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Chapter 71. Homeomorphy, phylogeny and natural classification: Case studies involving Palaeozoic ostracods

Chapter 71. Homeomorphy, phylogeny and natural classification: Case studies involving Palaeozoic ostracods

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1042 R. E. SCHALLREUTER



Detailed morphological investigations by Schallreuter (since 1964), on extraordinary preserved

material gained from glacial erratic boulders of Northern Germany, and phylogenetic studies

proposed that any natural systematics must take both the L-S sculptures and dimorphism into

consideration. The L-S sculptures are particularly important. in classifying lower taxa (genus and

family categories), while sexual dimorphism is especially important for higher taxa (family and

order categories).

The system built up on this basis is currently widely assumed to be a natural one. It provides

many homeomorphies which are ‘proof’ of a natural system.



In principal, all features of the ostracod shell can be possible homeomorphic features. Homeomorphy affects both lobal-sulcal features as well as ornamental (including sexually dimorphic)

sculptures, as shown by the following examples.

A well-known example of homeomorphic lobal-sulcal features (L-S sculptures) is quadrilobation, which occurs in many Lower Palaeozoic ostracods. In the example illustrated (PI. 1, figs.

1, 6) the main difference between the two figured Ordovician species is expressed in their dimorphic

adventral sculptures, especially the development of a histium in Sigmoopsoides. Modifications in

quadrilobation at first led to the distinction of separate genera (for example, Cerutopsis, Kiesowiu),

which soon became sack genera too.

A general phylogenetical trend in Lower Palaeozoic ostracodes is the reduction of quadrilobation, a trend which can apparantly occur in many different lines. Its occurrence in different lines,

often simultaneously, implies the existence of homeomorphies. One form of lobal reduction is the

dissolution of the lobes into single nodes. Such forms were formerly united in the genus Kiesowia,

now recognized as a classical example of homeomorphy.

Of the 7 species assigned by Henningsmoen (1953) to Kiesowiu, only the type-species now remains

in the genus. The other species are now assigned to 5 or 6 different genera and subgenera of various

families and subfamilies. Two of these species and some similar species are illustrated herein (Pl.

1, figs. 2-5, 7, 8).

Kiesowiu is, by its almost perfect homeomorphy, a very good example of how difficult it is to

PLATE1-Fig. 1. Tetrudu memorubilis (Neckaja, 1953), 9 left valve (GPIMH 2595), ~ 7 0Backsteinkalk

.

erratic

boulder (no. G29) from the beach of the Isle of Gotland (Baltic Sea), S. of Klintehamn. Fig. 2. Homeokiesowiu

frigidu (Sarv, 1959), 9 right valve (GPIMH 2023a), x 60. Backsteinkalk erratic boulder (no. Ho2) of the beach

of Klein-Horst, Pomerania. Fig. 3. Snaidar radians (Krause, 1892), 9 right valve (SGWG 33/183), ~ 2 5 .

Backsteinkalk erratic boulder (no. 5B2) from the beach of the Klein-Zicker, Peninsula Monchgut, Isle of Rugen

(Baltic Sea), Pomerania. Fig. 4. Quudritiu (Krutatia) iunior Schallreuter, 1981, right valve (GPIMH 2468),

x 65. Ojle myrflint erratic boulder (no. G30) from the same locality as in fig. 1. Fig. 5 . PoIyceratellalsexpapillosu

(Troedsson, 1918), left valve (GPIMH 2697 = Silcoset cast of: Lunds Univ. Geologiska Institutionen, Avd.

f. Historisk geologi och paleontologi LO 2886t), x 65. Brachiopodskiffer (upper Harjuan) of Rostinga, Central

Scania. Fig. 6. Sigmoopsoides sigmoopsoides (Schallreuter, 1964), 9 right valve (GPIMH 2984), x 60. Some

boulder as in fig. 1. Fig. 7. Kiesowiu (Kiesowiu) dis.sectu (Krause, 1892), 9 right valve (GPIMH 2194), ~ 4 5 .

Same boulder as in fig. 4. Fig. 8. Polycerutellu uluverensis Sarv, 1959, 9 right valve (GPIMH 2986), x 70.

