Who Lies Sleeping?

Troodon Nest by Bill Parsons

While working on a piece on dinosaur reproduction, Greg Paul came to the following conclusions regarding hadrosaurs.

1. Tooth wear—That the teeth of baby hadrosaurs are worn never had any meaning, because they had to chew their food whether they got it on their own, or were fed by their parents.
2. Limb joints—That baby hadrosaurs had poorly ossified limb joints is not critical, because the same is true of fully grown, but not quite mature birds (like the chickens you buy at the store).
3. Hip ossification—The well ossified pelves of baby hadrosaurs do indicate a well developed locomotary ability.
4. On the other hand, hadrosaur chicks weighing up to 20 kg have been found in or near nests (at least 16 kg heavier than when they hatched), and the eggshells in the nests are trampled. Both factors indicate extended habitation of the nest.
5. The next question is whether the nestlings were dependent upon parental feeding, or went in search of food and returned to the nest. Baby crocodilians can stay near the nest for months or more than a year. However, they wait for prey to come into their territory, and crocodiles grow slowly (it takes them 4-5 years to grow to 20 kg), so they do not need a lot of prey to move their way.
6. The bone histology of hadrosaur chicks shows that they grew much more rapidly than reptiles, and they were herbivores. Both points mean that they would have had to range far and wide in search for food, and returning to the nest would probably not be practical.
7. The most logical reason for hadrosaur chicks to remain near the nest would be because that was where they received food from their parents. This system would have been a way for giant adults to take care of tiny offspring in a safe nest where they would not be trampled. This system would be highly advantageous for the chicks, because it would mean that at no expense to themselves they would receive large amounts of food, boosting growth rates. Ostrich chicks reach 20 kg in three months, and hadrosaurs may have grown even faster.
8. Hadrosaur nestlings lived in open pit nests, largely exposed to the elements. Bird chicks that live in open nests, and are not brooded, have very well developed thermoregulatory systems in order to survive exposure to the elements. This may have been true of hadrosaur nestlings. It is therefore interesting that bone isotope analysis by Barrick and Reese suggests the same.

Small chicks would not eat much but how efficient would a hadrosaur be as a food carrier? And since the babys teeth were worn does that mean the parents didn’t simply regurgitate food? Given the growth rates implied by the bone data, Maiasaura chicks would have a voracious appetite—much like the chick of modern birds. The parents would be kept busy, but given its large beak, and cheeks, a Maiasaura could probably carry a good bit of food.

Concerning the brooding oviraptors, it has been suggested that they were merely shading the eggs, rather than incubating them via high body temperatures. Birds certainly do shield their eggs from high temperatures, but also incubate their exposed eggs. The only logical reason to have the eggs exposed is so that they can be warmed by the parent’s body. Otherwise, it is best to bury the eggs so that sun heated soil or fermenting vegetation can keep them warm.

Eggs cannot be left exposed no matter what time of the day or night, or what the weather, be it hot, warm, cool or cold, rainy or dry. Eggs are fragile structures vulnerable to predation and in need of a stable humidity and temperature level. It would be shocking if Oviraptor were brooding its eggs only part of the day. No bird leaves its eggs exposed for more than a few minutes.

The evidence for brooding in some small dinosaurs—big dinosaurs would have crushed their eggs—and parental care in some dinosaurs, appears to be good. Not all dinosaurs took care of their eggs and young—megapode fowl do not do the latter. Dinosaur parenting may have been variable.

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