Fossil Profile: Antiktaalik

One of the first vertebrate fossils found within Dome 4 was that of an exceptionally preserved limb. Its arthropodal segmentation, along with what seemed to be rudimentary pseudodigits, suggested that it likely belonged to an ancestral form of the terrestrial placoderms that roam the habitat to this day. Dating to around the early Famennian, just 10 million years after the sampling of the station, it very possibly played a pivotal role in the antiarch invasion of land.

Following digs revealed numerous other equally well-preserved specimens, including even what seemed to be trace fossils. Using information from paratypes, modern descendants, and the other organisms that shared the strata with this leg, researchers were able to gain a fairly good understanding of this bizarre fish. Despite the portmanteau common name, antiktaalik, being far more widespread in use, this creature was still given a relatively conservative binomial name, Latapteron sirena, roughly translating to ‘wide-finned siren’.

Even from just the limbs, it is quite evident that antiktaalik was semi-terrestrial. Additional fossils displaying their eyes having migrated towards the top of their cephalon supported this hypothesis. Exploiting the new niches within swampy forests created by the paradisically controlled conditions in Dome 4, antiktaalik likely descended from herbivorous populations of Bothriolepids, which began adapting to a grazing lifestyle on and around shore-sides. This is supported by the intestinal contents of the 3rd discovered paratype, which included partially digested remnants of horsetails and Zosterophylls. Just like the Tetrapodamorphs on Earth, these terrestrial adaptations could have also granted them protection from the sarcopterygian predators that prowled the waterways.

Counterintuitively, antiktaalik is not the Antiarch equivilent of Tiktaalik, but would be more accurately compared to more advanced Tetrapods such as Ichthyostega. In life, antiktaalik was likely an awkward swimmer, with its bulky pectoral fins creating intense drag. Nevertheless, it made up for this with its greater terrestrial capabilities. Antiktaalik most likely crawled in a bichir-like manner, with its tail dragging behind. Tests on contemporary relatives with a similar body-plan find this to be a surprisingly swift method of locomotion, able to outpace giant chilopod predators it shared the early jungles with.

Unlike the Tetrapodamorphs on Earth, antiktaalik was a generalistic herbivore. Evolutionarily speaking, this route to land is significantly different from the one we took. With most early Tetrapods being at least partially piscivorous, the terrestrial food webs of the late Devonian to late Carboniferous were still very much linked to the water. Antiktaalik and its descendants, on the other hand, had no need to anchor itself to such bodies; their food sources were literally everywhere around them. Combined with their inheritance of placoderm viviparity, this accelerated the pull towards a greater degree of terrestriality. Forms comparable to the Permian Edaphosaurs would appear on the fossil record as early as the Carboniferous. Spared from the catastrophic Kellwasser-event in its extraterrestrial home, the descendants of antiktaalik evidently diversified into every niche under the sun.