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Crocodile Fossil Changes Picture of Animal Life

Jsertich 1
Joseph Sertich
Joseph Sertich

Fossils of an ancient crocodile with mammal-like teeth discovered in the Rukwa Rift Basin of Tanzania is changing the picture of animal life at 100 million years in what is now sub-Saharan Africa. The new species, found by an international team of scientists, including Joseph Sertich from Stony Brook, is named Pakasuchus. “Paka” is the Ki-Swahili name for “cat” and “souchos” is Greek for crocodile.  The scientists analyze the anatomical structure and evolution of the new species in the August 5 issue of Nature.

The scientists describe the new species of notosuchian crocodyliform as a small animal whose head would fit in the palm of a person’s hand.  The species wasn’t as heavily armored as other crocodiles, except along the tail. Other aspects of its anatomy suggest it was a land-dwelling creature that likely feasted on insects and other small animals to survive.

The research team, funded by the U.S. National Science Foundation and the National Geographic Society, found a complete specimen of the crocodile in 2008, and now have recovered portions of seven different Pakasuchus specimens in southwestern Tanzania. The tooth row with molar-like teeth initially puzzled many experts. Other ancient and living crocodiles typically boast relatively simple, conical teeth that serve to seize and tear prey; they swallow flesh in large chunks.

“This entire group of crocodiles deviates radically from the ‘typical’ crocodile, most notably in their bizarre dentitions, demonstrating a diversification not seen in the Northern Hemisphere during this time interval,” said Sertich, a doctoral student in Stony Brook’s Department of Anatomical Sciences whose expertise is in understanding the relationship of this new species to other crocodyliforms, the term for modern crocodiles and their extinct relatives.

“The presence of morphologically strange and highly specialized notosuchian crocodyliforms like Pakasuchus in the southern landmasses, along with an apparently low diversity of mammals in the same areas, has potentially profound ecological implications,” Sertich added.

Patrick M. O’Connor, lead author of the study and associate professor of anatomy in the Ohio University College of Osteopathic Medicine, concurred, and he pointed out that regarding the fossil find, “Once we were able to get a close look at the teeth, we knew we had something new and very exciting.”

While the specimens of the newly discovered animal and its close relatives are unusual, the study suggests that the creatures were abundant during the middle Cretaceous, from around 110 million until 80 million years ago. The new species isn’t a close relative of modern crocodilians, but is a member of a very successful side branch of the crocodyliform lineage that lived during the Mesozoic Era and in areas quite different from what is typically thought of for crocodiles.

The research team describes that the animals had heavily plated tails but relatively unarmored bodies with gracile limbs suggests that the creatures were quite mobile. They probably actively foraged on land, unlike water-dwelling crocodiles. Pakasuchus lived alongside large, plant-eating sauropod and predatory theropod dinosaurs, other types of crocodiles, turtles, and various kinds of fishes.

Little is known about the vegetation during this time period, but detailed sedimentological analysis of the Rukwa Rift Basin shows that “the landscape was dominated by a large, long-lived river system with multiple, crisscrossing channels and low-relief vegetated floodplains in between that apparently supported a relatively rich vertebrate fauna,” said Eric Roberts, an assistant professor of geology at James Cook University who collaborated on the research while at Southern Utah University.

During much of the Cretaceous Period, Afro-Arabia, along with India, Madagascar, Antarctica, Australia, and South America, were joined together as the southern supercontinent Gondwana. Relatively few Cretaceous-age mammals have been recovered from this part of the world, and most of those discovered don’t appear to be related to modern mammals. Notosuchian crocodyliforms may have taken up residence in a “mammalian niche” in Gondwana during the Cretaceous Period.

The research team continues to focus on working in different parts of the southern hemisphere, including Africa and Antarctica, because not as much exploration has been done in these locales. They say scientists are still piecing together the puzzle of what animal life was like in these places, and intriguingly note that maybe they just have not found the mammals yet.

Other study collaborators and co-authors include: Nancy Stevens and Ryan Ridgely of Ohio University; Michael Gottfried of Michigan State University; Tobin Hieronymus of the Northeastern Ohio Universities College of Medicine; Zubair Jinnah of the University of the Witwatersrand, South Africa; Sifa Ngasala of Michigan State University and the University of Dar es Salaam in Tanzania; and Jesuit Temba of the Tanzanian Antiquities Unit.

[Illustration on homepage of Pakasuchusby Mark Witton, University of Portsmouth.]

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