[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pre vs. post K/T mammal diversity: A fair question!

In a message dated 96-06-07 10:31:01 EDT, jbois@umd5.umd.edu (John
Bois) writes:

>     If size _per se_ were so important, why couldn't _any_
>animal of big dimensions step into the niche left vacant by the

I think you missed Mr. Orenstein's point.  Yes, big mammals are more
suited to these niches than are big birds, snakes, lizards, turtles,
or crocodiles.
 But big non-avian dinosaurs are better at filling these niches than
are small mammals.  Until the non-avian dinosaurs were out of the way,
mammals were prevented from growing large and filling the dinosaurs'

>Why don't we see big herds of grazing snakes crawling across the

Because that's not what snakes do.  Their locomotion, dentition, and
digestive systems are wholly unsuited for grazing animals.

> Why no big plain-living lizards, crocodiles, turtles?

Because mammalian limb structure (coupled with endothermy, IMHO) works
better for large, land-living animals.

>Why so very few ground-laying big birds (Ratites had their day, too.
>But still mammals dominated)?

Because there just aren't many niches for big, armless, toothless
bipeds.  I don't recall that ratites were ever all that common.

>So let me pose the question to Pharris, Rowe, and Orenstein: Given
>the species existing immediately after the dino extinction, why was
>it the mammals which finally prevailed in the niche formally [I
>assume you mean "formerly"] occupied by dinosaurs?

Because they were better suited to those niches than were the birds,
crocs, lizards, etc.  But those niches only became available to the
mammals after they had increased their body size, something they had
been unable to do with all the n-a dinos around.

Nick Pharris
Olympia, WA, USA