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Re: Mesozoic birds made insects shrink

I don't doubt that the pterosaurs were most diverse in the EK. But by that 
time, I believe they were mostly larger pterodactyloids, occupying niches that 
birds were too small at that time to usurp. Yet the smaller rhamphorhynchoids 
of the Triassic and Jurassic had mostly died off by the Cretaceous, and since 
most Mesozoic birds were also in their size range, I would imagine that they 
DID affect the long-tailed, primitive pterosaurs, possibly because of the more 
active lifestyle (endothermy) of the birds, or their efficient respiratory (air 
sac?) system; both factors would give Aves an advantage over the more reptilian 
physiology of pterosaurs. The pterodactyloids avoided competition w/ birds 
because they were in a larger size category--the biggest flying animals in 
history. By the Late Cretaceous, the birds may have expanded in diversity, thus 
restricting the pterosaurs to the largest forms, which birds couldn't compete 
with. I will research this more. I do think the fossil record is not adequate 
(yet?) to come up with solid conclusions on this.

T. Yazbeck--ameteur!

From: "Michael OSullivan" <Michael.OSullivan@port.ac.uk> 
To: tyazbeck@comcast.net, dinosaur@usc.edu 
Sent: Tuesday, June 5, 2012 1:26:18 PM 
Subject: Re: Mesozoic birds made insects shrink 

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 
PO1 3QL 

>>> 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 

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

The pterosaur issue is mentioned in these news stories: 



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