Pterosaur Fingers – Part 1, Basal Taxa and Dimorphodontids

Most pterosaur workers pay little attention to the hands of pterosaurs. That’s unfortunate. Here many traits, including the relative lengths of the metacarpals and manual phalanges, were found to be as distinctive and phylogenetically informative as the relative lengths of the metatarsals and pedal phalanges reported in the catalog of pterosaur pedes (Peters 2011). In today’s blog we’ll examine the hands of a basal clade of pterosaurs (Fig. 1), highlighting only a few outstanding traits and ignoring the wing finger. We’ll continue the examination of other pterosaur fingers in later blogs. Today it is not important which way the fingers flexed, but if you’re interested, look here.

Pterosaur fingers

Figure 1. Pterosaur fingers. Click to enlarge. Red arc arrow indicates twisted phalanges to show ungual shape. Otherwise blue shapes indicate ungual shape.

Basal Pterosaurs and Dimorphodontids
The configuration of the basal pterosaur manus reflects its fenestrasaur ancestors, like Cosesaurus, Sharovipteryx and Longisquama. The latter two and perhaps all three were derived late survivors of the original splits that produced pterosaurs. The elongation (asymmetry) of the lateral metacarpals and lateral digits goes back to a basal tritosaur lizard, Huehuecuetzpalli. The trend in several pterosaur lineages was toward a greater symmetry in the metacarpals and (less often) the digits.

MPUM 6009 – The manus of the most primitive pterosaur(Fig. 1) was relatively smaller than that of its phylogenetic predecessor, Longisquama and distinct in terms of metacarpal and phalanx proportions. In MPUM 6009 metacarpal 1 was ~60% the length of metacarpal 3, which was just shorter than metacarpal 4. Metacarpal 3 was more than half the diameter of metacarpal 4. Manual 1.1 was twice the length of m2.1. Digits 1 and 2 were subequal and shorter than digit 3.

Austriadactylus – In both of the pterosaurs attributed to Austriadactylus metacarpal 1 was relatively longer. Metacarpal 3 was more gracile and as long as metacarpal 4. Manual 1.1 was relatively smaller. Digit 2 was longer than digit 1.

GLGMV-0002 – This basal dimorphodontid had a more robust metacarpal 4. Manual 3.2 was shorter.  Digit 3 was relatively shorter and shorter than metacarpals 3 and 4.

Dimorphodon micronyx – The metacarpals were all relatively shorter and digit 3 was longer creating more asymmetry in relative finger length.

Preondactylus -The phalanges of digit 3 were more similar in length.

Peteinosaurus – Metacarpal 4 was more gracile as were the fingers and unguals. Digit 3 was 50% longer than digit 2.

MCSNB 8950 – Longer metacarpals appear. Manual 2.1 was longer. Manual 3.2 was shorter.

IVPP embryo – The IVPP embryo comes form the Early Cretaceous and thus represents a late-surviving representative of a Late Triassic/Early Jurassic radiation. Metacarpal 4 was longer and more robust, and wider than mc1-3 combined. Metacarpals 1-3 were more gracile and essentially subequal in length. Digits 1-3 were more gracile and relatively shorter and shorter than the metacarpus. The penultimate phalanges were subequal.

Dimorphodon? weintraubi – Metacarpal 4 was not much more robust than mc1-3. While mc1 remained slightly shorter than mc3, all three metacarpals were aligned. The digits were longer than the metacarpus. The digits were less asymmetric. Manual 3.2 was no longer than wide.

Anurognathids

Dendrorhynchoides – Metacarpals 1-3 remained robust and subequal. Digits 2 and 3 were subequal. Manual 2.1 and m 3.1 were subequal and short.

The Flathead anurognathidSMNS 81928) – Here metacarpals 1-3 were aligned, but mc1 was the longest in the set. Manual 2.1 was as long as m3.1+m3.2 and aligned with m1.1. Manual 3.3 was longer than m2.2.  Digits 2 and 3 were nearly subequal. Manual 2.1 was subequal to m3.1+m3.2.

Anurognathus ammoni – Metacarpal 4 was more robust and shorter such that the pulley joint was half the length of metacarpal 4. Metacarpal 4 was slightly shorter than mc1-3, which were subequal to each other. Manual 2.1 was half as long as m3.1. Manual 2.2 was subequal to m3.3. The unguals were nearly as long as the penultimate phalanges.

CAGS IG 02-81 – Manual 2.1 was subequal to m3.1 in this pterosaur attributed to Jeholopeterus. Metacarpal 4 was not so robust, similar to mc 1-3. Manual 3.2 was shorter than wide.

Jeholopterus – The metacarpus was relatively longer than in the CAGS specimen. Metacarpal 3 was the shortest. Metacarpal 1 was subequal to mc4. Digit 2 was slightly longer than digit 3. Distinct from other anurognathids and other pterosaurs, the unguals were narrow, strongly curved and elongated like surgical needles. This trait, among others, led to the hypothesis of vampirism in this taxon.

Batrachognathus – Metacarpal 4 was short and very robust with a broader base than in Anurognathus. Metacarpals 1-3 were shorter than mc4. Digits 1-3 were subequal. Manual 3.2 was a disc. Manual 1.1 was longer than m3.2 and m4.3. The unguals were shorter than in Jeholopterus.

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
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

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