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is that these dinosaurs were compensating for a weak leg, such as one injured from
an accident or combat.
One theropod trackway in a Late Jurassic stratum in Utah leaves no doubt that
its maker had a tough time walking, showing alternating long and short steps that
demonstrate how it was hobbling along with just one good leg. Because this track-
way is relatively easy to access and on public land, I've taken university students to
it, given them a tape measure, and said, “Measure this, then tell me what you think
this dinosaur was doing,” without saying anything more about it. One time there,
within about fifteen minutes one of the students, after writing down a few measure-
ments, looked up from the trackway with a huge grin on her face. “It was limping!”
sheshoutedtriumphantly.(Itwasoneofthoseproudmomentsthat,asateacher,I'll
never forget, and hopefully the students have not either.)
Oncethestudentshadalloftheinformationtheyneededtofurtherconfirmand
testthishypothesis,Ithenaskedthem,“Okay,whichlegwasinjured?”Ittookafew
more minutes for them to figure this out, but they did. The students reasoned that
thestrong(non-injured)legofthetheropodenabledittotakealongerstep,whereas
the hurt leg could not as easily bear the theropod's weight, so it would have taken
a shorter step when pushing off with that leg. Using this logic, they figured the left
leg was hurt, whereas the right leg was normal.
Othermaladiesshowupindinosaurtracks,suchasmissingordeformeddigits.
Paleontologistshavetobecarefulwhenmakingsuchjudgments,ofcourse,because
many,manydinosaurtracksdidnotfaithfullypreservearecordofeverydigitonthe
originalfeet,especially thosemadeasundertracks.Nonetheless,onceinawhilewe
noticethatatrackwayconsistently showsallexpected toesononefoot,butoneless
ontheotherfoot.OnesuchtrackwayisfromtheEarlyJurassicofMassachusetts,in
which three tracks in sequence—right, left, right—have a perfectly fine three-toed
theropod track on the left, but a two-toed one on the right, missing its innermost di-
git.
