Thursday 16 June 2016

Sclerocormus parviceps: A new species of Ichthyosaur from the Early Triassic of Anhui Province, China.

Ichthyosaurs were Marine Reptiles known from the Triassic to the Cretaceous. They were fully-aquatic with a Dolphin-like form, and known to have given birth to live young, rather than emerging from the water to lay eggs, as is the case in Turtles and Crocodiles. The origin of the group has for a long time been obscure, with large fully aquatic forms known from the Middle Triassic onwards. However several recent discoveries have suggested that they may have been related to the Hupehsuchians, an enigmatic group of Marine Reptiles known from the Early Triassic of China.

In a paper published in the journal Scientific Reports on 23 May 2016, a group of scientists led by Da-Yong Jiang of the Laboratory of Orogenic Belt and Crustal Evolution at Peking University, describe a new species of Ichthyosaur from the Early Triassic Nanlinghu Formation of Anhui Province, China.

The new species is named Sclerocormus parviceps, where 'Sclerocormus' means 'stiff trunk' and 'parviceps' means 'small skull'. The species is described from a single skeleton, 159.9 cm in length and partially compressed. The skull is notably small for an Ichthysaur, even for an early Ichthyosaur (which were generally shorter snouted), having a short snout and comprising only 6.25% of the total bodylength, compared to 12% in the earliest previously known Ichthyosaur, Chaohusaurus.

Sclerocormus parviceps. (a) Whole specimen. (b) Skull. (c) Close-up of gastral basket. (d) Close-up of U-shaped haemal arches. (e) Right forelimb. (f) Shoulder elements. (g) Pelvic girdle and hind limb. (h) Skull elements. Abbreviations: a, angular; ar, articular; as, astragalus; ca, calcaneum; car, caudal rib; ca.v, caudal vertebra; ce, centralia; cl, clavicle; d, dentary; dc, distal carpal; f, frontal; fe, femur; fi, fibula; he, hemal arch; il, ilium; in, intermedium; is, ischium; j, jugal, l, lacrimal; m, maxilla; mc, metacarpal; mt, metatarsal; n, nasal; p, parietal; pm, premaxilla; po, postorbital; pof, postfrontal; prf, prefrontal; pu, pubis; q, quadrate; sa, surangular; sc, scapula; scl, scleral ossicles; sq, squamosal; sr, sacral rib; st, supratemporal; ti, tibia; u, ulna; ul, ulnare. Scale unit in (a) is 1 cm, other scale bars are 2 cm. Jiang et al. (2016).

Sclerocormus parviceps has a short trunk with broad, flattened ribs and an extensive gastric basket covering its underside, similar to the condition seen in Hupehsuchians, strongly supporting a connection between the two groups. The fossil also dates from surprisingly close to the beginning of the Triassic; dating from the Olenekian (251.2-247.2 million years ago, with the beginning of the Triassic dated to 252.2 millions of years ago) which implies Marine Reptiles were colonising the oceans far sooner after the End Permian Extinction than had previously been supposed.

See also... new species of Hupehsuchian from the Early Triassic of Hubei Province, China.      The Hupehsuchians are a group of Marine... fresh look at the Albian Ichthyosaur Platypterygius hercynicus.                           The Ichthyosaurs were a group of marine tetrapods that resembled dolphins. They appear in the fossil record in the mid-Triassic about 245 million years ago, and survive till the mid-Cretaceous, about 90 million years ago. During the Jurassic they appear to have been the top marine predators, but in the Cretaceous they were overshadowed by other groups...
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