Dimorphodon

Dimorphodon macronyx

Dimorphodon macronyx (*)

Dimorphodon
Fossil range: 200–180 Ma

Early Jurassic

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Pterosauria
Suborder:	Rhamphorhynchoidea
Family:	Dimorphodontidae
Genus:	Dimorphodon Owen, 1859

Species

D. macronyx (Buckland, 1829)(type)
D. weintraubi Clark et al., 1998

Dimorphodon (pronounced /daɪˈmɔrfədɒn/; "two-formed teeth") was a genus of medium-sized pterosaur from the Early Jurassic Period (180-170 million years ago). It was named by paleontologist Richard Owen in 1859. Dimorphodon means "two-form tooth" (Greek δι/di meaning 'two', μορφη/morphe meaning 'shape' and οδον/odon meaning tooth), referring to the fact that it had two distinct types of teeth in its jaws - which is comparatively rare among reptiles. Dimorphodon lived approximately 200 million to 180 million years ago. Dimorphodon may be descended from the earlier European pterosaur Peteinosaurus.[1]

Discovery

Fossil remains of Dimorphodon have been found in England. Mary Anning made the first Dimorphodon (D. macronyx) discovery, at Lyme Regis in Dorset, UK in 1828.[2] This region of Britain is now a World Heritage Site, dubbed the Jurassic Coast. One incomplete specimen has been recovered from early Jurassic strata at the south bank of the Severn river.[1]

Anatomy

It had a large, bulky skull aproximately 22 cm in length, whose weight was reduced by large cavities separated from each other by thin bony partitions.[1] Its structure, reminiscent of the supporting arches of a bridge, prompted Richard Owen to declare that, in far as achieving great strength from light-weight materials was concerned, no vertebrae was more economically constructed.[citation needed] The front of the jaws had four or five fang-like teeth followed by thirty to forty tiny, pointed teeth.[1] Many depictions give it a speculative puffin-like 'beak' because of similarities between the two animals' skulls.

The body structure of Dimorphodon displays many primitive characters, such as a very small brain-pan[citation needed] and proportionally short wings.[1] The first phalanx in its flight finger is only slightly longer than its lower arm.[1] The neck was strong and flexible and may have had a membraneous pouch on the under side. Dimorphodon had an adut body length of 1 metre (3.3 ft) long, with a 1.4 meter (4.6 ft) wingspan.[1][3]

The tail of Dimorphodon was long and consisted of 30 vertebrae. The first five or six were short and flexible but gradually increased in length and were stiffened by elongated vertebral processes.[1] The terminal end of the tail may have borne a Rhamphorhynchus-like tail fin, although no soft tissues have yet been found of Dimorphodon have been found to confirm this speculation.[1]

Skeleton of Dimorphodon macronyx in the more conventional quadropedal pose.

Gait

It has been argued that Dimorphodon was a biped due to its relatively well developed hindlimbs and characteristics of its pelvis.[1] However, fossilised track remains of other pterosaurs (ichnites) show a quadrupedal gait while on the ground and these traces are all attributed to derived pterosaurs with a short 5th toe. Dimorphodon's was elongated, clawless, and oriented to the side.[1] Owen speculated that the fifth toe supported a membrane between the tail and the legs.[1]

Ecology

Our knowledge of how Dimorphodon lived is also very small. It probably inhabited coastal regions and had a very varied diet. Its teeth and jaws suggest it was a piscivore (fish eater),[1] although until quite recently it was suggested that it hunted small land animals. Related to the insect-eating anurognathid pterosaurs, Dimorphodon may also have eaten insects.