Backsteinkalk erratic boulder (no. G39), locality as in fig. 1. Fig. 9. Uvonhachtiu botulutu g. n. sp. n., holotype,

9 left valve (GPIMH 3263), x 75. Upper Viruan Hornstein erratic boulder (no. Sy225A) from the Upper

Kaolinsand (Lower Pleistocene) near Braderup, Isle of Sylt (N. Sea). Fig. 10. Pleurodelh pentuloculutu

(Schallreuter, 1978), right valve (GPI MH 2004), x 65. Ojlemyrflint erratic boulder (no. 789) from the beach

of Visby, Isle of Gotland (Baltic Sea). All figures in lateral view and SEM micrographs (except fig. 3). GPIMH

= Geologisch-PalaontologischesInstitut und Museum, University of Hamburg; SGWG = Sektion Geologische

Wissenschaften, University of Greifswald; Age of Backsteinkalk: Upper Viruan (upper Middle Ordovician);

Age of Ojlemyrflint : Upper Harjuan (upper Upper Ordovician).



Homeomorphy, Phytogeny and Classification of Palaeozoic Ostracods 1045



decide the correct systematic position for some genera. The affiliation of the type-species (K.

dissecta) to the Sigmoopsinae is demonstrated mainly by its (rudimentary) histium, a feature which

is completely developed in the older Sigmoopsoides (PI. 1, figs. 6-7). On the other hand, the

rudimentary histium is sometimes missing completely in Kiesowia specimens (Schallreuter 1979: PIS.

6, 86, fig. 5) and then there are no principial differences from the homeomorphic Homeokiesowia

and a generic separation becomes difficult or even impossible.

Another form of reduction of quadrilobation is the lobal dissolution into cristae, which can

sometimes copy the pattern of the quadrilobate precursor. This trend has produced homeomorphies such as that shown by the examples illustrated on PI. 1, figs. 9, 10.

The reduction of the quadrilobation has often led to uni- or nonsulcate forms which may or may

not exhibit similarities to their more markedly lobate ancestors. Among such forms there are

many potential cases of homeomorphy and also evolutionary convergences.

An excellent example of convergence are the beyrichiomorphs with ‘diffuse’ cruminal dimorphism. These forms are so similar to primary nonsulcate Aparchitidae that they were, even

recently, still placed together (Rozhdestvenskaya, 1972, cf. Jones, 1985: 158).

In examples of homeomorphic unisulcate representatives (PI. 2, figs. 1 4 ) the systematic differentiation of separate species is possible on the basis of the nature of the dimorphic adventral sculptures. They are, in part, so similar that some of them were formerly placed in a single genus; for

example, Henningsoenia gunnari and Sigmobolbina porchowiensis were assigned to the genus

Ordovicia and Henningsmoeniu (cf. Schallreuter, 1976: 199; 1982: 36).

Equally, the dimorphic adventral sculptures which permitted a ‘correct’ classification of the

examples cited can also be homeomorphic features, as for example in Severobolbina (Sigmoopsinae)

and Pentagonu (Perspicillinae) (PI. 2, figs. 5, 6). In both cases the histial dolon is united anteriorly

with the velar dolon and both genera are also similar in being unisulcate. However, differences exist

in their marginal sculptures (row of spines in Severobolbina; ridge in Pentagona) and in their

tecnomorphic vela (nearly missing in Severobolbina; keel-like ridge in Pentagona).

A much better case of homeomorphy affecting the adventral sculptures is the well-known example of locular dimorphism of many lower Palaeozoic ostracodes. Jaanusson and Martinsson

(1956) established the subfamily Ctenoloculininae (within the family Hollinidae) for such forms.

Bless and Jordan (197 1) transferred this subfamily to a family of its own, expanded and modified

the family and considered locular dimorphism as its main feature. However, already Henningsmoen

(1 965 : 386) and Schallreuter (1966 : 846) had considered that locular dimorphism at this systematic

level was a homeomorphic feature. Moreover, Schallreuter (1 974) drew the corresponding conclu-



PLATE2-Fig. 1. Henningsmoenia gunnuri (Thorslund, 1948), 9 right valve (GPIMH 2596), x 65. Backsteinkalk erratic boulder (no. lBl), beach of the Dornbusch, Isle of Hiddensee (Baltic Sea), Pomerania. Fig. 2.

