Rearing to go.

"A makeover for an old friend" (SN: 11/4/00, p. 300) stated that "paleontologists now know that Triceratops evolved from ancestors that walked on two legs," implying that it was quadrapedal. Yet the ratio of front and rear leg lengths was very similar to that of the reptile Eudibamus cursoris mentioned in "Early biped fossil pops up in Europe" (SN: 11/4/00.p. 292). This ratio was touted as being a determinant for bipedality. Shouldn't we by the same criteria assume bipedality in Triceratops? Or are there other determining factors not mentioned?

Richard Hill 

Tucson, Ariz.

Although Triceratops had rear legs that were somewhat longer than its forelimbs, the ratio of their lengths is nowhere near the ratio found in Eudibamus cursoris, says Ralph Chapman, a paleontologist at the Smithsonian's National Museum of Natural History in Washington, D.C.

Triceratops' leg bones, especially those in the forelimbs, were very robust. Several other factors, including Triceratops' general body proportions and the way the bones were arranged in its leg joints and front feet, indicate the animal walked on all fours.

The much slimmer and smaller Eudibamus cursoris probably, like many modern lizards, ran bipedally only in short sprints to escape predators--something that the multiton, detensively armored Triceratops neither needed to do nor could do.