Useful Notes / Prehistoric Life - Stegosaurs

Stegosaurs have always been one of the dinosaur groups with very few species described (The same cannot be said of their relatives the ankylosaurs). This explains the shortness of this page despite the fame of the stegosaurs.

Note that all the examples below are found outside North America; indeed, only one kind of stegosaur is known definitively to come from this landmass, the ever-popular Stegosaurus. Another North American genus was described in the 2000s, Hesperosaurus, but it could be another Stegosaurus species. A third genus, "Diracodon", was named during the Bone Wars, but now is regarded as an invalid synonym of "Stegosaurus". Among non-stock stegosaurs, you will see Tuojiangosaurus and Kentrosaurus more often than others, but you could also see Dacentrurus, Huayangosaurus, Wuerhosaurus, Lexovisaurus, and other relatives, as well as getting the occasional mention of "Dravidosaurus".


Cousins in Europe: Dacentrurus & Lexovisaurus

Two similar-looking stegosaurs are known from Middle Jurassic Europe. Both Dacentrurus and Lexovisaurus are found in several European countries (England, France, Portugal). Dacentrurus was described in the mid 1800s, before Stegosaurus itself, while Lexovisaurus was named in the 20th century. Unfortunately, both are known from incomplete remains, so their appearances and sizes are unknown. Some suspect Dacentrurus was a very large animal, maybe even larger than Stegosaurus itself, which is considered the largest stegosaur.

Recently, many alleged "Lexovisaurus" remains have been reclassified in another genus, Loricatosaurus. In 2009, a brand new stegosaur was excavated in Portugal: Miragaia. With its small but abundant plates and unusually long neck, it incidentally resembles Dinny from Alley Oop.


The unpronounceable: Tuojiangosaurus

Together with Kentrosaurus, the most portrayed non-stock stegosaur in popular dino-books has been Tuojiangosaurus — don't worry if you cannot pronounce that "jiang" correctly, unless you are Chinese or Chinese-speaking of course.

Discovered in the 1970s, Tuojiangosaurus was basically an Asian variant of Stegosaurus, slightly smaller and with armor intermediate between Kentrosaurus and Stegosaurus, with narrow, paired plates like the former, but the usual four tail-spikes (thagomizer) like the latter. With such small plates, it is unlikely that Tuojiangosaurus and Kentrosaurus would have used them as solar panels or radiators, unlike what was possible for Stegosaurus. Some pictures show Tuojiangosaurus with shoulder-spikes like those of Kentrosaurus, but it is unsure whether it had them.

Together with the carnivorous Yangchuanosaurus and the sauropod Mamenchisaurus, Tuojiangosaurus is one of the three classic dinosaurs from Late Jurassic Asia; however, this "Chinese Trio" has yet to appear in recent CGI documentaries. However, Tuojiangosaurus seems especially common in English dino-books, as a skeleton cast of it has been on display in the Natural History Museum of London since the 1980s, which is often shown in illustrations.

MOAR cousins, this time in China: Huayangosaurus & Wuerhosaurus

China has given us about half the steggies around the world. Other than Tuojiangosaurus, there is Chialingosaurus, similar to Kentrosaurus and more slender than other stegosaurs; Chungkingosaurus, which may actually be a juvenile Tuojiangosaurus; Huayangosaurus, with a big head and long limbs (see below); and Wuerhosaurus, a large stegosaur whose plate sizes were unknown. A recent find has been called Gigantspinosaurus, due to the gigantic spines on its shoulders (not a cross between a ''Giganotosaurus'' and a ''Spinosaurus'').

Huayangosaurus is notable because is the most primitive stegosaur known from good fossil material. It was only 4 m long, and preserved several ancestral traits in its skeleton, such as small frontal teeth on its upper jaw, a typical primitive trait among ornithischians, which were lost in more evolved stegosaurs. Its armor, however, was already fully stegosaurian, similar to Tuojiangosaurus, but with shoulder spikes like Kentrosaurus.


Under the sea: Dravidosaurus

Definitive stegosaurs appeared in the Middle Jurassic, and reached their heyday in the Late Jurassic with genera such as Stegosaurus, Tuojiangosaurus, Kentrosaurus. However, they began to decline in Early Cretaceous, perhaps due to competition from the more armored ankylosaurs, yet there were still a few holdouts such as Wuerhosaurus.

However, there was a stegosaur which, uniquely, survived until the Late Cretaceous, Dravidosaurus. One of the few dinosaurs discovered in Indian subcontinent, a huge separate landmass in the Late Mesozoic, Dravidosaurus somehow managed to arrive there, and flourished thanks to the absence of competition which other relatives faced in the mainland. Its status as the last stegosaur gave it several mentions in old books and documentaries. However, all this was shown to be false. In 1996, a re-examination of its extremely fragmentary remains has revealed our Last Stegosaur to be 1. not a stegosaur, 2. not a dinosaur, and 3. not even a land-dweller. It was a marine reptile, more precisely a plesiosaur.
http://tvtropes.org/pmwiki/pmwiki.php/UsefulNotes/PrehistoricLifeStegosaurs