Introduction

Concerning Mesozoic vertebrate palaeontology, the Afro-Arabian continent is still veiled in mystery. Except for South Africa, where systematic studies, mainly in Triassic and Lower Jurassic continental deposits have provided a comparatively diverse vertebrate fauna1, the information about the biota that lived during most of the Mesozoic Era in this region is extremely limited. This is particularly true for pterosaurs, an extinct group of flying reptiles that includes the major powered flying vertebrates for almost 160 mya2,3. The main African records of this group are restricted to isolated elements from the Jurassic deposits of Tendaguru4,5,6 from Tanzania, and the Upper Cretaceous Kem Kem Beds (Cenomanian)7,8,9,10,11 and Ouled Abdoun (Maastrichtian)12,13 from Morocco. The most complete pterosaur specimens from the Afro-Arabian continent have been recovered from Cenomanian marine deposits of Lebanon14 (Fig. 1). The first specimen was a partial left forelimb of a relatively small unnamed ornithocheiroid from Hâqel Lagerstätte15 and the second a crushed skeleton formed mainly by two wings and the shoulder girdle of the azhdarchoid Microtuban altivolans16 from the coeval14,17 Hjoûla Lagerstätte.

Figure 1
figure 1

Geographical location where the new pterosaur, Mimodactylus libanensis gen. et sp. nov., was collected. (a) Geological map of Lebanon (adapted from Dubertret14). (b) Detail showing the location of the most important fossil Lagerstätten of Lebanon (modified from Dalla Vecchia et al.65). (c) Position of Lebanon in the broad carbonate platform that surrounded the northern part of the Afro-Arabian continent during the late Cenomanian (modified from Philip and Floquet70). Abbreviations. a = Apulian Carbonate Platform (southern Italy); acp = Adriatic Carbonate Platform (Italy, Slovenia, Croatia); bd = Bei Daglari (Turkey); bih = Bihor Massif (Romania); bm = Bohemian Massif (Central Europe); et = Eastern Taurus (Turkey); g = Gavrovo (Greece); gm = Golija Massif (Serbia); inm = Insubrian Massif (Alps); sy = Seydisehir (Turkey); uks = Ukrainian Shield (Ukraine). The yellow star indicated on each map the location of the Hjoûla Lagerstätte(a,b), whilst the red asterisk Lebanon(c).

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The specimen described here (Fig. 2) is the first complete and articulated skeleton including the skull and lower jaw from the Afro-Arabian continent providing new insights on the diversity and potential palaeoecology of ornithocheiroids.

Figure 2
figure 2

Mimodactylus libanensis gen. et sp. nov. (a) Photo and drawing of the complete specimen. (b) Close up of scapula and coracoid. (c) Detail of the wrist, showing the relation of the pteroid and the carpus. (d) Detail of the humerus. Scale-bars, a: 50 mm; b-d: 10 mm. Abbreviations. car: carpus; cdv: caudal vertebrae; cor: coracoid; cra: cranium; cs: cristospine; cv: cervical vertebrae; d: dentary; dcar: distal carpals; dpc: deltopectoral crest; dri: dorsal ribs; dv: dorsal vertebrae; fe: femur; hu: humerus; man: mandible; mcI-III: first to third metacarpals; mcIV: wing metacarpal; mtar: metatarsals; pcar: proximal carpals; ph1d4: first wing phalanx; ph2d4: second wing phalanx; ph3d4: third wing phalanx; ph4d4: fourth wing phalanx; ppu: prepubis; ptd: pteroid; ra: radius; sca: scapula; sri: sacral ribs; stp: sternal plate; sym: mandibular symphysis; tar: tarsus; te: teeth; ti: tibia; ul: ulna; the abbreviations ‘l’ and ‘r’ represents respectively left and right.

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Results

Systematic palaeontology

Pterosauria Kaup, 1834.

Pterodactyloidea Plieninger, 1901.

