Dallasaurus

Name: Dallasaurus ‭(‬Dallas lizard‭)‬.
Phonetic: Dal-las-ore-rus.
Named By: G.‭ ‬L.‭ ‬Bell Jr‭ & ‬M.‭ ‬J.‭ ‬Polcyn‭ ‬-‭ ‬2005.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Squamata,‭ ‬Mosasauridae,‭ ‬Mosasaurinae.
Species: D.‭ ‬turneri‭ (‬type‭)‬.
Diet: Carnivore.
Size: Up to‭ ‬1‭ ‬meter long.
Known locations: USA,‭ ‬Texas,‭ ‬Dallas County‭ ‬-‭ ‬Kamp Ranch Limestone.
Time period: Turonian of the Cretaceous.
Fossil representation: 2‭ ‬partial specimens,‭ ‬together represented by a partial skull and disarticulated post cranial remains.

       Dallasaurus was‭ ‬a‭ ‬fascinating discovery,‭ ‬especially for lovers of the marine reptiles that swam the Mesozoic oceans,‭ ‬more particularly the mosasaurs of the Cretaceous.‭ ‬The skeletal features of Dallasaurus have‭ ‬helped to further cement the theory that the mosasaurs evolved from terrestrial‭ (‬land living‭) ‬reptiles like monitor lizards during the early/mid Cretaceous.‭ ‬A counter theory to‭ ‬this is that the mosasaurs evolved from primitive snakes,‭ ‬but this idea has gradually waned in acceptance with the advent of new fossil discoveries for both early mosasaurs and Cretaceous snakes.‭ ‬Also of interest is that while other well-known groups of marine reptiles such as the ichthyosaurs,‭ ‬plesiosaurs and pliosaurs are thought to have also evolved from land reptiles of the diapsid line,‭ ‬the mosasaurs appeared and adapted completely independently of them.
       Dallasaurus is seen as a transitory link because while its body and tail show adaptation for swimming,‭ ‬the legs still have a greater development for walking on land.‭ ‬This would suggest that Dallasaurus lived in coastal waters,‭ ‬perhaps estuarine waters‭ (‬where rivers meet oceans‭) ‬where they could take advantage of an abundant supply of aquatic prey but still had to return to the land,‭ ‬either to rest or possibly to hunt in different waters such as coastal lagoons.‭ ‬Roaming behaviour like this would lead to an oceanic expansion so that Dallasaurus could have access to an even greater number of prey.‭ ‬In later mosasaurs the legs would develop fully into flippers to support a completely aquatic life.
       It is still too early to say if Dallasaurus laid eggs or gave birth to live young as the fossils which indicate either method are still lacking.‭ ‬However later mosasaurs were too large to conceivably return to the land,‭ ‬and the reptiles as a group seem remarkably quick to adapt to live birth particularly in the other lines of marine reptiles,‭ ‬with evidence suggesting this being found in ichthyosaurs,‭ ‬but perhaps a more relevant example being that of Keichousaurus.‭ ‬Beyond this live birth can be seen in some lizards that are alive today,‭ ‬as well as other reptile groups like the sea snakes.
       Reptiles like Dallasaurus and the another early mosasaur named Russelosaurus would go onto to have an impressive lineage of descendants,‭ ‬from the giant Tylosaurus that was over fifteen meters long,‭ ‬to the advanced Platecarpus which had a tail fluke similar to an ichthyosaur,‭ ‬to specialist feeders like Globidens which had crushing teeth to eat armoured prey.

Further reading
- Dallasaurus turneri, a new primitive mosasauroid from the Middle Turonian of Texas and comments on the phylogeny of the Mosasauridae (Squamata). - Netherlands Journal of Geoscience (Geologie en Mijnbouw) 84 (3) pp. 177-194. - G. L. Bell Jr. & M. J. Polcyn - 2005.





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