Giant Leatherback

The giant leatherback replaced its ancestor the snapjaw thornback. With so many other relatives around filling in other niches its ancestor finally became extinct. On niche that was not filled yet was the large herbivore niche. Due to island gigantism it has grown to about 5 times its ancestor's size. This not only deters predators, but helps it sustain gigantothermy. Its leathery skin is much like the leathery skin on a leatherback sea turtle (who also sustains gigantothermy). It has a thick layer of fat all over its body not only to help keep in the heat but also help it survive during the long dark winters. It is most active the summer where it can stay light all day due to how close Fermi is to the south pole. They're now strictly herbivores, herds gorge themselves on all the larger flora that thrive in the summer. In the winter they will huddle in large herds to help retain heat. They hardly move at all, except for allowing those on the outside to make their way to the inside. They are too large for most predators, however juveniles still can be picked off so they are kept near the center of the herd. They are ovoviviparous and now only lay a 2 to 3 eggs inside the female. The offspring hatch inside and are kept in a nursery pool organ inside the female until they have gone though their metamorphosis from fish-like larva to reptile-like juveniles. The pools produce food for the lava to eat. Juveniles are birthed as soon as the snow melts because they must gain weight fast. The short summer only gives them a small window to gain enough weight to survive the winter. Those that don't gain enough body fat die in the winter. They generally grow a meter each year and thus take 5 years to be fully grown. However they become sexually mature around 3 years. Their shoulder spikes now are much thinner and sit on a primitive tympanic membrane. This allows them to "hear" low frequency sounds. They are not completely deaf anymore. They can still make colors under their chin for communication, but its mostly used to attract mates. Their necks are more flexible than they look and can reach down to the ground without kneeling. They can also bend their necks upward to show their color patch.