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Re: New Papers of the Damned
Butler, R.J., Upchurch, P., and Norman, D.B. 2007. The phylogeny of the
ornithischian dinosaurs. Journal of Systematic Palaeontology. doi:
[...] Lesothosaurus (the best-known 'fabrosaur')
occupies an unusual position as the most basal member of Thyreophora.
But *Stormbergia* does not.
This separation looks wrong:
Fabien Knoll, Kevin Padian & Armand de Ricqlès: The growth trajectory and
adult size of *Lesothosaurus diagnosticus* (Dinosauria: Ornithischia):
taxonomic implications, SVP meeting abstracts 2007, 100A
Questions about the taxonomic status, diversity, and pace of evolution of
basal ornithischian dinosaurs persist in part because some historically
important taxa have been based on incomplete material of uncertain
ontogenetic status. We analyzed the bone tissues of small (~1 m length)
specimens of *Lesothosaurus* and determined that they represent young
individuals that were rapidly growing. In contrast, a larger (~2 m length)
individual that has been referred alternatively to *Lesothosaurus* and to
"cf. *Stormbergia* & *Lesothosaurus*" shows the onset of adult histological
features. We infer that these and other specimens referred to the two taxa
are most reasonably interpreted as representing ontogenetic stages of a
single taxon that reached maturity in approximately four years. Of the two
character states that are supposed to distinguish the two taxa, one is
probably best ascribed to teratological and preservational differences, and
the other to ontogenetic change; there seems, therefore, no compelling
reason to separate *Stormbergia* from the senior taxon *Lesothosaurus*.
Diagnoses of taxa that are based on supposedly unique combinations of
character states can be problematic: they often cannot account for possible
polarity errors that result from comparing individuals that differ in
ontogenetic stage but may belong to the same taxon. For this reason it is
important to base taxonomic diagnoses on specimens with well-defined
ontogenetic stages, preferably adults. This is one of a very few examples so
far where bone histology has been used to determine taxonomic questions.
This means that the unfused neurocentral sutures of both *L.* and *S.*
really are markers of immaturity. Yet again something I need to change in my
M.Sc. thesis before publishing it (which won't happen very soon anyway).
It also has implications for certain pterosaur and amniote analyses...