Anchisaurus

*Anchisaurus polyzelus*

***Anchisaurus*** is a genus of sauropod, and was an early herbivorous dinosaur. Until recently it was classed as a member of the more primitive prosauropod family. The name comes from the Greek *αγχι*/*agkhi* <anchi-; "near, close" + Greek *σαυρος*/*sauros*; "lizard", probably referring to Marsh's interpretation of it as intermediate between more primitive dinosaurs (at the time *Palaeosaurus* was an example of what was thought to be a primitive dinosaur) and more derived dinosaurs. It was coined as a replacement name for *Amphisaurus*, which was itself a replacement name for Hitchcock's *Megadactylus*, both of which had already been used for other animals.

## Discovery and naming

   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 finds in Massachusetts, the number of these bones began to accumulate and, by 1855, they were at least recognized as reptilian.

Hitchcock collected these bones under the name *Megadactylus* in 1865. Unfortunately, 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

*Anchisaurus* was a rather small dinosaur, with a length of just over 2 meters (6.6 ft), which helps explain why it was once mistaken for human bones. It probably weighed around 27 kilograms (60 lb). However, Marsh's species *A. major* (also known as *Ammosaurus*) was larger, from 2.5 to 4 meters (8 ft 2 in to 13 ft 1 in) and some estimates give it a weight of up to 32 kilograms (70 lb). 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. This herbivore swallowed gastroliths (gizzard stones) to help break down the food in its stomach. 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 characterizes the later sauropods such as *Diplodocus*. Prosauropods represented a middle phase between the earliest bipedal herbivores and the later giant sauropods. Although it was not itself a prosauropod, *Anchisaurus* was mostly typical of this group, which flourished briefly during the late Triassic and early Jurassic. *Anchisaurus* teeth, used to rip food , were shaped like spoons but not reallly. It had fewer and more widely spaced teeth than true prosauropods, and as Peter Galton and Michael Cluver observed, narrower feet. *Anchisaurus* would have spent most of its time on four legs but could have reared up on its hind legs to reach higher plants.

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 unspecialized design is typical of the early dinosaurs.

## Classification

Due to its primitive appearance, *Anchisaurus* was previously classified as a prosauropod, a member of a group of animals related to or ancestral to the sauropods. Recent investigations show that Prosauropoda forms a monophyletic sister-group to Sauropoda and that *Anchisaurus* is instead 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.

## Paleobiology

Fossils of *Anchisaurus* were originally discovered in the Portland Formation of the Newark Supergroup in the Connecticut River Valley. This formation preserves an arid environment with strong wet and dry seasons, from the Hettangian age into the Sinemurian age, between about 200 and 195 million years ago, when it lived alongside theropods like *Dilophosaurus* and *Coelophysis kayentakatae*.

Digesting plant matter is a much more intensive biochemical process than digesting meat. This herbivore swallowed gastroliths (gizzard stones) to help break down the food in its stomach. 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 characterizes the later sauropods such as *Diplodocus*. Prosauropods represented a middle phase between the earliest bipedal herbivores and the later giant sauropods. As a prosauropod, *Anchisaurus* was mostly typical of this group, which flourished briefly during the late Triassic and early Jurassic. *Anchisaurus* teeth, used to rip food, were shaped like spoons. It had fewer and more widely spaced teeth than true prosauropods, and as Peter Galton and Michael Cluver observed, narrower feet. *Anchisaurus* would have spent most of its time on four legs but could have reared up on its hind legs to reach higher plants.

As a facultative biped, *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 unspecialized design is typical of the early dinosaurs.

## JPInstitute.com Description

Anchisaurus was one of the first dinosaurs discovered in the United States. This little plant-eater was an ancestor of the huge Sauropods that lived later in the Jurassic. It was discovered by workmen using dynamite to blast apart some rocks while building shops for the army. It was one of the most perfect dinosaur skeletons ever discovered and helped scientists understand these amazing creatures.

Like many early dinosaur discoveries, it went through several name changes and descriptions. It also exhibits many of the primitive characteristics of prosauropods. For example, a large finger on the front leg indicates that it could have moved about on its back legs and used its hands for feeding or defense.

## Links

https://web.archive.org/web/20030802074122fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_anchisss.html

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 Template:Cite book
2. ↑ 2.0 2.1 2.2 2.3 "Anchisaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. *The Age of Dinosaurs*. Publications International, LTD. p. 27. ISBN 0-7853-0443-6.
3. ↑ 3.0 3.1 Template:Cite book
4. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `olsen2002`