Re: K/T event and amphibians, birds

["David Marjanovic" <david.marjanovic@gmx.at>]

> a partial lower jaw for a putative psittaciforme from the Hell Creek.

Just for the record -- months ago I wrote "No Cretaceous parrot" into a
subject line. Then I was told about

Gareth J. Dyke & Gerald Mayr; Thomas A. Stidham: Did parrots exist in the
Cretaceous period?, Nature 399, 317f. (27 May 1999)

The first two write that
- it's suspect anyway as it "would be not only the oldest record of parrots
by some 15 million years, but also the earliest recorded occurrence of a
'terrestrial' modern bird in the Cretaceous. Other reports from this period
have been shown to be too fragmentary to be of any taxonomic value [...], or
to have been incorrectly assigned in the first place [...].    We therefore
recommend that this record be treated with caution until [...]";
- some "psittaciform" characters have a wider distribution among
Maniraptoriformes, "for example, a 'hook-like' dentary is seen in
caenagnathid theropods", while others occur "in other groups of modern
birds" such as "Ciconiiformes";
- the "K-shaped neurovascular canal pattern" occurs only in some (not all)
psittacids;
- the fossil differs a lot from "the oldest unequivocal parrots known in the
fossil record" from the London Clay and Messel which "lack the parrot-like
beak of modern Psittaciformes. Moreover, the mandibular symphysis in Eocene
forms is much smaller and narrower than in recent parrots and in the
specimen from the Lance Formation", so either the latter is a psittacid,
which is highly unlikely, or not a psittaciform at all.

Stidham replies:
- "I have presented a hypothesis for the identification of a Late Cretaceous
fossil as the oldest known parrot [...]. The specimen lacks the characters
distributed more widely in non-avian maniraptoriforms, such as abundant
teeth and unfused dentaries. It has many characters [...], including the
absence of an internal pillar of bone supporting a midline ridge, that are
not present in oviraptoroids [sic] ^2. To assign the specimen to a non-avian
clade requires a less parsimonious hypothesis of character evolution."
- "The K-shaped neurovascular canal pattern [...] is primitive for"
crown-group parrots, sometimes absent because it, like "most characters,
[...] exhibits homoplasy and variation within natural populations", totally
lost "due to the relative shortening of the jaw symphysis in some parrots"
- and "not found outside crown-group parrots, although it superficially
resembles the state in extant cathartid vultures";
- "the combination of characters seen in the fossil is not present outside
crown-group parrots, and Dyke and Mayr have not demonstrated what clade,
other than parrots, has this combination of characters."
- "various phylogenetic hypotheses [...] of neognaths [...] show that
parrots and most other neognath ordinal level clades are constrained to have
diverged from other orders of modern birds in the Cretaceous or early
Palaeocene".
- So will everyone please stick to parsimony: "The identification of the
Cretaceous jaw as a parrot is subject to test and refutation, like any
hypothesis. However, the accepted methods of the field, not statements about
gaps in our current knowledge and preconceived notions of character
evolution, must be used to falsify hypotheses and generate alternatives."

IMHO Stidham is right in general, but Dyke & Mayr are probably right in this
special case. I think that it is much more probable to find the first record
of a modern group after a mass extinction like the K-T than before it and
basal relatives long after. Who knows, it might easily represent an
otherwise unknown group of K birds, maybe some Enantiornithes, which
convergently evolved parrot beaks long before the parrots. Parsimony can
IMHO mislead when there isn't enough to build it on.

Is there anything new on this subject? Is the oviraptoroid (Sereno for
Caenagnathoidea + its stem) character still valid? Ref. 2 is the description
of *Caenagnathasia* which I haven't had time to copy so far:

P. J. Currie, S. J. Godfrey & L. A. Nesov: Can. J. Earth Sci. 30, 2255 --
2272 (1993)