Origins and dispersal of a brachiopod family - the systematics, biogeography and evolution of the Family Terebratellidae

13 Pages·1994·4.7 MB·

by  J R Richardson

ORIGINS AND DISPERSAL OF A BRACHIOPOD FAMILY-THE SYSTEMATICS,
BIOGEOGRAPHY AND EVOLUTION OF THE FAMILY TEREBRATELLIDAE
J. R. Richardson
Museum of Victoria, 328 Swanston Street, Melbourne, Victoria 3000
Richardson, J. R., 1994:12:31. Origins and dispersal of a brachiopod family—the systcmatics,
biogeography and evolution of the Family Terebratellidae. Proceedings of the Royal Society
of Victoria 106: 17-29. ISSN 0035-9211.
Three southern subfamilies of the Terebratellidae (Bouchardiinae, Anakineticinae,
Terebratellinae) are redefined using cardinal process shape and presence or absence of some
components of the cardinalia (crural bases, hinge plates). The subfamilies are confined to the
seas around Gondwana-derived land masses between Antarctic shorelines and latitudes of
approximately 30°S and, with the exception of 2 Late Cretaceous genera, to the Cainozoic
era. Species without adaptations for particular substrates in Antarctica, the subantarctic islands,
Australia, New Zealand and South America show certain similarities suggesting that they were
derived by vicariance from generalist stocks which occupied some sections of the shorelines
and shelf of Gondwana. This record of the Terebratellidae does not conform with the only
current model for brachiopod distribution (Zezina 1985) —that seas in low latitudes have provided
both a cradle and refuge for inarticulates and articulates.
THE PHYLUM Brachiopoda provides a record of The abundance of living members of the family
life on earth that is remarkable in the history of in these areas has provided information on the
its 2 divisions, one of which (Inarticulata) is static, variability of populations in most parts of its range
the other (Articulata) repetitive (Cooper 1970; and on factors that govern distribution. In add¬
Rudwick 1970). Despite the excellence (in length, ition many species arc sufficiently accessible for
continuity and abundance) and clarity of the the direct study of substrate relationships and
record, studies have yielded little information on behaviour. These studies of the living together with
the processes of macroevolution or on the nature the rich Tertiary faunas of Australia and New
of relationships within the phylum. Difficulties in Zealand mean that sufficient data are now avail¬
utilising the record can be attributed in large part able about the members of one family to enable
to the lack of knowledge of the variability of living speculation on the centres of origin of species, on
populations and so of the nature of relationships paths and rates of dispersal, and on relationships
between species —one consequence of the inaccess¬ among genera.
ibility of living species in many parts of the world.
For example. New Zealand is the only country
known in which species of polytypic genera are SYSTEMATICS
known to be accessible to direct study.
Superfamily Terebratelloidea King, 1850
During the last 2 decades studies of the members
of one family, the Terebratellidae, have given Family Terebratellidae King, 1850
greater biological understanding of articulate
Diagnosis. Non-strophic Terebratellacea without
brachiopods. This family provides more infor¬
spicules and dental plates and in which lateral
mation than others because it is the only one in
connecting bands are formed during development
which living outnumber fossil genera and because
of the loop. Upper Cretaceous to Recent.
of the abundance of its members in the Southern
Hemisphere. In the Ross Sea, for example, Foster
(1974, 1989) has observed that brachiopods out¬ Subfamily Bouchardiinae Allan 1940
number bivalve molluscs. They are common to
Diagnosis. Silicate, posteriorly thickened smooth
abundant in the Magellanic province of South
Terebratellidae with a hypothyrid or epithyrid
America (McCammon 1973; Cooper 1973), the
foramen, and with cardinalia consisting of socket
subantarctic waters of the Atlantic (Cooper 1982)
ridges and a cardinal process with a bilobed
and Indian (Cooper 1981) oceans and in the sands
posterior surface.
of the shelf of southern Australia (Richardson
1987). In New Zealand they are dominant members Genera included. Bouchardia Davidson, 1850;
of the benthos of many southern inlets and of all Bouchardiella Doello-Jurado, 1922; Malleia Thom¬
the fiords (Richardson 1981a). son, 1927; Neobouchardia Thomson, 1927.
17
18 J. R. RICHARDSON
Distribution. Cretaceous-Recent; Australia, New Distribution. Upper Cretaceous-Recent. South¬
Zealand, Antarctica, South America. ern Hemisphere between Antarctic shelf and
latitudes of approximately 35°.
