Geoscience Reference
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conservative in interpreting these abnormalities, offering a basic diagnosis—such
as“tibiafractured,laterbecameinfected”—andleavingitatthat.Perhapsmorepre-
ciseattributionstoboneinjuries—suchas“tibiafracturedby
Ankylosaurus
tailclub,
later became infected”—will be made in future studies. But in the meantime, one
can always turn to one of the most unambiguous of dinosaur trace fossils known:
toothmarks.
When Tooth Met Bone: Dinosaur Toothmarks as Trace Fossils
Dinosaur toothmarks are lovely trace fossils, simply because most leave little doubt
about the dinosaur's motivation, which was eating. Other than the few exceptions
of toothmarks interpreted in skin impressions mentioned earlier, almost every ex-
ample of a dinosaur toothmark described thus far was registered in bone. However
entertaining it might be to imagine dinosaurs gnawing random, non-living items in
theirsurroundings,suchassticks,mud,orrocks,notracefossilsofthisbehaviorare
known.Similarly,dinosaurtoothmarkshavenotyetbeeninterpretedinfossilplants,
despite our surety that sauropods, ornithopods, ankylosaurs, stegosaurs, ceratopsi-
ans,andsometheropodsenthusiastically consumedvegetation.Oneofthemostob-
vious problems with such a discovery is that plant material, such as leaves, stems,
roots, and so on, may not have readily preserved such evidence.
When a dinosaur bit into another dinosaur and its teeth reached bone, the res-
ulting punctures or scrapes are trace fossils of the dinosaur that did the biting. Just
like mentioned before, though, a good question to always ask about toothmarks as
trace fossils is whether that bone belonged to a living or already-departed dinosaur.
Forinstance,ifabittendinosaurhappenedtobealivewhenchompedbyanotherdi-
nosaur, it very likely would have reacted to this assault and may have added a trace
of its own behavior to the wound. Think about how the first reaction of a person
bitten by their pet dog, cat, parrot, snake, or Komodo dragon would be to pull away
fromthesourceofpain.Unlessthebiterhasreally clamped downonitsvictim, this
defensivemotionshouldcausethewoundtoelongate,makingthetraceacomposite
one that is a result of both the pet and pet owner's behaviors. The same principle
