Ancient crocodiles may have preferred chomping plants, not meat | Science News for Students

Ancient crocodiles may have preferred chomping plants, not meat

Eating greens appears to have evolved in crocs at least three times more than 60 million years ago
Jul 29, 2019 — 6:45 am EST
modern crocodile

Today’s primarily meat-eating crocodiles have simple, cone-shaped choppers. But some of their ancient kin had more complex teeth, suggesting they ate plants.

Paul Cools/iNaturalist (CC BY-NC 4.0)

Some extinct crocs may have been salad eaters. 

Studies of fossil teeth suggest some ancient kin of modern crocodiles ate plants. These ancient plant-eating crocs evolved at least three times during the Mesozoic Era. This era stretched from about 252 million to 66 million years ago. Researchers reported their findings June 27 in Current Biology

Today’s crocodiles eat mostly meat. Their simple, cone-shaped teeth are typical of meat eaters. Those teeth were different in certain of their ancient relatives. There was “tremendous diversity [in tooth shape] that we don’t see today,” says Keegan Melstrom. This paleontologist is a coauthor on the study. He works at the University of Utah and Natural History Museum of Utah. Both are in Salt Lake City. 

Melstrom and paleontologist Randall Irmis studied scans of 146 teeth from 16 extinct crocodilians. Modern-day cousins include alligators and crocodiles. No modern crocs rely on plants as their main food.

A computer program treated the ancient teeth like mini mountains and analyzed their shape. Then it gave each tooth a score based on how complex its shape was.

The most textured teeth belong to those that rely on plants for food. The teeth of meat-eating carnivores and of omnivores are usually less complex. (Omnivores eat both plants and animals.) Elongated, sharp teeth help carnivores kill and eat their prey. Broader, bumpier teeth are more useful in tearing leaves and grinding up plants.

Comparing the fossil teeth with those from modern reptiles helped the scientists figure out what the ancient crocs likely chewed.

Some of the fossil teeth were much bumpier than those of today’s plant-eating reptiles, such as iguanas. This suggests that the ancient crocs dined mostly on plants. Other fossil teeth looked specialized to crush bones, tear meat or eat insects.

crocodilian teeth
Among the group of reptiles that includes today’s crocodiles and alligators, the teeth of carnivores such as the modern caiman (left in these false color 3-D images) and the extinct Boverisuchus vorax (second from left) are simple and cone-shaped. The tooth of an extinct omnivore in the group (middle, Brachychampsa sp.) has more complexity. But teeth from two ancient herbivores (right two) have the most texture. That, researchers say, indicates those ancient crocs ate mostly plants. 
K.M. Melstrom and R.B. Irmis/Current Biology 2019

The teeth of the suspected plant eaters “really stand out,” says Domenic D’Amore. He’s a reptile specialist at Daemen College in Amherst, N.Y. “Few studies have quantified these differences,” he says. “This study really shows how different [the teeth] are.”

The researchers reviewed the family tree of ancient crocs. They found that veggie-munchers appear to have evolved at least three times during the Mesozoic. 

Ancient crocs lived on land as well as in fresh and saltwater, says Patrick O’Connor. He’s an evolutionary biologist at Ohio University in Athens. This study helps to figure out how the animals fit into their ecosystems, he says. 

Because plant-eating crocs lived in different kinds of environments, herbivory was likely a key strategy for survival.

Power Words

(more about Power Words)

biology     The study of living things. The scientists who study them are known as biologists.

caimans     Alligator-like members of the crocodile family that live along rivers, streams and lakes in Central and South America.

carnivore     An animal that either exclusively or primarily eats other animals.

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

computer program     A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

crocodilians     Large, semi-aquatic reptiles that evolved more than 80 million years ago. Many are long extinct. Their living descendants include alligators, caimans and crocodiles.

diversity     A broad spectrum of similar items, ideas or people. In a social context, it may refer to a diversity of experiences and cultural backgrounds. (in biology) A range of different life forms.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

evolutionary     An adjective that refers to changes that occur within a species over time as it adapts to its environment. Such evolutionary changes usually reflect genetic variation and natural selection, which leave a new type of organism better suited for its environment than its ancestors. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

evolutionary biologist     Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).

extinct     An adjective that describes a species for which there are no living members.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

herbivore     A creature that either exclusively or primarily eats plants.

herbivory     The eating of plants.

Mesozoic Era     An interval of geologic time from about 252 million to around 66 million years ago. Often called the Age of Reptiles, this era includes the Triassic, Jurassic and Cretaceous periods.

omnivore     (adj. omnivorous) An animal whose diet includes foods from both plants and animals.

paleontologist     A scientist who specializes in studying fossils, the remains of ancient organisms.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

reptile     Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.

strategy     A thoughtful and clever plan for achieving some difficult or challenging goal.

Citation

Journal: K.M. Melstrom and R.B. Irmis. Repeated evolution of herbivorous crocodyliforms during the age of dinosaurs. Current Biology. Published online June 27, 2019. doi: 10.1016/j.cub.2019.05.076.