some 15 million years at the start of the Carboniferous, called "Romer's gap". The gap marks the disappearance of the ichthyostegalian forms as well as the origin of the higher labyrinthodonts. Finds from this period found in East Kirkton Quarry includes the peculiar, probably secondarily aquatic Crassigyrinus, which may represent the sister group to later labyrinthodont groups. Early Carboniferous saw the radiation of the family Loxommatidae, a distinct if mysterious group that may have been the ancestors or sister taxon of the higher groups, characterized by keyhole-shaped eye openings. By the Visean age of mid-Carboniferous times the labyrinthodonts had radiated into at least three main branches. Recognizable groups are representative of the temnospondyls, lepospondyls and reptile-like amphibians, the latter which were the relatives and ancestors of the Amniota. While most labyrinthodonts remained aquatic or semi-aquatic, some of the reptile-like amphibians adapted to explore the terrestrial ecological niches as small or medium-sized predators. They evolved increasingly terrestrial adaptions during the Carboniferous, including stronger vertebrae and slender limbs, and a deeper skull with laterally placed eyes. They probably had watertight skin, possibly covered with a horny epidermis overlaying small bony nodules, forming scutes, similar to those found in modern caecilians. To the modern eye, these animals would appear like heavyset, lizards betraying their amphibious nature only by their lack of claws and by spawning aquatic eggs. In the middle or late Carboniferous, smaller forms gave rise to the first reptiles. In the late Carboniferous, a global rainforest collapse favoured the more terrestrially adapted reptiles, while the many of their amphibian relatives failed to reestablish. Some reptile-like amphibians did flourish in the new seasonal environment. The reptiliomorph family Diadectidae evolved herbivory, becoming the largest terrestrial animals of the day with barrel-shaped, heavy bodies. There were also a family of correspondingly large carnivores, the Limnoscelidae, that flourished briefly in the late Carboniferous. Heyday of the labyrinthodonts The herbivorous Diadectidae reached their maximum diversity in the late Carboniferous/early Permian, and then quickly declined, their role taken over by early reptilian herbivores like Pareiasaurs and Edaphosaurs. Unlike the reptile-like amphibians, the Temnospondyli remained mostly denizens of rivers and swampland, feeding on fish and perhaps other labyrinthodonts. They underwent a major diversification in the wake of the Carboniferous rainforest collapse and they too subsequently reached their greatest diversity in the late Carboniferous and early Permian, thriving in the rivers and brackish coal forests in continental shallow basins