Late Jurassic Cassiduloids of Argentina: Taxonomy & Paleogeography

LATE JURASSIC CASSIDULOIDS
(ECHINODERMATA, ECHINOIDEA)
FROM WEST-CENTRAL
ARGENTINA: TAXONOMIC AND
PALEOGEOGRAPHIC IMPLICATIONS
PATRICIO E. CACCIA1
CECILIA S. CATALDO1
M. BEATRIZ AGUIRRE-URRETA2
1
Laboratorio de Ecosistemas Marinos Fósiles, Instituto de Estudios Andinos Don Pablo Groeber (IDEAN), Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Pabellón 2 Ciudad Universitaria, Int. Güiraldes 2160, C1428EGA Ciudad Autónoma de Buenos Aires, Argentina.
2
Laboratorio de Bioestratigrafía de Alta Resolución, Instituto de Estudios Andinos Don Pablo Groeber (IDEAN), Universidad de Buenos Aires-Consejo Nacional de
Investigaciones Científicas y Técnicas (CONICET), Pabellón 2 Ciudad Universitaria, Int. Güiraldes 2160, C1428EGA Ciudad Autónoma de Buenos Aires, Argentina.
Submitted: 15 May 2023 - Accepted: 28 August 2023 - Published: 18 September 2023
To cite this article: Patricio E. Caccia, Cecilia S. Cataldo, & M. Beatriz Aguirre-Urreta (2023). Late Jurassic
Cassiduloids (Echinodermata, Echinoidea) from West-Central Argentina: taxonomic and paleogeographic
implications. Ameghiniana 60(6), 522–534.
To link to this article: http://dx.doi.org/10.5710/AMGH.28.08.2023.3565
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ORDOVICIAN–SILURIAN
CRYPTOSPORES OF COLOMBIA
JURASSIC CASSIDULOIDS
FROM ARGENTINA
PRE- AND POSTSANTACRUCIAN
INTERATHERIIDAE
Cryptospores demonstrate that
a land flora was already established
in the Late Ordovician–early
Silurian in northern South America.
New tithonian cassiduloid record
from the Neuquén Basin has
taxonomic and paleogeographic
implications.
New phylogenetic analysis based
on taxonomic revision of the genus
Protypotherium shares new clues
on the evolution of native ungulates.
ARTICLES
AMEGHINIANA - 2023 - Volume 60(6): 522–534
ISSN 0002-7014
LATE JURASSIC CASSIDULOIDS (ECHINODERMATA, ECHINOIDEA)
FROM WEST-CENTRAL ARGENTINA: TAXONOMIC AND PALEOGEOGRAPHIC IMPLICATIONS
PATRICIO E. CACCIA1, CECILIA S. CATALDO1, AND M. BEATRIZ AGUIRRE-URRETA2
1
Laboratorio de Ecosistemas Marinos Fósiles, Instituto de Estudios Andinos Don Pablo Groeber (IDEAN), Universidad de Buenos Aires-Consejo Nacional de Inves-
tigaciones Científicas y Técnicas (CONICET), Pabellón 2 Ciudad Universitaria, Int. Güiraldes 2160, C1428EGA Ciudad Autónoma de Buenos Aires, Argentina.
[email protected]; [email protected]
2
Laboratorio de Bioestratigrafía de Alta Resolución, Instituto de Estudios Andinos Don Pablo Groeber (IDEAN), Universidad de Buenos Aires-Consejo Nacional de
Investigaciones Científicas y Técnicas (CONICET), Pabellón 2 Ciudad Universitaria, Int. Güiraldes 2160, C1428EGA Ciudad Autónoma de Buenos Aires, Argentina.
