character 134 (Pol, 1999a: char. 148): Posterior (1), or anteroventrally (2). process of ectopterygoid: developed (0), or re- Character 151 (Pol, 1999a: char. 167): Quadrate duced±absent (1). distal end: with only one plane facing posteriorly Character 135 (Pol, 1999a: char. 149 and Or- (0), or with two distinct faces in posterior view, a tega et al., 2000: char. 13): Small foramen located posterior one and a medial one bearing the fora- in the premaxillo-maxillary suture in lateral sur- men aereum (1). face (not for big mandibular teeth): absent (0), or Character 152 (Pol, 1999a: char. 168): Antero- present (1). posterior development of neural spine in axis: Character 136 (Pol, 1999a: char. 150): Jugal well developed covering all the neural arch length posterior process: exceeding posteriorly the infra- (0), or poorly developed, located over the poste- temporal fenestrae (0), or not (1). rior half of the neural arch (1). Character 137 (Pol, 1999a: char. 151): Com- Character 153 (Pol, 1999a: char. 169): Prezy- pressed crown of maxillary teeth: oriented parallel gapophyses of axis: not exceeding anterior edge to the longitudinal axis of skull (0), or obliquely disposed (1). of neural arch (0), or exceeding the anterior mar- Character 138 (Pol, 1999a: char. 152): Large gin of neural arch (1). and aligned neurovascular foramina on lateral Character 154 (Pol, 1999a: char. 170): Postzy- maxilary surface: absent (0), or present (1). gapophyses of axis: well developed, curved lat- Character 139 (modi®ed from Pol, 1999a: char. erally (0), or poorly developed (1). 153): ϩ External surface of maxilla and premax- Character 155 (modi®ed from Pol, 1999b: char. illa: with a single plane facing laterally (0), or 212): Shape of dentary symphysis in ventral view: with ventral region facing laterally and dorsal re- tapering anteriorly forming an angle (0), U- gion facing dorsolaterally (1). shaped, smoothly curving anteriorly (1), or lateral Character 140 (Pol, 1999a: char. 154 and Or- edges longitudinally oriented, convex anterolat- tega et al., 2000: char. 104): Maxillary teeth: not eral corner, and extensive transversally oriented compressed laterally (0) or compressed laterally anterior edge (2). (1). Character 156 (Pol, 1999b: char. 213): Un- Character 141 (Pol, 1999a: char. 155): Poster- sculpted region in the dentary below the toothrow: oventral corner of quadratojugal: reaching the absent (0), or present (1). quadrate condyles (0), or not reaching the quad- Character 157 (Ortega et al., 1996 and Buckley rate condyles (1). et al., 2000: char. 13): Cheekteeth: not constricted Character 142 (Pol, 1999a: char. 156): Base of at base of crown (0), or constricted (1). postorbital process of jugal: directed posterodor- Character 158 (Ortega et al., 2000: char. 42): sally (0), or dorsally (1). Outer surface of squamosal laterodorsally orient- Character 143 (Pol, 1999a: char. 157): ϩ Post- ed: extensive (0), reduced and sculpted (1), or re- orbital process of jugal: anteriorly placed (0), in duced and unsculpted (2). the middle (1), or posteriorly positioned (2). Character 159 (Ortega et al., 2000: char. 74): Character 144 (Pol, 1999a: char. 158 and Or- Length/height proportion of infratemporal fenes- tega et al., 2000: char. 36): Postorbital-ectoptery- tra: higher than wide or equal (0), or very antero- goid contact: present (0), or absent (1). posteriorly elongated (1). Character 145 (Pol, 1999a: char. 161): Quad- Character 160 (Ortega et al., 2000: char. 90): 32 AMERICAN MUSEUM NOVITATES NO. 3445

