Australia: The Land Where Time Began

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Prosauropods

According to Norman1 the prosauropods are a puzzling group of saurischian dinosaurs. During the Late Triassic and Early Jurassic they were distributed almost worldwide, Antarctica being the only continent on which they haven't yet been found. They are so abundant where they are found that the authors1 have suggested they appear to have been the first major evolutionary radiation among the dinosaurs, and possibly among the archosaurs in general, to exploit plant food. Once therapsids had evolved, various herbivorous forms of them dominated life on land until the Late Triassic when the archosaurs replaced them in their role as dominant terrestrial animals. The archosaurs were almost exclusively carnivores during the Permian and Triassic.

The prosauropods were a very important group among the early dinosaurs according to the authors1 as they 'paved the way' for the sauropods of later times that were closely related to the prosauropods. The authors1 suggest many of the species that have been named are based on fossil material they regard as totally inadequate. There are 3 families of prosauropod, the anchisaurids, the melanorosaurids and the yunnanosaurids.

Anchisaurids

Deriving it name from Anchisaurus, a small prosauropod that was about 8.2 ft (2.5 m) long and lightly built from the Early Jurassic in the Connecticut Valley, eastern North America, this is a family encompassing the vast majority of all known prosauropods. In Orange Free State in South Africa remains of Anchisaurus have been found that are from the earliest Jurassic. The partial remains were originally named Hortalotarsus, Thecodontosaurus and Gyposaurus, later renamed by Drs Peter Galton and Mike Culver Anchisaurus capensis

Anchisaurus from the Early Jurassic was one of the smaller prosauropods, it had blunt pencil-shaped teeth and was lightly built. There has been a controversy regarding its diet, it has been variously described as a herbivore, a carnivore or an omnivore. The authors1 suggest it appears from the balance of evidence that it appears to be a herbivore. The partial skeleton from the Connecticut Valley consists of the major part of the skeleton, but lacking the tail and much of the neck. The head of Anchisaurus was small compared with the size of the body, and it had a long, slender snout. Its pencil-shaped teeth were slender, and the authors1 suggest the teeth may have had serrations down the front and back edges. These serrations differed from the serrations of the teeth of theropods that fine, sharp serration, in that they were large coarse ridges that a believed to be suitable for shredding plant fibres.

Because parts of the skeleton of Anchisaurus are missing the reconstruction was based on the neck and tail of other prosauropods such as Plateosaurus. It is believed the neck and back of Anchisaurus was long slender and flexible, overall the animal is believed to have had a long bodied appearance, especially when compared to theropods. The long tail counterbalance the front part of the body at the hips. The authors1 suggest the limbs are slightly unusual. The relatively sturdy hind limbs were designed to carry the bulk of the body when it was walking. The broad foot had 4 well-developed toes, the 5th toe being rudimentary. The forelimbs and shoulders were also well developed. With stout shoulders and relatively long that were capable of touching or resting on the ground suggests Anchisaurus was possibly quadrupedal, at least occasionally. On the hand, that is said by the authors1 to be curious, the slender 4th and 5th fingers are small and appear to have lacked claws, though the inner fingers are well-developed, especially the 1st finger that had a sharply curved claw that was much enlarged.

The skull of Anchisaurus is lightly built is is expected in a prosauropod that was small, 8.2 ft (2.5 m) long. The slender teeth have coarse serrations on the on the back and front. The jaw hinge is approximately level with the tooth row, a feature that differs from that of Plateosaurus. The skeleton has the appearance of a smaller, lighter version of that of Plateosaurus. The authors suggest it is possible that the similarities between the 2 skeletons of the 2 sauropods is the result of Anchisaurus being not well known, whereas that of Plateosaurus is well known, the reconstructions of Anchisaurus often requiring information from other specimens such as Plateosaurus. It has been suggested Anchisaurus may have been a high level browser, as indicated by its elongated back and long, flexible neck.

  • Information on the skeleton of Anchisaurus polyzelus from source 2.
  • Fossil remains: nearly complete skull and majority of skeleton
  • Anatomical Characteristics
  • Shallow, subtriangular skull
  • Arm : moderately long
  • Age: Early Jurassic, Pliensbachian and/or Toarcian 
  • Distribution and Formation: Connecticut, Massachusetts, Portland
  • Habitat: semi-arid rift valley with lakes
  • notes: shared its habitat with Ammosaurus

Sources & Further reading

  1. Dr. David Norman & Dr. Peter Wellenhofer, The Illustrated Encyclopaedia of Dinosaurs, Salamander Press, 2000
  2. Paul, Gregory S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press.

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last updated 12/11/2011 
 

 

Dinosaurs

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading