“three “primitive” frogs and two “modern” frogs (so named because they evolved more recently than the “primitive” species). Though all the frogs started their jumps similarly, the primitive frogs kept their legs extended when they land–keeping their Superman pose to the skidding end.”

Nope. These are all modern species. It’s entirely possible that the “primitive” species, as a species, is younger. You need data to say one way or the other. As a lineage, this frog and the others are exactly the same age since their split from a common ancestor.

“Old or new, the belly-flopping frogs come equipped with their own gut protection: “shield-shaped” pelvic cartilage and abdominal ribs which researchers believe may soften the blow.”

This sounds like a derived feature to me — or do the authors suggest that this is also the ancestral characteristic?

“Primitive” and “derived” refer to characters, not species.

Thanks for your comment. That makes sense–to call the motion itself primitive since the species itself is still living, but the wording we use comes directly from the published paper (http://www.springerlink.com/content/6w186u2565n05623/fulltext.pdf). It calls the frogs themselves “the most primitive living frogs of the family Leiopelmatidae.” Is there a disagreement in the field about this term?

No, no disagreement among people who understand phylogenies.

The issue is that there is no such thing as a primitive species. “Primitive” and “derived” refer to characteristics, not whole species. The authors of the paper seem confused about this as well, and certainly this is a common misconception even in the biology literature.

As an example, consider the platypus. Is it primitive? Well, it lays eggs, which is a primitive (= more like the ancestor) trait. But it also has venom and a bill, which are derived (= not like the ancestor).

Is this jumping style like the egg-laying of the platypus (primitive) or like its bill (derived)? I don’t know, but you certainly can’t assume that the ancestor had it because this is a “primitive” or “early branching” lineage any more than you can assume that the ancestor of mammals had bills.

It’s also a fallacy to say “more evolved” or “younger” in terms of whole lineages. These are all modern species, which means that their lineages have been evolving for exactly the same amount of time since they last shared a common ancestor.

The term “primitive frog” is used as a shorthand by many functional morphologists. It’s just easier to say “primitive frog”, rather than saying frogs with primitive anatomical or behavioral features.

The term “primitive frog” is used as a shorthand by many functional morphologists. It’s just easier to say “primitive frog”, rather than saying frogs with primitive anatomical or behavioral features.

Unfortunately, it’s not just used as shorthand, it impacts the entire interpretation of trait evolution.