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Re: Pterosaur size (Was: Great in the air, not so good underwater)

Modern birds nowhere near that size have a lot of trouble.

-----This is true. It appears to be related to two things., the first being the launch techniques available to birds, and the second being that membrane wings are capable of maximum steady-state lift coefficients about a third greater than the maximum that birds achieve (bat wings do not do quite as well as birds).

There is one more bit I would add in which is to consider the ecology of many of the largest birds. Because birds are very good cursors, it is not uncommon for birds to sacrifice some flight abilities for terrestrial performance. Several of the cursorial taxa fly very well, but others have reduced take-off rates which we see as "having trouble". This is why, for example, using bustards as a metric of near maximum sizes for volancy in birds is problematic. At the other extreme, some birds have jettisoned hind limb function for particular selective flight advantages; because the hind limbs are the primary launch power in birds, these species often need gravity assistance to launch. Such taxa (like Phaethon, Fregata, Apus, and Chordeiles) are clumsy on the ground but this has nothing to do with scaling (in fact, Apus and Chordeiles are quite small).

I think the mega-volants needed different conditions to find giantism advantageous,

------This may be true.

I agree this may be true; I also think such conditions may be more widespread than we give credit for. Mega-volants persisted for much of the Cretaceous, saw a short hiatus at the K/T (or K/Pg) extinction due to the loss of pterosaurs, and then re-emerged as a morphotype amongst birds via pseudodontorns in the Paleocene. Pseudodontorns then did well world wide until the Late Pliocene, so we've really only been without some kind of mega-volant for a short period of time. Given the advantages of large size for pelagic, soaring-adapted species (especially dynamic soarers), this isn't really surprising. It appears that pterosaurs ended up huge more regularly than birds (and became much large-bodied overall) because their membranous wings and launch system made large size especially viable.

Here we have in chronological order the flying vertebrates; pteros
(biggest)=> birds (smaller)=> and bats (smallest). Bats are the
most recent, and (correct me if I am wrong) the largest known bats are

The fact that the largest known bats are extant is probably an artifact. The largest microbats (Megadermatids, Rhinolophids) have been around for a very long time. The modern genus Megaderma may be go back to 25 mya (Megaderma lopezae, see Sevilla, 1990). Other megadermatids are known from 36-37 mya, and are not small, either. Rhinolophus, another modern genus, probably dates to 41 mya (and again, is roughly in the same size range at that time). What we're missing is a good megabat record, but ghost lineages demonstrate that they must be relatively old. Recent phylogenies tend to either recover a basal split (thereby placing the first pteropids in the Paleocene to early Eocene), or they recover pteropids within Rhinolophoids (placing their origin in the middle to late Eocene). The older pteropids could be smaller, but they could just as easily have been larger. We don't really have enough material to say. As far as I know, the indet. pteropids from La Colombiere are roughly within the modern megabat size range (at least for the known elements). Propotto is only a scrap, but it was not tiny, either (nor huge). Archaeopteropus transiens is reasonably small, if I recall correctly, but it's probably not a megabat, as it turns out.

Like I say, this is suggestive, given the consistency of the terrestrial record and the contrast with the aquatic record.

-----Not really. It can be more parsimoniously related to differences in wing mechanics between the three.

Agreed. In fact, if one looks at a combination of the wing mechanics and ancestry of each group (which are interconnected factors), the relative sizes and dominant morphotypes of all three groups of vertebrate flyers is rather predictable (though hindsight is 20/20). There are a few morphs that one might expect to see from bats that we haven't, but time constraints and competitive exclusion probably play a role.


--Mike H.