The discovery of terrible claw

In the summer of 1964 John Ostrom was prospecting for fossils in Cretaceous rocks near Bridger, Montana, and collected the fragmentary remains of a new and unusual predatory dinosaur. Further collecting yielded more complete remains, and by 1969 Ostrom was able to describe the new dinosaur in sufficient detail and to christen it Deinonychus ('terrible claw') in recognition of a wickedly hooked, gaff-like claw on its hind foot.

Deinonychus (Figure 16) was a medium-sized (2-3 metres in length), predatory dinosaur belonging to a group known as the theropods. Ostrom noted a number of unexpected anatomical features; these prepared the intellectual ground for a revolution that would shatter the then rather firmly held view of dinosaurs as archaic and outmoded creatures that plodded their way to extinction at the close of the Mesozoic world.

However, Ostrom was far more interested in understanding the biology of this puzzling animal than in simply listing its skeletal features. This approach is far removed from the pejorative epithet 'stamp-collecting' that palaeontology had attracted, and echoes the method of Louis Dollo in his earlier attempts to understand the biology of the first complete Iguanodon skeletons (Chapter 1). As an

Skeletal Diagrams Archeopteryx

16. Top: Three diagrams of a Deinonychus skeleton.

Bottom: Diagram of Archaeopteryx with feathers removed to show its basic theropod affinity.

Features of Deinonychus i) The animal was clearly bipedal (it ran on its hind legs alone) and its legs were long and slender.

ii) Its feet were unusual in that of the three large toes on each, only two were designed to be walked upon, the inner toe was held clear of the ground and 'cocked' as if ready for action (a bit like a huge version of the sharp retractile claws in a cat's paw).

iii) The front part of the animal was counterbalanced at the hip by a long tail; however, this tail was not of the deep, muscular variety normally expected in these types of animal, but was flexible and muscled near the hips, becoming very narrow (almost pole-like) and stiffened by bundles of thin, bony rods along the rest of its length.

iv) The chest was short and compact, and supported very long arms that ended in sharply clawed (raptorial) three-fingered hands that swivelled on wrists that allowed the hands to be swung in a raking arc (like those of a praying mantis).

v) The neck was slender and curved (rather like that of a goose), but supported a very large head, which was equipped with long jaws, lined with sharp, curved, and saw-edged teeth; very large eye sockets that seem to point forward; and a much larger than expected braincase.

approach, it has more in common with modern forensic pathology, driven as it is by a need to assemble broad ranges of facts from a number of different scientific areas in order to arrive at rigorous interpretation, or hypothesis, on the basis of the available evidence; this is one of several driving forces behind today's palaeobiology.

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