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hupehsuchia
Hupehsuchia is an order of diapsid reptiles closely related to ichthyosaurs. The group was short-lasting, with a temporal range restricted to the late Olenekian age, spanning only a few million years of the Early Triassic. The order gets its name from Hubei Province, China, from which many specimens have been found. They are probable members of the newly defined clade Ichthyosauromorpha.
==Description==
Hupehsuchians display an unusual combination of characteristics. The overall shape of the body is fusiform, with a long tail and large, paddle-like limbs. The skull is elongated and the jaws are edentulous. The rostrum is flatteded with the premaxilla thought to form most of the dorsal and lateral surface, while the maxilla is mostly restricted to the ventral surface beyond the base of the rostrum. An opening between the nasal and the prefrontal bones in one hupehsuchian specimen (known as IVPP V3232) was initially interpreted as an antorbital fenestra, but is now thought to be an artifact caused by the damage of the surrounding bones during preservation. Its position is not indicative of a narial opening, either. More likely, the naris lies between the nasal and the maxilla in an area anterior to that of the supposed antorbital fenestra, although the preservation of this area in known specimens is too poor to prove definitively that it is the external naris and not an artifact of preservation, as is the case for the fenestra.
The neck is relatively elongated and the cervical ribs are short. An unusual feature of the neural spines of the trunk region, from the 11 vertebra to the first caudal, is that each is divided into two distinct units by a suture line. One is proximinal to the rest of the vertebra and the other is distal to it. Some anteroposterior displacement of these two units occurs along the vertebral column, suggesting they are not ossified to one another. In vertebrae 8-14, the distal ends of the distal portions of the neural spines are expanded posteriorly. An additional anterior expansion of the neural spine is seen in all vertebrae after the 14th. These expanded distal regions exhibit some sculpturing, and may have penetrated the dermis. Another unusual characteristic of hupehsuchians is the presence of dermal plates over the neural spines of the approximately 34 presacral vertebrae. A small dermal bone overlies each space between the posterior expansion of one distal neural spine and the anterior expansion of the one behind it. Above these dermal bones lie even larger dermal plates that directly overly even numbered neural spines.
Gastralia are present in some specimens that form a type of ventral armor from the pectoral to the pelvic girdle. The medial row consists of large, overlapping, V-shaped elements, and lateral rows consist of smaller, cylindrical, widely spaced bones.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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