Highlights of 2009

There have been some remarkable finds published in 2009. Something of a stepping stone in the understanding of pterosaur evolution.

1. Changchengopterus pani was found in Upper Jurassic rocks in China. It is a basal, non-pterodactyloid pterosaur. Basal simply means a more primitive form of pterosaur with characteristics of much earlier species.

2. Darwinopterus modularis is a Middle Jurassic pterosaur with an interesting combination of Rhamphorhynchoid and Pterodactyloid features. A whole new branch of classification had to be devised to accommodate this fossil between the Rhamphorhynchoids and Pterodactyloids. This is a good example of what Darwin meant when he developed the idea of modular evolution. Different characteristics developing at different times within a family of animals.

3. Wukangopterus lii is another Upper Jurassic Rhamphorhynchoid from China. It has a long toothed skull and shows more primitive features than Rhamphorhynchus.

4. Another Pterosaur track way has also been published. Pteraichnus nipponensis is a distinct and new type of pterosaur track way from the Lower Cretaceous. It was originally discovered in 1990 at Kiladani Dinosaur Quarry in Japan and it has just been published. This paper makes the point that most Cretaceous pterosaurs are very large species, but this and other track ways were made by smaller pterosaur species. There must be many fossils out there still to find.

There are a number of other pterosaur finds which are being worked upon at present and some of them are remarkable fossils. Hopefully they will be published soon, so that they can enter the scientific discussions and shed new light on the development of this interesting group of ancient fossil animals.

Happy New Year.

1. Lü, J. 2009. A new non-pterodactyloid pterosaur from Qinglong County, Hebei Province of China. Acta Geologica Sinica (English Edition), 83(2): 189-199.
   
   
2. Lü J. Unwin D. M., Jin X., Liu Y. and Ji Q., 2009, Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B. Published on line 14 Oct 2009.
   
   
3. Wang X., Kellner A. W. A., Jiang S. and Meng X., 2009, An unusual long-tailed pterosaur with elongated neck from western Liaoning of China. Anais da Academia Brasileira de Ciências 81 (4):793–812.
   
   
4. Lee, Y.-N., Azuma, Y., Lee, H.-J., Shibata, M., and Lü, J., 2009., The first pterosaurtrackways from japan. Cretaceous Research

Comparative Studies

By looking at specific features of the fossil skeletons of pterosaurs it is possible to compare them to see how closely individuals are related. The science of comparative anatomy is limited in its application, but it is a very useful tool when dealing with fossil species. For instance - does Pterodaurstro fit more closely with the Pterodactyloids of the Rhamphorhynchoids.By looking at a comparison of wing bone lengths in relation to the wing metacarpal bone, it can be seen that the shape formed on the above graph places Pterodaustro clearly alongside that of a Pterodactyle. In many cases, the relationship of the wing bones to the wing metacarpal can be used to distinguish families of pterosaurs. However, this type of analysis should be used with caution as there are a few exceptions to the rule. Other features like skull anatomy, vertebra structure and pelvic anatomy are also needed to confirm any comparative relationships.

This graph shows the wing profile relationships between two individuals of the same species of pterosaur, found within the same sediment. The slight difference is likely due to natural variation.
Here is a wing profile graph that is generated from two unrelated pterosaurs from different sites at about the same geological age. The pterosaurs look similar in most features, but the analysis suggests significant differences in wing bone development.
When using comparators, patterns will emerge to indicate differences. Scatter graphs will often be a useful way of determining differences. The above plot shows the relationship between wing metacarpal length and first wing phalanx length in a random selection of pterosaurs. The differences between the Rhamphorhynchoid pterosaurs and the Pterodactyloid pterosaurs can be indicated by circling each group.
The final graph shows a calculated plot based on the relationship of measurements for the humerus, ulna and wing metacarpal. In this plot, there is no overlap between the two major pterosaur groups within this sample. The scales displayed are arbitrary units in the plot calculations.

Comparative anatomy is all that we can use for direct comparison of extinct fossil species. It gives a very good indication of relationships and enables structure to be developed in an evolutionary hierarchy. However, whilst this is a useful tool, it is only a guide and must be treated as such. It is often down to individual opinion as to how accurately the selected comparator work. This is why scientists develop slightly different evolutionary trees of the pterosaurs. Each may be valid within the scheme of analysis and each should be respected in that light.

Good science is all about debate and discussion but in the case of fossil analysis the picture is often quite disjointed. differences of opinion are what makes this subject interesting.

Pterosaur Eggs

Speculation about how pterosaurs reproduced has been enhanced over the years by lack of evidence. Many scientists believed that pterosaurs must have laid eggs, but were they hard shelled as in birds, or leathery as in reptiles. To some, the thought of how a long bony wing would work in an egg was a problem to imagine. Bats give birth to live young without the need for eggs, so perhaps pterosaurs could also give birth to, live young.

Speculation became analysis when, in 2004, a pterosaur egg fossil was found in China.


Avodectes pseudembryon (Wang and Zhou 2004), IVPP-v13758, was discovered in the Jehol Biota, being about 121 million years old. It was a complete embryo in a shell. The wings were coiled as they developed (sketch above) and the preservation indicates clearly that the bones were well ossified before hatching. This would enable the newly hatched pterosaurs to use the wings very quickly after emerging from the egg.

