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'''Anchisaurus''' (from Greek ''agkhi''
| Contents |
| Discovery |
| Description |
| Classification |
| In popular culture |
| External links |
Discovery
The first discovery of ''Anchisaurus'' remains was made before anything was known about dinosaurs and it was probably the first dinosaur discovery in North America. When, in 1818, some large bones were discovered in Connecticut, USA, it was assumed that they were of human origin. Gradually, as a result of further finds in Massachusetts, the number of these bones began to accumulate and, by 1855, they were at least recognised as reptilian. Hitchcock collected these bones under the name ''Megadactylus'' in 1865. Unfotunately, the name was in use, and the famous paleontologist Othniel Charles Marsh renamed it ''Anchisaurus'' in 1885. Remains thought to belong to this genus were found in South Africa and China, adding to the theory that these land masses were at the time joined in one super-continent, Pangaea, but these assignments have been contentious (''Gyposaurus''). A recovery from Nova Scotia may also be an ''Anchisaurus'' but this is unconfirmed.
Today, parts of ''Anchisaurus' skeleton are still missing. Reconstructions usually assume that the tail and neck were prosauropod-like. Recent analyses, however, put ''Anchisaurus'' firmly at the base of the Sauropoda, making it the most basal known sauropod.
Description
In order to have been mistaken for human bones, one would expect ''Anchisaurus'' to have been a rather small dinosaur and, with a length of just over 2 metres, indeed it was. It probably weighed around 27 kg. However, Marsh's species ''A. major'' (also known as ''Ammosaurus'') was larger, from 2.5 m up to 4 m and some estimates give it a weight of up to 70 kg. All species of ''Anchisaurus'' lived during the Early Jurassic Period; more specifically, the Pliensbachian to Toarcian ages, 200 to 188 million years ago.
Digesting plant matter is a much more intensive biochemical process than digesting meat, so herbivorous dinosaurs needed a huge gut. Since this had to be positioned in front of the pelvis, balancing on two legs became increasingly difficult, as dinosaurs became larger and they gradually evolved into the quadrupedal position that characterises the later sauropods such as ''Diplodocus''. Prosauropods, then, represented a middle phase between the earliest bipedal herbivores and the later giant sauropods. ''Anchisaurus'' was typical of this group that flourished briefly during the late Triassic and Jurassic. It would have spent most of its time on four legs but could have reared up on its hind legs to reach higher plants.
An old illustration of ''Anchisaurus'' from the early 20th Century.
On the other hand, some paleontologists believe ''Anchisaurus'' may also have eaten meat, as it was in the transition between these two ultimately distinct groups. The teeth were blunt but with file-like edges, suggesting mostly plant matter was eaten and the jaw hinge was arranged in a way not entirely suited for tearing meat. Nevertheless, there is still some debate. The thumb had a large claw and the large eyes were not entirely on the side (as would be expected in an animal of a natural prey species).
As a quadrupedal/bipedal crossover, ''Anchisaurus'' had to have multi-purpose front legs. As 'hands', they could be turned inwards and be used for grasping. It had a simple reversible first 'finger', similar to a 'thumb'. As feet, the five toes could be placed flat against the floor and were strong at the ankle. This unspecialised design is typical of the early dinosaurs.
Classification
Due to its primitive appearance, ''Anchisaurus'' was previously classified as a prosauropod, themselves considered ancestral to the sauropods. Recent investigations show that Prosauropoda forms a monophyletic sister-group to Sauropoda and that ''Anchisaurus'' is instead is a very basal sauropod.
Marsh was originally happy with Hitchcock's name ''Megadactylus'' but this name was already taken. Therefore, he renamed it ''Amphisaurus'' in 1882. However, this name was also already in use and therefore, it became ''Anchisaurus'' in 1885.
The type species is Hitchcock's ''A. polyzelus''. Marsh's ''A. major'' ("greater near lizard") is still often considered a valid species (as ''Ammosaurus'') but his ''A. colurus'' (1891), once known as ''Yaleosaurus'' (von Huene, 1932), is now generally accepted as a female ''A. polyzelus'', and his ''A. solus'' of 1892 is now reclassified as ''Ammosaurus major''. However, ''Ammosaurus major'' itself may well be a synonym of ''A. polyzelus''.
Broom named ''Gyposaurus capensis'' in 1911, from the bones discovered in South Africa but Peter Galton officially renamed it ''A. capensis'' in 1976. This species has since been reclassified again and is probably a juvenile of ''Massospondylus carinatus''. ''G. sinensis'' was also referred here, but appears to be a distinct animal. Other specimens are still awaiting reclassification. This confusion is typical of the first dinosaurs to be discovered, when classification was not considered as important and precise a process as today.
In popular culture
An ''Anchisaurus'' was attacked by a pack of ''Megapnosaurus'' in ''When Dinosaurs Roamed America'' and finally killed by a ''Dilophosaurus''.
External links
★ ''Anchisaurus'' at DinoData
★ Genus etymology courtesy of www.dinosaurnames.net
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