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| Samsarasuchus pamelae Ezcurra, Bandyopadhyay, Sengupta, Sen, Sennikov, Sookias, Nesbitt & Butler, 2023 DOI: 10.1098/rsos.230387 artwork: Gabriel Lio |
Abstract
Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae, which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae. Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction.
Keywords: phylogeny, biogeography, Proterosuchidae, Archosauromorpha, Induan, Mesozoic
Diapsida Osborn, 1903
Archosauromorpha von Huene, 1946
Archosauriformes Gauthier, Kluge & Rowe, 1988
Proterosuchidae von Huene, 1908 sensu Ezcurra, Butler & Gower, 2013
Chasmatosuchinae nov.
Phylogenetic definition: The most inclusive clade containing Chasmatosuchus rossicus von Huene, 1940, but not Proterosuchus fergusi Broom, 1903, ‘Chasmatosaurus’ yuani Young, 1936, Proterosuchus alexanderi (Hoffman, 1965), Proterosuchus goweri Ezcurra & Butler, 2015, Erythrosuchus africanus Broom, 1905, or Alligator mississippiensis Daudin, 1802. This is a maximum clade definition.
Composition: The composition is based on the reference phylogeny. Chasmatosuchinae includes Chasmatosuchus rossicus, Jaikosuchus magnus, Samsarasuchus pamelae, Archosaurus rossicus, Gamosaurus lozovskii, Tsylmosuchus spp., Vonhuenia friedrichi and indeterminate specimens from the Arcadia Formation and Bulgo Sandstone of the Sydney Basin of Australia and the Sanga do Cabral Formation of Brazil.
Diagnosis: Chasmatosuchines differ from other proterosuchids in the presence of anterior–middle and sometimes posterior postaxial cervical vertebrae with distally restricted transverse expansion of the neural spines (not mammillary process); third to eighth or ninth presacral vertebrae with diagonal, anterodorsally-to-posteroventrally oriented ridge that reaches the base of the prezygapophysis and is not connected to the diapophysis on the lateral surface of the neural arch; fourth to eight presacral vertebrae with posterior expansion of the dorsal portion of the neural spine, resulting in a posterodorsally tilted posterior margin set at an angle higher than 15° with respect to the anterior margin of the neural spine in lateral view; ninth presacral centrum with a ventral keel and anterior caudal vertebrae with surface lateral to the base of the neural spine with a very deep fossa, well-defined laterally and that transversely constricts the anterior half of the neural spine.
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| Geographical and stratigraphic occurrence of specimens of Samsarasuchus pamelae gen. et sp. nov. and Panchet cf. proterosuchid and proterosuchid specimens. (a) Gondwana basins of peninsular India showing the studied area of the Damodar Basin, which has yielded specimens of Samsarasuchus pamelae; (b) geological map showing the location of the Deoli locality that yielded Samsarasuchus pamelae bones discovered by the 2015 fieldtrip; (c) composite stratigraphic column of the Panchet Formation, including the occurrence of the Samsarasuchus pamelae bones discovered by the 2015 fieldtrip; (d) general overview of the sandstones of the Deoli locality on the shore of the Damodar River (January 2015); and (e) close up of the holotype of Samsarasuchus pamelae (ISIR 1091) as found in the field. |
Samsarasuchus pamelae gen. et sp. nov.
Diagnosis: Samsarasuchus pamelae is a chasmatosuchine proterosuchid that differs from other non-archosaurian archosauriforms in the following autapomorphies (among non-archosaurian archosauriforms) present in its holotype (ninth cervical vertebra): posteriormost cervical vertebra (ninth cervical vertebra) with two pairs (i.e. four in total) of mammillary processes on the neural spine; and posteriormost cervical vertebra (ninth cervical vertebra) with dorsolaterally oriented mammillary processes on the anterior region of the neural spine. In addition, the holotype of Samsarasuchus pamelae and the other postaxial cervical and anterior–middle dorsal vertebrae referred to this species share the following unique combination of character states that allow the species to be distinguished from other non-erythrosuchid, non-eucrocopod archosauriform nominal species: third cervical to anterior dorsal vertebrae ....
Etymology: The genetic epithet is formed by the Sanskrit word ‘Saṁsāra’ (Samsara) that in Hinduism is related to the cycle of re-birth, existence and death, and ‘Σοῦχος’ (Suchus), which is the name of the Egyptian crocodile-headed deity Sebek or Sobek in ancient Greek, referring to the re-birth of ecosystems after the end-Permian mass extinction and the most common ending (-suchus) of archosauromorph genera. The specific epithet is for the first name of the British palaeontologist Pamela Lamplugh Robinson (1919–1994) in honour of her contributions to Indian vertebrate palaeontology and especially for having prompted a renewed interest in the vertebrate palaeontology of the Panchet Formation in the 1960s after a long gap in research since the end of the ninteenth century. In addition, Pamela Robinson led the fieldtrip that resulted in the discovery of several referred specimens of this new proterosuchid species (NHMUK collection).
Martín D. Ezcurra, Saswati Bandyopadhyay, Dhurjati P. Sengupta, Kasturi Sen, Andrey G. Sennikov, Roland B. Sookias, Sterling J. Nesbitt and Richard J. Butler. 2023. A New archosauriform Species from the Panchet Formation of India and the Diversification of Proterosuchidae after the end-Permian Mass Extinction. R. Soc. open sci. 10230387. DOI: 10.1098/rsos.230387