Subfamily Anakineticinac Richardson 1991 Comments. Foster (1974), in a comprehensive
study of Recent terebratellid species from the
Diagnosis. Rectimarginate to sulcate, posteriorly
Southern Hemisphere, differentiated genera within
thickened, smooth Terebratellidae with permeso-
the Terebratellidae on loop form. He stated that
thyrid foramen, cardinalia consisting of socket
use of the loop seemed artificial but that it was
ridges, crural bases and a cardinal process with
the simplest means of classification in such a large
trifid posterior surface.
group with ‘the limited number of morphological
Genera included. Anakinetica Richardson, 1987; features of apparent taxonomic value, the high
Adnatida Richardson, 1991; Aliquantula Richard¬ degree of variability within individual species, the
son, 1991; Australiarcula Elliott, 1959; Elderra great amount of apparent convergence, and the
Richardson, 1991; Magadina Thomson, 1915; poorly known fossil record’ (1974, p. 97).
Magadinella Thomson, 1915; Parakinetica Rich¬ Work on Australian Tertiary Terebratellidae
ardson, 1987; Pilkena Richardson, 1991; Pirothyris (Richardson 1973, 1980, 1991) has clarified re¬
Thomson, 1927; Rhizothyris Thomson, 1915. lationships within the family to some extent in
that three of the subfamilies (Bouchardiinae,
Distribution. Cretaceous-Recent; Australia, New
Anakineticinae, Terebratellinae) can now be de¬
Zealand.
fined with greater precision using components that
make up the cardinalia. The subfamily Ncothyrinae
Subfamily Terebratellinae King 1850 is not retained because both Foster (1974) and
Richardson (1975, 1980) have shown that the
Diagnosis. Rectimarginate to sulcate to intra-
characters used by Allan (1940) to distinguish
plicate, smooth or costate Terebratellidae with
members of the subfamily (bifurcated septum and
cardinalia consisting of socket ridges, crural bases,
a hinge trough) are a consequence of the differential
hinge plates and a transverse cardinal process,
thickening of inner hinge plates; i.e. the Neo-
posterior thickening present or absent.
thyrinae was erected for genera that differ from
Genera included. Aero thyris Allan, 1939; Anebo- those included in the Terebratellinae only in degrees
concha Cooper, 1973; Austrothyris Allan, 1939; of calcification (Figs 1, 2).
Calloria Cooper & Lee 1993; Allan, 1939; Diedro- The other subfamily (Trigonoseminae) referred
thyris Richardson, 1980; Dyscritosia Cooper, 1982; to the Terebratellidae by Elliott (1965) includes
Fosteria Zezina, 1980; Gyro thyris Thomson, 1918; three genera from Upper Cretaceous deposits in
Jaffaia Thomson, 1927; Magasella Dali, 1870; Europe, North America and Western Asia. Loop
Magella Thomson, 1915; Mage/lania Bayle, 1880; characters indicate that it should be assigned to
Neothyris Douville, 1879; Pachymagas Ihering, the Terebratellidae but the nature of its relationship
1903; Stethothyris Thomson, 1918; Syntomaria to southern subfamilies is difficult to determine
Cooper, 1982; Terebratella d’Orbigny, 1846; Vic- without study of the cardinalia of juvenile speci¬
torithyris Allan 1940; Waiparia Thomson 1920. mens. Descriptions of the genera included in the
Fig. 1. Outline drawings of the cardinalia to show areas of attachment of the diductor and dorsal adjustor
muscles in representative adults of the 3 terebratellid subfamilies — Bouchardiinae (Bouchardia rosea), Anakineticinae
{Anakinetica cumingi), Terebratellinae {Magasella sanguinea).
