Friday 19 December 2014

A new species of Hupehsuchian from the Early Triassic of Hubei Province, China.

The Hupehsuchians are a group of Marine Reptiles known only from the Early Triassic of Hubei Province, China. Their origins and relationships are obscure, though it has been suggested that they might be related to Ichthyosaurs. They typically have heavily ossified, dense bones on their trunk (which is usually an adaptation to diving or bottom feeding in Marine Reptiles and Mammals, as it helps to reduce buoyancy), combined with inflexible bodies and elongate, flattened snouts.

In a paper published in the journal PLoS One on 17 December 2014, Xiao-hong Chen of the Wuhan Centre of the China Geological Survey, Ryosuke Motani of the Department of Earth and Planetary Sciences at the University of CaliforniaDavis, Long Cheng, also of the Wuhan Centre of the China Geological Survey, Da-yong Jiang of the Laboratory of Orogenic Belt and Crustal Evolution at Peking University and Olivier Rieppel of the Center of Integrative Research at The Field Museum in Chicago, describe a new species of Hupehsuchian from the Early Triassic Jialingjiang Formation at Yangping in Yuan’an County in Hubei Province.

The new species is named Eohupehsuchus brevicollis, where ‘Eohupehsuchus’ means ‘dawn-Hubei-Crocodile’ and ‘brevicollis’ means ‘short neck’. It is a small Hupehsuchian with an estimated length of about 40 cm, though much of the tail is missing giving it a preserved length of 23.6 cm. It has an elongated flattened snout, lacking any teeth, and the shortest known neck of any Hupehsuchian, with only six cervical vertebrae.

Eohupehsuchus brevicollis. Scale bar I cm. Chen et al. (2014).

As a new species notably smaller than other members of the group, which are also known from the same area, it was natural to consider the possibility that Eohupehsuchus brevicollis is in fact a juvenile of another species. However the long bones (limb bones) of the specimen appear well ossified, which is generally taen as a sign of maturity (these bones ossify slowly as an animal grows, and once fully ossified have little potential for further growth), and the number of neck vertebrae is smaller than any other known member of the growth, which, since vertebrates do not usually grow new vertebrae as they grow, strongly implies that it is a new species.

Pectoral and pelvic regions of Eohupehsuchus brevicollis. (A) Pectoral region. (B) Pelvic region. Symbols: Cl, clavicle; Co,coracoid; F, femur; Fi, fibula; H, humerus; h#, hemal spine; Icl, interclavicle; Il, ilium; Is, ischium; n#, neural spine; Pb, pubis; r#, rib; Sc, scapula; v# vertebralcentrum. Colors: blue, vertebral centra; brown, neural spine first segment; green, neural spine second segment; light blue, rib; light green, limb elements;light purple, hemal spines; light yellow, girdle elements; orange, gastral elements; pink, dermal armour second layer; red, dermal armour first layer; red-purple,dermal armour third layer; yellow, parapophysis. Scale bars are 1 cm long. Chen et al. (2014).

The tip of the left forelimb of Eohupehsuchus brevicollis appears to have been lost before burial, probably implying predation or scavenging. Since there are no other signs of scavenging, Chen et al. favour predation as an explanation (i.e. the tip of the limb was bitten off before the animal died), though there is no sign of any healing, which would suggest that the injury occurred shortly before death, though it is unlikely to have been fatal in itself.

Forelimbs of Eohupehsuchus brevicollis. Symbols: bb, broken bones that are kinked from damage; bp, broken bone pieces thatare dislocated; i, intermedium; i–v, metacarpal; H, humerus, R, radius; r, radiale; U, ulna; u, ulnare; 1–5, distal carpal. Scales are 1 cm long. Chen et al. (2014).

See also…

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