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From the Late Cretaceous of Mon$Olia: Anatomy and Relationships

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From the Late Cretaceous of Mon$Olia: Anatomy and Relationships Gobiosuchus kielanoc (Protosuchia) from the Late Cretaceous of Mon$olia: anatomy and relationships HALSZKA OSU6TSTR, STEPHANEHUA ANdERIC BUFFETAI.]'T Osm6lska, H., Hua S., & BuffetautE. L99'l. Gobiosuchuskielanae (Protosuchia)from the Late Cretaceousof Mongolia: anatomy and relationships.- Acta Palaeontologi.ca P o lnnica 42- 2 - 257-289 . The original description (Osm6lska 1972) of the skull, postcranial skeleton,and armour of a protosuchian, Gobiosuchuskielanae (GobiosuchidaeOsm6lska), is supplemented and revised on the basis of additional specimens from the type locality and horizon @ayn Dzak, ?early Campanian Djadokhta Formation). It is suggested that Gobiosuchus kiela- nae was an entirely terreshial and probably insectivorous a:rimal. Assignment of GoDlo- suchusto Protosuchiais supportedby the following characters:basisphenoid larger fhan basioccipital; extensive ventral contact between quadrate and basisphenoid; pneumatic pterygoid; quadrate condyles only slightly protouding beyond posterior margin of brain- case, and lack of retroarticular process. Gobiosuchus differs from other protosuchians in the following features: snout wider than high; palatal processesofpremaxillae contacting along their entire length; closed supratemporal and mandibular fenesftae; basioccipital extending dorsally onto occiput and separating on each side ventromedial part of quad- rate from contact with otoccipital; posterolateral process of squamosal extended far behind mandibular articulation; presence ofcranioquadrate passage; descending process of prefrontal contacting palate; armour of sutured osteoderms encasing at least some of long limb bones;presence of peculiar accessoryosteoderms in regions of articulation of limbs with girdles, and more than two longitudinal rows of dorsal osteoderms. Key words: Crocodyliformes,Protosuchia, Gobiosuchidae, Gobiosuchus, osteo- logy, habits, Late Cretaceous,Mongolia. Halszka Osm1lska[[email protected]],Instytut Paleobiologii PAN, ul. Twarda 5l/55, P L-00 -8 I 8 Warszawa, P oland. Eric Buffetaut [[email protected]] and StephaneHua [[email protected]], kt- boratoire de Pal4ontologie des Vertdbrds et de Pal4ontologie Humaine, Universitd Pierce et Marie Curie, Tour 15,4, place Jussieu,75252 Paris Cedex05, France. Introduetion Gobiosuchuskielanae Osm6lska, 1972 was a small (about60 cm long), long-necked and long-limbed, fully armouredcrocodile (Fig. 1), which lived approximately80 million yearsago on the territory of today'sGobi Desert.It representsa memberof the 258 Gobiosuchuskielarne: OSMOLSKA, HUA & BLIFFE'TAUT ProtosuchiaBrown, 1934,the primitive group of the CrocodyliaGmelin, 1788,lately renamedas Crocodyliformesby Clark in Benton & Clark (1988), and including 'protosuchians','mesosuchians' 'eusuchians'. and The Protosuchiaappeared in the Late Triassic and becameextinct in the Late Cretaceous,Gobiosuchus being, as far as known, their geologicallyyoungest member. As presentlyunderstood (t'7u et al.1994; Wu et al. t997), protosuchians form the sister-group to all other crocodylifonns (grouped as Mesoeucrocodyliaby Whetstone& Whybrow 1983). Protosuchiaare characterizedby severalunique characters,among others (Wu et aI. 1997): the struc- ture of the ventral surfaceof the braincasewhere the basisphenoidoccupies much more spacethan the basioccipital and the quadrateshave long contacts with the basisphe- noid, the distal, condyle-bearingends ofquadrates protruding only slightly beyond the posterior margin of the braincase,and the mandible lacking a retroarticular process. When G. kielanae was frst found in the sandstonesof the ?early Campanian DjadokhtaFormation (Gradzifski et aI. I977;Jerzykiewicz & Russell 1991)at Bayn Dzak locality (Pre-Altai Gobi, Mongolia) by the Polish-Mongolian Palaeontological Expeditions(Kielan-Jaworowska & Dovchin 1969;Kielan-Jaworowska & Barsbold 1972),it appearedisolated in time, other primitive crocodyliforms then known, mostly with a protosuchian-gradepalate, were few and either of the Late Triassic (one species) or Jurassic (four species) age (Table 1). Since then, the situation has changed and eleven new protosuchianspecies have beenreported from the Jurassicand Cretaceous. The majority of the protosuchians- ten species- are now known from Asia (mainly from China), four are reportedfrom North America, two from southernAfrica and one, the oldest,from SouthAmerica (Table1). Gobiosuchuskielanae was assignedby Osm6lska(1972) to the family Gobiosu- chidae, provisionally within the Protosuchia, among others becauseof the anterior position of the internal nares, located between the maxillae and palatines. Efimov (1983)considered the Gobiosuchidaeas a memberof the Notosuchiaand