Updated June 10, 2015 with a revised Dimorphodon takeoff (Fig. 3) that included a downstroke right at the start of the leap.
Earlier we looked at the inaccurate cartoon produced of the hind-wing glider, Sharovipteryx by author and illustrator, Mark Witton. Here we’ll continue up the phylogenetic line to consider the disfigurements Witton applied to a basal pterosaur.
As a purported pterosaur expert, Mark Witton, author of the new book “Pterosaurs,” should be able to accurately portray a pterosaur skeleton. Unfortunately his Dimorphodon drawing is filled with errors (Fig. 1). For comparison, an accurate portrayal based on a bone-by-bone tracing is shown below (Fig. 4).
- Apparent mandibular fenestra – caused by a slipped surangular detailed here and confirmed by Bennett (2013).
- All pterosaurs have eight cervicals (prior to ninth vert with deep ribs)
- 1st and 2nd dorsal ribs should be hyper-robust and 2nd articulates with sternal complex
- Prepubis is the wrong shape and should articulate with the ventral pubis at its stem and against the edges of the last gastralia at its anterior process
- Caudal vertebrae should align with the sacrals with neural spines rising above the ilium
- The radius in all tetrapods originates on the lateral humerus, not the medial
- The pteroid should originates on the proximal carpal, not the preaxial carpal (Peters 2009, Kellner et al. 2012)
- Metacarpals 1-3 should align palmar sides down, out and away from metacarpal 4. This provides room for all four metacarpals to have extensors tendons.
- Following a wrong hypothesis, Witton orients his pterosaur fingers posteriorly, but all pterosaur tracks show digits 1-2 were oriented laterally and only digit 3 oriented posteriorly due to a spherical metacarpophalangeal joint, as in many lizards.
- Pedal digit 5 never flexes at pedal 5.1 (Fig. 1), but does flex nearly 180 degrees at pedal 5.2 in fossils (Fig. 4). Witton disfigured toe 5 this way in order to have it frame a uropatagium, as has been suggested for Sordes and MSNB 8950, but both are misinterpretations detailed here and here. The actual orientation of pedal digit 5 is detailed in Peters (2000, 2011, Fig. 4) and here and here.
- The tail and torso both appear to be too short. Freehanding, like Witton does, is not conducive to accuracy.
Forelimb pterosaur leaping
One of the hypothetical practices Witton endorses for pterosaurs across the board is the much promoted, but wisely criticized, forelimb launch. We’ve discussed its failing before. There is still no evidence for it in the fossil record, although Witton pins his hopes on a three-year-old rumor. Witton illustrates nearly all of his pterosaurs in the forelimb launch configuration (fig. 1). What Witton doesn’t show is what happens shortly thereafter. Here (Fig. 2) is Witton’s Dimorphodon trying to become airborne after attempting a mighty pushup with folded wings beneath its body and mighty triceps extensors working their hearts out. Forelimb leaping is also tremendously difficult for athletes as seen here. Click the image (Fig. 2) to animate it if not already animated.
There has always been a better way for Dimorphodon to leap (Fig. 3), like a leaping lizard and the vast majority of all tetrapods: by using the hind limbs, like birds, frogs and kangaroo rats do.
Exceptions include tiny vampire bats (Fig. 4) which arrived at forelimb leaping secondarily, as a bi-product of their lifestyle and the extremely weak legs of bats in general. Primates, jumping rodents and flying lemurs are much better at hind limb leaping than bats are. Click here to see the video of the top 10 fastest, highest jumping animals.
Dimorphodon is not a large pterosaur. Even so, it is several times larger than a vampire bat (Fig. 4). Its not just the effect of gravity, which increases with the cube of height, but it’s also the cushion of air, that becomes so much more cushiony the smaller a creature gets and as it adds surface area. That’s why vampire bats can get away with forelimb leaping while pterosaurs larger than a vampire bat likely could not. And giraffe-sized pterosaurs could probably leap with their forelimbs about as high as a giraffe can leap with its forelimbs.
At least he’s consistent
Witton incorrectly pastes dorsal metacarpals 1-3 back-to-back against metacarpal 4 (now rotated palmar side posterior to enable wing folding, Fig. 1). That orients the free fingers palmside anterior during flight and all posteriorly when hyperextended during terrestrial locomotion (Fig. 1). Unfortunately that doesn’t match pterosaur handprints, which are lateral for digits 1 and 2 (sometimes anterior for digit 1) and posterior for digit 3 due to a spherical joint there. That also means when a pterosaur wants to clamber up a tree, it can’t because in Witton’s view the palms are face up, as if begging.
