The Origin and Migrations of Australasian Echinoderm Faunas Since the Mesozoic
[Read before the Wellington Branch, August 14,1952; received by Editor, September 10, 1952.]
The Generic Content of the Tertiary Echinoderm Faunas of Australasia.
The Origins of the Australasian Tertiary Echinoderm Faunas.
Tertiary Faunal Migration Routes to Australasia.
Faunal Migration Between New Zealand and South America.
Trans-Tasman Faunal Migration.
Summary and References.
Similarities in the Tertiary echinoderm faunas of New Zealand and Australia are such as to indicate a common origin from the northern Indo-Pacific. Southward migration probably has occurred along the Indo-Malayan archipelago, or its Tertiary equivalents; but northward movements of Australasian genera into the Indo-Pacific can be detected from the Miocene onward. In the late Tertiary a west to east trans-Tasman faunal migration can be detected. Such similarities as exist between the echinoderm faunas of New Zealand and South America are probably a result of faunal contributions from the former to the latter. Possible mechanisms enabling faunal migration of echinoderms are considered.
The aim of this paper is to examine the general character and the generic content of the echinoderm faunas of Australia and New Zealand since the close of the Mesozoic; and also to offer a tentative interpretation of the data so far as they bear upon the problem of the origins of the faunas, and their migration routes into, out of, and within the Australasian region. Finlay's trans-Tasman correlations of 1947 are employed. The New Zealand palaeontological evidence is mainly based on unpublished studies still in progress. I am indebted to Dr. J. Marwick, to the late Dr. J. M. Finlay and to Dr. C. A. Fleming, all of the Geological Survey of New Zealand, for age determinations of the New Zealand material. The Australian records are taken mainly from the literature, and as far as possible their age-determinations have been revised in accordance with Finlay's views. In this I have had the assistance of Dr. J. Marwick. The generic placing of some of the material from Australia differs from that assigned to it in the older literature, and is more in accord with current ideas. The reasons for the changes will be given in a later publication. I am indebted to the Director of the National Museum of Victoria for the opportunity to examine fossils, and to others who have sent Australian specimens.
1. The Generic Content of the Tertiary Echinoderm Faunas of Australasia
(a) Early Tertiary.
Our knowledge of the Australasian echinoid faunas of the Cretaceous and Eocene is very fragmentary. In New Zealand occurred the Cretaceous Micraster,
and the Senonian starfish Ophryaster is represented by a species which closely recalls those of the Danish and English Senonian. From Western Australia a Cretaceous cidarid is known, but its generic position is uncertain.
During the Eocene the holasterid echinoid Cardiaster was present in both Australia and New Zealand, though it had by then already become extinct at the close of the Cretaceous in all other areas, so far as we know. Nucleopygus (syn. Nucleolites), another Mesozoic genus, was established in Australasia; we know it with certainty from Australia, and it may well yet turn up in the New Zealand Eocene. Elsewhere it was in process of extinction. Its lineage was destined to follow a long history in Australia and-New Zealand, with Recent representatives in both areas (Apatopygus). In Australian Eocene sediments are also found Salenidia and Prenaster. In New Zealand are found Schizaster, Galeraster, Loveniidae of undetermined generic position (probably representing an undescribed genus), and some Echinometrid, possibly Heliocidaris. Brochopleurus, listed as an Oligocene immigrant below, has also been found in the Upper Eocene (Kaiatan) since this paper was set in type.
(b) Mid Tertiary.
Mesozoic holasterids continued to survive in New Zealand at the opening of the Oligocene, with Cardiaster and also Echinocorys, the latter genus not yet known earlier in New Zealand sediments. The two genera, however, do not seem to have survived into the mid-Oligocene. Another, and later, development of the holasterid stock is seen in Duncaniaster, which appears in the mid-Oligocene, and enters upon a prolonged history in the Australasian region.
Genera which first appear in the lower or middle Oligocene of New Zealand include a number of forms of large size. The assemblage includes the following, together with a few others not yet determined:-Histocidaris, Phyllacanthus, Stereocidaris, Goniocidaris, Eucidaris, Prionocidaris, Grammechinus, Brochopleurus (see Eocene), Echinocorys, Duncaniaster, Fibularia, Studeria, Echinolampas, Planilampas, Maretia, Lovenia, Pericosmus, Linthia, Brissopsis, Cyclaster, Eupatagus, Brissus. Also till such time as Nucleopygus is known with certainty from the New Zealand Eocene, it must be included here.
