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Australian Tertiary schizasteridechinoidsK.J. McNamara a & G.M. Philip ba Western Australian Museum, Francis Street, Perth, WesternAustralia, 6000b Department of Geology and Geophysics, The University ofSydney, New South Wales, Australia, 2006Version of record first published: 27 Nov 2008.

To cite this article: K.J. McNamara & G.M. Philip (1980): Australian Tertiary schizasteridechinoids, Alcheringa: An Australasian Journal of Palaeontology, 4:1, 47-65

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ALCHERINGA TERTIARY ECHINOIDS 47

Australian Tertiary schizasterid echinoids K. J. McNAMARA A N D G. M. P H I L I P

MCNAMARA, K. J. & PHILIP, G. M., 1980:3:25. Australian Tertiary schizasterid echinoids. Atcheringa 4, 47-65. ISSN 0311-5518. The taxonomy of schizasterid spatangoids is discussed and the term is restricted to

include only Schizaster-like echinoids. Within the genus Schizaster Agassiz the following morphological subgenera are recognized: Paraster Pomel, Dipneustes Arnaud and Ova Gray. Seven species are described from Palaeocene to Miocene rocks of Australia. New species are S. (Paraster) carinatus, S. (Paraster) tatei, S. (Schizaster) halli and S. (Dip- neustes)fosteri. Schizaster and its various morphotypes are thought to have evolved from a Linthia-like root stock through progressive morphological changes in test shape, form of ambulacra and adoral test morphology. Such changes are interpreted as being adaptations which allowed the sea urchins to occupy various levels of substrate in different sediment types. Morphotypes appear to have evolved iteratively, perhaps due to variation in the onset of sexual maturity. K. J. McNamara, Western Australian Museum, Francis Street, Perth, Western Australia, 6000; G. M. Philip, Department of Geology and Geophysics, The University of Sydney, New South Wales, Australia, 2006; received 17April 1979.

THIS article on Tertiary schizasterid c ipa l lybyF , and R. J. Foster, has provided a echinoids is our first contribution to the tax- diverse, albeit numerically small, onomy of the abundant fossil Australian schizasterid fauna of seven species which spatangoids. At the outset we emphasize that range in age from Palaeocene to Middle the term 'schizasterid' is used here to include Miocene. Four principal horizons in the Schizaster-like heart urchins. Specifically, Tertiary rocks of Australia yield these heart genera such as Linthia, Prenaster and urchins: the Palaeocene of Western Protenaster, whicil are usually placed in the Australia; the Late Eocene of South Family Schizasteridae (Mortensen, 1951; Australia; the Late Oligocene (Janjukian) of Fisher, 1966; Henderson, 1975)are excluded Victoria; and various restricted lithologies f rom consideration. The reasons for this are occurring in the Early and Middle Miocene explained in the section below on taxonomy. (Longfordian to Bairnsdalian) of South

More than 200 species have been assigned Australia, Tasmania and Victoria. to the genus Schizaster (Lambert & Thi6ry, In Australian seas, at the present time, 1925; Kier & Lawson, 1978)and acceptable Schizaster occurs north of 34°S on the taxonomic groupings of these species have eastern coast, but has not been found south not yet been defined (Mortensen, 1951; of 21°S on the west (McNamara & Philip, in Henderson, 1975). In description of the press). Its distribution in the Indo-Pacific Australian species we recognize a number of region, the Caribbean and Mediterranean morphological subgenera, for which pre- shows it to be restricted to essentially warm viously proposed names are available. We waters. Indeed, Henderson (1975, p. 65), believe that these categories are of value, not noting the present-day distribution of only in providing useful collocations of Schizaster, believed its presence in the fossil species, but also in depicting the evolution of record indicative of similar sea temperatures the group. Unfortunately many older in the past. The occurrence of Schizaster in descriptions of fossil species are based on the Tertiary rocks of southern Australia single, imperfect specimens, which are suggests that, up until the mid-Miocene at poorly or even inaccurately illustrated least, waters warmer than now existed of f (Moore, 1966, p. 272). For this reason we southern Australia. have not at tempted a comprehensive assign- On the basis of the occurrence of mar- ment of extra-Australian species to the sub- supiate echinoids, Foster (1974) has genera recognized here. suggested that at the close of the Eocene,

To date the only schizasterid echinoids breaching of the Andean-Antarctic described from the Tertiary rocks of mountain barrier allowed cold currents to Australia are Schizaster abductus Tate enter the Australian region. In South (1891) and S. sphenoides Hall (1907). Both Australia the early Late Eocene Tortachilla are f rom the Miocene of southern Australia. Limestone and Blanche Point Marls predate Extensive collecting in recent years, prin- this change; they contain schizasterid but not

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48 K.J. McNAMARA AND G. M. PHILIP ALCHERINGA

marsupiate echinoids. The overlying Port Willunga Beds, of late Late Eocene to mid- Oligocene age, however, contain marsupiate echinoids (Philip & Foster, 1971), but schiz- asterids are absent. The return of schiz- asterid echinoids, firstly into the Late Oligocene (Janjukian) of Victoria, then more commonly in the Early and Middle Miocene, along with progressive disappear- ance of the marsupiate forms, indicates the return of much warmer water conditions.

Most of the material studied has suffered post-depositional compaction and frac- turing. Consequently it was not possible to carry out useful numerical analyses. Registered specimens in the Tate Collection are now housed in the South Australian Museum (SAM) but retain their original Adelaide University Department of Geology numbers. Other specimens are housed in the Palaeontological Collection, Bureau of Mineral Resources, Canberra, (CPC); and the National Museum of Victoria (NMV).

Taxonomy of spatangoid echinoids The currently accepted classification of spatangoids is based largely on the character of fascioles and, to a lesser extent, the nature of the apical system (Mortensen, 1951; Fisher, 1966; Henderson, 1975). Distinctions based on fascioles allow Henderson's (1975, p. 9) conclusion that 'Many genera of spatangoids are strongly homeomorphic in test shape, even when they have evolved in entirely different lineages and separated by considerable taxonomic difference'.

Yet detailed studies have shown that fascioles are not an infallible guide to spatangoid affinities. Nichols (1959, p. 80), in his study of the British Cretaceous Micraster lineage, concluded 'that large and conspicuous features of the test, such as the sub-anal fasciole, do not necessarily make useful taxonomic criteria, because they may appear and disappear in closely-related forms'.

Beside lacking persistence in an evolu- tionary sense of characters emphasized in the present classification, spatangoids show other morphological changes and trends. For example, Palaeocene and some Eocene species of the genera Linthia and Schizaster (and its subgenera) have double pores in phyllodes, whereas younger species have

pores that are single. This has already been recognized as a broad evolutionary change in spatangoids, although there are some ex- ceptions (Kier, 1974, p. 27-29). This almost isochronous change in unrelated lineages appears to be due to the development of pen- ciliate tube feet surrounding the peristome which, by analogy with living spatangoids, would be adapted to grasping food particles and passing them to the mouth. Such tube feet would be no longer used for respiration, and so do not need separation of incurrent and excurrent channels (Kier, 1974). To date this obvious change has not been reflected at all in the taxonomy of spatangoids. No doubt, had the group been analysed by modern biostratigraphic palaeontologists then this quite obvious and remarkable change would already have been reflected in generic taxonomy.

