Many species were characterised by elaborate head crests. Herbivore An animal that feeds only on plants, and is specially adapted to be able to extract nutrition from tough foliage. Herrerasaurus Herrerasaurus was a late Triassic archosaur from about 230 million years ago. This was one of the first flesh-eating dinosaurs and is known from several skeletons found in Argentina. The holotype of a species is the first specimen to be given the name.
Holotypes are reference specimens kept in museums as a guarantee of the definition of a species.
Horseshoe Crab A horseshoe crabs are not actually crabs they are primitive arthropods. Their ancestry can be traced back to the Cambrian period, but in wasn't until the Jurassic period that the true horse-shoe shape developed. By the Late Cretaceous period, they were less common although five species of horseshoe crab still exist today. Horsetail A group of plants that originated in the Devonian period and were particularly successful in the Carboniferous period when some species grew up to 30 metres tall. Horsetails are regular symmetrical plants with jointed stems and circles of leaves.