A new paper on the evolution of pterosaur pelves (Hyder, Witton and Martill 2012?) just came out. It’s twofold purpose: 1) pterosaur pelves may carry phylogenetic signatures that could be incorporated into studies of pterosaur evolution, and 2) the pelvis probably played different functional and mechanical roles in different groups (i.e. differing roles in locomotion, trunk mechanics and support, internal anatomy, reproductive functionality etc.). Here, we assess both of these possibilities with an overview of pterosaur pelvic evolution presented in the phylogenetic model of Lü et al. (2010), and we present functional hypotheses that may have influenced its development.”
Ontogeny in the Pelvis
Hyder et al report, “Pterosaur pelvic morphology is known to reflect likely ontogenetic (Bennett 1993, 1995) and sexual (Bennett 1992; Lü et al. 2011a) variation.” Unfortunately this statement reflects acceptance without phylogenetic testing. Testing here reveals the opposite case. Several pterosaur embryos and a few verifiable juveniles demonstrate that not much changes during ontogeny. Thus all other differences overall and in the pelvis, represent distinct species, not genders or maturity levels. The Rhamphorhynchus pelves (Fig. 1) retraced from Bennett (1992) retraced from Wellnhofer (1975) reflect phylogenetic changes as demonstrated by the large pterosaur family tree. The largest Rhamphorhynchus by far does not fuse the pubis to the ischium. The darkwing specimen of R. muensteri does not have a fused pubis/ischium. A tiny R. longicaudus sutures the pubis to the ischium.
Ossification in the Pelvis as an Ontogenetic Marker
Hyder et al. report, “Pterosaur pelvic bones ossify before fusing with the ribs of the sacral vertebrae to form a synsacrum, suggesting this is the final stage of fusion in the development of the hindlimb girdle (Codorniú et al. 2006).” Testing here reveals the opposite case. Ossification follows phylogenetic patterns with some very large pterosaurs ossifying more poorly than some very small pterosaurs.
Supraneural Plate in the Pelvis as an Ontogenetic Marker
Hyder et al. report, “The supraneural plate of the pterosaur synsacrum is worthy of attention. This structure seems to develop late in ontogeny, although this is currently only – and by no means unambiguously – demonstrated in ornithocheiroid pterosaurs.” Testing here reveals the opposite case. As mentioned above, the supraneural plate appears in only a few clades, demonstrating its phylogenetic pattern.
Sacrum as an Ontogenetic Marker?
Hyder et al. report, “The sacral vertebrae between each set of pelvic bones fuse to form a continuous sacrum comprising at least three, but more typically four or more vertebrae in all pterosaurs. As with other archosaurs, the precise number varies with age as the sacrum incorporates posterior dorsal vertebrae and, in some cases, anterior caudal vertebrae (Bennett 2001; Unwin 2005).” Unfortunately, this too is false and misleading. First, pterosaurs are not archosaurs, they are lizards, as demonstrated by testing both in the large reptile family tree. Second, the precise number of sacral vertebrae varies phylogenetically and may increase or decrease, fuse or lose fusion depending on a pterosaur’s place in the family tree. Outgroup taxa, such as Cosesaurus had four sacrals. Sharovipteryx had more.
Hyder et al. report, “Sexual dimorphism in pterosaur pelves has been noted in at least Pteranodon and Darwinopterus, with both genera demonstrating relatively broad pelvic canals in putative females (Bennett 1992; Lü et al. 2011).” Testing here reveals the opposite case. The purported female Pteranodon is a big Nyctosaurus. No comparative reconstructions of male and female Darwinopterus pelves have ever been published. Here several Darwinopterusreconstructions demonstrate phylogenetic differences, not gender differences. Hyder et al. report, “Other pelves appear to remain unfused along their ventral margins; a feature that has been suggested as exclusive to female individuals (Lü et al. 2011). Unfortunately no one-to-one gender differences have ever been demonstrated. Rather all such differences are demonstrated to be phylogenetic when plotted on the large pterosaur family tree.
No Reference to the Prepubis?
Strangely Hyder et al. virtually ignored the prepubis. Not sure why. Here’s what they said, “Uniquely, the pterosaur pelvis possesses prepubes, a pair of bones that articulate anteroventrally with the pubes.” Not uniquely. Prepubes are also found in fenestrasaurs starting with Cosesaurus and basal mammals, the latter by convergence.
No Outgroup References?
Strangely Hyder et al. ignored outgroup pelves. Not sure why. You can see Cosesaurus here, Sharovipteryx here and Longisquama here. The most primitive pterosaur, MPUM 6009, is here. Austriadactylus is here. This Triassic pterosaur is also more primitive than the Jurassic Dimorphodon. All have an elongated ilium and incorporate four or more sacrals.
Is the Fossil Record Biased Toward Young Individuals?
Hyder et al report, “Moreover, because sacral vertebral count is so variable through ontogeny, and the pterosaur record is biased in favour of immature individuals (e.g. Bennett 1995), we do not discuss it further here.” In no other fossil clade is the record biased towards immature individuals. And pterosaurs were no exception. The continual resistance to testing the tiny pterosaurs to see if they were indeed immature or simply tiny is a continuing problem plaguing pterosaur paleontology. As long as the leaders, the experts, refuse to even discuss the possibility that tiny pterosaurs are sparrow-sized adults, then the science can’t move forward. Again, inclusion in phylogenetic analysis will solve so many problems – but only if the fear to do so subsides.
Dimorphodon and Peteinosaurus
Hyder et al. reported on Dimorphodon, “The preacetabular process is distinctively short, barely projecting beyond the anteriormost extension of the pubis and it is subequal in size to the postacetabular process.” Unfortunately, the preacetabular process of the ilium is broken off in all known Dimorphodon. Hyder et al. only present tracings of prior renditions of pelves, not photographs or original tracings, so I wonder if their diagnoses were based on drawings alone? Impressions in the matrix of the ilium (plus the broken bone) indicate a further extension was present.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
Hyder ES, Witton MP and Martill DM 201X. Evolution of the pterosaur pelvis. Acta Palaeontologica Polonica 5X (X): xxx-xxx. http://dx.doi.org/10.4202/app.2011.1109