A contrasting type of evolutionary change in schizasterids is the progressive modifi- cation of test morphology related, as we believe, to changes in ecological setting. Such progressive change in Schizaster is reflected in the morphological subgenera recognized below.

The generally unsatisfactory nature of the existing familial classification of spatangoids is well illustrated by the Family Schiz- asteridae, as used by Mortensen (1951) and later authors. According to Mortensen, representatives of the Family Schizasteridae are characterized by the possession of both peripetalous and lateroanal fascioles. But, among genera included in the family, we find that in Proraster the lateroanal fasciole may be incomplete or absent. The genus A batus possesses a lateroanal fasciole in the juvenile stage, but this is lost in adults. Amphineustes lacks both peripetalous and lateroanal fascioles, yet is also included with Mortensen's and Fischer's Schizasteridae. In Brisaster the lateroanal fasciole may be reduced or lost in the adult (Mortensen, 1951, p. 280). Both Tripylus and Parabrissus possess an incomplete lateroanal fasciole; in Parabrissus the lateroanal fasciole is 'not observed' (Mortensen, 1951, p. 348). The Tertiary New Zealand genus Kina, placed by Henderson (1975) in the Family Schiz- asteridae, lacks a lateroanal fasciole.

Within the Schizasteridae, however, there is a group of genera which share the gross test features of Schizaster, viz. an apical surface with a posteriorly located apical system and with the apex of the test posterior

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ALCHERINGA TERTIARY ECHINOIDS 49

to this, a long, usually incised, poriferous ambulacrum III, and sunken petals, the posterior pair of which are markedly shorter than the anterior ones. We would include in this group the genus Schizaster Agissiz 1838 and recognize as its morphological sub- genera Dipneustes Arnaud 1891, Paraster Pomel 1869 and Ova Gray 1825 (= Diplo- poraster Mortensen 1951). Other genera are Brisaster Gray 1855, Kina Henderson 1975, Moira Agassiz 1872 (= Moiropsis Agassiz 1881), and Proraster Lambert 1895 (= Hypselaster Clarke 1917).

We suggest that this group of genera should be recognized as a separate spatangoid subfamily or family. Formal proposal of a category is deferred until the relationships of other genera previously placed in the Family Schizasteridae are better understood.

Systematic Palaeontology Family SCHIZASTERIDAE Lambert 1905

SCHIZASTER Agassiz 1836

Type Species. Schizaster studeri Agassiz 1836, p. 185; by subsequent designation of the Thirteenth International Congress of Zoology in Paris; opinion 209, 1948 (Bull. Zool. Nomenclature London 4, p. 527).

Emended Diagnosis. Test small to large with ambulacrum III and anterior notch shallow to deep. Apical system located posterior of centre, with 2-4 genital pores. Ambulacrum III shallow to deep with pore pairs oblique or transverse and arranged in single or irregular, double rows. Anterior petals long and almost straight although at times distally flexed; at least twice the length of the posterior petals. Both peripetalous and lateroanal fascioles present and complete.

Remarks. Mortensen (1951, p. 216)used the number of genital pores as a generic character in the Schizasteridae. He dis- tinguished Paraster from Schizaster as it possessed, he believed, four genital pores in contrast to Schizaster with only two. Lambert & Thi~ry (1925) did not consider the number of genital pores to be of generic significance. Likewise Duncan & Sladen (1882), Currie (1925) and Cooke (1942) have considered this feature only to be of value in separating species. Kier (1957) and Henderson (1975) regarded Paraster as distinct in possessing four genital pores, but

regarded it as a subgenus of Schizaster. Chesher (1966, 1972) and more recently Kier (1975) have interpreted forms with four genital pores as generically distinct f rom those with two.

The number of genital pores possessed by the type species of Schizaster, S. studeri, is not known with certainty. Cotteau (1886, p. 36) believed it to have four although Mortensen (1951, p. 287) thought it had two. Henderson (1975, p. 14) believed that S. studeri 'will probably prove to have four gonopores ' but accepted the concept of Sch&aster as applied to species with only two.

We show elsewhere (McNamara & Philip, in press) that in some species of Schizaster the number of genital pores may vary between two and four within a single population. This suggests that the number of genital pores is of little taxonomic sig- nificance in the Schizasteridae. However, we "are able to recognize morphological sub- genera of Sch&aster on other criteria. Beside Sch&aster we separate Paraster Pomel and Dipneustes Arnaud as defined below. In addition, we recognize (McNamara & Philip, in press) the subgenus Ova Gray (= Diplo- poraster Mortensen) for species of Sch&aster in which the pore pairs of ambulacrum III are arranged in irregular double rows in the adult stage (Fig. 8). Certainly, some species are transitional between morphological sub- genera, so that a certain arbitrariness must enter their application. But, as explained below, the subgenera are based on concepts that we believe to be useful.

Subgenus PARASTER Pomel 1869 Type Species. Sch&aster gibberulus Agassiz 1847; by original designation of Pomel 1869, p. 14. Emended Diagnosis. Species of Schizaster with test small to moderate size, with shallow anterior notch. Apical system slightly posterior of centre. Ambulacrum III shallow with pore pairs inclined at about 45 ° and arranged in single rows. Anterior petals almost straight, diverging at an angle of up to 110 °. Remarks. We employ Paraster as a subgenus for species which differ from typical species of Schizaster in having a more shallow ambulacrum III, a more circular test, a less posteriorly situated apical system, and anterior ambulacral petals which are straighter and diverge more strongly. The

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50 K.J. McNAM,/kRA AND G. M. PHILIP ALCHERINGA

B

Fig. 1. Schizaster (Paraster) carinatus sp. nov. A, B, CPC 4822, holotype C, CPC 4823, paratype. From the Pirie Calcarenite (Middle or Late Palaeocene), Giralia Anticline, 15 km southeast of Bullara, Carnarvon Basin, Western Australia. All xl.

pore pairs in ambulacrum III are set more transversely in Schizaster.

SCHIZASTER (PARASTER) CARINATUS sp. nov. (Fig. 1A-C)

Type specimens. Holotype CPC 4822 from the Pirie Calcarenite from the western flank of the north end of the Giralia Anticline, 15 km southeast of Bullara, Carnarvon Basin, Western Australia. Paratypes CPC 4823 from the same locality and horizon as the holotype, and CPC 4824 from the same horizon at CY Creek, 10 km ENE of No. 10 Bore, Cardabia Station on the western flank of the Giralia Anticline (Condonet al., 1956).

Other material. In addition to the type specimens, a number of desert-weathered and mostly crushed specimens are present in older collections from the Pirie and Cashin Calcarenites from various localities in the northwestern part of the Carnarvon Basin, Western Australia. Recent collections made by us in the Carnarvon Basin reveal the species to be widespread and common in the calcarenites and coarser grained marl horizons of the Wadera, Pirie and Cashin Formations, outcropping on the flanks of the Giralia Anticline. McWhae et al. (1958, p. 121) identified these formations as Palaeocene in age. McGowran (1978, fig. 2) correlates them with P4.

