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

Turner AH - PLoS ONE (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York, United States of America.

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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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.
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pone.0118116.g013: 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.

Mentions: Efimov [11] described the third Shamosuchus species from the Nemegt Fm. from the Nogoon Tsav locality. Shamosuchus tersus is based on a partial skull (PIN 3141-501) that includes most of the snout and a partial but very well preserved braincase (Figs. 8E, F and 12B and 13). Some isolated osteoderms were also referred to this taxon. Efimov provided little morphological diagnosis, citing a more anteriorly extended interorbital crest and the round posterior shape of the choanae. I find no appreciably difference in these features with other putative Shamosuchus specimens and therefore consider Shamosuchus tersus as a junior synonym of S. gradilifrons.


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

Turner AH - PLoS ONE (2015)

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.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4340866&req=5

pone.0118116.g013: 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.
Mentions: Efimov [11] described the third Shamosuchus species from the Nemegt Fm. from the Nogoon Tsav locality. Shamosuchus tersus is based on a partial skull (PIN 3141-501) that includes most of the snout and a partial but very well preserved braincase (Figs. 8E, F and 12B and 13). Some isolated osteoderms were also referred to this taxon. Efimov provided little morphological diagnosis, citing a more anteriorly extended interorbital crest and the round posterior shape of the choanae. I find no appreciably difference in these features with other putative Shamosuchus specimens and therefore consider Shamosuchus tersus as a junior synonym of S. gradilifrons.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York, United States of America.

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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Related in: MedlinePlus