The Very Very Latest Paper From 2006!!!

[don ohmes <d_ohmes@yahoo.com>]

> them in their histology. Especially in *Mammuthus*,
> the presence of typical 
> LAGs has not been established, and additional work
> is necessary. 

"Definitely. It would be odd to have none, given that
the fossil record does not suggest these were
migratory (OTOH,..."

Assuming the data were available-- Wouldn't the absence of LAGs in large 
animals, especially if a 'definition gradient' from small to large body size 
exists, support the idea of primarily temperature-driven effects? And if the 
body size that LAGs disappear at is much larger in dinosaurs than in mammals, 
might that speak to thermoregulatory systems?

----- Original Message ----
From: evelyn sobielski <koreke77@yahoo.de>
To: dinosaur@usc.edu
Sent: Wednesday, March 7, 2007 8:03:32 AM
Subject: Re: The Very Very Latest Paper From 2006!!!


> crocodiles. Except for ratites such as ostriches and
> moas, birds are poorly 
> suited for comparison because of their much smaller
> body size and their 
> adaptation to flight rather than to a terrestrial
> lifestyle, despite being 
> surviving dinosaurs. Large herbivorous mammals over

Birds, here, is obviously Neorn(see Cambra-Moo et al
2006
http://www.academie-sciences.fr/publications/comptes_rendus/pdf/CRPalevol_article.pdf)

> "While CHINSAMY & HILLENIUS (2004 and references
> therein) argue that 
> regularly spaced LAGs in dinosaur bones indicate a
> metabolic rate below that 
> of modern mammals, which are believed to generally
> lack LAGs, PADIAN & 
> HORNER (2004 and references therein) take a
> phylogenetic perspective by 
> pointing out that LAGs in dinosaurs may be a poor
> indicator of metabolic 
> status because they are plesiomorphic. According to
> PADIAN & HORNER (2004), 
> LAGs thus simply may be inherited from some
> ectothermic ancestor of the 
> dinosaurian lineage and have no particular meaning
> in terms of 
> thermoregulation.

I'd agree; they seem to be more a life-history
indicator. And I don't know if they've been studied in
such detail already, but I wouldn't be surprised if
LAGs are not just plesiomorphic (as in LAGs vs no
LAGs) but actually homoplasies (as indicated by the
mammal examples) if one looks at the precise pattern,
i.e. at which stage in life did bone growth occur at a
very low rate. They may be a character that occurs
ALWAYS when certain life-history conditions are met,
and how exactly they occur would depend on how these
conditions are met.

> In addition, PADIAN & HORNER note
> that LAGs have been 
> occasionally observed in large mammals such as elk
> (*Cervus elaphus* [...]), 
> seals (*Phocoena phocoena* [...]), and polar bears
> (*Ursus maritimus* 
> [...]). Elk in particular are of interest because
> unlike bears, they do not 
> hibernate.

Yes, but males have marked growth cycles in their long
bones which serve as mineral reservoirs for antler
growth. There should be more in the recent papers on
_Megaloceros_ because there was some discussion on the
matter in the last years.

> them in their histology. Especially in *Mammuthus*,
> the presence of typical 
> LAGs has not been established, and additional work
> is necessary. 

Definitely. It would be odd to have none, given that
the fossil record does not suggest these were
migratory (OTOH, the fossil record might be
exceptionally patchy, given that the expected
"wintering grounds" would be largely in taiga areas -
where a) little fieldwork has been done and b)
podsolic soil conditions virtually prohibit bone
preservation).


Regards,

Eike


        
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