[email protected]
Abstract. Cassiduloids are relatively well-represented in the fossil record, especially in Europe and Northern Africa, ever since their first
occurrence in the Lower Jurassic. The group shows an increase in diversity and abundance at the end of the Jurassic. In Argentina, cassiduloids
are represented from the Middle Jurassic upwards. This paper describes a Tithonian cassiduloid from the Picún Leufú Formation (Neuquén
Basin, Argentina) identified as Mepygurus? andinus new comb. according to the poorly developed bourrelets, straight phyllodes that are
continuous up to the margin, and a subpentagonal outline. The species was originally described from the Baños del Flaco Formation on the
Chilean slope of the Neuquén-Aconcagua Basin. This record extends the stratigraphical range of the genus to at least the Tithonian and provides
further evidence to the interpretation of the spatial continuity of shallow-water platforms during the Late Jurassic in the Andean region.
Key words. Irregularia. Cassiduloida. Tithonian. Neuquén Basin.
Resumen. Los casiduloideos se encuentran relativamente bien representados en el registro fósil desde su aparición en el Jurásico Temprano,
especialmente en Europa y norte de África. El grupo muestra un aumento en diversidad y abundancia hacia finales del Jurásico. En Argentina,
se encuentran representados a partir del Jurásico Medio. En el presente trabajo se describen casiduloideos del Tithoniano de la Formación
Picún Leufú (Cuenca Neuquina, Argentina) determinados como Mepygurus? andinus nueva comb. en función de sus burreletes poco desarrollados,
filodes rectos y continuos hasta los márgenes, y de su ámbito subpentagonal. La especie fue originalmente descripta de la Formación Baños
del Flaco, en la vertiente chilena de la Cuenca Neuquina-Aconcagüina. Este registro extiende el rango estratigráfico del género por lo menos
hasta el Tithoniano y proporciona evidencia adicional para la interpretación de la continuidad espacial de las plataformas de aguas someras
durante el Jurásico Tardío de la región andina.
Palabras clave. Irregularia. Cassiduloida. Tithoniano. Cuenca Neuquina.
CASSIDULOIDS are a group of irregular echinoids that appeared
group to the few dozen species known today are linked to
on Jurassic seas as a consequence of the Mesozoic Marine
competition with clypeasteroids, generalized water cooling,
low tests, different types of spines, and characteristic
Oyen, 1989).
Revolution (Vermeij, 1977). These organisms typically have
bilateral symmetry in both larvae and adults (Kier, 1962).
and taxonomic stochastic downfall (Kier, 1962; McKinney &
The fossil record of the group starts in the Toarcian and
These traits make them capable of burying themselves
is distributed worldwide, even in Antarctica (e.g., Kier, 1962;
defense mechanism against predators and environmental
et al., 1994; Srivastava, 2003; Radwańska & Jain, 2020). In
shallowly within the substrate, which in turn offers a
Larrain & Biró-Bagóczky, 1985; McKinney et al., 1988; Pons
processes (Kier, 1974).
Argentina, cassiduloids are represented in the Upper
Mesozoic and Cenozoic. They represented ~40% of the
record of cosmopolitan genera in the Picún Leufú Formation
Cassiduloids have an important fossil record in the
echinoid diversity during the Eocene, after which their
decline began (Kier, 1974). The factors that hypothetically
would have led to the fall in diversity and abundance of the
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Jurassic–Lower Cretaceous of the Neuquén Basin, with the
(Tithonian) (Leanza, 1973; Leanza & Hugo in Leanza et al.,
1997; Rodríguez, 2007; Aguirre-Urreta et al., 2008, 2011), in
the upper Berriasian–Valanginian of the Chachao Formation
AMGHB2-0002-7014/12$00.00+.50
CACCIA ET AL.: JURASSIC CASSIDULOIDS FROM ARGENTINA
(Weaver, 1931) and the upper Hauterivian of the Agrio
took place (Arregui et al., 2011). The early Tithonian–
in the lower Callovian (Middle Jurassic) of the Los Patillos
and Picún Leufú formations (and lateral equivalents),
Formation (Rodríguez, 2007). Cassiduloids are also recorded
Formation (Álvarez, 1996; Rodríguez, 2007), the Tithonian
Baños del Flaco Formation on the chilean slope of the
Neuquén-Aconcagua Basin (Larrain & Biró-Bagóczky, 1985),
and in the Paleogene of Patagonia (Parma & Casadío, 2005;
del Río et al., 2022).
