Geoscience Reference
In-Depth Information
• Can we even discern a given dinosaur's medical history, that is, did it have
some injury or other affliction that modified its behavior enough that we
can notice its effects?
• On a much grander scale, what do dinosaur tracks tell us about the timing
of their origins or demise?
As you can see from these questions, just identifying what dinosaur made a track
is actually a very small part of understanding how dinosaurs behaved. So with this
humbling thought in mind, let's go on to those most exciting facets of divining di-
nosaurs' lives from their tracks, starting with their evolutionary origins.
First Steps of the Dinosaurs: Origination
When were the first dinosaur tracks pressed fresh into the ground? Naturally, the
answer to this question also depends on when the first dinosaur existed, a difficult
problem to address. It's like trying to answer the question “When did we first be-
come human?” But the dinosaur-track one has the decided advantage of lacking all
of the anthropocentric baggage accompanying the latter inquiry.
The current claim for “oldest dinosaur from the fossil record,” a label guaran-
teed to cause a fight among dinosaur enthusiasts, lies with
Eodromeus
(“dawn run-
ner”). This dinosaur, which was discovered in Late Triassic (230
mya
) rocks of Ar-
gentina, was a small bipedal theropod that weighed about the same as a big turkey.
Despite itsantiquity,
Eodromeus
isnicely preserved,withabout90%ofitsskeleton
known, including its hind limbs.
From these bones, we know it had four toes on its rear feet, and three of those
toes would have likely left impressions as it walked. Thus we can use its feet as
a predictor for what its tracks looked like, or those of its close kin. Other dino-
saur fossils from rocks of nearly the same age in Argentina include one other thero-
pod,
Herrerasaurus
, a basal sauropodomorph,
Eoraptor
, and a primitive prosaur-
opod,
Panphagia
. Although
Eoraptor
was chicken-sized and
Herrerasaurus
was
more like a two-legged German shepherd, they both had three prominent toes on
