| Tupandactylus | |
|---|---|
 | |
| ReconstructedT. imperator skeleton,National Museum of Brazil | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Pterosauria |
| Suborder: | †Pterodactyloidea |
| Clade: | †Azhdarchoidea |
| Family: | †Tapejaridae |
| Subfamily: | †Tapejarinae |
| Tribe: | †Tapejarini |
| Genus: | †Tupandactylus Kellner & Campos, 2007 |
| Type species | |
| †Tapejara imperator Campos & Kellner, 1997 | |
| Species | |
| Synonyms | |
List of synonyms
| |
Tupandactylus (meaning "Tupâ or Tupan finger", in reference to a personification of theTupi supreme deity) is agenus oftapejaridpterodactyloidpterosaur from theEarly CretaceousCrato Formation ofBrazil. It is known from two species,T. imperator andT. navigans, though it has been suggested that there is only a single, highly sexually dimorphic species (which would then beT. imperator).T. imperator was described in 1997 by D. A. Campos andAlexander W. A. Kellner, who assigned it toTapejara. Six years later,T. navigans was named and also assigned toTapejara. In 2007, two efforts to reallocate both species to a new genus were made, and ultimately the nameTupandactylus came into use.
The largerTupandactylus species,T. imperator, has an estimated wingspan of 3–4 m (9.8–13.1 ft) and may have stood 1.5 m (4.9 ft) tall when measured to the tip of its crest, whereas the smallerT. navigans had a wingspan of about 2.7 m (8.9 ft). Like other tapejarids,Tupandactylus had a large head crest, formed bykeratinous fibres and supported by a dorsal extension of therostrum and a rearward extension of theparietal bone. InT. imperator, the crest was large and rounded, whereas inT. navigans, it was tall and vertical. An additional crest was formed by a projection at the front of the lower jaw. The anatomy ofTupandactylus was standard for a tapejarid, with a large opening formed from the combination of thenasal cavity and theantorbital fenestra, and aneye socket set fairly low in the skull.
Theholotype specimen ofTupandactylus isMCT 1622-R, a skull and partial lower jaw, found in theCrato Formation, dating to the boundary of theAptian-Albian stages of the earlyCretaceous period, about 112 Ma ago.[1] It was initially described as aspecies ofTapejara,T. imperator, by D. A. Campos andAlexander W. A. Kellner in 1997.[2] A second taxon,T. navigans, was named in 2003.[3] In 2007, two efforts to reassign them to a new genus were made. One, by David Unwin and David Martill, would have seen them both assigned to the new genus "Ingridia";[4] the other, by Campos and Kellner, erected the genusTupandactylus;[5] ultimately, the latter name was used, since the publication by Unwin and Martill was published in a book months after the competing study. The genus nameTupandactylus derives from the name of the Tupí-Guaraní "Tupâ" or "Tupan", referring to a manifestation of the supreme deity Nhanderuvuçu which takes the form of thunder, and the Greekdaktylos ("finger").[4] A second species ofTupandactylus,T. navigans, was named in 2003; like thetype species, it, too, was initially assigned toTapejara.[3]
A 2021 study describing a very completeT. navigans specimen suggested that the two species might represent different sexes of onesexually dimorphic species, but cautioned that further study was needed to test this.[6]
Tupandactylus imperator has been estimated to have had a wingspan about 3 to 4 m (9.8 to 13.1 ft), whileT. navigans is smaller, with a wingspan of 2.7 m (8.9 ft).[6][7] In 2013,Mark P. Witton suggestedT. imperator had a wingspan of about 3 m (9.8 ft), and a standing height of 1.5 m (4.9 ft), when measured to the tip of its head crest.[8][a]
Tapejarids overall were characterised by short faces, the product of an abbreviated rostrum (snout) and a downturned jaw tip.[8] As a pterodactyloid,Tupandactylus bore a so-called nasoantorbitalfenestra, a structure created by the fusion of thenaris (nasal cavity) andantorbital fenestra.[8][9] When viewed from alateral (side) view, thepremaxilla formed a triangular plate above the nasoantorbital fenestra.[9] The premaxillas andmaxillas of pterodactyloids formed a single unit, the premaxillomaxilla, whose fusion occurred early inontogeny.[6] Theanterior (front) andventral (lower) margins of the resultant structure, as well as thedentary (the front portion of the lower jaw), were covered in arhamphotheca, or beak.[6][9] Rhamphotheca are known from multipleTupandactylus specimens.[6] The orbit (eye socket) was pear-shaped,[9] and as in other azhdarchoids, was positioned below the dorsal (upper) margin of the nasoantorbital fenestra;[8] however, whereas some taxa such asCaupedactylus had very low orbits, the orbit ofTupandactylus was more akin to that ofCaiuajara andTapejara.[6] The dentary had amandibular symphysis which was slightly downturned towards the front.[6] Like the skull, the dentary was crested. InT. imperator, the dentary crest is straight, whereas inT. navigans it is recurved.[9]
