The fossil traces, described in the journal Scientific Reports, show that lungfish attempted to leave the water about 10 million years before the earliest known fully land-dwelling four-legged animals, or tetrapods, the naukawpolsce.pl website has reported.
The team, led by Piotr Szrek from the Warsaw-based Polish Geological Institute (PIG-PIB), included Katarzyna Grygorczyk, Sylwester Salwa, Patrycja Dworczak and Alfred Uchman from the Jagiellonian University in the southern city of Kraków.
They discovered the traces in sandstone quarries near the villages of Ujazd and Kopiec in central Poland during fieldwork in 2020 and 2021.
The fossils, assigned to a new ichnospecies named Reptanichnus acutori ("crawling pioneer"), record more than just fin marks. They preserve impressions of the body, tail and even the snout, which the animal used to anchor itself in the sediment while pulling the rest of its body forward.
According to Szrek, the lungfish moved in very shallow water or possibly across exposed sediment, where the lack of buoyancy made swimming impossible and all parts of the body were involved in locomotion.
Such early lungfish fossils are rare. The same research group had found the first Devonian lungfish remains in Poland in 2016 near the Krzyżtopór Castle, sparking years of investigation.
The exceptional preservation of the newly reported tracks was due to a sudden covering of volcanic ash, which protected them from erosion.
To interpret the finds, scientists used 3D scanning and compared the traces with those made in experiments using modern African lungfish (Protopterus annectens), which can crawl in search of water or burrow into sediment during droughts. The modern tracks closely matched those in the Devonian sandstone, supporting the identification.
Fossil trackways of the first vertebrates to colonise land are known from only a handful of sites in Europe, and one in Australia, according to naukawpolsce.pl.
Until now, the oldest came from mid-Devonian rocks in the same mountain range, left by tetrapods. The new lungfish traces suggest that vertebrates were testing land locomotion significantly earlier and in more than one evolutionary line.
The study also offers what may be the earliest known evidence of lateralisation, that is the dominance of one side of the body over the other, in vertebrates.
The researchers found that nearly all the lungfish tracks showed the snout pressed into the sediment with the head turned to the left, implying right-brain dominance. Analysis of 35 such "left-turn" traces from Ujazd and Kopiec showed the pattern was statistically significant.
The discovery indicates that evolution was exploring multiple strategies for adapting to life on land at roughly the same time, challenging the view that tetrapods were the sole pioneers of terrestrial movement, Szrek said.
The Devonian, part of the Paleozoic era, spanned some 60 million years, from about 420 to about 359 million years ago, and saw the first significant expansion of life on land.
(rt/gs)
Source: naukawpolsce.pl