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sphenos, oil & living fossils



 Just a few comments:

Sphenodontids are rather neat and are major components in some old
localities. Hans Sues et al. describe one as a major part of their
Triassic locality in Nova Scotia - which, if I recall, is the same
locality where the greyhound-like crocs were found, etc.

This brings up the topic of living fossils, which are discussed in bursts
in the literature. From my viewpoint, it mostly indicates a group with
apparently slow evolution in some morphological characters - ones typically
used by systematists. However, comments about them not being changed are
generally flat wrong. You always hear about sharks being unchanged from
the Devonian but all the Devonian sharks I've seen are a good bit different
than those we think of as sharks now. Horseshoe crabs also have changed
but have been generally conservative in overall apprearance. Carboniferous
forms like Euproops look not all that similar to Limulus, just follow the
same basic body plan or "bauplan". I think the term living fossil is a relict
from times where progress was considered to be evident in the fossil record
and where organisms march from the low protistan level to the grandeur of
man. I suspect most paleontologists now view the record rather differently
and evolution serves to move along all sorts of vectors simultaneously,
sometimes with true innovations along some lines, but also frequently coming
to the same solution at times. The croc niche has bee filled more or less
continuously by major groups since, what, the Carboniferous. Also, some
living fossils also end up being rather simple morphologically in which
case the lack of difference between old and young is more an expression of
lacvk olf characters than lack of evolution. For example, there are forams,
I believe, with a Cambrian to Recent range which turn out to be simple
morphologies that have been re-arrived at many times in history. So, yes
the tuatara is from a relatively ancient group and looks like it's breathern
in the group, but that's not all that uncommon. That also brings up atavistic
characters that disappear in lines but pop back up through various complex
developmental pathways. It's a fun area that is probably the least understood
and less well-presented part of paleo presented to the public by whoever. It's
good press to say something's not changed since the Carboniferous, even the
the real answer is very different and much more complex.

The dino/oil connection has really blossomed since the ads many years back -
wasn't there a reference also in the old movie Airport? I've heard many
references and stements about dinos generating oil. Derek, I think it was him,
was pretty much on the mark though. Oil comes from the proper cooking of any
concentration of organic material that then migrates and concentrates in
one place, molstly through various traps. The latter are one age, the former
most typically of another, generally older than the trap but not necessarily
given structural complexity. I know source rocks range greatly in age from
pretty young back to the Cambrian (I believe there's Cambrian oil in Russia).
It's a neat and tough field to work in, have had friends do it. Dinos
probably have contributed to some oil fields - probably small ones or small
contributions, since biomass is much greater in lots of plants or marine
things

Ralph Chapman, NMNH