ORIGINS AND DISPERSAL OF TEREBRATELLIDAE 19
Trigonoseminae indicate that, like the Anakine- trate differences in the cardinalia that distinguish
ticinae and free-living Bouchardiinae, the cardinalia the 3 southern subfamilies. They differ in cardinal
are thickened and without hinge plates but other¬ process shape (bilobed, trifid, transverse), in the
wise they do not resemble any southern taxa. presence or absence of hinge plates and in the areas
Furthermore, neither cardinalia nor the cardinal used for the attachment of the dorsal adjustor
process appear to be consistent in form within the muscles. In the Terebratellinae these muscles are
subfamily. attached anterior to the cardinal process and to
In the classification proposed herein, precedence hinge plates which occupy the area bounded by
is given to those characters associated with the the socket ridges. In the Anakineticinae and
substrate relationships of a species for 3 reasons: Bouchardiinae the muscles are attached to respec¬
1. Variability of the pedicle system. The ped¬ tively pits and furrows that flank the cardinal
icle system may vary intra- and interspecifically and process. The pits of the Anakineticinae are con¬
within and between all higher taxa (Richardson fined to the posterior part of the platform, the
1981) whereas other soft parts (gut form, numbers furrows of the Bouchardiinae extend the length of
of coelomoducts) may differ between orders but the platform. Differences in function associated
appear to be consistent in form and function in with the position of attachment of the muscles
the members of each order. are described under substrate relationships. The
2. Functional morphology. Features of the absence of crural bases in the Bouchardiinae is
shell used in classification are directly related to linked to the absence of descending branches of
differences in the pedicle system and therefore to the loop which consists of a ring supported by a
substrate relationships. They are: high median septum.
the beak and cardinalia that house and therefore The hinge plates that characterise the Tere¬
reflect any differences in the pedicle system, e.g. bratellinae occupy the area bounded by the socket
the area of attachment of the dorsal adjustor ridges. Hinge plates also differentiate genera within
muscles differentiates forms with a free or the subfamily according to their relationship with
bonded pedicle (Figs 1, 2, 3); crural bases, socket ridges, median septum, and
the size of the cardinal process which is deter¬ whether they are lamellar or solid, excavate or
mined by the area of attachment required by sessile i.e., adpressed to the valve floor.
the diductor muscles. The size of the process in The common pattern of the cardinalia in living
free forms indicates that greater leverage is terebratellinids is one in which the socket ridges
needed to open the shell in free than in fixed and crural bases are fused or confluent or are
forms; and narrowly separated by outer hinge plates with
differential thickening which is found in free inner hinge plates meeting on the septum. In these
forms only and is the means by which the shell species the crural bases are traces of the crura.
is stabilised and oriented. In two Recent species, Magellania joubini and
3. Species of polytypic genera and populations Magellania fragilis, the crural bases separate inner
of species studied show that they are differentiated and outer hinge plates which are roughly equal in
on characters reflecting differences in substrate width. In this character, the hinge plates are similar
relationships, e.g. the free and sedentary popu¬ to those in the Tertiary genera, Diedrothyris and
lations of Calloria inconspicua and of Magasella Stethothyris. The crural bases of Austrothyris and
sanguinea (Aldridge 1981; Stewart 1981) and Cudmorella (Fig. 3C) differ from those of all other
species of Neothyris (Aldridge 1991). genera in that they are prominent structures with
Some families of the Terebratellidae (Laqueidae, sharp ridges which, in ventral view, project above
Dallinidae, Terebratellidae) arc differentiated on the level of the hinge plates. In these genera also
the nature of loop development but the stage of the inner hinge plates are adpressed to the valve
development does not define lower categories. floor and extend onto the median septum for
Adult loop patterns within a family appear to be approximately half its length. Foster (1974) has
correlated with the amount of space available noted that the hinge plates of Aerothyris kergue-
within the mantle cavity since no species with a /crisis vary in position, most are sessile, others are
large mantle cavity is known with an axial loop excavate. The significance of differences in the
and no species with a small mantle cavity is known position and prominence of crural bases and in
with a teloform loop. From studies of Mesozoic the angle at which hinge plates lie relative to the
Terebratelloidea, Owen (1977) has also stressed the valve floor and septum is unknown. Richardson
importance of the cardinalia in defining taxa at & Mineur (1981) compared the hinge plates of
subfamily levels. Magasella sanguinea with those of Calloria incon¬
The cardinalia and classification. Figs 1-3 illus¬ spicua and concluded that the greater elevation of
20 J. R. RICHARDSON
the plates of the former species was related directly The cardinal process of the Bouchardiinae is bi~
to the line of action of the dorsal adjustor muscles lobed with the posterior striated surface extending
and indirectly to shell curvature and to beak and as an inverted V from the posterior tip of the dorsal
pedicle size. Analyses of hinge plate condition in valve. Differences in the extent of the lobes in
relation to the functioning of the dorsal adjustor different genera are presumably associated with life
muscles in other species would be a productive style. Bouchardia is a free living form with a
study. free pedicle which probably functions in similar
Fig. 2. Dorsal valve interiors of species from the subfamilies Bouchardiinae and Anakineticinae which show
differences in the cardinal process and in the areas used for attachment of the dorsal adjustor muscles. A, B,
Malleia portlandica (x 12) and Bouchardia rosea (x 5) (Bouchardiinae) with bilobed cardinal processes and with
areas of attachment of the dorsal adjustor muscles lying between the socket ridges and the cardinal process.
