Dinocephalosaurus

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Dinocephalosaurus
Temporal range: Middle Triassic, 244 Ma
Dinocephalosaurus-embryo-3.jpg
Diagrams (a-d) and life reconstruction (f) of specimen LPV 30280, which contains an fetus (c-d) and a perleidid fish (e)
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Protorosauria
Family: Tanystropheidae
Genus: Dinocephalosaurus
Li, 2003
Type species
Dinocephalosaurus orientalis
Li, 2003

Dinocephalosaurus (meaning "terrible-headed reptile") is a genus of long necked, aquatic protorosaur that inhabited the Triassic seas of China.[1] Specimens belonging to the genus were discovered near Xinmin in Guizhou Province, China in 2002.[2][3]

Description[edit]

Restoration

Dinocephalosaurus is mostly closely compared with Tanystropheus, both being protorosaurs with necks twice as long as their bodies. While the neck of Tanystropheus was composed of twelve elongated cervical vertebrae, the neck of Dinocephalosaurus has becoming elongated through additional cervical vertebrae (at least 25 in total), producing a neck with a length of 1.7 metres (5 ft 7 in). The necks of both taxa are thought to have evolved convergently. The use of the long neck in Tanystropheus is not fully understood, but it was used for prey capture in Dinocephalosaurus. Dinocephalosaurus differed from all other protorosaurs in the fact that it was the only one that was fully aquatic. Where most protorosaurs had ossified limbs adapted for terrestrial life, Dinocephalosaurus was neotenic, as with many other aquatic tetrapods.[3]

Classification[edit]

As of February 2017 Dinocephalosaurus is considered to be a member of the Protorosauria. It was closely related to Tanystropheus; they share a narial recess in the skull, elongation of the neck, and the association of the cervical vertebrae with the cervical ribs.[4] Dinocephalosaurus also shares a number of traits with Macrocnemus specimens, in terms of skull anatomy (e.g. a low and narrow skull with a short and narrow postorbital region; the nasals are longer than the frontals; and the posterior process of the jugal is reduced) and the presence of more than seven cervical vertebrae.[4] The results of a phylogenetic analysis conducted in 2017, showing the relationships of Dinocephalosaurus among protorosaurs, is shown below.[5]

Protorosauria

Jesairosaurus





Megalancosaurus




Drepanosaurus



Vallesaurus






Boreopricea


Tanystropheidae


Macrocnemus




Langobardisaurus




Tanystropheus



Tanytrachelos






Dinocephalosaurus






Paleobiology[edit]

Feeding ecology[edit]

Researchers have suggested that Dinocephalosaurus lived in the shallow murky waters of the sea, and presumably had a diet of fish and squid. Recently, a fossil with a perleidid fish in the abdominal region has been described.[5]

Reproduction[edit]

One specimen of Dinocephalosaurus was discovered with an fetus in its pelvic region, suggesting that it was viviparous, which was likely a consequence of Dinocephalosaurus being unable to come on land.[5] Dinocephalosaurus is the first viviparous archosauromorph[5] asides from possibly metriorhynchids.[6] While the otherwise absence of viviparous archosaurs has been historically attributed to common attributes inherited from the archosaurian stem-lineage, the discovery that Dinocephalosaurus was viviparous suggests that this phenomenon is due to lineage-specific lifestyle restrictions.[5]

References[edit]

  1. ^ Wang, Y.; Yang, D.; Han, J.; Wang, L.; Yao, J.; Liu, D. (2014). "The Triassic U–Pb age for the aquatic long-necked protorosaur of Guizhou, China". Geological Magazine. 151 (4): 749–754. doi:10.1017/S001675681400003X. 
  2. ^ Li, C. (2003). "First record of protorosaurid reptile (Order Protorosauria) from the Middle Triassic of China". Acta Geologica Sinica. 77 (4): 419—423. doi:10.1111/j.1755-6724.2003.tb00122.x. 
  3. ^ a b Li, C.; Rieppel, O.; LaBarbera, M.C. (2004). "A Triassic Aquatic Protorosaur with an Extremely Long Neck". Science. 305 (5692): 1931. doi:10.1126/science.1100498. 
  4. ^ a b Rieppel, O.; Li, C.; Fraser, N.C. (2008). "The Skeletal Anatomy of the Triassic Protorosaur Dinocephalosaurus orientalis Li, from the Middle Triassic of Guizhou Province, Southern China". Journal of Vertebrate Paleontology. 28 (1): 95–110. 
  5. ^ a b c d e Liu, J.; Organ, C.L.; Benton, M.J.; Brandley, M.C.; Aitchison, J.C. (2017). "Live birth in an archosauromorph reptile". Nature Communications. 8. doi:10.1038/ncomms14445. ISSN 2041-1723. 
  6. ^ Herrera, Y.; Fernandez, M.S.; Lamas, S.G.; Campos, L.; Talevi, M.; Gasparini, Z. (2017). "Morphology of the sacral region and reproductive strategies of Metriorhynchidae: a counter-inductive approach". Earth and Environmental Science Transactions of the Royal Society of Edinburgh: 1–9. doi:10.1017/S1755691016000165. 

See also[edit]