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Acanthostega ankyla (name meaning "fused spiny roof") is a species of primitive stem-tetrapod tetrapodomorph that originally lived in the late Devonian period (Famennian age) about 365 million years ago and was once extinct, but has since been brought back from extinction by SciiFii due to demands from many people for extinct aquatic animals as pets and aquarium animals. The genus Acanthostega is among the first vertebrate animals to have recognizable limbs and is anatomically intermediate between lobe-finned fishes and those that are fully capable of coming onto land. The 60 centimeter (24 inche) long Acanthostega ankyla has eight digits on each hand and feet linked by webbing, it lacks wrists, and is generally poorly adapted for walking on land. It also has a remarkably fish-like shoulder and forelimb. The front limbs of Acanthostega ankyla could not bend forward at the elbow, and therefore could not be brought into a weight bearing position, and are much more suitable for paddling and for holding on to aquatic plants. Acanthostega ankyla is the earliest known stem-tetrapod to show the shift in locomotory dominance from the pectoral girdle to the pelvic girdle. There are many morphological changes that allow the pelvic girdle of Acanthostega ankyla to become a weight-bearing structure. In more ancestral states the two sides of the girdle were not attached. In Acanthostega there is contact between the two sides and fusion of the girdle with the sacral rib of the vertebral column. These fusions make the pelvic region more powerful and equipped to counter the force of gravity when not supported by the buoyancy of an aquatic environment. It has internal gills that are covered like those of fish. It also has lungs so it could breath air in case the water quality or oxygen levels in the water become low, but its ribs are too short to support its chest cavity out of water. Acanthostega ankyla is a carnivore that primarily feeds on small fish, smaller amphibians, and many invertebrates. It is a solitary animal that lives in most of its entire life alone except during the breeding seasons. It is one of the most popular prehistoric aquarium animals, being about as popular as a goldfish due to being easy to keep, breed, and care for.