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Therizinosaurs



 Hello, all.
 Been out of town for a few days and have 1032 messages sent to me.Took 
two days to read them. I read some interesting debates on therizinosaurs 
and want to give you my two cents. 
 Therizinosaurs lack the basic prosauropod features. Prosauropods are 
very differen osteologically. Prosauropods have a list of features that 
unite them ( Galton; Dinosauria).
 
1)  Skull about half the lengh of femur. This feature is seen in most 
dinosaurs and seem to be a plastic feature.
 2) Jaw articulation situatated slightly below the level of  the 
maxillary row. Seen in most herbivorous dinosaurs. It is not seen in 
Segnosaurus.
 3) Dendition of small, homodont or slightly heterodont, 
spatulate-shaped  teeth with coarse,obliquely angled serrations. Compare 
the pictures in the Dinosauria, Prosauropod and Segnosauria sections. 
Therizinosaurs lack coarse, obliquely angled serrations.
 4) Digit I of manus bears a twisted first phalanx and an enormous, 
trechant ungual that is medially directed when hyperextended. Part of 
the problem in the prosauropod/therizinosaur hypothesis is the 
completely different strucures of the manus. The therizinosaur manus 
lacks a twisted first phalanx. The therizinosaur manus bears three 
manual digits of elongated, slender phalanxes, and it bears elongate, 
laterally compressed unguals. The prosauropod manus is robust , bears 
robust phalanxes, and robust >ventrally< compressed claws. 
 5) Digits II and III subequal in length and bear small, only slightly 
recurved ungual phalanges. See above.
 6) Digits IV and V reduced and lack ungual phalanges. This is not 
useful because therizinosaurs lack digits IV and V. 
 7) Typical phalangeal formula 2-3-4 ( 3 or 4). Plesiomorphic. 
 8) Bladelike distal pubes form broad apron. This is the reverse of that 
of therizinosaurs.
 9) Pes with vestigal digit V. This is not useful because it is 
homoplastic among several dinosaur groups. 
 
 As you can see the automorphies of the Prosauropoda are basically 
absent in the Therizinosauridea. 

 I advocate that theriziunosaurs are the sister group to the 
Ornithomimosauria. Here are the synapomorphies.

 1) Bulbous, pnematized parashenoid.
 2) Teeth with a constriction between the root and crown.
 3) Large acromion process on a broad, rectangular coracoid with a long 
posteroventral process and a tubercle for the M.biceps.
 4) Rectangular anterior protuberance on the scapula.
 5) Elongate, strap-like posterior scapula end that is elongate 
rectangular. 
 6) Long, slender humerus with elongate proximal deltapectoral crest ( 
Alxasaurus.) 
 7) Manual phalanges subequal ion length.
 8) Reduction of the number of caudals ( 25-30.)

 If this is right therizinosaurs are therefore Maniraptoriformes, 
Arcometatarsalians, and Bullatosaurians. 

 WMattTroutman  


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