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4. Migration Between New Zealand and South America
If there are any South American or Falkland elements in the Tertiary echinoderm faunas of Australasia, they cannot as yet be recognised. Characteristic central and southern American Tertiary genera such as Oligopygus, and the family Scutellidae, have no Tertiary or Recent representatives in either New Zealand or Australia. Genera which spread from the old world down through the Americas, such as Micropsis, Psammechinus, Lutetiaster and Agassizea, have not reached Australasia at any stage, so far as we know. The Antarctic genus Abatus is absent. Characteristic genera of Australia and New Zealand are not shared with South America, or at most, have a single Tertiary representative * in South America. The genera which are common to Australasia and to South America are likewise shared with the old world. There are more genera shared with the old world than with South America.
However, a small but perhaps significant South American relationship can be detected in the Recent echinoderm fauna of New Zealand. It is most marked in the southern half of the New Zealand plateau, especially in the sub-Antarctic Islands which stand on the Campbell Plateau, or on the somewhat deeper eastern extension of that plateau. Here are found four genera which have South American representatives, and three of them are without representation in Australia; there are, in addition, a few species of cosmopolitan genera (Amphiura magellanica, Cucumaria calcarea, Gorgonocephalus chilensis) which are shared by South America and New Zealand.
H. L. Clark (1946), apparently impressed by these facts (though he does not specify the grounds for his opinion in other than general terms), contended that the New Zealand Recent echinoderm fauna is of southern origin, whereas that of Australia he holds to be of Indo-Pacific derivation. His views were based only on Recent faunas. The presence of some Australian echinoderms in New Zealand was explained by Clark as resulting from the trans-Tasman drift of dead tests, in sea-weed. Proof that living specimens of these species do in fact inhabit northern New Zealand has since been furnished (Fell, 1949c). Mortensen (1925, 1951) strongly opposes the views of Clark. He deduces, again on the basis of Recent faunas, a common Indo-Pacific derivation for the echinoderm faunas of both New Zealand and Australia. His conclusions are concordant with the fossil record as analysed in this paper.
What, then, is the significance of the element in the Recent New Zealand echinoderm fauna which suggests some South American connection? The following interpretation is offered as an attempt to reconcile the Tertiary and Recent evidence. New data on the Recent sub-Antarctic faunas have become available
[Footnote] * Namely, the problematic “Echinus” andinus Philippi.
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as a result of the New Zealand Cape Expedition of 1941-45, and subsequent expeditions; these have added to our knowledge of the echinoderms of the Snares, Auckland Islands, Campbell Island and Antipodes Island (Fell, 1953). Supplementary data are also supplied by the collections at Macquarie Island and Heard Island, material which is now coming to hand, from the Australian Antarctic Research Expedition.
First, Amphiura magellanica, like the other species mentioned with it above, is to be regarded as circumpolar. It was collected on two occasions from Macrocystis holdfasts by W. H. Dawbin at the Auckland Islands. The tougher portions of the large southern brown algae can drift for long distances in the circumpolar west to east currents, or before the west wind drift. A recent observation of drifted Durvillea in Australian waters is relevant (Moore and Cribb, 1952); the nearest known source to the west is Kerguelen Island, 5,000 miles distant.
Secondly, we have to account for the presence in New Zealand and South America of representatives of the genera Pseudechinus, Calvasterias, Asterodon and Stichaster.
The majority of the Recent species of Pseudechinus are Australasian, and about half of the total number are restricted to New Zealand. The remainder are scattered around the sub-Antarctic Islands, with no more than a single species (usually endemic) at each point; one of these, P. magellanicus occurs in Patagonia. The genus has been well represented in Australasia at least since mid-Pliocene times. A supposed South American Miocene species is inadmissible on present evidence, and certainly cannot be used as proof of the earlier origin of the genus in South America. On the other hand, all the evidence points to Australasia as the original (and present) home of the genus. The other species are therefore odd derivatives, or “escapes” from the Australasian parent stock.
All the New Zealand species of Calvasterias, Asterodon and Stichaster are endemic; some are restricted to the sub-Antarctic Islands standing on the Campbell Plateau, which runs south from New Zealand. Like Pseudechinus, Asterodon is more highly speciated in New Zealand than in South America. There is one New Zealand species of this genus which is so distinctive that it has been considered as a distinct genus (Diplodontias) by earlier workers. These facts suggest that Asterodon can hardly have been a recent immigrant to the New Zealand area (where its species do not exhibit mere geographic speciation to any marked extent)—but Asterodon might well have been a relatively late immigrant to South America. The endemism exhibited by Calvasterias and Stichaster likewise argues against a recent derivation from South America. Further, it might be noted that each genus includes in New Zealand at least one eurytopic species. This feature, as has been pointed out elsewhere (Fell, 1949b) characterizes some of the most typical of New Zealand echinoderms; forms like Evechinus for example, so morphologically separated from exotic types, are widely ranging within the New Zealand area, though absent elsewhere—so that morphology and distribution both point to a relatively early differentiation within the New Zealand area. We can conclude that New Zealand is probably the older home of these genera, whilst South America is more likely to have been a later recipient of occasional offshoots from the New Zealand stock. Mortensen (1925) recorded an observation of drifting algae carrying Calvasterias during his visit to the Auckland and Campbell Islands. Epiplanktonic material
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of this type might well drift before the west to east circumpolar currents, or the west wind drift, to reach the Magellanic area, or even to be carried north on the Humboldt Current to the coasts of southern Peru. Climatic factors would prevent any great spread to the warmer waters (of the surface) to the north.
The whole echinoderm fauna of the New Zealand sub-Antarctic Islands has a close affinity with that of the mainland area. It can hardly be doubted that this southern New Zealand fauna shares a common origin with that of New Zealand proper, and that it reached its present situation by way of the New Zealand submarine plateau. It is unlikely that it came from South America; it is quite likely that it supplied contributions to the southern South American fauna.