Diagnosis. Test low anteriorly but high posteriorly where prominent keel developed m interambulacrum V. Anterior and posterior ambulacral petals relatively short. Apical system with four genital pores. Labrum broad, long and nearly parallel- sided posteriorly.

Description. Test subcircular but truncated posteriorly; low anteriorly, rising quite steeply to apex, two-thirds test length from anterior, formed by a prominent keel in interambulacrum V (Fig. 1B). Keel does not overhang periproct. Apical system situated at or slightly more than half test length from anterior. It is ethmolytic and has four genital pores (Fig. 1A). Ambulacrum III broad and relatively shallow, forming a slight anterior notch. Pore pairs obliquely located, few in number and widely spaced (Fig. 8). A specimen of test length 31.5 mm possesses only fourteen pore pairs. Anterior petals short, being 35 per cent of length of test; almost straight and diverging at about 100 °. Posterior petals very short, half length of anterior pair; posteriorly diverging at about 60 °. Lateroanal fasciole extends to ambitus posteriorly far below periproct which is set slightly closer to aboral surface.

Adoral surface gently convex; ambulacra weakly impressed. Labrum long, broad and narrowest at half length (Fig. IC). Anteriorly only slightly projecting over peri- stome where bordered by narrow, raised rim. Plastron small, 35 per cent length of test; slightly longer than broad. Tubercles, except on plastron, sparsely distributed, par- ticularly in the region of the peristome. Pores in phyllode paired, the pair separated by prominent, raised interporal partition. Discussion. S. (P.) carinatus can be dis- tinguished from the living S. (P). gibberulus by its broader, less inflated test, well- developed keel in interambulacrum V and petals which are shorter and do not extend as close to the ambitus. Kier (1957) described two new Palaeocene species from Somalia as Paraster hunti and P. duroensis. S. (P.)

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A L C H E R I N G A TERTIARY E C H I N O I D S 51

carinatus differs from S. (P.) hunti in possessing a less inflated test and shorter petals. Both species have a similar posterior truncation which tilts toward the aboral surface so that the periproct is visible from above. In S. (P.) duroensis the tilt is reversed such that the periproct cannot be seen from above. The test of S. (P.) duroensis is relatively longer than that of P. carinatus, a keel is not developed in interambulacrum V, the petals are relatively longer and the anterior notch is more indented.

S. (P.) carinatus is morphologically closest to "Linthia" indica Duncan & Sladen (1882) from the Ranikot Series in western Sind. The sub-centrally placed apical system, posterior petals less than half the length of the anterior pair, and a broad, well-developed ambulac- rum III all indicate that this species is best referred to the subgenus Paraster. S. (P.) carinatus can be distinguished from S. (P.) indica by its less inflated test, narrower ambulacrum III and better developed posterior keel.

B

Duncan & Sladen's (1883) S. (P.) beluchis- tanens& d'Archiac var. from the Tertiary of Kachh is similar to P. carinatus in possessing short petals. However, its apical system is more posteriorly located and the test is more inflated. S. (P.) granti (Duncan & Sladen, 1884) from the Oligocene of Western Sind similarly has short petals, but its test is longer and more inflated than that of S. (P.) carinatus, and interambulacrum V over- hangs the periproct; its anterior petals are less divergent.

SCHIZASTER (PARASTER) TATEI sp. n o v . (Fig. 2A-E) Type specimens. Holotype (NMV P55467) and paratypes (NMV P55468 and 55470) are from the early Late Eocene (close to the P15- 16 boundary) Tortachilla Limestone in the Maslin Beach - Port Willunga district, south of Adelaide, South Australia. Other material. Five other topotype specimens were available for study. In addition, two specimens from a similar, or

Fig. 2. Schizaster (Paraster) tatei Sp. nov. A-C, NMV P55467, holotype, xl. D, E, NMV P55468, paratype. D, anterior aboral surface of test showing nature of peripetalous fasciole and pore pairs in ambulacra II-1V, x2.6. E, paired pores in adoral phyllode, x6. From the Tortachilla Limestone (Late Eocene), Maslin Beach - Port Willunga district, South Australia.

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52 K.J . McNAMARA AND G. M. PHILIP A L C H E R I N G A

slightly younger horizon at 'Happy Valley' (SAM P3336 and 3343) are referable to this species, as are two specimens (SAM P6873 and 6880) from Kimbers Well at Klemzig, S.A. One specimen (SAM P5390) was collected from a well at a depth of 16 m at Campbelltown, S.A., in a lithology similar to the Blanche Point Formation of late Late Eocene age, f rom which five crushed specimens referable to this species have been collected from Blanche Point, south of Maslin Beach. One badly crushed specimen (NMV P55471) f rom the coastal cliff north of Hart 's Mine on the east coast of Yorke Peninsula in the Late Eocene Muloowurtie Formation (equivalent in age to the Blanche Point Marl Member in the lower part of the Turborotalia aculeatea zone) is probably referable to this species. Diagnosis. A species of the subgenus Paraster with only two genital pores; ambulacrum III broad and open; ambulacral petals comparatively deep; anterior pair almost straight and diverging at 110 °. Posterior pair relatively long, half of the length of the anterior pair.

Discussion. This species differs from S. (P.) carinatus in possessing a more posteriorly pointed and inflated test (Fig. 2B); two (not four) genital pores; a broader ambulacrum III which has more pore pairs (Fig. 8); no obvious posterior adapical keel; relatively longer posterior petals; and a deeper anterior notch. S. (P.) tatei is similar to the living species S. (P.) gibberulus and S. (P.) floridiensis (Kier & Grant, 1965)) but has fewer genital pores, shorter petals, and a more open ambulacrum III. S. (P.) tatei can be distinguished from the Somalian Palaeocene and Eocene species of the subgenus Paraster described by Kier (1957) in the possession of fewer genital pores and in having shorter petals. It is morpho- logically closer to the Palaeocene species S. (P.) hunti and S. (P.) duroensis than to the Middle Eocene S. (P.) karkarensis Kier (1957) and S. (P.) beluchistanensis, as these Eocene species both possess a more posteriorly placed apical system and less divergent anterior petals. S. (P.) exoletus (Hutton) from the Late Eocene of New Zealand (Henderson, 1975) is similar to S. (P). tatei, but its test is less inflated, the apical system has four genital pores, and a distinct keel is present in interambulacrum V.

Subgenus SCHIZASTER Agassiz 1836

Type species. See above.

Emended diagnosis. Moderate to large species of Schizaster with deep anterior notch. Ambulacrum III deep and long; pore pairs almost transversely oriented and in single rows. Anterior petals long, deep and flexed; diverging at a low angle usually less than 80 ° .