C, D, Anakinetica cumingi (Anakineticinae), young (x 30) and adult ( x 5) specimens with trifid cardinal processes
and attachment for the dorsal adjustor muscles at the antero-lateral corners of the posterior surface of the
cardinal process.
ORIGINS AND DISPERSAL OF TEREBRATELLIDAE 21
ratchet-like fashion to that of Anakinetica. Malleia sists of three surfaces approximately equal in size,
(Tertiary) was probably sedentary in habit in that two lateral surfaces flanking one ventrally facing
its small size and beak, plano-convex shape and median surface.
hypothyrid foramen are features associated with The cardinal process of most of the species
fixed forms in modern seas. included in the Terebratellinae is transverse with
The striated posterior surface of the cardinal a median notch at the junction of the striated
process of the Anakineticinae is trifid, i.e. it con¬ posterior and smooth anterior surfaces. The car-
Fig. 3. Dorsal valve interiors of species of terebratellinae genera which illustrate cardinal process shape (trans¬
verse), differences in the disposition of hinge plates which provide areas of attachment of the dorsal adjustor
muscles, and the effects of differential thickening on the appearance of the cardinalia. A, Neothyris lenticuluris
juvenile (x 30). 13, Stethothyris pectoralis (x 6) juvenile in which crural bases separate inner and outer hinge plates.
C, Cudmorella corioensis (x3) juvenile in which crural bases with sharp ridges project above the level of the
hinge plates and in which inner hinge plates extend anteriorly onto the septum. D, Cudmorella corioensis adult
(x 1.5) in which differential thickening gives a superficial appearance of bifurcation of the septum.
22 J. R. RICHARDSON
dinal processes of young specimens of Anakinetica many species and, since members of the species
cumingi and Neothyris lenticularis (Figs 2C, 3A) are small, separation on this one morphological
show the differences in shape characteristics of feature may not be justifiable.) There seems little
the two subfamilies. In terebratelline species with doubt, as recommended by Cooper (1981) that
differential thickening, the anterior surface of the M. flavescens (the type species) and M. venosa
cardinal process is large and may be globose or should be in different genera and it would be
columnar in outline. Neothyris lenticularis, in desirable if a worker with access to good collections
particular, shows great variability in the shape of Magellania venosa would take this step. Foster
of the process and, as noted by Foster (1974), (1989) states that a better understanding of this
specimens may display lateral flanges with strong species is essential in order to evaluate the number
inwards curvature and a trefoil posterior surface. of similar species that occur in the same area and
Similar convergent trends have been described by which may be variants of M. venosa. They include
Cooper for the Productacea ‘Each of the major species of Aneboconcha, Syntomaria and Dys-
families of the Productacea has its own type of critosia. Until such a study can be undertaken,
cardinal process, characteristic of the family morphological and distributional patterns suggest
as shown by young or young adults but in old that the most natural grouping of these species
age all tend toward a common trilobed cardinal would be as follows:
process’ (1969, p. 229). 1. Magellania flavescens.
2. Aerothyris macquariensis and A. kerguelensis.
Morphological variability. The genera included 3. Magellania venosa, M. joubini, M. fragilis,
in the Bouchardiinae and Anakineticinae can be Fosteria spinosa, Aneboconcha obscura, Dvs~
clearly defined but the variability of species within critosia secret a, Syntomaria curiosa.
