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Re: Convergence and Macelognathus, a Perspective -- and Supplement



I had written:

<The hindlimbs are very long, slender, and gracile. While the ilium is close to
40mm long, the femur (75mm) and tibia (40mm) have a combined length of 115mm,
close to three times the length; the tarsals add 8mm, and the preserved
metatarsals add 35mm, suggesting a limb length of ~200mm (assuming pedal digits
approximating metatarsal length) and a possible hip-height (with the knee bent)
around 140mm (just over 5 inches), so it was a very small animal.>

  I erred and used the preserved iliac length (40mm) for the tibia; the tibia
in question, LACM 5572/150148, is shattered in the median, and has a preserved
gross length of 82mm; the authors estimate the length at 89mm, so this emmends
the figures for a limb length to ~250mm and a hip height of 183mm. Also note
that if the mandible of the type specimen is 3.6 times longer in the symphysis
than the referred material, isometric scaling gives a leg length of 900mm and a
hip height of 659mm, which suggests that *Macelognathus* may have attained a
length of 3m or more.

  I also declined to note in discussing the tibia that there is no indication
of a fibular crest on the tibia.

  Many of these features show similarities to some dinosaurs, especially in the
distal tibia, but the medioventral flange of the tibia, and the proximal
morphology, clearly indicate non-dinosaurian identity for these bones, along
with the elongate symphysis, medial jaw morphology, dorsal vertebral anatomy,
and the proximal femoral anatomy which differs strongly from *Silesaurus*,
*Lewisuchus*, *Marasuchus*, *Lagerpeton*, *Lesothosaurus*, *Eoraptor* or
*Herrerasaurus*, and demonstrates clear crocodylomorph affinities in the
morphology of the calcaneum and tibia. It should also be noted that these
features are absent in *Scleromochlus*, implying less of a close affinity as
has been suggested by some.

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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