Sunday 8 June 2014

A Metriorhynchid Crocodylomorph tooth from the Late Jurassic of Chesil Beach, England.

The Metriorhynchids were a group of Crocodylomorphs that adopted a fully marine lifestyle in the Middle Jurassic and persisted into the Early Cretaceous. They were a highly successful group, producing a wide range of body shapes, and therefore, by implication, survival strategies. One group of Metriorhynchid Crocodylomorphs, the Geosaurini, apparently specialized in the capture and consumption of large prey, attaining large sizes and having wide gapes and specialized jaws adapted to shearing bites, with fewer, but larger teeth. Within this group one genus, Dakosaurus, became particularly specialized, with the shortest tooth-row of any known Metriorhynchid, and further specialized teeth and jaws. The morphology of Dakosaurus has been compared to both Killer Whales and False Killer Whales.

In a paper published in the journal Historical Biology on 16 May 2014, a group of palaeontologists led by Mark Young of the Institute of Evolutionary Biology at the University of Edinburgh and the School of Ocean and Earth Science at the University of Southampton describe an of Dakosaurus tooth recovered by a dredger from of Chesil Beach in Dorset, England. 

The tooth is 53 mm high, 21 mm deep and 19 mm wide, being single cusped and slightly compressed. It is curved backwards, but only on its middle and apex. The root is missing, but by comparison with other teeth it is thought to be the tip of a Dakosaurus tooth about 55 mm in length, and assigned to the species Dakosaurus maximus.

Dakosaurus maximus, isolated tooth in (a) lingual view, (b) labial view, (c) mesial view, (d) distal view, (e) basal view and (f) apical view. This specimen is from Chesil Beach, near Weymouth, England (Kimmeridge Clay Formation). Scale bar is 10 mm. Young et al. (2014).

Kimmeridge Clay Formation outcrops in the Dorset type area. Young et al. (2014).

See also…

The Slender-snouted Crocodile, Mecistops cataphractus, is found throughout West and Central Africa. It is the only species in the genus Mecistops, which apparently diverged from the related genus...

The Metriorhynchids were Mesozoic Crocodylomorphs adapted to a fully aquatic marine lifestyle. Their limbs were modified into paddle-like flippers, they has a shark-like tail-fin and had lost the...

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