Dino of the Week: Isanosaurus

Type Species: Isanosaurus attavipachi

Classification: Dinosauria - Saurischia - Sauropoda

Time Period: Late Triassic

Location: Thailand

Diet: Herbivore

Isanosaurus’ name means ‘Isan lizard,’ and Isan is the name used to refer to northeast Thailand where the specimen was found. Isanosaurus’ discovery caused quite a stir, because upon examination of the few bones preserved, it became apparent that this creature was a sauropod – and it was found in Late Triassic rocks! Up to that point, it was believed that sauropods didn’t come onto the scene until the Early Jurassic, with Vulcanodon being the first of its kind. Isanosaurus pushed sauropod evolution back into the Triassic, upsetting plenty of cherished beliefs. Though some paleontologists question Isanosaurus’ geographical placement, insisting that it actually lived in the Early Jurassic, this is done more for philosophical than scientific reasons. Isanosaurus’ identification of a sauropod doesn’t mean it rivaled the titanic-sized sauropods of the later Jurassic, but it would put the sauropod genesis far earlier than traditionally believed. 

Many supersized prosauropods existed in the Late Triassic – take, for example, Camelotia – but these creatures’ morphologies still place them in the prosauropod camp. Isanosaurus’ remains include a neck vertebra, a back vertebra, and part of a second, six tail vertebra, two chevrons (features of the tail), fragmentary ribs, the right sterna plate, the right shoulder blade, and the left thigh bone. Even these scant finds give us a wealth of information that sets Isanosaurus apart from its prosauropod contemporaries. Its dorsal neural spines were high like those of some later sauropods, unlike the low neural spines of prosauropods; and the lateral sides of the vertebrae were concave, though not deeply excavated as in later sauropods. 

The Isanosaurus specimen shows a quadrupedal locomotion, and the legs were column-like, as shown by the robust and straight thigh bone. The individual discovered likely measured around twenty feet head-to-tail when alive, but the fact that the vertebral neural arches were found separated from the vertebral centra indicates that these remains weren’t fused with each other; this implies that the animal probably wasn’t fully grown, so it’s only a guess as to how large Isanosaurus grew in real life.