Ancient Amphibian Burrowed
September 3, 2013

Giant Extinct Amphibian Likely Burrowed In Dry Months

Brett Smith for - Your Universe Online

An ancient enormous amphibian known as Metoposaurus diagnosticus that once roamed modern day Poland some 230 million years ago probably spent the drier months in an underground burrow, according to a new report in the Journal of Vertebrate Paleontology.

With their flat heads, wide hands, and large tails, study investigators described Metoposaurus as a species that swam in transient lakes during the region’s wet season and most likely used its head and forearms to burrow under the ground during the dry season. These water-loving, alligator-like amphibians could grow up to 10 feet long and weigh as much as a ton.

To reach their conclusion, the researchers analyzed cross-sections of the amphibian’s fossilized bones. They were particularly interested in the bones’ growth rings, or annuli. Similar to tree rings, the annuli’s alternating light and dark bands indicate years of growth. In other early amphibians, one annulus contains a broad zone of rapid growth marking the wet season – followed by a thin band of slow growth that occurred during the dry season. However, the annuli of Metoposaurus exhibited a period of prolonged slow growth followed by a halt of growth during the dry season.

"The histology of Metoposaurus long bones seems to be unique,” said study author Dorota Konietzo-Meier, of the University of Opole in Poland. “In our interpretation it corresponds to the two-seasonal climate with a short, more favorable wet season and a long dry part of the year when life conditions were worse."

Michel Laurin of France's Muséum National d'Histoire Naturelle, though not directly involved with this study, said he was somewhat skeptical of its findings.

"This interpretation is interesting, but problematic in some respects,” Laurin said. “This animal was much larger than any extant burrowing species I know of, and if it dug, I suspect that the snout and tail played a far greater role than the limbs, as we observe in most extant aquatic vertebrates."

Study co-author P. Martin Sander said the research also allowed them to determine accurate ages for the Metoposaurus specimens at the time of death.

"A common problem with these large amphibians is that you can't tell from the shape of their bones if they are grown or not; sometimes the youngsters get described as a different species from the grown-ups,” said Sander, of the University of Bonn in Germany.

The study analysis showed that all of the specimens analyzed were juveniles. While the smallest specimen was only one year old, the largest was four. Metoposaurus is thought to have reached adulthood at about seven years.

The authors say they aren't yet sure if the amphibians’ burrowing habits were unique to juveniles.

“It amazes me time and again how much we can learn from these extinct animals,” Sander said. “The techniques we used have been around since the 1840s, but only in the last 20 years have researchers asked the right questions and drawn comparisons with living animals."

The watery havens for Metoposaurus were very transient during the Late Triassic period. Scientists have uncovered several mass graves of the animals – thought to be the results of pools that evaporated during the dry season.