The first discovery of Anchisaurus ("near lizard") remains was made before anything was known about the 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. The great paleontologist Othniel Charles Marsh named Anchisaurus in 1885, and Megadactylus became part of the genus Anchisaurus. More bones belonging to the genus were found in South Africa, suggesting that those two land masses were at the time joined in one super-continent (Pangaea). A recovery from Nova Scotia may also be Anchisaurus but this is unconfirmed.
Today, we are still missing parts of Anchisaurus' skeleton. Reconstructions usually assume that the tail and neck are like that of other dinosaurs of the same family, prosauropods. Anchisaurus was quite typical of this group and so this assumption is probably justified.
In order to have been mistaken for human bones, one would expect Anchisaurus to be a rather small dinosaur - and, with a length of just over 2 metres, indeed it was. It probably weighed around 27kg. However, Marsh's species A. major was larger, from 2.5m up to 4m, and some estimates give it a weight of up to 70kg. All species lived during the late Jurassic era; more specifically, the Pliensbachian to Toarcian periods, 200 to 188 million years ago.
Digesting plant matter is a much more intensive biological process than digesting meat, and so herbivorous dinosaurs needed a huge gut. Since this had to be positioned in front of the pelvis, balancing on two legs became increasingly tricky, and they gradually evolved into the quadripedal 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 raised up on its hind legs to reach higher plants.
On the other hand, 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 used to being prey).
As a four-legs / two-legs 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.
- Order: Saurischia
- Sub-order: Sauropodomorpha
- Family: Prosauropoda
- Sub-family: Anchisauridae
- Genus: Anchisaurus
Anchisaurus is sometimes known as Yaleosaurus, due to Huene (1932).
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 preoccupied! Therefore, it became Anchisaurus in 1885.
The type species is Hitchcock's A. polyzelus. Marsh's A. major ("greater near lizard") is still considered among the Anchisaurs. However, his A. colurus of 1891 is now generally accepted as a female A. polyzelus, and his A. solus of 1892 is now reclassified as Ammosaurus major. However, Ammosaurus itself may well be a synonym of A. polyzelus. Broom named "Gyposaurus" in 1911, from the bones discovered in South Africa, but Peter Galton officially named it A. capensis in 1971. This species has since been reclassified again, and is now Massospondylus carinatus. Other specimens are still awaiting reclassification. This confusion is typical of the first dinosaurs to be discovered, when classification was not considered such an important process.