Ornithocheiroidea Seeley, 1870 sensu Kellner (2003)18.

Pteranodontoidea Marsh, 1876 sensu Kellner18.

Lanceodontia Andres et al.19.

Istiodactyliformes clade nov.

Branch-based definition

The most inclusive clade containing Istiodactylus latidens, but not Anhanguera blittersdorffi.

Diagnosis

Slender-built lanceodontian pterodactyloids with the following synapomorphies: mandibular rostral end pointed, teeth confined to the anterior half of the jaws, and labiolingually compressed crowns with a cingulum.

Included taxa

Istiodactylidae, Mimodactylidae, and Hongshanopterus lacustris.

Mimodactylidae clade nov.

Branch-based definition

The most inclusive clade containing Mimodactylus libanensis gen. et sp. nov., but not Istiodactylus latidens, Ikrandraco avatar, and Anhanguera blittersdorffi.

Diagnosis

Istiodactyliforms with cone-shaped teeth, crowns with a slight labiolingual compression, and sternal articular surface of the coracoid slightly concave.

Included species

Haopterus gracilis and Mimodactylus libanensis gen. et sp. nov.

Mimodactylus libanensis gen. et sp. nov.

Etymology

Mimodactylus, from the acronym MIM (Mineral Museum) for the museum housing the specimen, in recognition of both the museum and the wishes of the anonymous philanthropist who facilitated the acquisition of the specimen thus keeping it in Lebanon, and the Greek ‘dactylos’ (δάκτυλος), meaning digit; libanensis from Lebanon, where the specimen was found.

Holotype

Almost complete skeleton, including the skull and lower jaw, housed at the Mineral Museum (MIM) of Beirut, Lebanon, MIM F1. Cast at the University of Alberta, Edmonton and Museu Nacional/UFRJ (MN 7216-V).

Locality and horizon

Hjoûla Lagerstätte of the Sannine Limestone (late Cenomanian17), near the town of Hjoûla located 35 km NNE of Beirut and 10 km inland from Jbail, Lebanon.

Diagnosis

Mimodactylid with the following autapomorphies: humerus with a rectangular deltopectoral crest; humerus smaller than half the length of the second phalanx of the wing finger (hu/ph2d4 < 0.5). This species can be further distinguished from other ornithocheiroid pterodactyloids by the following combination of characters: discrete palatal ridge; 11 and 10 cone-shaped teeth on each side of the upper and lower jaws, respectively; scapula slightly longer than coracoid; humerus much longer than femur (hu/fe ~1.3); deltopectoral crest extends for around 40% of the humerus shaft length (see Supplementary Information for further details and measurements).

