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. 2015 Feb 25;10(2):e0118116.
doi: 10.1371/journal.pone.0118116. eCollection 2015.

A review of Shamosuchus and Paralligator (Crocodyliformes, Neosuchia) from the Cretaceous of Asia

Affiliations

A review of Shamosuchus and Paralligator (Crocodyliformes, Neosuchia) from the Cretaceous of Asia

Alan H Turner. PLoS One. .

Abstract

The crocodyliform Shamosuchus is known from numerous Late Cretaceous localities in southern and eastern Mongolia and fragmentary remains from Uzbekistan. Seven species of Shamosuchus have been named from six localities in Mongolia and three in Uzbekistan. Six species originally described as Paralligator were later referred to Shamosuchus. Only the type species, Shamosuchus djadochtaensis has been examined in detail. Many of the named species of Shamosuchus show striking similarity in size and cranial morphology but most are based on partial remains suggesting that the true species diversity is overestimated. A review of all species referred to Shamosuchus recognizes three valid taxa: Shamosuchus djadochtaensis, S. gradilifrons, and S. major. Shamosuchus sungaricus, S. borealis, and S. karakalpakensis are nomena dubia, whereas S. ancestralis, S. ulgicus, S. tersus, and S. ulanicus are junior subjective synonyms of S. gradilifrons. Phylogenetic analysis of 318 phenotypic characters recovers a Paralligatoridae clade consisting of Shamosuchus, Rugosuchus, Batrachomimus, Glen Rose Form, and Wannchampsus. Shamosuchus is non-monophyletic: S. djadochtaensis is near the base of Paralligatoridae whereas S. gradilifrons + S. major are the most deeply nested. The name Paralligator is resurrected for this clade. Rugosuchus and Batrachomimus are sister taxa to Paralligator. Paralligatoridae is closely related to Theriosuchus, hylaeochampsids and a speciose Allodaposuchus clade, which together are the sister group of Borealosuchus plus Crocodylia. These results support the presence of a diverse clade in eastern Asia and western North America throughout the Cretaceous with origins in the Late Jurassic.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Geographic map showing the distribution of Asian paralligatorid species across China, Mongolia, and Uzbekistan.
Stars = Nemegt Formation (Fm.) taxa; circles = Djadokhta Fm. taxa; squares = Bayanshiree Fm. (or equivalent) taxa; polygon = Lower Cretaceous. 1. Shamosuchus ancestralis; 2. S. ulanicus; 3. S. tersus; 4. S. djadochtaensis; 5. S. gradilifrons; 6. S. major; 7. S. ulgicus; 8. S. borealis; 9. Rugosuchus nonganensis.
Fig 2
Fig 2. AMNH FARB 6412 (holotype), Shamosuchus djadochtaensis, Djadokhta Fm., Campanian, Mongolia.
Photographs in A, dorsal, B, ventral, C, left lateral, D, occipital views.
Fig 3
Fig 3. IGM 100/1195, Shamosuchus djadochtaensis, Djadokhta Fm., Campanian, Mongolia.
Photographs in A, lateral, B, dorsal, C, ventral views. Line drawings in D, lateral, E, dorsal, F, ventral views. Abbreviations: an, angular; ar, articular; bo, basioccipital; bs, basisphenoid; d, dentary; ect, ectopteryoid; f, frontal; j, jugal; la, lacrimal; m, maxilla; n, nasal; ot, otoccipital; pa, parietal; pf, prefrontal; pl, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangular; sp, splenial; sq, squamosal.
Fig 4
Fig 4. Skull morphology of Paralligatoridae.
A, Shamosuchus djadochtaensis, AMNH FARB 6412, dorsal view; B, S. djadochtaensis, AMNH FARB 6412, left lateral view; C, S. ulanicus (= Paralligator gradilifrons), PIN 3140-502, left lateral view.
Fig 5
Fig 5. Paralligatorids from Bayanshiree Fm, Cenomanian to Santonian.
A, Shamosuchus (= Paralligator) major (PIN 3726/501, holotype), dorsal view; B, PIN 3726/501, ventral view; C, line drawing of PIN 3726/501, dorsal view; D, line drawing of PIN 3726/501, ventral view; E, Shamosuchus (= Paralligator) gradilifrons (PIN 554-1, holotype), dorsal view; F, PIN 554-1, ventral view; G, line drawing of PIN 554-1, dorsal view; H, line drawing of PIN 554-1, ventral view; I, Shamosuchus ulgicus (= Paralligator gradilifrons) (PIN 3458/501), ventral view; J, line drawing of PIN 3458/501, ventral view. Abbreviations: an, angular; ar, articular; bo, basioccipital; d, dentary; ect, ectopteryoid; f, frontal; j, jugal; la, lacrimal; m, maxilla; n, nasal; ot, otoccipital; pa, parietal; pf, prefrontal; pl, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangular; sp, splenial; sq, squamosal.
