Continuing a story of the low-key, not-Spinosaurus paleontological papers recently published, discussing our bizarre Mesozoic macrofauna, this installment covers a few pterosaur tidbits.
The first of these is an amazing assemblage of scattered bones of numerous different-sized individuals that are all almost certainly a single species of pterosaur. What is remarkable about this assemblage is that there are several extremely well-preserved remains of individuals, including skulls, with further support for sexual-dimorphism of the cranial crest in some pterosaurs. The second of these is a paper on the tail of an heretofore otherwise un-tailed group of pterosaurs, Anurognathidae, and the implications of this tail relating to their phylogenetics.
The First Tail – What of the Crest?
The first of these describes the new non-pterodactyloid-ish Hamipterus tianshanensis, an ornithocheiroid with some istiodactylid-like features and a vaguely Darwinopterus-like skull. Described by Wang Xiaolin and colleagues and to be published in Current Biology, this pterosaur is known from an extensive series of bonebeds in close layering, suggesting likely gregarious behavior. Much ado was made of this just very recently by Darren Naish at Tetrapod Zoology, so check it out.
The basal nature of Hamipterus tianshanensis within Ornithocheiroidea, the group containing Pteranodontidae, Nyctosauridae, Istiodactylidae, and the large complex of “Ornithocheiridae” (=Anhangueridae, Loncodraconidae, Ornithocheiridae proper) — and also called Pteranodontoidea by more recent workers as the stem opposing all other Pterodactyloidea (Ctenochasmatoidea and “Dsungaripteroidea“) — is speculative. A phylogenetic analysis supported inclusion of Hamipterus tiqnshanensis within pteranodontoids in an unresolved grouping to which Pteranodon longiceps is the sister taxon. The cranial morphology is very similar to various “Pterodactylus-grade” and “Darwinopterus-grade” pterosaurs, by which is meant a large nasoantorbital fenestra, relatively numerous and well-spaced teeth, a high-placed orbit and a generalized rear of the skull. Absence of the flexed skull with a ventrally-facing occiput as in ctenochasmatoids, and divergent tooth morphology with much larger rostral teeth or a rosette, excludes it from other more specialized groups.
The largest skulls sport a tall, rounded mid-line crest along the rostrum which peaks in front of the nasoantorbital fenestra and extends to between the orbits. The crest is bony, high, and scored by numerous thin grooves which curve anteriorly from the base of the crest, a characteristic similar to the bony crests in Dsungaripteridae and Normannognathus wellnhoferi, suggesting that the small-toothed, upward-curving jaws that compose all that is known of the latter may actually be ornithocheiroid in nature, rather than either dsungaripterid as originally assumed or even ctenochasmatoid as has been thought more recently. It is notable that the rostra of most anhanguerid-grade ornithocheiroids, including istiodactylids and Normannognathus wellnhoferi and Hamipterus tianshanensis, are all gently curved upwards. This characteristic has long been a “classic” of ctenochasmatoids, and was instrumental in referral of Normannognathus to that group (Buffetaut et al., 1998). Due to the presence of a distally-twisted deltopectoral crest of the humerus (the absence of a distinct medial ridge, but instead a gradual curvature, distinguishes this from “typical” warped-crested humeri), tall and spike-like neural spines of the cervical vertebrae, and a longer coracoid than the scapula, Hamipterus tianshanensis is almost certainly a pteranodontoid/ornithocheiroid, but more certain affinities are unresolved.
In addition, ovoid masses collected with the bonebeds (not collected in one area, but scattered amongst the specimens) indicate the presence of leathery-shelled eggs, confirmed by SEM examination. This confirms more recent work implying pterosaurs typically laid leathery, squamate- and crocodilian-like eggs rather than the highly calcified hard-shelled eggs of birds. Like eggs of Pterodaustro guinazaui, the shells of these eggs exhibit a crystalline outer layer also characteristic of some squamates, but unlike that of most other pterosaurs.
The authors considered the likelihood that the bonebeds, containing specimens varying in size with the largest over twice that of the smallest, represented not merely an age-independent colony but also that it was composed of individuals of various sexes. To confirm this, they analyzed the skulls and found that at varying sizes skulls either had a shallow or a tall, ornate cranial crest, the first mid-line crest of its type known for any ornithocheiroid, and assumed that sexual selection was at play, with females bearing the smaller crests. However, deeper work, such as investigating long bones for the possible presence of medullary bone (built up in birds during the nesting season and used to deposit layers of the hard shell when laying), has not yet been done.
Buffetaut, E., Lepage, J.-J. & Lepage, G. 1998. A new pterodactyloid pterosaur from the Kimmeridgian of the Cap de la Hève (Normandy, France). Geological Magazine 135 (5): 719-722.