Observations of the porosity of the egg shell suggested possible burial during development and the form of the shell was soft and leathery like a reptilian egg, having a shell that was non-laminar and 0.25mm thick. The embryo wingspan was estimated to be 27cm. The bone proportions are unlike any known pterosaur, but show similarities with Anhanguera and Istiodactylus specimens. This should not be taken as an indication of species, since the bone development and proportions may have been subject to changes during juvenile life.

A second egg, JZMP-03-03-2, was somewhat similar, but the skeletal bones were not articulated in the same clear way, so interpretation is a little more complex.
In the same year, a pterosaur egg, MHIN-UNSL-GEO-v246, was discovered in the Lagarcito Formation in Argentina. This formation is well known for the Pterodaustro fossils and this egg was clearly a Pterodaustro egg. The embryo was intact and articulated.
The egg was also from the Lower Cretaceous deposits about 100 million years ago, and the proportions of the embryo closely matched those of known juvenile specimens. Measurements of the shell indicated a very thin (30μm) leathery shell which was long and oval in shape measuring 22mm by 66mm. The estimated embryo wingspan was 27cm. This egg has many differences from the Chinese finds, but it does support the idea that all pterosaurs probably laid eggs.
The questions that are difficult to resolve are;

1. How many eggs did pterosaurs lay?
2. Did pterosaurs care for their young?
3. Where did pterosaurs nest and what nesting structures did they create?

I suspect that the answers to these types of questions will be different for each type of pterosaur. These creatures would have been subject to the same variations and constraints in their habitats as modern animals are subject to today.

Wang, X., and Zhou, Z., 2004, Pterosaur embryo from the Early Cretaceous: Nature, vol.429, p.621.

Chiappe, L. M., Codorniu, L., Grellet-Tinner, G., and Rivarola, D., 2004, Argentinian unhatched pterosaur fossil: Nature, vol.432, p. 571-572. (2 Dec 2004) 

Pterosaur Database Topics - eggs
 

The Pterosaur Brain

In 1888, Newton published the first account of a pterosaur brain exposed in a skull from the Lias at Whitby, North Yorkshire. The skull fossil had to be excavated to reveal the exposed brain more fully. Before the work, a number of casts of the original were made and one such cast is shown below.

Perhapsicephalus purdoni, National Geographic Survey, Nottingham.

The brain fossil showed the main lobes clearly and the auditory and semicircular canal structures were identified during excavation of the skull. The analysis applied to the brain by Newton suggested that the brain of the pterosaur was in many ways similar to the brain of a lizard, but in some respects it was charactaristically similar to the brain of birds. His conclusion was that pterosaurs, birds and lizards evolved from common ancestors.

In 1941, Tilly Edinger, a German physiologist, examined two distinct pterodactyl fossils where the brain was exposed. Her findings were similar to those of Newton, but with the advantage of the intervening progress of science since the earlier investigation, Edinger was able to make a more defined conclusion about structure.

Pterodactylus elegans, MCZ, No. 1505

The pterosaur fossils that Edinger worked with had been described by several earlier and well respected German scientists, though the work that they did was descriptive and comparative. This later work looked more closely at the structures and extrapolated the knowledge to a general description of the pterosaur brain for the first time.

Developments in the brains of pterosaurs show similarities with the development of the brain in birds. These changes are attributed to the requirements of flight, with a more developed optic lobe and a fissure (Vallecula Silvii) like that found in the fore brain of birds. At this point there is no evidence for the structure of the base of the pterosaur brain.

These are the two defining works on the nature of the pterosaur brain. With the advance in medical scanning techniques, the destructive analysis of pterosaur brains is a thing of the past. It is now possible in some cases, to examine the cranial cavity of a fossil by electronic means to develop an understanding of its brain anatomy.

Newton E. T., 1888, On the skull, brain and auditory organ of a new species of Pterosaurian (Scaphognathus purdoni) from the Upper Lias near Whitby, Yorkshire. Proceedings of the Royal Society, London. 43, pages 436–440.

Edinger T., 1941, The brain of Pterodactylus. American Journal of Science. 239, 665–682.

Darwinopterus

The concept of evolution is based on a simple idea. If an organism can survive to pass on its genes to the next generation it is said to be fit. Fit organisms will survive best and develop into dominant or abundant species.

Charles Darwin was the scientist who published this idea in 1858 On the Origin of Species… He proposed that a small and useful change, developed in relation to the environmental conditions would lead to a change in form or behaviour that, if advantageous, would persist in the species. Such small changes would lead to evolutionary change over time. These small changes can be seen to happen is some modern day species over time.

In examining different species, Darwin observed in many cases, that the change of form was significant. He proposed the idea of modular evolution where changes happened very quickly and locally at one time, giving a change that, if advantageous, was seen as a leap forward in evolution. Over time, where the environmental conditions were stable, the form and behaviour of species would be stable and show little change. Only when a significant factor changes the conditions within a habitat would other random changes become more advantageous. This concept is difficult to observe in reality, but it does rationalize the changes seen in fossils.

