SVP abstracts: Dr. Padian and Pterosaur Ichnites
Dr. Kevin Padian has written extensively on pterosaur locomotion. He promoted a bipedal configuration until quadrupedal pterosaur tracks were widely reported in 1995. This year at the SVP convention he presented the following [abridged] abstract, “We performed a meta-analysis of nearly 100 reports and reviews of alleged pterosaur tracks. More than a third were redundant reports; fewer than 10% examined the evidence for attribution. There was a significant correlation among (1) attribution of trackways to pterosaurs, (2) no consideration of alternative hypotheses of trackmakers, (3) lack of anatomical or kinematic evidence for the attribution, and (4) referral of justification for the attribution to two (or a very few) recurrent publications. We found no skeletal anatomical apomorphies of pterosaurs reflected in any diagnosis of trackways, including reformulations of the original diagnosis of Pteraichnus saltwashensis. In almost all cases of trackways referred to pterosaurian trackmakers (with the notable exception of the tracks from Crayssac, France) there is no evidence of pterosaurian apomorphies. Some of these assigned trackways, such as Purbeckopus, show clear crocodilian apomorphies reflected in their diagnoses. Others, such as Haenamichnus, show no discernible anatomical features. Over 90% of the ichnological literature contains no analysis of skeletal or functional features that an assignment to a pterosaurian trackmaker requires. Because no trackways assigned to pterosaurs are well enough preserved to determine either a manual or pedal phalangeal formula, it is impossible to reconstruct the skeletal manus and pedes of the trackmakers assigned to any Pteraichnidae (traditionally presumed to be tracks of pterosaurs). Nearly all trackways attributed to pterosaurs show (1) a gleno-acetabular ratio lower than commensurate with known pterosaurs, (2) a length-width ratio of the pes (metatarsals + phalanges) incommensurate with known pterosaurs, and (3) a preservation so poor as to make attribution of a trackmaker impossible. The Crayssac tracks differ in derived respects from all other attributed trackways, despite deficient preservation, because they show true pterosaurian apomorphies; they should be systematically separated, as other authors have advocated. It is difficult to assign most tracks referred to Pteraichnidae to pterosaurs or any taxon. We propose morphological and preservational criteria by which to evaluate alleged pterosaur tracks.”
Well, in the wake of the “catalog of pterosaur pedes as a guide to identifying trackmakers” (Peters 2011), this comes as something of a surprise.
Figure 1. Pteraichnus nipponensis along with a matching trackmaker. Atypical for pterosaurs, finger four points anteriorly. The loose lizardy finger joints permit this sort of odd extension.
Pteraichnus tracks are quite distinct, despite their morphological variation. Typically four toes point anteriorly and the lateral fifth toe is often absent or tiny if impressed. A heel print is often present. These represent pterodactyloid grade pterosaurs. In anurognathid tracks (Peters 2011), like cosesaurid tracks (Rotodactylus) (Peters 2000) four toes point anteriorly, the heel imprint is missing and the fifth toe makes an impression far behind the others. These represent basal forms.
In many pterosaur tracks the hand impression is also the dead giveaway. Digits 1 and 2 typically point laterally. Digit 3 points posteriorly. Digit 4 is totally absent. Sometimes the hand impressions are absent (imagine pteros bipedal). Sometimes only the hand impressions are present (imagine pteros floating and poling along the shallow bottom).
Let’s take Padian’s points one at a time.
1. “We found no skeletal anatomical apomorphies of pterosaurs reflected in any diagnosis of trackways” Contra this finding, the catalog of pterosaur pedes (Peters 2011) presented dozens of pterosaur feet alongside the few Pteraichnus tracks wherever good matches could be made.
2. Purbeckopus show[s] clear crocodilian apomorphies. This is a difficult assignation, but is a close match to tiny anhanguerid feet (Peters 2011). I earlier (Peters 2000) made a mismatch with a cycnorhamphid foot based on the drawn outline, which did not capture all the details of the specimen, which I later traced.
3. Haenamichnus, show[s] no discernible anatomical features. A messy imprint, to be sure, but the general outline is pterosaurian, as the original authors suggested. Peters (2011) matched it to an azhdarchid pes.
4. “Because no trackways assigned to pterosaurs are well enough preserved to determine either a manual or pedal phalangeal formula, it is impossible to reconstruct the skeletal manus and pedes of the trackmakers assigned to any Pteraichnidae.” Pterosaur tracks are like gloves. They mask what’s inside (the bones), but sometimes in certain tracks clues appear, as detailed in Peters (2011) and the references therein.
5. “It is difficult to assign most tracks referred to Pteraichnidae to pterosaurs or any taxon.”
Having had a look at the gamut of possible trackmakers while creating ReptileEvolution.com, I can tell you that no other taxon comes closer than pterosaurs to Pteraichnus track, taking into account their wide variety, especially so when manus tracks are present. The lateral of rotation of the manus and posterior rotation of manual digit 3 can only come about in a secondarily quadrupedal form, like a pterosaur.
Figure 2. Click to animate. Plantigrade and quadrupedal Pterodactylus walk matched to tracks
5. “Nearly all trackways attributed to pterosaurs show (1) a gleno-acetabular ratio lower than commensurate with known pterosaurs,”
That’s because pterosaurs walked more upright than most authors, including Padian, imagine them (fig. 2).
6. “a length-width ratio of the pes (metatarsals + phalanges) incommensurate with known pterosaurs.”
Not true. Close matches can be found if reconstructions of dozens of pterosaur pedes serve as your catalog. There is wide variation in the feet, so much so that they are as good as fingerprints, all documented in Peters (2011).
7. “a preservation so poor as to make attribution of a trackmaker impossible.”
This is no time to be throwing up your hands in surrender! And it is not asking too much of a fossil created in wet mud or sand. The process of elimination and the process of matching solves this problem.
Kevin Padian was the first paleontologist I ever corresponded with as he was the go-to expert for the Giants book that came out in 1986. I have been to his house and his lab. Padian’s brilliance was recognized early and he has been a spokesperson for evolution and all things pterosaurian for several decades. Even so, he has been slow to recognize the lizard ancestry of pterosaurs, preferring to keep them in the Archosauria without testing alternatives. It has meant several decades of frustration that he has never embraced my work, much of which supported his work (digitigrady, bipedal configuration, narrow wing chord), when others were distancing themselves from it. I still hold out hope that we will find common ground someday.
Unfortunately, Padian, like so many other pterosaur workers, tends to promote all-or-nothing hypotheses regarding pterosaur configuration and behavior, when the evidence demonstrates that several configurations and behaviors were present based on the bones and tracks.
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.
References
Padian K 2012. Meta-analysis of reported pterosaur trackways: Testing the correspondence between skeletal and footprint records. Abstracts, Journal of Vertebrate Paleontology.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
2012-10-18 19:02:25
Source: http://pterosaurheresies.wordpress.com/2012/10/19/svp-abstracts-dr-padian-and-pterosaur-ichnites/
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