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Re: Tar and feathers

Mike Taylor wrote:
> Mike [Keesey] points out that the big, naked animals we have now -- elephants,
> rhinos, hippos -- all have young that are proportionally much closer
> in size to the adults than a fresh-hatched _Carnotaurus_ would be to
> its parents, so there would have been more _advantage_ for a baby
> 'taur having fluff than for a baby elephant.  But still, I'd be
> hesitant about claiming to be _confident_ about something that we
> don't see in broadly analogous (= "big" :-) animals today.

Hippos are aquatic, and water tends to retain heat better than air, so
perhaps hairless young aren't all that surprising. The problem with
using mammals as analogues for endothermic reptiles is that mammalian
young have to stay close to their mothers in order to suckle. So if a
young rhino or 'hephalump' get cold, they have only to snuggle up to mum
in order to get warm. Since the very young require feeding at frequent
intervals, they are already in close proximity to begin with.

Can we be sure that dinosaurs had the same close bond with their
offspring as mammals do? I have trouble imagining an adult Maiasaura
snuggling up to tiny hatchlings to keep them warm. Even pandas
occasionally smother their tiny young to death - imagine the damage an
adult hadrosaur could do shifting in its sleep. In fact, a mother hippo
here in Melbourne rolled onto her offspring at night and killed it not
too long ago.

Ostrich chicks are completely covered in feathers, whereas adult males
have naked heads and necks. I suspect chicks also have fuzz on their
thighs (which adult males lack). Cassowary chicks also have fully
feathered necks and heads, which become bald as adults. Megapode chicks
are also fully fledged, whereas the adult males have naked heads and
necks. I suspect the same is true for bald-necked vultures and storks. 

So some ontogenic loss of feathers is known amongst modern theropods.
Take away the need to fly, and make the adult body sizes larger, and who
knows how many feathers adult birds could do without?


Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/