The better orientation is palm side down while flying (or palms medial (like clapping) when walking). That also gives all four forelimb digits plenty of room to have extensor tendons. The preferred configuration also means the fingers hyperextend laterally when walking with the exceptional digit 3 oriented backwards to match ichnites. Details here.
But not always consistent
Witton’s figure 7.10 has the palms facing each other while the pterosaur is floating. They should be palms up in his view.
Whether pterosaurs had their fingers oriented laterally or posteriorly, that’s arrived at secondarily, because no tetrapods do this plesiomorphically. Their fingers always point in the direction of travel. The secondary lateral placement of the fingers on the substrate occurred after a bipedal phase shown in Cosesaurus/Rotodactylus and emphasized in Sharovipteryx. In Witton’s hypothetical scenario, the one that ignores real fossils, pterosaurs and their ancestors were never bipeds.
No Bipedal Footprints?
Along with the adoption of the forelimb launch, Witton (2013) rejects the bipedal capabilities of pterosaurs, first promoted by Padian (1983) and later by Peters (2000a, b, 2011). Peters (2000a, b) recognized that pterosaur tracks known at that time were all plantigrade and quadrupedal but recognized that pterosaurs anatomy could vary and that even the quadrupdal pose included having the toes directly beneath the center of gravity, the shoulder glenoid (Fig. x). That enabled the forelimbs to be raised without changing elevating the back. Witton ignored this data. He also reports there are no records of digitigrade pterosaurs, but his book includes an illustration of one (his figure 7.9) and he ignores the several digitigrade pterosaurs in other published works (Peters 2011, Fig. 5) mentioned, referenced and illustrated here, here, here, here and here.
Not Digitigrade? It pays to be specific here.
Witton referenced Clark et al. (1998) who reported that basal pterosaurs, like Dimorphodon, had flat feet because they could not bend the metatarsophalangeal joint due to the squared-off (butt joint) shape. Peters (2000a) showed that Cosesaurus, an ancestor to pterosaurs, had the same sort of butt-joint metatarsophalangeal joints, and that its feet exactly matched Rotodactylus tracks, but only when the proximal phalanges were all elevated (because they could not be bent), in accord with the findings, but not the conclusions of Clark et al. (1998). Peters (2000a) also showed that many pterosaurs, from Dimorphodon Pteranodon, raised the metatarsals and proximal phalanges in the same way to produce a digitigrade pes. The reduction of pedal digit 5 in derived pterosaurs led to their becoming plantigrade. Beachcomber pterosaurs also rested on their ski-pole like arms and became quadrupeds, but those forelimbs did not provide thrust due to the placement of the hands in front of the shoulder sockets.
while Witton favors the archosaur model for pterosaur origins, he rejects digitigrade pedes in pterosaurs, a trait widely found in basal dinosaurs and basal bipedal crocs.
Bipedal capability (in the manner of modern bipedal lizards), a narrow chord wing membrane and twin uropatagia solve all sorts of problems introduced and sustained by Mark Witton and the other experts he hangs with. And, there’s fossil evidence for all of this (throughout this blog and reptileevolution.com)! And none for the Witton follies.
Extension and Flexion Forelimb Limitations
Pterosaur arms cannot fully flex if they have large pteroids. The elbow joint also prevents this. Pterosaur arms cannot fully extend due to elbow limitations and the presence of the propatagium, which, as in birds, prevents overextension. These problems limit the ability of the forelimbs to flex and extend completely, like frog legs, to produce the best leap possible.
No Such Limitations in the Hind Limb
Simply leaping (or running and leaping) gets the job done so much better than an exaggerated pushup. Like birds, pterosaurs used their wings to flap and fly. That thrust can be employed during the initial hind limb leap, but not during the initial forelimb leap.
If you want to have a good laugh while watching a rather ordinary lizard leap 3x its body length, check out this YouTube video. Just think how far a pterosaur could leap with those much longer frog-like hind limbs and elongated hips providing power at the femur, the tibia, the metatarsus and the toes in coordinated fashion, accentuated by powerful thrust provided by large flapping wings.
Clark J, Hopson J, Hernandez R, Fastovsk D and Montellano M. 1998. Foot posture in a primitive pterosaur. Nature 391:886-889.
Kellner AW, Costa FR, and Rodrigues T. 2012. New Evidence on the pteroid articulation and orientation in pterosaurs. Abstracts, Journal of Vertebrate Paleontology.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos, 18: 2, 114 —141