Sigmobolbinaporchowiensis (Neckaja, 1958), pre-adult 9 left valve (SGWG 33/115), x 70. Backsteinkalk erratic

boulder (no. 1B74), locality as in fig. 1. Fig. 3. Sigmobotbina eichbaumi Schallreuter, 1980, tecnomorphic right

valve (GPIMH 2278), ~ 6 5 Local

.

erratic boulder of Sularp shale (no. Gis29) (Upper Viruan), beach of

Gislovshamrnar, SE-Scania. Fig. 4. Naevhithis naevus Schallreuter, 1981, 9 carapace (GPIMH 2486) from

the left side, X60. Ojlernyrflint erratic boulder (no. Sy106). Locality as in P1. 1, fig. 9. Fig. 5. Pentagonu

joehviensis (Sarv, 1959), 9 right valve (GPIMH 2030a), x90. Same boulder as in PI. 1 , fig. 2. Fig. 6.

Severobolbinu etlipticu (Steusloff, 1895), 9 left valve (GPIMH 2985), ~ 4 0 Same

.

boulder as in PI. 1, fig. 1.

Fig. 7. Eotomatelta bicuspidata Schallreuter, 1981, tecnomorphic left valve (GPIMH 2478), x 80. Upper Viruan

Hornstein erratic boulder (no. SylOS),same locality as in PI. 1, fig. 9. Fig. 8. Semibotbina ordoviciana Schallreuter,

1977, tecnornorphic left valve (GPIMH 2644), x80. Ojlernyrflint erratic boulder (no. G6), beach N of

Lickershamn, Isle of Gotland (Baltic Sea). Fig. 9. Thuringobolbina? australis Reynolds, 1978 (Pl. 2, fig. 2),

tecnornorphic left valve (lost), x 70. Devonian of New South Wales, Australia. Fig. 10. Acinacibolbina

unteropinnatu Reynolds, 1978 (Pl. 3, fig. 6b), holotype, tecnomorphic left valve (Australian National University

Canberra 36862/1/1), x 60. Locality as in fig. 9.

All figures in lateral view and SEM micrographs (except fig. 2).



1046 R. E. SCHALLREUTER



sions in the systematics of the family Hollinidae. The genera united by Jaanusson and Martinsson

in the Ctenoloculininae were thereby distributed in three subfamilies, each of which contains

locular and non-locular (= botulate) dimorphic forms. The basis for distinguishing the three

subfamilies is a combination of the L-S sculptures and/or the nature of the tecnomorphic adventral

sculptures ; the presumed systematics were supported by phylogenetic considerations. Within and

between these subfamilies homeomorphies exist not only involving locular dimorphism but also

between the respective tecnomorphs and involving the development of two tecnomorpic ventral

spurs (Pl. 2, figs. 7-10). The anterior spur is in any case a velar spur, the posterior spur can also

either be a velar spur or a posteroventral lobal spine. That it is in one case a velar spur and in

the other case a lobal feature is demonstrated in the females: the spur is either incorporated in

the dolon, or it lies above the velum [cf. Reynolds, 1978: P1. 2, figs. 1, 2 (fig. 2=this paper: PI. 2,

fig. 9), PI. 3, figs. 6b, 7b (fig. 6b=this paper: P1. 2, fig. 10) or Schallreuter, 1977: P1. 5, figs. 1, 7

(fig. 7=this paper: PI. 2, fig. 8) and Lethiers et al., 1985: PI. 9, figs. 26-29]. For the latter forms (with

a spine-like/distinct posteroventral lobe) the subfamily Tetrasacculinae was established. The forms

with a velar spur were placed in the subfamilies Hollininae and Triemilomatellinae. In most Tetrasacculinae the velum is developed ventrally (behind the anterior spur) as a keel-like ridge but, as

shown by Thuringobolbina? australis, it could also be developed as a spur (Pl. 2, fig. 9).

