Coprolites

Another slightly less romantic branch of palaeobiological
investigation focuses on the dung of animals such as dinosaurs.
This material is refered to as coprolites (copros means dung, lithos
means stone), and their study has a surprisingly long and relatively
illustrious history. The recognition of the importance of preserved
dung dates back to the work of William Buckland of Oxford
University (the man who described the first dinosaur,
Megalosaurus). A pioneering geologist from the first half of the
19th century, Buckland spent considerable time collecting and
studying rocks and fossils from his native area around Lyme Regis
in Dorset, including fossil marine reptiles. Alongside these,
Buckland noted large numbers of distinctive pebbles that often had
a faint spiral shape. On closer inspection, breaking them open and
looking at polished sections, Buckland was able to identify shiny
fish scales, bones, and the sharp hooks of belemnite (a cephalopod
mollusc) tentacles in great concentrations. He concluded that these
stones were most probably the lithified excreta of the predatory
reptiles found in the same rocks. Clearly, though at first sight
somewhat distasteful, the study of coprolites had the potential to
reveal evidence concerning the diet of the once-living creature that
would not otherwise be obtainable.

As was the case with footprints, the question ‘who did this?’, though
obviously amusing, can present significant problems. Occasionally,
coprolites, or indeed gut contents, have been preserved inside the
bodies of some fossil vertebrates (notably fish); however, it has been
difficult to connect coprolite fossils to specific dinosaurs or even
groups of dinosaurs. Karen Chin of the US Geological Survey has
devoted herself to the study of coprolites and has had singular
difficulty in reliably identifying dinosaur coprolites – until quite
recently.

In 1998, Chin and colleagues were able to report the discovery of
what they referred to in the title of their article as ‘A king-sized
theropod coprolite’. The specimen in question was discovered in
Maastrichtian (latest Cretaceous) sediments in Saskatchewan and
comprised a rather nobbly lump of material, over 40 centimetres
long, that had a volume of approximately 2.5 litres. Immediately
around and inside the specimen were broken fragments of bone,
and a finer, sand-like powder of bone material was present
throughout the mass. Chemical analysis of the specimen confirmed
that it had very high levels of calcium and phosphorous, confirming
a high concentration of bone material. Histological thin sections of
the fragments further confirmed the cellular structure of bone and
that the most likely prey items that had been digested were
dinosaurian;as suspected, this specimen was most likely a large
carnivore’s coprolite. Surveying the fauna known from the rocks in
this area, the only creature that was large enough to have been able
to pass a coprolite of these dimensions was the large theropod
Tyrannosaurus rex (‘king’ of the dinosaurs). Examination of the
bone fragments preserved in the coprolite showed that this animal
had been able to pulverize the bones of its prey in its mouth, and
that the most likely prey was a juvenile ceratopian ornithischian
(from the structure of the bone in the histological sections). The fact
that not all the bone had been digested in this coprolite indicated
that the material had moved through the gut with considerable
speed, which could be used by some as evidence that T. rex was
perhaps a hungry endotherm.