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Ontogeny and gender dimorphism in pterosaurs – SVP abstract 2016

Saturday, November 5, 2016 14:01
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(Before It's News)

Unfortunately,
and apparently, this is yet another study (Anderson and O’Keefe 2016) with a priori species assignations prior to a robust phylogenetic analysis and the creation of precise reconstructions. I hope I’m wrong, but no mention of phylogenetic analysis appears in the abstract. Nor do they mention creating reconstructions. Bennett (1993ab, 1995, 1996a, 2001ab, 2006, 2007) failed several times in similar fashion (with statistical analyses) to shed light on the twin issues of pterosaur ontogeny and dimorphism, coming to the wrong conclusions every time, based on results recovered by creating reconstructions and analyses. Further thoughts follow the abstract.

From the Anderson and O’Keefe abstract:
“The relationships of pterosaurs have been previously inferred from observed traits, depositional environments, and phylogenetic associations. A great deal of research has begun to analyze pterosaur ontogeny, mass estimates, wing dynamics, and sexual dimorphism in the last two decades. The latter has received the least attention because of the large data set required for statistical analyses. Analyzing pterosaurs using osteological measurements will reveal different aspects of size and shape variation in Pterosauria (in place of character states) and sexual dimorphism when present. Some of these variations, not easily recognized visually, will be observed using multivariate allometry methods including Principle Component Analysis (PCA) and bivariate regression analysis. Using PCA to variance analysis has better visualized ontogeny and sexual dimorphism among Pterodactylus antiquus, and Aurorazhdarcho micronyx. Each of the 24 (P. antiquus) and 15 (A. micronyx) specimens had 14 length measurements used to assess isometric and allometric growth. Results for P. antiquus analyses show modular isometric growth in the 4th metacarpal, phalanges I–II, and the femur. Bivariate plots of the ln-geometric mean vs ln-lengths correlate with the PCA showing graphically the relationship between P. antiquus and A. micronyx which are argued here to be sexually dimorphic and conspecific. Wing schematic reconstructions of all 39 specimens were done to calculate individual surface areas and scaled to show relative intraspecific wing shape and size. Finally, Pteranodon, previously identified having with sexually dimorphic groups, was compared with ln-4th metacarpal vs ln-femur data, bivariately, revealing similarities between the two groups (P. antiquus and A. micronyx = group 1; Pteranodon = group 2) in terms of a sexual dimorphic presence within the data sets.”

The Pterodactylus lineage and mislabeled specimens formerly attributed to this

Figure 3. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus

If these two workers actually had 24 P. antiquus specimens to work with,
then it was only because the labels told them so. Or they came across a cache on a slab of matrix I’m not aware of. Pterodactylus has been a wastebasket taxon for a long time (Fig.1) that, apparently the authors didn’t bother to segregate with analysis. Anderson and O’Keefe do not indicate they arrived at a large clade of P. antiquus specimens after phylogenetic analysis. Having done so, I can tell you that no other tested Pterodactylus is  identical to the holotype and no two adult pterosaurs I’ve tested are alike, even among RhamphorhynchusGermanodactylus and Pteranodon. The differences I’ve scored are individual to phylogenetic and they create cladograms that illuminate interrelationships, not sexual dimorphism or ontogeny. There are sequences of smaller species and larger ones. These can appear to be two genders, but that is a false result.

Embryo to juvenile pterosaurs
are isometrically miniaturized versions of their parents as the evidence shows time and again across the pterosaur clade. These facts have been known for over five years and it’s unfortunate that old traditions continue like this unfettered and untested under phylogenetic analysis… or so it seems… I could be wrong having not seen the presentation.

References
Anderson EC and O’Keefe FR 2016. Analyzing pterosaur ontogeny and sexual dimorphism with multivariate allometery. Abstracts from the 2016 meeting of the Society of Vertebrate Paleontology.
Bennett SC 1993a. The ontogeny of Pteranodon and other pterosaurs. Paleobiology 19, 92–106.
Bennett SC 1993b. Year classes of pterosaurs from the Solnhofen limestone of southern Germany. Journal of Vertebrate Paleontology. 13, 26A.
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett SC 1996a. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Bennett SC 2001a, b. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260:1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260:113–153.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Bennett SC 2007. A review of the pterosaur Ctenochasma: taxonomy and ontogeny. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 245:23–31.

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