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In this lecture we will look at four assemblages: 1), the Newark
Supergroup, 2) the Glen Canyon Group; 3) the Stormberg Group;
and 5) the Lias of England. Also shown is 4, the Lufeng Formation
of China.
A classic area for fossils of the Lias is the southern coast of Great Britain, particularly the town of Lyme Regis and its neighbor to the east, Charmouth.
Lyme Regis has always been a "destination" and famous for its sea cliffs and beauty. It was featured in the very well reviewed novel and movie, A French Lieutenant's Woman by John Fowles (who lives in the town). As were many English gentry, the male lead of the story, Charles (Jeremy Irons) is attracted to Lyme Regis by the famous Early Jurassic fossils where he falls in love with first Emestina (Lynsey Baxter) and then Sarah (Meryl Streep).
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During the early 19th century Mary Anning became locally
famous as a fossil collector in Liassic rocks. She collected many fine
specimens which she sold to many a more wealthy paleontologist, notably
Sir Richard Owen.
The phrase, "She sells sea shells by the sea shore", is about Mary Anning. Anning found the first well-preserved ichythosaurs and the first plesiosaurs. |
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A later discovery in the Charmouth area was the nearly complete skeleton of an armored dinosaur Owen named Scelidosaurus in 1860 and 1861.
Scelidosaurus from Owen 1861.
Skull of Scelidosaurus, from Owen (1861) |
The pelvis of Scelidosaurus is typically ornithischian. The skull is particularly interesting, however, because the tooth row is deeply inset. This deep concavity in the skull is almost certainly to support cheeks. This character turns out to be a major one for ornithischians and is a shared derived one for the group known as the Genasauria. Cheeks are important for keeping the food in the mouth when chewing. The armor consisting of plates or spines over the body is a shared derived character for a subgroup within the Genasauria, the Thyreophora ("shield bearers"). |
Reconstruction of Scelidosaurus, redrawn form Paul (1987). Armor is shown in brown.
The upper, Jurassic, part of the Stormberg has produced a rich fauna of advanced therapsids and mammals, turtles, sphenodontians (lizard-like diapsids), crocodylomorphs, and dinosaurs. Especially important are a series of fine skeletal remains of the early ornithischians Lesothosaurus and Heterodontosaurus.
Lesothosaurus is a small, very delicate ornithischian. Its pelvis is typically ornithischian, with a backwardly projecting part of the pubis. The forelimbs are delicate and there is a fully five-fingered hand, with relatively small digits.
Reconstruction of the skeleton of Lesothosaurus. Modified from Weishampel and Witmer (1990).
Lesothosaurus, unlike Scelidosaurus, lacks the deeply inset tooth row. Although it probably had cheeks to some extent they could not have been as well-developed as in Scelidosaurus. This suggests to most authors that Lesothosaurus is the most primitive known of all ornithischians. In fact it is difficult to find characters that show that Lesothosaurus belongs to a monophyletic group.
| The peculiar, small, ornithischian Heterodontosaurus is known from the same beds as Lesothosaurus. Heterodontosaurus, however, differs markedly in the skull and hands. The skull does have the deeply inset tooth margin seen in Scelidosaurus. However, the tooth pattern is considerably more complicated. There are canine-like teeth in the upper and lower jaw in most specimens. The individuals lacking these teeth may be juveniles or a different sex. The teeth in the dentary and maxilla are arranged so that they make a blade-like apparatus. |
Skull of Heterodontosaurus. Based on Weishampel and Witmer (1990). |
The individual teeth have thicker enamel on the outside on the uppers and the inside on the lowers. This is a shared derived character with many later ornithischians and defines the monophyletic group, the Cerapoda. Many familiar dinosaurs such as the hadrosaurs ("duck-billed" dinosaurs) are within this very large group.
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BASIC RELATIONSHIPS OF THE ORNITHISCHIA
Together, Lesothosaurus, Scelidosaurus, and Heterodontosaurus provide characters that allow us to look at the relationships of major groups within the Ornithischia. The characters are: 1, open acetabulum; 2, backwardly directed process on pubis; 3, tooth row inset from jaw margin (cheeks); 4, enlarged and twisted digit I on manus; 5, no well defined shared derived characters; 6, armor on body as plates or spines; 7, enamel distributed differently on the sides of the teeth. |
The lower three quarters of the Stormberg has also produced a rich fauna of sphenodontians (lizard relatives), a turtle, mammals, very advanced cynodont therapsids (tritylodonts and trithelodonts), crocodylomorphs, and prosauropod dinosaurs, in addition to the dinosaurs mentioned thus far.The uppermost part of the Stormberg Group consists of basaltic lava flows interbedded with sandstones. In one of the sandstones on an island in Lake Kivu, a large partial skeleton of what has been named Vulcanodon was found.
