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Re: Psittacosaurus adult found with 34 juveniles



While some dinosaurs are clearly precocial (born ready to roll soon after they emerge from the egg), there is still some debate as to whether or not some dinosaurs are altricial. Also in question would be whether or not all dinosaurs are nidifugous (immediately leaving the nest) or if some are nidicolous (they stay in the nest for some time, and are fed by the parents there).

There are advantages to being altricial: larger adult brains in relation to body size, and altricial eggs hatch faster, so there is less time spent as a vulnerable egg. However, given the number of nest and hatchling predators that would likely evolve in any habitat, I would tend to think that all ground nesting dinosaurs would want to either hide their eggs, and then have their offspring emerge as precocial as possible; or be darn good at defending their nests. The ideal offspring would then want to be nidifugous so that a parent would not have to abandon them in the nest while they looked for food.

While most ground nesting birds are fully precocial and nidifugous, this is not the case with all ground nesting birds. The Larids (gulls and terns) are semi-precocial beach nesters. Auks have some precocial, nidifugous varieties: never feeding in the nest and headed out to sea in a few days; intermediate Auks that are semi-precocial, such as the razorbill; and some that are semi-precocial, and nidicolous, such as puffins, which feed at the nest for 25?75 days. I believe that this all has something to do with how Auks are best able to survive the trip from the nest to the sea: by gliding or walking. Some intermediate auks, for example, can glide rather than walk, but may crash on the rocks.

< Scott Hartman <DinoBoyGraphics@aol.com> wrote:
< I saw this specimen in Japan recently before it was put on display. I
< assume I can start to share photographs now that it is published. Here are a
< few thoughts:


< After staring at it for a few hours, I've concluded that there is little
< chance of fraud. The lithology appears inconsistent with transport (e.g. fine
< grain sediments). Also, while paleo-topography was hard to visually confirm
< from the sediments (i.e. whether there was an obvious ground plane), the fully
< articulated skeletons did appear to be in contact with a nest-shaped depression.
< So it really looks like 34 baby psittacosaurs in a nest.


< That being said, unless the babies were born the size of a thimble and had
< already increased in size 10-fold, it's hard to understand how they could have
< all come out of one animal. Maybe extremely delaid incubation and simultaneous
< hatching could explain it (they were pretty close in size), but it seems more
< likely that the juveniles were from more than one animal, so my best guess is we
< are seeing communal nesting. Ostriches engage in communal parental care, so it
< doesn't require lots of smarts to pull off.


It is possible that they all came from the one parent, the eggs could have been mass shelled at the same time. The psittacosaurs may not have yet fully developed the more avian ovary system of shelling one egg at a time down the chute, although it is certainly possible. In this case you would probably be right about the dump nesting, I am sure that some dinosaurs do this.

I am having a hard time understanding why, if these hatchlings are as large as they appear, and if they are in a shallow open nest, that they are still in the nest. The Psittacosaurus bristles may dissuade theropods from dropping out of trees on them, but it does not seem like that good of a defense againsed nest predators. So why, as it appears, would Psittacosaurus hatchlings be semi-precocial and nidicolous? Do they return to the nest and hide under the mother?

Is it possible that this nest is just an indentation caused by water rushing around the animals?

From: Dann Pigdon <dannj@alphalink.com.au>

Ostriches are an interesting example, as each pair will attempt to drive
off other pairs and claim their hatchlings as their own. A really
agressive pair may end up with over a hundred chicks to look after. The
theory is that the parents benefit by having their own offspring
protected by the sheer number of other chicks around them. The chicks
benefit by having a very agressive and dedicated pair of adults to
supervise them.

The fact that males will mate with multiple females, and that females
themselves will allow multiple males to mate with them, complicates
matters further. There is always the chance that any single male will be
protecting babies that have no genetic relationship to him what-so-ever.
However by spreading the genes around, no single animals risks putting
all it's eggs in one basket (an appropriate metaphor!)

Very interesting. I was wondering how that came about. I have seen it suggested that ostrich creche guardians keep their own young close by, and then allow the offspring of other ostriches to run on the outside of the crèche as decoys for predators. African catfish use baby cichlids for this purpose. I would hope not (personnel bias), but they do use a similar strategy with their eggs.


Brian Bertram did a study of ostriches in Tsavo, Africa and found that a male established a territory by driving out the other males, he then made a scrape in the ground for a nest and tried to interest a female in it. The first female to lay in a male?s nest became what was called ?the major hen?. She would lay one egg in the nest about every two days, and would later share in the guarding of the nest and in the incubation of the eggs. As you mentioned, other hens (which are called minor hens) were allowed to lay eggs in the nest also. These hens did not sit on or help guard the nest, but only showed up to lay eggs in it. Thus the nests filled up with from 15-29 eggs. The ostriches cannot incubate more than 19-25 eggs, so the extras (always those belonging to minor hens) are pushed to the outside perimeter of the nest by the major hen, who could recognize her own eggs. These are thought to act as decoys to predatory mammals. After the eggs hatch the ostriches abandon their territories.

Although they might, the psittacosaurs presumably do not incubate their eggs by sitting on them, so any quantity in the nest should be possible. However, if this is the case, then as asked by Scott Hartman, how would they then all hatch at the same time?

Thanks,

Evan Robinson

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