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The Lias, Glen Canyon, and Stormberg Assemblages

Early Jurassic World

Map of the Early Jurassic

Pangea was still mostly intact, although the rifting process was proceeding so that by 180 million years ago, the sea was working its way into the rift valleys formed between North America and Africa.

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.
 

The Lias

The term "Jurassic" was first imposed on strata overlying the Triassic in the Jura Mountains of Europe. Strata recognized to be of Early Jurassic age came to be called the Lias in Europe, particularly England. While the Late Triassic sequence in Europe is largely continental in origin, that of the Jurassic, including the Lias, is largely marine, reflecting a broad encroachment of the sea over Europe in Early Jurassic time. A large number of marine tetrapods have been found in Liassic rocks in Europe, as well as one very important dinosaur.

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).
Town of Lyme Regis from the Cobb
Cliffs of Liassic Limestone west of the Cobb in Lyme Regis
Town of Lyme Regis from the Cobb, looking northeast.
Cliffs of Liassic (Early Jurassic age) limestone, outcropping to the west of Lyme Regis.
Large Ammonites in situ, west of the Cobb, Lyme Regis.
Large ammonite weathering on the beach, west of the Cobb, Lyme Regis.
Large Ammonites in situ in limestone, west of the Cobb, Lyme Regis.
Large ammonite weathering on the beach, west of the Cobb, Lyme Regis.
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.
Mary Anning
Sir Richard Owen
 
Mary Anning
Bronze of Sir Richard Owen at the British Museum

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.

Scelidosaurus

Skull of Scelidosaurus
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").

Scelidosaurus Reconstruction

Reconstruction of Scelidosaurus, redrawn form Paul (1987). Armor is shown in brown.

The Stormberg

A series of Late Triassic and Early Jurassic sedimentary and volcanic rocks caps the Karroo basin sequence over much of southern Africa. This is the Stormberg Group, the basal part of which consists of Late Triassic coals and gray mud and sandstones, and the upper part of which is red beds and eolian dune sandstones and thick lava flows of Early Jurassic age.

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.

Lesothosaurus

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.
Heterodontosaurus Skull

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.

Basic Ornithischian Cladogram
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
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.

Saurischian Cladogram

The Glen Canyon Group

Glen Canyon Group strata at Glen Canyon Dam
Glen Canyon Group strata at Glen Canyon Dam.


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.

Scutellosaurus
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.

Dilophosaurus
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).

Head of Dilophosaurus
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.

Tracks

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.

Moenave Eubrontes

REFERENCES


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.


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