yet more ranting on trochanters

[Nick Longrich <nrlongri@midway.uchicago.edu>]

>- lesser trochantor not wing-like (it appears to be fused into a
>trochanteric crest, which would place it with pygostylians, among other
>things- troodontids, Bagaraatan, mononykines, Rahonavis, etc.)

everything with a semilunate except for basal forms like Coelurus has this,
actually. It's an example of just how poorly understood the characters
we're using- and therefore, the phylogenies we're building on top of them-
really are.
Q: how many trochanters are there on the head of the plesiomorphic
maniraptoriforme femur?
A: FIVE: greater, lesser, accessory, posterior, and fourth.
Q: How many in adult dromaeosaurs, troodontids, therizinosaurs,
oviraptorosaurs and Mononykus?
A: FOUR: fourth, posterior, and two processes on the top of the femoral head.
Q: where's that last trochanter gone to? And which one did we lose-
greater, lesser, or accessory?

If you compare the position of these two "trochanters" to immature
maniraptorans- Saurornithoides, Microvenator, Caudipteryx,
Protarchaeopteyrx- you will find that in the immature specimens there are
actually 5 distinguishable trochanters, just where you would find them in
an ornithomimid or tyrannosaur; the greater and lesser trochanter actually
occupy the same space as the "greater" trochanter of adult maniraptorans.
You can assemble something like a growth series using Microvenator to
represent the juvenile oviraptorosaur form, Caudipteryx as the subadult
which is beginning to fuse up the greater and lesser trochanters, and
Ingenia as an adult with greater and lesser trochanters completely fused
into a trochanteric crest. Throughout ontogeny, a large process- the
accessory trochanter, usually mistaken for the lesser trochanter- is
present in front of the greater and lesser trochanters. Later in ontogeny-
relatively late it would appear in oviraptorosaurs, possibly much earlier
in troodontids- greater and lesser trochanter completely fuse and form an
articular surface that butts against an antitrochanter. Now you've got two
processes, which if you're not paying a lot of attention will look like
greater and lesser. Ontogeny is a bitch. It will also bite you with fourth
trochanters- juveniles of derived maniraptorans do not have fourth
trochanters (Microvenator and Sinornithoides, e.g.). They have small pits.
Older individuals, the ones with tarsometatarsuses and fused
scapulocoracoids- will often have a fourth trochanter (Velociraptor,
Deinonychus, Avimimus, e.g.). So it would appear to be aquired over time. I
don't use the character "presence or absence of fourth trochanter", I use
the character "absence of fourth trochanter in juveniles and subadults". Of
course, if all you have to work with is adults with fourth trochanters, you
have to use a "?" in the box.

Bagarataan seems to be doing something weird that sort of resembles this
condition but isn't it, as far as I can tell.