|Pakasuchus, among the most mammal-like notosuchians.|
08 April 2014
Fossil (Gondwanan) Vertebrate(s) of the Month: Notosuchia
I'll be heading to the Southern Hemisphere twice this (northern) summer, in honor of which my Fossil Vertebrates of the Month between now and August will all be from Gondwana, the former southern continent of which Australia, South America, Antarctica, Africa, India, Madagascar, and New Zealand are the primary remnants. I was going to start this series in May, but this recent publication inspired me to start this month.
The traditional story of vertebrate life on land in the Mesozoic is a relatively simple one, particularly in regards to mammals (small and shrew- or rat-like according to this view), dinosaurs (diverse and dominant), and crocodilians (aquatic ambush predators, then as now). The beauty of nature, of course, is that it is seldom simple, and one of the more exciting accomplishments of paleontology in recent decades has been the elucidation of the glorious complexity of ecosystems from the woefully misnamed "Age of Dinosaurs." Several mammalian paleobiologists, spearheaded by Zhe-Xi Luo, have shown that mammals were much more diverse than had previously been thought (some of them even preying upon dinosaurs). Even crocodiles, long used as the exemplar of a group that found its niche early on and succeeded by staying there, were not all swamp lurkers in the Mesozoic. In fact, one group of Cretaceous crocodilians on the southern continents evolved to inhabit ecological roles generally associated with mammals today. Known as notosuchians (literally 'southern crocodiles'), their most remarkable features can be found in and around the jaws. Much has been made of the complex teeth of mammals and how this allowed them to diversify to take advantage of a wide variety of diets, but notosuchians show that our own class does not have a monopoly on such adaptations. Unlike most reptiles, many notosuchians had heterodont dentition, as do mammals, and the wide ranges of niches into which the group evolved led to some of the strangest animals that have ever lived. Some members of the group were likely predatory, making them at least superficially similar to living crocodilians, but other members of the group have been interpreted as omnivores or even herbivores. Malawisuchus likely processed food through a forward-backward motion of the jaw, Anatosuchus had a duckbill, Yacarerani had huge, procumbent incisors, and the eponymous Notosuchus may have had cheeks and a pig-like snout. Not all bizarre adaptations among notosuchians were related to eating: as its name suggests, Armadillosuchus evolved interlocking, flexible armor that anticipated that evolved by armadillos millions of years later.