Reconstruction of the partial skeleton of Vulcanodon.
Although lacking a neck and head and much of the pelvis, the large relative size of the forelimbs and the structure of the hands and feet show that Vulcanodon was a sauropod dinosaur. The shared derived character of the Sauropoda, of which Vulcanodon is a member, is the addition of extra cervical vertebrae to the neck. This is done by moving the shoulder girdle posteriorly. More familiar examples of the Sauropoda include Brachiosaurus and of course Apatosaurus (AKA Brontosaurus).
| BASIC RELATIONSHIPS OF THE SAURISCHIA
Now we can look at the basic relationships of the major groups of the Saurischia. The characters are: 1, open acetabulum; 2, enlarged and twisted manus digit I; 3, small head and peg-like teeth (and elongated cervical vertebrae); 4, backwardly directed process on pubis; 5, pelvic bones fused in adult; 6, functionally three-toed foot; 7, digits IV and V lost on manus; 8, apron-like pubis; 9, addition of extra cervical vertebrae to the neck. |
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Lying on top of the Chinle Group over much of the western US is the Glen Canyon Group. Except perhaps for its basal-most strata, the Glen Canyon Group is of Early Jurassic age. Reptile bones are quite common in some portions of the group, especially the Moenave and Kayenta Formations. Frogs, apodans (more-or-less legless lissamphibians), turtles, mammals, tritylodonts, crocodylomorphs, and ornithischian and saurischian dinosaurs are represented by excellent material.
Skeletal remains of a small thyreophoran, Scutellosaurus,
have been found. It closely resembles a very slender version of Scelidosaurus.
In fact, very scrappy remains of Scelidosaurus itself have been
found in the Glen Canyon Group.
The skeleton of Scutellosaurus with armor shown in brown. Modified
from Colbert.
Most exciting is the discovery of several skeletons of the large ceratosaurian theropod dinosaur Dilophosaurus, found in the Navajo Nation near the village of Moenave, AZ.
Reconstruction of the skeleton of Dilophosaurus. Based on Paul
(1988).
| Besides its considerable size, Dilophosaurus is
characterized by having a large, although delicately constructed, double
crest on its nose and forehead (hence the name).
On the right is a reconstruction of the head of Dilophosaurus. This is part of a full size model by the Rush Studios on display at Dinosaur State Park in Connecticut (see below). |
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Dilophosaurus was prominently featured in the movie "Jurassic Park", in which the genus is pictured with an expandable neck frill and the ability to spit poison. Unlike virtually all of the other dinosaurs in "Jurassic Park", which were reconstructed larger than they really were, Dilophosaurus was made considerably smaller. While Dilophosaurus might have possibly been able to spit venom (for which there is no evidence anyway), it certainly did not have a frill.
Dilophosaurus is however very unusual in that its' skeletons
have been found in relatively close proximity to footprints plausibly made
by the dinosaur.
Track-bearing surface near the town of Moenave, AZ. An especially deep track can be seen in front of the running girl (for scale).
| The larger of the tracks are the right size and proportions
for Dilophosaurus. They have been dubbed Dilophosauripus.
However, they are clearly identical (although not as well preserved) to
tracks found in abundance in eastern North America and named Eubrontes
giganteus.
On the left is an example of one of the better Eubrontes (water filled) from the village of Moenave, AZ. Note the lens cap for scale (about 6 cm). The Glen Canyon Group has produced many other kinds of footprints as well, most being the same kinds as in eastern North America. |
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Owen, R., 1861, A monograph on the fossil Reptilia of the Lias Formations.
I Scelidosaurus harrisonii. Palaeontograhical Society Monograph,
v. 13, p. 1-14.
Paul, G. S., 1987, The science and art of restoring the life appearance of dinosaurs and their relatives. in Czerkas, S. J. and Olson, E. C. (eds.) Dinosaurs Past and Present, Vol. II, Natural History Museum of Los Angles County, p. 5-49.
Paul, G. S., 1988, Predatory Dinosaurs. New York, New York Academy of Sciences, 464 p.
Weishampel, D. B. and Witmer, L. M., 1990, Lesothosaurus, Pisanosaurus, and Technosaurus. In Weishampel, D. B., Dodson, P., and Osmolska, H. (eds.), The Dinosauria., University of California Press, Berkeley, p. 416-425.