Comparative description

The specimen is well preserved with most parts of the skeleton articulated or only slightly displaced from their anatomical position (Fig. 2a). The skull and lower jaw are exposed in ventral view, with the occipital region and the craniomandibular articulation flattened. It is a comparatively small individual, with a wingspan of ~1.32 meters, and long wings, resulting in a high aspect ratio. Based on the unfused scapula and coracoid, pelvic elements and sacral vertebrae but fused dentaries at the symphysis, and dorsal vertebrae not fused into a notarium, it is likely that it was a very young animal at the time of death, having reached an ontogenetic stage between 2 and 320. The skull has a broad rostrum in dorsopalatal view (Fig. 3), but not as rounded as in Istiodactylus21,22,23 and also differing from other istiodactyliforms24,25. The rostral tip is pointed, unlike the rounded terminus of Istiodactylus21,22,23. There are 11 and 10 cone-shaped teeth on each side of the upper and lower jaws, respectively (Fig. 3a), similar to Haopterus26 and Linlongopterus27. Crowns are labiolingually compressed with a cingulum (Fig. 3b; SI) as in Haopterus and other istiodactyliforms. This cingulum was previously reported in Istiodactylidae28 and related taxa, but the teeth of this latter lineage is characterised by wide crowns, which have also a marked labiolingually compression21,22,23,24,25. The palate is concave and shows a small palatal ridge. Choanae are large and divided by the vomers. The postpalatinal fenestra has an elongated egg-like shape as in the basal istiodactyliform Hongshanopterus25. Ceratobranchials I of the hyoid apparatus are fork-like, thin, and elongate elements. An odontoid process is present at the tip of the lower jaw as in Istiodactylus latidens23, but this process could also be recognised in Haopterus26 and Lonchodraco giganteus29. The dorsal vertebrae (Fig. 2b; Supplementary Fig. S1) are exposed in ventral view and are not fused into a notarium. A total of 7 caudal vertebrae were identified (Supplementary Fig. S2), all of which lack a duplex centrum and decrease rapidly in size posteriorly, suggesting that this species had a short tail. The cristospine of the sternum is comparatively short and deep, similar to those of Nurhachius and Istiodactylus; the anterior portion of the sternum is more rounded in lateral view than that of istiodactylids, being, in this respect, more similar to that of the Anhangueridae. The scapula is stout and shares with istiodactylids and anhanguerids a constricted shaft (Fig. 2b). However, it differs from both by being longer than the coracoid18. The coracoid sternal articulation is slightly concave as in Haopterus25 and has a developed posterior expansion that is not present in istiodactylids. The humerus (Fig. 2d) has a rectangular deltopectoral crest with an unusual straight distal margin and extends approximately 40% down the humerus shaft, more than in any other ornithocheiroid except for Pteranodon and related taxa30. Mimodactylus has some wing elements longer relative to the humerus compared to istiodactylids, in particular the first and second phalanges. The distal portion of the last phalanx of the wing finger is curved as in most pterosaurs. The feet are relatively small, similar to istiodactylids30. The pteroid (Fig. 2c) is quite large (longer than the humerus). This bone is clearly articulated with the proximal syncarpal and directed towards the body. There has been a long discussion about the position of this unique pterosaur bone with the carpal elements31,32,33, which is clearly settled in the present specimen whose forelimb bones are perfectly articulated.

Figure 3
figure 3

Mimodactylus libanensis gen. et sp. nov. (a) Skull and lower jaw. (b) Detail of the dentition. Scale bars, a: 10 mm, b: 1 mm. Abbreviations. hy: ceratobranchial I of the hyoid apparatus; man: mandible; odp: odontoid process; pl: palatine; pm: premaxilla; pplf: postpalatine fenestra; prid: palatal ridge; sym: mandibular symphysis; te: teeth; vo: vomer. Arrows point to the cingulum at the base of the teeth.

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Discussion

Despite the incompleteness of the two other pterosaur specimens described from the upper Cenomanian of Lebanon, both of which lack cranial elements, those specimens can clearly be distinguished from Mimodactylus. The only complete bones of the ornithocheiroid MSNM V 38818 are the wing metacarpal and the radius + ulna, whose proportions differ from those of Mimodactylus showing that the latter has a proportionally longer forearm. Furthermore, the diameter of the radius of MSNM V 3881 is less than half that of the ulna, contrary to the condition of Mimodactylus. The second specimen, the holotype of Microtuban altivolans16, has a much shorter wing, a humerus with a different deltopectoral crest and a scapula that lacks the constricted shaft observed in Mimodactylus.