Remarks. The species referred to Schizaster differ from those assigned to Paraster in possessing a more elongate, narrower test, a more posteriorly positioned apical system, and an ambulacrum III which is generally deeper and has steeper sided walls. Ambu- lacrum III also has a greater concentration of pore pairs (Fig. 8) which are more trans- versely orientated. Usually the anterior notch is deeper, the anterior petals are more flexuous and less divergent and the labrum is larger and projects more strongly over the peristome.

SCHIZASTER (SCHIZASTER) HALLI sp. nov. (Fig. 3A-D)

Type specimens. The holotype (NMV P19036) and paratypes (NMV P53219 and 53220) are from the Longfordian Table Cape Beds, at Table Cape, Tasmania.

Other material. Sixteen other specimens are known from the type locality and from the Cape Grim Beds at Cape Grim, Tasmania. These beds are also Longfordian (Early Miocene) in age. Four specimens from strata of Janjukian (Late Oligocene) age at Bird Rock Cliffs, Torquay, Victoria are also referable to this species.

Diagnosis. A small species of Schizaster s.s. with two genital pores; shallow anterior notch; narrow; moderately deep ambula- crum III; anterior petals relatively shallow, diverging at 80°; labrum long and narrow, almost parallel-sided posteriorly; plastron small.

Description. Maximum known test length 50.5 mm; slightly longer than broad, moderately inflated, with highest point close to posterior end. Apical system situated at about 57 per cent of test length from the anterior end and with two genital pores (Fig. 3A). Ambulacrum III narrow and moderate- ly deep, but becomes shallower anteriorly so that anterior notch is slight. Pore pairs arranged in single row; orientated somewhat

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ALCHERINGA TERTIARY ECHINOIDS 53

obliquely adapically, but more nearly trans- verse toward the ambitus. Specimens of test length greater than 40 mm with about 22 pore pairs in ambulacrum III. Anterior petals only slightly reflexed; deep and broad; diverging at 85 ° (Fig. 3A). Posterior petals straight and narrow; half length of anterior pair. Periproct high and overhung by posterior of test. Peristome broad and lunate. Pores in phyllode paired (Fig. 3D). Labrum anteriorly projecting and bordered by stout, raised rim; tong, narrow and broadening only slightly posteriorly. Oval plastron small; slightly longer than broad. Tubercles large and sparsely distributed anteriorly; diminishing in size and increasing in concentration posteriorly (Fig. 3B). Peri- plastronal area broad and strongly curved. Adoral interambulacral tuberculation sparse. Discussion. S. (S.) halli is similar to the type

species, S. (S.) studeri from the Eocene of France (Mortensen, 1951). It differs in possessing straighter anterior petals, a narrow ambulacrum III, a less elongate and less inflated test, a less posteriorly placed apical system, a narrower, more anteriorly located peristome, and a narrower labrum. S. (S.) halli also resembles S. (S.) simulans Duncan & Sladen (1884) from the Khirthar Series, Baili, west of Tong, Sind. It can be distinguished by its more posteriorly located apical system ~nd the anterior petals which do not extend as close to the ambitus. S. (S.) halli is similar to S. (S.) vincinalis libycus Fourtau (1908) from Libya. The disposition of the petals is similar in both species, although they are slightly narrower in S. (S.) halli. The posterior keel is lower in S. (S.) halli and does not overhang the periproct to such an extent. Furthermore the anterior notch is deeper in S. (S.) vincinalis libycus.

(.

P'ig. 3. Schizaster (Schizaster) halli sp. nov. A-D, NMV P19036, holotype. A-C xl. D shows nature of labrum and paired pores in phyllode, x3. From the Janjukian Table Cape Beds (Late Oligocene), Table Cape, Tasmania.

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54 K . J . M c N A M A R A A N D G. M. P H I L I P A L C H E R I N G A

Fig. 4. Schizaster (Schizaster) aft. halli sp. nov. NMV P55470, from pre-Janjukian (Oligocene) Ettrick Marl at Tailem Bend, South Australia, xl.

SCHIZASTER (SCHIZASTER) aff. HALLI sp . nov. (Fig. 4)

Material, locafity and horizon. A single specimen (NMV P55470) from Tailem Bend, collected by R. J. Foster from spoil from an excavation of the Coonalpyn Pipeline Pump Station in pre-Janjukian (Oligocene) Ettrick Marl.

Discussion. This specimen differs from typical representatives of S. (S.) halli in its slightly shallower ambulacrum III, its narrower anterior and shorter posterior petals, and a broader, shorter labrum. Additional material should justify its separation from S. (S.) halli. It differs from S. (P.) tatei in its more posteriorly located apical system and shorter posterior petals.

SCHIZASTER (SCHIZASTER) ABDUCTUS Tate 1891 (Fig. 5A-E)

1891 Schizaster abductus Tate, p. 281-282. 1907 Schizaster abductus Tate; Hall, p. 52,

pl. 15, figs 9-10, pl. 16, fig. 11. 1946 Schizaster abductus Tate; Clark,

p. 368. 1975 Schizaster (Paraster) abductus Tate;

Henderson, p. 17.

Type specimens. The two specimens upon which Tate (1891) based this species are labelled as coming from the River Murray Cliffs. The larger of the two specimens (AUGD T.265A)(Fig. 5B), that for which Tate (1891, p. 281) gave measurements, was selected as the lectotype by Hall (1907, p. 52); the other specimen (AUGD T.265B) is the paralectotype.

Material, localities and horizon. This species is common in Early Miocene strata along the

Murray River. Fifteen specimens collected by F. A. Cudmore and now housed in the National Museum of Victoria are labelled as coming 'from near Overland Corner to 4 miles below Morgan, S.A.'. R. J. Foster collected thirteen specimens from the quarry on the Waikerie-Taylorville road, 1.2 km from Waikerie Punt, in the Cadell Marl Lens of the Morgan Limestone. Mr Foster (written communication 17.7.78) informs us that S. D. Giles (Esso (Australia), Sydney) has dated this unit as being of Balcombian age. Other specimens are known from a similar horizon at Waikerie pump station, Murray River Cliffs (two specimens), right bank of the River Murray at Swan Reach in a quarry one mile inland from the river (one specimen) and at Bryant's Creek Reserve on the right bank of the Murray River just upstream of Morgan (one specimen). British Museum specimen E17725 is an internal mould best referred to this species. It is labelled as coming from Fyansford, i.e. probably from the Balcombian Fyansford Clay. Diagnosis. A large species of Schizaster s.s. with strongly developed keel in inter- ambulacrum V which greatly overhangs periproct (Fig. 5C); petals incised, posterior pair long and narrow; weakly developed anterior notch; genital pores four (Fig. 5A, E); labrum constricted medially.

Discussion. S. (S.) abductus can be distin- guished from the type species, S. (S.)studeri, in its more centrally placed apical system and less strongly curved anterior rim of the labrum. It differs from the older species S. (S.) halli by its possession of four genital pores, the more steep-sided ambulacrum III and more incised, narrower, ambulacral petals; the deeper anterior notch; the more densely tuberculated adoral interambulacra; and the phyllodal pores which are single, not double (Fig. 5D). The strongly raised inter- poral partition is still present, but pores are only developed on the adoral side. On the other side a faint depression is present, but there is no connection through to the internal part of the test.