Foramen intramandibularis oralis: small or absent posed on lateral surface of mandible (0), or shift- (0), or big and slotlike (1). ed to the ventral surface of mandible (1). Character 161 (Ortega et al., 2000: char. 146): Character 172 (Wu et al., 1997: char. 112): Pos- Ectopterygoid medial process: single (0), or teroventral edge of mandibular ramus: straight or forked (1). convex (0), or markedly de¯ected (1). Character 162 (modi®ed from Gomani, 1997: Character 173 (modi®ed from Wu et al., 1997: char. 46 and Buckley et al., 2000: char. 113): char. 119): Quadrate ramus of pterygoid in ventral Cusps of teeth: unique cusp (0), one main cusp view: narrow (0), or broad (1). with smaller cusps arranged in one row (1), one Character 174 (Wu et al., 1997: char. 121): main cusp with smaller cusps arranged in more Pterygoids: not in contact anterior to basisphenoid than one row (2), or several cusps of equal size on palate (0), or pterygoids in contact (1). arranged in more than one row (3). Character 175 (Wu et al., 1997: char. 122): Character 163. Posterolateral edge of squamo- Olecranon: well developed (0), or absent (1). sal: without descending ornamented process (0), Character 176 (Wu et al., 1997: char. 123): Cra- or with descending ornamented process (1). nial table width respect to ventral portion of skull: Character 164. Cross section of distal end of as wide as ventral portion (0), or narrower than quadrate: mediolaterally wide and anteroposteri- ventral portion of skull (1). orly thin (0), or subquadrangular (1). Character 177 (Wu et al., 1997: char. 127): De- Character 165. Palatine-pterygoid contact on pression on posterolateral surface of maxilla: ab- palate: palatines overlie pterygoids (0), or pala- sent (0), or present (1). tines ®rmly sutured to pterygoids (1). Character 178 (Wu et al., 1997: char. 128): An- terior palatal fenestra: absent (0), or present (1). Character 166 (Wu et al., 1997: char. 103): Character 179: Paired ridges located medially Squamosal descending process: absent (0), or pre- on ventral surface of basisphenoid: absent (0), or sent (1). present (1). Character 167 (modi®ed from Wu et al., 1997: Character 180: Posterolateral end of quadrato- char. 105): ϩ Development of distal quadrate jugal: acute or rounded, tightly overlapping the body ventral to otoccipital-quadrate contact: dis- quadrate (0), or with sinusoidal ventral edge and tinct (0), incipiently distinct (1), or indistinct (2). wide and rounded posterior edge slightly over- Character 168 (Wu et al., 1997: char. 106): hanging the lateral surface of the quadrate (1). Pterygoid ¯anges: thin and laminar (0), or dor- Character 181: Orientation of quadrate body soventrally thick, with pneumatic spaces (1). distal to otoccipital-quadrate contact in posterior Character 169 (Wu et al., 1997: char. 108): view: ventrally (0), or ventrolaterally (1). Postorbital participation in infratemporal fenestra: Character 182 (Gasparini et al., 1993: char. 3): almost or entirely excluded (0), or bordering in- Wedgelike process of the maxilla in lateral surface fratemporal fenestra (1). of premaxilla-maxilla suture: absent (0), or pre- Character 170 (Wu et al., 1997: char. 109): Pal- sent (1). atines: form margin of suborbital fenestra (0), or Character 183: Choanal opening: opened pos- excluded from margin of suborbital fenestra (1). teriorly and continuous with pterygoid surface Character 171 (Wu et al., 1997: char. 110): An- (0), or closed posteriorly by an elevated wall gular posterior to mandibular fenestra: widely ex- formed by the pterygoids (1).

