(Water beast lizard).
Named By: Samuel Paul Welles - 1943.
Classification: Chordata, Reptilia, Sauropterygia, Plesiosauria, Elasmosauridae.
Species: H. alexandrae (type).
Size: Up to 13 meters long.
Known locations: USA - California - Moreno Formation.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Almost complete individual.
is comfortably placed within the Elasmosauridae, a group of
plesiosaurs noted for having proportionately long necks. Also like
these other genera, Hydrotherosaurus had long
pointed teeth, but
these seem to have projected more to the sides rather than just up and
down. This however is quite a common feature seen in piscivorous
(fish eating) animals where the outward pointing teeth actually
increase the available catch area for trapping prey (just think
catchers mitt). Palaeontologists do need to be certain before
making such claims though, since this idea was also proposed for a
genus of pliosaur called Simolestes.
When first described Simolestes
had outward pointing teeth, but then it was realised that the teeth
were actually pushed out by the weight of the sediment above pushing
down on them during the fossilisation process.
Hydrotherosaurus was described from fossils discovered in the Moreno Formation of California, with other plesiosaur genera from here including Aphrosaurus, Morenosaurus and Fresnosaurus. Interesting facts concerning these four genera is that not have all four of these plesiosaurs come from the Moreno Formation, but they were all described by Samuel Paul Welles and all in 1943. Other marine reptiles include the mosasaurs Plesiotylosaurus and Plotosaurus.
- Elasmosaurid plesiosaurs with a description of the new material from California and Colorado, S. P. Welles - 1943.