Tupandactylus is notable for its large cranial crest, composed partly of bone and partly of soft tissue fibres,[6][9] likelykeratin.[8] The crest was supported by a raised process on the premaxillomaxilla, often itself referred to as a crest, and a bony prong extending from the back of the head, formed from theparietal bone.[6][9] The crest shapes of the two species differed substantially.T. imperator had a large, rounded crest, fairly backswept, with an irregular rear margin, and with a length and height equal to about one-third of its total wingspan;T. navigans, meanwhile, had a more vertical cranial crest, with a straighterposterior (rear) edge, and a blunt posterior skull face, unlike other tapejarids.[8]
Hyoid bones are known from both species ofTupandactylus, ceratobranchials in both instances.[6][9] Little data exists on thehyoid apparatus in pterosaurs, though from what can be seen, those ofTupandactylus are typical for the clade.[9]
Eightcervical (neck)vertebrae, including theatlas (first) andaxis (second), were present in the skeleton ofTupandactylus navigans.[6] The main bodies of the vertebrae, thecentra, wereprocoelous, meaning that they were concave anteriorly and convex anteriorly. Theneural arches of the cervical vertebrae were inflated laterally, as is typical for pterodactyloids.Tupandactylus' dorsal vertebrae could be divided into three regions. The first fivedorsal (back) vertebrae are fused into anotarium,[6] like in some other pterosaurs and birds,[10] and particularly ornithocheiroids.[11] The notarium supported the shoulder girdle during flight, and prevented the ribcage from being compressed by the wing muscles during each stroke.[12] Posterior to the notarium was a set of five freely-moving mid-dorsal vertebrae, and posterior to that was a set of fivesynsacral vertebrae, dorsal vertebrae which had been incorporated into thesacrum for support. Fivecaudal (tail) vertebrae are preserved, described as "spindle-like". It is unlikely this is the full extent of the tail, though given the paucity of caudal remains from azhdarchoids it is difficult to say.[6]
Thesternum ofTupandactylus was wide and roughly square. Like that ofTapejara, it was perforated dorsally by apneumaticforamen (a hole connected to air spaces within the bone). Thescapulocoracoids (structures formed from the fusion of thescapula andcoracoid bones) were like those of other azhdarchoids, wherein the scapula was far longer. Thedeltopectoral crests were strongly developed, forming a significant portion of theshaft of thehumerus (the bone of the upper arm). The humeral shaft is straight, and is less anteroposteriorly compressed than inTapejara. Theradius andulna, the two bones of the forearm, were straight and lightly built. Thecarpal (wrist) complex was composed of two syncarpal bones, the paraxial carpal, and thepteroid bone, a structure found exclusively among pterosaurs.[6] The pteroid was oriented inwards, pointing towards the deltopectoral crest, and supported thepropatagium. Specialized muscles allowed it to move slightly.[13] InTupandactylus, the ulna was over half the length of the ulna. The first threemetacarpals (manus or hand bones) were slender and rod-like. The fourth metacarpal comprised roughly 37% of the length of the wing, minus the wing finger.Tupandactylus had twophalanges (finger bones) on the first of the ground-contacting finger, three on the second, and four on the third. In theT. navigans specimen, the ungual phalanges, the bones to which the claws were attached, preserve keratinous outlines. The first phalanx of each wing finger was roughly two-and-a-half times the length of the humerus, typically for tapejarids; the following phalanx was shorter, the third was even shorter, and the fourth is short and "mainly featureless".[6]