the Terebratellinae make generic separation diffi¬ Magellania flavescens is distinguished from all
cult as noted by Foster (1974, 1989) and by Cooper other species by beak characters (long with deltidial
from his studies of species from the subantarctic plates invariably fused with a round mesothyrid
waters of the Atlantic (1982) and Indian (1981) foramen) and ornament. Species of Aerothyris are
oceans. smooth with a short beak, a keyhole mesothyrid
The genera included in the Terebratellinae are foramen and short deltidial plates which are
similar in folding, sulcate to intraplicate; foramen commonly but not invariably disjunct. The third
position lies within the range submesothyrid-meso- group includes smooth forms with a short beak,
thyrid-pcrmesothyrid; the loop is cither free or submesothyrid to mesothyrid foramina and del¬
with transverse bands connecting the descending tidial plates that are short and commonly con¬
branches and the septum; the shell may be smooth, junct in species that are moderate to large in size
partially or fully ribbed. The only consistent (Magellania venosa, M. joubini, M. fragilis)
associations of characters appear to be foramen and rudimentary in species that are small in
type with shell thickness, a submesothyrid foramen size (Fosteria spinosa, Aneboconcha smithi, A.
with an unthickened shell and a permesothyrid obscura, Syntomaria curiosa, Dyscritosia secret a).
foramen with a thickened shell (thick shells how¬ Pirothyris was included in the Anakineticinae
ever are not necessarily permesothyrid). The shells (Richardson 1991) on the form of the cardinal
of species with a mesothyrid foramen may be process although earlier studies on the develop¬
differentially thickened (Neothyris, all species), ment of P. vercoi (Richardson 1975) had shown
unthickened (Magellania flavescens, M. fragilis, that inner hinge plates form and thicken early in
M. joubini) or variable in thickening (Magellania ontogeny. Pirothyris is an atypical terebratellid with
macquariensis, M. kerguelensis, M. venosa, links to the Terebratuloidea in shell shape (depth
Terebratella dor sat a). greater than width) and folding (uniplicate) and
The difficulties in separating terebratelline line¬ cases could be made for including it in either the
ages is well illustrated by those species which have Anakineticinae or the Terebratellinae.
been attributed to Magellania by Foster (1974,
1989). Cooper (1981) considers that the species
SUBSTRATE RELATIONSHIPS
macquariensis and kerguelensis should be placed in
Aerothyris and Zezina (1985) has placed spinosa Knowledge of the substrate relationships of species
in her new monotypic genus Fosteria. (Foster, in is of the greatest importance in any family study
1974, had described the species as very similar to firstly because distribution is governed by the
M. fragilis and M. joubini except in the possession capacities of different species to colonise sub¬
of spinose descending branches. Spinosity occurs strates, secondly because of the strength of the
to a varying extent in the loop development of correlation between substrate type, morphology
ORIGINS AND DISPERSAL OF TEREBRATELLIDAE 23
and life style. The strength of this association in which the components vary in size; e.g. the till of
articulate brachiopods is evident in the numerous Antarctic shelves. They may also be retrieved,
instances of homeomorphy they provide. although not in large numbers, from shelf sedi¬
All terebratellid species are pediculate but they ments of more uniform grain size. For example,
differ in relationships with the substrate and these the distribution of Magel/ania flavescens on shelf
differences are evident in the variability of the sediments has been studied in southern Australia
pedicle and of its housing —the beak and cardinalia. where the middle and outer shelf is covered with
Some species are generalist in character and occupy bryozoan sands. M. flavescens has been dredged
an apparently unlimited range of substrates, others from this area together with forms specialised
are highly specialised forms which function only for this particular sediment (Richardson 1987).
in a particular type of sediment. However, collections by scuba in this high energy
Species defined as generalist have the capacity environment show that M. flavescens occurs only
to settle and survive on substrates of any size. In as a sedentary form, individuals being bonded to
these species the pedicle functions as a pivot when the scattered reefs and outcrops that occur on the
bonded with large substrates and as a moving shelf. Specimens from these areas are smaller and
part when bonded with small (Richardson 1986). squatter than individuals from shoreline habitats.
Therefore life style varies according to the size of Of the living terebratellid species studied none,
the substrate used for settlement, bondage with a like the micromorphic members of the Kraus-
large substrate such as a rock lace resulting in a sinidae, Megathyrididae and Platidiidac are ex¬
sedentary life style, bondage with a small (relative clusively sedentary in habit. All members of the
to shell size) substrate in free life on the sea floor. Bouchardiinae and Anakineticinae are free forms
The movement of either the shell or the pedicle specialised for life in bryozoan sands. Members
(with its bonded substrate) prevents the build-up of the Terebratcllinae are more varied morpho¬
of sediment on the shell surface. The phrase logically and less specialised in life style. Two
‘bonded substrate' is used in preference to ‘attached genera, Neothyris and Gyrothyris, arc free forms
substrate' because of the confusion associated with which do not appear to be specific to a particular
the latter. The word ‘attach’ has been used to des¬ sediment, they are invariably thickened with a
cribe the union between the pedicle and substrate mesothyrid foramen and a variably curved beak.
