dravidosaurus

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Dravidosaurus blanfordi: Identity Crisis

Size: 10 feet (3 meters)

Time Period: The Coniacian Stage of the Late Cretaceous, about 89 to 85 million years ago.

Locale: Marine deposits near Ariyular in South India.

Name: Dravidosaurus means “Dravidanu lizard” after the region in Southern India where the remains of the animal were discovered.

Sometimes an extinct animal’s remains will be so fragmentary that only a tentative classification of it can be obtained. This was the case with Dravidosaurus, once thought to be a late-surviving representative of the stegosaurs, a group of thyreophoran dinosaurs that were successful during the Jurassic.

To talk about Dravidosaurus, I must first tell you about the oddness of its supposed family. The stegosaurs were the only major dinosaur group since the prosauropods to die out during the Mesozoic. The general tendency among dinosaur groups is for them to appear and dwell alongside other, more primitive forms. This is why dinosaurs were considerably less diverse earlier in the Mesozoic, then reached a heyday of diversity in the Late Cretaceous. Stegosaurs lived from the Middle Jurassic to the Early Cretaceous, when they were then replaced by the more successful ankylosaurs, who had shadowed them since the Late Jurassic, where Gargoyleosaurus and Mymoorapeta lived alongside the famous Stegosaurus. The last well-known representative of the stegosaurs is Wuerhosaurus, a Chinese stegosaur with long, low plates. From then on, no trace of them has been found.

You could then imagine why Dravidosaurus seemed so important. It lived in India during the Late Cretaceous, at a time where India was an island subcontinent. Scientists were led to believe that India was the last stronghold of the family at a time when it had once died out. It seemed plausible, because relic animals living on islands are an evolutionary trend. Look at the lemurs of Madagascar. Due to their isolation, they survived when all of their relatives died out. Unfortunately, further inspection of Dravidosaurus remains revealed that it was not such a relic animal, but rather a plesiosaur. The discovery of the animal in marine deposits was then held as evidence of its true identity, and not a result of the body washing out to sea. This mistake has been made before, and ‘stegosaur teeth’ from Madagascar’s Maevarano formation were eventually linked to the herbivorous crocodilians that lived there in the late Cretaceous.

It also no longer seems plausible that Dravidosaurus would have lived on India. Provided that it split from another landmass during the Late Jurassic, we would have also found animals present during that time in the formation. Instead, Late Cretaceous India was home to more advanced animals, like abelisaurids, noasaurids, and strange titanosaurs.

We should not be so quick to assign classifications to fragmentary remains that are in bad condition, as they can severely skew our perception of the fate of entire groups of extinct animal. Dravidosaurus remains but one example of how many accidents can be found in the science of paleontology.