Selenariidae Busk 1854 (Bryozoa) is considered endemic to Australia and New Zealand. Here we describe a new species of Selenaria Busk 1854 from the lower Miocene Monte León Formation (Patagonia, Argentina). Selenaria lyrulata sp. nov. is characterized by autozooids with a lyrula-like, anvil-shaped cryptocystal denticle, opesiular indentations and lateral condyles, as well as avicularia with a shield of fused costae. This is the first record of a selenariid bryozoan in South America.Facultad de Ciencias Naturales y Muse

Griffin, Miguel

López Gappa, Juan José

Pérez, Leandro Martín

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First record of a fossil selenariid bryozoan in South
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Juan López-Gappa, Leandro Martín Pérez & Miguel Griffin
To cite this article: Juan López-Gappa, Leandro Martín Pérez & Miguel Griffin (2017): First
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First record of a fossil selenariid bryozoan in South America
JUAN LÓPEZ-GAPPA, LEANDRO MARTÍN PÉREZ and MIGUEL GRIFFIN
LÓPEZ-GAPPA, J., PÉREZ, L.M. & GRIFFIN, M. February 2017. First record of a fossil selenariid bryozoan in South America. Alcheringa XX,
xxx-xxx. ISSN 0311-5518.
Selenariidae Busk 1854 (Bryozoa) is considered endemic to Australia and New Zealand. Here we describe a new species of Selenaria Busk 1854
from the lower Miocene Monte León Formation (Patagonia, Argentina). Selenaria lyrulata sp. nov. is characterized by autozooids with a
lyrula-like, anvil-shaped cryptocystal denticle, opesiular indentations and lateral condyles, as well as avicularia with a shield of fused costae. This
is the first record of a selenariid bryozoan in South America.
Juan López-Gappa [lgappa@macn.gov.ar] CONICET—Museo Argentino de Ciencias Naturales. Av. Ángel Gallardo 470, C1405DJR, Ciudad
Autónoma de Buenos Aires, Argentina; Leandro Martín Pérez [pilosaperez@gmail.com] and Miguel Griffin [patagonianoyster@gmail.com],
CONICET—División Paleozoología Invertebrados, Museo de La Plata. Paseo del Bosque s/n, B1900FWA, La Plata, Argentina. Received
20.7.2016; revised 5.12.2016; accepted 21.12.2016.
Key words: Bryozoa, Selenariidae, lyrula-like denticle, lower Miocene, Monte León Formation, Patagonia, Argentina.
LUNULITIFORM bryozoans are characterized by
convergently evolved, free-living, cup-shaped colonies
adapted for life in sandy or muddy sediments (Lagaaij
1963, Cadée 1975, among others). They belong to sev-
eral phylogenetically unrelated genera and families.
Among them, Selenariidae is presently monogeneric,
including only Selenaria Busk, 1854, with 27 Cenozoic
species, almost exclusively confined to Australia, and
one species, S. concinna Tenison Woods 1880, also
occurring in New Zealand (Bock & Cook 1999, Conroy
et al. 2001). Other genera formerly classified within
Selenariidae were later transferred to Lunulitidae and
Otionellidae (Cook & Chimonides 1986, Bock & Cook
1998), or are presently regarded as incertae sedis [e.g.,
Discovibracella Voigt 1964, see Voigt (1964), P. Bock,
D. Gordon, personal communication].
The diagnostic characters of Selenaria are: zooids
budded radially; colonies partitioned into concentric
astogenetic zones of zooids with different functions;
avicularia large and isolated, usually placed at the bifur-
cation of radial autozooidal rows, with a well-developed
condyle system and frontal areas covered by a porous
cryptocyst (Cook & Chimonides 1987, Bock & Cook
1999). It has been shown that at least one species,
Selenaria maculata Busk 1852, is capable of locomo-
tion (Cook & Chimonides 1978). Selenariidae shares
with the related Otionellidae the possession of free-liv-
ing, lunulitiform colonies. The latter family differs in
having avicularia with paired, often fused condyles
(Bock & Cook 1998).
The fossil species described herein comes from the
shell-beds at the top of the Punta Entrada Member of
the Monte León Formation, which outcrops along the
coastal cliffs of the Monte León National Park (Fig. 1).
The siliciclastic section at the locality known as
‘Cabeza de León’ is ca 47 m thick and consists of bio-
turbated muddy siltstone and fine sandstone with abun-
dant bivalves, gastropods, bryozoans, brachiopods,
echinoids, cirripedians, polyplacophorans and scapho-