Fig 6
Fig 6. Skull morphology in the holotype of Shamosuchus (= Paralligator) gradilifrons.
A, PIN 554-1, dorsal view of orbital region; B, PIN 554-1, left lateral view of squamosal; C, PIN 554-1, posterolateral view of right surangular.
Fig 7
Fig 7. Skull morphology in Paralligatoridae.
A, Shamosuchus ulanicus (= Paralligator gradilifrons) (PIN 3140-502), dorsal view; B, S. ancestralis, (= Paralligator gradilifrons) (PIN 551-29/1), dorsal view; C, S. ancestralis, (= Paralligator gradilifrons) (PIN 551-29/1), left lateral view.
Fig 8
Fig 8. Paralligatorids from Nemegt Fm, Maastrichtian.
A, Shamosuchus ulanicus (= Paralligator gradilifrons) (PIN 3140-502), dorsal view; B, PIN 3140-502, ventral view; C, line drawing of PIN 3140-502, dorsal view; D, line drawing of PIN 3140-502, ventral view; E, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), dorsal view; F, line drawing of PIN 554-1, dorsal view; G, S. ancestralis (= Paralligator gradilifrons) (PIN 551-29/1), dorsal view; H, line drawing of PIN 551-29/1, dorsal view. Abbreviations: bo, basioccipital; bs, basisphenoid; d, dentary; f, frontal; j, jugal; la, lacrimal; m, maxilla; n, nasal; ot, otoccipital; pa, parietal; pf, prefrontal; pl, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; q, quadrate; qj, quadratojugal; sq, squamosal.
Fig 9
Fig 9. PIN 3458/501, Shamosuchus ulgicus (= Paralligator gradilifrons).
A, skull in right lateral view; B, skull in posterior view; C, partial skull table dorsal view; D, frontal with partial prefrontals and lacrimals in dorsal view; E, posterior portion of mandible in medial view; F, posterior portion of mandible in lateral view; G, dorsal osteoderms in dorsal view.
Fig 10
Fig 10. Jugal morphology in Paralligatoridae.
A, Shamosuchus ulanicus (= Paralligator gradilifrons) (PIN 3140-502), right side; B, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), right side; C, S. (= Paralligator) gradilifrons (PIN 554-1, holotype), left side; D, S. ancestralis (= Paralligator gradilifrons) (PIN 551-29/7), right side.
Fig 11
Fig 11. Orbitonasal sulcus variation in Paralligatoridae.
A, Shamosuchus ulanicus (= Paralligator gradilifrons) (PIN 3140-502), left side; B, S. (= Paralligator) gradilifrons (PIN 554-1, holotype), left side; C, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), left side.
Fig 12
Fig 12. Lateral braincase morphology in Paralligatoridae.
A, Shamosuchus ulanicus (= Paralligator gradilifrons) (PIN 3140-502), left side; B, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), left side. Abbreviations: fo, foramen ovale.
Fig 13
Fig 13. Braincase and suspensorium morphology in Paralligatoridae.
A, Shamosuchus tersus (= Paralligator gradilifrons) (PIN 3141-501), occipital view; B, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), line interpretation; C, S. tersus (= Paralligator gradilifrons) (PIN 3141-501), left quadrate and exoccipital. In C, dashed line marks path of open cranioquadrate canal. Abbreviations: bo, basioccipital; bs, basisphenoid; ex, exoccipital; fcp, posterior carotid foramen; fv, foramen ovale; leu, lateral Eustachian foramen; meu, median Eustachian foramen; pt, pterygoid; qj, quadratojugal; qu, quadrate; sf, siphoneal foramen; XIIa, foramen for anterior branch of hypoglossal nerve; XXIp, foramen for posterior branch of hypoglossal nerve.
Fig 14
Fig 14. Reduced strict consensus of 108 equally optimal trees recovered from maximum parsimony analysis of 101 ingroup taxa and 318 phenotypic characters.
Trees rooted on Gracilisuchus stipanicicorum. Two equally optimal positions of Bernissartia fagesii shown with dotted line (length = 1662, CI = 0.239, RI = 0.700).
Fig 15
Fig 15. Systematic variation in palate morphology among neosuchians.
Numbers indicate character number from phylogenetic dataset using in this study, with state value following the period (i.e., char.charstate). A, Theriosuchus pusillus (NHMUK 48330); B, Iharkutosuchus makadii (MTM 2006.53.1); C, Isisfordia duncani (QM F44320); D, Shamosuchus ulgicus (= Paralligator gradilifrons) (PIN 3458/501).

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