Your Daily Fossil

Saurosuchus 

Mounted specimen from Ischigualasto Provincial Park, San Juan, Argentina

Reconstructed model from the Titanes de Ischigualasto (Titans of Ischigualasto) exhibit while at the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina. 

When: Late Triassic (~231 to 226 million years ago)

Where: Argentina

What: Saurosuchus is a very large basal member of the crocodile lineage within the Archosauria. It lived in what is now Argentina during the late Triassic, where it was a dominante apex predator, reaching lengths of up to 23 feet (~7 meters).  A good deal of this length was its massive skull filled with pointy recurving teeth. Saurosuchus is a member of the Rauisuchia, one of the first branches to come off of the Crurotarsi (crocodile line archosaurs) lineage.  Like other rauisuchians Saurosuchus had an erect leg posture, you can see this in the model above, it looks very much like a large crocodile (albiet with more dinosaur looking like head on), but its legs are directly underneath its body, not sprawling out like in modern crocodiles. This posture is the same as in mammals and dinosaurs, but was accomplished in a different way. Mammals and dinosaurs modify the femur itself for erect posture, but in rauisuchians it was the pelvis that was transformed. Saurosuchus was a fully terrestrial creature capable of fast speeds as it hunted its prey (including the much smaller dinosaurs) in the ancient flood plane. 

Saurosuchus fossils are from the Ischigualasto formation (and national park!) in Argentina. This area is open to the public and is more popularly called the Valle de la Luna (Valley of the Moon).  Not only do basal crocodile line archosaurs come from this formation, but some of the oldest dinosaurs as well. These animals, which would go on to dominate later in the Mesozoic, were a minor part of the fauna. The Triassic here was dominated by rhynchosaurs and cynodonts, these groups would both suffer great losses during the end Triassic extinction event. 

Pterodaustro

Slab specimen from the Museo Histórico Nacional in Buenos Aires, Argentina. 

Reconstruction by Mark Witton 

When: Cretaceous (~110 - 100 million years ago) 

Where: Argentina

What: Pterodaustro is a pterosaur. It is a great example of the tremendous amount of diversity present within the clade in its heyday. Look at those crazy things in its mouth, coming out of its lower jaw. They are so long that when the mouth was closed they extended past the top jaw. They are not baleen, but extremely elongated teeth.  They are about 3cm long on average and just a couple of millimeters wide. This extreme height width difference would have allowed the structures to be somewhat flexible. Pterodaustro had over 1000 of these teeth, and they were not in individual sockets, but instead tightly packed into a pair of parallel grooves on each jawbone. The top teeth were small and flat, and also in grooves instead of separate sockets. Pterodaustro would use these elongated teeth to filter feed on small aquatic animals, like the living flamingos do. But even better, because it would not have had to turn its head upside down to feed. Take that dinos!!! Due to this shared ecology some reconstructions have made Pterodaustro colored bright pink… I do not really buy this. Many animals filter feed and are not bright pink.  

Many many specimens of Pterodaustro have been recovered, we are approaching 1000 collected specimens. The ages of these individuals range from unhatched juveniles to fully grown adults, which had wing spans of over 8 feet (~2.5 meters). Studies of the growth series of  Pterodaustro have revealed that the pterosaur grew rapidly for the first  two years of its life, and then grew much more slowly for the next three to four years. It is likely it reached sexual maturity shortly after the onset of the slow growth period. This means that Pterodaustro had more of a determinant growth ( a set adult size) pattern as seen in modern birds rather than indeterminate growth (growing forever) seen in many ‘reptiles’ such as crocodiles and lizards. 

Argentavis magnificens 

When: Late Miocene (~6 million years ago)

Where: Argentina

What: Argentavis is the largest flighted bird there ever was. Its wingspan has been estimated at 23 feet (~7 meters), almost double that of the largest flying bird that soars today’s skys, the wandering albatross (Diomedea exulans). All specimens of this avaian have been found in Argentina, hence its name, which means ‘magnificent Argentine bird’. Recent studies looking at the biomechanics of flight in Argentavis have determined that it was a soaring bird, like today’s condors and vultures. It would have easily glided upon the strong thermals above the Argentine pampas, but getting up to those winds was a bit more of a challenge. It was too large to just flap its wings and take off, even when it was standing in a strong headwind. Instead Argentavis would have had to run down a steep hill or jumped from a high perch in order to take to the skies. Once it was up there, however, it is estimated it could have soared for hours, hunting for prey as it rode the late afternoon thermals.