pterosaurs

[J M V Rayner <J.M.V.Rayner@bristol.ac.uk>]

> 
> I have read of a small pterosaur found in Russia in 1970 that left fur
> impressions. Has any other pterosaur been found with fur or hair impressions?
> And is the 1970 find of good quality, or is there some doubt that the
> pterosaur did have hair?
> 
> 

The pterosaur you refer to is _Sordes pilosus_, which was found in
Kazakhstan, and described by Sharov in 1971

Sharov, A. G. 1971 New flying reptiles from the Mesozoic of Kazakhstan and
Kirghizia. Trudy Paleont. Inst. Akad. Nauk SSSR 130, 104-113.

This specimen had extensive `fibrous' material, which Sharov described as
hair, and hence gave rise to the animal's name. Some further comments on
this specimen were made by Unwin & Bakhurina in Nature September 1994.
They attributed the `hair' to the structural fibres which (some of us,
at least, believe) are an essential mechanical component of the pterosaur
wing.

In this view, the fibres form an array of probably keratinous strips across 
the entire surface of the wing membrane. They acted as stiffeners giving
the membrane its structural rigidity under aerodynamic load (a bit like
the spokes of an umbrella), and transmitted the mechanical force from the
wing surface to the skeleton. These fibres (or their imprint/mould) are
commonly preserved in specimens from Solnhofen, and also occasionally in
other material from (among other places) Holzmaden, Santana, Bergamasque
Alps, from Triassic to late Cretaceous deposits in all groups of
pterosaurs. It is expected therefore that Sordes would have such fibres,
and if the preservation is sufficiently good, as it appears to be, that
the fibres would be present. In some specimens, particularly from
Solnhofen, the preservation is spectacular with the wing shape evident and
with fibres extending over all or large parts of it: particularly noteworthy
are a Pterodactylus in Vienna, the Marsh Rhamphorhynchus at Yale, and a
Rhamphorhynchus wing (the Zittel wing) in Munich. 

For more details, references and a list of (around 80) pterosaur specimens
with fibre and other soft tissue preservation see

Padian, K. & Rayner, J. M. V. 1993 The wings of pterosaurs. Am. J. Sci.
293-A, 91-166.

The fibres were first described in the 19th C (classic papers by Zittel
and Marsh), and were worked on most recently by Peter Wellnhofer at Munich
and Kevin Padian at Berkeley: you'll find all of the references in the above
paper. 

I should note that Pennycuick argued that the fibres were nothing more
than wrinkles in a homogeneous membrane (this claim was disproved by P & R).

Pennycuick, C. J. 1988 Biol. Rev. Cam. Phil. Soc. 63, 209-231.

Muscle Fibres
-------------
The fibres often appear as fragmented areas of striations around a
specimen, most usually in the area of the wings or the trunk. The patchy
distribution is presumably due to the nature of the substrate and the
process of fossilization. Abel identified these areas as muscle fibres in
two Pterodactylus specimens in the AMNH. This is probably a
misinterpretation: they look just like wing fibres. This is probably where
the idea of muscle fibres originated. As far as I know there is no evidence
of skeletal muscle preservation in any pterosaur, apart from the Santana
specimen analysed by Unwin & Martill, which is of uncertain topography and
has recently been described (by Kellner) as not belonging to the wing.

Abel, O. 1925 On a skeleton of Pterodactylus antiquus ... with remains of
skin and musculature. Am. Mus. Novit. 192.

Martill, D. & Unwin, D. M. 1989 Nature 340, 138-140.

One correspondent commented muscle fibres could not appear in the middle
of a membrane. I'm not certain they were there in pterosaurs, and am sure
that is not what we are seeing. However, muscles in membrane are an
essential component of the way the bat wing functions.


Hair 
---- 
This is equivocal at the moment. Many of the better preserved
specimens from Solnhofen and Holzmaden have two separate evidences of
hair: regions of `fluffy' striations, less regular and organized than
fibres usually are, or regions interpreted as smooth skin with patterns of
pitting which resemble hair follicles. For more details see Padian &
Rayner, above; the earliest workers on this were Doederlein and Broili,
both at Munich; Broili was obsessed with finding hair on Mesozoic
reptiles, and amassed an impressive collection; his findings with
pterosaurs do hold up to modern reexamination, however. The pitted 
skin areas are often far from the wing, and cannot be interpreted as wing
fibres. Unwin & Bakhurina have claimed that the hair on Sordes is actually
wing fibres (I have not seen the Sordes specimen so cannot comment on
this), and the same might be true for some of the other specimens such as
the Holzmaden _Dorygnathus_. 

It would be nice to think that pterosaurs had hair (and could
thermoregulate), as this makes better physiological sense for an active
flier than reptilian poikilothermy. The jury is, however, still out. 

Contact me for any further details.

Jeremy Rayner


+++++++++++++++++++++++++++++++++++++++++++

Dr Jeremy M. V. Rayner 
School of Biological Sciences
University of Bristol
Woodland Road
Bristol BS8 1UG   
U.K.

tel. +44 117 928 8111, messages 117 928 7476, fax 0117 925 7374

e-mail J.M.V.Rayner@bristol.ac.uk