Geoscience Reference
In-Depth Information
tion of these three criteria, their distinction is a little more assured. The only other
complicating factoriswheretheropodandthree-toed birdtracksoverlapinsizeand
shape, but that's another story and one far too long to tell here and now.
Prosauropod tracks are also challenging to identify, partly because they wer-
en't made for very long, geologically speaking. Prosauropods only lived from the
Late Triassic through the Early Jurassic periods, from about 230 to 190
mya
. These
relatives of sauropods, the largest land animals of all time, developed into the
world'slargestherbivoresduringtheirgeologicallybrief40-million-yeartimespan,
and were among the first dinosaurs to get around on all fours. However, many pro-
sauropod tracks also show them walking on their rear feet only.
Sauropodtracksarenotsodifficulttospot,butaretoughtorecognizeforwhat
they are. Inthe early days ofdinosaur tracking, probably more than one paleontolo-
gist or geologist walked by their footprints without a second glance, thinking they
were some sort of large erosion-caused features. Once these footprints were correl-
ated with the sizes and shapes of sauropod feet, though, this oversight was quickly
rectified, and sauropod tracks magically appeared in the search images of paleonto-
logists worldwide. So where we originally had none, we now frolic in the land of
plenty, as sauropod tracks have been found on all continents except for Antarctica,
and in rocks ranging from the Late Triassic (230
mya
) through the Late Cretaceous
periods (65
mya
). Other than the extraordinary size of the largest tracks, sauropod
footprints are oblong (rear) to crescent-shaped (front), and often form two-by-two
diagonalpatterns.Thebest-preservedrear-foottracksshowclawsattheendofeach
digit, too. Despite artistic recreations and skeletal mounts depicting sauropods rear-
ing up on their hind legs, no tracks have yet demonstrated that sauropods did any-
thing more than walk on all fours.
Stegosaur, ankylosaur, and ceratopsian tracks, like sauropod tracks, were sim-
ilarly considered rare, but were not identified until just in the past few decades. For
example, the first undoubted stegosaur tracks were not found until 1994, in Middle
Jurassic (about 170
mya
) rocks of England. Now stegosaur tracks are becoming