Thepelvis ofTupandactylus is mostly known, lacking only a few elements such as theprepubis. Thepubis is short and blunt; together with theischium, it forms the ischiopubic plate. Like most azhdarchoids (barring, for example,Caiuajara andZhejiangopterus), thefemora (the bones of the upper leg) were slightly longer than the humeri. The femora are typical for azhdarchoids, having a femoral shaft which appears bowed when viewed laterally, yet straight anteriorly or posteriorly. Thetibia andfibula, the two bones of the lower leg, were lightly built, roughly half as long again as each femur.Tupandactylus'proximal (upper) tarsals (pedal, or foot bones) were thecalcaneum and theastragalus, which were similar to those ofSinopterus andTapejara. As in all late-diverging pterodactyloids, only four pedal digits were present. The pedal phalanges were thin and elongated. As in other pterodactyloids, the manual (forefoot) unguals were considerably larger than those of the pes.[6]
Some specimens ofTupandactylus imperator preservepycnofibres,[7][14] filamentous structures similar to mammalian hair found in all pterosaurs.[8][15] A well preserved fossil ofT. imperator was found to have pigment cells with similar forms to those seen in modern birds, more complex in organization than those previously known from other pterosaurs. This specimen also suggest the presence ofStage IIIa feathers, further indication of more complex filament structures in pterosaurs. Supporting a model of common ancestry with the filaments of birds, the authors termed these structures as pterosaur feathers rather than pycnofibres.[16] This common origin had been suggested before, but remains controversial.[8][17][18]
Beginning in 2006, several researchers, including Kellner and Campos (who namedTupandactylus), had found that the three species traditionally assigned to the genusTapejara (T. wellnhofferi,T. imperator, andT. navigans) are in fact distinct both in anatomy and in their relationships to other tapejarid pterosaurs, and thus needed to be given newgeneric names. However, just how the species should be split proved controversial. Kellner and Campos considered onlyT. imperator to warrant a new name, creatingTupandactylus.[5] However, another study published in 2007 by Unwin and Martill found thatT. navigans, previously assigned toTapejara, was actually most closely related toT. imperator and belonged with it in a new genus separate fromTapejara. In 2007, at a symposium held in honor of renowned pterosaur researcherPeter Wellnhofer, Unwin and Martill announced the new genus nameIngridia, in honor of Wellnhofer's late wife Ingrid. However, when they published this name in a 2007 volume, they assignedimperator as thetype species of their new genus, rather thannavigans, which they also included as a species ofIngridia.[19] Furthermore, Unwin and Martill's paper was not published until several months after the similar paper by Kellner and Campos. Therefore, because both sets of authors usedimperator as the type,Ingridia is considered ajunior objective synonym ofTupandactylus.[20] It was not until 2011 thatT. navigans was formally reclassified in the genusTupandactylus, in a subsequent study supporting the conclusions of Unwin and Martill in 2007.[7]
The cladogram below follows the 2014phylogenetic analysis by Brian Andres and colleagues. They found bothT. navigans andT. imperator within the tribeTapejarini, which in turn was within the larger groupTapejaridae.[21]
Like other azhdarchoids, including other tapejarids,Tupandactylus may have largely been a terrestrial forager. Examination of the specimen GP/2E 9266 suggests that the pterosaur was capable of flight, but seemingly spent much of its time on the ground thanks to its large crest, longer forelimbs, and a relatively long neck, only taking short flights to possibly escape from predators. Simultaneously, it was not adapted to the same terrestrial stalking lifestyle asazhdarchids are believed to have utilized.[6][22] Rather, the skull anatomy ofT. navigans closely resembles that ofTapejara itself, a taxon suggested to have subsisted upon plant material.[6] The mandible portion of the well-preservedT. imperator skull is directly associated with plant material, either representing ataphonomic phenomenon or possibly a tentative evidence of herbivory.[9]
The impact of a large head crest onTupandactylus' flight has seen some discussion in the literature.[6] In their 2003 paper describingT. navigans, Eberhard Frey, David Martill, and Marie-Céline Buchy argued that it would have significantly impacted its aerodynamics, and that adaptations to counteract it (i.e. a reduced neck with tendon locks on each cervical vertebra) were conspicuously absent.[3] Accordingly,Tupandactylus may have been restricted to flying only short distances.[6]