Contemporary Australian lower and middle Oligocene beds of marine origin are believed to be unrepresented stratigraphically. They may well have carried a similar faunal assemblage to those of New Zealand, since we find much the same kind of fauna in the Janjukian, which Finlay (1947) attributes to upper Oligocene plus lower Miocene. The Janjukian yields the following genera:-Phyllacanthus, Stereocidaris, Goniocidaris, Eucidaris (to which the unnamed club-shaped spines of Chapman and Cudmore (1934) must certainly be ascribed), Prionocidaris, Paradoxechinus, Brochopleurus, Duncaniaster, Fibularia, Studeria, Echinolampas, Plesiolampas, Australanthus, Cassidulus, Echinoneus, Maretia, Lovenia, Pericosmus, Linthia, Schizaster, Brissopsis, Cyclaster, Eupatagus, Scutellina, Sismondia, Conoclypus, Monostichia, Coelopleurus, Gualtieria and Hemiaster; as well as Nucleopygus which was earlier present.
New Zealand Miocene marine sediments are mainly of a non-calcareous and sandy facies, yielding little direct information on the echinoid faunas. We do know that Schizaster and Pericosmus persisted, the latter at least into the lower Miocene, the former till near the close of the period. It would seem probable that, where the environment was suitable, the Oligocene genera would have per-
sisted—in other words, the fauna would have resembled that known from the Australian Janjukian.
It will be seen that the two portions of the mid-Tertiary represented in Australia and New Zealand by echinoderm-bearing beds contain a similar assemblage of genera. The similarities, indeed, extend to the specific level, as in the case of Brochopleurus, which has similar or identical species on either side of the Tasman (Fell, 1949a), and Duncaniaster (unpublished evidence).
(c) Late Tertiary.
Profound changes in the Australasian echinoid faunas towards the close of the Miocene parallel those observed in the mollusca and other groups. These latter have been attributed to a cooling climate (Fleming, 1949), and the same conclusion might be drawn from the echinoid evidence. Thus, the disappearance of Schizaster, a supposedly warm-water genus, takes place in New Zealand at the close of the Tongaporutuan stage (Upper Miocene). The warm-water genus Phyllacanthus last occurs in New Zealand in the Kapitean stage (Uppermost Miocene).
Genera which disappeared from south-eastern Australia include Duncaniaster, Lovenia, Linthia, Hemiaster, Gualtieria, Coelopleurus, Brochopleurus, Paradoxechinus, Monostichia, Sismondia, Scutellina, Nucleopygus, Cassidulus, Australanthus, Studeria, Plesiolampas and Echinolampas.
The New Zealand pre-Pliocene extinctions removed the following genera from the fauna:-Schizaster, Duncaniaster, Lovenia, Linthia, Brochopleurus, Studeria, Planilampas, Echinolampas, Grammechinus, Fibularia, Maretia, Pericosmus, Eupatagus, and all the cidarids, except apparently Stereocidaris, and perhaps Goniocidaris.
The following Miocene genera of Australia are still represented in the Recent East Australian Fauna, though not known from the Pliocene; they may have survived in warmer waters of the northern or north-eastern coasts:-Prionocidaris, Eucidaris, Fibularia, Echinoneus, Maretia, Lovenia, Pericosmus, Schizaster, Brissopsis, Eupatagus; and also the Nucleopygus-Apatopygus lineage, known from the Recent of Western Australia.
These losses were partly balanced by an accretion of new genera of modern aspect. Clypeaster, Arachnoides, Peronella and probably also Pseudechinus appeared in the Australian Lower Pliocene, whilst in the corresponding sediments of New Zealand (Waitotaran and Nukumaruan) we first meet with Arachnoides, Pseudechinus, Echinocardium and Evechinus.
The Recent echinoderm faunas of the two regions need not be summarized here; see, for Australia, Clark (1946), and for New Zealand, Fell (1949b).
2. The Origins of the Australasian Tertiary Echinoid Faunas
In seeking the origins of the faunas we need to compare the foregoing data with the known geological and geographical ranges of the genera concerned. The comparison may be simplified by treating the genera common to New Zealand and Australia as one group, and those not shared in common as two subsidiary groups.
(a) Tertiary Genera Common to Australia and New Zealand.