and also as an adjective synonymous with pedicu¬ The remaining taxa are generalist to the extent that
late and sedentary, i.e. an attached brachiopod. they appear to live as either free or sedentary
Many adult articulates retain the larval substrate individuals but shape, size range, pattern of distri¬
but live as free forms on soft sediments and bution all indicate tendencies towards one or other
would therefore be described as both permanently life style. For example, Magasella sanguinea is as
attached and free. Thus, ‘attach’ and all its deri¬ common on soft sea floors as it is on hard sub¬
vatives perpetuate the falsity of the assumption that strates, whereas species of Calloria are more
articulate brachiopods are uniform in life style and commonly found (Stewart 1981; Doherty 1979)
that free brachiopods are ‘fallen’ forms. on rocky substrates. Stewart has shown that
The generalist species most extensively studied differences in the habitats of populations of C.
in situ is Magasella sanguined (Richardson 1981a, inconspicua are also evident in the mean size and
1981b; Foster 1989). It is a common inhabitant of shape of individuals.
shallow subtidal waters in New Zealand, both on All other tercbratelline taxa are known from
rock faces (sedentary individuals) and the sea floor dredged material only. Species of Aerothyris,
(free individuals) where it is as common in mud Magellania venosa, Terebratella dorsata are all
as in coarser sediments. Free individuals are found variably thickened which would suggest that they
lying on either valve. The shell is invariably un¬ occur predominately, if not exclusively, on soft
thickened, biconvex, the beak short with a large sediments. They are not as specialised for free life
submesothyrid to mesothyrid foramen. It is highly as species of Neothyris and Gyrothyris in which
variable in shape and size and, in these and other shell thickening is of early inception and invariably
attributes, closely resembles Terebratalia transversa present. Unthickened dredged forms (Syntomaria,
(Schumann 1991) and T. coreanica (Richardson Aneboconcha, Dyscritosia) occur in the size range
et al. 1989), examples of generalist species from recorded for Calloria. They were collected (Cooper
the Laqueidac and which occupy eastern and 1982) from the vicinity of islands in the South
western shorelines of the northern Pacific Ocean. Atlantic and Foster (1989) considers that they may
Generalists are found in areas in which sites represent young populations of Magellania venosa.
for settlement show a wide variation in size; i.e. Differences in the capacity for colonisation are
they occupy shoreline areas or shelf sediments in important to note in any studies of dispersal. Since
24 J. R. RICHARDSON
generalists have the capacity to colonise substrates slope. Terebratella dorsata commonly occurs with
of any type they are also less affected by environ¬ Magellania venosa on the shelf but has not been
mental events that cause changes in substrates. recorded from the slope.
Specialists can colonise only those substrates All terebratelline species appear to live on varied
that they are morphologically adapted to occupy. shelf substrates and in situ observations in Aus-
The patterns of settlement and survival in one tralian and New Zealand waters show that they may
area illustrate the latter point. New Zealand’s be occupied by free (.Neothyris, Gyrothyris) or free
Paterson Inlet contains 4 species all of which settle and/or sedentary forms (Magellania flavescens>
at random on surfaces of any size and composition Magasella sanguined, Calloria inconspicua). The
(Richardson 1981a). Only the generalists (Magasella sites from which Aerothyris kerguelensis has been
sanguined and Calloria inconspicua) survive as collected are recorded (Cooper 1981) as gravels,
adults on larval substrates of any size, one species coarse and fine sands and muds. The greater part
(Notosaria nigricans) is restricted to large sub¬ of the Ross Sea shelf is covered with till —unsorted
strates, the other (Neothyris lenticularis) to small. material ranging from rock flour to boulders.
Fossil members of the Bouchardiinae and Ana-
kincticinae occupy the same type of sediment in
DISTRIBUTION
the same geographical areas as living members.
