The Tradition
Based on known plantigrade and quadrupedal pterosaur tracks (Mazin et al. 1995, Lockley et al. 1995, and more below), ALL, yes, ALL pterosaurs must be considered plantigrade (flat-footed) and quadrupedal. No exceptions. And we are to ignore the widely held hypothesis that all traditional sisters, such as Scleromochlus and dinosaurs, were digitigrade (heels elevated), bipedal and lacked a large manual digit 4 and a large pedal digit 5.
Figure 1. Dimorphodon pes with shadows. Pedal digit 5 can swing beneath the metatarsus. Note elevated proximal phalanges (Peters 2011). The weight of the animal is centered at the shoulder, which would have been over the toes, not the ankles. So there is no overwhelming pressure on the heel to collapse digit V.
The Heresy
According to Peters (2000, 2011) careful matching trackmakers to tracks reduces the clade of then (prior to 2009) known trackmakers to the Ornithocheiridae, the Ctenochasmatidae, the Azhdarchidae and the Pterodactylidae. All these pterosaurs shared a reduced pedal digit 5 and a plantigrade pes affirmed by parallel interphalangeal lines (PILs) analysis (Peters 2000, 2010). Based on Cosesaurus, Rotodactylus (see below) and PIL analysis, basal fenestrasaurs and pterosaurs with an elongate pedal digit 5 (and several that did not) had a digitigrade pes with raised proximal phalanges with digit 5 impressing behind the others (Figs. 1, 2). Furthermore, new individual digitigrade footprints published in Peters (2011) can be matched to anurognathid and rhamphorhynchid pterosaurs (Figs. 3, 4). Digitigrade trackways are not yet known, other than Rotodactylus.
Figure 2. Click to enlarge. Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).
Evidence for the Heresy
Little Cosesaurus aviceps nests here as a Middle Triassic sister to the ancestor of pterosaurs. Rotodactylus (Fig. 2) is an unusual Middle Triassic ichnite in which pedal digit 5 impresses far behind the other toes and digit 1 barely impresses. Put them together and you have a match in size and morphology.
Rotodactylus Trackmaker –
Not a Dinosaur Precursor
A recent paper by Brusatte et al. (2011) included several Rotodactylus tracks and attributed them to a purported dinosaur precursor, Lagerpeton. Unfortunately no dinosaur precursors have digit 4 longer than 3 and Lagerpeton was not a dinosaur precursor. In any case, it is not likely that Lagerpeton made the tracks as digit 1 extended no further than metatarsal 2 and digit 5 could not reach the substrate. Cosesaurus was not considered as a potential trackmaker in Brusatte et al. (2011).
Figure 3. A pterosaur pes belonging to a large anurognathid, "Dimorphodon weintraubi," alongside three digitigrade anurognathid tracks and a graphic representation of the phalanges within the "Sauria aberrante" track. Track D (Harris and Lacovara, 2004) a Late Jurassic anurognathid ichnite. Track C (Harris and Lacovara, 2004) a Late Jurassic anurognathid ichnite. ‘Sauria aberrante’ (MLP 61-IX-4-1; Casamiquela, 1962) an Early Jurassic anurognathid ichnite. Hypothetical phalanges drawn to match the Casamiquela (1962) ichnite. Note the impression of proximal phalanges in "Sauria aberrante" indicates the metatarsophalangeal joints were cylindrical enough to enable this, unlike the D. weintraubi pes. From Peters (2011).
Digitigrade Ichnites Matched to a Large Anurognathid Pterosaur
Three unidentified western hemisphere ichnites (Fig. 3) were published by Casamiquela (1962) and Harris and Lacovara (2004). All three most closely match a large Mexican anurognathid, “Dimorphodon” weintraubi. The four anterior digits diverged widely due to angled metatarsophalangeal joints. The presence of a digit 5 impression behind the others indicates these are fenestrasaurian in origin. D. weintraubi did not produce these tracks, but a sister pterosaur did. No other anurognathid and no other pterosaur is a closer match.
By the way, it is typical, but not necessary for digit 5 to make an impression in digitigrade pterosaur tracks. Simple extension of the proximal phalanx could elevate digit 5 from the substrate.
Figure 4. Crayssac track different from all others. Inset: Pes of Rhamphorhynchus muensteri JME-SOS 4009, no. 62 in the Wellnhofer catalog
A Rhamphorhynchus Track
An unusual Crayssac track (Mazin et al. 1995) can be matched to a Rhamphorhynchus specimen. Not all Rhamphorhynchus pedes would match, but this one, JME-SOS 4009, no. 62 in the Wellnhofer catalog, is close.
For More Information
Please see this earlier blog on Bipedal vs. Quadrupedal Pterosaurs. See a selection of basal pterosaurs at reptileevolution.com. Or ask for a copy of Peters (2011).
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
Bennett SC 1997a. The arboreal leaping theory of the origin of pterosaur flight. Historical Biology, 123(4): 265–290.
Bennett SC 1997b. Terrestrial locomotion of pterosaurs: a reconstruction based on Pteraichnus trackways. Journal of Vertebrate Paleontology, 17: 104–113.
Brusatte SL, Niedzwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B 278:1107-113. doi: 10.1098/rspb.2010.1746 online pdf
Casamiquela RM 1962. Sobre la pisada de un presunto sauria aberrante en el Liassico del Neuquen (Patagonia). Ameghiniana, 2(10): 183–186.
Chatterjee S and Templin RJ 2004. Posture, locomotion, and paleoecology of pterosaurs. The Geological Society of America Special Paper 376:1-63.
Clark, J, Hopson J, Hernandez R, Fastovsky D and Montellano M 1998. Foot posture in a primitive pterosaur. Nature 391: 886-889.
Lockley, MG, Logue TJ, Moratalla JJ, Hunt AJ, Schultz RJ. and Robinson JW 1995.The fossil trackway Pteraichnus is pterosaurian, not crocodilian; implications for the global distribution of pterosaur tracks. Ichnos 4: 7-20.
Mazin J-M, Hantzpergue P, Lafaurie G, and Vignaud P 1995. Des pistes de ptérosaures dans le Tithonien de Crayssac (Quercy, France). Comptes rendus de l’Academie des Sciences de Paris 321: 417-424.
Padian K 1983a. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum. Postilla, 189: 1–44.
Padian K 1983b. A functional analysis of flying and walking in pterosaurs. Paelobiology, 9: 218–239.
Padian K and Olsen P 1984. The fossil trackway Pteraichnus: Not pterosaurian, but crocodilian. Journal of Paleontology, 58: 178–184.
Padian K 2003. Pterosaur stance and gait and the interpretation of trackways. Ichnos, 10: 115–126.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7(1): 11-41.
Peters D. 2010. In defence of parallel interphalangeal lines. Historical Biology 22:437-442.
Peters David 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos, 18: 2, 114 —141
Stokes WL 1957. Pterodactyl tracks from the Morrison Formation. Journal of Palaeontology 31: 952-954.
Unwin DM 1989. A predictive method for the identification of vertebrate ichnites and its application to pterosaur tracks. In Gillette, D. D. and Lockley, M. G. (eds.) Dinosaur Tracks and Traces. Cambridge University Press, Cambridge. 259-274.
Unwin DM 1997. Pterosaur tracks and the terrestrial ability of pterosaurs. Lethaia 29: 373-386.
The Pterosaur Heresies 