Geoscience Reference
In-Depth Information
the remainder of the Mesozoic Era—as well as the preservation of these tracks in
rocks from river floodplains, lakeshores, and seashores—birds spread very quickly
throughout the world and adapted to a wide variety of environments. For example,
bird tracks are preserved in Cretaceous rocks formed in previously polar environ-
mentsofAlaskaaswellasafewIrecentlyco-discoveredwithcolleaguesinVictor-
ia, Australia. These trace fossils and a few body fossils show that birds, within only
50 million years of evolving from non-flighted theropods, already had a worldwide
distribution.
Explaining the evolutionary history of birds is a massive undertaking, and oth-
erpeoplehavewrittenexcellent,lengthy topics on this topic,suchasThorHanson's
Feathers: The Evolution of a Natural Miracle
(2011) and
Living Dinosaurs: The
Evolutionary History of Modern Birds
(2011), a volume with many authors and ed-
ited by Gareth Dyke and Gary Kaiser. Accordingly, I will not attempt to duplicate
their fine efforts here. Instead, I will point out that soon after the extinction of the
non-aviandinosaurs,aviandinosaursfilledecologicalnichesleftbehindbytheiran-
cestors, while also carving out new ones. Birds of the past also had their own awe-
inspiringqualitiesworthknowing,someofwhichmadetracesweknowof,whereas
others we may discover some day.
For example, if you took a trip back in time to the Eocene of North America,
you might meet up with
Gastornis
(formerly known as
Diatryma
), a flightless bird
astallasthelargestknowncassowaries.Mostlybecauseofitssize,butalsobecause
of its massive hooked beak, this bird was originally interpreted as carnivorous. It
also lived when the ancestors of modern horses were the size of domestic dogs.
Hence, paleontologists painted lurid scenarios of these birds eating horses, which
artists then literally painted. Regrettably for people who enjoy the concept of a bird
sayingtheEoceneequivalentof“I'msohungryIcouldeatahorse,”notracefossils,
such as sliced or crunched little horse bones with beak marks, have confirmed this
reputation for
Gastornis
. Owing to this lack of evidence, as well as recent research
on this bird's skull and its shearing capabilities, this rapacious image of
Gastornis
