Re: FARCICAL: Extinction due to "blue balls"

["David Marjanovic" <david.marjanovic@gmx.at>]

> A corrollary to this that is similar and probably
> descriptive of the sex-characteristic is that birds do not become
> endothermic until after they developed wings and flight, as indicated in
> the histology of *Confuciusornis* (De Ricqlès, A.J.; Padian, K.; Horner,
> J.R.; Lamm, E.-T.; and Myhrvold, N. 2003. Osteohistology of Confuciusornis
> sanctus (Theropoda: Aves). _Journal of Vertebrate Paleontology_ 23(2):
> 373-386).

Hey, hey, wait a little. How do you get the idea that the relation of growth
speed and adult size, and the presence or absence of LAGs, would have
anything to do with being endothermic or not? The authors of that paper
_oppose_ this idea.

p. 384:
    "Histological examination of most of the long bones of *Confuciusornis*
has allowed a test of previous hypotheses about the changes in growth rates
that characterized the early evolution of birds (Chinsamy et al., 1994,
1995, 1998; Ricqlès et al., 2001). It was initially thought that the tissues
of some basal birds, such as enantiornithines, grew so slowly as to reflect
incompletely evolved metabolic levels compared to living birds (Chinsamy et
al., 1994, 1995). It was later hypothesized that either these tissues were
those of old, slowly growing individuals, or that overall growth rates had
slowed in these taxa (Ricqlès, 2000; Ricqlès et al., 2001; Padian et al.,
2001a).
    Our study suggests that the last hypothesis is most likely, but not
completely correct. In most vertebrates, growth is most rapid just after
birth or eclosion [is that hatching?]; it slows and eventually stops
altogether, at least among extant endotherms such as large living birds and
mammals. Large extinct dinosaurs and pterosaurs generally fit this pattern
(Horner et al., 1999, 2000; Ricqlès et al., 2000). Reduction in body size in
the first birds was not achieved simply by lower overall growth rates during
the entire ontogeny. Rather, there was (1) a relatively small reduction in
overall growth rates, compared to ancestral theropods; (2) considerable trun
cation of the more rapid phas of growth, characterized by deposition of
fibro-lamellar bone organized in well-vascularized laminae with numerous
circumferential and radial anastomoses; and (3) acceleration (sensu Alberch
et al., 1979) of the parameters of shape change that retained most features
of the ancestral trajectory, but allowed peramorphic evolution of certain
features such as longer arms, hands, and feathers (Padian et al., 2001a;
Ricqlès et al., 2001)."

Besides, I can't for the life of me imagine a fully feathered poikilothermic
vertebrate... and especially, I can't imagine a flying bradymetabolic
vertebrate. Remember Ruben's calculations that showed a bradyaerobic Archie
could have flown for a minute or so _before requiring half an hour or more
of resting_?

> While crocs have temperature-dependant sex change, and modern
> birds do not, this does not tell us that all animals leading to birds that
> weren't crocs, including dinosaurs, were not temp-dependant ... it only
> tells us that the change in birds, or the change in crocs from a primitive
> and likely temp-based condition, changed in one of these lineages.

Yes -- but I wouldn't recommend temp-dependent sex determination to a
brooding endotherm, so I'll take the evidence for brooding in Maniraptora
sensu Sereno as evidence for chromosome-dependent sex determination
throughout at least that clade.