Examples of homeomorphies exist not only within the beyrichiocopes but also in the other

orders of Palaeozoic ostracodes. For example, after demonstrating that the two stoppegs in the

left valve of metacopes (order Podocopa) is a very important and characteristic taxonomic feature,

some species which were formerly united in special genera were unmasked as good examples for

homeomorphy (Schallreuter, 1979: 26). The two stoppegs are a very characteristic feature within

the metacopes but, on the other hand, they themselves could be homeomorphic: they also occur

within the leperditiocope family Kiaeriidae Schallreuter, 1984, but in the larger right valve (Copeland, 1974: P1. 9. fig. 18).



IV

Similar to a children’s puzzle in which numbered points must be connected to show a figure,

for reconstructions of phylogeny (‘evolutionary lines’) a certain number of points must be given

(basic number) to come to a solution approximating the probable path of evolution. Below the

basic number, attaining the real derivation is more or less accidental. The correct sorting of the

correct points is in this respect, of course, very important, especially at the beginning and this is

dependent to some degree on the ‘form feeling’ of the palaeontologist. The ‘sorting’ procedure

could be helped by recognising characteristically important features, such as dimorphic adventral

sculptures as in the examples mentioned above, or (in the case of the Ordovician metacopes) the

two stoppegs. In other groups such features may not be recognized or are maybe not present at

all; the deciphering of such sack genera (for example Bollia or Ulrichia) is therefore especially

difficult. In such cases more ‘points’ are necessary to connect the correct points, i.e. the basis

number is higher and more species (than in other groups) must be known. Unfortunately, the

relatively featureless forms present special problems and are especially neglected ; they tend to

be more seldom and less well described than the more ‘beautiful’ species rich in features. Furthermore, the more featureless (‘simpler’), the more danger of homeomorphic trends exists.



Homeomorphy, Phylogeny and Classification of Palaeozoic Ostracods 1041



V

The examples cited above demonstrate that, on one hand, uncritical hasty, wholesale generic

assignment or the aversion to erecting new monotypic genera both hinder the process of achieving

scientific ‘truth’; pragmatical ‘paths’ must be ‘refused’ as unscientific. On the other hand, the

over-hasty and uncritical establishment of new genera can sometimes also veil ‘real’ relationships

and other (for example palaeobiogeographic) connections (Schallreuter and Kruta, 1984; Schallreuter, Siveter and Kruta, 1984; Schallreuter and Siveter, 1985). Though time and energy consuming

and often viewed as relatively unattractive and unspectacular, careful taxonomy is absolutely

essentially to any serious palaeontological work. It is the basis for many further conclusions and

the edifice built on these conclusions stands or falls with the quality of the taxonomy.



VI (APPENDI

x)

Sometimes in some hollinids an additional spur occurs in the anterocentral region, besides the

anteroventral spur (Lethiers et al., 1985: P1. 9, figs. 25, 29). Such an isolated spur was observed

first by Becker (1968) in Nodella hamata. Becker called this spur a hamus, considered its occurrence

as a special kind of dimorphism (hamal dimorphism) and founded a whole suborder (Nodellocopina) on this kind of dimorphism. The assignment of the nodellids to the Palaeocopa or the

Hollininae was considered by Schallreuter (1 972 : 140; 1976: 234, 235). The evidence cited strengthened the understanding that the hamus and hamal dimorphism is only a special modification

or rudimentary form of the well documented hollinomorph antral dimorphism and is in this

respect comparable with the perimarginal dimorphism of the Primitiopsacea (Schallreuter, 1979:



735).

Thuringobolbina australis Reynolds, 1978 is very similar to Semibolbina (cf. Reynolds, 1978:

P1. 2, fig. 1 and Schallreuter, 1977: P1. 6, fig. 2). According to Reynolds (1978: 160) Thuringobolbina australis possesses a dolonate (botulate) antrum whereas in Semibolbina it is locular.

Schallreuter (1 974) placed Semibolbina in the Tetrasacculinae because of its spine-like posteroventral lobe; Thuringobolbina was placed within the Hollinini. T. australis possesses (like Semibolbina) a spine-like posteroventral lobe and belongs, therefore, in the Tetrasacculinae. The

holotype of the type-species of Thuringobolbina, T. thuringica, (Zagora, 1967: P1. 6, fig. 2) seems

not to be (as stated) a female valve, but a tecnomorph (or perhaps male) valve if compared with

corresponding figures in Reynolds (1978: P1. 2, fig. 2). The assumed male of Zagora (op. cit. PI.

