A THE D,NOSAUR REPORT

Dino Art Notes

Brooding OverDinosaur Nesting

by Gregory S. Paul

SUMMER 1996

the babies are not fed mother's milk they die.Starring in 1978, John Horner and co-workers

found colonies of nests comaining hadrosaur eggs andjuveniles. They concluded that hadrosaur babiesremained in the nest for a month or two and were fedby their parems. One reason was that nestlinghadrosaurs leg joints are made largely of cartilage, butthe same is true of adult dinosaurs and active butimmature birds. Nicholas Geis.t and Terry Jones haveshown that baby hadrosaur hips bones were well formedlike those of bird chicks that live outside the nest. Inthis view baby hadrosaurs quickly left the nest, whichwere open pits exposed to chilling rain and baking sun.On the other hand, hadrosaur chicks had the very shortsnouts that elicit parental care. Smashed egg shells implythe nestlings used the nest, and rhe remains of fastgrowing hadrosaurs as big as dogs have been found in ornear their nests. Reptiles take years to grow to dog size,

In this speculative scene a pair of adult sauropods Pleurocoelus care for a large creche of juveniles.Bones of both sizes have been found in the Cretaceous of MaryianS' (source: G. S. Paul)

THE DINOSAUR REPORT SUMMER 1996

and incubating their eggs in the manner of birds is notsurprising considering the close relationships of the twOgroups. What is not yet known is whether Ooiraptorshad feathers to better cover the eggs with (if they did,then they would have needed a naked brooding batch towarm the' eggs with). Also unknown is whetherOuiraptors cared' (or the babies once out of the eggs.

It is probable that parental care was highlyvaried among the dinosaurs. For example, rhe very longsnouts and big teeth of young tyrannosaurs suggest theyhunted on their own from the start. The artist has somegeneral rules to follow. Do not draw giam dinosaursmoving in big herds with babies fresh from the eggs, thewee little ones would have quickly become the Mesozoicequivalent of road kill. Trackways and skeletalassociations suggest that some juveniles moved inindependent gr0!lps, and only joined adult herds whenthey were big enough to do so safely. Juvenileceratopsids and hadrosaurs, for instance, did not mergewith the big herds until they were one fifth to one halfof adult dimensions respectively. The famous Davenportsauropod trackway from Texas shows two adults ofunder 20 tonnes, accompanied by twenry-one juvenilesof 1 to 10 tonnes. A typical elephant herd consists of afew adult cows accompanied by twice as many subadulrsand juveniles, including a couple of babies. This points

Back when I was a youngster, only a few dinosaurrestorations showed their ancient eggs or offspring, andif they did the parents were assumed to abandon thepoor things as soon the eggs were laid and buried. Therewere exceptions. Charles R. Knight once painted aTriceratops pair guarding their little one from aTyrannosaurus. How things have changed. Illustrationsshowing dinosaurs caring for their young have becomethe standard. Recently new fossil finds have added tothe evidence of parental care in dinosaurs. At the samerime some researchers assert that the evidence forparental care in dinosaurs is not very good. What is thedinosaur artist to do?

As usual, life present and past is complicated.Parental care of young and/or eggs is not limited tobirds and mammals. Some fish, amphibians and reptilesprotect and take care of their nests and young. Pythonsactually wrap their bodies around a pile of eggs, andwarm them with heatgenerated by rhythmiccontractions of their sinuousbody muscles. Among birds,megapode fowl bury andincubate their eggs in bigmounds of fermentingvegetation. Megapodes go togreat pains to make sure theinternal temperature is justright, but once the eggshatch the chicks-which canfly within hours-arecompletely on their own.The young of giant groundbirds leave the nest soon afterhatching and feedthemselves, bur they remainunder the carefulguardianship of adults untilthey are big birds themselves.Only mammals have to carefor their young, because if

Two examples of fossil dinosaur nests from the Cretaceous, shown at the same scale. A rhino-sized hadrosaur Maiasaura tends to its pit nest. AIthe bottom of the nest are two possible sizes of hatchlings. which numbered as high as two dozen. Walking out of the nest is an older juvenile.Lying on a nesl of eggs is a brooding Oviraptor, figure courtesy of Mark Norell (artwork. Mick Ellison, AMNH).

so they must leave the nesting area at a smaller size. Itseems that young hadrosaurs remained in the nest wherethey could be protected by their parents bur not betrampled. \Xlelldeveloped thermoregulation allowed thenestlings to cope with the weather. Growth was so rapidbecause the lazy babies were fed large quantities of foodby their hard working parents. However, if the parentsdiedor left, the hungry but strong hipped chicks couldleave and fend Ior themselves.

Also controversial are the brooding Ouiraptorskeletons and nests recently found in Mongolia bypaleontologists from the American Museum of NaturalHistory. Increasing numbers of Oriraptors have beenfound arop complete nests, so it is unlikely that they alldied while laying eggs. Were these small, bird-likedinosaurs incubating their eggs like birds' Or, didOvi1'l1ptor brooding not differ significantly from thatpracticed by reptiles, as Geist and Jones have asserted?Only Ooiraptors and large birds lay eggs in flat rings inopen nests, then sit directly on tOP of them, andcarefully drape their arms over the eggs. It is unlikelythat the Ouiraptors were JUStshading their eggs from theheat of the desert they lived in, because there is no pointto leaving eggs exposed unless they are going to beincubated with bodv heat-and deserts become bittercold at night. That predatory dinosaurs were protecting

THE DINOSAUR REPORT

to a flaw of many dinosaur scenes (including my own),which is to show one or two large juveniles under thecare of adults, like big slow breeding mammals. But bigdinosaurs were more similar to big birds because theylaid many eggs. As per the latter, a few adults may havehad large numbers of charges under their care, at leastuntil attrition cut down their numbers. Nature is harsh,and it is harshest to the young and the weak.

Gregory S. Paul is a paleontologist and artist living in Baltimore.

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