Comparison of the apical surface of specimens of S. (S.) abductus and S. (S.) halli of similar size (37 mm and 39 mm respectively) shows both to possess relatively straight petals. However, S. (S.) abductus, with growth to a larger size than S. (S.) halli, develops curved petals distally, both of the

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Fig. 5. Schizaster (Schizaster) abductus Tate 1891. A, C-E, NMV P55474 from quarry on the east side of the Waikerie-Taylorville road, 1.2 km from Waikerie Punt, South Australia, Cadell Marl Lens of the Balcombian (Early Miocene) Morgan Limestone. A, C, xl. D, enlargement of peristomal region showing single pores in phyllode, x2.5. E, enlargement of apical region and ambulacrum Ill, x3. B, AUGD T205A, lectotype, from Early Miocene strata, Murray River cliffs, xl.

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56 K.J. McNAMARA AND G. M. PHILIP A LCHERINGA

anterior and posterior pairs (Fig. 5A). At the same test length the petals of S. (S.) halli are a little longer than those of S. (S.) abductus, and S. (S.) abductus has fewer pore pairs in ambulacrum III than S. (S.) halli. However, large specimens (test length of 64.5 mm) of S. (S.) abductus have more pore pairs (up to 27). A specimen 70 mm long has 32 pore pairs. The course of the peripetalous fasciole of S. (S.) abductus is somewhat different from that of S. (S.) halli, bending in between the anterior and posterior petals to extend much closer to the apical system (Fig. 5A). Posteriorly the fasciole is transverse in S. (S.) abductus but curves outward in S. (S.) halli. S. (S.) eurynotus Agassiz, from the Miocene of Sardinia (Lambert, 1907), like S. (S.) abductus, has a strongly developed posterior keel. It can be distinguished by its deeper ambulacrum III and more posteriorly located apical system.

SCHIZASTER (SCHIZASTER) SPHENOIDES Hall 1907 (Fig. 6A-E)

1907 Schizaster sphenoides Hall, p. 51-52, pl. 14, figs 7, 8, pl. 16, fig. 12.

1946 Schizaster sphenoides Hall; Clark, p. 369.

Type specimen. Of the three specimens on which Hall based this species, the largest (NMV P15058) is herein chosen as lectotype. This was also the only figured specimen (Hall, loc. cit.). It is from the 'base of cliffs at mouth of Sherbrooke River', Port Campbell, Victoria, from the Bairnsdalian (Middle Miocene) Port Campbell Lime- stone.

Other material. Fourteen other specimens are in the collections studied and all are from the Port Campbell Limestone of the type locality, or between the mouth of the Sherbrooke River and Port Campbell. Specimens collected by R. J. Foster include one known to be from the Rutledge Marl Member of the Port Campbell Limestone at the mouth of Rutledge Creek, 1 km WNW of the mouth of Sherbrooke River. All the other known specimens are preserved in a similar lithology and all probably derived from more marly lenses within the Port Campbell Limestone.

Diagnosis. Large, subcircular species of Schizaster in which test is low anteriorly but rises steeply posteriorly. Apical system 58-62 per cent of test length from anterior; with

four genital pores. Ambulacrum II! very deep and partially overhung by adjacent ambulacra (Fig. 6E); anterior notch also very deep. Petals relatively short, narrow and slightly curved distally. Plastron raised strongly above level of adjacent inter- ambulacra. Labrum strongly constricted medially (Fig. 6B); bearing tubercles. Peristome large and situated relatively close to anterior of test.

Discussion. As Hall (1907, p. 52) has noted, many of the specimens still have spines attached; these are mainly the stouter adoral spines of the plastron and their inter- ambulacra. Their presence on the test suggests fossilization in situ in life position. The best preserved specimen (Fig. 5C) has spines on the anterior of the plastron 5 mm in length; posteriorly they are shorter and finer. Like the modern species, the ends of the plastronal spines are spatulate. No pedi- cellariae have been observed.

S. (S.) sphenoides can be distinguished from the slightly older S. (S.) abductus by its more circular outline, resulting from the absence of a prominent posterior keel, a deeper ambulacrum III and anterior notch, shallower, relatively shorter, more open petals, a strongly raised plastron, and a tuberculate labrum which has a less well- developed anterior rim.

The overall test morphology of S. (S.) sphenoides is similar to that of Kina gracilis Henderson (1975) from the Late Eocene and Oligocene of New Zealand. Both have a deep ambulacrum III, four genital pores and similar petals. According to Henderson, Kina lacks a lateroanal fasciole. The pore pairs in ambulacrum III of K. gracilis are numerous and arranged in an irregular double series as in the living species of S. (Ova).

The living Australian schizasterid S. (Schizaster) sp. nov. A (McNamara & Philip, in press) also has a very deep ambulacrum III. It differs in possessing a more elongate test, longer, broader, more strongly curved petals and a labrum which is not constricted posteriorly.

Subgenus DIPNEUSTES Arnaud 1891 ( = Schizopneustes Thi6ry 1907)

Type Species. Dipneustes aturicus Arnaud 1891, p. 152, pl. 19, figs 11-12 from the Palaeocene (Danian) of Rivi~res, Landes, France.

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A L C H E R I N G A TERTIARY E C H t N O I D S 57

Emended Diagnos&. Species of Schizaster with subcircular test and deep anterior notch. Apical system almost central.

Ambulacrum III deeply incised with pore pairs in a single series. Anterior petals long, straight and deep, diverging at about 100°;

D

Fig. 6. Schizaster (Schizaster) sphenoides Hall 1907 from the Rutledge Marl Member of the Port Campbell Limestone (Bairnsdalian). A, NMV P55476 from Ingles Creek, 1 km west-northwest of mouth of Sherbrooke River, Victoria, xl. B, labrum of NMV P20187, from 'Sherbrooke River', x4.5; C-E, NMV P55475 from mouth of Sherbrooke River. C, E xl, D, enlargement of apical region, x3.

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58 K.J. McNAMARA AND G. M. PHILIP ALCHERINGA

posterior petals short, up to one-third of the length of the anterior pair. Peristome small; labrum not strongly projecting anteriorly.

Remarks. Thi6ry (1907) introduced the name Schizopneustes for Dipneustes as he thought the name Dipneustes had been used earlier for a gastropod genus by Hoernes in 1866. However, as Mortensen (1951, p. 232) has noted, the Nomenclator Zoologicus lists only Arnaud's Dipneustes. The Zoological Record for 1866 has no gastropod genus Dipneustes, nor is there record of a paper by Hoernes in that year. Consequently Schizo- pneustes must be regarded as a junior synonym of Dipneustes.

Dipneustes is recognized as a morpho- logical subgenus of Schizaster for species with a circular outline; a centrally positioned apical system; longer, straight and divergent anterior petals; and a small peristome and labrum. Such species would otherwise be referred to Schizaster s.s. In the discussion given below of the evolution of Australian schizasterids, we interpret the other sub- genera of Schizaster as morphotypes developed in response to changing ecological settings, but with Dipneustes it is difficult to attribute special significance to its mor- phology.

