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Published August 4, 2010

The discovery of ancient crocodile fossils in Tanzania by a National Geographic grantee shows the croc was more like a mammal than other reptiles of its era. (Read the full story of the mammal-like fossil crocodile.) The reptile had mammal-like teeth and legs as well as nostrils on the front of its head, indicating that the animal spent more time on land than crocodiles of today.

Video courtesy: National Science Foundation

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UNEDITED TRANSCRIPT

Voice of Patrick O’Connor, Paleontologist, Ohio University

Our group, our research team, has been working in southern Tanzania for a few years now and we've found a very exciting new type of crocodile. This animal is very small compared to what you think of for typical crocodiles. The skull was about three and a half inches in length. It would easily fit in the palm of your hand, and the rocks in which this animal were found are dated at about 105 million years so it's actually quite old. It's during the time of the dinosaurs, during the Cretaceous period. And what's so special about this new crocodile, it's what the teeth look like in this, and if you were find just a tooth from this animal, there's no way that you would ever think it was a crocodile of any kind.

A couple of other interesting things about this new crocodile that, once again, make it stand out is that the nose openings, the nose holes, if you will, actually were directed forward instead of up, and that's very suggestive of an animal that, in fact, does not live in water at all but was actually an animal that was up and living in what we call the terrestrial environment, or land-living animal. And one other interesting bit of anatomy about this new animal is its limbs, its fore and hind limbs. This animal had relatively long and slender limbs. We might think about it moving around in quite an agile way amongst the vegetation. The best comparison of animals that are alive today would be something like a standard housecat or, you know, maybe a possum, you know, so we're talking an animal of about that body size.

One of the things that stands out about this crocodile is the nature of the teeth, and it's very different in a couple of ways. First off, it has distinct types of teeth. Instead of having just a basic conical tooth like you would see in most crocodiles, here we see a distinct canine-like tooth followed by a series of small conical teeth and towards the back of the jaw, two large molar-like teeth. And having teeth that are distinctive like that along the tooth row is something that we typically think of as a mammalian feature. And if we consider how these teeth may have functioned, you might consider that those large canine-like teeth at the front of the jaw would've been used for acquiring the food; the middle teeth are moving the food product further back into the mouth, and then those molars, that's where the business is being done, in that those teeth are working together to process food.

So to place this Tanzanian crocodile into a comparative perspective, I've been doing museum work in different parts of the world, different parts of the United States. I've spent time in the Kenyan National Museum in Nairobi, Kenya and in doing so, looking at other crocodiles that had been discovered from, in this case, east Africa. So that's kind of our first point of comparison. When we find something in Tanzania, might make sense, well, what did the other crocodiles that were alive at that time and living close by, what did they look like? Are they similar? Are they different?

So, taken together, we see a number of features in this group of small-bodied terrestrial crocodiles, that is, land-living crocodiles, that is suggestive that they may be exploiting a niche that would otherwise belong to the mammals, and we know that the mammals occupied that niche in the Northern Hemisphere, small body size, a diversity of different skull shapes and tooth shapes. So mammals were doing that in the Northern Hemisphere. In the Southern Hemisphere, the Notosuchian crocodiles seem to be diversifying in such a way that they were likely exploiting a niche that otherwise would be considered a place where mammals would be very successful.

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