Fossil Coast’s Geo Travel blog explores the Świętokrzyskie Mountains or Holy Cross Mountains in Poland where the evolutionary fossil record of early terrestrial tetrapods has been rewritten.
The Zachelmie Quarry has the oldest known trace evidence of "terrestrialisation" or adaptations that made it possible for aquatic vertebrate animals to live and sustain life on land.
The Zachelmie Tracks show a time when animals with limbs rather than animals with paired fins waded across the sediments of a Middle Devonian marine tidal flat.
Tetrapods are vertebrate animals that have a backbone inside their body and four limbs or leg-like appendages. In taxonomy or the science of classifying animals tetrapods belong to the superclass Tetrapoda (meaning four legs). The superclass Tetrapoda includes amphibians, reptiles, mammals, and birds.
The Świętokrzyskie Mountains are a part of the Łysogóry the largest mountain range of the Little Poland Uplands and also among the oldest mountains in Europe. The highest peaks look down on the city of Kielce the capital of the Świętokrzyskie Province.
In 2002 a team of scientists led by Grzegorz Niedźwiedzki from Warsaw University found the tetrapod tracks in the Zachelmie Quarry. The Zachelmie Quarry is now among the “First 100 Geological Heritage Sites” designated by the International Union of Geological Sciences (IUGS) in 2022. It is also located within the 526 Km2 of The Holy Cross Mountains UNESCO Global Geopark.
The best place to understand more about the fossils found and geology of the Świętokrzyskie Mountains is to visit "The Geological Museum" in Kielce run by the Polish Geological Institute and also the Geonatura Kielce - Centrum Geoedukacji.
The Zachelmie Trackways suggest that tetrapods transitioned from a life in water onto the land approximately 18 million years earlier than previously thought. Tetrapods are now generally considered to have widely colonised land during the Carboniferous from 359 million years ago.
Research indicates that tetrapods evolved from marine environments during times of higher oxygen levels and environmental conditions that favoured their evolution.
Before the Trackways of Zachelmie were discovered the earliest complete fossils of tetrapods were known as elpistostegids ("lobe-finned fishes"). These included the Panderichthys and Tiktaalik which indicated a terrestrialisation transition during the Frasnian Stage (382.7 - 372.2 million years ago) the first of the two ages within the Late Devonian Epoch. However, at this time the elpistostegids still had evidence of paired fins.
Among the oldest tetrapods found that have recognisble limbs are the Acanthostega and Ichthyostega (meaning "fish roof"). Described as the "..Rosetta Stones of tetrapods,” Robert Gess, a paleontologist at the Albany Museum in South Africa. They are among the most complete fossils of the first vertebrate creatures to leave the seas and walk on land during the Famennian Stage (372.2 - 358.9 million years). They may have possibly existed into the Early Mississippian Epoch (358.9 - 323.2 million years) first of two major subdivisions of the Carboniferous Period.
The Zachelmie Quarry rocks are classified as Dolomite. This is a sedimentary carbonate or limestone rock that has a high concentration of the mineral dolomite CaMg(CO3)2.
The local geology suggests that the trace fossil tracks of the early tetrapods were formed mostly under shallow water conditions by wading and walking. The tracks would have been created in a well-aerated shallow tidal flat or lagoonal environment separated from an open marine basin by sparsely vegetated islands and spits. These rocks are within the Wojciechowice Formation dating to 395 million years.
The Zachelmie Trackways suggest that these tetrapods transitioned onto land with pairs of limbs instead of pairs of fins earlier during the Eifelian Stage (407.6 - 393.3 Million years ago) or more specifically between 390–391 million years.
These fossil finds have created some debate and reassessment within the paleontology community around the timing, ecology, and environmental setting of the early tetrapod transition. Watch this space!