Brachylophus
Encyclopedia
The genus
Brachylophus consists of three extant iguanid species
native to the islands of Fiji
and a giant extinct species from Tonga
in the South Pacific
. One of the extant species, B. fasciatus, is also present on Tonga, where it has apparently been introduced by man.
Brachylophus species are the most geographically isolated iguanas in the world. Their closest extant relatives (the genera Amblyrhynchus, Conolophus
, Ctenosaura
, Cyclura
, Iguana
and Sauromalus) are present in primarily tropical
regions of the Americas
and islands in the Galápagos
and Lesser
and Greater Antilles
. Several of these genera are adapted to xeric
biome
s. The location of members of Brachylophus, so distant from all other known extant or extinct iguanids, has long presented a biogeographical
puzzle.
These iguanas have been hypothesized to have evolved from New World iguanas that rafted
9000 km west across the Pacific Ocean
with the aid of the South Equatorial Current
. While a rafting voyage of four months or more might seem implausible, the ancestors of Brachylophus may have been preadapted for such a journey by having water requirements that can be satisfied by food alone, as well as comparatively long egg incubation periods.
An alternative hypothesis, based in part on an estimated divergence date of 50 million years ago, is that these species are the descendants of a more widespread but now extinct lineage of Old World
iguanids that migrated overland from the New World
to Asia or Australia, and then dispersed by some combination of continental drift, rafting and/or land bridges to their present remote location. However, no other fossil or extant species of this putative lineage have been found to date in Southeast Asia
, Australasia
or the western Pacific
outside of Fiji and Tonga.
The extant species are:
Brachylophus bulabula ('bula' is the Fijian
word for 'hello') was discovered in the central regions of Fiji by a team led by a scientist from the Australian National University
. Detailed genetic and morphological analyses were made to conclude that B. bulabula represents a third species.
A giant Tongan species, Brachylophus gibbonsi
, similar in size and build to an iguana of the genus Cyclura
once existed but became extinct in prehistoric times due to predation by humans and their domestic animals on Lifuka
and Tongatapu
.
An even larger extinct iguana of the separate genus Lapitiguana
was formerly present on Fiji.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Brachylophus consists of three extant iguanid species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
native to the islands of Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
and a giant extinct species from Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
in the South Pacific
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
. One of the extant species, B. fasciatus, is also present on Tonga, where it has apparently been introduced by man.
Etymology and taxonomy
The name, Brachylophus, is derived from two Greek words: brachys (βραχῦς) meaning "short" and lophos (λοφος) meaning "crest" or "plume", denoting the short spiny crests found along the backs of these species.Brachylophus species are the most geographically isolated iguanas in the world. Their closest extant relatives (the genera Amblyrhynchus, Conolophus
Conolophus
The Galápagos land iguanas comprise the genus Conolophus of the Galápagos Islands. The name Conolophus is derived from two Greek words: conos meaning "spiny" and lophos meaning "crest" or "plume", denoting the spiny crests along the backs of these species...
, Ctenosaura
Ctenosaura
Ctenosaura is a genus of lizard commonly known as spinytail iguanas. The genus is part of the large lizard family, Iguanidae and is native to Mexico and Central America. The species range in size from about 5 inches to well over one meter. The distinctive feature of this genus is presence of the...
, Cyclura
Cyclura
Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies...
, Iguana
Iguana
Iguana is a herbivorous genus of lizard native to tropical areas of Central America and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena...
and Sauromalus) are present in primarily tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
regions of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
and islands in the Galápagos
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
and Lesser
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
and Greater Antilles
Greater Antilles
The Greater Antilles are one of three island groups in the Caribbean. Comprising Cuba, Jamaica, Hispaniola , and Puerto Rico, the Greater Antilles constitute almost 90% of the land mass of the entire West Indies.-Greater Antilles in context :The islands of the Caribbean Sea, collectively known as...
. Several of these genera are adapted to xeric
Deserts and xeric shrublands
Deserts and xeric shrublands is a biome characterized by, relating to, or requiring only a small amount of moisture.-Definition and occurrence:...
biome
Biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
s. The location of members of Brachylophus, so distant from all other known extant or extinct iguanids, has long presented a biogeographical
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
puzzle.
These iguanas have been hypothesized to have evolved from New World iguanas that rafted
Rafting event
Oceanic dispersal is a type of biological dispersal that occurs when organisms transfer from one land mass to another by way of a sea crossing on large clumps of floating vegetation. Such matted clumps of vegetation are often seen floating down major rivers in the tropics and washing out to sea,...
9000 km west across the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
with the aid of the South Equatorial Current
South Equatorial Current
The South Equatorial Current is a significant Pacific, Atlantic, and Indian Ocean current that flows east-to-west between the equator and about 20 degrees south. In the Pacific and Atlantic Oceans, it extends across the equator to about 5 degrees north....
. While a rafting voyage of four months or more might seem implausible, the ancestors of Brachylophus may have been preadapted for such a journey by having water requirements that can be satisfied by food alone, as well as comparatively long egg incubation periods.
An alternative hypothesis, based in part on an estimated divergence date of 50 million years ago, is that these species are the descendants of a more widespread but now extinct lineage of Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
iguanids that migrated overland from the New World
New World
The New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...
to Asia or Australia, and then dispersed by some combination of continental drift, rafting and/or land bridges to their present remote location. However, no other fossil or extant species of this putative lineage have been found to date in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
or the western Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
outside of Fiji and Tonga.
The extant species are:
- Fiji banded iguana, Brachylophus fasciatus
- Fiji crested iguanaFiji Crested IguanaThe Fiji crested iguana is a critically endangered species of iguana native to some of the northwestern islands of the Fijiian archipelago, where it is found in dry forest.-Taxonomy and etymology:...
, Brachylophus vitiensis - Brachylophus bulabulaBrachylophus bulabulaBrachylophus bulabula is a species of iguanid lizard endemic to some of the larger central and northwestern islands of Fiji , where it occurs in Fijian wet forest. It was discovered by a team led by a scientist from the Australian National University in 2008...
Brachylophus bulabula ('bula' is the Fijian
Fijian language
Fijian is an Austronesian language of the Malayo-Polynesian family spoken in Fiji. It has 450,000 first-language speakers, which is less than half the population of Fiji, but another 200,000 speak it as a second language...
word for 'hello') was discovered in the central regions of Fiji by a team led by a scientist from the Australian National University
Australian National University
The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...
. Detailed genetic and morphological analyses were made to conclude that B. bulabula represents a third species.
A giant Tongan species, Brachylophus gibbonsi
Brachylophus gibbonsi
Brachylophus gibbonsi is an extinct species of large iguanid lizard from Tonga in the South Pacific Ocean. Its remains have been found associated with cultural sites on Lifuka, four other islands in the Haʻapai Group, and Tongatapu...
, similar in size and build to an iguana of the genus Cyclura
Cyclura
Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies...
once existed but became extinct in prehistoric times due to predation by humans and their domestic animals on Lifuka
Lifuka
Lifuka is an island in the Kingdom of Tonga. It is located within the Haapai Group in the centre of the country, to northeast of the national capital of Nukualofa...
and Tongatapu
Tongatapu
Tongatapu is the main island of the Kingdom of Tonga and the location of its capital Nukualofa. It is located in Tonga's southern island group, to which it gives its name, and is the country's most populous island, with approximately 71,260 residents , 70.5% of the national population...
.
An even larger extinct iguana of the separate genus Lapitiguana
Lapitiguana
Lapitiguana is an extinct genus of giant iguanid from Fiji. It probably went extinct following the human colonization of Fiji 3000 years ago....
was formerly present on Fiji.