6, fig. 2) presumably represents a larval valve. In larvae spine-like sculptures are often more

persistent than flange-like sculptures. The dimorphism of Thuringobolbina is therefore unknown.

The possibility exists that this genus is a junior synonym of Semibolbina. The designation of T.

australis is therefore questionable, A distinct difference between T. thuringica and T. ? australis

is the development of a second velar spur behind the anteroventral spur in front and ventrally

of the posteroventral spine in T.? australis (PI. 2, fig. 9).

BOTULATA n. gen., n. sp.

UVONHACHTIA



Derivatio nominis.-In honour of Ulrich Von Hacht, Hamburg, collector of the boulder with

the holotype (PI. 1, fig. 9) and alluding to the botulate antrum.

Diagnosis.-Unisulcate. With cristae copying the former quadrilobate design: L1 represented



1048 R. E. SCHALLREUTER



by two, L2 (at least ventrally) by one, L3/4 by three vertical ridges. C1 and C3/4 are united dorsally in cusps. Velum in 9 antero- and centroventrally as a flange-like dolon forming (with the

marginal area) an admarginal-dolonate botulus (antrum).

Relations.-The new genus is characterized by a botulate antrum in combination with its pattern

of cristae. Consonopsis Schallreuter, 1967 possesses a similar antrum, but has distinct lobes (L2,

L3) and fewer cristae (op. cit. fig. 4). Pleurodella resembles Uvonhachtia in lobation and cristation

but exhibits locular dimorphism (Schallreuter, 1978).

Occurrence.-Known only from an erratic boulder of the Isle of Sylt, Germany (Age: Keila

Stage, D2 of Estonia, Upper Viruan, middle Ordovician).



ACKNOWLEDGEMENTS

The author thanks Prof. Noriyuki Ikeya, and Prof. Tetsuro Hanai and the organisation committee of the 9th International Symposium on Ostracods for making participation at the congress

possible. Dr. David Siveter (University of Leicester) kindly read and corrected the manuscript.



REFERENCES

and JORDAN, H . 1971. Classification of Palaeocopid ostracodes belonging to the families Ctenoloculinidae, Hollinidae and Hollinellidae. In OERTLI, H.J. (ed.). Paleoecologie des Ostracodes. Bull. CenfreRech. PauSNPA, 5 SUPPI.,869-890.

COPELAND, M.J. 1974. Middle Ordovician Ostracoda from southwestern district of Mackenzie. Bull. Geol. Surv.

Canada, 244.

HENNINGSMOEN, G. 1953. Classification of Paleozoic stratight-hinged ostracods. Norsk Geol., 31, 185-290, 2 pls.

- 1965. On certain features of Palaeocope ostracodes. Geol. Foren. Stockholm Forh., 86, 329-334.

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JAANUSSON, v. 1957. Middle Ordovician ostracodes of central and southern Sweden. Ibid., 37 (3/4), 173-442,75 pls.

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MCKENZIE, K.G. 1982. Homoeomorphy : Persistant joker in the taxonomic pack, with the description of Brudleycypris

gen. nov. In BATE, R.H. et al. (eds.). Fossil and Recent Ostracods, 407-438. Ellis Horwood, Chichester.

OPIK, A. 1937. Ostracoda from ihe Ordovician Uhaku and Kukruse Formations of Estonia. Tartu iilikoofij.o.loodusuurijateseltsiaruanded(= Ann. SOC. rebus naturaeinvest. Univ. Tartu constitutne), 43 (1/2), 65-138,15 pls. [= Tar

tu iilikooli geo1.-inst. toimetused (= Publ. Geol. Inst. Univ. Tartu), 50.

REYNOLDS, L. 1978. The taxonomy and palaeoecology of ostracodes from the Devonian Receptaculites Limestone,

Taemas, New South Wales, Australia. Pulueontographica (A), 162 (3/6), 144-203, pls. 33-46.

ROZHDESTVENSKAYA, A.A. 1972. Ostrakody verchnego devona Baskirii. Moskva (Nauka).

