Dimorphodon

Dimorphodon (dy-MOR-fə-don) was a medium-sized pterosaur that lived in Europe during the early Jurassic, around 201 to 191 million years ago. Paleontologist Richard Owen gave it its name in 1859. The genus name comes from Greek words meaning "two-form tooth," because its jaws held two distinct kinds of teeth—an uncommon trait among reptiles. Researchers have debated what Dimorphodon ate. Early ideas suggested it fed on insects or fish, but more recent work indicates it likely hunted small vertebrates, though it probably also ate small invertebrates like insects.

In terms of body structure, Dimorphodon had several "primitive" features. Owen noted its small braincase and relatively short wings. The first bone in its flight finger was only a little longer than its lower arm. Its neck was short but strong and flexible, and may have had a membranous pouch underneath. The vertebrae had pneumatic foramina—openings that let air sacs reach the hollow interior. An adult Dimorphodon measured about 1 meter (3.3 feet) in body length, with a wingspan of 1.45 meters (4.6 feet). Its long tail contained thirty vertebrae. The first five or six were short and flexible, while the rest grew longer and were stiffened by elongated processes. The tail tip might have had a vane like that of Rhamphorhynchus, but no fossil impressions have been found to confirm this.

The skull was large and bulky, roughly 23 centimeters (9.1 inches) long. Its weight was reduced by big openings separated by thin bony partitions. Owen compared the skull's structure to a bridge's supporting arches, saying no vertebra was more economically built for strength with light materials; he thought the vertebrate skull was a combination of four vertebrae modified from an ideal type. The front of the upper jaw held four or five fang-like teeth, followed by an unknown number of smaller teeth—the back of the maxilla is damaged in all known specimens. The lower jaw had five longer teeth and thirty to forty tiny, flattened, pointed teeth shaped like lancets. Because of superficial skull similarities, many reconstructions give Dimorphodon a speculative puffin-like beak.

The first fossils now assigned to Dimorphodon were found in England by fossil collector Mary Anning at Lyme Regis in Dorset, UK, in December 1828. That area is now a UNESCO World Heritage Site called the Jurassic Coast, where Blue Lias layers from the Hettangian-Sinemurian are exposed. William Buckland acquired the specimen and reported it at a Geological Society meeting on February 5, 1829. In 1835, after a thorough study by William Clift and William John Broderip, an expanded report was published in the Transactions of the Geological Society, describing and naming the fossil as a new species. Like many early pterosaur finds, Buckland placed it in the genus Pterodactylus, calling it Pterodactylus macronyx. The species name comes from Greek makros ("large") and onyx ("claw"), referring to the large hand claws. That specimen, now NHMUK PV R1034, was a partial, disarticulated skeleton on a slab, missing the skull. In 1835, Buckland also assigned a jaw piece from Elizabeth Philpot's collection to P. macronyx. Later, as many species assigned to Pterodactylus became too anatomically diverse, they were split into separate genera.

In 1858, Richard Owen reported two new specimens, NHMUK PV OR 41212 and NHMUK PV R1035—again partial skeletons, but this time including skulls. Because the skull differed greatly from that of Pterodactylus, Owen gave Pterodactylus macronyx its own genus, which he named Dimorphodon. His first report had no description, so the name was a nomen nudum. In 1859, a later publication by Owen provided a description. After several studies of Dimorphodon's anatomy, Owen in 1874 made NHMUK PV R1034 the holotype.

Though not a very common fossil, other fragmentary Dimorphodon specimens have been found. Some were acquired by Othniel Charles Marsh between 1873 and 1881 from London fossil dealer Bryce McMurdo Wright. One came from early Jurassic strata on the south bank of the Severn River at Aust Cliff. An additional species, D. weintraubi, was named by James Clark and colleagues in 1998 from a partial skeleton found in siltstones at Huizachal Canyon in the La Boca Formation in Tamaulipas, Mexico, dating to the Early Jurassic (Pliensbachian). That site also yielded sphenodontians, dinosaurs, and mammaliaforms. The type specimen, IGM 3494, includes articulated pieces of the skeleton: the back of the skull, four cervical vertebrae, the scapulocoracoids, left humerus, part of the right wing, and the right leg from below the mid-tibiotarsus. This specimen is larger than D. macronyx, and its well-preserved foot shows that pterosaurs did not have a digitigrade hindlimb posture but instead a plantigrade gait, as footprints had suggested. The species name honors Dr. Robert L. Weintraub. Later studies found this species not closely related to Dimorphodon macronyx, but instead an early relative of Anurognathidae.