[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Segnosaurs Analyzed as Prosauropods



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  I have done this using Adam Yate's unpublished analysis (seen at SVPCA), with his permission of course.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and contains more characters and taxa than Gauffre's 1995 analysis (165 vs. 34; 21 vs. 13), though the latter is unpublished.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