Pregnant hummingbird-like pterosaurs

Earlier
here and here we looked at pregnant pterosaurs. As you may recall, as lepidosaurs pterosaurs could retain their young in utero much longer than archosaurs do. Archosaur embryos are microscopic when laid and they develop in the egg outside of the uterus. Some extant lepidosaurs retain their young in utero to the stage of viviparity. Others lay eggs at an advanced stage. Today, two more tiny pterosaurs are shown to be adult females, based on the embryo inside of each of them.

As long-time readers know, 
phylogenetic analysis of the Pterosauria that includes the tiniest hummingbird-sized individuals from the Solnhofen formation nest them all as adults. They have been phylogenetically miniaturized and generally they nest at the bases of major clades. Generally the smallest pterosaurs are transitional from larger taxa and to larger taxa, but they are also often surrounded by other tiny transitional pterosaurs. That’s how we arrive at pterodactyloid-grade pterosaurs at least 4x. By convergence anurognathids and wukongopterids also added some, but not all, pterodactyloid traits.

Other workers,
who refuse to test the tiny ones, mistakenly assert that the tiny ones are babies. If that were true then, as the other workers suggest, pterosaurs would have to develop isometrically, changing shape with maturity. Several examples of embryo and juvenile pterosaurs demonstrate irrevocably that that is not true. Juveniles and embryos are carbon copies of the adults.

The smallest adult pterosaur is
Pterodactylus? kochi? B St 1967 I 276 (No. 6 of Wellnhofer 1970, (Figs. 1,2).

Figure 1. Pterodactylus? kochi? B St 1967 I 276 (No. 6 of Wellnhofer 1970) is the smallest known adult pterosaur. It is also pregnant. Note the relatively enormous sternal complex, analogous to that of a hummingbird of similar size.

Figure 1. Pterodactylus? kochi? B St 1967 I 276 (No. 6 of Wellnhofer 1970) is the smallest known adult pterosaur. It is also pregnant. Note the relatively enormous sternal complex, analogous to that of a hummingbird of similar size.

I did not realize
how large the sternal complex was on this pterosaur, Such a large pectoral anchor suggests the wings were flapped strongly or rapidly or both, possibly as in similarly-sized hummingbirds. The coracoids are also larger than earlier reconstructed.

Figure 2. The torso of B St 1967 I 276 (No. 6 of Wellnhofer 1970) showing the pectoral girdle and embryo.

Figure 2. The torso of B St 1967 I 276 (No. 6 of Wellnhofer 1970) showing elements of the pectoral girdle, pelvic girdle and embryo. The coracoids are also quite large. 

Nesting with the smallest known pterosaur
in the large pterosaur cladogram, is another tiny Solnhofen specimen, BMNH 42736, which also has a large sternal complex and is, by coincidence, pregnant.

Figure 4. Two of the smallest pterosaurs that both have a large sternal complex. BMNH42736 and B St 1967 I 276.

Figure 4. Two of the smallest pterosaurs that both have a large sternal complex. BMNH42736 and B St 1967 I 276. If your screen resolution is 72 dpi, these are shown > 1.5x larger than they were in life.

All I really wanted to do
was gather the data on this pterosaur to see where mistakes had been made. Finding tiny extra bones in the base of the abdomen was a surprise. These two, despite their differences, nest together in the large pterosaur tree.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

Figure 6. BMNH 42736 showing various bones, soft tissues and embryo.

References
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.SMNS
Hedges SB and Thomas R 2001. At the Lower Size Limit in Amniote Vertebrates: A New Diminutive Lizard from the West Indies. Caribbean Journal of Science 37:168–173.
Hone and Benton 2006. Cope’s Rule in the Pterosauria, and differing perceptions of Cope’s Rule at different taxonomic levels. Journal of Evolutionary Biology 20(3): 1164–1170. doi: 10.1111/j.1420-9101.2006.01284.x
Unwin D M 2006. The Pterosaurs From Deep Time. 347 pp. New York, Pi Press.
Wang X, Kellner AWA, Zhou Z and Campos DA 2008. Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China. Proceedings of the National Academy of Sciences, 106(6): 1983–1987. doi:10.1073/pnas.0707728105
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodactylus

 

 

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