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Posture of *Edmontosaurus annectens*



I went to the Royal Ontario Museum on the weekend to make some observations on the dinosaurs, especially the hadrosaurines. A few that I would like to discuss:

The mounted skeleton of *Edmontosaurus annectens* (ROM 867) in the alleged walking posture is unusual in that many of the dorsal ribs (no. 6-10) overlap distally on the visible side. No. 7 is the most lateral, with the rest becoming increasingly medial as they move away from this rib. There's also a noticeable gap where the neural spines above ribs 9 and 10 appear to be too far apart- the gap is almost the length of a neural spine. These anomalies might disappear if the dorsal arch was straighted out some- this might have the effect of lifting the forelimbs above the quadrupedal level and making the animal more likely a biped. Unfortunately, the anterior dorsal vertebrae are not visible in the display. The skeleton of *Gryposaurus incurvimanus* (ROM 764) has a similar posture, but its ribs are spaced normally. Perhaps these hadrosaurines did not have the same posture in life? (Possibly relating to the subject of bipedal vs. quadrupedal hadrosaurines, I observed some interesting variation in the forefeet of various species. In *E. annectens*, metacarpals III and IV are most strongly developed and appressed; metacarpal II is more slender and not appressed to III. *Maiasaura peeblesorum* has all three slender and not appressed (they are in fact mounted as a bit divergent); and *Prosaurolophus maximus* (ROM 787) has II-IV all appressed.)

ROM 867 has the only truly droopy, dragging hadrosaur tail on display. I was a little surprised that I could see no obvious places where the tail bones had been broken or disarticulated. How is it universally known that no hadrosaurids dragged their tails? ROM 867 as displayed has no ossified tendons over the tail, but I do not know if this is characteristic of *Edmontosaurus annectens*, or an artifact of preservation/preparation.

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