Mimodactylus
Mimodactylus is a genus of istiodactyliform pterosaur that lived in what is now Lebanon during the Late Cretaceous, 95 million years ago. The only known specimen was discovered in a limestone quarry near the town of Hjoula, belonging to the Sannine Formation. The owner of the quarry allowed the specimen to be prepared and scientifically described by an international team of researchers. When it was eventually sold, the buyer donated it to the MIM Museum in Beirut. In 2019, the researchers named the new genus and species Mimodactylus libanensis; the generic name refers to the MIM Museum, combined with the Greek word daktylos for "digit", and the specific name refers to Lebanon. The well-preserved holotype specimen is the first complete pterosaur from the Afro-Arabian continent, and the third pterosaur fossil known from Lebanon.
The holotype specimen is comparatively small, with a wingspan of, and was probably a young individual. Its snout is broad and the cone-shaped teeth are confined to the front half of the jaws. The tooth crowns are compressed sideways and have a cingulum, and lack sharp carinae. The skeleton is distinctive in that the deltopectoral crest of the humerus is rectangular and that the humerus is less than half the length of the wing-finger's second phalanx bone. The describers of Mimodactylus classified it in the new clade Mimodactylidae along with Haopterus, this group being part of Istiodactyliformes. The teeth of Mimodactylus suggest its feeding habits differed from other pterosaurs. Possibly it foraged for decapod crustaceans from water surfaces. The marine deposits of Hjoula are late Cenomanian in age and are well known for fish fossils. Lebanon was submerged in the Neotethys ocean at the time, but some small islands were exposed.
History of discovery
The only known specimen of this pterosaur was collected from a private limestone quarry near the town of Hjoula, Lebanon, more than fifteen years before its 2019 scientific description. Hjoula is located northeast of the capital Beirut and inland from the city of Byblos. The locality is considered a Lagerstätte, a place with fossils of exceptional preservation, and belongs to the Sannine Formation, which dates to the late Cenomanian age of the Cretaceous period. Lebanese Cretaceous deposits have been known for well-preserved fish and invertebrates since the Middle Ages, but fossils of tetrapod animals are very rare. Information about Mesozoic fossils of the Afro-Arabian continent is generally very limited, with only South Africa having been systematically studied.The very fragile but well-preserved pterosaur specimen was split in two pieces when discovered on the limestone slab, and apart from a fracture caused by the pickaxe of a quarry worker, its skull was intact, as were the wings, legs, and body. The owner of the quarry allowed a team of researchers from the University of Alberta in Canada to prepare and describe the specimen, while intending for the fossil to be eventually sold, which is legal in Lebanon. The palaeontological community in Lebanon lacked the technology needed to prepare the fossil material in a way that would most effectively reveal information from the specimen. The specimen spent about eight years at the University of Alberta, where it was prepared, assembled, and studied. Subsequently, the owner of the quarry sold the specimen, but around 2016, after years of negotiations, the anonymous buyer donated it to the MIM Museum, part of Saint Joseph University of Beirut, so that it could be kept in Lebanon.
The Canadian palaeontologists Michael W. Caldwell and Philip J. Currie teamed up with an international group of researchers to scientifically describe the specimen, including the Brazilians Alexander W. A. Kellner, Borja Holgado, and Juliana M. Sayão, Italian Fabio M. Dalla Vecchia, and Lebanese Roy Nohra. In interviews, the researchers expressed pleasure in the specimen being returned to Lebanon, where it can be used for education and research, and in having the opportunity to collaborate internationally. The majority of fossil type specimens from Lebanon are stored in collections outside the country, and Lebanese researchers are typically not included in publications about Lebanese fossils; a 2024 study therefore concluded Lebanon is impacted by scientific colonialism.
In 2019, Kellner and colleagues named the new genus and species Mimodactylus libanensis; the generic name refers to the MIM Museum, in recognition of where the specimen is housed and according to the wishes of the philanthropist who acquired the specimen, combined with the Greek word daktylos for "digit". The specific name refers to Lebanon. The holotype specimen is catalogued as MIM F1, and casts are present at the University of Alberta and the National Museum of Brazil. The holotype skeleton is well-preserved and mostly articulated, with some bones slightly displaced from their anatomical position; the skull and lower jaw are exposed from below, and the occipital region at the back of the skull and the jaw joint flattened.
The holotype is the first complete and articulated pterosaur specimen known from the Afro-Arabian continent, which had otherwise only yielded a few fragmentary specimens. The previous most completely known pterosaur specimens from the continent were also from Lebanon: a partial forelimb of an unnamed ornithocheiroid from the Hakel Lagerstätte of the same age, and Microtuban, an azhdarchoid consisting mainly of the wings and shoulder girdle, also from Hjoula. Although these specimens are less complete, their anatomical features can be clearly distinguished from Mimodactylus. The specimen has become the centrepiece of the fossil vertebrate collection at the MIM Museum, where it is nicknamed "Mimo" and is exhibited alongside a hologram, a movie, a life-sized reconstruction, and a game.
