Saturday, 15 March 2014

The power of X-rays

It is often the case that fossil specimens are preserved within a matrix of rock where some parts lay over other parts. In the case shown below, the skull of this pterosaur is laying across the wing bones. Without some form of scan, the skull would have to be removed to see the bones below.
An X-ray of the fossil matrix can, in many cases, reveal the bones that are concealed below the skull. X-rays of fossils depend upon variations in radio-density of the materials. If the fossil bones are replaced with different material than the surrounding matrix and have variations in density within the structures themselves, an X-ray can reveal quite a lot of detail.
Interpretation of X-rays is quite a skilful task. analysis of detail requires a great deal of knowledge about the nature of the materials that the X-rays are passing through. The analysis of this X-ray shows the interpreted wing bone positions marked.
It shows in this case, that the Wing Metacarpal has sustained a stress fracture, probably during launch for flight. This break does not have the radial signature of an impact fracture and it was probably caused by the bone at the point of fracture being too thin to sustain the stress of extreme latteral pressure. If this animal fell into the sea with one wing broken in this way, it would be unable to take off and would probably have starved to death or become a victim of small marine carnivores picking at its flesh.  There is no lower jaw associated with these remains, so that probably detached prior to fossilization.
The fossil X-ray will only show the preserved hard parts of an animal. The use is very limited, unlike this X-ray of one of my cats, which shows a good deal of soft tissue structure and variation in bone density where the bones are in their living orientation.

Wednesday, 18 December 2013

Pterodactyl Bookmark

 This little offering came from Webberleys bookshop in Hanley, Stoke-on-Trent.  It is by Cool Creations Ltd, Rudgate Business Park, Tockwith, York, YO26 7RD.  Most good bookshops should have one.

Monday, 21 October 2013

Thoughts on a head crest

 The skull of Tapejara wellnhoferi has bony extensions to the upper and lower mandible and a long spinous bone extending back over the top of the skull.  There is no evidence of soft tissue crests in this species, but since the other tapejarids; Tupandactylus navigens and  Tupandactylus imperator have soft tissue crests it is probable that T. wellnhoferi also had a soft tissue crest.
We can speculate that without the bony spine above the mandible, the crest would need to be small, or flexible.  Perhaps it was inflatable using blood or air sacs.  This would be an interesting notion!
As soft tissue is seldom preserved and in the case of pterosaurs, occasionally seen as just a residue with no structural detail preserved, any speculation could be valid.
Many illustrators see colour preserved in these crests.  I am not sure of this and it seems more likely that the difference in colour seen in some fossils may actually be an artifact of the preservation.  The impression of colour is more likely to be due to differences in tissue density, tissue type or the chemistry of fossilisation.  Give a thought to the scientists who have to interpret this evidence.  It is easy to see things that are not there, just to make sense of the evidence that is there.  Anyway, I like the thought of pterosaurs being able to fold and display soft tissue crests, even if the evidence is not present in the fossil record - or is it?

Friday, 11 October 2013

Royal Mail Dinosaur Stamps

 The Royal Mail have issued their dinosaur stamps.  Fist day covers were only available at Post Offices on 10 Oct 2013, but the stamp sets are still available where stocks last.
 The art work on these stamps is by John Sibbick.  His work is found in many pterosaur publications.  Text on the cover card is by Angela Milner from the NHM London.  There are two pterosaur stamps in the set of 10 fist class stamps.  It is interesting that all of the stamps have an area of printed image that extends beyond the normal edge of the stamp, requiring a special perforation cut for the sheets.
 Ornithocheirus represents the pterodactyloid pterosaurs. This species was first described by Harry Govier Seeley in 1869, though the fossils had been known of since 1827.
Dimorphodon represents the older rhamphorhynchoid pterosaurs and was described by William Clift and William John Broderip in 1835.  This description was based on a fossil that was discovered by Mary Anning in 1828.

These stamps are available over the counter at all UK post offices whilst stocks last.

Royal Mail Collectible stamps

Tuesday, 17 September 2013

Pterosaur toy

This 8cm high orange wind up hopping dinosaur toy is distributed by H. Grossman, the Scottish Dinosaur Toy company.  You wind it up and it hops for a good few seconds.  No pterosaur enthusiast worth their salt should be without one.  It has kept our cats amused for seconds.

Friday, 7 June 2013

Can You Help

Isidro Martínez has just sent me a photograph of a pterosaur skull in the Museum Mensch und Natur in Münich, Germany.  It displays a very good crest and the teeth are preserved mainly in situ.
The fossil is new to me and I would like to know more about it.  The museum display has no label or information and I have been unable to contact the staff directly. Can any one help with information on the specimen?

Sunday, 12 May 2013

Axial Skeleton

Recently, I have been asked to identify a number of pterosaur vertebrae.  Most of them were of small theropod dinosaur cervicals from the Kem-Kem formation in Morocco.  Pterosaur vertebrae in isolation requires a skilled eye to identify them, so I thought it would be a good idea to look at the axial skeleton of Pteranodon as the vertebrae are quite well documented.  I am going to gloss over the pectoral and pelvic girdles here.

This is a drawing from the website of the combined atlas and axis and the first cervical vertebra of pteranodon.  It is based on a drawing by Eaton.  Notice the pneumatic foramen (pn) where an air sac tube would pass to permit the interior of the bone to be filled with air.  This considerably lightens the skeleton for flight - pneumatic bones are also found in theropod dinosaurs like T-Rex and in the suropods.
The dorsal vertebrae of most pterosaurs are very short and have attachments for ribs.
Sacral vertebrae are fused and support the pelvis.  There are no articular surfaces and the vertebrae are joined by suture jointing, known as ankylosis.
Caudals are short and uninspiring and often look like the caudals of many other species, so in isolation they are indistinguishable from ichthyosaurs and many other large vertebrates.

The axial skeleton is seen to be arranged in functional sections.  The pectoral and pelvic girdles have been omitted here.

Ax is the combined atlas and axis which joins the spine to the skull.  This was quite a solid bone.

A shows the cervical vertebrae that make up the neck.  In Pteranodon, these were sturdy and had large dorsal spines to anchor the muscles that positioned the skull, with its large occipital head crest.  The joints had a good range of movement.

B is the Notarium.  This is a region of the spine where the thoraxic vertebrae are ankylose and support a fused region of bone that articulates with the scapulae.  The scapulo-coracoid is a strong bone that was anchored at the notarium and the sternum.  This forms the pectoral girdle which had to take the strain of the wings in flight.

C is a region where the dorsal vertebrae are not fused.  This region gave a small amount of flexion between two very solid and rigid regions of the back.  These few vertebrae held floating ribs.

D is the sacral region.  Like the thoraxic vertebrae attached to the notarium, the sacrals were fused and attached to the pelvis.

E In pterodactyloid pterosaurs, the caudal vertebrae were simple and very lightly muscled.

Half of the length of the axial skeleton in pteranodon is neck.  The neck is of a similar length to the skull.  The spine behind this region is mostly rigid, forming a solid box which gives the skeleton a sturdy structure to stabilise the wings in relation to the body, when the animal is in flight.  This was a very well adapted animal for flight.

Most large pterosaur axial skeletons show close similarities to pteranodon.  Most of the small pterosaurs also have these overall features, with minor variations.  This type of spine is essential for flying animals and this principle structure is also seen in all flying birds.