pods (Parras et al. 2012). The age of this sequence is
ca 18 Ma, as proposed by Parras et al. (2012), based on
87Sr/86Sr age dates.
The aim of this study is to describe a new species
of Selenaria, the first recorded outside Australasia,
based on specimens found in the lower Miocene
deposits of the Monte León Formation, Argentine
Patagonia.
Material and methods
The material was collected by G. Pastorino and M.
Griffin in 1995. It comes from ‘Cabeza de León’
(50°21ʹ32ʺS–68°52ʹ58ʺW), Monte León Formation,
Santa Cruz Province, Argentina (Fig. 1). Fragments of
Selenaria lyrulata sp. nov. were recovered by sieving
the loose sediment and then picking the material under
a binocular microscope. They were coated with
gold/palladium and digital images were obtained using
a SEM (Phillips XL-30) at the Museo Argentino de
Ciencias Naturales (MACN). Specimens are housed in
the collection of the División Paleozoología Invertebra-
dos—Museo de La Plata (MLP).
© 2017 Geological Society of Australia Inc., Australasian Palaeontologists
http://dx.doi.org/10.1080/03115518.2017.1283054
Systematic palaeontology
Family SELENARIIDAE Busk, 1854
Selenaria Busk, 1854
Type species: Lunulites maculata Busk 1852, by mono-
typy.
Selenaria lyrulata sp. nov. (Fig. 2A–D)
Types. Holotype: MLP 35534, ‘Cabeza de León’, Monte
León Formation (lower Miocene), Santa Cruz Province,
Argentina. Paratype: MLP 35535, same locality as
holotype.
Description. Colony unattached, lunulitiform. Basal
surface with extrazooidal calcification, tuberculated,
radially grooved (Fig. 2D). Autozooids ordered quin-
cuncially, subhexagonal, with distinct zooidal bound-
aries; proximal and distal zooidal margins concave and
convex, respectively (Fig. 2A). Cryptocyst well devel-
oped proximally, tapering laterally, sunken, its whole
surface coarsely tuberculated (Fig. 2B). Opesia some-
what trifoliate, rounded distally, constrained by a pair of
robust, pointed condyles projecting proximally
(Fig. 2B). Opesiular indentations reniform, defined by
the condyles and a large, anvil-shaped, lyrula-like denti-
cle (Fig. 2B). Avicularia vicarious, longer than auto-
zooids, asymmetrical, with a wedge-shaped proximal
margin, placed at the bifurcation of radial autozooidal
rows (Fig. 2A, C). Avicularian cryptocyst tuberculated,
composed of 10–12 costae, fused medially (Fig. 2A-C).
Condyle smooth, on the left-hand side, asymmetric,
robust, projecting distally and upwards (Fig. 2A, B).
Peripheral zooids, ancestrula and early astogeny not
seen.
Measurements. Autozooid length, 0.23–0.27 mm (n: 5);
autozooid width, 0.21–0.26 mm (n: 5); opesia length,
0.14–0.15 mm (n: 5); opesia width, 0.11–0.12 mm
(n: 5); avicularium length, 0.33–0.35 mm (n: 2);
avicularium width, 0.14–0.17 mm (n: 2).
Remarks. The material consists of two small fragments
representative of the zone of autozooids and avicularia.
The central primary zone and the subperipheral and
peripheral zones were missing. The position of the
vicarious avicularia at the bifurcation of zooidal rows as
well as the structure of the avicularian condyle and
cryptocyst are, however, typical of Selenaria.
Although most species of Selenaria have subcircular
opesia which lack condyles, opesiular indentations, or a
proximal denticle, these structures are present in some
Australasian representatives of the genus. In S. macu-
lata (Busk 1852) and S. watersi Cook & Chimonides
1985a, the opesia may be laterally constricted and
divided centrally by a proximal tongue of cryptocyst
(Cook & Chimonides 1985a 1987), but the avicularian
cryptocyst is finely punctate. Selenaria hexagonalis
Fig. 1. Map of the study area.
2 JUAN LÓPEZ-GAPPA et al. ALCHERINGA
Maplestone, 1904, shares with S. lyrulata the fused
costae of the avicularian cryptocyst, but the autozooidal
opesia are subcircular and devoid of any other morpho-
logical structure (Cook & Chimonides 1987).
Some otionellids also share certain morphological
features with S. lyrulata sp. nov. Petasosella alata
(Tenison Woods 1880), from the Australian Miocene,
has a trifoliate opesium but lacks the median proximal
denticle. In addition, its avicularia have paired condyles
and lack the shield of cryptocystal fused costae (see
Cook & Chimonides 1985b, Bock & Cook 1998).
Selenaria lyrulata sp. nov. adds to other lunulitiform
bryozoans already recorded from the Paleogene
