Great leap forward
World’s oldest frogs show evolution of jumping in action
June 1, 2011
An internet search for “belly-flopping frogs” brings up videos on websites ranging from the BBC and Discovery Magazine to YouTube, where one fan set the jumping critters to an epic Star Wars soundtrack. The footage was captured by Ohio University Professor of Biological Sciences Stephen Reilly and his colleagues at Southern Illinois University and the University of Otago, New Zealand, in an effort to learn about the evolution of locomotion in amphibians.
Leaping leiopelmatids land on their chins or bellies. The frogs usually dive into water or land on moist vegetation surrounding the cascading streams in their native habitat of the Pacific Northwest and New Zealand. Photos: courtesy of Stephen Reilly.
The team studied several frogs, including the leiopelmatids, the oldest known frogs. They exist in only two places in the world: the cold, cascading streams of the Pacific Northwest and New Zealand, which were once connected by land masses in earlier geological times. Videos of the North American species and the New Zealand frogs show similar jumping patterns in both native habitats.
“The frogs’ bizarre landing behavior hasn’t changed much in 125 million years,” Reilly says.
The leiopelmatids also swim in an unusual way, he notes. They use a trot-like gait, similar to a dog paddle, instead of using a typical frog-kick with both legs extended. The animals do jump with a leg extension, however, like other types of frogs. It’s the landing action that differs.
“Sometimes they land on their chin, sometimes on their belly,” Reilly says, explaining that the frogs usually dive into water or land on the moist vegetation surrounding cascading streams. “They’re also the only frogs to have ‘abdominal ribs’ in their belly that appear to help take the impacts.”
The leiopelmatids show that jumping in frogs happened in stages. Frogs first learned how to jump with their hind legs, and later added controlled landing by extending their arms and legs. Research by Reilly’s graduate student Mike Jorgensen on the anatomy of the frogs’ muscles and pelvic bones further supports the two-step pattern of jumping evolution. Leiopelmatids have a more primitive pelvis and simpler muscles in their legs compared to frogs that land on their limbs, he explains.
“The leiopelmatids are the best model of the first original frogs that could jump but hadn’t perfected landing,” Reilly says.
The belly-flopping frogs research was published earlier this year in the German journal Naturwissenschaften, which is similar to the American journal Science. Another paper on the pelvic anatomy was published in the Journal of Morphology.
In the next stage of the research, Reilly and his team will use new 3-dimensional X-ray video cameras to watch how the limbs and pelvic bones move during jumping, landing, and swimming.
Watch a video of a leiopelmatid in action.
By Katie Brandt
This article appears in the Spring/Summer 2011 issue of Perspectives magazine.