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quantifying bias in the fossil record



I haven't obtained the Dodson paper on dinosaur diversity yet.  I hope I
will be able to get it, but as usual I am not optimistic.

Meanwhile, I am wondering if this or any other paper looked at the patterns
of fossilization of extant taxa to get an idea of how the fossil record is
biased.  Looking at extant amniote species, it seems that large species are
well represented in the Pleistocene record, and the proportion of fossil
species decreases dramatically with size.  I wonder if anyone has
quantified this, and/or looked at the skeletal characteristics of the
species involved in relation to their appearance in the fossil record.

It has been argued that small dinosaur species were there but are simply
missing from the fossil record.  Basically I agree, but there are a number
of small mammals from the Mesozoic.  Are many of these species only known
from teeth?  Also, it is curious to me that there are so many passerine
bird fossils from the late Cenozoic.  Is this because birds are so mobile
and fall into more environments that promote fossilization?

It has also been argued that time removes fossils from the record.  But
during the course of the Cenozoic, we see the number of fossil genera among
amniotes fluctuating within fairly well-defined limits until the
Pleistocene.  Then we see a sudden surge in the diversity of all amniotes,
which is surely an artifact.  Other than this I don't really see much
evidence of the loss of fossils from the record over the course of the
Cenozoic.

With regard to the selective fossilization of forms by habitat, the
numerous Pleistocene mammal fossils should give a good idea of this.  Many
of these are small mammals and it seems to me that very clear relationships
could be drawn between body size, habitat, and probability of fossilization.

It is striking how few lizard fossils exist, considering there are over
4000 species of lizards alive today.  Most lizards are small and the fossil
record is tremendously biased toward large species.  The same is true of
snakes.

With all of these data it should be possible to build a fairly coherent
picture of fossilization, particularly with regard to body size.  Just as
astronomers have built a picture of asteroid size distribution,
paleontologists should be able to reconstruct an approximate size
distribution of dinosaur species, and get fairly good estimates of dinosaur
diversity.  No doubt there are pieces of evidence that can be brought to
bear that I have not mentioned or even thought of.

Of course we will never see many dinosaur species as fossils.  But when we
consider that we have literally only scratched the surface for fossil
remains, it is tantalizing to consider what is probably still out there.
Thoughts of volcanic ash falls really get my juices going.

Best regards,

Dave