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Re: Protopenguins and pterosaurs
Cambra-Moo et al., in press. Histological observations of enantiornithine
bone (Saurischia, Aves) from the Lower Cretaceous of Las Hoyas (Spain).
Comptes Rendus Palevol.
The pdf is available online. The specimen is a partial leg.
Ah. I don't have access (yet), but here's the abstract:
"New material from a small, presumably adult enantiornithine bird
(Saurischia: Aves) from the Lower Cretaceous of Las Hoyas (Spain) provides
new data on the bone histology of those Mesozoic birds, which became extinct
at the Cretaceous-Tertiary boundary. The material is referred to cf.
*Concornis lacustris*. The outer cortex of the studied long bones is formed
of a rather typical parallel-fibered bone tissue, with sparse flattened
osteocyte lacunae, evidence of lines of arrested growth (LAGs) and no
vascularization. This structure matches the outer circumferential layer
(OCL) of many extant mature, small to tiny birds and also agrees with
earlier descriptions of enantiornithine cortical bone. The deeper cortex
progressively contains a much more plentiful component of osteocyte lacunae,
which are more plump than flat. This region is also permeated by a few
vascular canals surrounded by bone lamellae that form osteonal structures.
The relationship of the osteonal material to the neighbouring primary tissue
strongly suggests that the osteons are secondary. In some sections, it is
possible to follow those osteons as formed by outward extensions from the
endosteal bone tissue into the deep primary cortex. This specimen shows more
histodiversity than the few enantiornithine samples previously reported.
This further suggests that although growth may have been slow when the adult
size was approached, it was more rapid at earlier stages. Even if as yet not
enough is known of those early stages to document just how rapid early
growth may have been, and whether enantiornithines grew differently from the
basal avian models known from other early birds, the new data do not
necessarily suggest that they had growth regimes quite distinct from extant
birds of similar body sizes nor, by implication, completely different
metabolic patterns or regimes."
I was surprised to see just how poorly Waimanu was supported as a penguin-
"Waimanu is closer to penguins than to any other bird group in the
following combination of characters: some thoracic vertebrae are not
heterocoelous; synsacrum has 11-12 ankylozed vertebrae; hypotarsal crests
and grooves of the tarsometatarsus are not well-developed (but medial
hypotarsal crest is distinct)."
Those look like three plesiomorphic states to me.
This may have more to do with the size of the matrix -- 148 characters --
than with the fossil.