A recent find from China, Darwinopterus modularis, demonstrates this concept quite well. This is an advanced pterosaur in many features, but it has retained the long tail of the early pterosaurs. This species helps to link the changes between the Rhamphorhynchoidea and the Pterodactyloidea.

This pterosaur has been placed in a group called the Monofenestrata, which includes Darwinopterus and also encompasses all of the Pterodactyloidea.

Darwin C R, 1859, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London, John Murray.

Lu J, Unwin D M, Jin X, Liu Y and Ji Q., 2009, Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull, Proceedings of the Royal Society B., Published online before print October 14, 2009, doi: 10.1098/rspb.2009.1603

Proceedings of the Royal Society B - October 2009

The Problem With Ornithocheirus

The Ornithocheiridae are a group of large pterosaur fossils from the Cretaceous. They represent several distinct species and most are known only from fragmentary remains of jaws or bone joints. In many cases it is not clear which bones belong to which jaws.
In the late 1800's, this group of pterosaurs was represented mainly by remains in the Sedgwick Museum, Cambridge and the British Museum of Natural History (Now the Natural History Museum, London). The classification was a dumping bin for any pterosaur material from the Cretaceous that were not easily placed in an existing structural hierarchy. Many of the specimens were attributed to the work of Richard Owen or Harry Seeley.

This problem arose from specimens collected from the Cambridge Greensand. The specimens were deposited within the Greensand from elsewhere, perhaps from moving sediments or as fossils eroded from other rocks and re-deposited. In many cases, the age and location of the original deposition is unknown.
It has long been accepted that the Ornithosaur fossils represent a wide range of species that may well be unrelated. With little evidence of accociations, the work to sort the fossils out has not been done. Some time ago, David Unwin made a brave attempt at sorting out the problem and was successful in pulling some specimens out of the Ornithcheirus group, but with limited evidence, the problem will not be resolved easily.
Above is a sketch of a lower jaw fragment of Ornithocheirus fittoni, showing the staggered tooth pattern which is unusual amongst pterosaurs
Ornithocheirus sedgwickii shows a very different tooth pattern on its lower jaw. It may be that these specimens have enough similarities to place them in the same family group. If more was known about the rest of the skeletal remains, then a clearer perception would lead to a better conclusion. There are many more Ornithocheirids. Should they remain associated until such a time as there is more available fossil evidence. I personally do not have a problem with the idea of a dumping bin for odd bits and peices of remains. Science is full of problems and grey areas, so some means of containing these problems within a classification system is not a bad thing. The process often works well when a new specimen is found. You can take a look in the dumping bin from time to time and see if anything starts to look familiar.

Bowerbank J. S., 1851, On the Pterodactyles of the Chalk Formation. Proc. zool. Soc. Lond.,
pp. 14–20 & Ann. Mag. nat. Hist.(2) 10, 372–378.

Fritsch A. & Bayer F., 1905 Neue Fische und Reptilien aus der böhmischen Kreideformation.
Prague, privately published. pp. 30–32 & pl. 8

Newton E. T., 1888, Notes on pterodactyls. Proc. Geol. Ass. Lond. 10, 406–424.

Owen R. & Bowerbank J. S., 1852, On a new species of pterodactyle (Pt. compressirostris,
Owen) from the Chalk. Ann. Mag. nat. Hist. 10, 372–391.

Owen R., 1859 On remains of new and gigantic species of Pterodactyle (Pter. fittoni and Pter. sedgwickii) from the Upper Greensand near Cambridge. Rep. Br. Ass. Advmnt Sci. 28 (1858), 98–103.

Seeley H. G., 1870, The Ornithosauria: an elementary study of the bones of pterodactyls,
Proceedings of the Cambridge Philosophical Society, 2(1870) p.186

Seeley H. G., 1876, On the organisation of the Ornithosauria. J. Linn. Soc. Lond. Zool. 13, 84–
107.

Unwin D. M., 1991, The morphology, systematics and evolutionary history of pterosaurs from the Cretaceous Cambridge Greensand of England, University of Reading (Unpublished), Ph.D. Thesis

Pterosaur skeletal sculptures

Bruce Mohn is a comparative anatomist, palaeontologist and Palaeo-Sculptor with a specialism in mesozoic vertebrates. He has recently completed skeletal models of pterodactylus and rhamphorhynchus for the Carnegie Museum and the quality of his work is outstanding.
The model components are crafted from observations of fossil material and investigative techniques to give a realistic life-like shape to each individual component of the skeleton. The assembly of the individual components uses wired supports to give an accurate representation of the complete skeletal structure of the animal. This technique allows the skeleton to be wired into any orientation or possition that was possible in life.
If you are able to visit the Carneige Museum, it is worth finding these skeletal models to view the 3D structure of these pterosaurs, which cannot be fully appreciated from diagrams.

Bruce is able to make bones or skeletons to order - this is fine bespoke craftsmanship of the best museum quality. His work can be seen at - Bruce Mohn sculptures at Dinoart

Bruce Mohn

Carnegie Museums