Cardiaster and Nucleopygus entered Australasia in the Eocene. They had previously been abundant in the northern old world in the Cretaceous. Of the
genera which entered Australasia during the early and mid-Oligocene, Phyllacanthus and Cyclaster had already become established in northern India in the Eocene. Fibularia, Studeria, Pericosmus and Lovenia likewise occur in the Eocene of Egypt, though they do not occur in Australasia till the Oligocene. Echinolampas, another Oligocene immigrant to Australasia, had had a wide northern distribution in the Eocene, in India, Borneo, North Africa, and Europe. Pericosmus had also occurred in the Eocene of Persia, and reached India by the Oligocene at least, probably earlier. Linthia, Schizaster and Brissopsis had all had a widespread northern distribution during Cretaceous and Eocene times. The remaining Oligocene genera, Duncaniaster, Goniocidaris and Brochopleurus are not known earlier in the geological record; they probably originated within the Australasian region, and will be further considered below. Of late Tertiary and Recent immigrants to Australasia, Centrostephanus and Echinocardium had already appeared in Europe in the Miocene,Brissus in the Miocene of Java, Laganum in the Eocene of the Mediterranean. Holopneustes and Pseudechinus are perhaps Australasian derivatives of the Temnopleurid stock previously present in the Miocene. Clypeaster is probably an immigrant from the north-west Pacific, from an original Pliocene Californian stock. Arachnoides and Monostichia are Australasian.
(b) Tertiary Genera of New Zealand, Not Yet Known From Australia.
Galeraster and Echinocorys, in the New Zealand Eocene and Oligocene, are the last remnants of ancient northern stock. Grammechinus, in the lower Oligocene, seems to have been the first of its type-it reappears in the Miocene of India, and is known only from these two records. The genera Evechinus and Ogmocidaris are both restricted to the New Zealand submarine plateau, the former first appearing in the mid-Pliocene.
(c) Tertiary Genera of Australia, Not Yet Known from New Zealand.
Echinoneus, Sismondia, Conoclypus, Cassidulus, Prenaster and Plesiolampas all had Eocene representatives in India or Europe; they are not known from Australia earlier than the Janjukian, save for Prenaster, which occurs in an Aldingan (lower) sediment, attributed to the late Eocene. Coelopleurus occurred throughout the Oligocene in India; it is present in the Australian Janjukian.
From the foregoing we may conclude that the main source of the Australasian Tertiary echinoderm faunas has been the old world, and more particularly, the northern Indo-Pacific region. Genera which occur in India in the Cretaceous reached Australasia in the Eocene. Genera which occur in the Indian Eocene reached New Zealand by the early or mid-Oligocene; they may well have reached Australia at the same time, but the absence of earlier Oligocene beds from Australia precludes our recognizing these forms earlier than the Janjukian. This Old Indo-Pacific stock, as it might be termed, seems to have remained with but little change until the close of the Miocene. Then, with extinction of the old fauna, came a New Indo-Pacific stock, which, together with stock of Australasian origin, brought into being the late Tertiary and Recent faunas. We find the earliest members of this new stock in the Waitotaran and Nukumaruan stages of the New Zealand early and mid-Pliocene and in the Kalimnan (early Pliocene) of Australia.
Genera of Australasian Origin.
It would seem that the genera Brochopleurus, Goniocidaris, Gramechinus and Duncaniaster originated in or near Australasia during early or mid-Oligocene times. All except Duncaniaster had reached India by the Miocene, and Brochopleurus also spread to Egypt during the latter period. The Indian species of Brochopleurus resemble the Egyptian, and both differ in the same way from the Australasian forms, (especially as regards the specialized transverse epistroma of the ambulacra). The Australasian lineage includes extremely similar forms in the Waitakian-Duntroonian of New Zealand (lower to mid-Oligocene) on the one hand, and in the Janjukian of Australia on the other. Goniocidaris has left a trace of its northern passage in a Miocene Indonesian species. The main development of the genus occurred during the Tertiary in Australasia, and it is still well represented in the latter region at the present time, though there is also a Recent distribution are running northwards through Indonesia and Malaya as far as Japan. Duncaniaster, which is restricted to Australia and New Zealand, ranges from mid-Oligocene to mid-Miocene (Balcombian of Australia).
