Scathing Book Review – Pterosaur hind limb muscles and the prepubis: Witton vs Peters

Earlier here, here and here we had a critical look at the hypotheses regarding various aspects of pterosaur phylogeny and morphology. Today we’ll look at the muscles of the pterosaur hind limb and how Witton (2013) emaciated them.

Pterosaur hind limb muscles according to Witton (2013, above) and based on lizard musculature (Fig. 2).

Figure 1. Pterosaur hind limb muscles according to Witton (2013, above) and based on lizard musculature (Fig. 1, below and Figs. 2, 3). Witton does not extend femoral muscles to the prepubis or the anterior ilium. Evidently it’s important for those who do not want pterosaurs to exhibit any bipedal abilities to denigrate hind limb muscle strength, as shown by the emaciated appearance Witton gives them and by reducing their anchorage.

Make sure those hind limbs look emaciated
if you want to convince others that pterosaur hind limbs were not capable of providing bipedal locomotion (in step with quadrupedal locomotion for most) or hindlimb leaping/launching/takeoff. Witton 2013 emaciates his pterosaur femoral muscles and reduces their points of origin on the ilium and prepubis. Why? He supports the forelimb launch hypothesis for pterosaurs big time.

Two dead lizards, dorsal and ventral views. Note the meaty thighs.

Figure 2. Two dead lizards, dorsal and ventral views. Note the meaty thighs. Same as in birds and crocs. Witton emaciates them.

Real lizard femoral muscles are robust and meaty (Figs. 2,3 ). The muscles get thicker at mid thigh. This even happens in birds and crocs! Why would Witton emaciate them?

Lizard muscles according to Romer (1956. 1062,1971). Ilium muscles in red. Pubis and ischium muscles in blue. Caudal muscles in yellow.

Figure 3. Lizard muscles according to Romer (1956. 1062,1971). Ilium muscles in red. Pubis and ischium muscles in blue. Caudal muscles in yellow. Curious that no muscles arise from the posterior ilium.

No Prepubis Anchor
Pterosaurs extend their ventral muscle anchorage by adding a prepubis, which can be very long indeed in Rhamphorhynchus (Fig. 2) and Campylognathoides (Fig. 3). No muscles attach to the prepubis in Witton’s version (Fig. 1). One wonders why not, especially when the prepubes and femora are aligned during normal locomotion (Figs. 2-4).

Instead Witton 2013 follows Claessens et al. (2009) mistake when he reports the prepubes “were capable of moving up and down with each breath taken by their owner.” This “rotating prepubis” hypothesis was falsified earlier based on the Claessen et al. use of a flipped and partial prepubis to support their hypothesis. They got the bone upside down!! No other prepubes in any other pterosaurs support the Claessen et al. hypothesis. The pubis/prepubis joint is a butt joint in all pterosaurs. So it basically cannot move. The prepubis acted as an extension to the pubis. Pubofemoralis muscles probably extended down the prepubis as if it were an elongated pubis. Respiration occurred by expansion of the ribs, as in all tetrapods, not by the rotation of the prepubes. Correctly configuration shown below (Figs. 2-4).

The darkwing Rhamphorhynchus JME SOS 4785

Figure 2 The darkwing Rhamphorhynchus JME SOS 4785. Note the depth of the prepubis. Even if this prepubis could rock back and forth it would not further deepen the torso.

 The Pittsburgh specimen of Campylognathoides. This pterosaur had the largest prepubes of all pterosaurs. Note the ventral orientation, aligned with the femora during normal standing.

Figure 3. The Pittsburgh specimen of Campylognathoides. This pterosaur had the largest prepubes of all pterosaurs. Note the ventral orientation, aligned with the femora during normal standing. Note the butt joint between the pubis and prepubis.

The Triebold Pteranodon, one of the most complete ever found. The metacarpals are quite a bit longer here. So is the beak.

Figure 4. The Triebold Pteranodon, one of the most complete ever found. I have this skeleton cast. The prepubes extend ventrally, in line with the femora and unable to expand the torso during respiration. Expanding ribs, as in all tetrapods, provided all the necessary torso expansion for respiration.

Witton's prepubis mistakes, based on mistakes by Claessen et al. 2009. (Above) in Rhamphorhynchus the prepubis is waaaay too small. In both the prepubis is incorrectly oriented and incorrectly attached to the pubis.

Figure 5. Witton’s prepubis mistakes, based on mistakes by Claessen et al. 2009. (Above) in Rhamphorhynchus the prepubis is waaaay too small. In both pterosaurs the prepubis is incorrectly oriented and incorrectly attached to the pubis.

Elongate ilia
And why would the all pterosaur ilia extend so far anterior (especially so in Sos 2428), framing so many sacrals (Fig. 1), without bringing a few muscles with them? After all, that’s what mammals and dinosaurs do. And the muscles arising from the ilium in lizards concentrate anteriorly. Finding homologies and analogies is how we find the most parsimonious answer.

The missing caudofemoralis
Lizards and most dinosaurs have a robust tail with elongate transverse processes and deep chevrons. These are muscle anchors for the caudofemoralis, tail muscles that pull the femur posteriorly, contributing to the step cycle. In birds and pterosaurs these muscle anchors are largely, but not completely missing. The pelvis (and prepubis) have taken over those duties. The caudofemoralis is largely, but not completely missing in birds and probably pterosaurs. As in birds, pterosaur the anchoring transverse processes are vestigial or missing and their chevrons, where present, extend parallel to the caudal centra, not ventrally. In pterosaurs, chevrons are not caudofemoralis anchors, but secondarily adapted as tail stiffeners. They are essentially absent in basal pterosaurs, like MPUM6009. They redevelop in several taxa. These same caudal patterns (attenuated tails) are found in pterosaur precursors, the fenestrasaurs, evolving from less attenuated tails in tritosaur lepidosaurs, a key trait that ties them all together.

It’s important to examine living animals to see their muscle patterns in order to reconstruct them in prehistoric animals. It’s important to know what new bones, like the prepubis, are used for (not respiration). It’s important to note the details in a skeleton, establishing articular surfaces and creating accurate reconstructions.

References
Claessens, LPAM, O’Connor PM and Unwin DM 2009. Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism. PLoS ONE 4(2):e4497.http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004497
Romer AS 1971. The Vertebrate Body (shorter version). WB Saunders Co. 452 pp.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.x

2 thoughts on “Scathing Book Review – Pterosaur hind limb muscles and the prepubis: Witton vs Peters

  1. Sharing this on Facebook, David. The Orthodox Repress-ocricy will hate me for it, but their idea of science is too repressive of ideas and lacking in discussion for me to believe them wholesale.
    You DO have some allies there and I hope to expand that base quite a bit.

  2. In every creature whose pubic musculature I’ve been able to study…informally, of course…all of the bone structures have muscles attached, mammals, archosaurs, reptiles, and birds. Muscles bulge when contracted and most every skeletal muscle I’m familiar with does NOT have a straight outline from attachment point to attachment point. Tendons will have straight line outlines, not skeletal muscles. Thus, your claims here carry a lot of resonance with me.

    Plus, I’ve yet to see you wholesale condemn anyone or their entire volume of work, which speaks loudly of confidence based on the quality of your work and the quality of your integrity.

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