Valanginian marine cycle is represented by the Vaca Muerta
marking the maximum marine expansion within a shallow
embayment (Leanza et al., 2011).
From a paleontological standpoint, the Neuquén Basin
presents a high global relevance. It has one of the most
diverse and abundant records of Jurassic and Cretaceous
Cassiduloid taxa previously described from the
marine invertebrates and vertebrates in the southern
the Tithonian–Valanginian interval (Rodríguez, 2007);
& Fernández, 2011; Riccardi et al., 2011), including bivalves,
Neuquén Basin are the genus Pygurus Agassiz, 1839 from
Clypeopygus robinaldinus (d’Orbigny, 1856) from the upper
Valanginian–lower Hauterivian (Haupt, 1907; Windhausen,
1914; Weaver, 1931; Rodríguez, 2007; Aguirre-Urreta et al.,
hemisphere (e.g., Aguirre-Urreta et al., 2008, 2011; Gasparini
cephalopods, gastropods, corals, echinoderms, annelids,
fish, and marine reptiles, among others. This extensive
record has allowed the development of an accurate
2008); Pygopyrina gerthi (Weaver, 1931) from the lower
biostratigraphic framework for the western margin of
2007; Aguirre-Urreta et al., 2008), and Pygorhynchus
Riccardi et al., 2000; Aguirre-Urreta et al., 2007), providing
early Barremian (Rodríguez, 2007; Aguirre-Urreta et al.,
and with foreign faunas and sedimentary successions. In
Valanginian–lower Hauterivian (Bernasconi, 1959; Rodríguez,
ovobatus (Agassiz, 1836) also from the upper Hauterivian–
2008). From the La Ramada Basin, the record is represented
by the genus Clypeus Leske, 1778 (Álvarez & Parma, 1997;
Rodríguez, 2007) from the Callovian of the Los Patillos
Formation.
The previous work on Argentinian cassiduloids is
mainly of a taxonomic nature. Information on the paleo-
Gondwana (e.g., Aguirre-Urreta & Rawson, 1999a, 1999b;
a high-resolution tool for correlation within the basin
addition, its macroinvertebrate faunas have proven
excellent study cases for biofacial and taphonomic analysis
(Lazo, 2006, 2007; Riccardi, 2015).
The Picún Leufú Formation
The Picún Leufú Formation is recognized in southern
autoecology and behavior of these organisms, as well as
Neuquén. Its type locality is at the intersection of National
limited. In this context, the main goals of this paper are: 1)
The Picún Leufú Formation was defined by Leanza
their interactions within the Mesozoic marine basins is
to report the occurrence of cassiduloids from the Picún
Road 40 with the Arroyo Picún Leufú (Fig. 1).
(1973) to designate the “set of limestones, clays and
Leufú depocenter of the Neuquén Basin, west-central
whitish sandstones that lie concordantly between the
the paleoecology of the species by comparing with extant
of the Carrín Curá Formation and the sandstones of the
Argentina; 2) to formally describe the record; 3) to analyze
taxa; and 4) to analyze the occurrence of the species at a
regional scale.
GEOLOGICAL SETTING
shales of the Vaca Muerta Formation or the distal deposits
Bajada Colorada Formation” (Leanza et al., 2011: 41),
giving rise to a succession 350 meters-thick in its type
locality (Fig. 2).
The strata are very fossiliferous, and the areas of
The Neuquén Basin, located in the Andes foothills of
exposure are well correlated through biostratigraphy with
Meso-Cenozoic depocenters of Western Gondwana. It
Leanza & Garate Zubillaga, 1987). In the type locality, the
Argentina and central Chile, is one of the most important
ammonoids and bivalves (Weaver, 1931; Leanza, 1973;
presents a thick stratigraphic succession made up of
Tithonian–Berriasian interval is represented through marine
sedimentary rocks (Howell et al., 2005).
