As reported earlier
the theropod community is not happy with the large reptile tree nesting of Yutyrannus with Allosaurus (see discussion yesterday). Today we’ll look at the heretical (non-traditional) nesting of Microraptor with Compsognathus (Fig. 1).
The traditional nesting of Microraptor
is with other ‘raptors’, like Velociraptor (Fig. 1). By contrast, the large reptile tree nested Microraptor between Compsognathus and Sinornithosaurus, and not far from Tianyuraptor at the base of the Tyrannosaurus clade.
The following traits
are shared between Microraptor with Compsognathus to the exclusion of Velociraptor in the large reptile tree, a study that includes a wide gamut of reptiles, not just theropods.
- lacrimal not deeper than maxilla
- narial opening dorsolaterally
- naris at snout tip, not elevated
- frontal separated from upper temporal fenestra
- posterior parietal 20-40º
- jaw joint descends
- caudal transverse processes present beyond eighth caudal
- Mc2-3 align at or beyond m1.2
- Mt2-3 align with p1.1
there is also a list of traits shared between Compsognathus and Velociraptor to the exclusion of Microraptor. And indeed there is also a list of traits linking Microraptor to Velociraptor to the exclusion of Compsognathus.
Look at that face!
If you had to lump and split Compsognathus, Microraptor and Velociraptor based just on the skull alone (Fig. 2), which two would you lump together?
The presences of extensive feathers on all four limbs of Microraptor — not in the direct ancestry of extant birds — points to a possible convergent evolution in this clade… OR more extensive (bit not preserved) feathers in a last common ancestor, like Compsognathus.
The presence of only protofeathers
in the contemporaneous Sinosauropteryx indicates a likely reduction in plumage in that short-legged taxon, slightly off the main line of bird evolution represented by Archaeopteryx of the Late Jurassic. Previously (Ji and Ji 1996) Sinosauropteryx was considered the basalmost taxon with the basalmost protofeathers. Not so both chronologically and phylogenetically.
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