Sinophoneus is an extinct genus of carnivorous dinocephalian therapsid belonging to the family Anteosauridae. It lived 272 to 270 million years ago at the beginning of the Middle Permian (Lower Roadian) in what is now the Gansu Province in northern China. It is known by a skull of an adult individual (the holotype GMV1601), as well as by many skulls of juvenile specimens. The latter were first considered as belonging to a different animal, named Stenocybus, before being reinterpreted as immature Sinophoneus. Sinophoneus shows a combination of characters present in other anteosaurs. Its bulbous profile snout and external nostrils located in front of the canine are reminiscent of the basal anteosaur Archaeosyodon, while its massive transverse pterygoids processes with enlarged distal ends are more similar to the more derived anteosaurs Anteosaurus and Titanophoneus. First phylogenetic analyzes identified Sinophoneus as the most basal Anteosaurinae. A more recent analysis positioned it outside the Anteosaurinae and Syodontinae subclades, and recovers it as the most basal Anteosauridae.
| Sinophoneus Temporal range: Middle Permian (Roadian),
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| Skull, Paleozoological Museum of China | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Dinocephalia |
| Family: | †Anteosauridae |
| Genus: | †Sinophoneus Cheng and Ji, 1996 |
| Species: | †S. yumenensis
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| Binomial name | |
| †Sinophoneus yumenensis Cheng and Ji, 1996
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| Synonyms | |
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Description
editThe holotype of Sinophoneus is a somewhat dorsoventrally deformed skull measuring 32 cm in length from the tip of the snout to the occipital condyle[1] and about 35 cm in total length to the posterior border of the squamosal.[2] The upper part of the orbits is crushed, giving them an oval shape. They had to be originally circular. Most of the temporal arches are missing, as is the dentition of the upper jaws. The lower jaw is not preserved. The skull is mainly characterized by the presence of a median ridge starting between the eye sockets (where it is poorly developed) and extending to the tip of the snout (where it is more robust) which it protrudes beyond in dorsal view. The nostrils are smaller than in other anteosaurs. As in Archaeosyodon, the nostrils are entirely located in front of the upper canine whereas in other anteosaurs they are mainly located above or behind the canine. The snout profile is bulbous as in Archaeosyodon. The transverse processes of the pterygoids have a very enlarged distal end giving them a palmate morphology in ventral view as in Anteosaurus and Titanophoneus.[2][3][1]
Synonymy with Stenocybus
edit
In 1997, Cheng & Li described the small dinocephalian Stenocybus acidentatus, from a complete skull (IGCAGS V 361) and jaw remains from a second specimen, found in the same site as Sinophoneus. Although in their article, Cheng and Li did not compare Stenocybus directly with Sinophoneus, they consider the first sufficiently different from Anteosauridae to place it in a new family, the Stenocybusidae.[4] The name of this clade was later correctly modified in Stenocybidae by the Russian paleontologist Mikhail Feodosievich Ivakhnenko.[5] The latter was also the first researcher to suggest that Stenocybus could be the juvenile form of Sinophoneus.[5][6] In 2011, Christian Kammerer also considered Stenocybus as a young Sinophoneus, the proportions of the first (absence of pachyostosis, tall and narrow skull, relatively large orbits, and smaller temporal fenestra) being typical characters of juvenile therapids. In addition, the immature skull of Stenocybus already shows a beginning of the median ridge of the snout characteristic of Sinophoneus, as well as the same bulbous profile of the snout as in the latter. As a result, Kammerer regards Stenocybus acidentatus as a junior synonym of Sinophoneus yumenensis.[3] A conclusion shared by Liu and Li from new specimens mentioned in a short note published the same year.[7] In 2014, Jiang and Ji described two new specimens of Stenocybus: a snout with articulated jaws, and a right dentary with an almost complete dentition, belonging to two individuals slightly larger than the holotype. Although providing new information on the anatomy of the animal, such as the number of teeth on the mandible, Jiang and Ji believe that the phylogenetic position of Stenocybus remains difficult to confirm, and that the synonymy of Stenocybus with Sinophoneus proposed by Kammerer, Liu and Li must be proved by the discovery of more complete specimens.[8] However, Jiang and Ji's wishes had been realize a few months earlier. In 2013 Liu described the seven new skulls of Sinophoneus (including one associated with postcranial remains) that had only been mentioned in the short note of 2011. These skulls all belong to specimens smaller than the holotype, but they represent various ontogenetic stages. They confirm that the skulls of Stenocybus actually represent several juvenile stages of Sinophoneus.[1]
Ontogeny
