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Re: Mesozoic birds made insects shrink

I was actually on pterosaur.net a few days ago, so I'm not a neophyte, more of 
a Lazarus getting back into the world of Vert-Paleo. I am impressed by the 
wealth of info we are getting about the pterosaurs these days, although I don't 
like some of the radical new paleo-art out there (no offense!). I think I see 
what you are getting at, but I still wonder if the extinction of 
rhamphorynchoids (yes, I know they're paraphyletic, Dave) and/or the apparent 
decline of small pterosaurs had anything to do with the rise of birds, or if 
it's just Cope's law at work ;-)

From: "Mark Witton" <Mark.Witton@port.ac.uk> 
To: dinosaur@usc.edu 
Sent: Tuesday, June 5, 2012 4:29:54 PM 
Subject: Re: Mesozoic birds made insects shrink 

T. Yazbeck, 

There has been a _lot_ of research into pterosaur takeoff, flight, physiology 
and ecology that you seem unaware of. Point yourself at Pterosaur.Net and the 
Pterosaur.Net blog for a start, or track down a copy of Dave Unwin's book 'The 
Pterosaurs from Deep Time' (even better, wait for my own pterosaur book to come 
out at the end of the year). As David M. has also already alluded, there is a 
wealth of discussion of many of your points in the archives of this list. 
Still, to briefly address some of your specific points... 

The notion of birds out-competing pterosaurs stems from the same oversimplified 
logic that has been applied to many fossil groups (e.g. bivalved molluscs vs. 
brachiopods; early dinosaurs vs. other Triassic reptiles). Each of these groups 
are superficially similar and occupy the same approximate ecospace, so it has 
been assumed that one excluded the other in protracted evolutionary battles. In 
each case, close scrutiny suggests that these competitions did not occur. There 
is _no_ evidence at all that birds competitively excluded pterosaurs, for 
instance. Richard Butler and colleagues provided a good overview of this topic 
in 2009, and concluded that 1) there is no correlation between the fossil 
record of Mesozoic birds and pterosaurs (at least as we know them today) and 2) 
the fossil records of both groups are a little too incomplete to say either 
way. Your assertion that "...the advancement of birds would cause at least a 
few problems for the flying reptiles" is not supported by the fossil record at 
all: pterosaurs become more diverse once birds have evolved. The idea that 
birds replaced small pterosaurs is complicated by evidence that hyperprecocial 
pterosaur offspring acted as distinct 'species' within Mesozoic ecosystems, 
occupying different ecospace to the adults. 

Likewise, as David M. has already outlined, there is no indication that birds 
were somehow physiologically superior to pterosaurs, or that they  could 
inhabit places that pterosaurs couldn't. If anything, recent research into 
pterosaur endocasts and respiratory physiology suggests that both were very 
bird-like. Some researchers are considering the possibility that pterosaur fuzz 
and early feathers are homologous. I don't really have an opinion on that at 
the moment, and, to my knowledge, no-one has tackled this issue head on, but it 
does not seem unreasonable. 

Pterosaur flight also appears to be very sophisticated and, to my knowledge, 
pterosaurs were the first vertebrates to develop flight sophisticated enough to 
hunt aerial insects (specifically anurognathids, which seem to be little 
bundles of aerial awesomeness that inspire respect-levels normally reserved for 
raptorial birds from biomechanicists). Membranous wings can also take a lot 
more damage that you'd think. Bats can fly with ripped and perforated 
membranes, so pterosaurs probably could, too. Presumably, like the digits 
supporting torn bat wings, the stiffening fibres of pterosaur wings would keep 
their membranes taut even if they had been torn. Note that membranous wings may 
also be more compliant than those of feathers, and can make their owners _more_ 
manoeuvrable, not less, than feathered fliers. There is also good evidence that 
pterosaurs were not inept when grounded, and could walk and run very 
competently. In terms of overall terrestrial efficiency, pterosaurs were 
probably more akin to birds than most bats (we should remember that some bat 
species are pretty hot on the ground, after all). 

Gosh, that's a lot longer than I intended. To summarise, the fact that birds 
are here and pterosaurs are not does not mean anything. Establishing 
competitive displacement between two lineages is very difficult considering the 
biological, ecological and environmental factors at work. As with studying any 
macroevolutionary trends, the more we discover, the less we know. 



Dr. Mark Witton 
Honorary Researcher 
Palaeobiology Research Group 
School of Earth and Environmental Sciences 
University of Portsmouth 
Burnaby Building 
Burnaby Road 
PO1 3QL 

Tel: (44)2392 842418 
E-mail: Mark.Witton@port.ac.uk 

If pterosaurs are your thing, be sure to pop by: 

- Pterosaur.Net: www.pterosaur.net 
- The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/ 
- My pterosaur artwork: www.flickr.com/photos/markwitton 

>>> <tyazbeck@comcast.net> 05/06/2012 20:46 >>> 
I'll look up the take-off and landing info later. What about the speed of 
flight in pter. compared to birds? I don't doubt that they were warm-blooded, 
but it seems that pterosaurs would be less agile in flight, and very 
voulnerable on the ground. Wouldn't feathers be better (more durable?) than 
skin? Wouldn't a pterosaur with a torn wing be SCREWED, i.e. theropod bait? 
Still, I suspect that the advancement of birds would cause at least a few 
problems for the flying reptiles. 

----- Original Message ----- 
From: "David Marjanovic" <david.marjanovic@gmx.at> 
To: dinosaur@usc.edu 
Sent: Tuesday, June 5, 2012 3:32:31 PM 
Subject: Re: Mesozoic birds made insects shrink 

> I meant to say that they were not as efficient as birds 

But what gives you _that_ idea? 

> What about the intelligence of the pterosaurs? 

Good question. Very difficult to answer from a few braincase endocasts. 

> And weren't pterosaurs bad at taking off/landing? 

No. That has been discussed on this list in great detail. 

> With their thicker integument, I would venture to say that 
> birds were able to survive in colder regions than pterosuars could. 

1) Are you sure it's thicker? 2) What colder regions? Pterosaurs did fine even 
in temperate Liaoning. 

> And as far as I know, Pterosauria can only belong to one class: 
> Reptilia. 

Even if you insist on having classes, alternatives are available. You could 
give them their own class (has been done), or you could give something like 
Ornithodira class status (has also been done -- "Endosauropsida")...