Abstract
Tetrapod fossil tracks are known from the Middle Devonian (Eifelian at ca. 397 million years ago - MYA), and their earliest bony remains from the Upper Devonian (Frasnian at 375–385 MYA). Tetrapods are now generally considered to have colonized land during the Carboniferous (i.e., after 359 MYA), which is considered to be one of the major events in the history of life. Our analysis on tetrapod evolution was performed using molecular data consisting of 13 proteins from 17 species and different paleontological data. The analysis on the molecular data was performed with the program TreeSAAP and the results were analyzed to see if they had implications on the paleontological data collected. The results have shown that tetrapods evolved from marine environments during times of higher oxygen levels. The change in environmental conditions played a major role in their evolution. According to our analysis this evolution occurred at about 397–416 MYA during the Early Devonian unlike previously thought. This idea is supported by various environmental factors such as sea levels and oxygen rate, and biotic factors such as biodiversity of arthropods and coral reefs. The molecular data also strongly supports lungfish as tetrapod's closest living relative.
Highlights
Terrestrialization may be defined as the series of processes that makes an aquatic organism capable of living and sustaining itself on land
The major amino acid properties affecting the similar regions in the genes of amphibians, lungfishes, and coelacanths are Equilibrium constant, Surrounding hydrophobicity, Power to be at the N-terminal, Solvent accessible reduction ratio, Hydropathy, Compressibility, Mean r.m.s. fluctuation displacement, Thermodynamic transfer hydrophobicity, Polarity
Equilibrium constant is the property that has influenced the genes to the second highest extent (Table 1), it drives a more product driven reaction in tetrapod mitochondrial proteins which is why we find a higher value of it affecting the genome
Summary
Terrestrialization may be defined as the series of processes (adaptation) that makes an aquatic organism capable of living and sustaining itself on land. A modern version of this scenario is that tetrapods evolved from the elpistostegids, probably in brackish to freshwater environments, in response to the modification of their environment [6] This scenario has been strongly contradicted as early as the 1950s (refs in [5]) and replaced by the idea that the transition from fish to tetrapod occurred in marine to land/sea transitional environments (tidal, intertidal or lagoonal zones) [7,8,9,10,11]. The recent discovery of tetrapod tracks from Poland [11] suggests that the earliest evolution of tetrapods could have taken place in marine to land/sea transitional environments Study of such relationships between living organisms and environmental conditions at global scale is generally known as geobiology (biosphere-geosphere interactions)
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