Geoscience Reference
In-Depth Information
ecosystems, piecing together food webs in dinosaur-dominated ecosystems from
more than 65 million years ago.
What else can dinosaur trace fossils tell us? Considering extreme ranges in
dinosaur sizes, diversity, numbers, geographic dispersal—including the North and
South Poles—and evolution throughout their 165-million-year history, dinosaurs
clearly played key roles in the functioning of land environments. Again, this is
where dinosaur trace fossils have been and will be used to augment or surpass oth-
er fossil or geological information. For example, did sauropods and other dinosaurs
actually change the courses of rivers or otherwise alter landscapes through their
tracks, trails, and other traces? All signs point to
yes
. Did polar dinosaurs live year-
round in those icy environments, or did they migrate seasonally like modern cari-
bou? Trace fossils, such as dinosaur tracks and burrows in sedimentary rocks from
formerly polar environments, tell us that they likely stayed put during the winters.
Howaboutdinosaurevolutionandextinction:Whatdotracefossilstellusaboutthe
timing and causes of these large-scale biological facts of life for dinosaurs? In one
recent study, the earliest ancestors of dinosaurs were proposed on the basis of not-
quite-dinosaur tracks in 245-million-year-old rocks in Poland from the earliest part
of the Triassic Period.
Another important evolutionary step in dinosaurs we've documented quite
well is that birds evolved from a lineage of small theropods. This relatedness has
been certified through many lines of evidence, including fossilized feathers direc-
tly associated with the skeletons of more than thirty species of theropods. But we
still have questions about this evolutionary transition that are hard to answer from
just bones and feathers. For example, when did these small dinosaurs start to climb
trees, or fly from the ground up, or land after flight?
The hotly debated question of whether any dinosaurs survived a post-apoca-
lyptic landscape caused by a meteorite impact 65 million years ago is also poten-
tially answerable by trace fossils. A single dinosaur bone in 64-million-year-old
rocks is nearly always regarded suspiciously, the fossil equivalent of an online-dat-