and Neogene of Argentina, such as the otionellids
Petasosella bioculata (Canu 1904) and Otionella
parvula (Canu 1904), and the cupuladriids Discoporella
depressa (Conrad, 1841) (Canu 1904, as Cupularia
punctata, see Cook 1965) and Cupuladria sp. (Pérez
et al. 2013). Petasosella bioculata, from the late Oligo-
cene of Patagonia (San Julián Formation), differs from
the new species in having opesiulate autozooids and
vicarious avicularia lacking the shield of cryptocystal
costae. Living lunulitiform bryozoans are absent from
the Magellanic Region (López Gappa 2000) and only
Discoporella depressa occurs today in the warm-
temperate zone of the Argentine Sea off Buenos Aires
Province (Silén 1942, Buge 1975, López Gappa &
Lichtschein 1990).
The denticle of S. lyrulata sp. nov. is a distal projec-
tion of the cryptocyst, i.e., it is located under the frontal
membrane of the zooid. Although its morphology is
strikingly similar to lyrula in ascophoran cheilostomes,
the two structures can not be regarded as homologous.
As recently discussed by Berning et al. (2014), the dis-
tal margin of a true lyrula fulfils the function of stop-
ping the operculum in a vertical position during
opening. We infer that the function of this denticle is to
protect the bryozoan from predators trying to gain
access to the polypide. The lateral pointed corners of
this structure also set the limits of the opesiular indenta-
tions, a space traversed by muscles depressing the fron-
tal membrane of the zooid.
Opesiulate selenariids (see species descriptions in
Cook & Chimonides 1985a) may have originated from
taxa with trifoliate opesiae, such as S. lyrulata sp. nov.
Opesiules may eventually be produced by the closing of
opesiular indentations, after the median denticle meets
and fuses with the lateral condyles that constrict the
Fig. 2. Holotype (MLP 35534): A, general aspect of the colony surface. Arrows show three vicarious avicularia (scale bar = 200 μm); B, detail of
autozooid, showing the lyrula-like denticle, opesiular indentations and condyles. An avicularian condyle and cryptocystal costae can be seen on the
right side (scale bar = 80 μm); C, avicularium showing a detail of the fused cryptocystal costae (scale bar = 100 μm); the condyle is broken.
Paratype (MLP 35535): D, lower surface of the colony (scale bar = 100 μm).
ALCHERINGA FOSSIL SELENARIID IN SOUTH AMERICA 3
opesia. This trend is suggested in the lateral extensions
of the median cryptocystal denticle of S. lyrulata sp.
nov., and is fully expressed, for instance, in the sexual
dimorphism between male (opesiulate) and female
zooids (trifoliate) of S. watersi Cook & Chimonides,
1985a. A trifoliate opesia with notches at the proximo-
lateral corners to accommodate the parietal muscles has
also been interpreted as a primitive evolutionary state in
the Pyrisinellidae (Di Martino & Taylor 2012).
This constitutes the first record of a selenariid bry-
ozoan in the South American continent. The occurrence
of Selenaria in lower Miocene deposits of Patagonia is
a further confirmation of the strong palaeobiogeographic
links that probably existed between the southern tip of
South America and the Australasian region at the begin-
ning of the Neogene, as has been discussed by previous
authors (Casadío et al. 2010, Pérez et al. 2015, and ref-
erences therein).
Acknowledgements
Fabián Tricárico operated the Scanning Electron
Microscope at MACN. We are grateful to Dennis
Gordon and Phil Bock for insightful comments on
selenariid taxonomy. Two anonymous reviewers made
useful comments on an earlier version of this paper.
Financial support by CONICET (PIP 2013–2015 No.
00247 to JLG) and ANPCyT (PICT 2012–1043 to JLG
and PICT 2012–1726 to MG) is acknowledged.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The work was supported by Agencia Nacional de Promoción
Científica y Tecnológica [grant number PICT 2012-1726, PICT 2012–
1043]; Consejo Nacional de Investigaciones Científicas y Técnicas
[PIP No. 00247]
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4 JUAN LÓPEZ-GAPPA et al. ALCHERINGA


First record of a fossil selenariid bryozoan in South America

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First record of a fossil selenariid bryozoan in South America

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