editThe ontogenetic series of the genus Sinophoneus is incomplete with an unrepresented size range between the known juvenile skulls measuring between 12 and 18 cm in length and the only known adult skull measuring 32 cm. However, this ontogenetic series makes it possible to identify the important morphological changes between the juveniles and the adults of this genus. The skull of the juvenile is relatively tall and narrow, and pachyostosis is absent. In the adult, the skull becomes much wider and lower, notably the bones of the palate which widen considerably, and a pachyostosis is observed on the bones surrounding the orbits. The medial ridge on the skull roof is weak in the smallest known specimen, but a pair of bosses is present on the midline of the inter-orbital region. This ridge extends from the pineal foramen to a point slightly beyond the orbit in the juvenile. It is more pronounced in adults where it extends to the end of the snout that ends prominently. The nostrils and orbits increase only slightly in size during growth. In contrast, the dimensions of the temporal fenestrae increase dramatically. They are triangular in shape and much smaller than orbit in the smaller specimens, have a size close to that of the orbits in somewhat larger specimens, and are much larger than the orbit in the adult. The latter were therefore equipped with a mandibular adductor musculature much more developed than that of the juveniles, and could inflict proportionally much more powerful bites. These differences indicate that in Sinophoneus, juveniles and adults certainly occupied distinct ecological niches and did not covet the same preys.[1] This pattern is also known in the South African genus Anteosaurus.[9][10]
Geographic and stratigraphic distribution
editAll fossils of Sinophoneus come from a single locality, the Dashankou site, near Yumen City, in western Gansu Province, China. Stratigraphically, they belong to the Qingtoushan Formation (which before 2012 was called the Xidagou Formation),[11] whose sediments are of fluvial origin.[12] No radiometric dating is known for the Qingtoushan Formation, but Liu et al. assigns it a lower Roadian age (lowermost Middle Permian), thus partially filling the Olson Gap.[12][13] The latter corresponds to a period of time with a poor fossil record, located between the lower Permian, dominated by the pelycosaurs, and the mid-middle Permian (Wordian), where the therapids take the first place in terrestrial ecosystems. The Roadian age attributed to the Qingtoushan Formation is an estimate derived from the degree of evolution of the Dashankou fauna. This fauna is composed both of animals belonging to ancient lineages, rather typical of Upper Carboniferous and Lower Permian, such as the temnospondyl dissorophoid Anakamacops[14] and the Bolosauridae Belebey,[15] and also of more derived forms, rather typical of the middle and upper Permian, such as the anthracosaurs Chroniosuchidae Ingentidens and Phratochronis,[14] the moradisaurine Gansurhinus,[16] and several therapsids. The latter are, however, exclusively represented by phylogenetically basal taxa. These are Raranimus, the most basal therapid known to date,[12][17] and Biseridens, the most basal anomodont.[18][19] The new classification of Sinophoneus, identified by Liu as the most basal Anteosauridae, is an additional argument in favor of a Roadian age for the Dashankou fauna.[1] Moreover, the latter was correlated with the Russian Parabradysaurus silantjevi assemblage zone of Roadian age.[17] Coinciding with its basal phylogenetic position, the Lower Roadian age of Sinophoneus makes it one of the oldest known anteosaurs to date, together with the Russian genus Microsyodon being of comparable age.[20]
Classification and phylogeny
editIn 2011 Christian Kammerer published the first phylogenetic analysis including all anteosaurs. This one recognized the monophyly of Anteosauridae, which contain two main clades: Syodontinae and Anteosaurinae. Sinophoneus is identified as the most basal Anteosaurinae and is the sister group of an unresolved trichotomy including Titanophoneus potens, T. adamanteus and Anteosaurus.[3]
Below, the cladogram of the anteosaurs presented by Kammerer in 2011 :[3]
In describing the new Brazilian anteosaur Pampaphoneus, Cisneros et al. presented another cladogram confirming the recognition of the clades Anteosaurinae and Syodontinae. Sinophoneus occupies the same position there as in the cladogram proposed by Kammerer.[21]
The cladogram of Cisneros et al. published in the main paper and excluding the genus Microsyodon.[21]
One of the four cladograms of Cisneros et al. published in the Supporting Information of the same article, and including Microsyodon.[21]
In 2013, Jun Lui presented a new cladogram in which Sinophoneus is reinterpreted as the most basal anteosauridae and is thus excluded from Anteosaurinae.[1]
The cladogram published by Jun Liu in 2013 :[1]
References
edit- ^ a b c d e f g Liu, J. (2013). "Osteology, Ontogeny, and Phylogenetic Position of Sinophoneus yumenensis (Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China". Journal of Vertebrate Paleontology. 33 (6): 1394–1407. doi:10.1080/02724634.2013.781505. S2CID 85577626.
- ^ a b Cheng, Z.-W.; Ji, S. (1996). "First record of a primitive anteosaurid dinocephalian from the Upper Permian of Gansu, China". Vertebrata PalAsiatica. 34 (2): 123–134.
- ^ a b c d Kammerer, C.F. (2011). "Systematics of the Anteosauria (Therapsida: Dinocephalia)". Journal of Systematic Palaeontology. 9 (2): 261–304. doi:10.1080/14772019.2010.492645. S2CID 84799772.
