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Re: Mesozoic birds made insects shrink



And there weren't many huge insects in the Mesozoic, either. In fact, I wonder 
if there are more now than back then.

----- Original Message -----
From: "Mark Witton" <Mark.Witton@port.ac.uk>
To: dinosaur@usc.edu
Sent: Tuesday, June 5, 2012 5:50:20 PM
Subject: Re: Mesozoic birds made insects shrink

The thing that bugs me about all this is the assumption that the first birds 
were capable of hawking insects out of the skies. This seems to be a mean feat 
even for modern birds and it seems very unlikely that early avians in the 
process of perfecting their flight mechanics would be able to catch nimble 
aerial prey. To my knowledge, the Jurassic fossil record offers only 
anurognathid pterosaurs with the necessary anatomy for insect hawking. Their 
first appearances in the fossil record (Late Jurassic), of course, tie in 
nicely with the proposed decline of large aerial insects. 

Still, all this talk of aerial predators pushing large insects into decline 
troubles me. Firstly, simply considering oxygen availability and predation 
effects on insect evolution seems rather simplistic when other factors could 
also be affecting the evolution on giant arthropods (e.g. climate, species 
packing, primary productivity, etc.). Secondly, we should not ignore the fact 
that each flying insect species is, in effect, two ecomorphs in one: an 
aquatic/terrestrial larvae and flying adult. To have giant flying insects, we 
also need giant larvae. Ergo, there is a whole life stage (and often the 
dominant one) where the presence of hawking vertebrates may have had little 
impact on these species, but grounded/aquatic predators would instead. Of 
course, there's a whole bunch of other pressures tied to grounded/aquatic 
settings that flying animals would also not worry themselves with. My point, I 
guess, is that there are a lot of factors to consider here, and the correlation 
noted in the Clapham and Karr study may not imply causation.

Also, hasn't the link between hyperoxia and arthropod size been only 
partially-established experimentally? I recall lab studies on this topic that 
produced fairly unimpressive results when trying to induce size increases under 
high oxygen regimes. And it's not like we don't have massive terrestrial 
arthropods today with our middling O2 levels, it's just that they're rather 
rare:

http://www.jaunted.com/files/16133/Coconut_Crab_385.jpg

Mark

--

Dr. Mark Witton
www.markwitton.com
Honorary Researcher
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
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 


>>> "Michael OSullivan" <Michael.OSullivan@port.ac.uk> 05/06/2012 18:26 >>>
I would have to disagree there. Pterosaur diversity is at its highest in the 
Early Cretaceous, which actually coincides with the increased diversity of 
birds. I would suspect, and not something I've looked into so just speculation, 
birds expanded to fill the niches left by reduced pterosaur diversity in the 
Late Cretaceous rather than birds being a contributing factor. The same may be 
said for an increase in small avian diversity in the Early Cretaceous, evolving 
to fill empty niches rather than being the factor of extinction.

It's an interesting idea about the bird insect relationship. Won't lie, little 
sceptical on the outset, but I'll have a read next week, see what it says. 

Were birds massively successful from the beginning? I don't know. The quality 
of the Jurassic fossil is such that I'd be hesitant about trusting any 
diversity signals it gives. It think Aves was a well adapted group early on, 
but I don't know if they were exceptionally successful...annnnd now I've given 
myself a spare time research topic.


---

Michael O'Sullivan

Palaeobiology Research Group
Postgraduate Student
School of Earth & Environmental Sciences
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Email:michael.osullivan@port.ac.uk 
>>> 05/06/12 5:20 PM >>> 
It reminds me of the idea that birds out-competed pterosaurs. I would imagine 
that had the K/T extinction not occured, the birds would still eventually lead 
the pterosaurs to extinction. They must have been quite diverse/advanced by the 
Campanian when only very large pterodactyls were left. And since the 
ramphorynchoids and small pterosaurs died out as the birds were just starting 
to emerge, it seems to me that the Aves were explosively successful from the 
outset (Archaeopteryx). Does anyone have more info on this idea? 

Tom Yazbeck 


From: "Ben Creisler" 
To: dinosaur@usc.edu 
Sent: Monday, June 4, 2012 6:49:57 PM 
Subject: Re: Mesozoic birds made insects shrink 

From: Ben Creisler 
bcreisler@gmail.com 



"Does this suggest that pterosaurs had a negligible effect on insect sizes?" 



The pterosaur issue is mentioned in these news stories: 

http://news.nationalgeographic.com/news/2012/06/120601-insects-birds-giant-prehistoric-clapham-proceedings-science-bugs/
 

http://www.sciencedaily.com/releases/2012/06/120604155703.htm 



For other details about the topic of giant insects in the Triassic: 

http://news.sciencemag.org/sciencenow/2012/06/where-have-the-hawk-sized-insect.html