Re: Apomorphy-based definitions (of mammals [...])

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

>        As for the refined scientific definition of a mammal, this is the
way
> I understand it.  Tritheledontidae (ictidosaurs), an advanced cynodont
> therapsid family, has both reptile and mammal jaw articulations

Thanks for the confirmation.

> (transitioning to the mammalian condition).  The mammal boundary has been
> barely crossed in the Upper Triassic mammal _Adelobasileus_, which
> possesses:  an incipient promontorium housing the cochlea (and absence of
a
> reptilian jaw articulation).

Absence of a reptilian jaw articulation in *Adelobasileus*? Is that region
known -- I thought all that's known of it is a braincase?
        Didn't you know that _heaps_ of animals closer to us than (to)
Tritheledontidae _likewise_ have both? ~:-| *Sinoconodon*, *Morganucodon*,
Docodonta (incl. Megazostrodontidae), Haramiyida, *Kuehneotherium* _all_
have a double jaw articulation, secondary one lateral, primary one medial!
The secondary jaw joint appeared in a common ancestor of us +
Tritheledontidae, below the abovementioned forms, and the primary one was
dislodged into the skull in a common ancestor of (crown group +
*Hadrocodium*) or the crown group alone!
        Probably no complication of that sort will arise with the
promontorium. But how can we then ever possibly assign things like the tooth
*Tricuspes* to Mammalia or not?

>   And it would almost certainly be called a mammal unless it happened to
> still have both the mammal and reptile jaw articulations (possible I
> suppose, but doubtful in my opinion, and would require a bit more
refinement
> of the definition at that time).

This is the _normal condition_. See above and below.

Mammaliamorpha (node)
|--Tritylodontidae
`-- ______________________________
__/ 1--Tritheledontidae
      `--traditional Mammalia (apomorphy)
         |--*Adelobasileus*
         |--*Sinoconodon*
         |   inc. sed. Haramiyida
         `--Mammaliaformes (node)
            |--Morganucodontidae
            `--+--Docodonta
                `--+--*Kuehneotherium*
                    `-- ___________________
____________/ 2--*Hadrocodium*
                          `--crown-group Mammalia (node)
                             |--+--*Shuotherium*
                             |   `--Australosphenida
                             |--Multituberculata
                             |--Triconodonta s. str.
                             `--Trechnotheria
                                 |--Spalacotherioidea
                                 `--Cladotheria (node) (inc. Theria)

1 = secondary jaw joint appears, primary one stays in full function
2 _or_ crown-group = primary jaw joint separated from lower jaw =
"detachment of ear ossicles"

!!!_between 1 and (2 or crown-group) all have double jaw joints_!!!

Refs for the cladogram:

Luo Zhexi, Richard L. Cifelli & Zofia Kielan-Jaworowska: Dual origin of
tribosphenic mammals, Nature 409, 53 -- 57 (4 January 2001)
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)