The tracks made by tetrapod animals, between 280 and 290 million years ago, has been found in the Manyanet Valle by researchers from the Universitat Autònoma de Barcelona (UAB), the Miquel Crusafont Catalan Institute of Palaeontology (ICP) and the Jaume Almera Institute of Earth Sciences (CSIC). According to the research team, these are the most ancient fossil footprints in Catalonia.
The researchers identified the ichnites or fossilised footprints in two areas with different environments. One was a meandering fluvial systems, or sinuous rivers, and another was unconfined waters. The tetrapods would have inhabited these two environments during the Permian Period.
The footprints of the temnospondyls, the predecessors of present-day amphibians, were found in the fluvial zone. The researchers say that these species had similar life patterns like today’s salamanders.
The fluvial zone contained more significant biodiversity than the unconfined waters zone, harbouring species like seymouriamorphs, which grew to almost one metre in length and diadectomorphs, which grew up to two metres in length.
The tracks of captorhinids, primitive reptiles with several rows of teeth that grew up to half a metre in length, were found where the open water used to be. Additionally, the researchers also discovered footprints of synapsids, the predecessor of today’s mammals, and pelycosaurs, a group of synapsids with sail along their spine and grew up to four metres long.
The scientists believe that the differences may be attributed to climate differences. Study researcher Josep Fortuny, from ICP, explains that the changes matched the different palaeoclimate zones raised on their models.
The early tetrapods, or four-footed in the ancient Greek language, were the first vertebrates to step on land, develop lungs to inhale atmospheric oxygen and turn fins into legs. Their life cycle was still tied to the aquatic environments but they correspond to different groups of early reptiles and amphibians that paved the way for mammals.
Ninety percent of the species went extinct at the end of the Permian, which began 300 million years ago and ended 250 million years ago. During this time, all land masses formed a single super-continent called Pangaea, located on the Equator and reached the Poles. However, another group of synapsids, called cynodonts, survived and gave rise to mammals.