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

Re: Carboniferous Endothermy



Christian Kammerer wrote:
<With hair evolving probably among the more advanced theriodont therapsids,
there becomes a 120 million year gap between your fuzzy salamanders and hair,
a gap filled with scaly, smooth- skinned, or scuted animals of every color,
race, and creed, but with no follicles similar to or ancestral to those found
in modern mammals and birds.
    I would advise both Mr. Hopp and Mr. F to drop this debate as it is almost
entirely an untenable position, and I hate to sound like I'm ranting.>

and LarryF wrote:
<I`ll drop the "debate" for now, but feel that some type of test of a possible
"one-time" development of endothermy should be performed against a recognized
phylogeny. Can anyone suggest how I may go about this? Is there a formula I
can use? (P.S. I`m new to computers as well,...is there a program that I can
run to test my ideas cladistically?).>

on another thread, Dinogeorge wrote:
<It is also possible that scales and feathers developed independently from the
same kind of dermal structure in the common diapsid ancestor of both lizards
and birds. I suppose that tests of the chemical composition of scales, croc
scutes, and feathers in extant reptiles would shed some light on the issue.>

So here goes:
    One parting pronouncement, if I may.  Watch out for genomics.  The human
genome (not to mention mouse, chicken, and gosh knows what else) is well on
the way to a complete "printout."  Among the molecular fossils that will be
uncovered are a bevvy of gene sequences that derive from common ancestral
genes and can still be related by homology.  When such gene products as
keratins, metabolic enzymes and homeotic (body structure) genes are marched
out, lined up, and compared, much revelation will be at hand.  This should all
take place in the next ten years, so don't dig any entrenchments too deeply.
    One of the first-ever looks into keratin gene structures showed that
feather keratins appear to have evolved out of scale keratins via gene-
duplication and divergence at least [emphasize AT LEAST] 120 million years ago
(K. Gregg et al., "A comparison of genomic coding sequences for feather and
scale keratins: structural and evolutionary implications." The EMBO Journal
3:175-178, 1984).  More recently, the genes that cause asymmetry in embryonic
feather buds have been traced to three loci (by my old buddy Cheng-Ming Chuong
et al., "Asymmetric expression of Notch/Delta/Serrate is associated with the
anterior-posterior axis of feather buds." Developmental Biology 188:181-187).
If these loci haven't been sequenced yet, they will be soon.
    Regarding endothermy, it may seem like we'll never get the origins of this
physiological process out of the fossil record, but don't you bet on it.  The
hypothalamus regulates body temperature via nervous and hormonal signals to
such body parts as brown fat tissue, skeletal muscle (for shivering) and a
bunch of as-yet-poorly understood metabolic pathways.  As the genes that
regulate these structures/processes are identified and sequenced -- let me
make you a prediction -- the fossil trace of the origins of endothermy will be
there to be seen, all written out in A's, T's, G's and C's, and will tell a
tale of single-origins.  And when they calculate the molecular mutation-rate
clock backward in time, I think they will come up with Devonian. Can't hardly
wait, myself. How 'bout you?
    Tom Hopp
P.S. For future reference, I led the team of molecular biologists that cloned
and sequenced Interleukin-1, a fever producing hormone that can raise body
temperature by several degrees.