Another interesting feature of Mimodactylus is the dentition (Figs. 3a and SI), which differs from that of most ornithocheroids. As in Haopterus25 and Linlongopterus26, the new species has cone-shaped dental crowns and they are confined to the anterior half part of the jaws. Such a configuration is present in other istiodactyliforms and cannot be established in Lonchodraco giganteus due to preservation29, which also present cone-shaped teeth. As in Haopterus but unlike Linlongopterus and Lonchodraco, teeth are characterised by a cingulum at the base of the crown (Supplementary Fig. S3), which is also present in the Istiodactylidae and closely related species. Mimodactylus, however, lacks the lancet-shaped teeth with marked labiolingually compressed crowns that are diagnostic of the istiodactylids20,21,22,23,24. The new species also lacks the sharp carinae reported in Istiodactylus21. The first upper tooth of Mimodactylus is comparatively small and has a sub-circular transverse section. It is followed by the largest teeth in the upper jaw, which have slight labiolingually compressed crowns with a cingulum, convex labial surfaces and thin, lingually inclined, needle-like tips. This general morphology is present in the remaining teeth, also from the lower jaw. This kind of dentition is more similar to that of the basal archaeopterodactyloids18 Pterodactylus and Germanodactylus rhamphastinus24 than to istiodactylids and ornithocheiroids. The sole other derived pterodactyloid with a comparable dentition is Haopterus gracilis, first regarded as an archaeopterodactyloid26, later as an ornithocheroid close to Istiodactylidae28, and even the sister taxa of Ornithocheiroidea13,19. Here we recovered Haopterus at the base of Laceodontia as in more recent phylogenetic analyses34,35, forming a clade with Mimodactylus libanensis (Fig. 4a; see Supplementary Information for further details).

Figure 4
figure 4

An overview of Mimodactylus libanensis gen. et sp. nov. (a) Phylogenetic relationships of Mimodactylus libanensis gen. et sp. nov. within Ornithocheiroidea. Colours show their continental origin: Afro-arabia (brown), Asia (orange), Europe (red), North America (blue), and South America (green). Outgroup relationships are not shown (see Holgado et al.34 and Supplementary Information for further details). Intermittent bars show uncertain temporal range. Stratigraphic chart modified from Cohen et al.71. (b) Reconstructed silouette of Mimodactylus libanensis showing the long wings regards the body. Scale bar: 50 mm.

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The Mimodactylidae clade nov. is diagnosed by the following synapomorphies: cone-shaped teeth on each side of the upper jaws, crowns with a slight labiolingual compression, and sternal articular surface of the coracoid slightly concave. In addition, all mimodactylids have the teeth confined to the anterior half of the jaws and are widely spaced. Although several characters presented previously are recorded in mimodactylids and other istiodactyliforms, some of them are recovered as symplesiomorphies shared by other lanceodonts (e.g., character state 77(1): presence of an odontoid process in the lower jaw; character state 95(1): cone-shaped teeth) or are of unclear origin (e.g., character state 15(3): elongated egg-shaped postpalatine fenestra; character state 56(3): quadrate inclined about 150° posteriorly to ventral margin of the skull). In addition, two synapomorphies that support the Mimodactylidae should be considered with caution due to the missing data in most of lanceodontians30 (see Supplementary Information for further details) and the potential of ontogenetic variation in derived pterodactyloids18,36.

Despite the inherent difficulties of establishing the diet of extinct vertebrates with no suitable modern analogues such as pterosaurs, the following feeding habits have been proposed for derived pterodactyloids37, mainly based on their dentition (or absence of teeth) and the shape of their rostra: piscivory for Anhangueridae and their kin30,38,39,40, Ikrandraco41, Pteranodontidae30, Nyctosauridae42, Chaoyangopteridae43, and Thalassodrominae44; frugivory for Tapejarinae45,46; durophagy for Dsungaripterus and related species30; insectivory for Nemicolopterus47; scavenging for Istiodactylus21,22; cutting or ploughing through unconsolidated sediments for Argentinadraco48, and terrestrial stalking for the long-necked azhdarchids49. The dentition of Mimodactylus differs from all of them, suggesting that this lineage of derived pterodactyloid had a different feeding habit.

Studies on the shapes of teeth of extant insectivorous tetrapods emphasise that insectivorous species profit from having slimmer teeth that could be more easily used to breakdown arthropods due to the slight radius of curvature50,51,52,53. Within the pterosaur spectrum, the anurognathids that have well-spaced and isodont teeth have been regarded as insectivores25,54. Although wider, the tooth structure of Mimodactylus may suggest a similar feeding habit, allowing them to break up arthropod exoskeletons.