Wang X.-l., Kellner, A. W. A., Jiang S.-x., Wang Q., Mia Y.-x., Paidoula Yahefujiang, Cheng X., Rodrigues, T., Meng T., Zhang J.-l. Li N. & Zhou Z.-h. in press (2014). Sexually dimorphic tridimensionally preserved pterosaurs and their eggs from China. Current Biology 24: 1-8. DOI:10.1016/j.cub.2014.04.054
The Second Tail – Well, What About It?
Anurognathids are known by many things: A broad, short head on the end of a longish-neck and short trunk, broad wings, and a very short tail. Of the known four species of Anurognathidae, only one has markedly deviated from this pattern, Dendrorhynchoides curvidentatus. When first discovered at Mutoudeng in Qinglong, Hebei Province, China, the holotype of Dendrorhynchoides curvidentatus (GMV 2128; Ji & Ji, 1998) had undergone some … plastic surgery of a sort, in the form of reconstruction of the skeleton in various places. Where once the base of the tail was incomplete and a series of elements further distal were interpolated with fake, plaster tail segments, complete with long processes as in “typical” rhamphorhynchoids composing elongated rods of the prezygapophyses and haemal arches. Comparison of this most-complete anurognathid (at the time) to later material suggested that the long tail was not merely fake, but unlikely; all other anurognathids sported tail vertebrae that became progressively shorter over the length until it tapered not much longer than the knee, if that long. A later specimen of anurognathid (JZMP-04-07-3; Lü & Hone, 2012) from Mutoudeng (which Lü & Hone named Dendrorhynchoides mutoudengensis on the basis primarily of disparate sizes in teeth in the new species, which based merely on two specimens seem speculative) purported that this tail length was unlikely, that the original reconstructed length (though not its morphology) may have been correct.
Now, yet a newer specimen (IVPP V16728) from the same locality is reported by Jiang Shun-xing and colleagues (much of the same as the previous paper’s in Tail 1, above; and will appear in paper in the same volume as mine on Banguela oberlii) suggests that not only was the tail in Dendrorhynchoides atypically long, it may have sported what no other anurognathid tail known yet possessed, elongated supporting rods formed from anterior processes of the prezygapophyses and haemal arches, characteristic in campylognathoidids, “eudimorphodonts,” “dimorphodontids,” rhamphorhynchoids, and wukongopterids, but absent in later taxa. I previously discussed the discovery of a “pterodactyloid” with a characteristically short tail bearing elongated rods (Pterosaur, Inter-Modulated), but as the specimen was a juvenile it leaves one worried about the effect ontogeny has on length length and morphology, a subject that, due to problems in preservation of small pterosaurs, has received next to no attention. This specimen supported that the “rhamphorhynchoid” grade shortened their tails then lost the stiffening rods, but while the tails were short, they remained stiff, implying retention of stiffening agents elements was enforced: there was a functional constraint maintaining their presence as the tail became abbreviated. The same seems to be true at least in anurognathids, but it also suggests something more intriguing.
(This isn’t the first anurognathid specimen reported with this morphology. In an abstract presented to the Rio Ptero conference in 2013, Fabiana Rodrigues Costa and colleagues — again, part of the same authorship as this and the previous paper — infer the similar presence of elongated rods in a long anurognathid tail in a referred specimen to the Kazaqstani anurognathid Batrachognathus volans, but this material remains unpublished.)
In various analyses, Anurognathidae tends to be favored as one of the most basal groups of pterosaurs. But given the enormously apomorphic cranial and wing morphology, it is questionable whether the effects placing them basally are reversals to a plesiomorphic condition relating to many unique characteristics of their wing anatomy and cranial morphology and not, rather, evidence of their plesiomorphic condition. If this is the case, if the analyses of Dalla Vecchia (2009) and Andres et al. (2010) are robust in comparison, and in the end correct, this implies that anurognathids are one of the more derived younger groups of pterosaurs, placing them back amongst their conical-toothed kin rather than with the cuspidate-toothed “eudimorphodonts.” Moreover, it places them near the modular evolution of characters with respect to Pterodactyloidea, that realm that gave us Darwinopterus and the rest of the wukongopterids, and Monofenestrata. It may make anurognathids the sister lineage to all other monofenestratans. Time will tell.
Andres, B., Clark, J. M. & Xu X. 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs. Journal of Vertebrate Paleontology 30 (1): 163-187.
Dalla Vecchia, F. M. 2009. Anatomy and systematics of the pterosaur Carniadactylus gen. n. rosenfeldi (Dalla Vecchia, 1995). Rivista Italiana Paleontogia i Stratigraphia 115 (2): 159-188.
Jiang S.-x., Wang X.-l., Cheng X., Rodrigues Costa, F., Huang J.-d. & Kellner, A. W. A. in press. (2014) Short note on an anurognathid pterosaur with a long tail from the Upper Jurassic of China. Historical Biology DOI:10.1080/08912963.2014.954570
Lü J. C. & Hone, D. W. 2012. A new Chinese anurognathid pterosaur and the evolution of pterosaurian tail lengths. Acta Geologica Sinensis (English Edition) 86 (6): 1317-1325.