Description
The only known Mimodactylus specimen is comparatively small, with a wingspan of. It was probably a young individual when it died, based on some bones not being fused; the dentary bones are fused at the mandibular symphysis, where the two halves of the lower jaw connect at the front. This indicates the specimen had reached an ontogenetic stage between stages 2 and 3 out of 6, according to a system for determining the age of pterosaur fossils devised by Kellner in 2015. The adult size of Mimodactylus is unknown. As a pterosaur, Mimodactylus would have been covered in hair-like pycnofibres, and had extensive wing-membranes, which were distended by the long wing-finger. In an interview, Caldwell described Mimodactylus as having long, narrow wings, but with a body the size of a sparrow, a head longer than its body, and being rather like "wings with a mouth".Skull
The preserved part of the skull of Mimodactylus is long, and the preserved part of the lower jaw is. The rostrum is broad when seen from above and has a pointed tip, and not rounded as in the istiodactylid Istiodactylus, and also differs from other istiodactyliforms, the group they both belonged to. The upper jaws have eleven cone-shaped teeth on each side, and the lower jaws have ten on each side, and the teeth are confined to the front half of the jaws, as in the related Haopterus and Linlongopterus. A similar configuration is also seen in other istiodactyliforms.The tooth crowns are compressed sideways and have a cingulum, as in Haopterus and other istiodactyliforms. A cingulum is also known from the teeth of istiodactylids and related pterosaurs, but these have wide crowns, which are also compressed sideways. Mimodactylus does not have the lancet-shaped teeth with sideways compressed crowns which are characteristic of istiodactylids, though, and also lacks the sharp carinae seen in Istiodactylus. The first upper tooth of Mimodactylus is small, with an almost circular cross-section, and the following teeth are the largest of the upper jaw, and have slightly sideways compressed crowns with a cingulum, convex outer surfaces, and thin, needle-like tips which are inclined inwards.
The dentition of Mimodactylus is similar to that of more basal archaeopterodactyloid pterosaurs such as Pterodactylus and Germanodactylus, and the only other derived pterodactyloid with comparable teeth is Haopterus. The palate of Mimodactylus is concave and has a small palatal ridge, and the choanae are large and separated by the vomers. The postpalatinal fenestra is elongated and egg-shaped, as in Hongshanopterus. The lower jaws have an odontoid process at the tip, as seen in Istiodactylus, Haopterus, and Lonchodraco. The ceratobranchials of the hyoid are thin, elongated, and fork-shaped.
Postcranial skeleton
The front dorsal vertebrae of the back are not fused into a notarium in Mimodactylus. Seven caudal vertebrae of the tail are visible, which lack a duplex centrum, and quickly diminish in size towards the rear, indicating that the tail of this species was very short. The cristospine on the underside of the sternum is comparatively short and deep, similar to those of Nurhachius and Istiodactylus. The front part of the sternum was more rounded when seen in side view than in istiodactylids, and thereby more similar to those of anhanguerids. When complete, the sternal plate would have been square in shape overall, and probably had a straight side edge and convex hind margin. The scapula is long. It is stout and has a constricted shaft, as in istiodactylids and anhanguerids, but differs in being somewhat longer than the coracoid. The coracoid is long. The articulation between the coracoid and the sternum is slightly concave as in Haopterus, with a backward protrusion that is not seen in istiodactylids.The humerus of Mimodactylus is long. The deltopectoral crest of the humerus is distinctive in being rectangular, and has an unusual, straight, lower edge. This crest extends 40% of the humeral shaft's length, more than what is seen in all other ornithocheiroids, except Pteranodon and its relatives. The ulna is long. Some of the wing-bones are longer in relation to the humerus than in istiodactylids, especially the first two phalanx bones of the wing-finger; the humerus is unique in being less than half the length of the second phalanx. The first wing phalanx is long, the second, the third, and the fourth. The outer part of the wing-finger's last phalanx is curved, as in most pterosaurs.
The pteroid bone of Mimodactylus is rather large, and longer than the humerus at. The pteroid clearly articulated with the proximal syncarpal and pointed towards the body; the position of the pteroid in pterosaurs had been a point of contention among researchers, but was settled due to the perfect articulation of the forelimbs in Mimodactylus. The humerus is much longer than the femur, the preserved part of which is long. The tibiotarsus is long. As in istiodactylids, the feet are relatively small. The exact combination of its various anatomical features also distinguishes Mimodactylus from other ornithocheiroids.