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Clarifications of Paul's new DA taxa
Some comments to clear up some confusion about the new taxa in DA.
As I spend some considerable time explaining in the text, it is important to
understand that Avepoda, Averostra, Avepectora and Avebrevicauda are
apomorphy + CLADE labels, which are very distinct from the entirely cladistic
node taxa that have become the norm, or the old apomorphy taxa of yore. A+C
taxa could only appear at phylogentic node if we had all extinct and living
taxa available and correctly placed, which will never happen, so in practical
terms A+C taxa never appear at a node in a phylogenetic chart.
Equally importantly, A+C taxa are always more inclusive than clade node taxa
that incorporate a key character in the name, which, because we have an
incomplete fossil record, always leave the basal members of the clade with
the key character out. For example, any clade node taxa that incorporates all
known theropods that lack contact between the 1st metatarsal and distal
tarsals and are in the clade that includes birds inherently excludes more
basal members that share the character but have not been found yet, or were
never preserved. Avepoda does include every single such dinosaur and bird.
This means that A&C names in practical terms are never ever synonymous with
any clade node taxa. Avepoda can never be the equivalent of Neotheropoda,
Eutheropoda or anything else. That's one of the beauties of these A+C taxa,
you can try to drive stakes through their hearts and shoot them with silver
bullets and it does not matter, they cannot be killed off. This is unlike
clade node names where if a name is applied to two nodes, and it later turns
out that the nodes are actually the same, then the junior synonym goes belly
up, its legs feebly kicking and its only hope being eventual demostration
that its node is distinct after all. From now on all dinosaurs that lack
contact between Mt1 and the distal tarsals and belong to the clade that
includes birds are avepods forever and ever, and no one can do anything about
it. They finally and will always have the etymologically accurate name they
Neotheropoda and Eutheropoda remain valid and are included within Avepoda.
Note that if a dinosaur is found that lacks contact between Mt1 and the
distal tarsals but is shown to have evolved this feature separately from the
clade that has this character and includes birds, then the new dinosaur is
not an avepod, it is an avepod mimic. Subsequent loss of a character is of
course not important, so therizinosaurs are still avepods even though they
were weird enough to recontact Mt1 with the distal tarsals, just as snakes
remain tetrapods even though they've lost those pods.
Currently Averostra includes ceratosaurs (which I and other consider not
allied with coelophysoids) and the rest of avepods closer to birds.
Dilophosaurus appears to be a coelophysoid that evolved a promaxillary
fenestra independently of averostrans, so it is an averostran mimic. In the
less likely event that that Dilophosaurus is closer to the ceratosaur-bird
clade than coelophysids then it is an averostran. Or, in the unlikely event
that the Ceratosauria is a monophyletic clade then both ceratosaurs and
dilophosaurs are probably not averostrans, unless coelophysoids lost the
extra fenestra. Again, averostra is not the junior synonym of any clade node
It is important that Avepectora includes averostrans in which the coracoid is
flexed so strongly relative to the scapula that the outer surface of the
coracoid faces so strongly anteriorly that it articulates with the sternum at
an angle of over 45 degrees from the midline - basically the avian system
also found in the most bird-like dinosaurs. This is not synonymous with, and
probably includes Maniraptora.
It is interesting that Maryanska et al. in their new Acta Palaeont Pol paper
place Oviraptorosaurs (incl avimimids) were even I do not go, in the
Avebrevicauda above Confuciusornis. Although I agree with the post-urvogel
neoflightless statues, I doubt this high placement. But if they are correct
the longer tail of the dinosaurs probably represents a reversal (unless some
basal birds evolved very short tails independently of a oviraptorosaur-modern
bird clade), and Avebrevicauda excludes the most basal short tailed birds
while probably including Ornithothoraces.