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DINOSAUR PARENTING (fairly long)
Including the article in the latest EARTH, there has been a lot lately about
the possibility of NONparenting in dinosaurs such as Maiasaura. For some
reason Peter Dodson seems to be enjoying applying terms like based on
"gossomar" and "unscholarly" to recent work favoring parenting. While working
on the section on dinosaur reproduction for an upcoming dinosaur enyclopedia,
I came to the following conclusions regarding hadrosaurs.
1 - Tooth wear: That the teeth of baby hadrosaurs are worn never had any
meaning, becasue they had to chew their food whether they got it on their
own, or were fed by their parents.
2 - Limb joints:
That baby hadrsoaurs 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 9at 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 can wait for prey to come into their territory. Also, crocodilians grow
slowly (it takes them 4-5 years to grow to 20 kg), so they do not need for 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
8 - It appears that 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 (see my paper in DINOSAUR EGGS & BABIES book). It is therefore
interesting that bone isotope analysis by Barrick and Reese (latest
PALEOBIOLOGY) suggests the same.
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 I do not know of any bird that does not also incubate their exposed eggs
(if anyone has an example please let me know). 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
vegetaton can keep them nice and toasty.
In conclusion, 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. This by no means all dinosaurs took care of
their eggs and young, megapode fowl do not do the latter. Dinosaur parenting
may have been very variable.