Leurospondylus

The only known fossil of Leurospondylus is a juvenile that was about 2 meters long. Adults may have been much larger.1

Its name means 'smooth vertebra' because its backbone bones were flat and wider than they were long.1

Leurospondylus lived in brackish water (a mix of fresh and salt water) in rivers and estuaries. This is unusual because most plesiosaurs lived in the open ocean.1

When it was first described in 1913, Leurospondylus was thought to be the last known plesiosaur fossil. Its species name 'ultimus' means 'last' in Latin.1

Scientists are not sure which family Leurospondylus belongs to. Its vertebrae look like those of pliosaurs, but its shoulder and hip bones resemble those of elasmosaurids.1

The fossil was found on the east bank of the Red Deer River in Alberta, Canada, in rocks that are about 72 to 66 million years old.21