endothermic mesozoic ovavores
Rob Janes
I'm wondering if anyone has done any research on the subject of egg
eaters in the mesozoic, or generally on archaic ecological niches no
longer viable, or that no longer will support specialization.
Speculations on likely characteristics of such species:
This niche would be viable in the mesozoic, but not now, due to the
dominance then of terrestrial egg-laying animals. The food source is
of course still available, but is not present in the same quantity,
nor is it as accessible, and no longer can support specialization.
Not having to subdue their prey, they would likely rely on stealth.
This would put pressure on them to reduce their size, and probably
become nocturnal. The reduction in size would be limited if they had
to manipulate or move the eggs, or consume the eggs whole. If they
managed to find some way of eating eggs without moving them, their
size reduction would only be limited by other factors. Dinosaurs are
effective carnivores. The best defence would be avoidance, further
increasing pressure on reducing size.
Their competitors would be snakes. Snakes would also be predators.
However, being endothermic, this would only put pressure on them to
occupy cold climates where snakes are not effective. However, their
prey is more likely to be found, relatively unguarded, in warm areas.
Easy prey for them would be the eggs of large dinosaurs. Due to the
size difference between the adult dinosaur and the egg, those eggs
would be laid in hatcheries, but not tended like birds eggs. In cold
climates such dinosaurs would likely set out hatcheries in naturally
warm areas, perhaps geothermically, or lay eggs big enough to keep
warm by themselves, with a little bit of shelter.
The egg eaters would loose the gizzard. Most other terrestrial
vertebrates higher than an amphibian possess this feature, but it
would be an appendix to a specialized egg eater.
Feeding their young is a problem. It's unlikely their young were able
to forage for themselves immediately after hatching. Current warm
blooded hatchlings are unable to do so, it seems reasonable to suppose
similarly in those times. Otherwise, one would suspect high mortality
rates. Large clutches of eggs would be laid. For a small animal to
lay large quantities of eggs, the eggs would have to be very small,
which is a big problem for small endotherms. More likely some way was
found to bring food to the young. Carrying the eggs away is a big
problem if your primary defense is stealth, so some other means has to
be found. Similarily for the embryo in the egg.
It's possible the egg eaters were furred. If so, the egg matter may
have been congealed somehow on the fur, and brought back that way.
The adult animals would have eaten with lapping or licking motions
once the egg was pierced, so it's not hard to imagine the young doing
the same. Or, the adults could have bled themselves, perhaps as an
evolutionary stepping stone. Other possibilities are a mouth pouch,
to hold egg matter, or hands to hold egg fragments to carry egg matter
back (but I think that's a bit far-fetched).
Their teeth would become specialized for piercing or shearing, to gnaw
through the leathery egg shell. Such teeth could also be used well
for eating insects, which may have provided an alternate diet.
Insects could be brought back to feed the young. Perhaps the young
were fed insects instead of egg remains. Problems with that scenario
are that they wouldn't be specialized egg eaters then, and dinosaur
eggs are probably more nutritious, and numerous. Feeding the young
insects would then likely be a stop-gap measure, until some means is
found to bring egg matter back to the young.
They would have held the niche of cold-climate egg eaters to themselves.
Obviously, I'm hypothesizing that mammals are descended from
egg-eating triassic therians. There would be pressures on the animals
to perfect food transfer to the young. Mammary glands are the obvious
solution, and the animal would evolve from licking egg remains off the
fur, to licking milk off the fur, as does the platypus. Being best as
cold-climate egg eaters, they would have evolved behavioural patterns
to keep their small eggs warm. The inconvenience of such
round-the-clock attendance applies evolutionary pressure to reduce the
hatching time. Hypothesizing a very small size for the animals allows
oxygen transfer to the egg/embryo while still inside the mother,
without specialized structures such as a placenta, which could bring
hatching time to zero. Or, a pouch could be evolved to carry the egg
around, but one wonders about the breakage rate.
--
Rob Janes <ro...@mccoll.mlnet.com>
SysProg/SysAdmin/DbAdmin
Macaulay McColl
Vancouver, Canada
Tim Benham
>Triassic therians specializing in egg eating:
How do you know that?
>Easy prey for them would be the eggs of large dinosaurs.
Would they? Not if the shells were too tough to break open?
>Due to the
>size difference between the adult dinosaur and the egg, those eggs
>would be laid in hatcheries, but not tended like birds eggs.
How do know that dinosaurs didn't tend their eggs?
>In cold
>climates such dinosaurs would likely set out hatcheries in naturally
>warm areas, perhaps geothermically,
Dinosaurs relied on geothermal power to reproduce? I find this a bit
hard to swallow.
> or lay eggs big enough to keep
>warm by themselves, with a little bit of shelter.
>The egg eaters would loose the gizzard.
This fable has me on the verge of loosing my gizzard.
> Most other terrestrial
>vertebrates higher than an amphibian possess this feature, but it
>would be an appendix to a specialized egg eater.
>Feeding their young is a problem. It's unlikely their young were able
>to forage for themselves immediately after hatching. Current warm
>blooded hatchlings are unable to do so, it seems reasonable to suppose
>similarly in those times. Otherwise, one would suspect high mortality
>rates.
I'm not sure I see the connection.
>Large clutches of eggs would be laid.
If mortality rates weren't high why would they lay large quantities of
eggs?
[more and more speculation]
--
People who like this sort of thing
will find this the sort of thing they like.
Tim J.Benham ben...@cs.adfa.oz.au
Flyinggoat
t...@duh.cs.adfa.oz.au (Tim Benham) writes:
Check out Digging Dinosaurs by John R. Horner. It covers studies that
prove that different dinosaur species treated the subject of egg-laying
and rearing young differently. Maiasaurs were very likely doting parents
and raised their young in bird-like rookeries. No dinosaurs were
geothermic, and if you'd have bothered to check on what was current
knowledge of dinosaur egg-laying habits, you'd find they tended to lay
them in upland areas, near streams, in groups, and that several varieties
tended the eggs AND young after hatching. Other species of dinosaur were
hatched ready-to-go and did not need doting parents in order to survive.
The book also covers growth rates of Maiasaurs from embryo to adult very
well. And they grew fast.
Tim Benham
>In article <1994Oct1.1...@sserve.cc.adfa.oz.au>,
>t...@duh.cs.adfa.oz.au (Tim Benham) writes:
> Check out Digging Dinosaurs by John R. Horner. It covers studies that
>prove that different dinosaur species treated the subject of egg-laying
>and rearing young differently. Maiasaurs were very likely doting parents
>and raised their young in bird-like rookeries.
Thanks for the reference.
>No dinosaurs were
>geothermic, and if you'd have bothered to check on what was current
>knowledge of dinosaur egg-laying habits, you'd find they tended to lay
...
None of the statements you impute to me were made by me. You should
take the time to study the documents available in news.announce.newusers.