wuerhosaurus

WUERHOSAURUS
“Wuerho lizard”
Early Cretaceous, 135-120 million years ago, uncertain

Named for the area of China where it was found, this Stegosaurus-like dinosaur survived much later than any of its predecessors from the Jurassic. Its plates were wider and flatter than Stegosaurus, although some scientists believe the fossils found simply to be broken. The plates’ molar-like appearance has led some dinosaur enthusiasts to refer to Wuerhosaurus affectionately as “jawback,” a particularly odious ethnic slur.

W is for Wuerhosaurus

Wuerhosaurus homheni was a stegosaur from the Early Cretaceous of China, about 135 million years ago. It probably reached a length of around 7m (23ft). It was one of the very last stegosaurs to have existed, with most others found in the late Jurassic.

Although often depicted with low, stubby-looking back plates, the only known fossilized plate appears to be broken, so the actual size and shape is still a mystery. One spike is known, which was interpreted as being from the shoulder, but I’ve seen hardly any other reconstructions actually including one there.

In 2008, a proposal was made to reclassify Wuerhosaurus as a species of Stegosaurus instead of having its own genus — which would make the correct name Stegosaurus homheni — but this opinion hasn’t been widely accepted yet. Without more complete specimens we can’t know for certain just how similar these two stegosaurs really were.

3

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.

The Wuerho lizard, Wuerhosaurus (1973)

Phylum : Chordata
Class : Reptilia
Order : Ornithischia
Suborder : Stegosauria
Family : Stegosauridae
Subfamily : Stegosaurinae
Genus : Wuerhosaurus
Species : W. homheni, W. ordosensis

  • Early Cretaceous (120 - 110 Ma)
  • 7 m long and 2 400 kg (size)
  • Xinjiang province, China (map)

Wuerhosaurus homheni was probably a broad bodied animal. Gregory S. Paul in 2010 estimated the length at 7 metres and the weight at four tonnes. Only a few scattered bones have been found, making a full restoration difficult. Its dorsal plates were at first thought to have been much rounder or flatter than other stegosaurids, but Maidment established this was an illusion caused by breakage: their actual form is unknown. W. homheni had a pelvis of which the front of the ilia strongly flared outwards indicating a very broad belly. The neural spines on the tail base were exceptionally tall.
W. ordosensis was estimated by Paul to have been 5 metres long and weigh 1.2 tonnes. It too has a broad pelvis but the neural spines are shorter. The neck seems to have been relatively long.

Wuerhosaurus was lower to the ground than most other stegosaurids; scientists believe that this was an adaptation to let it feed on low-growing vegetation. Wuerhosaurus, like other stegosaurids, perhaps had a thagomizer on the end of its tail, like that of Stegosaurus which featured four bony spikes that would most likely have been used for self-defense. A single spike was found but was seen by Dong as being positioned on the shoulder.