(Leanza & Hugo in Leanza et al., 1997; Armella et al., 1999;
alternating cycles of marine and continental sedimentation
genera Subdichotomoceras, Lytohoplites, Corongoceras, and
siliciclastic, carbonate, and evaporitic marine and continental
Between the Early Jurassic and the Early Cretaceous,
deposits accumulated during a high sea level interval
Spalletti et al., 2000). The presence of the ammonoid
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AMEGHINIANA - 2023 - Volume 60(6): 522–534
Figure 1. 1, general map of the Neuquén Basin with location of the studied section (red star). 2, satellite image of the study area, type locality
of Picún Leufú Formation, portraying the estimated location of the transitional boundary between the Vaca Muerta and Picún Leufú formations
and collection site (red star); image © 2021 Maxar Technologies; Google Earth, accessed November 2021. 3, outcrop photo of the uppermost
beds of the Vaca Muerta Formation and the basal portion of the Picún Leufú Formation, with the approximate position of the transitional
boundary between them.
Substeueroceras allows an attribution to the late Tithonian–
early Berriasian interval (Leanza, 1973, 1981).
Concerning the paleoenvironment, a low slope carbonate
platform comprising facies indicative of a protected coastal
the Colección de Paleontología de la Universidad de Buenos
Aires (CPBA), Buenos Aires, Argentina, under the number
CPBA 21815. Additional material housed in the Museo
Provincial de Ciencias Naturales Dr. Prof. J. A. Olsacher
system, with shallow and well-oxygenated temperate
(MOZ), Zapala, Neuquén, Argentina, was analyzed. MOZ-PI
Caracoles area, the marine facies are deeper, corresponding
Formation.
posits developed next to low-energy facies of protected en-
tips, an ARO 8315-B model pneumatic hammer, 15 x 15 cm
formed, comprising corals, bivalves, and algae as the frame-
stereomicroscope with camera were used.
waters was proposed by Armella et al. (2008). In the Cerrito
to the inner platform margin, where bar and channel devironments (lagoon). Also, patch reefs of lenticular geometry
work organisms (Armella et al., 1999, 2007).
MATERIAL AND METHODS
The analyzed material consists of nine specimens from
the type locality of the Picún Leufú Formation (S 39º 12’
50.6”; W 70º 02’ 52.1”). They are housed in the repository of
524
5580 and MOZ-PI 1099 were collected from the Picún Leufú
For the mechanical cleaning process, 5 mm flat widia
foam rubber sheets, glue (cyanoacrylate), and a binocular
The descriptive and morphological terminology applied
are from Kier (1962) and Melville and Durham (1966). We
followed the diagnoses of Cassiduloida by Kier (1962) and
Barras (2006). The classification above order follows Kroh
and Smith (2010). The attribution of Mepygurus to the
Cassiduloida follows Barras (2006).
CACCIA ET AL.: JURASSIC CASSIDULOIDS FROM ARGENTINA
Figure 2. Sedimentary log of the lower third of the Picún Leufú Formation.
SYSTEMATIC PALEONTOLOGY
Class ECHINOIDEA Schumacher, 1817
Crown group MICROSTOMATA Smith, 1984
Crown group NEOGNATHOSTOMATA Smith, 1981
Order CASSIDULOIDA Agassiz & Desor, 1847
Comments. The first cassiduloids sensu Kier (1962)
appeared in the Early Jurassic, gradually increasing their
diversity and reaching their acme in the Eocene (Kier, 1974).
Family indet.
Genus Mepygurus Pomel, 1883
Type species. Pygurus depressus L. Agassiz in Agassiz & Desor, 1847:
162 [=Pygurus michelini Cotteau, 1849]; by subsequent designation
of Lambert and Thiéry (1921: 356).
