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Image of a dinosaur

Paleoartist Mary Parish's depiction of a Cretaceous Maryland scene

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This painting conveys a lot more information about the animals living in this ecosystem than just what they looked like. We show them doing things they probably did frequently -- activities a time-traveling visitor could have observed in a Cretaceous wetland in Washington DC. How can we know how extinct animals behaved? Fossils provide many types of evidence about feeding behavior, reproduction and parental care, and movement. Scroll through this page to learn about the evidence and how it is interpreted.

The painting shows two adult-baby pairs of dinosaurs. Why do we think that some dinosaurs cared for their young?


There are three lines of evidence pointing to parental care in dinosaurs.

The skeleton of a Citipati is preserved along with a clutch of eggs.  The position of the bones suggests that it was crouched over the oblong eggs, with its arms stretched out to cover them.

Fossilized skeleton and eggs of Citipati, a theropod dinosaur. Click to zoom. Image courtesy of The American Museum of Natural History. See Credits page for image source.

Nests. Fossil eggs and nests provide important clues. Skeletons of the theropod dinosaur Citipati (SIT-ee-PAT-ee) have been found in brooding positions, suggesting that the adults protected their eggs. There is also evidence that some dinosaurs cared for their babies for some time after hatching. This comes from the discovery of bones of older babies in nests of the duckbill dinosaur Maiasaura (MY-uh-SORE-uh), and the fossil of an adult Psittacosaurus (sih-TACK-oh-SORE-us) preserved together with dozens of tiny babies.




A trackway covered with three-toed tracks of different sizes, all moving in the same direction.

This theropod trackway discovered in Maryland by Ray Stanford appears to contain the tracks of several babies and an adult of the same species. Click to zoom.

Trackways. Some fossil trackways show the prints of adult and baby dinosaurs of the same species moving in the same direction, supporting the hypothesis that some dinosaurs lived in family groups.



Evolution. Most bird and crocodilian species, the closest living relatives of dinosaurs, provide some parental care for their eggs and babies. This supports the hypothesis that parental care evolved in the common ancestor of all three groups. If so, it is likely that parental care was an inherited characteristic of most dinosaurs, as well.

Photograph of a modern flamingo sitting on a nest.  The head of a baby flamingo pokes up from between the adult's feathers.

American Flamingo brooding a chick. Click to zoom. Image courtesy Meghan Murphy of the Smithsonian's National Zoo.

Three birds, an adult and two baby tinamous, walk side by side.

An Elegant Crested Tinamou family group. Click to zoom. Image courtesy Meghan Murphy of the Smithsonian's National Zoo.




Some of the dinosaurs in the painting are poised to run, while others walk slowly by. How do we know how dinosaurs moved?

Scientists study living animals for clues to how dinosaurs stood and moved. They reason that because the bodies of dinosaurs had to obey the same laws of physics as those of living animals, a dinosaur with bones dimensions, joint arrangements, and muscle attachment sites similar to a modern animal's must have moved like that animal. For example, scientists know from the shape of the dinosaur hip joint that dinosaurs stood with their legs directly underneath their bodies, as horses and elephants do, not with their legs splay out to the sides, like crocodiles and lizards.

The painting of the two huge Pleurocoelus dinosaurs depicts them as walking on four sturdy legs.

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The giant sauropod dinosaurs in the background of this reconstruction are shown walking because these enormous animals had straight, column-like legs that were poorly suited to running and jumping.



Painting of an ornithomimid dinosaur.  It is standing on one slender hind leg, the other leg stepping forward.  The tail is stretched out behind.

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Ornithomimid dinosaurs, on the other hand, had long, slender legs and narrow, shock-absorbing feet very much like those of ostriches. These may have allowed them to run fast.


Fossil footprints and trackways provide direct evidence of movement. They may show an animal's stride length, used to estimate speed, and whether the animal walked on two legs or four. Sometimes other marks associated with trackways show how a dinosaur sat and rested.




How do we know what extinct animals ate?


Fossils provide several different kinds of clues about the diets of extinct animals.

The skeleton of this Late Cretaceous fish, Xiphactinus, was fossilized along with that of the smaller fish (marked in white) that was its last meal. Click to zoom.

Stomach Contents. Very rarely, fossils are preserved along with their stomach contents. Although this may not reveal what an animal ate regularly, it does record its last meal.

Teeth and Jaws. The teeth and jaws of modern animals show adaptations for different feeding behaviors and diets. For example, animals adapted for killing large prey by biting tend to have massive jaws and large muscles for holding the jaws closed. Their teeth can vary from thin and knife-like (good for slicing meat) to thick and banana-shaped (better for piercing and tearing out chunks of bone and flesh). When scientists find similarities between the teeth and jaws of extinct and modern species, they infer that their diets may have been similar. This type of analysis has led to the hypothesis that the predators from this time period were good biters, but their teeth were not well adapted for chewing bones.

Studies of living mammals show that chewing tough or gritty food leaves wear marks (or microwear) on tooth enamel. Hard foods, such as nuts, twigs and bone, leave pits on the teeth, while tough, grit-covered foliage pulled from plants growing near the ground leaves scratches. Tooth microwear analysis is just starting to be used to understand dinosaur diets. New studies may help scientists distinguish between plant eaters that grazed on low-growing ferns from those that browsed on the leaves and twigs of trees.

This coprolite contains several small fish vertebrae. Its overall shape is a clue that the coprolite was made by a small shark. Click to zoom.

Feces. Fossilized feces, called coprolites, usually contain partially digested animal or plant tissues. Close examination of these tissues provides information about the foods the animals that deposited the coprolites were eating. Unfortunately it is rare to know the exact identity of the animal that produced any particular coprolite, but there may be a probable source. In this ecosystem, for example, a very large, plant-filled coprolite would more likely be from the large sauropod, Pleurocoelus, than from the smaller ornithopod.



RELATED VIDEOS

How do we know that some dinosaurs cared for their young?

Why do we think that some dinosaurs cared for their young?

Watch Dr. Matthew Carrano, Curator of Dinosauria, and Ray Stanford show evidence that some dinosaurs cared for their young.



How Do We Know How Dinosaurs Moved?

How Do We Know How Dinosaurs Moved?

Dr. Matthew Carrano, Curator of Dinosauria, describes how comparisons with modern animals help us understand dinosaur movement.



How Do We Know What Dinosaurs and Other Extinct Animals Ate?

How Do We Know What Dinosaurs and Other Extinct Animals Ate?

Dr. Nicholas Pyenson, Curator of Fossil Marine Mammals, examines the forms of evidence scientist use to infer the diets of extinct animals.



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