A 112-million-old plesiosaur

Mar 25, 2008 08:51 GMT  ·  By

One group of huge marine reptiles that dominated the seas during the dinosaur eras (Jurassic and Cretaceous, 200 to 65 Ma ago) was represented by the plesiosaurs, long-necked small-headed carnivore animals with flippers resembling those of the sea turtles. These were the animals that inspired the legend of the Loch Ness monster.

Now, one of the oldest North American plesiosaurs, belonging to a completely new lineage in this group, has been described in the German research journal "Palaeontographica Abteilung A."

The new species, 8.5-ft (2.6-m) long, was named Nichollsia borealis in memory of the late paleontologist Elizabeth Nicholls, who described the largest-ever sea reptile, a 76-ft (23-m)-long ichthyosaur encountered in northern British Columbia, in 1999. Nichollsia, that lived 112 Ma ago, is a dwarf in the group of the plesiosaurs, which could reach lengths of over 39 ft (12 m), but it fills a gap of 40 million years in the fossil records of the group.

The fossil was found in a Syncrude Canada Ltd. mine in the northeastern Alberta (Canada), in 1994, 197 ft (60 m) below the ground, but releasing the fossil from its rock bed has taken years for the team of the University of Calgary. This is the most complete plesiosaur coming from American Cretaceous; only the left forelimb and shoulder blade are missing.

"This specimen was preserved in sandstone and was not crushed as much as most specimens, which have typically been found in shale. Because of this I was able to have its three-dimensional skull CT-scanned so we can see the details of the insides of its braincase. This has helped us understand this animal in more detail than almost any other plesiosaur ever found," said co-author Patrick Druckenmiller, a former University of Calgary graduate student.

Nichollsia could also explain more on the sea that covered the Great Plains of North America during the dinosaur era, splitting the continent in two.

"This individual was a pioneer in the marine waters that would eventually become the Cretaceous Western Interior Seaway, which ran the length of North America during much of the Cretaceous and was home to one of the world's most diverse communities of marine reptiles. It represents the oldest known forerunner of this amazing period in North American history," said Druckenmiller.

Other plesiosaurs and ichthyosaurs were discovered at the same site, too, some being new species.