Geographic
distribution.
France,
Sweden,
England,
Madagascar, Somalia, Chile, and Argentina (Agassiz &
Desor, 1847; Cotteau, 1849; Larrain & Biró-Bagóczky,
1985; this work).
Stratigraphic range. Bajocian–Tithonian (Middle–Late
At present, the group is represented by a few species
Jurassic).
the polar regions (Ghiold, 1989). The group is highly
low, wide, slightly rounded; apical system central to slightly
(Mooi, 1990), distributed throughout the planet except for
conservative in terms of morphology (Wagner, 2000;
Souto et al., 2019). However, some of the characters within
the group have evolved convergently (Souto et al., 2019).
Diagnosis (from Kier, 1962: 48, and Pomel, 1883). Skeleton
anterior; phyllodes depressed, narrow. Three to four series
of paired pores in each unconjugated ambulacral half, first
pore pair very close to the edge of the peristome. Periproct
inframarginal and oval.
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AMEGHINIANA - 2023 - Volume 60(6): 522–534
Discussion. This genus was originally described from Europe
and Madagascar. In this work, the stratigraphic range of the
Pygurus montmonilli [Agassiz, 1836], Pygurus blumenbachi
[Koch & Dunker, 1837], Pygurus (Pygurus) arabicus Kier,
genus is extended to the upper Tithonian.
1972). They also show rounded or poorly rectified outlines
morphological features that separate it from Pygurus
(Pygurus) mendelssohni Greyling & Cooper, 1993, Pygurus
The genus was proposed by Pomel (1883), identifying
Agassiz, 1839, i.e., the shape of its flosceles and the
presence of large tubercles in the oral region of the test.
However, the similarities between the two genera
generated controversy about the taxonomic level to which
they should belong. This led Beurlen (1933) and Mortensen
(e.g., Pygurus (Pygurus) coplanatus Tanaka, 1965, Pygurus
(Pygurus) posteroexpansus Tanaka, 1984).
However, the characters that allow differentiation at the
genus level are based on the morphology of the bourrelets
and the arrangement and shape of the phyllodes. The
phyllodes of Mepygurus are straight, and the width
(1948) to consider Mepygurus as a subgenus of Pygurus, a
remains constant up to the thecal margin, presenting
as the least complex taxon of the genus. However, Barras
the ambulacrum. Pygurus has well-developed bourrelets,
position later used by Kier (1962) to propose Mepygurus
(2006) retained the status of genus, noting that the
differences mentioned by Pomel (1883) were sufficient
justification.
Mepygurus vs. Astrolampas
Further controversy is added through the synonymy of
Mepygurus with Astrolampas Pomel, 1883. According to Kroh
and Mooi (2022), Mepygurus is a subjective posterior
synonym of Astrolampas. However, the publication in which
between two and three rows of paired pores in each half of
raised and tooth-shaped, variable phyllodes, having in some
species the maximum width close to the peristome, with
three rows of paired pores in each half of the ambulacrum.
Mepygurus? andinus new comb.
(Larrain & Biró-Bagóczky, 1985)
Figures 3–6
LSID urn:lsid:zoobank.org:act:D46F6511-17BA-4F92-AA4E-7BD53A48BBFD
only mentioned the synonymy but not its justification.
1985 Pygurus andinus Larrain & Biró-Bagóczky, p. 1411, figs.
3–4.4.
2007 Pygurus (Mepygurus) sp. Rodríguez, p. 167–170, fig.
4.29.
in Agassiz & Desor, 1847), while that of Astrolampas is A.
