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two or three sacral vertebrae?
I am confused about an article in SCIENCE, v. 258 (13 Nov., 1992), p.
1137-1140, by Paul Sereno and Fernando Novas. The article is about
insight into basal dinosaur phylogeny from discovery of an essentially
complete skeleton, with skull, of _Herrerasaurus ischigualastensis_.
On p. 1138 (2nd column, 2nd paragraph), they state that a valid
synapomorphy of the Dinosauria is the addition of a dorsal vertebra to
the sacrum. That would indicate that dinosaurs have three sacral
However, on p. 1139, they state that there are only two fully
incorporated sacral vertebrae in _Herrerasaurus_ and _Staurikosaurus_.
In fact, they used that observation to conclude that full incorporation
into the sacrum of at least one additional dorsal vertebra must have
occurred independently in ornithischians and saurischians (i.e., after
the time of _Herrerasaurus_ and _Staurikosaurus_).
There seems to be a contradiction here. I have tentatively concluded
that "full incorporation" is the key phrase. In other words, should
their statement on p. 1138 be interpreted as meaning that the additional
dorsal vertebra in the sacrum of the Dinosauria doesn't necessarily have
to be _fully incorporated_, thus allowing _Herrerasaurus_ and
_Staurikosaurus_ to qualify as dinosaurs?
Bottom line question: What IS the minimum sacral vertebrae count for
Thanks in advance for replies.
Norman R. King tel: (812) 464-1794
Department of Geosciences fax: (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712 e-mail: email@example.com