APPENDIX 2

DATA MATRIX USED IN PHYLOGENETIC ANALYSIS 00000?00000?000??0?000?000????00???0 This matrix is available electronically at http:// 10??0?000000?010?0000?0200000101??01 research.amnh.org/vertpaleo/norell.html 100??00000?00100??10?00?110?0?0??[0 1]110????00000????00?0???0????00??0? Gracilisuchus 0???0?0 000000??0?000000000000?0?000000000?0 ??0?0?00000?000???0000?0???00000?100 Dibothrosuchus 000?00000000?0???0000?0?000001012?00 000?00?020??001???000000??????001100 ?00????0?01?01000??1?01???000001002? 00000?00000?0000?00000?0?0101000?010 0????0000?????0??0???0000?00000?0?00 100?0010?000?????2000?0?????01010?01 000 100?0?00000001001010?00?1?0001010111 Terrestrisuchus 00???000001??00000?010001000100?0?00 000??00??0??000000?000?0?00?000?1100 000 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 33

Protosuchus 12?[01]?00001???0?00???0110111??1011 2100000120?0000110100021000001000100 ?10111000 01010?00201001111110010101102011?110 210001010100011100[1234]00?120011010 Fruita form 201??0012001000100001001000001100100 111021001010000[01]000000?01??01??10 21?11?0020112?1???0?0??0??1?2?31???? 010[01]01010000000???010000000001200 ?1?0111101011?1?00011112?0??1???[01] 00011110??0100 00???1?1001?001?0?0100100??101?0011? Hemiprotosuchus 01110???0??00?10?00001?1???000????10 ?00?00?10??????10010?0??00?0010?11?0 1?0?0? ??01??0020?00?11?1100101??1?2?11??1? Hsisosuchus 21????01?????????0????1200?1?101??0? 211????1?01?000?0?1?0?0?10?01??????0 ?????????000?000??10?00???00000??10? 2???1?00[12]???11????001?01????1?1?? ???0?00???????0?0000?12???001??10?0? ?[14]?0?[01]?2?11?10???????000?1000? 000 ??101?0021??1?????01001???????0000?? Orthosuchus 00??1?11?1???00????????0??01????10?0 21100001201?0001001000[01]1000001000 ?0111[01]?00??1 1000?000?002011001111100??1?1?02011? Notosuchus 0?0?0?001000100011100000?12001001021 101?00110101001110001111110011000100 1421001?10010?100000001?010100000000 2110110021112011?1000010?1102111112? 00?0??0?00001???0000000?12?000011110 0101110001[01]111?1?200001000??01220 ?00100 11???1100101[01]1101[01]01?010000001 Kayenta form 111111111?00001111001000010111101100 [12]01110?1200000?10010?0??00????0?0 001110110001 ???11110?002010011111100001011?2011? Comahuesuchus 0102100?1010??0????00??0?12001011011 103??0?101??00?????0112????????0010? 12?????0????01100?00?01000111?101001 2????1??11?1?????????????????131???? ?01?100000000011?0??4?0012??00011??0 ??0?10101???????????????????????[01] ?00??0 13???1??????0?10?101?01?01?????011?? Gobiosuchus 0?1?????11???11?00100??1?0??000???10 101000?110000011001?[01][01]?1?00001 0??0?? ?10?0001000?0020112011111000?1????20 Uruguaysuchus 1???1?20100[01]010?0?1???????0?10101 201?001101??00??10??1??1????1???0100 10[01]012002??0000???0010[01]0000100 2?101?0011????1?????0??0???01111[12] 0000?00001001211?00000???1100000010? ???000110100??1?1??????0000?0??01?21 121000011?00?0?000 002100?00?000?[01]???01?1?00????1?01 Sichuanosuchus 11?11??????11?????1?00011????????0?? [12]01??0?1200[01]00?10010[01]1?110? ?10?????1 ??1?00?001?10?00020?1?011?1100?????? Chimaeresuchus ?2?11????1?000011?1??1?????000?????? 101?0001111?00?????????????????????? ??1?11?0?1????0??100100??1??10?0???? ?????????????????????????????12??011 00111[01]1210???00?????1?????0110111 0?01010??1?1?????2100?00????11[12]?3 011111100?11000 14210??00?0100111111111??????0?0110? ??????????10?11?????3????????????1?0 Shantungosuchus 0???0? 2?1????1?0???0?1??1????11??????????? 1?1[01]100020?1?011?1100?10????????1 Malawisuchus 01?1?000??10???????0??????????????1? 101?00?1110000?[01]10001[01][01]1100 ??????1?????0010???????00??10?00??11 ?110001?02110100011??20???1000?10?1? 1211???001?????0?0?001????1011111??0 02?111[01]2?0101110001????1??2100000 ?110?0 10??01[12]2111???01?0???01100101?110 00???110110101?0?01001???0?100??2111 Zosuchus 10?100001110000001 201??0?1200000??001010[01]110?001110 ?00211010012?1??011?11000?0?1?021111 Candidodon 0????0?01111????????????????????1?12 ???????????????????????????????????? ?3????1?????00100011011?000110?00101 ???????????????????????????????????? 34 AMERICAN MUSEUM NOVITATES NO. 3445

