Geoscience Reference
In-Depth Information
snorkel.(Ifyoudon'tbelieveme,trymakingonelikethisandletmeknowhowthat
worked out for you.) Yet another anatomical trait was an elongated snout that led
to the nickname of “duck-billed dinosaurs” for hadrosaurs, which imagines them as
favoring soft aquatic plants as food. Again, a reexamination of their teeth and jaws
as well as their trace fossils (coprolites and microwear on their teeth, explained in
a later chapter) revealed that hadrosaurs could eat all sorts of land plants. In short,
just calling a hadrosaur “duck-billed” doesn't make it a duck.
This explanation of body fossil evidence favoring aquatic lifestyles for dino-
saurs was even extended to dinosaur tracks. In 1938, paleontologist Roland Bird of
the American Museum of Natural History learned that the area around Glen Rose,
Texas, had lots of dinosaur tracks. Once he investigated, he confirmed the presence
of exquisitely preserved three-toed theropod tracks, but also made an astonishing
discovery:thefirstknownsauropoddinosaurtracksfromthegeologicrecord.These
huge tracks faithfully matched the size and anatomy of sauropod feet: five toes in
therear,andaroundedpadinthefront.However,amongthesesauropodtrack-ways
were ones in which only the front feet registered. Why would the weightiest part
of a sauropod—its rear end, with long tail—not connect with the sediment surface?
Bird surmised that this was a result of a sauropod floating along, only touching the
bottom with its front feet.
Later, a closer look at these tracks showed that the missing tracks in the se-
quenceofstepscouldbeattributedtodifferencesintrackpreservation.Ifthesesaur-
opods had applied more pressure in the front while walking on land, these would
havebeenmorelikelytobepreservedasundertracksthantherearfeet.Hence,Bird
had not been looking at tracks from the original surface where sauropods placed
their feet (or not), but more at the ghostly prints below. Once this alternative ex-
planationcaughthold,peoplerealizedthatBirdwaslikelywrongabout“swimming
sauropods” at the Texas site.
Ironically, Bird's recognition of sauropod tracks in the first place led from an
initial view of sauropods as aquatic dinosaurs that, with more such discoveries,