Arachnoides, a sand-dollar, is a genus of Australasian origin which arose at the end of the Miocene, apparently as a development of the Monostichia stock then present in Australasia. Monostichia itself, likewise an Australasian stock, is of unknown derivation. The main development of the Arachnoides group of species has been in Australia, with one early Pliocene species, and three Recent. It had already entered New Zealand by the early Pliocene (Waitotaran stage), and there is one Recent species. Arachnoides also spread northward into Java during the Pliocene, and apparently its northern extension has been proceeding actively since that time. Its north-western limit in Recent faunas is located at the Andaman Islands, whilst Samoa marks its north-eastern boundary. It has not spread elsewhere, and is absent from the sub-Antarctic portion of the New Zealand plateau.
3. Tertiary Migration Routes to Australasia
A Tertiary archipelago like the existing Indonesian-Malayan are, with its associated marginal shallows, and relatively narrow deeper-water gaps, would provide an adequate migration path for all the faunal movements inferred above. The movement of lineages must have been mainly southward but, as indicated, appreciable traces of northern migration out of Australasia seem discernible. This northward efflux seems to have occurred from the Miocene period onwards.
Southward migration has probably been fairly continuous since Eocene times. It appears that New Zealand had a relatively direct link with the Indo-Pacific during the greater part of the Tertiary. South-eastern Australia must have had a similar connection in the Eocene, and from Janjukian times onwards-perhaps also in the Oligocene, for which we lack evidence at present. So far as faunal movements are concerned, these links can be treated as one, and they may well have been mainly one and the same in fact. Just as we are justified in using the term “Australasian “to describe the echinoderm faunas (instead of distinguishing the two component portions), so also it would be justifiable to speak of an “Australasian” shallow-water link with the Indo-Pacific. It is desirable to make this point, since recently H. L. Clark (1946), without recourse to the fossil record, has maintained an entirely different derivation for the New Zealand echinoderm fauna from that of the Australian; his views are further considered in the next section of the present paper.
The Australasian shallow-water route to and from the northern Indo-Pacific may well have been interrupted by partial barriers, such as land, or deep-water gaps, during early and mid-Tertiary times, because it would seem that it could not be traversed rapidly in either direction by shallow-water, bottom-dwelling forms. Genera moving either northwards or southwards appear at the opposite extremity of the arc several geological stages later than the date of their first appearance in the geological record.
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.
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
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.
5. Trans Tasman Migration
The earlier and mid-Tertiary successions on either side of the Tasman Sea are insufficiently complete to make any deductions as to faunal migrations within Australasia. Certain features of the echinoid time-ranges have suggested to me that possibly the Janjukian includes a middle Oligocene horizon; but the evidence of forams and molluses apparently does not support this view. The presence of the large fossil penguin Palaeeudyptes in supposed Miocene sediments of Australia does, however, invite comparison with the lower Oligocene (Duntroonian) of New Zealand (a point to which Dr. C. A. Fleming kindly drew my attention). At all events, the echinoid succession on either side of the Tasman is not yet adequately correlated in regard to finer details at or near the specific level. The evidence from the late Tertiary is clearer and, I think, susceptible to inductive treatment.
Pliocene and Post-Pliocene trans-Tasman echinoderm migrations have occurred, and they have been essentially from east to west. So far as Recent species are concerned, the movement has been, more precisely stated, from eastern Australia towards northern New Zealand, particularly to that northern extension of the North Island coastline now usually referred to by Finlay's term Aupourian. Common Australian Recent echinoids, for example Centrostephanus rodgersii, Holopneustes inflatus and Heliocidaris tuberculata, occur in small numbers at various points in North Auckland, notably at Cavalli Island. Phyllacanthus parvispinus occurs at the Kermadec Islands. On the other hand, correspondingly common New Zealand echinoids are completely unknown from any Australian fauna. Evechinus, for example, the commonest and most widespread New Zealand echinoid, would seem to be admirably equipped to take advantage of any reverse east to west dispersal mechanism if it existed. It is eurytopic (ranging through eighteen degrees of latitude), it has a large pelagic larva, it has already succeeded in traversing the deep water gap between New Zealand and the Kermadec Islands, and it has been present in New Zealand at least since the lower Nukumaruan (early middle Pliocene). Yet it is known only from the New Zealand region.
Another argument in favour of deducing that any trans-Tasman migration must have been from west to east, and not the reverse, is provided by the high proportion of endemic Recent species of New Zealand echinoderms (some 80 per cent. of species). It is recognised that this is indicative of Tertiary isolation, especially of late Tertiary and Recent isolation. But the isolation implied is rather that of an outpost with a one-way traffic highway, along which new im-
migrants can occasionally travel from without, and along which few forms can return.
