After Surviving on Earth for More Than 200 Million Years, Researchers Have Determined the Body Mass of Two Extinct Amphibians

After surviving on Earth for more than 200 million years, the last of the temnospondyls, amphibians that resemble crocodiles more than amphibians, went extinct during the Cretaceous period, about 120 million years ago.

Now, a group of researchers under the direction of Lachlan Hart, a paleontologist and Ph.D. candidate in the School of Biological, Earth & Environmental Sciences at UNSW Sydney, have examined different approaches to calculating the weight of these rare extinct animals. Paleontology has published the team's research.

Temnospondyls

(Photo : Etienne Assenheimer/Unsplash)

Some reached enormous lengths of six or seven meters. Like living amphibians, they went through a larval (tadpole) stage.

Some species, like Australia's Koolasuchus, which was recently designated as the Victorian State Fossil Emblem, had very broad, rounded heads, while others, like the temnospondyls we used in this study, had heads that were more crocodilian in appearance.

While the slightly longer Paracyclotosaurus davidi is known from the Triassic of Australia, the 1.8-meter-long Eryops megacephalus lived during the Permian period in what is now the United States.

Eryops weighed in at a more manageable 160 kilograms, while the more aquatically oriented Paracyclotosaurus tipped the scales at about 260 kilograms.

The scientific team had to put together a collection of five contemporary "analogs" (such as the Chinese Giant Salamander and the Saltwater Crocodile) because temnospondyls do not have any close living relatives.

They tested a total of 19 different body mass estimation techniques on these five modern "analogs" to see if they were suitable for use in temnospondyls.

According to Dr. Nicolas Campione from the University of New England, Armidale, a body mass estimation expert who was also involved in the study,

"We found several methods which gave us consistently accurate body mass estimations in our five living animals, which included using mathematical equations and 3-dimensional digital models of the animals.

We hypothesized that as these methods are accurate for animals which live and look like temnospondyls, they would also be accurate for temnospondyls," as per ScienceDaily.

Temnospondyls

Temnospondyls were a successful and incredibly diverse group of "labyrinthodont" tetrapods, as per Paleos.

The reptilomorphs and lepospondyls, the other two main labyrinthodont evolutionary lines, are represented by them.

Although some temnospondyls were entirely aquatic as adults-some even had external gills-others probably evolved into creatures more akin to reptiles on land, only returning to the water to lay their eggs.

The Early Carboniferous is when the Temnospondyli evolved. The majority of Paleozoic forms died out before or during the Lopingian period (Late Permian).

However, in the early Mesozoic, two aquatic Gondwanan clades-the stereospondyls and dvinosaurs-survived and even thrived.

Koolasuchus, a Middle Cretaceous (Barremian) temnospondyl from Australia, is the newest one that is currently recognized.

The majority of temnospondyls had relatively large heads and flat, immobile skulls. The skull's shape was quite variable and frequently recognizable.

Some had their mouths drawn out into the traditional "longirostrine" shape associated with reptiles that hunt small fish, such as Archegosaurus.

Some, like the jawless fish species Gerrothorax, had odd, wide, parabolic heads resembling those of galeaspids or other "cornuate" fish.

Some, like Laidleria, had extremely flat, triangular heads that couldn't be easily compared to any other group of vertebrates, ancient or modern.

The temnospondyl post-cranial body plan, on the other hand, was conservative and comparatively unspecialized.

From one group to another, the body proportions varied greatly. As a result, we might surmise that some had a propensity for swimming in an eel-like manner or moving about on land with almost no legs.

Others likely used their limbs for both land and water locomotion because of their relatively stiff, massive bodies.

However, unlike the reptilomorph lineage, no temnospondyl group evolved any limb specializations. The forefoot of temnospondyls had only four toes, while the hindfoot had five.

Similar to early Devonian tetrapods and osteolepiform lobe-finned fish, the vertebral structure was primarily of the primitive intercentra and pleurocentra type.