With the exception of the Trigonoseminae, the Bouchardia rosea, the only living species of the
subfamilies of the Terebratellidae are confined Bouchardiinae, occurs in bryozoan sands off Brazil
to the Southern Hemisphere between Antarctic (Tommasi 1970). Mancenido & Griffin (1988) note
shorelines and latitudes of approximately 30°S that records of the genus range from Palaeogene
and, with the exception of 2 genera, to the (palaeolatitudes of 75°S to Neogene of 45°S) and
Cainozoic era. The subfamilies Bouchardiinae and that the present position of the genus at 35°S
Anakineticinae contain a larger number of fossil indicates displacement in a northward direction
than living genera while the Terebratellinae con¬ along the eastern margin of South America. The
tains more living than fossil. The earliest fossil distribution of one memb_e r o< f the Bouchardiinae,*
genera of the Bouchardiinae (Bouchardiella) and Neobouchardia minima, is significant — it has not
the Anakineticinae (Australiarcula) occur in the been recorded from modern seas but conspecific
Cretaceous while the Australian Eocene genus populations occur in the Oligocene-Pliocene of
Diedrothyris is the oldest terebratelline known. both New Zealand and Australia (Richardson
Living Bouchardiinae occur only in Brazil, Ana- 1973).
kineticinae in Australia while the Terebratellinae Living anakincticinids are found only in the
occur around the coasts and on the shelves of all bryozoan sands of the southern Australian shelf
land masses found between the Antarctic and and these communities replicate those found in
latitudes of 35°S. Australian Eocene-Pliocene calcarenites (Richard¬
Foster (1974) showed that members of the son 1991). New Zealand Oligocene deposits contain
Terebratellinae exist in very large numbers in the numerous species of each of 2 anakineticinid
Southern Hemisphere in areas shallower than genera, Magadina and Rhizothyris, none of which
1000 in and noted that Magellania fragi/is and have survived the reduction of shallow marine
M. joubini are the most prominent species on the shelf environments during regressive phases in the
entire antarctic shelf. The map of distribution Miocene. Like the Australian anakineticinid genera
(Fig. 4) of the Terebratellinae is derived from they were forms that were specific to carbonate
Foster’s figure (1974, p. 31) and has been extended sands.
to include the Australian species Magellania New Zealand is the most valuable source of
flavescens and Cooper’s genera Dyscritosia, Ane- information on the distribution of living and
boconcha, Syntomaria and Calloria. fossil Terebratellinae. In the first place, all those
The bathymetic range at which many species are genera with living species also occur in Tertiary
found may be correlated with shelf depth. For deposits, secondly, abundant fossil deposits (shelly
example, the Ross Sea shelf is wide and deep (100 limestones) contain aggregates of species that
to 1000 m) and species occur at all depths. The replicate the brachiopod assemblages found in
New Zealand shelf and neighbouring rises habitats on modern rocky shorelines (Richardson
(Chatham Rise, Campbell Plateau) rarely exceed 1984). Similar deposits are rare components of the
depths of 400 m. Magellania venosa is most fossil record in other parts of the world. Two
common at shelf depths approximately 300 m) groups of genera can be distinguished in the New
but has been recorded from 5 to 1900 m and is Zealand record. The first consists of extinct genera
the only terebratelline species known from the (Waiparia, Stethothyris, Pachymagas) all of which
ORIGINS AND DISPERSAL OF TEREBRATELLIDAE 25
show the morphological characteristics of forms and Tertiary species (Magasella, Calloria) which
specialised for a free life and which are known only are common at or near modern rocky shorelines
from the Late Oligocene to Middle Miocene. The and in Eocene and Oligocene shelly limestones
second group consists of genera with both living (Allan 1960; Richardson 1984). Species of Neo-
Fig. 4. Distribution of the species of the subfamily Terebratellinae from the records of Cooper (1973, 1981,
1982), Cooper & Doherty (1993), Foster (1974, 1989), McCammon (1973), Richardson (1981a, 1987).
1, Magellanic! joubini; 2, Magellania fragilis; 3, Fosteria spinosa; 4, Terebratella dorsala; 5, Magellanic! venosa;
6, Aneboconcha obscura; 7, Calloria inconspicua; 8, Magasella sanguinea; 9, Neothyris lenticularis; 10, Synlomarla
curiosa; 11, Dyscritosia secreta\ 12, Calloria variegala; 13, Magasella haurakiensis; 14, Neothyris conipressa;
15, Neothyris dawsoni; 16, Gyrothyris mawsoni; 17, Magellania flavescens; 18, Jaffaia jaffaensis; 19, Aerothyris
macquariensis; 20, Aerothyris kerguelensis.
