when did amphibians begin to colonize land as the first terrestrial vertebrates
Vertebrate land invasion The aquatic to terrestrial transition of vertebrate organisms occurred in the late Devonian era and was an important step in the evolutionary history of modern land vertebrates. The transition allowed animals to escape competitive pressure from the water and explore niche opportunities on land. Fossils from this period have allowed scientists to identify some of the species that existed during this transition, such as Tiktaalik[1] and Acanthostega.[2] Many of these species were also the first to develop adaptations suited to terrestrial over aquatic life, such as neck mobility and hindlimb locomotion.
Cane toads in Australia The cane toads bred immediately in captivity, and by August 1935 more than 102 young toads were released in areas around Cairns, Gordonvale and Innisfail in northern Queensland. More toads were released around Ingham, Ayr, Mackay and Bundaberg. Releases were temporarily limited because of environmental concerns but resumed in other areas after September 1936. Since their release, toads have rapidly multiplied in population and now number over 200 million and have been known to spread diseases affecting local biodiversity.[6] Unfortunately, the introduction of the toads has not only caused large environmental detriment, but there is no evidence that they have affected the cane beetles they were introduced to predate. The toads have steadily expanded their range through Queensland, reaching the border with New South Wales in 1978 and the Northern Territory in 1984. The toads on the western frontier of their advance have evolved larger legs;[7] this is thought to be related to their ability to travel farther. As a consequence of their longer legs, larger bodies, and faster movement, about 10% of the leading edge cane toads have also developed arthritis.[8] It was estimated that cane toads migrate at an average of 40 kilometres (25 miles) per year as of 1994,[9] but new research in 2014 indicated that the migration rate had increased to 60 km per year on the western front.[10]