The Bucerotidae include about 55 living species, though a number of cryptic species may yet be split, as has been suggested for the red-billed hornbill. Their distribution includes Sub-Saharan Africa and the Indian Subcontinent to the Philippines and the Solomon Islands, but no genus is found in both Africa and Asia. Most are arboreal birds, but the large ground hornbills (Bucorvus), as their name implies, are terrestrial birds of open savanna. Of the 24 species found in Africa, 13 are birds of the more open woodlands and savanna, and some occur even in highly arid environments; the remaining species are found in dense forests. This contrasts with Asia, where a single species occurs in open savanna and the remainder are forest species.[2] The Indian subcontinent has 10 species of hornbills, of which 9 are found in India and adjoining countries, while the Sri Lanka grey hornbill is restricted to the island. The most common widespread species in the Indian subcontinent is the Indian grey hornbill. According to the International Union for Conservation of Nature (IUCN), Indonesia has 13 hornbill species: 9 of them exist in Sumatra, and the rest exist in Sumba, Sulawesi, Papua and Kalimantan. Kalimantan has the same hornbill species as Sumatra, except that the great hornbill is not found there.[7] In the Neogene (at least in the late Miocene), hornbills inhabited North Africa and South Europe. Their remains have been found in Morocco[8] and Bulgaria.[9]