SCHIZASTER (DIPNEUSTES) FOSTERI sp. nov. (Fig. 7A, B)

Type specimen. The holotype (NMV P55472) was collected by R. J. Foster from a quarry 1.5 km from the right bank of the Murray River at Swan Reach. Mr Foster (written communication 17.7.78) is uncertain whether the horizon is the Mannum Formation or the Morgan Lime- stone. Other material. The occurrence of this species in the Longfordian Nelson Formation at the left bank of the Glenelg River at Nelson town bridge whence R. J. Foster collected one specimen (NMV P55473), suggests that the holotype may be from the Longfordian Mannum Formation. One further specimen (NMV P17911) was collected from the cliffs of the bank of the Murray River at Mannum. Diagnosis. Apical system subcentral, 53 per cent of test length from anterior. Ambulacrum III deep and broad (Fig. 7A). Petals very broad; posterior pair very short, one-quarter length of anterior pair. Peri- stome very small and situated relatively distant from the anterior margin of the test (Fig. 7B). Discussion. S. (D.) fosteri differs from S. (D.) aturicus Arnaud, the type species (Mortensen, 1951, fig. 115), in possessing slightly less divergent anterior petals, shorter posterior petals, a broader ambulacrum III and a more prominent keel in

~ ( ii ~ ?~!i~'

~!ii ̧ ~ ~F• ~

Fig. 7. Schizaster (Dipneustes)fosteri sp. nov. A, B NMV P55472, holotype, from quarry 1.5 km from right bank of Murray River at Swan Reach, South Australia; ?Longfordian (Early Miocene) Mannum Formation, x 1.

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ALCHERINGA TERTIARY ECHINOIDS 59

interambulacrum V aborally. Schizaster sphenoides is similar to S. (D.)fosteri in possessing a very deep ambulacrum III and deep anterior notch. The two forms can be readily distinguished by the more circular outline of S. (D.) fosteri, its shorter ambulacrum III (as the apical system is placed more centrally), more divergent, straighter anterior petals, shorter posterior petals and smaller peristome.

The largest available specimen of S. (D.) fosteri has a test length of 73 mm and the smallest 39 mm. Both have the same number of pore pairs in the paired petals, twenty-two in each of the anterior pair and seven in each of the posterior. Although exact numbers cannot be ascertained from the material at hand, there is a much greater number of pore pairs in ambulacrum III in the larger specimen. This indicates that the number of ambulacral plates in ambulacrum III increased with growth, as opposed to the other ambulacra in which there was only a size increase. Whereas other Australian Tertiary species of Schizaster, albeit to varying degrees, possess conjugate pore pairs in the petals, S. (D.)fosteri has no furrow linking the pores.

Progressive morphological changes in Australian schizasterid echinoids The close similarity between the earliest species of the Paraster morphotype, which appeared in the Palaeocene, and Linthia, which is first recorded from the Senonian (see Lambert & Thi6ry, 1925, p. 519), has been noted by Kier (1957, p. 882). Differ- ences between the Paraster morphotype and Linthia (including test shape, position of the apical system, form of the ambulacra and nature of the adoral surface of the test) are more clearly seen in later species, as there was continuing progressive change in test morphology with time. Early species referred to Schizaster s.s., such as S. (S.) halli, are morphologically closer to the Paraster morphotype than are later species of Schizaster s.s. Both the Schizaster and Paraster morphotypes are seen in extant schizasterids; Linthia probably became extinct during the Pliocene, although Mortensen (1951, p. 236) records a frag- mentary specimen from the seas near Japan as being possibly Linthia.

Although progressive morphological changes can be traced in the Australian record from Linthia to Schizaster s.s. through the Paraster morphotype, this does not necessarily mean that Australian Tertiary schizasterid species evolved endemically within the Australian region from local progenitors along a single phyletic pathway. The appearance of species at restricted horizons, presumably when climatic and environmental conditions were suitable, suggests periodic immigration o f species. The morphological trends apparent in Schizaster s.1. through the Tertiary can also be identified elsewhere in the world (principally in the Tertiary of France, eastern Africa, the Caribbean, eastern U.S.A. and India) but the timing of appearance of particular morphotypes may vary. For instance there is a close similarity between S. (S.) studeri from the Eocene of France and S. (S.) halli from the Late Oligocene and Early Miocene of Australia. This leads to the suggestion that the morpho- types (or morphological subgenera) may have evolved iteratively.

The morphological changes which are described are thought to reflect adaptation to the occupation of new ecological niches, principally by burrowing deeper in the sediment, and by inhabiting a wider range of sediment types.

Whereas in Linthia the test is not strongly vaulted (the apex being flat and situated in the anterior half of the test) there is a trend through the Paraster morphotype to Schizaster s.s. for the apex to become situated increasingly closer to the posterior of the test. In S. (S.) abductus it is situated more than three-quarters of the test length from the anterior. The resultant higher angle of slope of the aboral surface of Schizaster s.s. is enhanced in some species by the swelling of interambulacrum V posteriorly to form a prominent raised keel. The test in the Paraster morphotype became longer than that of Linthia, in which the test is about as wide as long, and the widest part of the test is set more posteriorly in Schizaster than in Linthia.

The apical system similarly migrated posteriorly from Linthia through the Paraster morphotype to Schizaster s.s., being one-third the test length from the anterior in Linthia, slightly posterior of centre in the Paraster morphotype, and as much as two-thirds the test length from the

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60 K.J. McNAMARA AND G. M. PHILIP ALCHERINGA

anterior, as in the Middle Miocene S. (S.) sphenoides. There is also a general trend toward reduction of the number of genital pores. Linthia generally has four, as have Palaeocene species of Schizaster, whilst the younger species of Schizaster may carry only two.

Accompanying the posterior migration of the apical system there were concomitant changes in the form, orientation and lengths of the petals. The anterior ambulacral petals of Linthia are generally long and diverge at a high angle (up to 130°). There is a pro- gressive trend for this angle to decrease (to as little as 75 ° in some living species of Schizaster s.s.).

As the angle of divergence of the anterior petals decreased and the adapical part of the petals moved posteriorly, the extremities of the petals retracted from the ambitus in the Paraster morphotype, but the petals still remained straight. Further posterior movement of the apical system resulted in the anterior petals becoming curved abapically in the Schizaster morphotype. The posterior petals are much shorter in Schizaster than in Linthia. Topologically, this can be interpreted as the extremities of the petals remaining in the same relative position during the posterior migration of the apical system. In Linthia the petals are only slightly depressed below the surrounding surface of the test. In S. (P.) carinatus they are slightly deeper. This trend continued through to the Miocene species of Schizaster s.s. where the petals are deeply incised and, as in S. (S.) abductus and living species, overhung by the adjacent inter- ambulacra.

