Re: Jurassic Park

[Jeff Poling <jpoling@dinosauria.com>]

At 12:49 PM 9/27/98 -0400, TRUETT GARNER wrote:
>About as many as has been found with feathers.

   If you are going to be consistent then you need to draw them with no skin
and soft tissue at all since none have been found.

> Prove they had feathers and
>I'll draw them that way .

   Prove they had bumpy, naked skin.

>Last time I looked ,
>Dromaeosaurids were still considered non-avian theropods , not birds.

   One non-avian theropod had feather-like integument, while two theropods
the authors consider non-avian had true feathers.

>And
>BTW, I didn't say ANY Velociraptor had been found with skin
>impressions( note ' etc. ' ). I was referring to the meager amount of skin
>impressions found with any dinosaurs  to date . Parsimony or not , 
>there's enough gaps in the fossil record to justify drawing them without
>feathers .

   Then what justification do you have of drawing them with any other type
of skin?  Those "fossil gaps" apply just as well to the bumpy skin you
prefer.  The argument for no integument is even shakier since none of the
skin impressions were found where such structures would have been preserved
had they been present.

>The relationship between Dromaeosaurids and Aves
>is the best educated guess at the moment , untill the ' latest and greatest
>' find proves it wrong 

   An **educated guess**?  I think it's worthwhile reprinting something
Gregory Paul sent to the list in 1996.  He draws the same conclusion you've
apparently drawn (that palentology is full of "guesses," not rigorous
science) for exactly the OPPOSITE reason.  It also addresses the issue at
hand (note that it is somewhat dated).

FROM GREGORY PAUL:

<P>I have over the years been concerned that paleontology is not always
practiced as a rigorous science (some nonpaleontologist scientists have
expressed the same concern to me). The issue of feathered dinosaurs well
illustrates the problem.

<P>Back in the mid 70's Disco was King, and at that time the [first
suggestions were presented] that the probable ancestors of birds, the
possibly endothermic theropods, were feathered. This inspired some artists,
including me, to illustrate small dinosaurs with some form of pelage
[insulatory covering], usually some form of feathers. This is were the
science problem began.

<P>A number of paleontologists vigorously objected to restorations of
feathered dinosaurs. Sometimes they did so derisively and harshly -- odd how
emotional people can get about a little dinofluff. The basic scientific
argument was something like this. Dinosaur "mummies" show that dinosaurs had
scales, like ectothermic reptiles, not feathers like endothermic birds. No
feathers had been found adorning small dinosaurs. Parsimony therefore
favored scales in dinosaurs; feathers were too speculative. Some researchers
had somewhat more complex and subtle arguments as to why

<P>This argument was always false. The scaly skin was and is limited to
large dinosaurs. If mammals were extinct, and only the skin of fossil
elephants and rhinos were preserved, then some form of insulation would be
ruled out in small mammals by the above logic. Parsimony would favor scales
in small dinosaurs only if both their ancestors AND descendants were scaly.
As it is, with scaly ancestors, and feathery relatives, parsimony was
neutral on the issue. The question could be answered only by direct fossil
evidence. The evidence was also neutral because no integument had been
clearly preserved on any small dinosaur. Example -- claims that the lack of
feathers on the famous <I>Compsognathus</I> specimen contradicted their
presence were spurious because scales were not found either! Nor are body
feathers present on all but one of the <I>Archaeopteryx</I> specimens from
the same sediments. Viewed objectively, restoring <I>Compsognathus</I> and
other small dinos with feathers, scales or nonscaly skin was equally
speculative and plausible! Yet the majority opinion always nonobjectively
presumed that scales were less speculative than feathers. I took a gamble
and consistently restored small theropods with feathers, a bet that seems to
have paid off at least in part.

