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Friends,
The structure illustrated in the recent
National Geographic article as occurring on the "unnamed ovoraptor=Nomingis
brevicauda" is certainly open to an alternative interpretation. Note that
the fusion of bones occurs distally on the elongated tail, not at the very base
as in modern birds. It could be that this is simply a pathological condition of
bone fusion. Recall that the entire posterior portion of the avian skeleton is
subject to fusion (e.g. distal limb bones, synsacrum, pygostyle). The condition
illustrated double page spread (p 104?), might be only a fusion of tail
vertebrate. In the figure caption the structure is refereed to as"an
incipient version of the pygostyle, which provides a foundation for tail
feathers.
This is boat a cautions and ambiguous
statement. Fusion of the most distal tail vertebrate may or may not be related
to the development of a pygostyle. The structure may not develop by fusion of
the tip to the base, but as a process related to the fusion of the sacral
vertebrate. It is also possible that the author was implying that the pygostyle
in modern birds "provides a foundation for tail feathers". There is,
of course, no evidence for the existence of tail feather in this particular
specimen. The reconstructed figure clearly has a fan of tail feathers as do most
modern birds.
The only other direct evidence bearing
on this issue is Archaeopteryx which had a lengthy tail with modern style
rectrices attached in series along its length and perhaps Protarchaeopteryx.
However the mechanism that relates the reptilian tail and the pygostyle is still
unknown. While there are some good guesses from development, the evolutionary
course is still speculative.
Alan H.
Brush
92 High St. Mystic, CT 06355 brush@uconn.cted.edu
860-572-1717 |