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