???????????????????????????????????? 2?1010001??12??1?101??1??1??2?21???? ???????????1????????????????0??0???? ?00??0[12]11????????????????????1??? ????????????1????2?????????????????? 00???00?????0?00???1?110?00???00011? ??? 0??1???0??????010???01?11??10??01?10 Simosuchus 00??11 10301011000000100010111110?011000101 Peirosaurus 1?10100011?11011?1000010?1?020112121 201?011??1??00??????10?1????????0??? 010110000???????02100?2010?10002010C 2?10???????????????????????????1???? ???01??????1101101012000010100111002 ??????[12]1????????????????????????0 11000120???211[12]00011111011001[01] 00????????????0????1???0???????0?1?? 1?10000001 ?????????????[01]??????0???????????? Sphagesaurus ???00??1? 101?000101??00??100?????110????????? Theriosuchus 21101?00?????011?1000????????13?2??? 201101111101001100001101111001100110 ?????100????????1???????????????312? 211010001?11?01111000?????1?20211?41 ???0???????1111110111111111111111001 001010101101111100011112001001010002 11011111?0?11?0??0?11?0?10??01??0000 ?00?10?110110[01]001?1100?00?0?00100 001 ??01??00?00??10100000??11?010??01?10 Bretesuchus 000??1 1[01]0??01121??00???????????0??????? ???2???10011????????1011?1??????13?1 Alligatorium ??1?00?10110?????????????????????0?1 ?0??????1?0000?1000010?1111?0?100?1? 00????1???????01??0????01??0???0??1? ???0??00??11??1??1000???????20?1???? 0????????????[01]0[01]?1?10??1???1?? 00101?101?011111000???1?00100??????? 001??00????1 ????10??1???????????????????0??????? ?????????????????0?????????????????? Baurusuchus ?0? 100??0?121??00?1101????111?0110????0 2?10110011112011?1000?10??10??311121 Goniopholis 010111111?????????????????????12103? 203?1211110010111000100111?001000100 ???1?????110111010101110011001111011 2?101000?1112011?1010?10?1?021312?41 0?01111???[01]0[01]11110?11101?00001 00[01]0[12]02011?1??1??0?00?1200?11? ?00010001 000002100010?1101100??101100?0000100 10001?1????0000110020000001100100001 Iberosuchus 1110?0101 1?0?00012?0?00111000111111?01?000?00 ??10100111?12??1?101??10?1????111??1 Eutretauranosuchus 0?0?1011011??????[12][1234]00??00??? 203????1?10010111000100111?00?000100 00?[12][01]0?2??0000???11001101010?1 1110?000?1112011?1010??0?1?0?121204? ?0??100?11001?0??0101???[01]?0111?01 00001020111???1??0??0?1?????????000? 01101?0??01?10000101 ??00?????0?100????110???????0??00??? Araripesuchus gomesii 1????0????10?2???0001?0??000?1?110?0 201000110100001110001011111011[01]00 1?1 1002110100011112011?10000?0?11020112 Pholidosaurus 1210001101[01][01]1[01]11111?1[234]0 212?111101??11?11101100111?001000100 001000100111100210010010101001001001 211?100001112111?101??10?100?1311?30 000000100110002100010110?0011[01]000 0???2?0???11?1???0??0??2?0?????????? 01111101000011100?0001 ???????????1????11110?????0?0010???? Araripesuchus patagonicus ????????????0?1?00001???10?001?100?0 201000?1010000?1[01]000101111?011100 101 1002?10100011?12?11?1000??0?1?02?112 Sokotosuchus 12?0?011[01]1??1?1??????????1000??01 2?2???1101??10????001001???101001?01 11100???01???0?01?01101?010000??1001 2?1??????1112?11?1?11??0???1?1?0???? 10102?0??101????0??[01]10001111?0100 ?????01????????????????????????????? 001110?00001 ???????????1????????????????0??0???? Lomasuchus ?????????????????00????????????????? 201????1211?00?11000101111??11000100 ??? 2004 POL AND NORELL: CROCODYLIFORM FROM MONGOLIA 35