The morphological change in ambulacrum III from Linthia to Schizaster is most striking. In Linthia it is short, shallow and broad, bearing a relatively small number of pore pairs. It became progressively a more steep-sided, deeper furrow, being deepest in S. (S.) sphenoides among Australian Tertiary species. In addition, the pore pairs increased in number and size (Fig. 8). The pore pairs, which are inclined at about 45 ° in Linthia and in the Paraster morphotype are almost transverse in Schizaster s.s. In Miocene and later species of Schizaster the pore pairs become more numerous and more crowded. Further increase in the number of pore pairs is seen in the subgenus Ova, where adults develop double rows of pores. The anterior notch is moderately developed in

Linthia and the Paraster morphotype, but in the Schizaster morphotype it is much deeper (Fig. 8).

The peristome shows little change in position, though in later species of Schizaster s.s. it is located somewhat more anteriorly. The labrum underwent major modification, becoming longer both anteriorly and posteriorly and developing an anterior rim. Its anterior expansion in the Schizaster morphotype resulted in it projecting over the peristome. Species referred to the morphological subgenus Dipneustes have a small peristome, set back from the anterior margin of the test, and the labrum also is small and does not project strongly over the peristome. Species referred to Dipneustes therefore appear to diverge from the general progressive morphological trends seen during the development of Schizaster s.s. from Linthia.

The plastron occupies a much greater area of the adoral surface of the test of the Schizaster morphotype (particularly Miocene to Recent species) than it does in either the Paraster morphotype or in Linthia. The adoral tubercles also become more densely concentrated on both the plastron and the interambulacral areas.

Kier (1974, pp. 27-28) has noted how Late Cretaceous to Middle Eocene species of Linthia possess double pores in the phyllode. Later species possess single pores. A similar change can be observed in Schizaster. Australian Palaeocene, Eocene and Oligocene species of Schizaster s.l. have double pores, Early Miocene and later species have only single pores.

Functional significance of schizasterid morphological development Linthia is morphologically similar to the living spatangoid Spatangus purpureus Mtiller which inhabits shallow burrows in shell gravel (Nichols, 1959, p. 37). They have in common broad tests which are not very vaulted aborally; anteriorly positioned apical systems; broad, shallow, short, open ambulacrum III; strongly divergent anterior petals, and long posterior petals. Con- sequently, Linthia may also be considered to have inhabited a similar shallow burrowing environment to S. purpureus. Information regarding the palaeoecology of fossil species

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A L C H E R I N G A TERTIARY ECHINOIDS 61

V

A B C D

EL_ / . . . •° ° . ° ° , .

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M. Miocene Recent Fig• 8. Outline of anterior notch and nature of pore pairs in ambulacrum III. A, Schizaster (Paraster) carinatus sp. nov. B, Schizaster (Paraster) tatei sp. nov. C, Schizaster (Schizaster) halli sp. nov. D, Schizaster (Schizaster) abductus Tate. E, Schizaster (Schizaster) sphenoides Hall. F, new species of Schizaster (Ova) from Port Jackson, N.S.W. (McNamara & Philip, in press)• All x2.

is l imi ted, but in the Pa laeocene o f Wes te rn Aus t r a l i a Linthia occurs in a coarse cal- careni te facies.

Spatangus raschi, which bur rows in f iner , s andy mud, has a n a r r o w e r longer , more highly vaul ted test t han S. purpureus; it has a deeper an te r ior notch; a deeper , longer , a m b u l a c r u m I I I which conta ins more po re pai rs ; a more pos te r io r ly pos i t ioned apical system; less an te r io r ly divergent an te r ior petals ; shor ter pos te r io r petals; and a re la t ively more an te r io r ly loca ted per i s tome. These dif ferences m a y be compared with those between Paraster and Schizaster m o r p h o t y p e s , but they are more accentua ted in this morpho log i ca l series.

The differences be tween Linthia and the Paraster m o r p h o t y p e para l le l those de- scr ibed in d i f ferent species of Micraster, which Nichols (1959) in terpre ts as a d a p - ta t ions to bu r rowing at d i f fe ren t depths . The cu lmina t ion o f these t rends, seen in ' ex t r eme ' Schizaster morpho types , by

ana logy with living species o f Spatangus, p r o b a b l y reflects i nha b i t a t i on o f a f iner- g ra ined sediment . Consequent ly , it is suggested tha t the progress ive m o r p h o - logical changes f rom Linthia to Schizaster reflect the change f rom living in coarse sediment and bu r rowing sha l lowly (Linthia), to bur rowing deeper in s imilar sediment (Paraster m o r p h o t y p e ) , to bur rowing deeply in f iner-gra ined sed iment (Schizaster m o r p h o t y p e , Fig. 9). The order o f ap pe a ra nc e o f the m o r p h o t y p e s in the geological record seems to fo l low this inter- p re ta t ion .

W h a t little is k n o w n o f the ecology o f schizaster ids also suppor t s such an inter- p re ta t ion . In the Pa laeocene o f Wes te rn Aus t r a l i a the Paraster m o r p h o t y p e , l ike Linthia, occurs in re la t ively coarse cal- careni te . It is a lso present in a s imilar facies in the Late Eocene o f the St. Vincent G u l f region in South Aus t ra l ia • In regard to living forms , Chesher (1966) has recorded S.

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62 K.J. McNAMARA AND G. M. PHILIP ALCHERINGA

(Paraster) floridiensis from coarse calcite sand in which it burrows to a depth of 25 cm. A living species of Schizaster s.s. is known only from the finest-grained sediments in Moreton Bay, Queensland (McNamara & Philip, in press), whilst the Tertiary species occur mainly in fine-grained marl lenses within coarser calcarenites and bioclastic limestones. McNamara & Philip also'record deep burrowing in living species of Schizaster. Kier (1975) recorded S. (S.) doederleini living in mud to a depth of 10 cm. This species has more pore pairs, a more incised ambulacrum III and less divergent, deeper and more flexed anterior petals than S. (P.) floridiensis.

The morphological adaptations in Schiz- aster seem to derive from the need to produce more efficient current flow over the aboral surface of the test in a sediment of low permeability. Although Chesher (1966) has noted that S. (Paraster) floridiensis constructs a funnel to link it to the sediment- water interface, water would also be able to percolate through the coarse sediment and bathe the aboral surface of the test as Nichols (1959, p. 365) has observed for Spatangus purpureus which inhabits coarse sediment. In Schizaster s.s. the flow of water would be largely restricted to that passing down the funnel in sediment of low permeability. The morphology of the test of Schizaster shows many other adaptations which contribute to efficient utilization of such a localized water source.

The posterior migration of the apex meant that more water would flow over the anterior of the test toward the peristome. An increase in declination of the anterior slope would also increase the flow of water to the anterior. Lengthening of the test would also allow a further posterior migration of the apex. The posterior migration of the apical system coupled with the increased anterior slope of the test also would result in relative increase in size of the anterior petals (with their respiratory tube feet). Water would be efficiently channelled over these tube feet by the development of deeply sunken petals and prominently raised interambulaeral keels between them.

