morphological analysis, is more closely related to lissamphibians (living amphibians) and amniotes than to any other crown group. Role in Fish-Tetrapod Transition Ventastega has helped further research on the Fish-Tetrapod transition, the event during the Devonian when digit bearing tetrapods evolved from finned, fish ancestors. Research on rates of character changes in tetrapods have shown that there were high rates of character changes in the Devonian, which led to the conflicting hypotheses of either the tetrapods had few major changes that occurred during the Devonian or had many small but rapid morphology changes. The braincase of Ventastega has a mixture of fish-like and tetrapod-like characteristics, indicating that changes in the braincase during the fish-tetrapod transition occurred through a series of many small changes instead of one large change. The skull morphology of Ventastega has helped informed the hypothesis that changes in skull roof pattern proportions also occurred gradually, with the snout elongating and eyes increasing in size while moving dorsally over time. Due to anoxic conditions in aquatic ecosystems during the Famennian (see Paleoenvironment below), early tetrapods such as Ventastega would have had a significant fitness advantage with the ability to exploit terrestrial environments. Locomotion No limb remains from Ventastega have been discovered to inform researchers about its locomotion, but paleontologists have been able to infer some basic information about its limbs and locomotion due to its overall morphological similarity to Acanthostega, a limbed tetrapod with digits. While no fossilized trackways from Ventastega have yet been discovered, discoveries of late Devonian trackways from closely related Ichthyostega and Acanthostega along with other early tetrapods indicate that the most stable gait for early tetrapods, including Ventastega, would a lateral-sequence walk. The trackway patterns, including marks from the tetrapods dragging their tails and bellies on the ground, have both been subaerial and subaqueous, indicating that the origin of terrestrial locomotion originated in tetrapods, not in their fish ancestors. Ventastega likely had subaqueous locomotion, which can be inferred from its close relation to Acanthostega, which researchers hypothesized moved subaqueously. Paleoenvironment Paleogeologists estimate that the Famennian, the global average temperature was about 19.5 °C. CO2 levels in the atmosphere during the Famennian were approximately 0.3%, higher than present, while O2 levels were lower than present, making up only 16% of the atmosphere. Plants were undergoing rapid diversification during the middle and late Devonian, and beginning to occupy vast tracts of land instead of being restricted