Dyrosaurus Hylaeochampsa 002??1?101?010?11?00100011?101001101 00???????11???11????1?01???0????0?0? 2?10101001112011?1011?10?10?01302?3? 2?1?1011?????????101??1??1?????10??? 00??2?000????????0?00??????1???????? ???????????????????????????????????? ???????????1????????????????0??0???? ???0???????10????????????0??0??????0 ????????????021?00001????0??????00?? ?????????????2??000????????????????? 1?1 ??1 Pelagosaurus Borealosuchus 202?1111?100110201010000000000000100 203?1211110010111000100111?001000100 211010000001101111001001?10001200?30 211010111111211111010010?110?1310031 000020000110111?0000001200011101?00? 000110?011111111113111?110?00?000002 ??10???????1?1??????0000??010010?001 110?100100?101??11110??000000010001? 0??1?00????0001000?01120100001100000 1??1?0000110?20?00001100100001110000 1?1 101 Teleosauridae Gavialis 012?11110100110101001000000000001100 212?12111100111111011011111001000100 21?01000?001101111001011?1?001200?3? 2110101101112011110110101110[01]1310 000?200002101111?0000?12000101011?0? 03100012000001111110131112111100?000 ??10??01001101??1011000011000010100? 002110?100100?101??121100?0000000100 0??00000??10001000?011?010?011100010 0101?10?00001?0?20?00001100100001110 101 0001?1 Metriorhynchidae Crocodylus 002?1211010011?201011000?00000001100 203012111100[01]01110001?21111001000 21?0?000?001101111001011?1?001200?30 1002110?01111112011110100101110[01] 001?200002101?11?0000????????012?0?? [01]31003100010010121111110131112021 ?100?01001101??1011?000??000010102?0 100?0000021100100100?101??111100?000 ??0?000????001000?011?01000?11000001 00001001101011100001?0?2000000110010 01 0001110000101 Bernissartia Alligator 203??21111??00111000?00111?001000?00 203112?101?0[01]01110001021111001000 2?????0001112?11?10100?0?1???1?1??41 ?002110101111112011110100101110[01] 0010102011?1?11??020021110110100000? [01]31203100010020121111111131112021 ?00????????1????1????????0??0?10???0 1?0?00000211001001001101??111000?000 1????0????1?120000001????0??????00?? 00001001[12]010111000011[01]12000000 101 1100100001110000101

APPENDIX 3

FOSSIL TAXA USED IN PHYLOGENETIC ANALYSIS Orthosuchus stormbergi (Nash, 1975; SAM-K 409) Gobiosuchus kielanae (OsmoÂlska, 1972; ZPAL Collection numbers of the specimens that were MgR-II/67, MgR-II/68, MgR-II/69, MgR-II/70, revised ®rst-hand by the authors are added after MgR-II/71) the bibliographic reference. Shantungosuchus hangjinensis (Wu et al., 1994b) Gracilisuchus stipanicicorum (Romer, 1972) Sichuanosuchus shuhanensis (Wu et al., 1997; Terrestrisuchus gracilis (Crush, 1984) IVPP V 10594) Dibothrosuchus elpahros (Wu and Chatterjee, Zosuchus davidsoni (IGM 100/1304, 100/1305, 1993; IVPP V 7907) 100/1306, 100/1307, 100/1308) Protosuchus richardsoni (Colbert and Mook, Fruita form (Clark, 1985, 1994; LACM 120455a) 1951; AMNH 3024, MCZ 6727, UCMP Hsisosuchus chungkingensis (Young and Chow, 130860, UCMP 131827) 1953; Li et al., 1994; Wu et al., 1994a; cast of Hemiprotosuchus leali (Bonaparte, 1971; PVL CNM V 1090) 3829) Notosuchus terrestris (Gasparini, 1971; MACN- Kayenta form (Clark, 1986; UCMP 97638, RN 1037) 125359, 125871) Comahuesuchus brachybuccalis (Bonaparte, 36 AMERICAN MUSEUM NOVITATES NO. 3445