The deepening of ambulacrum III and the anterior notch assisted in channelling water to the peristome. Chesher (1963, p. 567) has noted how in Moira a major water current passes along ambulacrum III and continues to the peristome. To concentrate further the

nutrient-bearing water toward the peri- stome, it migrated closer to the anterior margin than in either Linthia or the Paraster morphotype. Moreover, the development o f a projecting labrum assisted the entrapment of water to restrict its flow past the peri- stome. The deep and long ambulacrum III further enabled more funnel-building tube feet to be accommodated by the generation of many more ambulacral plates. Presumably this was a response to the need for more funnel-building tube feet in the finer-grained sediment. The longer, deeper ambulacrum III would carry more current- producing cilia and clavules (Chesher, 1963, p. 567).

The increase in density of tubercles on the adoral surface in the Linthia-Schizaster morphological series compares with similar increases in Micraster, related by Nichols (1959) to deeper burrowing. A similar explanation may be invoked for Schizaster, for burrowing in finer-grained sediment would require more activity and con- sequently a greater number of plastronal spines.

An evolutionary explanation of schizasterid morphological development Two points need to be stressed in regard to the progressive morphological changes described and interpreted above. Firstly, evolution of a new morphotype need not necessarily mean the extinction of the ancestral morphotype, for the new morpho- type enabled, the occupation of a new ecological niche. Thus displacement of the ancestral morphotype which inhabited a different ecological niche was unnecessary. Consequently, species of Schizaster are living today which possess the 'extreme' Schizaster morphological characteristics, such as S. orbignyanus Agassiz in the Red Sea (see Mortensen 1951, pl. 23, figs 4-6, 10) and new species of Schizaster in eastern Australia (McNamara and Philip, in press). There are also living species such as S. (P.) floridiensis from eastern North America, very similar to the Palaeocene forms con- forming to the Paraster morphotype. This present-day temporal, though not ecological coexistence, has a great bearing on postulating the mechanism of evolution of different morphotypes, as the similarity of

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Recent Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Palaeocene

Senonian

f I 9 I I I I I I I I I I I I I I I I I I I t I I I i I I I I I I I ! i I I I I I I I ! I I I I I I I I I I I I I I I I I I I I I I

i ..... @ X moPra;~S~;pe

L in th ia

Linthia

Sand-dwel l ing Paraster morphotype

!

in termediate I m o r p h o t y p e s ~ !

! |

# / t Schizaster /

/ m o r p h o t y p e

/ /

Mud-dwel l ing Schizaster morphotype

Fig. 9. Ranges and suggested relationships of Linthia, and Paraster and Schizaster morphotypes. Profiles show depth and nature of sediment inhabited. Reconstructions x0.5.

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64 K.J. McNAMARA AND G. M. PHILIP ALCHERINGA

Recent and Palaeocene forms does not necessarily imply direct phyletic relation- ship.

The second point is that the general trend in phyletic development of Schizaster can be demonstrated in regions other than Australia. But the timing of appearance of new morphotypes appears to have differed. For example, S. halli from the Late Oligocene of southern Australia resembles S. studeri from the Eocene of France, suggesting that the attainment of the more 'extreme' Schizaster morphology was achieved earlier in that region. Similarly S. tatei from the Australian Late Eocene resembles Palaeocene forms from Somalia (see above), whereas Somalian Middle Eocene forms compare more closely with Late Oligocene/Early Miocene Australian forms. Kina, the Eocene and Oligocene New Zealand genus, has double rows of ambulacral pores in ambulacrum III similar to living species conforming to the Ova morphotype.

To understand the mechanism whereby there is an appearance of advanced morpho- types at different geological horizons, we may consider the ontogenetic development of Schizaster. Many of the morphological changes occurring in the development of Schizaster parallel those seen during the ontogeny of an 'extreme' form of Schizaster. McNamara & Philip (in press) have shown that, as with the morphological development of the genus, during ontogeny there is a relative elongation of the test with growth; the test becomes less tumid; the apical system migrates posteriorly; the anterior notch deepens; ambulacrum III deepens and narrows and there is an increase in the con- centration of pore pairs; the anterior petals becomes less divergent anteriorly and become reflexed distally; the peristome becomes situated more anteriorly; and the labrum elongates anteriorly.

With the phylogenetic development of the Schizaster morphotype, there is also a pro- gressive increase in the maximum size attained. This corresponds with a delay in attainment of sexual maturity, allowing a longer period of rapid, pre-adult growth, followed by a correspondingly longer period in the adult stage (i.e. evolution by hyper- morphosis, Gould, 1977). As morphological development in the pre-adult stage is greater than would be expected from normal allo- metric growth, a longer pre-adult period

results in the species being able to pass through more stages of morphological development. Consequently, alteration in the timing of attainment of sexual maturity and its phyletic fixation, results in evolution of differing morphotypes. The early onset of sexual maturity would result in morpho- logical development being relatively retarded (evolution by progenesis), whereas delayed maturation would result in increased morphological development of adults (hypermorphosis).

It is still an open question whether the opening of genital pores corresponds exactly with the onset of maturity. However, it has been shown (McNamara & Philip, in press) that the change from positive to normal allo- metric growth occurs at a test length of about 25 mm in the population studied from eastern Australia, and this corresponds with the opening of the genital pores. In this species, growth occurs to a maximum known test length of 71.2 mm. S. (P.)floridiensis (Chesher, 1966) possesses genital pores at a test length of 7.7 mm, and a maximum known test length of 16 mm. This species is similar to Palaeocene species of Schizaster; by the attainment of sexual maturity at an early growth stage, the progenetic S. (P.) floridiensis homeomorphically resembles Palaeocene species.

Thus, the correspondence between the phylogenetic and ontogenetic development of species of Schizaster s.s. suggests that the progressive delaying of attainment of sexual maturity allowed the evolution of new morphotypes by hypermorphosis. One might also surmise that the 'primitive' Paraster morphotype could also evolve by progenetic retardation in development relative to an ancestral form.

Summary

The evolution of Schizaster from Linthia or from a Linthia-like root-stock involved morphological changes to adapt to the occupation of new ecological niches (Fig. 9). Species conforming to the Paraster morpho- type developed a slighly longer test than Linthia; a more posteriorly positioned apex and apical system; less divergent anterior petals; shorter posterior petals; and longer, deeper more poriferous ambulacrum III. These changes parallel some of the morpho- logical changes which occurred through the Micraster lineage and are likewise considered to reflect adaptations to deeper burrowing.

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A L C H E R I N G A T E R T I A R Y E C H I N O I D S 65

The culmination of these trends is seen in the Schizaster morphotype which reflects the occupation of finer-grained sediments. The morphological characteristics of mud- dwelling species of Schizaster were developed in order to utilize the localized flow of water in the most efficient manner. The advanced morphotypes seem to have evolved iteratively, due to the delay of the onset of sexual maturity.

Acknowledgements We would like to thank Drs P. A. Jell (National Museum of Victoria) and N. Pledge (South Australian Museum), and Mr R. J. Foster for the loan of material on which this study was based. Drs P. M. Kier, R. Henderson and E. P. F. Rose are thanked for constructive criticism of the manuscript. This work was supported by the Australian Research Grants Committee.

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