Concepción (CPUC) RM./85-5 Río Maitenes, Cajón del Fierro,
such as the presence of narrow, straight phyllodes, which
Analyzed material. Nine specimens (CPBA 21815.1–9) from
this nomenclatural act is justified has not been found under
the research carried out in the present work. Barras (2006)
The type species of Mepygurus is M. depressus (L. Agassiz
productus (Agassiz, 1836). These species have similarities,
Holotype. Colecciones Paleontológicas Universidad de
Baños del Flaco Formation, upper Tithonian, 02/8-28/65.
are continuous up to the margin, with two series of paired
the Picún Leufú Formation in its type locality, Neuquén
bourrelets. However, Astrolampas productus has a longitu-
Measurements. See Table 1.
pores in each half of the ambulacrum, and poorly developed
dinal periproct displaced anteriorly in the oral region of the
test, contrary to the inframarginal position of the periproct
in Mepygurus depressus. In addition, A. productus has a
slightly rounded anterior margin compared to the straight
margin present in M. depressus. However, a detailed revision
of both genera and their type species is beyond the scope
Province. Upper Tithonian.
Description. Test elongated, longer than wide, with average
width-to-length ratio of 0.88. Outline subpentagonal,
with straight anterior margin; posterior margin slightly
elongated, projecting a rostrum. Maximum width over
posterior two-thirds of the body, at interambulacra 1a and
4b, varying between 34.2–46 mm. Apical system slightly
of this paper.
displaced anteriorly, tetrabasal, with four genital pores.
Mepygurus vs. Pygurus
petals up to test ambitus. Petal III slightly narrower than
Species within the genus Pygurus usually have an
ambitus with an incised anterior margin, rounded lateral
margins, and a rostrated posterior margin with notches (e.g.,
526
Madreporite plate in center of apical system. Lanceolate
paired petals. Posterior petals subequal. Poriferous zone with
conjugated pores. External pores elongated and internal
pores simple. Interporiferous zone large, at least three times
CACCIA ET AL.: JURASSIC CASSIDULOIDS FROM ARGENTINA
Figure 3. Mepygurus? andinus new. comb.; 1, 3, CPBA 21815.4; 2, 5, CPBA 21815.1; 4, 6 CPBA 21815.6; 7, 9 CPBA 21815.2; 8, 13 CPBA 21815.3;
10, 11 CPBA 21815.7; 12, 16, CPBA 21815.9; 14, 17, CPBA 21815.5; 15, 18, CPBA 21815.8. 1, 5, 6, 8, 9, 11, 12, 14, 18 in aboral view; 2–4, 7,
10, 13, 15–17 in oral view. Scale bars equal 10 mm.
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TABLE 1. Measurements of Mepygurus? andinus new comb. Asterisks (*) represent incomplete specimens that were not considered when
calculating the averages.
Specimens
Maximum length (cm)
Maximum width (cm)
Width-to-length ratio
CPBA 21815.1
5.04
4.60
0.91
CPBA 21815.2
4.92
4.40
0.89
CPBA 21815.3*
4.52
4.22
0.93
CPBA 21815.4
3.89
3.59
0.92
CPBA 21815.5
4.15
3.82
0.92
CPBA 21815.6
4.67
3.42
0.73
CPBA 21815.7
3.69
3.44
0.93
CPBA 21815.8*
4.16
3.47
0.83
CPBA 21815.9*
4.12
3.53
0.86
Averages
4.39
3.88
0.88
wider than poriferous zone in the maximum width and equal
specimens to Pygurus andinus. Unfortunately, the specimens
up to the margin. Columns a and b observed near the middle
from Central Chile present only the aboral region of the test,
depressed; high density of primary tubercles within
from the Neuquén Basin in greater detail.
of petaloids IV and V (in CPBA 21815.7). Adoral region
interambulacral plates. Phyllodes straight up to margin of
test, phyllopores not observed. Peristome anterior,
pentagonal. Bourrelets poorly developed, slightly bulged,
making it difficult to compare them with the specimens
It should be noted that in specimen CPBA 21815.2
(Fig. 3.7 and 3.9) proportions are different than in the
others. It has longer lateral margins towards the anterior
with rounded edges. Periproct inframarginal, subtriangular.