<P>What do we currently know about the integument of small dinosaurs? I have
only seen a rather poor color photo of the Chinese theropod
[<I>Sinosauropteryx</I>]. However, Currie has seen the original and says
that it clearly has feather-like structures similar to those of birds from
the same sediments. Although the feathers are entirely peripheral to the
body on the slab, this is typical of bird fossils. A full body covering is
very possible if not probable. There is some evidence that the structures on
the underside of the tail base are intermediate to scales and feathers.
There may be more specimens from the same sediments, [and] certainly more
can be expected [which] will help solidify the data base one way or another.
The rest of the discussion assumes the specimens do have short ratite-like
feathers, but no contour or long feathers.  [09/27/98 NOTE:  now that
_Sinosauropteryx_ is known to be a compsognathid, parsimony dictates that
members of the clade comprised of the  most recent common ancestor of
_Sinosauropteryx_ and feathered things (most notably birds) had some sort of
pelage.  That includes _Velociraptor_.]

<P>The E. [Early] Cretaceous theropod appears to be broadly similar in form
to L. [Late] Jurassic <I>Compsognathus</I>, with short arms, and a long
rather heavy tail. If so it is a basal tetanuran, much less advanced than
more bird-like theropods which show flight adaptations.

<P>A partial small theropod from the E. Cretaceous of South America was
reported to have naked nonscaly skin in <I>Nature</I> (1996, 379:32). No
clear photos of the skin surface were published, and it is not clear whether
the outer skin layer had been lost. More data is needed.

<P>Also in <I>Nature</I> (1994, 370:363) it was reported that the E.
Cretaceous ornithomimid <I>Pelecanimimus</I> has an integument of uncertain
nature. Again more data is needed.

<P>The only small ornithischian skin reported was a nonscaly, punctured
surface on <I>Thescelosaurus</I> earlier in this century, but the integument
was not figured and is not accessible.

<P>The combined data suggests but does not prove that feathers evolved in
terrestrial theropods well before the evolution of birds, at least by the L.
Jurassic and in tetanuran theropods. How much earlier feathers may have
evolved is not clear, so Triassic and earlier Jurassic theropods may or may
not have been insulated.   Therefore artists should feel free to restore
<I>Coelophysis</I> with or without feathers. If someone tries to tell you
otherwise just subtly roll your eyes, or smile enigmatically yet knowingly -
its what I used to do.  Feathers are highly probable in the advanced
bird-like theropods. What small ornithischians were wearing is up for grabs.

<P>The probable presence of feathers in at least some small theropods has
important metabolic and thermoregulatory implications. Recently it has been
asserted that the presence of feathers does not necessarily indicate
endothermy, contrary to a long opinion otherwise. This is based on [several]
arguments.  [One argument is that] early birds could only have powered
flight with the small reptile-type muscles their small sternal plates were
able to support.  This is false because some modern flying birds have flight
muscles much smaller than the avian norm, and early bird arms and shoulder
girdles were large enough to support them. Another argument is that early
bird bones show they grew slowly like reptiles. However, the thin walled
bones of the fossil birds do not preserve the period of juvenile growth,
which may have been rapid (the growth rings only indicate that the birds
continued to grow slowly as adults). Last, some birds bask. This, however,
only shows that endotherms bask with insulation. The observed temperature
rise is too modest for reptiles.

<P>Which brings us to the point that all the many thousands of insulated
tetrapods are endothermic. Even furry insects tend to be endotherms.
Insulation prevents ectotherms from rapidly absorbing the large amounts of
heat they need from the environment. This problem is so serious that even
desert reptiles cannot use insulation as a solar screen. Only endotherms
that need to retain body heat are insulated. Ergo, insulation is always
excellent evidence for endothermy. Also for resting metabolic rates above
the reptilian level. Therefore, ecothermy is effectively falsified in
insulated dinosaurs and birds.
** Dinosauria On-Line. Home of THE DINOSTORE ** "Those who trade a        **
** (Dino stuff for sale), Jeff's Journal of  ** little freedom for a      **
** Dinosaur Paleontology, Jeff's Dinosaur    ** little security will soon **
** Picture Gallery, and The DOL Dinosaur     ** find they have none of    **
** Omnipedia. http://www.dinosauria.com      ** either." -- Jeff Poling   **
*************** The official website of the new millennium! ****************