- ^ Cheng, Z.-W.; Li, J.-L. (1997). "A new genus of primitive dinocephalian - the third report on Late Permian Dashankou lower tetrapod fauna". Vertebrata PalAsiatica. 35 (1): 35–43.
- ^ a b Ivakhnenko, M.F. (1999). "Biarmosuches from the Ocher faunal assemblage of eastern Europe". Paleontological Journal. 33 (3): 289–296.
- ^ Ivakhnenko, M.F. (2003). "Eotherapsids from the East European Placket (Late Permian)". Paleontological Journal (37): 339–465.
- ^ Liu, J.; Li, J. (2011). "Osteology and phylogenetic Position of Sinophoneus yumenensis (Therapsida, Dinocephalia) from the Dashankou Fauna (Middle Permian)" (PDF). 71st Annual Meeting Society of Vertebrate Paleontotology, November 2 – 5, 2011: 145.
- ^ Jiang, S.; Ji, S. (2014). "New specimens of Stenocybus acidentatus (Therapsida: Dinocephalia) from the Middle Permian Dashankou fauna of China". Acta Geologica Sinica (English Edition). 88 (3): 730–737. doi:10.1111/1755-6724.12233. S2CID 128691778.
- ^ Kruger, A. (2014). Ontogeny and cranial morphology of the basal carnivorous dinocephalian Anteosaurus magnificus from the tapinocephalus assemblage zone of the South African Karoo (MS dissertation). Johannesburg: University of the Witwatersrand.
- ^ Kruger, A.; Rubidge, B.S.; Abdala, F. (2017). "A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny". Journal of Systematic Palaeontology. 16 (2): 139–158. doi:10.1080/14772019.2016.1276106. hdl:11336/67088. S2CID 90346300.
- ^ Liu, J.; Sun, K.-Q.; Li, L. (2012). "The vertebrate fossil-bearing horizon in Yuman, Gansu and the Permian-Triassic strata in north Qilian area". Vertebrata PalAsiatica. 50 (4): 373–381.
- ^ a b c Liu, J.; Rubidge, B.S.; Li, J. (2009). "New basal synapsid supports Laurasian origin for therapsids" (PDF). Acta Palaeontologica Polonica. 54 (3): 393–400. doi:10.4202/app.2008.0071. S2CID 55062279.
- ^ Liu, J. (2010). "Dashankou Fauna : A Unique Window on the Early Evolution of Therapsids" (PDF). Bulletin of the Chinese Academy of Science. 24 (2): 83–85.
- ^ a b Li, J.; Cheng, Z. (1999). "New Anthracosaur and Temnospondyl Amphibians from Gansu, China – The Fifth Report on Late Permian Dashankou Lower Tetrapod Fauna". Vertebrata PalAsiatica. 37 (3): 234–247.
- ^ Müller, J.; Li, J.-L.; Reisz, R.R. (2008). "A new bolosaurid parareptile, Belebey chengi sp. nov., from the Middle Permian of China and its paleogeographic significance". Naturwissenschaften. 95 (12): 1169–1174. Bibcode:2008NW.....95.1169M. doi:10.1007/s00114-008-0438-0. PMID 18726080. S2CID 34304658.
- ^ Reisz, R.R.; Liu, J.; Li, J.-L.; Müller, J. (2011). "A new captorhinid reptile, Gansurhinus qingtoushanensis, gen. et sp. nov., from the Permian of China". Naturwissenschaften. 90 (5): 435–441. Bibcode:2011NW.....98..435R. doi:10.1007/s00114-011-0793-0. PMID 21484260. S2CID 20274349.
- ^ a b Duhamel, A.; Benoit, J.; Rubidge, B.S.; Liu, J. (2021). "A re-assessment of the oldest therapsid Raranimus confirms its status as a basal member of the clade and fills Olson's gap". The Science of Nature. 108 (26): 26. Bibcode:2021SciNa.108...26D. doi:10.1007/s00114-021-01736-y. PMID 34115204. S2CID 235403632.
- ^ Li, J.; Cheng, Z. (1997). "First discovery of eotitanosuchian (Therapsida, Synapsida) of China". Vertebrata PalAsiatica. 35 (4): 268–282.
- ^ Liu, J.; Rubidge, B.; Li, J. (2010). "A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont". Proceedings of the Royal Society B. 277 (1679): 285–292. doi:10.1098/rspb.2009.0883. PMC 2842672. PMID 19640887.
- ^ Golubev, V.K. (2015). "Dinocephalian Stage in the History of the Permian Tetrapod Fauna of Eastern Europe". Paleontological Journal. 49 (12): 1346–1352. doi:10.1134/S0031030115120059. S2CID 130694755.
- ^ a b c Cisneros, J.C.; Abdala, F.; Atayman-Güven, S.; Rubidge, B.S.; Şengör, A.M.C.; Schultz, C.L. (2012). "Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 109 (5): 1584–1588. Bibcode:2012PNAS..109.1584C. doi:10.1073/pnas.1115975109. PMC 3277192. PMID 22307615.