Geoscience Reference
In-Depth Information
the beginning of the twentieth century. This dinosaur is probably
the tallest of all, with an extremely long neck extending above its tall
shoulders.
Titanosaurs range from medium to gigantic in size. The titanosaur
Argentinosaurus, with its 100-ton, 120-foot-long body, is the largest
dinosaur ever found. It may well have shaken the Patagonian landscape
with every step it took. Titanosaurs are the most diverse group of
sauropods; their skeletons are known from South America, North
America, Africa, Europe, and Asia. Most lived during the Cretaceous
period, although the earliest known form is Janenschia, from the late
Jurassic of Tanzania, and more than a dozen species inhabited South
America. Titanosaurs evolved from a common ancestor that had
small oval air holes in their vertebrae, an important adaptation for
lightening their heavy skeletons. There were as many as thirteen ver-
tebrae in the neck, twelve in the trunk, six in the sacrum, and more
than thirty in the highly flexible tail. The spines on top of the neck and
trunk vertebrae were simple, instead of being split as in diplodocids.
Advanced titanosaurs had tail vertebrae with a concave front surface,
and their teeth resemble the pencil-like teeth of diplodocids. The front
legs of these animals were shorter than the hind legs. One of their
most remarkable characteristics is the bony covering of armor formed
by thousands of small, rounded lumps and a few larger plates,
although it is unclear that this formidable armor developed in all
members of the titanosaur lineage.
This abbreviated cladogram of dinosaurs provided us with a list of
potential victims that could have perished inside the dinosaur eggs
at Auca Mahuevo. Our next job was to begin eliminating candidates
by determining what kinds of dinosaurs had previously been found
in Patagonian rocks, especially ones that were from about the same
age as the dinosaurs collected at Auca Mahuevo.
Many diverse lineages of dinosaurs have been discovered in Pata-
gonia's vast Mesozoic rock layers, extending from the late Triassic up
to the very end of the Cretaceous, a period of more than 130 million
years. In the past, only a handful of discoveries of omithischians had
been made, but recent findings are demonstrating that the history of
omithischians in Patagonia is much richer than previously thought. All
Patagonian omithischians are restricted to the Cretaceous. Although
specimens of ceratopsians, stegosaurs, and ankylosaurs are known from
Search WWH ::




Custom Search