Keichousaurus

Keichousaurus Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N
Keichousaurus hui fossil at the North American Museum of Ancient Life
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Family:	† Keichousauridae
Genus:	†Keichousaurus Young, 1958
Species
†K. hui Young, 1958 (type) †K. yuananensis Young, 1965

Keichousaurus (meaning "Kweichow lizard") is an extinct genus of pachypleurosaurian marine reptile from the Chialingchiang and Falang Formations of China with two known species attributed to the genus: K. hui and K. yuananensis.^[1][2]

Keichousaurus is among the most common

The holotype of K. hui, was discovered in the Falang Formation of Guizhou Province, China in 1957 by Hu Chengzhi and was named by Young (1958).^[1]

The second species, K. yuananensis, was discovered in the Chialingchiang Formation of Hebei, China and was named by Young (1965) based on the holotype specimen IVPP V.2799, a partial skeleton.^[2]

Description

Keichousaurus, like all sauropterygians, was highly adapted to the aquatic environment. Most specimens had small body, males sexually mature with 12.6 centimetres (5.0 in) snout-vent length (SVL), and in females by 12.2 centimetres (4.8 in) SVL. Mean SVL for mature males is approximately 16.1 centimetres (6.3 in) SVL, and for mature females, at most 14.9 centimetres (5.9 in) SVL.^[3] It had both long necks and long tails, with elongated, five-toed feet. The pointed head and sharp teeth in this genus also indicate that they were fish-eaters. Some recovered specimens feature an especially developed ulna suggesting they may have spent some time on land or in marshes.

In addition fossil evidence suggest also a pair of fossilized pregnant marine reptiles called Keichousaurus hui, show they had a mobile pelvis to give birth to live young rather than laying eggs.

Morphology

Keichousaurus hui was found in 1958 in Guizhou, China by palaeontologist Hu Chengzhi.^[1]

This fossil is distinguished by its broad ulna which makes it unlike other European genera. The broad ulna increased the surface area of the forelimbs, making it more effective in locomotion. Keichousaurus shows many characteristics of its family Pachypleurosauridae such as its short snout and elongated temporal openings. Keichousaurus also had a long serpentine neck with a relatively small head and long tail. The anterior caudal vertebrae possess lateral transverse processes. The morphology of Keichousaurus is most like that of

growth.

Locomotion

The locomotion of Keichousaurus probably resembled (in part) the "underwater flight" that

plesiosaurs

employed. The flattened forelimbs would likely have acted as hydrofoils. The hindlimbs show less specialization, and may therefore have acted as stabilizers and control surfaces, such as is seen in extant sea turtles. The intermediate nature of the limb morphology implies that there was also, to some extent, the kind of 'crawling through the water' seen in small freshwater turtles. The powerfully built pectoral girdle allowed for the attachment of strong muscles, but their location beneath the shoulder favours the underwater flight model. Despite the specialization of the limbs, the tail also shows adaptations to an aquatic existence. Lateral transverse processes of the anterior caudal vertebrae show that powerful muscles enabled the tail to beat or at least undulate from side to side. This would imply some distal lateral compression, but this is not recorded in soft-tissue preservation. The long neck was primarily concerned with prey-capture. The combination of powerful limbs and tail would have made K. hui an adept and maneuverable predator.

Reproduction

Although there is no direct evidence, Keichosaurus was potentially ovoviviparous (eggs form and hatch within uterus). Fossil Keichousaurus display a simplified elbow joint and a lack of ossification in the olecranon process of the ulna. This would make crawling up the beach to lay eggs awkward. Specimens at different developmental stages, found in the same type of sediment at the same locality, also support an ovoviviparous reproduction model. However, fossils have been found of female Keichousaurus with fetuses within the lower portion of the thoracic cavity. Their position implies that they are not victims of cannibalism.

References

1. ^ ^{a b c} C.-C. Young. (1958). On the new Pachypleurosauroidea from Keichow, south-west China. Vertebrata PalAsiatica 2(2-3):72-81
2. ^ ^{a b c} C.-C. Young. (1965). On the new nothosaurs from Hupeh and Kweichou, China. Vertebrata PalAsiatica 9(4):337-356
3. S2CID 86480962
   .

• "keichousaurus". Archived from the original on 2003-05-16.
• peripstus.com/Keichousaurus
• Functional morphology and ontogeny of Keichousaurus hui