FNZ 9 - Protura (Insecta) - Zoogeography
Tuxen, SL 1986. Protura (Insecta). Fauna of New Zealand 9, 52 pages.
(
ISSN 0111-5383 (print),
;
no.
09.
ISBN 0-477-06765-4 (print),
).
Published 24 Feb 1986
ZooBank: http://zoobank.org/References/6B017956-58FF-4405-9795-98BA1D6FE682
Zoogeography
The zoogeographical considerations just mentioned (Tuxen 1978a) were based on the theory of continental drift in its more recent guise of plate tectonic theory. I took the distribution of Delamarentulus tristani (Silvestri) in northern South America and western Africa, but nowhere else, as a starting point and based my conclusions as to the distribution of Protura on three suppositions.
- That the Protura are of early Devonian origin. This is supported by the phylogenetic placement of Protura as a sister-group to Collembola, and Collembola (the genus Rhyniella) being known as Devonian fossils from the Old Red Sandstone of Scotland.
- That the evolution in time of the Protura has been a very slow process. This is corroborated by the distribution of D. tristani (and of Brasilentulus), since the parts of Brazil and West Africa where it is found were divided by the South Atlantic 100 million years ago and it is still the same species on both continents.
- That the distribution in space of the Protura has been a very slow process. This, too, is corroborated by the distribution of D. tristani, which from its presumed origins has spread only along the Gulf of Guinea in Africa and only to Pernambuco, Amazonas, and Colombia in South America (where it may have been elevated from lowland rainforest to 3500 m in the Andes during the uplift of these mountains in the last 15 million years). The means of dispersal of Protura are limited because these insects are very vulnerable to salt water and susceptible to desiccation.
The place of origin of the Protura is not known - probably in a moist and warm climate, since they are not known in arctic or antarctic countries. But that is not of decisive importance here; it is their presence in New Zealand that matters. My understanding of this I draw from the most inspiring and comprehensively illustrated book New Zealand Adrift, by Graerne Stevens (1980). The association and separation of landmasses used to explain present-day biogeography are based on the supposition of an expanding earth, as set out by Owen (1976, 1981), from a diameter in the early Jurassic of 80% of its present value. This theory has the drawback that nobody knows why the earth should expand, but it helps to understand some problems of distribution.
What is now New Zealand originated at the outskirts of Gondwana. Sediments from Australia and Victoria Land, Antarctica, founded the New Zealand Geosyncline, which collided along an earlier subduction zone with continental sediments from Marie Byrd Land, giving rise to the Rangitata Orogeny in the late Jurassic and early Cretaceous, 140 - 110 million years ago. New Zealand thus became a big land mass connected to other parts of Gondwana, and could receive plant and animal immigrants from these sources (Figure 1). It is supposed that mosses, kiwis, podocarps, and Nothofagus immigrated to New Zealand at this time, and Protura may have come the same way. The position of the subduction zone is still visible; it is characterised by ophiolites, as in the Dun Mountain Ophiolite Belt along the west coast of both main islands. Eighty million years ago, however, in the late Cretaceous, the Tasman Sea between New Zealand and Australia began opening up, isolating New Zealand from the rest of Gondwana. This continued for 20 million years. Fifty-five million years ago the Southern Ocean began opening up between Australia and Antarctica. At this time the South Atlantic had long been in existence, Africa had left Antarctica, and India had started its journey towards Laurasia. The Southern Ocean is still opening up, and New Zealand is placed at the boundary between the Indo-Australian tectonic plate and the Pacific plate. The visible expression of this transform fault is the Alpine Fault.
In Cenozoic time, i.e., for the last 65 million years, New Zealand has sometimes been partly under water, and at other times (e.g., during successive glaciations) has occupied a greater land mass than now. Never was it completely inundated, so survival possibilities for its fauna and flora must always have been present.
A biotic connection across Gondwana from South America via Africa (see Tuxen 1978a), Antarctica, and Australia to New Zealand was thus open at the end of the Jurassic and in the Cretaceous. Such a connection stopped at the beginning of the Tertiary, say 60 million years ago, after which time New Zealand's fauna took its own course insofar as it took any course. Now, how does this equate with the known distribution within and outside New Zealand of the proturan species known from this country?
If we leave out of consideration the unfortunately indefinable specimen of Australentulus (p. 34), fourteen species are here recognised from New Zealand. Of these, eight are new to science, but it is possible to draw conclusions from their systematic relationships. Besides the new species, one more species is endemic to New Zealand. The five species known also from outside New Zealand are:
- Eosentomon wygodzinskyi Bonet - known from the Seychelles, Pacific Islands, and Brazil. This is a fine Gondwana distribution.
- Proturentomon minimum (Berlese) - known only from Europe; must certainly be an introduced species. In New Zealand found only at Parkes' Farm (NN) on several occasions.
- Gracilentulus gracilis (Berlese) - decidedly a European species; probably introduced to the recorded localities in South Africa, Australia, amd New Zealand, though the single New Zealand record is from Little Barrier Island, habitat unknown.
- Kenyentulus kenyanus (Condé) - known from Kenya, the Seychelles, southern India, Brazil, Puerto Rico, and Bermuda. A decidedly Gondwana distribution, with migration to the Caribbean Islands.
- Berberentulus nelsoni Tuxen - southern Brazil; in New Zealand, the Kermadec Islands and Pigeon Valley (NN). Decidedly Gondwana. Exactly the same distribution pattern is shown by Acerentulus kermadecensis Ramsay & Tuxen, which has clear affinities with the Argentinian species A. nemoralis Najt & Vidal.
Leaving apart the two probably introduced species, a Gondwana character is evident in the distribution of all the species known outside New Zealand. Now for the affinities of the endemic species:
- Eosentomon dawsoni Conde and E. zelandicum n.sp. - closely related to E. australicum Womersley, which is known from Australia and, fairly commonly, from North America (Michigan; E. C. Bernard).
- Eosentomon macronyx n.sp., E. maximum n.sp., E. gracile n.sp. - no close relationship can be established.
- Yinentulus paedocephalus n.sp. - no clear relationship.
- Amphientulus zelandicus n.sp. and Tasmanentulus intermedius n.sp. - distinct relationships to Gondwana species, Tasmanentulus embracing two other species from Australia and Amphientulus six from Australia (one of them recently found in the Andes; Tuxen 1984), a doubtful one from North Korea, and one from Madagascar.
Thus, if we disregard the two species probably introduced by man, the New Zealand fauna of Protura is distinctly Gondwana in character with connections to the Pacific islands (Solomon Islands, Vanuatu), Australia, southern India, the Seychelles, Madagascar, East Africa, and South America. This means that the species have arrived at the present New Zealand before the opening of the Tasman Sea 80 million years ago, and in all probability in the late Jurassic after the Rangitata Orogeny, when the present New Zealand formed part of a greater land mass connected to the rest of Gondwana.
As to distribution within New Zealand, the records of most species are too scattered to allow of any conclusions. Only two species are sufficiently common to give hints, viz Amphientulus zelandicus and Tasmanentulus intermedius. Both are known from many localities (see Material Examined, pp. 37 and 40), but whereas Amphientulus is found both on the North Island and the northern South Island, Tasmanentulus is found only on the South Island, but widely scattered. The two genera are very closely related, and in a few localities have been found together. It might be tempting to suppose the immigration of both species via the South Island, with Amphientulus the earliest. Certainly a connection between present distributions and the changing inundation of the islands is more difficult to envisage.