Geoscience Reference
In-Depth Information
Thusbasicichnologyiscombinedwithbasicpaleopathologywheneverapale-
ontologist looks at a dinosaur skin impression or bone and notices an abnormality:
holes, dents, breaks, enlargements, or other traits that stand out as something extra,
somethingthatwasnotpartofitsoriginalanatomy.Evenchippedteethfallintothis
category,inwhichatheropodlostpartofatooth.Whenthishappens,themostbasic
ofquestionsapaleontologistcanaskis“Deadoralive?”Asin,wasthedinosaurout
ofcommissionforgood,orwasitstillmovingunderitsownpowerwhenthefeature
was added? If living, the trace fossil might be attributed to the dinosaur itself, al-
though in some instances another dinosaur might have caused it while the two were
tangling with each other. If dead, though, another tracemaker was entirely respons-
ible for whatever trace fossil is preserved in a dinosaur's bones or teeth, which in
some instances might have been a dinosaur, too. However, a composite trace fossil
also could have been made from the behavior of the dinosaur with the preserved in-
jury combining with the behavior of the dinosaur that dealt the injury.
Paleontologists and paleopathologists alike also must remember to be good
scientists by asking a follow-up question, “How could I be wrong?” This is when
they contemplate the possibility that their supposed paleopathologic evidence is
anythingbutthat.Afterall,holes,dents,breaks,andothermarksinMesozoicbones
(dinosaurianorotherwise)couldbetracefossilsfromothervertebrates,tracefossils
from invertebrates, or—most upsetting of all—not trace fossils at all.
Among vertebrate trace fossils on dinosaur bones, these could be toothmarks
made by animals that lived in environments completely separate from dinosaurs.
Weknowthatbecause,forexample,somedinosaurbonesendedupinshallow-mar-
ine sediments. Yet because they were land-dwelling animals, their decaying gas-
filled bodies must have washed out from land and floated along until they had a
burial at sea. (This explanation for how dinosaur parts got into marine sediments is
nicknamedthe“bloat-and-float” hypothesis.)Amazingly,afewoftheseboneshave
toothmarks and embedded teeth from scavenging sharks, which evidently could not
pass up an exotic (albeit rotting) carcass passing through their neighborhood.
