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The Late Cretaceous I - Mongolia
Roy Chapman Andrews and the AMNH expeditions to Mongolia
Most famous formations, Djadochta and Nemegt
Based on Carpenter (1997).
Pinacosaurus is a common dinosaur in the Mongolian deposits. It is an ankylosaurid (member of the Family Ankylosauridae) as opposed to a nodosaurian as we saw in Sauropelta from the Cloverly in the previous lecture.
Ankylosaurids differ from nodosaurians in retaention of a primitive configuration of the skull roof (e. g. there are still paired plates). However, ankylosaurids also have the novel shared derived character of having a bony club at the end of the tail (above). Ankylosaurids, such as Pinacosaurus also tend to have broader skulls than nodosaurids and tend to have spikes on the rear corevers of their box-like skulls.
Postcrania based loosely on Parasaurolophus from Brett-Surman (1997) and skull after Norman and Weishample (1990).
Saurolophus is a medium-sized hadrosaurian (member of the Hadrosauria) ornithopod from Mongolia. It is also a crested hadrosaur, which means that it has a crest composed largely of the nasal bones, a condition that seems to have evolved independently among different hadrosaur groups (hense having a crest has little phyogenetic significance.
Hadrosaurian ornithopods are among the most common of all dinosaurs in the Late Cretaceous, in general, although not especially so in Mongolia. In many ways they are similar to Iguanodontids, except they tend to have a more superficially duck-like snout - thus the common name "duck-billed" dinosaurs.
The duck-like snout of Saurolophus can clearly be seen in the skull on the right. The portion of the snout lacking teeth was covered by a keratinous beak (as in birds or turtles).
In this case the crest is small, especially compared with other crested hadrosaurs.
Species of Saurolophus are know from Western North America, as well as Central Asia.
Skull of Saurolophus, after Weishample and Horner (1990)
The shared derived character for the Hadrosauria is the loss of digit I of the manus. This completes a trend seen in the ornithopod of the reduction of digit I starting with the complete digit in hypsilophodontids and Heterodontosaurus, with reduction in Camptosaurus and other iguanontids, culminating in the hadrosaurians.
On the left are the manus and pes of a hadrosaur (Lambeosaurus in the Royal Tyrrell Museum in Alberta Canada showing the loss of digit I of the manus.
Prenocephale: postcrania based loosely on Stegoceras from Forester and Sereno (1997) with skull of Prenocephale from the same source.
Prenocephale, is a member of the Pachcephalosauria, the shared derived charcter for which is the thickened skull roof, which in this case makes a massive dome. The Pachcephalosauria, or dome heads, are the sister group to the Ceratopsia within the Marginocephalia.
In general, pachycephalosaurs tend to be small lightly-built dinosaurs, comparable in size to sheep or antelope (although there are exceptions). Like sheep, it is thought that pachycephalosaurs butted heads during dominance rituals, and the massively thickened skull protected their small brains.
The skull (right) of Prenocephale shows the spectacular domed skull roof. Despite its cerebral appearance, the high forehead is all bone.
Another pachycephalosaur from Mongolia is Homalocephale. It is not known from nearly as abundant material as Prenocephale and it is considerably more primitive.
Unlike Prenocephale, Homalocephale does not have a dome at all. In stead the skull roof is flat and thickened.
Protoceratops redrawn from from Paul (in Dodson, 1997).
Skull of Protoceratops andrewsii. Based on Paul (in Dodson, 1997)
3. armor as plates covering back
4. armor as spikes or plates
5. uneven enamel
6. back part of skull makes shelf
7. rostral bone
9. reduced hands
10. domed head
11. jaw joint below tooth row
12. elongate hands
13. prepubic process well developed
14. ridge on teeth
15. reduction in manus digits I and V (and large nares)
16. manus digit 1 spike-like
1. three-toed foot
2. digits IV and V lost on hand
3. long arms
4. semilunate carpal
5. fused pelvis
6. large hole in lacrimal bone in skull
7. ?no unique derived characters?
8. giant, hook-like claw on digit II of pes
9. flight feathers
10. ?no unique derived characters?
11. proximal half of metatarsal of digit III pinched
12. teeth lost in front of mouth and very large claws on manus
Brett-Surman, M. K., 1997, Ornithopods. In Farlow, J. O. and Brett-Surman, M. K. (eds.) The Complete Dinosaur, Indiana University Press, Bloomington, p. 330-346.
Carpenter, K., 1997, Ankylosaurs. In Farlow, J. O. and Brett-Surman, M. K. (eds.) The Complete Dinosaur, Indiana University Press, Bloomington, p. 307-316.
Forster, C. A. and Sereno, P. C., 1997, Marginocephalians. In Farlow, J. O. and Brett-Surman, M. K. (eds.) The Complete Dinosaur, Indiana University Press, Bloomington, p. 317-329.
Weishample, D. B. and Horner, J. R., 1990, Hadrosauridae. In Weishample. D. B., Dodoson, P., and Osmolska, H. (eds.) The Dinosauria. University of California Press, Berkeley, p. 534-561.