Pterodactylus? kochi? B St 1967 I 276 (No. 6 of Wellnhofer 1970) was the smallest all of all known pterosaurs (with the possible exception of the embryo Ornithocephalus) and smaller than three embryo pterosaurs, yet it was probably an adult. Derived from a sister to SMNS 81775, No. 6 phylogenetically preceded No. 12 at the base of the Germanodactylia.

Overall smaller than and distinct from SMNS 81775 and No. 31, the skull of No. 31 had a longer antorbital fenestra and taller orbit. The premaxilla was slightly larger. The jugal descended.

Distinct from No. 31, the cervicals and torso were longer.

The deltopectoral crest was squared off. The humerus was straight. The metacarpus and ulna were longer.

The hind limb was more robust. The unguals were shorter. Digit V was straight and shorter.

Size comparisons between No. 23, No. 12 and No. 6 can be found here and here.

The surface/volume ratio is maximized in this species and its hatchlings. Considering that living lizards with a snout/vent length under 18mm (Hedges and Thomas 2001) dry up and die when removed from their moist leaf litter environment, the younger, smaller juveniles of this pterosaur were likewise destined to always fend off desiccation. The adults had a snout/vent length of just over 40 mm, so hatchlings would have been in the range of 5mm, perhaps too small to fly in dry air, unless they had a novel method for conserving moisture with their wings outstretched. They would have been the size of house flies.

Hone and Benton (2006) reported, "The remarkable extinct flying reptiles, the pterosaurs, show increasing body size over 100 million years of the Late Jurassic and Cretaceous, and this seems to be a rare example of a driven trend to large size (Cope’s Rule)." They arrived at this "result" by drawing a straight line from early pterosaurs, like Anurognathus, to the Late Cretaceous pterosaur, Quetzalcoatlus over time and by deleting all purported juveniles. They did not realize that 1) there were four pterodactyloid-grade lineages; 2) the purported juveniles were actually adults; and 3) any sort of a roller-coaster effect of size increase/decrease/increase/decrease over time would be negated by drawing a straight line.

Ornithocephalus continued the size reduction that originated with Scaphognathus and was at the base of a new clade of pterosaurs, the Ornithocephalia, defined as Pteranodon, Ornithocephalus, their last common ancestor and all of its descendants.

A recent report (Lü et al. 2010) on Darwinopterus claimed it was the transitional taxon between so-called 'rhamphorhynchoids', like Scaphognathus, and so-called 'pterodactyloids', like Germanodactylus. Here Darwinopterus nests deep with the Germanodactylia. The metacarpus was secondarily reduced anbd the long tail was overlooked but retained in sister taxa. Claims of 'modular evolution' (= head evolves first, post-crania evolves later) are not supported by any other evolutionary sequence and certainly not by the present pterosaur family tree, which can be seen in its entirety here.

Papers disputing the findings of Lü et al. (2010) were rejected on the grounds that tiny pterosaurs were held to be hatchlings and juveniles despite the evidence. The gray circles here represent taxa once considered to be juveniles and hatchlings.

Tiny pterosaurs
Nemicolopterus was hailed as the smallest pterosaur (Wang et al. 2008). As you can see, it is not. No. 6 was described in 1970. It remains the smallest pterosaur outside of an eggshell. Nemicolopterus (Wang et al. 2008) is nearly twice as tall.

Another smallest pterosaur! On the left is BMNH 42736 traced from a photograph in Unwin 2006 (p. 151). It nested between No. 6 and No. 12 representing both a transitional taxon and a sterile offshoot with an elongated scapula, a larger sternal complex, a deeper skull, a fused puboischium and a few more vertebrae than either sister. Contra Unwin's (2006) assertion that it was a "flapling," BMNH 42736 did not nest as a juvenile to any larger taxon.

BMNH 42736 GIF movie showing bones and embryo/fetus.

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