Before considering the probable generic content of the faunas which must have crossed the Tasman at successive stages since the Miocene, we may pause to discuss briefly the relative importance for echinoderm dispersal of ocean currents on the one hand, and former shallow ridges (such as the New Zealand Ridge, or Lord Howe Rise) on the other.
The East Australian current flows southward along the eastern coast of Australia to about latitude 40 degrees south, where it encounters the west wind drift. The junction results in a counter-clockwise swirl, which strikes towards New Zealand. According to Sverdrup, Johnson and Fleming (1942) the February surface isotherms along the 40 degrees parallel in the Tasman form east-west zones of water, the temperature of which is around 18 degrees Centigrade. Mortensen (1921) has provided some minimum figures for the life-span of the pelagic stage in some New Zealand and Australian echinoderms, from which it appears that a free-swimming larval stage of five or six weeks may well be common (for example, Evechinus larvae showed no sign of metamorphosis over the developmental period from December 18 to January 22; the pelagic stage of Heliocidaris tuberculata is over five weeks); the total pelagic life-span may well be longer. However, comparative embryology would lead one to deduce that the total pelagic life is not likely to exceed appreciably a tally of about eight weeks. On the evidence of Fleming (1952), this seems scarcely sufficient to enable a trans-Tasman crossing on the existing East Australian current of between four and a-half and nine miles per day (unless the pelagic stage were succeeded by an epiplanktonic phase on drifting algae, such as does occur in some starfish and ophiuroids). However, Fleming (1952) points out that it is possible that parts of the East Australian current may flow at speeds up to 30 miles per day, so that we cannot yet dismiss the possibility that genera like Heliocidaris may make the trans-Tasman crossing in the larval stage. Astropecten, with a larval period of a little over three weeks, could not; yet Astropecten polyacanthus seems undoubtedly to be a relatively recent immigrant to New Zealand from the Australian-Indo-Pacific area.
One cannot dismiss the possibility of migration along the present shallow-water ridge through the Lord Howe Rise during late Tertiary and Pleistocene lowerings of sea-level. In this connection the evidence from the sub-Antarctic is apposite. The present echinoderms faunas of Auckland and Campbell Islands have clearly been derived from New Zealand. These islands are linked with the New Zealand mainland by the shallow Campbell Plateau (Fleming and Brodie, 1951), which is nowhere deeper than 500 fathoms. Macquarie Island, in the same area, is separated from them by deep water of over 2,000 fathoms. Its echinoderm fauna is almost entirely Antarctic in character, and clearly has not been derived from New Zealand, though a single echinoid (Pseudechinus novaezelandiae) is shared; the latter has a pelagic development. This evidence seems to imply that a shallow route is more effective for echinoderm dispersal than is a much narrower, but deeper, gap—unless the gap is traversed by a favourable current. Thus, so far as the Tasman is concerned, I am inclined to attach some importance to the Lord Howe Rise as at least a former, if not a present, dispersal route.
Considering now the generic content of the faunas concerned in trans-Tasman immigration:—Arachnoides, as already noted, had entered New Zealand by early Pliocene (Waitotaran) times, and no doubt came from eastern Australia. A mid-Pliocene New Zealand species much resembles a species still' found in Recent Queensland waters. The Recent New Zealand species is distinct, but it too occurs in east Queensland seas. It may well be a second, later immigrant to New Zealand. Peronella, an Indo-Pacific genus, had reached Australia by the Pliocene, and it may well have spread to New Zealand at about the same time, for the one Recent New Zealand species is endemic. Australia has five Recent species, three of them endemic. Perhaps Ctenamphiura was a Pliocene immigrant—the genus is confined to north-east Australia and New Zealand, with an endemic species at either extremity of its range; its fossil history is unknown.
Of genera which probably crossed the Tasman Sea later on, in Pleistocene or Recent times, the following may be noted as having one (or more) identical Recent representatives on both the New Zealand and east Australian coasts:—Araeosoma, Holopneustes, Heliocidaris, Clypeaster, Laganum, Stichopus, Lipotrapeza, Mensamaria, Chiridota, Asterodiscus, Astrobrachion, Ophiocreas, Ophiactis; and perhaps a second instalment of Arachnoides.
