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What chance is there that *Gansus* actually belongs into Hesperornithes?
As explained in their supplementary information, You et al. (2006) found 24
MPTs, in which *G.* was either outside of (Hesperornithes + Neornithes) or
closer to Neornithes than *Ichthyornis* or (as in the majority-rule
consensus tree in the paper itself) closer to (Neornithes + *Ichthyornis*)
than to Hesperornithes.
Neither *Enaliornis* nor *Pasquiaornis* (nor, unsurprisingly, *Potamornis*)
were included; the only representatives of Hesperornithes are *Baptornis*
and *Hesperornis*. The supp. inf. states that *E.* was excluded because it
shows hesperornithean autapomorphies and would therefore predictably have
come out as the sister-group to *Baptornis* + *Hesperornis* -- but I can't
see why that's an argument. It would after all have broken up the very long
branch that leads to (*B.* + *H.*); I wonder if we are seeing long-branch
attraction of (*B.* + *H.*). away from *G.*. The occurrence of MPTs where
*G.* is outside (Hesperornithes + Neornithes) shows that the phylogenetic
position of (*B.* + *H.*) is unstable.
According to the supp. inf., *Gansus* shares the following character states
with *Ichthyornis* and Neornithes but not (*B.* + *H.*):
- "three sacral vertebrae with dorsally-directed costolateral eminences"
(...sacral ribs + transverse processes?)
- "lateral process of coracoid present"
- "medial surface of coracoid in vicinity of N. supracoracoideus foramen
flat to convex"
- "ischium straight, with no dorsal process"
I wonder: could the first and the last character states be related to
foot-propelled diving, and could the other two be flight-related and
therefore reversed in (*B.* + *H.*)?
Fig. S1C is intriguing. That cnemial crest is enormous.