|
It was suggested that segnosaurs be included in an
analysis focusing on prosauropods. I have done this using Adam Yate's
unpublished analysis (seen at SVPCA), with his permission of course. His
analysis is in my opinion much better than Sereno's 1999 prosauropod analysis
and contains more characters and taxa than Gauffre's 1995 analysis (165 vs. 34;
21 vs. 13), though the latter is unpublished. The consensus of Yate's
analysis (5 MPT's, 354 steps) is-
____Crurotarsi
|____Marasuchus
|____Ornithischia
|____Herrerasauridae
|____Neotheropoda
|____Saturnalia
|____Thecodontosaurus
|____"Efraasia"
|____Plateosaurus
|____Anchisaurus
|____Riojasaurus
|____Coloradisaurus
|____Lufengosaurus
|____Massospondylus
| |__Yunnanosaurus
|_____Euskelosaurus
|____Melanorosaurus
|___Blikanosaurus
|__Vulcanodon
|_Eusauropoda
I entered Beipiaosaurus, Alxasaurus,
Therizinosaurus and "Segnosauridae" as separate OTU's and ran the data with PAUP
4.0b8. This resulted in 12MPT's of 396 steps each. The topology
is-
____Crurotarsi
|____Marasuchus
|____Ornithischia
|____Herrerasauridae
|____Neotheropoda
|____Saturnalia
|_________Thecodontosaurus
|
|_______"Efraasia"
|
|_______Anchisaurus
|
| |___Riojasaurus
|
|______Coloradisaurus
|
|______Lufengosaurus
|
|______Plateosaurus
|
|______Massospondylus
|
|__Yunnanosaurus
|__________Euskelosaurus
|_________Melanorosaurus
|________Therizinosaurus
|_______Beipiaosaurus
| |___Alxasaurus
| |___Segnosauridae
|_______Blikanosaurus
|____Vulcanodon
|__Eusauropoda
Quite an interesting result. Keep in mind no
neotheropod, tetanurine, coelurosaur, etc. synapomorphies were used, nor any
segnosaur or therizinosauroid synapomorphies. Bootstrap support for
the node containing segnosaurs, sauropods and Blikanosaurus is 10%. I
wished to see how strongly this was supported over segnosaurs as theropods, so I
enforced a constraint tree grouping segnosaurs with neotheropods and got 20
MPT's of 397 steps each. So by adding only one step, we get segnosaurs as
theropods. The following tree is found-
____Crurotarsi
|____Marasuchus
|____Ornithischia
|____Herrerasauridae
|____Neotheropoda
| |___Segnosauridae
| | |__Therizinosaurus
| |___Beipiaosaurus
| |___Alxasaurus
|____Saturnalia
|____Thecodontosaurus
|____"Efraasia"
|____Plateosaurus
|____Anchisaurus
|____Riojasaurus
|____Coloradisaurus
|____Lufengosaurus
|____Massospondylus
| |__Yunnanosaurus
|_____Euskelosaurus
|____Melanorosaurus
|___Blikanosaurus
|__Vulcanodon
|_Eusauropoda
Not only is the constraint tree only one step longer, it preserves Yates'
phylogeny, a monophyletic Segnosauria and groups "segnosaurids" with
Therizinosaurus, as suggested by recent analyses that put both together in the
Therizinosauridae. I was curious what might happen if an undoubted
maniraptoran were included in the analysis. I decided Caudipteryx was a
good choice due to its proximity to segnosaurs in recent analyses.
Including Caudipteryx resulted in 20 MPT's of 408 steps each.
These had the same topology of the above tree, except the theropod
section-
|____Neotheropoda
| |__Caudipteryx
| |___Segnosauridae
|
| |__Therizinosaurus
| |___Beipiaosaurus
| |___Alxasaurus
Seems the presence of intermediate taxa helps a lot. And this was
accomplished without the inclusion of any characters designed to characterize
neotheropods, tetanurines, coelurosaurs, maniraptorans,
(segnosaurs+oviraptorosaurs) or segnosaurs. The taxa grouped like this
based on the distribution of dinosaurian, saurischian and prosauropod
synapomorphies. Enforcing a monophyletic Theropoda (Caudipteryx +
Neotheropoda) and a segnosaur-sauropodomorph clade resulted in 36 trees of 442
steps each. As this is 34 steps longer than the above tree, it is
seriously doubted. However, such statements are not really fair, as all
relevent synapomorphies were not included.
Mickey Mortimer |