Auca Mahuevo.
Auco Mahuevo, from the Spanish menaing “more eggs”, a site in Patagonia, Argentina is a Cretaceous lagerstätte discovered by Luis Chiappe, Lowell Dingus, and Rodolfo Coria during two expeditions in 1997 and 1999. The site is famous for revealing an almost perfectly preserved dinosaur nesting site, including embryos, eggs and soft tissue preservation.
Geological Setting and age. The rocks of Auca Mahuevo comprise of sandstones, siltstones and mudstones deposited in a fluvial system. The nesting site occurs in a reddish-brown siltstone, which is believed to represent an over bank flooding deposit from the fluvial system. There appears to be several "layers" of nests, perhaps showing that the Sauropods nesting here did so year after year. Analysis of the palaeotopographic surfaces shows that the some of the nests sit in small depressions about 30cm deep. The site has been dated at 70ma- Late Cretaceous.
Important Discoveries.
The Auca Mahuevo fossil site yielded several important fossils, but the most special are the unhatched dinosaur embryos, found undisturbed in their nests, and these are the first dinosaur embryos found in the Southern Hemisphere. The tiny embryos show fossilised skin, which is similar to that of a modern lizard. One of the fossils shows a stripe of large scales near the centre, and this would almost certainly have been a stripe running down the animals back. Tiny teeth found within the eggs show what type of Sauropods were nesting here, the Titanosaurs. Remains of titanosaurs have been found close by to the sire, and they were also the only sauropod type dinosaurs alive at the end of the Cretaceous period. Other fossilsied skin samples from the Titanosaurs shows that this group of dinosaurs had armoured plates embedded in their skin. The embryo fossils do not show this, indicating that these plates grew after the dinosaurs had hatched.
Preservation
The siltstones covering the Auca Mahuevo nesting site have allowed palaeontologists to ascertain that a flood swept through the area, submerging the nests and preserving them for millions of years. It was this rapid preservation that allowed the soft tissue preservation at the site.
Further Reading; http://www.sciencedaily.com/releases/1998/11/981118081844.htm http://www.lowellcarhart.net/ebay/papers/sauro.pdf http://curiosity.discovery.com/question/what-is-auca-mahuevo (Short Video) http://www.h2g2.com/approved_entry/A684425
-LL