[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: smallest pterosaurs

> www.pterosaurinfo.com/smallest_pteros.html

One off-thread comment: What have you done to the lower jaw of the
*Anurognathus*? You gave it a humongous coronoid process. It looks
mammalian. Why? Wellnhofer identifies the coronoid process as the skull
parts caudoventrally to the lower temporal fenestra, and this looks much
more reasonable, especially considering the fact that your reconstruction
lacks that fenestra altogether.

> [...]
> Some have a long snout. Some have small eyes.

Only one: the "micro *Pterodaustro*". It skull looks almost adult -- as far
as I can see this at that resolution. The others do look juvenile compared
to their probable adults.
        Perhaps this is because its head may not even exist.

> If these pterosaurs are juveniles, how can we tell?

For one, we can tell _for sure_. This is *Eudimorphodon cromptonellus*,
whose bone histology has been checked. Although not a hatchling, it's not
adult either. You've certainly read the JVP article meanwhile.

For the others, someone has to look at least at their bone surface textures
(if nobody has already done that). The famous immature grainy texture seems
to hold for all vertebrates, so parsimony says it holds for pterosaurs, too.
        As long as I don't know their bone textures, I have to go by gross
morphological proxies.
        Look at the braincases of all those beasties, probably including the
*Pterodaustro* (but what will seven pixels tell me...!). They are pretty
large, I think. Larger, in relative terms, than what we're used to from the
presumed adults, right?
        Then look at their snouts. They are tiny. Short and very thin -- low
dorsoventrally -- as if they had just started growing out of a globular
head. Even the ephemeral *Pterodaustro* snout, which (again) may well not
exist, is only about half as long as in the adult, according to your
reconstructions at http://www.pterosaurinfo.com/pterodaustro.html.
        MPUM 6009 is less extreme in this regard. Still, its snout is hardly
longer than the rest of the skull -- and it's the biggest of the entire
        TM 10341 looks even more adult -- but not when compared to a
*Pterodactylus antiquus* in the old sense, which is itself most probably
just subadult! Huge orbit. Babyface.

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:

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. 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. Moreover, critical
components of the fore and hind limbs show isometric growth patterns while
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
nesting site. 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
Pterosauria. 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]."