Temporal range: Early Jurassic
|A restoration of Dimorphodon macronyx in flight|
| Dimorphodon macronyx|
Dimorphodon was a rhamphorhynchoid from the early Jurassic period, 190 mya. It had a big head, a small brain, a tall beak, and two types of teeth. Variation in teeth is rare in pterosaurs.
Like Rhamphorhynchus, Dimorphodon is only found in Jurassic strata. It was the first pterosaur found in England, by Mary Anning, in 1828.
Dimorphodon had a large, bulky skull about 22 centimetre in length, that was lightened by large openings separated from each other by thin walls of bone. Its structure, reminiscent of the arches of a bridge, led Owen to say that, in terms achieving great strength of light-weight materials.  The front of the top jaw had 4 or 5 fang-like teeth followed by countless smaller teeth; the jaw of all exemplars is damaged at the back. The lower jaw had 5 longer teeth and 30 to 40 tiny, flattened pointed teeth.
Dimorphodon shows many "primitive" traits, such as, as Owen said, a very small brain-pan and proportionally short wings. The first bone in its flight finger is only slightly longer than its lower arm. The neck was short but strong and flexible and may have had a membraneous pouch on the bottom. The vertebrae had openings through which the air sacks could reach the hollow inside. Dimorphodon was 3.3 ft long, with a 4.6 ft wingspan.
The tail of Dimorphodon was long and made up of 30 vertebrae. The first 5 or 6 were short and flexible but the rest grew bit by bit in length and were stiffened by elongated vertebral processes. The end of the tail may have borne a Rhamphorhynchus-like tail vane, but no soft tissues have yet been found of Dimorphodon to prove this.
In 1870 Seeley put Dimorphodon in its own family, the Dimorphodontidae, with Dimorphodon as the sole member. In 1991, German paleontologist Peter Wellnhofer said that Dimorphodon might be descended from the earlier European pterosaur Peteinosaurusbut later studies dispute this. Unwin thinks Dimorphodon was related to, though likely not a descendant of, Peteinosaurus, both forming the clade Dimorphodontidae, the most basal group of the Macronychoptera and within it the sister group of the Caelidracones. This would mean that both dimorphodontid species would be the most basal pterosaurs known save for Preondactylus. Alexander Kellner thinks Dimorphodon is far less basal and not a close relative of Peteinosaurus.
We don't know much of how Dimorphodon lived. It probably lived in coastal regions and might have had a very mixed diet. Buckland thought it ate bugs.  Later it became common to depict it as a fish eater, though Buckland's first thought is more well backed up by studies. Dimorphodon had advanced jaw muscles skilled for a "snap and hold" way to feed. The jaw could close very fast but not with much force or tooth piercing. This and the short and high skull and longer, pointed front teeth suggest Dimorphodon ate bugs, though it may have ate small land animals and carrion from time to time as well. 
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