SCHALLREUTER, R. 1966. Zur Taxonomie und Phylogenie der OstrakodenfamilieTetradellidae Swartz, 1936 (Palaeocopina, Hollinacea) und eine neue Familie der Hollinacea. Geologie. 15 (7), 846-875.

-1967. Postskriptum zur Taxonomie der Tetradellidae (Ostracoda). N . Jb. Geol. Palaont. Mh., 7 , 431-446.

- 1972. Drepanellacea (Ostracoda, Beyrichicopida) aus mittelordovizischen Backsteinkalkgeschioben IV. Laterophores hystrix sp. n., Pedomphallella germanica sp. n. und Easchmidtella fragosa (Neckaja). Ber. dt. Ges.

geol. Wiss., (A) 17(1), 139-145, 165-166.

- (1974). The Ostracode Family Hollinidae. Rev. ESP. Micropaleont., 6(2), 163-172.

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BLESS, M.J.M.



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- 1977. Taxonomie und Phylogenie der palaozoischen Ostrakodengattung Semibolbina Jordan. Palaont. Z., 51

(1/2), 32-51.

- 1978. On Tetradella pentaloculata Schallreuter sp. nov. Stereo-Atlas Ostracod Shells, 5 (I), 65-72.

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-__

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~



DISCUSSION

Adamczak: Your Ordovician podocopids with the duplicature are a peculiar fauna in which

this element (the duplicature) is presumably an artefact. I have never seen a Silurian podocope

ostracod (and I have seen thousands of them in thin sections) with a duplicature.

The stop-ridge is an element which appears in many genera of podocopids but it has, in some

only, a selective value.

Schallreuter: The duplicature in my specimens is certainly not an artefact. It occurs in certain

species only and in these species in nearly all (adult) specimens (sometimes hundreds of valves).

whereas in other sympatric podocopes (metacopes) it does not.

The stop-ridges (stop-pegs) in the Ordovician metacopes are so persistent that I consider that

this feature is an important one. I observed it in many genera, for example, Kroemmelbeinia, Balticella, Steuslofina, Duplicristatia, Bulbosclerites, Pachydomelloides, Longiscula, Trianguloschmidtella,

Platyrhomboides, Rectella, Medianella and others.



This Page Intentionally Left Blank



Is Neckajatia an Ancestor of the Platycope Ostracodes?



ROBERT

F. LUNDIN

Arizona State University, Tempe, U.S.A.



ABSTRACT

Neckujutiu Schallreuter, 1974 and a closely related genus are known from a complex of at least

four species from the Silurian of Gotland, Great Britain (where the related genus has been recorded

as species of Primitiu), Podolia and the eastern Baltic states of the U.S.S.R. The oldest of these

species, N . modestu Neckaja, 1958, occurs in rocks older than the rocks which yield the oldest true

platycopes which are from the upper Llandoverian of Gotland and Estonia. Neckajutiu and the

related genus possess characters which are basic to the definition of the platycope ostracodes, but

lack others which are equally fundamental to that definition. The combination of characters, which

is a) right-over-left overlap, b) a contact groove along all or most of the free margin of the right

valve, c) a relatively long straight hinge with a groove in the right valve hinge, d) poorly-developed

straguloid processes, but e) the absence of any well-defined dimorphic characters, suggests Neckujutiu and related forms are a primitive stock from which the platycopes evolved. It is suggested

that this occurred through reduction of the straight hinge, improvement of the contact groove

(holoselenic groove) in the right valve and introduction of a distinctive domiciliar dimorphism.

Present knowledge indicates that this occurred during the Llandoverian.



INTRODUCTION

Neckujutiu Schallreuter, 1974 is based upon Althu modestu Neckaja, 1958; designated the

latter as the types species for the genus Althu Neckaja, 1958, which is a junior homonym of Altha

Walker, 1862, an insect (Schallreuter, 1974; see also Schallreuter, 1975). Neckaja (1958) also

described another species, Althu latu Neckaja, 1958, but since that time references to the genus

have primarily had to do with stratigraphical occurrences of these species. Pranskevichius (1972)

added another species, A . minima, to the genus. The genus is well-represented in the Silurian of

Gotland and the Welsh Borderland and a study of well-preserved materials from these areas as well

as from the Soviet Union demonstrates that Neckujutiu has characteristics which are basic to the

definition of the Platycopa, whereas it lacks other characteristics which are equally fundamental

to that definition.

