Tuojiangosaurus

Saturday, December 10, 2016

Tuojiangosaurus

Tuojiangosaurus (meaning “Tuo River lizard”) is a genus of herbivorous stegosaurid dinosaur from the Late Jurassic Period, recovered from the Upper Shaximiao Formation of what is now Sichuan Province in China.

Tuojiangosaurus has the typical narrow and low head, bulky body, and low teeth of other stegosaurids. The limbs, especially the arms, are rather short. There are at least twenty-five dentary teeth. The teeth have a thick base, cingulum, merging at the inside into a triangular vertical median ridge. The dorsal vertebrae have tall neural arches. The shoulderblade has a rectangular acromion.

Tuojiangosaurus multispinus by Pachyornis

Tuojiangosaurus was by Dong placed in Stegosauridae in 1977, more precisely in the Stegosaurinae. In 2004, a cladistic analysis by Galton recovered Tuojiangosaurus in a rather derived position, as a sister species of Chialingosaurus. An analysis by Susannah Maidment in 2006, confirmed its status as a member of the Stegosauridae.

Like KentrosaurusTuojiangosaurus had two rows of plates along the spine, which became taller over the hip region. Those at the neck and front trunk were rounded or pear-shaped; the plates at the rear back became more triangular and pointed. All plates have a thickened central section, as if they were modified spikes. Dong estimated there were about seventeen pairs of plates and spikes. Tuojiangosaurus had at least two outward-pointing, rather robust, spikes on each side of the end of the tail, angled at approximately 45 degrees to the vertical. In stegosaurids, this spike arrangement has become affectionately known as the “thagomizer”. Dong thought it were possible that there were four pairs of spikes. Paul, based on “Chungkingosaurus sp. 3″ specimen CV 00208, interpreted the thagomizer as a “pin-cushion array”, with two vertical pairs of thick spikes and a third pair of narrow spikes pointing to behind.

Reconstructed skeleton of Tuojiangosaurus

Another two stegosaurs-Chialingosaurus and Chungkingosaurus-lived in China alongside Tuojiangosaurus in the late Jurassic. Both of these were smaller than Tuojiangosaurus, and they may have coexisted by dividing up the plants they ate based on the height at which they fed. Alternatively, the smaller stegosaurs may have inhabited more enclosed forests, which would have protected them from predators, while the larger Tuojiangosaurus lived in a more open environment, protected by its size.

In 1974, during construction of the Wujiaba dam in Zigong, Sichuan, the remains of stegosaurians were found.

The type and only species of TuojiangosaurusTuojiangosaurus multispinus, was named and described in 1977 (exactly a hundred years after the naming of Stegosaurus by Othniel Charles Marsh) by Dong Zhiming, Zhou Shiwu, Li Xuanmin and Chang Yijong. The generic name is derived from the River (jiang) Tuo. The specific name is derived from Latin multus, “many”, and spina, “spine”.

Yangchuanosaurus attacking Tuojiangosaurus. Author: Foolp

The holotype, CV 209, was found in a layer of the Upper Shaximiao Formation, dating from the Oxfordian-Kimmeridgian. It consists of a rather complete skeleton that however lacks parts of the skull., lower jaws, tail and limbs. In 1977, it represented the most complete stegosaurian skeleton found in Asia. The paratype was specimen CV 210, a sacrum. Subsequently, more material has been referred, including juveniles. This complemented the holotype with elements of the skull, especially the braincase, and the lower jaws.

A mounted skeleton of Tuojiangosaurus multispinus is on display at the Municipal Museum of Chongqing. In addition, a mounted cast is on display at the Natural History Museum, in London.

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