May 22, 2013
Crocodiles Species Were Abundant Just A Few Million Years Ago
April Flowers for redOrbit.com - Your Universe Online
The largest number of crocodile species is currently found in northern South America and Southeast Asia, and as many as six species of alligator and four true crocodiles exist. However, no more than two or three ever live alongside one another at any one time.
Approximately nine to five million years ago, however, it was a different story. A total of 14 crocodile species existed, with at least seven of these occupying the same area at the same time, according to a new study from an international team of researchers led by University of Zurich paleontologists Marcelo SÃ¡nchez and Torsten Scheyer. According to the study, the deltas of the Amazonas and the Urumaco — a river on the Gulf of Venezuela that no longer exists — boasted an unparalleled abundance of extremely diverse, highly specialized species of crocodile.
The findings of the team´s study were recently published in the journal Nature Communications.
The team discovered two new crocodile species — the“¯Globidentosuchus brachyrostris which belonged to the caiman family and had spherical teeth, and“¯Crocodylus falconensis, a crocodile that the researchers assume grew to well over four meters long — while studying a treasure trove of crocodile fossils from the Miocene in the Urumaco region. According to the researchers, the fossils in Venezuela include relatives of all the families of crocodile species that still exist all over the world today. This includes the Crocodylidae, the so-called true crocodiles; the Alligatoridae, which, besides the true alligators, also include caimans; and the Gavialidae, which are characterized by their extremely long, thin snouts and are only found in Southeast Asia currently.
The researchers are convinced that the extremely different jaw shapes of the crocodilians reveals that the species were highly specialized feeders. For example, the fossil gharials must have preyed on fish with their pointed, slender snouts.
"Gharials occupied the niche in the habitat that was filled by dolphins after they became extinct," SÃ¡nchez suspects. Globidentosuchus brachyrostris´s spherical teeth suggest that it specialized in shellfish, snails or crabs, while giant crocodiles (sometimes up to 36 feet in length) fed on turtles, giant rodents and even smaller crocodiles. "There were no predators back then in South America that could have hunted the three-meter-long turtles or giant rodents. Giant crocodiles occupied this very niche," explained Scheyer.
Around 5 million years ago, the unusual variety of species in the coastal and brackish water regions of Urumaco and Amazonas came to an end when all the crocodile species died out. The team says that the extinction was not due to changes in climate — the temperatures in the Caribbean are known to have remained stable around the Miocene-Pliocene boundary. Rather, the extinction was caused by a tectonic event.
"The Andean uplift changed the courses of rivers. As a result, the Amazon River no longer drains into the Caribbean, but the considerably cooler Atlantic Ocean," explains SÃ¡nchez.
We know from the Orinoco and Amazon regions that an entirely new fauna emerged from the destruction of the habitat. Since the Urumaco River dried up, however, a very dry climate has persisted in what was the Urumaco region.