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re: smallest pterosaurs
David Marjanovic wrote the following:
Have you already read the following SVP meeting abstract for this year? It
agrees that all those small pterosaurs are well ossified and were most
likely able to fly and independent from their parents -- it just says they
weren't adult or anywhere near:
>>>>>Question I pose is -- how do Unwin and Deeming know they are indeed
>>>>>juvenile, and not some sort of small adult? They could be juveniles. I
>>>>>just need a way of knowing for sure.
DM quotes from JVP:
(I think it is inappropriate to comment on abstracts before their presentation,
but it is not inappropriate to ask the questions that will need to be asked
after the presentation.)
David Unwin & Charles Deeming: Babes on the wing -- evidence for
hyper-precocial flight ability in pterosaurs, 124A
"Typically, birds and bats must grow to adult or near adult size before they
are capable of flight. Pterosaurs, by contrast, ppear to have been able to
fly at only twenty percent of adult body length and five percent of adult
mass. The primary evidence for this is provided by several near-hatchling
size fossils of *Pterodactylus kochi* [sic] from the Upper Jurassic
Solnhofen Limestone of Germany.
>>>> Is the holotype of P. kochi (No. 23 of Wellnhofer) a juvenile? Or an
>>>> adult? It 'looks' like a smaller version of the larger germanodactylids,
>>>> but cladistic analysis indicates that it is phylogenetically derived from
>>>> even smaller taxa, such as No. 12 and before that, No. 9. The
>>>> narrow-snouted, gracile-necked pterosaurs universally referred to ?P.
>>>> kochi, such as No. 21, are not ?P. kochi, but not far removed either. So,
>>>> the question is, which 'P. kochi' will be presented? And which purported
>>>> juveniles will be referred to it?
In these individuals all skeletal elements
of the flight apparatus including the pteroid are ossified and, in addition
to containing structural fibres, the flight membranes were approximately the
same shape and proportions as those of the adults.
>>> Are U & D describing adult characters above?
components of the fore and hind limbs show isometric growth patterns
>>>> Are these isometric growth patternsphylogenetic or ontogenetic in nature?
>>>> In support of the latter U & D will have to connect each juvenile, or at
>>>> least some juveniles, to conspecific, or at least congeneric, adults
>>>> using cladistic analysis or reconstructions, using matching body parts
>>>> that are not subject to isometric growth patterns.
calcualtions of the aerodynamic performance of these individuals indicate
that wing loading and other parameters were similar to those of adults and
that, theoretically, they were capable of flight. This is further supported
by the discovery of these fossils preserved in locations far from any likely
>>>> Are U & D leaving the door open to the possibility that they're looking at
Near hatchling, or early juveniles [sic] are known for several
other pterosaurs, including *Rhamphorhynchus*, *Ctenochasma*,
*Pterodaustro*, a dsungaripterid and *Azhdarcho*, suggesting that
hyper-precocial flight ability was widespread, perhaps even universal within
>>>>> While the literature labels every tiny pterosaur a juvenile, I wonder if
>>>>> U & D has tested previous assertions? And if so, what is their "litmus
>>>>> test"? [see below for questions regarding the currently accepted "litmus
>>>>> tests" for immaturity]
This has two important implications. First, and contrary to the
popular image of pterosaurs feeding helpless young, it suggests that, post
hatching at least, there may have been little or no requirement for parental
care. Secondly, a hyper-precocial flight ability may have imposed a limit on
minimum hatchling size and thus also on minimum adult size. This might
explain why, unlike birds and bats, there are no species of pterosaur with
an adult wingspan of less than approximately 0.4m [sic]."
>>> Okay, Dr. Unwin has set a minimum adult wingspan of 40 cm. Which pterosaur
>>> is this? Does it have a pelvis large enough to pass an egg of the correct
>>> size? And among the pterosaurs that are just a wee bit to a lot smaller,
>>> what sets them apart in shape or structure and defines them as immature?
And yes, I'm aware of the various size-independent characters used previously,
but the questions to those tests are:
1. why in cladistic analylsis do entire clades of pterosaurs (basal
ornithocheirids + cycnorhamphids) appear to be immature using these tests?
2. why do some tiny pterosaurs (Mesadactylus and Nyctosaurus gracilis, for
instance) appear to be mature according to these tests?
3. why in cladistic analysis, do the tiny pterosaurs appear at the bases of
major clades and complete the spectrum of pterosaur diversity to create a
single most parsimonious tree?
4. considering the alternative theory for a moment: why should a 'hypothetical'
tiny adult pterosaur, hypothetically stunted by a premature hormone surge (or a
phylogenetic series of same over thousands of years), ever develop 'mature'
bone characters when nothing else about them, except perhaps their hypothetical
ability to reproduce, appears to be 'mature'?
I'll be glad to wait until after the podium session in Denver to hear an
answer. As a courtesy to Unwin & Deeming, perhaps all thoughts that follow this
thread should also be phrased in the form of questions.