Wednesday, June 23, 2010

Semilunate Carpal



In the standard cladograms presented by the dino-to-bird enthusiasts, the Tyrannosaurs are placed just before the Maniraptors. And the most primitive "maniraptora" creatures are the Therizinosauria. Let's look at how similar/different these creatures actually are.

http://rspb.royalsocietypublishing.org/content/early/2010/02/24/rspb.2009.2281.full

Here is a table, showing the degree of wrist flexibility of various creatures.
Guanlong wucaii () is a Tyrannosauroidea
Alxasaurus elesitaiensis(39°) is a Therizinosauria
Falcarius utahensis(26°) is a Therizinosauria.

Table 1.
Radiale angles in various theropods. (Bold indicates specimens that we examined directly.)
taxon angle specimen/source
Allosaurus fragilis Chure (2001, fig. 2c)
Huaxiagnathus orientalis 18° Hwang et al. (2004, fig. 8a)
Sinosauropteryx prima Currie & Chen (2001, fig. 8a)
Guanlong wucaii IVPP V14531
Alxasaurus elesitaiensis 39° IVPP RV93001
Falcarius utahensis 26° Utah Museum of Natural History, Salt Lake City, USA (UMNH) VP 12294
Caudipteryx sp. 76° IVPP V12430
Haplocheirus 15° IVPP V15988
Sinovenator changii 35° IVPP V14009
Deinonychus antirrhopus 31° YPM 5208
Eoconfuciusornis zhengi 55° IVPP V11977
Meleagris gallopavo 59° IVPP 1222

Notice the low numbers up to Tyrannosauroidea (Guanlong wucaii) and the much higher numbers beginning with the Therizinosauroids (Alxasaurus elesitaiensis).

These two groups are not related. The creatures labeled "maniraptora" have just been artificially tacked onto the dinosaur group.

Here is what the authors said about the discontinuity between Tyrannosauroidea and Therizinosauroids:

"Therizinosauroids are probably the most basal [primitive] maniraptoran theropods (Zanno et al. 2009). In a well-preserved left carpus of Alxasaurus (IVPP, RV93001), the SLC is strongly convex and distinctly trochlear, despite being made up of two separate ossifications (figure 2). The radiale, in contrast to that of Guanlong, [Tyrannosauroidea] is distinctly wedge-shaped."

Also see here:
http://pterosaurnet.blogspot.ca/2014/10/wrists.html

4 comments:

  1. This is simply because of the fact that tyrannosauroids had very short arms. You think paleontologists believe Tyrannosaurs, for some reason, evolved into birds? No.
    The Coelurosauria evolved. PERIOD.
    Right from the beginning three groups evolved.
    The compsognathids, tyrannosauroids and MANIRQAPTORIFORMES.
    From the maniraptoriformes, evolved the Maniraptora (-Ornithomimosauria).

    See, Tyrannosauroidea is unrelated and is just an "offshoot" branch of the Coelurosauria.

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  2. Give me the name of an actual ancestor of maniraptoriformes. Not a group name like Coelurosauria but an actual creature.
    And it would be very helpful to show fossils and even a picture if possible.
    That would be great.

    ReplyDelete
  3. Marco I don't know what you are getting at. Care to elaborate?

    ReplyDelete