New Caledonia and its Links to Gondwana

The Cagou - Quartl

Various plant and animal species on the main island of New Caledonia provide evidence that it was once a part of the supercontinent Gondwana.

Grand Terre, the main island of New Caledonia, is situated on the Australian tectonic plate, a crustal plate that is moving northwest at a speed of approximately 7.3 cm per year. It separated from Australia and Antarctica during the Cretaceous period, around 65 million years ago. Although subsequent subductive earth movements account for much of its igneous rock formations, Grande Terre’s older rock formations are from the Gondwana era.

The Absence of Mammals Showing a Link to Gondwana

Interestingly, although a wide range of New Caledonia’s flora displays links with Gondwana species, its fauna does not. The mammalian life present is limited to several species of bats that have colonised the island via the air. Some groups of vertebrates, including reptiles and birds, do, however, show a relationship (to the genera level) to those in New Zealand, while various invertebrates such as spiders and snails show affinities with Australian and New Guinean species.

This disparity may be explained by the apparent submersion of most of Grande Terre during the Eocene era. This, combined with the fact that the environmental conditions on an island are not suitable for the survival of animals that need large territories to search for food, may explain why mammals from Gondwana did not survive.

The Cagou – A Vertebrate With Connections to Gondwana

The Cagou (see above) is an example of a New Caledonian vertebrate species that does show links to Gondwana. This endangered bird is a member of the Rhynochetides family of flightless birds thought to have had their origin in New Zealand. The distribution of similar flightless birds (collectively known as ratites) on former Gondwana continents, is generally regarded as evidence for both the Plate Tectonics theory and Darwin’s theory of evolution by natural selection.

These birds, which also include the emu in Australia, the kiwi in New Zealand and the Ostrich in Africa, are thought to have evolved from a flightless ancestor that lived on the supercontinent before it broke apart. As with the plant species on former Gondwana continents, the ratites are believed to have then evolved in isolation, with their own unique environmental conditions acting as selecting agents.

Plant Species with Gondwana Origins in New Caledonia

Around 2400 of the 3000 plant species in New Caledonia are endemic. This is explained by the fact that after it separated from Gondwana new species evolved in isolation in a process biologists call ‘adaptive radiation’. Despite this, around 26% of New Caledonia’s flora shows affinities with Australian species.

Perhaps the most notable examples of this are members of the genus Araucaria, which can be found in Australia, New Caledonia, New Guinea and other former Gondwana continents. The Hoop Pine (Araucaria cunninghamii) is present in both Australia and New Caledonia (see figure 2), while similar Araucaria genera are endemic to New Caledonia. In fact thirteen out of the nineteen known species of Araucaria are found in New Caledonia, with the large stands of Araucaria columnaris on the Isle of Pines being among the most spectacular.

Other plant families in New Caledonia showing connections to former Gondwana continents include the Proteaceae (including Grevilleas, Persoonia and Stenocarpus species), the Myrtaceae and the Cunoniaceae. The Rhizophoraceae, a family of mangrove species, is also common to these continents, with the species Rhizophora apiculata (see figure 3) occurring in New Caledonia, Australia, India and New Guinea.

The Uniqueness of New Caledonian Flora and Fauna

Despite some of these relationships to former Gondwana species, the flora and fauna of New Caledonia is still among the most unique in the world. Besides having a large percentage of endemic species, New Caledonia also boasts the world’s largest bio-diversity of organisms per square kilometre.

This is partly a result of the wide range of micro-habitats present in the mountainous regions of the country, along with the rich soils formed from oceanic crust during the Eocene era. In addition, New Caledonia’s long period of geographic isolation has greatly contributed to the distinctiveness of its animal and plant life.

References

Croixdusud.info, ‘Biodiversity in New Caledonia: Land Animals and Flora’, croixdusud.info

Netbiome, 2011, ‘New Caledonia’, netbiome.org

Sum.org, 2006, ‘New Caledonia’, sum.org

Weston,P., 2006, ‘The origin of Species: The Australian Connection’, Australian Academy of Science,science.org.au