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Some thoughts on AVES and MAMMALIA



Why *Confuciusornis* isn't used for defining Aves? Because it's used for
Pygostylia. It would make better sense IMHO to call this clade Aves, but
nobody asked me :-) , therefore what I'm trying to do all the time is
actually to put *Tyrannosaurus* into Aves.

----- Original Message -----
From: <NJPharris@aol.com>
Sent: Friday, November 02, 2001 6:49 AM
Subject: Re: Some thoughts on AVES

> I, for one, am not at all averse to apomorphy-based definitions, as long
as certain protocols are followed.

Neither is the current draft of the PhyloCode. But there a species will have
to be included to avoid problems with convergence. Mammaliamorpha (see
below) might be "the first organism that possessed multi-rooted teeth
homologous to those in *Homo sapiens* and all its descendants", for example.

> A definition for Mammalia along the lines of "the first organism to
possess three auditory ossicles homologous to those of living mammals and
all of its descendants" would be absolutely lovely, as far as I'm concerned
(since it both captures exactly a traditional conception of Mammalia [...]).

Are you sure? If you mean "the first organism in which the articular,
prearticular, angular, surangular, quadrate and quadratojugal are involved
in hearing airborne sounds", because none of the auditory ossicles is a
neomorph, then that may be *Tetraceratops* and therefore Mammalia a senior
synonym of Therapsida/Neotheropsida. If you mean "the first organism in
which the articular, prearticular, angular and surangular are separate from
the dentary + splenial + coronoid", it lived in the Middle or maybe Early
Jurassic and was a direct ancestor of (crown group + *Hadrocodium*); in this
case Mammalia would not include *Sinoconodon*, Morganucodontidae, Docodonta,
*Kuehneotherium* and others that are traditionally included. Mammalia would
also be a part of Holotheria which is anchored on *Kuehneotherium* =8-)

*Probainognathus* is a bad example. It has a double jaw joint like node 2
below and apparently Tritheledontidae, but while in these 2 groups the new
joint is between the squamosal and the dentary, in *Probainognathus* the new
joint is between the squamosal and the _surangular_. Convergence.
Tritylodontids only have the plesiomorphic joint AFAIK.

2 days ago I cited

Wang Yuanqing, Hu Yaoming, Meng Jin, Li Chuankui: An Ossified Meckel's
Cartilage in Two Cretaceous Mammals and Origin of the Mammalian Middle Ear,
Science 294, 357 -- 361 (12 October 2001)

and forgot to mention the following: (DMME = definitive mammalian middle
ear, PDU = postdentary unit = the bones mentioned above, m = lower molar)
"The phylogeny based on 112 craniodental characters from 20 taxa (Fig. 3) is
largely in keeping with other recent phylogenetic hypotheses of mammals and
their relatives [...]. Whithin the phylogeny, acquisition of the DMME in
*Repenomamus* and *Gobiconodon* is consistent with the prediction that
triconodontids have ear ossicles [sic] [...]. Whether the DMME is a
synapomorphy for [crown group] Mammalia, which probably occured in the
middle Jurassic, or it is shared by Mammalia and *Hadrocodium* and thus
evolved in the early Jurassic [...], depends on the interpretation of
*Hadrocodium*. The type specimen of *Hadrocodium* [...] was originally
regarded as a juvenile *Morganucodon* [...], but is now considered an adult,
or subadult, of a distinctive taxon in which the PDU is detached from the
dentary [...] [its description is cited]. In our view, however, many
features, such as its small size, erupting first upper postcanine tooth
[...], only two molars, slender mandible, large space between m2 and the
coronoid proceess, large promontorium, and large brain vault [...], suggest
that [...] [it] is a postsuckling juvenile. Whether the common ancestor of
*Hadrocodium* and mammals evolved the DMME in the early Jurassic requires
further testing (Fig. 3)."

So *Hadrocodium* is a youngster after all... phew. Short version of Fig. 3:

1--Tritylodontidae
`--2--*Adelobasileus*
    |--*Sinoconodon*
    `--3--Morganucodontidae
         `--+--Docodonta
              `--+--*Hadrocodium*
                   `--4--5--+--*Gobiconodon*
                        |    |     `--*Repenomamus*
                        |    `--+--*Jeholodens*
                        |         `--Triconodontidae
                        |--+--Monotremata
                        |    `--Multituberculata
                        `--6--Spalacotherioidea
                             `--+--Dryolestida
                                  `--+--*Vincelestes*
                                       `--+--Eutheria
                                            `--Metatheria

1 = Mammaliamorpha
2 = traditional Mammalia as used in Benton's book
3 = Mammaliaformes
4 = crown-group Mammalia, used in the paper
5 = cries for being called Triconodonta or Eutriconodonta
6 = Trechnotheria

Contrary to claims that have been made on this and the PhyloCode mailing
list, the crown group is quite stable. The "triconodonts" might yet fall out
of it, but in the paper on Australosphenida they come out as sister to
Trechnotheria and thus well within the crown group. The
Monotremata-Multituberculata clade is IMHO odd but has occurred in several
recent papers; I've also read that they share something with the
"triconodonts" in their feet. Spalacotherioidea is what's left of
"Symmetrodonta"; *Zhangheotherium* was used in the analysis. Trechnotheria
is stable in all analyses I've seen since the description of
*Zhangheotherium*.