Scales helped reptiles conquer the land—when did they first evolve?

Tipping the scales

Sebastian Voigt is the director of the Urweltmuseum GEOSKOP in Germany and the lead author of this paper. Evidence of segmentation within the toes of their footprints along with the tail drag scale impressions are “a further argument that diadectids had scales at least on the underside of the tail and feet,” he told Ars. “One cannot automatically assume that scales developed evenly and quickly all over the body. For example, scales could have developed first on the parts of the body that were most likely to be in contact with the ground in terrestrial vertebrates (feet, belly, underside of the tail).”

But either way, “the epidermal scales in diadectids and other terrestrial tetrapods prevented the evaporation of water from their bodies in a dry environment,” Calábková noted, which may have helped them survive “the desert climate that prevailed on [the supercontinent of] Pangea during the Permian.”

Adriana Cecilia Mancuso is a researcher from Argentina who specializes in the evolution of terrestrial ecosystems. She was not involved in the research, but says this discovery is “highly significant. Fossil skin impressions are rare in the deep geological record. Furthermore, the quality of the reported impressions provides strong evidence regarding the origin of epidermal scales in early tetrapods.”

“By studying these fossil traces,” she explained to Ars, “scientists can reconstruct ancient ecosystems, understand how organisms responded to environmental and climatic changes, and trace the evolution of key features in the history of life on Earth. This information not only helps us better understand our geological and biological past but also offers insights into how modern ecosystems may respond to current and future environmental challenges.”

Help on the ground

Access to the two Polish quarries where these fossils are found is a direct result of “support from the employees and management of the quarries,” said Izabela Ploch, co-author and stratigrapher and paleontologist with the Polish Geological Institute. She added that “in the case of very heavy sandstone slabs, they help us extract them from the quarry, often using heavy equipment.”

“We often talk about fossils to quarry workers,” she continued, “which really piques their interest. The result of this is, for example, the creation of [an exhibit space] in Radków, initiated by the management of a nearby quarry after they saw what beautiful trace fossils we found there.”

“We want local people to understand what they have in this area and what interesting stories the ichnofossils tell,” she said. And that includes plans to encourage geotourism to the area as well as exhibits displaying the trace fossils found in the quarries.

Ploch mused about how much we have yet to uncover. “There are so many mysteries still to be discovered,” she said. “Without knowing our past, we will not know our future and the processes that guide the evolution of life on Earth. By learning about even a modest fragment of the Earth's past, we add an element to a larger puzzle.”

Biology Letters, 2024.  DOI: 10.1098/rsbl.2024.0041