Xinminosaurus

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Xinminosaurus
Temporal range:
Ma
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Ichthyosauria
Family: †Cymbospondylidae
Genus: †Xinminosaurus
Jiang et al., 2008
Type species
†Xinminosaurus catactes
Jiang et al., 2008

Xinminosaurus is an

Guizhou Province, China
.

Etymology

The

dentary
.

Discovery

Xinminosaurus is known only from the

junior synonym of Tholodus.[2] Although Jiang et al. regarded Tholodus to be a possible nomen dubium,[1] Maisch rejected this opinion, stating that Tholodus is easily recognized and characterized by unequivocal dental autapomorphies, so that even jaw and tooth fragments are diagnostic, and it is thus a valid taxon. Furthermore, he noted that Tholodus is clearly distinguishable from all other known marine reptiles, except Xinminosaurus. The only difference between the taxa, according to Maisch, is that Tholodus specimens are on average twice as large as the holotype of Xinminosaurus.[2]

Mulder and Jagt (2019) demonstrated that the putative mosasaur "Globidens" timorensis is not a mosasaur and instead represents a Xinminosaurus-like ichthyosaur.[3]

Description

The holotype specimen of Xinminosaurus has a total length of 2.32 metres (7.6 ft), while its skull measures 29 centimeters long. The skull is poorly preserved, which obscures much of its anatomy. The teeth of Xinminosaurus lack constrictions. In the

pulp cavities, instead being present as a second row of teeth. The very tips of its jaws, however, may have been toothless, while the teeth at the front of the denataries are cone-shaped.[1]

Postcranial skeleton

Xinminosaurus has a total of 140

neural spines slope forwards. In Xinminosaurus, the tail is bent downwards at a 35° angle, starting at caudal vertebra 38.[1]

Each scapula (shoulder blade) is composed of a broad, fan-like blade and a process that forms the shoulder joint, separated by a shaft. The latter of these structures has an outwards-bowed lower end with a notch and extends further forwards than backwards.[1] The coracoids (a pair of shoulder bones) are greater in width than length.[4] Xinminosaurus has short, wide collarbones.[1] The interclavicle (a shoulder bone between the collarbones) does not have a backwards projection.[4]

The long limb bones of Xinminosaurus are atypical for an ichthyosaur. The

phalanges (digit bones) are long and at least the upper ones are hourglass-shaped.[1][4]

The upper and lower hindlimb bones are shorter than those of the forelimb. The upper ends of the

metatarsals and phalanges are similar to the metacarpals and the phalanges in the foreflippers, although the exact number of phalanges in each digit in the hindflippers is unknown.[1]

References

  1. ^
    doi:10.1016/j.pnsc.2008.01.039
    .
  2. ^ a b Maisch, Michael W. (2010). "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art" (PDF). Palaeodiversity. 3: 151–214.
  3. S2CID 199112423
    .
  4. ^
    S2CID 85621052
    .
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