In a classical study of the functional morphology of the shell of platycope ostracodes, Jaanusson

(1985) has pointed out that the basic shell characteristics of the platycopes were already well

established in the earliest (late Llandoverian) true members of the suborder. Since the early Silurian,

only minor changes in the adductor muscle scars and extent of the domatium and details of the

1051



1052 R. F. LUNDIN



arrangement of eggs in it have occurred (Jaanusson, 1985, p. 81, 82). Through his analysis of the

modern cytherellid platycope Cytherella abyssorurn G. 0. Sars, Jaanusson explained, from the

standpoint of the functional morphology of the carapace, the reasons for the very conservative

phylogeny of this group once it came into existence. On the other hand, neither Jaanusson (1985)

nor other authors have discussed in detail the ancestors of the platycope ostracodes. It has been

generally supposed that the kloedenellacean ostracodes represent the roots of the platycopes (see

Guber and Jaanusson, 1964, p. 9; Adamczak, 1966, p. 13; and Schallreuter, 1968, p. 128).



REPOSITORIES

Ostracodes illustrated in this paper are housed in the type collections of the Department of

Geology at Arizona State University (ASU X). Sample numbers used in the plate explanations

have the prefix “MS” or “RFL”.



PURPOSE

In view of the above, the purpose of this paper is to evaluate the morphoiogy of Neckajatiu

and a related genus and compare that morphology to the morphology of the platycope ostracods.

This will provide a basis for the conclusion arrived at here, that Neckajatia is ancestral to the

Platycopa. It is not the purpose of this paper to undertake species level taxonomic revision or even

to describe and/or illustrate all species of the genera involved. Accordingly, my observations and

conclusions are based upon a few forms which demonstrate the important morphological characters.



THEPLATYCOPA

The platycope ostracodes have the following combination of shell characteristics which are

diagnostic for the group :

1) The right valve is larger than the left and overlaps it along all or nearly all of the free margin.

The overlap may be reduced anteriorly.

2) The contact structure along the free margin consists of a groove in the right valve into which

the edge of the left valve fits. The contact groove may be reduced or even absent anteriorly in some

species (Adamczak, 1968, p. 30; Jaanusson, 1985, p. 74).

3) The hinge is also an edge and groove arrangement, the groove being in the right valve into

which the edge of the left valve hinge fits. The detailed morphology of the hinge is somewhat

variable but the hinge groove of the right valve is, in all cases, to a greater or lesser degree a conPLATE1-Figs.



1-3, 5, 6,9. Neckujutiu modesfa (Neckaja). 1,2, 9. Right lateral ( x 71), ventral ( x 78) and slightly

oblique dorsal (anterior two-thirds of specimen, x 126) views of adult carapace (ASU X-73): note R/L overlap

and anterior straguloid process (fig. 9). 3. Dorsal view ( x 83) of adult carapace (ASU X-74). 5. Interior view

( X 92) of adult left valve (ASU X-75). 6. Interior view ( X 83) of adult right valve (ASU X-76) to show contact

groove and straight hinge. All specimens from the Silurian at Nyharnn, Gotland (MS 17). Figs. 4,7. Neckujutiu

h f u(Neckaja). Dorsal ( x 56, ASU X-77) and right lateral ( x 68, ASU X-78) views of adult carapaces from the

Silurian (early Wenlockian, Jaani Stage) of Estonia : note R/L overlap and anterior and posterior straguloid

processes. Fig. 8. “Primitiu” vuriolufu Jones and Holl. Ventral view ( x 72) of adult carapace (ASU X-81) from

the Silurian Much Wenlock Ls. Fm. at Lincoln Hill (RFL # 13), Welsh Borderland, showing R/L overlap

(anterior end abraded). Figs. 10, 11. Neckujufiu cf. N. lutu (Neckaja). Interior views of parts of adult left

( X 123, ASU X-79) and right ( x 132, ASU X-80) valves from the Silurian Mulde Beds at Dapps, Gotland

(RFL 1970) to show hinge details.



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Chapter 71. Homeomorphy, phylogeny and natural classification: Case studies involving Palaeozoic ostracods

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