26 J. R. RICHARDSON
thyris are found in a variety of originally soft of origin was Gondwana and that shallow sea^
sediments from the Pliocene and Pleistocene around land bridges would have provided routes
periods (Allan 1960; Neall 1972). for the dispersal of ancestral forms. They cam^
Australian Tertiary deposits consist almost ex¬ to this conclusion in view of:
clusively of originally soft sediments. As noted 1. the unlikelihood that transoceanic dispersal
above, an almost continuous Tertiary record of could occur with a non-planktotrophic larva;
anakineticinids is available from the Eocene period. 2. the endemic nature of the faunas of Sout^
In addition, a number of terebratelline genera occur America, New Zealand and Australia;
in sediments deposited during the Oligocene and 3. the lack of evidence of land bridges cork
Miocene in embayments of the southern coast¬ necting these southern lands during the Tertiary,
line—the Otway, Gippsland and Murray basins. This view of the distribution of southern faunae
These genera were specialised to varying degrees has not substantially altered. Plate tectonics, of
for soft sediments (limestones). The only living course, has provided the means of distribution
terebratellines found in Australian waters are without the need to postulate land bridges. It ha$
Magellania f/avescens and Jaffaia jaffaensis. also been shown that substrate type, in addition
Foster (1974) records that brachiopods similar to the length of larval life, is a limiting factor in
or identical to the Recent South American species distribution (Richardson 1986). While the broad
Magellania venosa and Terebrate/la dorsal a occur view of terebratellid distribution is shared with
in Antarctic strata of Oligocene and Miocene age. earlier workers, recent work on the subfamily
No fossil records are known of Aerothyris, Anebo- Tercbratellinae has made it possible to make n
concha, Dyscritosia, Syntomaria. more educated guess as to the nature of ancestral
All terebratelline genera, living and fossil, are stock.
endemic with the single exception of Stethothyris Work on the Terebratellidae in all parts of their
sufflata. This species, like another form (Neo- geographical range has shown consistency in pak
bouchardia minima) specialised for free life in terns of distribution with the nature of species.
carbonate sands occurs in Oligocene deposits of Undifferentiated or generalist species may b^
both Australia and New Zealand. widely distributed (with geography and substrate)
In general then, members of the southern sub¬ and they are variable in those characters linked
families of the Terebratellidae appear to be con¬ with the environment (differential thickening, beak
sistent in nature and distribution and in their characters, shape and size). Species specialised for
response to environmental changes. They occupy shelf sediments are limited in distribution and are
rocky shorelines and shelves but not the slopes (with less variable morphologically, both distribution and
the exception of Magellania venosa) or the abyss variability being related to extent of specialisation.
and similar forms occur in similar habitats. Species It seems unlikely that the patterns of distribution
with specialist characters occur only in sediments of terebratellid brachiopods in earlier periods
of a specific nature (although generalists may also would differ appreciably from those evident
occur therein), e.g. greensands, bryozoan sands. throughout the Cainozoic. In other words, given
As could be predicted, response to environmental the evidence available, the most valid working
change differs in generalist and specialist forms. hypothesis is that the shorelines and shelf of
The New Zealand record shows the sediment Gondwana would have been occupied by generalist
changes that accompanied Miocene regressions led species and by species specialised to varying degrees
to the extinction of all specialists for soft sediments for shelf life. With the break-up of the continent
while generalists appear to have occupied shoreline their survival would have been related to the extent
habitats since the Eocene. Members of both the of substrate loss or change. Differences in the
Anakineticinae and Bouchardiinae are all substrate- requirements of generalists and specialists means
specific forms and so arc limited in distribution. that generalists are more likely to survive periods
The Terebratellinac are not substrate specific of environmental change as illustrated by the
and are widely distributed within the Southern extinction of all taxa specialised for shelf sediments
Hemisphere. during a period of instability in the New Zealand
Miocene.
The break-up of Gondwana together with the
ORIGINS
differential survival of species would account for
The origins and the means of distribution of the the present distribution in which generalists and
Terebratellidae have been discussed by Thomson near-generalists occur around all Gondwana-
(1918), Blochmann (1908), von Ihering (1903) and derived land forms. The only specialists shared are
Allan (1963). They agree that the probable source 3 conspecifics (1 cancellothyrid and 2 terebratellid