Some Indo-Pacific forms also arrived at a late date, perhaps by way of the Lord Howe Rise—for example, Brissopsis, Brissus, Astropecten and Coscinasterias all have identical, or very similar species both within and beyond New Zealand waters.
Apatopygus and Goniocidaris probably owe their present distribution on either side of the Tasman, not to any trans-Tasman migration of the type that has been considered above, but to the fact that their Recent species are a heritage from the former mid-Tertiary common fauna of Australasia. The ancestors of these forms may have arrived along shallow-water routes no longer existing. They represent an archaic element shared by Australia and New Zealand. Apatopygus has one abundant, endemic species in New Zealand, and one rare southern Australian species. The differences between the New Zealand and the Australian species seem at least as great as those between either of them and their Tertiary ancestors in the Nucleopygus lineage. The lineage is a conservative one, showing but little change over its long history; and the name Apatopygus, which is applied to the two Recent species, does not really cover any generic difference from the fossil genus—as Mortensen has shown (1948).
The Australian and New Zealand Tertiary echinoderm faunas show marked similarities throughout those portions of the stratigraphical record represented by comparable deposits on either side of the Tasman Sea. They stem from a common origin in the northern Indo-Pacific.
The Indo-Malayan archipelago, or its Tertiary equivalents, could well have provided the shallow-water migration route, both into Australasia and from Australasia. The route may never have been a very easy one for echinoderms to traverse, as considerable time-delays seem to elapse between the first occurrence of a genus at one end of the arc, and its first appearance at the opposite extremity.
Migration of genera has been mainly southward. Nevertheless, northward movement of genera believed to have originated in Australasia, can be detected from the Miocene onward.
Trans-Tasman faunal migration is not, on present evidence, determinable for the early and mid-Tertiary faunas, but in the late Tertiary and Recent it has been from west to east—that is, from Australia to New Zealand.
A small archaic element common to the Recent faunas of Australia and New Zealand stems from a common mid-Tertiary fauna, and does not indicate later trans-Tasman movement.
Certain genera of New Zealand, or Australasian, origin have supplied contributions to the South American fauna, probably by means of the west to east circumpolar and west wind drifts. There is so far no evidence of South American elements in the Tertiary echinoderm faunas of Australasia.
The Recent echinoderm faunas of the Auckland, Campbell, Snares and Antipodes Islands, in the sub-Antarctic, have drawn their component genera and species from the New Zealand mainland fauna. These islands have a relatively shallow-water connection with New Zealand. The Recent echinoderm fauna of the nearby Macquarie Island, which stands in deep water, has been derived from the Antarctic, with the exception of one New Zealand echinoid. The latter has a pelagic larva.
It is concluded that shallow-water routes are of more importance in the dispersal of echinoderms than are relatively narrow deep-water gaps, unless the latter are traversed by a favourable ocean current. Trans-Tasman migration has probably made use of both former shallow-water routes and of planktonic dispersal of larvae in the East Australian current.
Chapman, C. and Cudmore, F. A., 1934. The Cainozoic Cidaridae of Australia. Mem Nat. Mus. Victoria, 8, p. 125.
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— 1949c. The Occurrence of Australian Echinoids in New Zealand Waters. Rec. Auckland Inst. Mus., 3, p. 343
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Finlay, H. J., 1947. The Forammferal Evidence for Tertiary Trans-Tasman Correlation. Trans. Roy. Soc. N.Z., 76 (3), p. 327.
Fleming, C. A., 1949. The Geological History of New Zealand. Tuatara, 2 (2), p. 72.
— 1951. Some Post-Miocene Changes in New Zealand Environments. New Zealand Science Review, 9, p. 166. (Including map by Brodie and Fleming.)
— 1952. Ecological Aspects of Palaeontological Study New Zealand Science Review, 10, p. 60.
Moore, L. B. and Cribb, A. B., 1952 Nature, 169, p. 1100.
Mortensen, Th., 1921. Studies of the Development and Larval Forms of Echinoderms (Copenhagen).
— 1925 Echinoderms of New Zealand and the Auckland-Campbell Islands. Parts 3-5. Vid Medd. Dansk Nat For., 79, p. 261.
— 1948. Monograph of the Echinoidea. 4 (1).
— 1951. Ibid., 5 (2).
Sverdrup, H. U., Johnson, M. W. and Fleming, R. H, 1942. The Oceans. Charts II and VII.