erectedtwo monotypic subfamilies, the Gobiosuchinaeand the Artzosuchinae,within this family. He changedhis opinion later (Efimov 1988a)re-assigning the Gobiosuchidaeto the Protosuchia. The protosuchiannature of GobiosuchlrJwas supportedamong others by Hecht & Tarsitano(1983), while Clark (in Benton & Clark 1988)considered that Protosuchia did not form a clade, and that Gobiosuchusoccupied a more derived position within the CrocodyliformesClark (in Benton& Clark 1988),constituting a sistertaxon to the Mesoeucrocodylia. Accordingto the morerecent phylogenetic analyses by Wu et al. (I994),Wu & Sues (1995),and Wu et al. (1997),the Protosuchiaare monophyletic and Gobiosuchus is a memberof this clade,as was earliersuggested by Osm6lska(1972). A secondspecies of Gobiosuchus,G. parvus wasdescribed by Efimov (1983)from 'Barungoyotskaya the depositsof the Svita' (a possibleequivalent of the Barun Goyot Formation:Gradzirfuki et al. t977) at Udan Sair (= Uden Khovol), basedon a single specimen(housed in the PalaeontologicalMuseum, Russian Academy of Sciences, Moscow).In our opinion,the validity of G. parvus is at the momentuncertain, because of the poor illustrations and the inadequatediagnosis of this species(see p. 283). Gobiosuchussp. was mentionedby Efimov (1988a)from the DjadokhtaFormation at Tugrikin Shire(= Toogreegof Gradziriskiet al.1977). This specimen,which is housed ACTA PALAEONTOLOGICA POLOMCA (42) (2) 259 - Table 1 Distribution of protosuchian species(Fm - Formation' Sv Svita)' Species Age Occurence H etniprotos uchus lcali Los Colorados Fm, Late Triassic Ischigualasto,Argentina Bonaparte,1971 OrangeFree State, Protosuchushaughtoni Elliot Fm, Early Jurassic @ubsey& Goq 1984) southernAfrica Protosuchusmicmac McCoy Brook Fm, EarlYJurassrc Nova Scotia, Canada Sueset al.,1996 Ortho suchus sto rmbe rg i Elliot Fnr, Early Jurassic Lesotho. southernAfrica Nash, 1975 rti Eoonewnato 'Cromptonsuchus c o lbe Kayenta Fm, Early lurassic Arizona" United States & Smith, 1980 Platyognathus hsui Lower Lufeng Fm, EarlY Jurassic Yunnan, China Young, 1944 Diano suchus c hnng chiw aensis Lower Lufeng Fm, EarlY Jurassic Yunnan,China Young, 1982 ni P rot os ut hus r ichardso Moenave Fm, ?Early Jurassic Arizona, United States (Brown, 1933) srs Sichuarn suchw haidong en ShangshaximiaoFm, Late Jurassic Sichuan, China Peng,1995 Shantung osuchtts chuhs ienen sis Mengyin Fm, ?Late Jurassic Shandong,China Young, 1961 Shantung o s uchus brac hycephalus Early Cretaceous ?Ordos,China Young, 1982 gj i ensis Shnntung osuc hus han LuohandongFm, EarlY Cretaceous Ordos, China Wa et al.,1994 Edent o suchru tinnshanensi s Tugulu Group, Early Cretaceous Xinjiang, China Young,1973 Si chua no su c h us sha ha n e nsi t ?F,arlyCretaceous Sichuan, China Wuet a1.,1997 Gobiosuchuskielanae Diadokhta Fm, Late Cretaceous Pre-Altai Gobi, Mongolia Osm6lska,1972 panus Gobiosrchus(?) Barun Govot Sv, I-ate Cretaceous Pre-Altai Gobi, Mongolia Efimov, 1983 THoplosuchuskayi Morrison Fm, Late Jurassic Utah, United States Gilmore, 1926 in the regional museumat Dalan Dzadgad- the administrativecentre of the Mongolian southem Gobi province (Omnogov) - consists of the almost complete postcranium entirely encasedin the osteodermalarmour. It hasbeen briefly studiedby H. Osm6lska, who concludedthat the ornamentationof osteodermsvery closely resemblesthat in G. kielanae.Some osteoderms from the Turonian-Coniaciandeposits atDzharaKhuduk (Kyzylkum Desert,uzbekistan), were also quoted by Efimov (1988b) as probably assignableto Gobiosuchr,t,but neithera descriptionnor illustrationwere given. ihe descriptionbelow is basedupon five specimensof G. kielanae, including fragmentary skulls, some postcranial bones, and armour. This additional material allowed us to coffect some mistakesmade in the previous description(Osm6lska Ig7z),which was basedmainly on the holotypespecimen. 260 Gobiosuchuskielanae: OSMOLSKA, HUA & BUFFETAUT Material The collectiondescribed is housedin the Instituteof Paleobiology,Polish Academy of sciences,warsaw, for which the abbreviationzPALisused. All specimenscome from the fine-grainedsandstones of the DjadokhtaFormation(Campanian) at sitescalledthe 'Ruins' 'Volcano' and in Bayn Dzak. ZPAL MgR-IV67 - holotype:almost complete skull, somewhatflattened dorsoven- trally, with damagedcranial roof; mandiblelacking; disarticulated postcranial skeleton including distal dorsalvertebrae, left humerus,proximal portionsof the left ulna and radius, damagedleft and right femora and tibiae, left fibula, fragmentary left carpus and metacarpus,fragmentary dorsal ribs, disarticulatedaflnour (Figs 4, 5, 11A, 13C- F); site:Volcano. ZPAL MgR-IV68 - posteriorhalf of the skull, neck,thorax and proximal two thirds of the tail encasedin armour,fragments of the proximal elementsof the fore- and hind limbs (Figs2,3); site:Volcano. ZPAL MgR-n169 - skull with articulated mandible,
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