1991; MUC-PV 202; MACN-N 30, 31; MOZ Eutretauranosuchus delfsi (Mook, 1967; Clark, P 6131) 1986, 1994; AMNH 570) Uruguaysuchus aznarezi (Rusconi, 1933) Goniopholis (Mook, 1942; Clark, 1986, 1994; Chimaeresuchus paradoxus (Wu and Sues, 1996; Salisbury et al., 1999; AMNH 5782) IVPP V8274) Pholidosaurus decipiens (Owen, 1878; Clark, Malawisuchus mwakayasyunguti (Clark et al., 1986, 1994) 1989; Gomani, 1997; MAL 45, 49) Dyrosaurus phosphaticus (Buffetaut, 1978; Clark, Candidodon itapecurense (Carvalho, 1994) 1986, 1994) Simosuchus clarki (Buckley et al., 2000; UA Pelagosaurus typus (EudesDeslongchamps, 1863; 8679) BSP 1890.I.5) Sphagesaurus huenei (Price, 1950; Pol, in press; Teleosauridae (Buffetaut, 1982; Clark 1986, 1994; RCL 100) AMNH 5138, BSP 1945.XV.1, GPIT Auer- 1909-f.22, MB 1921.12) Araripesuchus gomesii (Price, 1959; AMNH Metriorhynchidae (KaÈlin, 1955; Gasparini and 24450) Diaz, 1977; AMNH 997, BSP AS.I.504, Araripesuchus patagonicus (Ortega et al., 2000; MACN-N 95, SMNS 10116) MUC-PV 269, 270) Hylaeochampsa vectiana (Clark and Norell, 1992; Baurusuchus pachecoi (Price, 1945; DGM 299- Ortega et al., 2000) R) Bernissartia fagessi (Buscalioni and Sanz, 1990; Bretesuchus bonapartei (Gasparini et al., 1993; Norell and Clark, 1990) PVL 4735) Borealosuchus formidabilis (Erickson, 1976; Bro- Iberosuchus macrodon (Antunes, 1975; Ortega et chu, 1997b) al., 2000) Gavialis gangeticus (Clark, 1994; Brochu, 1997a) Theriosuchus pusillus (Owen, 1879; Clark, 1986, Crocodylus niloticus (Clark, 1994; Brochu, 1994; Ortega et al., 2000) 1997a) Alligatorium (Wellnhofer, 1971; Clark, 1986, Alligator mississippiensis (Clark, 1994; Brochu, 1994) 1997a)

APPENDIX 4

ANATOMICAL ABBREVIATIONS occ occipital condyle otocc otoccipital ach anterior choana pal palatine ad anterior diastema par parietal alv alveolar groove pch posterior choana ang angular pd posterior diastema aof antorbital fenestra pmx premaxilla apal anterior palpebral po postorbital bocc basioccipital ppal posterior palpebral bsf basisphenoid prf prefrontal can lower caniniform tooth pt pterygoids chg choanal groove q quadrate den dentary qf quadrate fenestrae fr frontal qj quadratojugal j jugal sang surangular lac lacrimal sob suborbital fenestra ltsf laterosphenoid socc supraoccipital mx maxilla spl splenial nar external nares sq squamosal nas nasal stfo supratemporal fossa ntc premaxilla-maxilla notch sym mandibular symphysis