Aerial insectivory is closely linked to the ability to maneuver during flight55,56,57. Extant vertebrate aerial insectivores exhibit short wings with low aspect ratios that allow them to be highly maneuverable in the air56,57,58, contrary to Mimodactylus libanensis, which had long wings with high aspect ratio (Fig. 4b). In Mimodactylus, as open-sea flyers, the ability to maneuver during flight appears to be limited and it was likely high stable during flight as observed in albatrosses and other birds (Fig. 5). This might also have been the case for some large pterosaurs such as anhanguerians, istiodactylids and pteranodontians, which are considered to have conducted a dynamic soaring58. Therefore, alternately to the insectivore hypothesis, Mimodactylus and their relatives might also have been capable of foraging for decapod crustaceans on surface waters, just like some albatross species feed upon caridean or penaeid shrimps59. In addition, a broad rostrum60 and spaced but relatively robust and pointed teeth61,62 could be good tools to seize shrimps in the water.

Figure 5
figure 5

Life reconstruction of Mimodactylus libanensis gen. et sp. nov. Artwork of Julius T. Csotonyi.

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Observing the fossil content of the Hjoûla Lagerstätte as well as of other Cretaceous Lebanese Lagerstätten, no insects were recovered so far63,64. Even terrestrial plants are extremely rare at Hjoûla65, suggesting that this Lebanese Lagerstätte was far away from emergent areas such as islands, with the continent several hundred kilometres away. On the other hand, decapod crustaceans are the most common invertebrates found in Hjoûla66,67. No taphonomic bias was detected to explain the absence of insects, pointing to fishes and zooplankton as potentially the main local source of food for pterosaurs. Mimodactylus libanensis also has a broad rostrum, which is consistent with a faunivorous feeding habit - or primarily feeding on crustaceans - as present in extant ducks, boat-billed herons, and shoebills68. Although insectivory cannot be ruled out, all available evidence suggests that Mimodactylus was feeding on crustaceans.

This new pterosaur lived in archipelagos and scattered islands, which were present during the Late Cretaceous in the gigantic carbonate platform bordering the northern part of the Afro-Arabian continent with the Neotethys (Fig. 5). The discovery of Mimodactylus libanensis expands the spectrum of possible feeding strategies in derived pterodactyloids, a group of fascinating volant reptiles for which we still know very little.

Methods

Nomenclatural acts

This published work and the nomenclatural acts it contains have been registered in ZooBank, the proposed online registration system for the International Code of Zoological Nomenclature. The ZooBank Life Science Identifiers (LSIDs) can be resolved and the associated information viewed by appending the LSIDs to the prefix http://zoobank.org/. The LSID for this publication is urn:lsid:zoobank.org:pub:E77F30DB-D268-4C96-9849-1B65BCDDCAA3:, and the LSIDs for the new erected groups and taxa are: urn:lsid:zoobank.org:act:E33BF241-AD34-4878-AE3D-45F13A97F327 (Istiodactyliformes), urn:lsid:zoobank.org:act:A482B812-EA6A-4EDA-8986-3EFF1D7451B2 (Mimodactylidae), urn:lsid:zoobank.org:act:28DC7F4E-C3C3-4459-B3F1-FF58BBEF3A66 (Mimodactylus), and urn:lsid:zoobank.org:act:DCD7BFC3-0F35-4AA3-91B4-89A7604EAEB7 (Mimodactylus libanensis).

Phylogenetic analysis

We performed a phylogenetic analysis using the software TNT 1.569. This analysis is based essentially on Holgado et al.34 (for further details see Supplementary Information). Search for the most parsimonious trees (MPTs) was conducted via Traditional Search (TBR swapping algorithm), 10,000 replicates, random seed and collapsing trees after search.