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

Keratin Preservation (was Ostrom Symposium)



I am quoting a passage from the abstract volume for The Dinofest Symposium, 
April
17-19, 1998, presented by The Academy of Natural Sciences, Philadelphia,
Pennsylvania.  I am providing this information in the interest of clearing up 
some
confusion about Mary Higby Schweitzer's work on the fossils of _Rahonavis 
ostromi_
(referred to below as "a bird from Madagascar") and _Shuuvuia deserti_ (referred
to as "_Mononykus_").  I would appreciate learning of any further articles or
abstracts which document this research, which, as far as I know, has yet to be
thoroughly documented in a scientific paper.  Ultimately, Schweitzer may publish
papers in the 1998 Dinofest Volume or the Ostrom Symposium volume.  Until then,
this brief description will have to suffice.

The latest cladistic analyses characterize the alvarezsaurids (i.e. _Mononykus_)
as nonavian dinosaurs (in contrast to earlier diagnoses which placed them within
Aves).  This being the case, _Shuuvuia_ can be distinguished as the fourth
nonavian dinosaur discovered with the preserved remains of a fiber or feather
integument.  With this in mind, the following passage should be of particular
interest to those seeking to understand the relationship between theropod
dinosaurs and birds.  The quotation follows immediately:

----

CLAWS, BEAKS, SCALES AND FEATHERS: THE EVOLUTIONARY IMPLICATIONS OF KERATIN
PRESERVATION IN THE FOSSIL RECORD

Mary Higby Schweitzer, Dept. of Biology, Museum of the Rockies, Montana State
University, Bozeman, MT  59717

Keratin is the structural protein responsible for making skin waterproof and
durable, and it is the key component of hair, nails, claws, and other epidermal
structures.  The durability and "hardness" of keratinous elements is a result of
the molecular composition and structure of these proteins.

The keratins are a phylogenetically significant family of proteins.  Alpha 
keratin
arose from alteration and subsequent divergence in a protein which constitutes 
the
cytoskeletal system of epidermal cells.  This alteration arose with the
vertebrates, and the cornified skin layers of all vertebrates contain alpha
keratin.  Beta keratin, on the other hand, is a family of proteins which arose
from an unidentified cellular precursor, sometime after the divergence of 
mammals,
and so is unique to reptiles and birds among extant taxa.

Traces of keratinous structures are recorded often in the fossil record.  The 
most
well known of these are feathers, which are found in sediments dating to the
Jurassic, and which are used to identify the geographical and temporal range of
birds.

Although structures originally composed of keratin are not exceedingly rare in 
the
fossil record, it has been assumed that none of the original molecular 
components
persist, and that the structures are mineral replications.  Recent studies,
however, support the hypothesis that some remnants of the original protein
structures remain in at least some specimens, preserved in unique depositional
settings.

Antibodies specific to keratin proteins were applied to two Cretaceous 
specimens.
Fibrous material adhering to the ungual of a bird from Madagascar reacted
positively and strongly to both alpha and beta keratin antibodies, and did not
react to non-specific antibodies present in normal sera, or to antibodies raised
against a non-relevant protein.  This supports the conclusion that both alpha 
and
beta keratins were present in this material, as is the case for keratinous claw
sheaths for modern birds.

A specimen of _Mononykus_ was recovered from the Gobi desert, and small white
fibers were noted in the sediments surrounding the skeleton.  The fibers were
localized to the skeleton, and arrayed in a manner suggestive of feathers.
Microscopic and chemical analyses eliminated plant material or fungal hyphae as 
a
source for these fibers.  Antibodies specific for beta keratin reacted strongly
with these fibers, while antibodies against alpha keratin, antibodies present in
normal sera, and antibodies raised against a non-relevant protein were negative
for binding, a pattern consistent with modern feathers.

These two specimens demonstrate that useful molecular information can be 
recovered
from the fossil record.  In addition, these data may be useful in shedding light
on evolutionary processes within the bird/dinoaur lineage.

----

Ralph W. Miller III  <gbabcock@best.com>