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RE: LAG (was Tyrannosaurid Growth Spurts)
As a palaeohistologist I have followed this tyrannosaur bone histology
discussion with interest. I haven't got a copy of the Nature paper, because
my institution does not have a library. Anyone got a PDF?
Mammals and birds can exhibit LAG within their bones. Conversely, many
reptiles do not have them, or have them only rarely, and may also have
Haversian systems, which we associate with 'warm bloodedness'. However, some
dinosaur bones often contain many LAG- see for instance the sauropod limb
material published by Martin Sander recently, and which was mentioned by
someone on the list.
The important factor in bones is the level of vascularisation. It is
possible for an animal to grow rapidly (highly vascular bone) but
discontinuously (presence of LAG, with or without zones and annuli, for
example some pterosaurs). I think too much importance is placed upon LAG. As
many people have shown, they are not necessarily linked to annual growth
cycles. The main caveat in this field is that different bones from the same
individual can exhibit quite different histology. Anyone wanting more info
should look at anything by de Ricqles, Chinsamy, Reid, Castanet, Sander and
de Buffrenil. Apologies to any other authors that I've forgotten!
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