In 2005, Dr. David Unwin, one of the top experts on pterosaurs, authored a popular book on pterosaurs, The Pterosaurs from Deep Time. Essentially it updated the pterosaur facts and hypotheses of its predecessor, The Encyclopedia of Pterosaurs (Wellnhofer 1991). Unwin wrote: “Much has changed since the Encyclopedia first appeared. The many critical ideas about pterosaur biology that were fought over in the 1990s… have been resolved into a convincing and (among pterosaurologists) widely agreed-upon picture.”
That is true. Most pterosaurologists do agree with the concepts, observations and hypotheses contained in Deep Time. However one pterosaurologist, the heretic among us, tends to disagree … often. That goes both ways, of course. Dr. Unwin completely ignored the pterosaur foot, origin and flight membrane hypotheses published by Peters (2000a, b, 2002) and they were not included in his otherwise complete and extensive bibliography. Rather than exploring opposing topics and throwing arguments against them, Dr. Unwin pretended that they never existed. That’s a shame, because that was a great opportunity for Dr. Unwin to really let me have it.
Today’s topic of juvenile and tiny pterosaurs will highlight several topics and ideas from Deep Time that do not agree with the evidence.
Unwin, p 142
“As a rule, this means that juveniles tend to be uncommon in the vertebrate fossil record, and individuals at very early stages of growth (newborn or even prenatal), are rare or unknown — except, oddly enough, in pterosaurs.”
Unfortunately Dr. Unwin considered all tiny pterosaurs to be newborns and juveniles when phylogenetic analysis (and other evidence, see below) indicates that they, too, are adults. In pterosaurs size reduction was a trait of transitional taxa in most clades. Most pterosaurologists do indeed consider a short snout and large orbit to be a juvenile character, but actually it is just a scaphognathine trait. As lizards, pterosaurs did not follow archosaur growth patterns but developed isometrically (embryos looked just like parents). The JZMP and Pterodaustro embryos falsify the traditional short-snout, large-orbit hypothesis. Many other tiny pterosaurs also had a long snout (see below). The third embryo, the IVPP specimen, came from parents with a short snout, but the eyes were still smaller than originally published.
Dr. Unwin, p. 151
“The snout often grew faster than neighboring regions, so that large-eyed short-face flaplings finished up with long, low skulls and relatively small eyes.”
Some tiny pterosaurs, like B St 1936 I 50 (no. 30 in the Wellnhofer 1970 catalog) and Senckenberg-Museum Frankfurt a. M. No. 4072, (no. 12 of Wellnhofer 1970), do not have a short snout and large orbit. (Click the blue links to see them).
Dr. Unwin, p. 156
“…there doesn’t seem to have been any “small” species, which is even stranger than you may think. Consider that the vast majority of birds and bats are less than one-third of a meter in wingspan. By contrast, adutls of the smallest pterosaur species known at present, such as Anurognathus ammoni, are at least 40 cm in wingspan, and most of them are bigger. A biased fossil record? Hardly. Otherwise, we wouldn’t have found all those flaplings and juvenile…”
Once again, if something is apparently missing, but replaced by something identical to it, it’s not wise to prejudicially ignore what is present. Test the oddities and autapomorphies with a phylogenetic analysis and you too will discover that those “flaplings” were adults of several “small” species.
Dr. Unwin p. 156
“This suggests a rather surprising conclusion: Young pterosaurs were the small species, or at least occupied some of the living spaces (niches) in which one might have expected to encounter small adults.”
So close, yet so far… mmmm. If only Dr. Unwin had performed a phylogenetic analysis instead of taking a falsified tradition at face value. Phylogenetic analysis is key to understanding the pterosaurs. But it only works when they are all included, as demonstrated here.
More on Deep Time later.
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.
Unwin DM 2005. The Pterosaurs: From Deep Time. Pi Press, New York.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London: Salamander. 192 pp.