region of the body, thus having a more elongated
specimens is relatively complete, and individuals can be
groove is observed towards the peristome, which can
21815.8) are poorly preserved. Both physical (i.e., fractures
may be due to intraspecific variation. Due to the relatively
Mode of preservation. The general preservation of the
identified, although some (CPBA 21815.3, 21815.5, and
and disarticulation) and chemical (i.e., dissolution, with
enhanced features in the ambulacral regions and loss of
tubercles) modifications are observed. All individuals
appearance on the anteroposterior axis. In turn, a concave
represent the contour of the anal groove. This morphology
poor preservation of the available material, it is difficult to
make a more detailed description of the morphological
variability of the species. However, the rest of the material
have some type of modification in their skeleton, likely
conforms to the description above (Fig. 4).
some specimens the phyllopores cannot be observed due
to the genus Mepygurus, contrary to what was proposed by
material.
material of Pygurus andinus from Central Chile. The mor-
associated with post-depositional compaction. Also, in
to the loss of relief owing to the mechanical cleaning of the
The subpentagonal morphology is more closely related
Larrain and Biró-Bagóczky (1985) based on the original
Discussion. The subpentagonal test outline, straight
phology and development of the bourrelets, together with
region of the body, and the same morphology of the
outline of the periproct further reinforce the determination
anterior margin, longer lateral margins on the anterior
petaloids (Fig. 3), allow us to assign the Picún Leufú
528
the shape and length of the phyllodes and the position and
of the species as belonging to Mepygurus. Therefore, the
CACCIA ET AL.: JURASSIC CASSIDULOIDS FROM ARGENTINA
Figure 4. Diagnostic features of Mepygurus? andinus new. comb. 1, CPBA 21815.5, aboral view, detail of apical system (arrow) with four
gonopores; 2, CPBA 21815.7, oral view, detail of subtriangular periproct (arrow); 3, CPBA 21815.4, oral view, detail of poorly developed bourrelet
(arrow). Scale bars equal 2 mm (1) and 5 mm (2, 3).
new combination will be established as Mepygurus? andinus.
andinus new comb. in having a subcircular test and drop-
been found in the Cretaceous of South America. Pygurus
It is important to highlight the description made by
Other species belonging to the genus Pygurus have
shaped periproct.
jagueyanus Cooke, 1955, from the Albian of Colombia, differs
Rodríguez (2007) of the material from the Picún Leufú
with rounded margins and posterior notches that end in a
Cerro Lotena, and Cerro del Burro, Neuquén province. The
from M.? andinus new comb. in presenting an elongated test
small rostrum in the posterior region of the test. Also from
the Lower Cretaceous of Colombia, Pygurus columbianus
Formation collected by J. Garate Zubillaga in Picún Leufú,
specimens MOZ PI 5580 and 1099, determined by that
d’Orbigny, 1842 should be mentioned, which features a
subcircular test with narrow petaloid ambulacra continuous
up to the margin. It differs from M.? andinus new comb. in
the circular morphology of the test and in presenting
petaloids with their maximum width distal to the mid-length
of the ambulacra. Pygurus tinocoi Beurlen, 1966 from the
Lower Cretaceous of Brazil differs from M.? andinus new
comb. in presenting a higher test and a posterior margin
with notches. Mepygurus depressus, from the Bathonian–
Callovian of France, Switzerland, England, Madagascar, and
Somalia, has a subpentagonal test with slightly rounded
margins, straight phyllodes in its oral region that are
continuous up to the margin, poorly developed bourrelets,
and an inframarginal periproct of longitudinal morphology.
It differs from M.? andinus new comb. in its more rounded
test and the elongated shape of its periproct. Mepygurus
michelini, from the Oxfordian of Great Britain, has a
subcircular test with strongly rounded margins. In its oral
region, it has straight phyllodes that are continuous up to
the margin, slightly developed bourrelets, and a drop-
shaped inframarginal periproct, with its apex pointing
toward the anterior region of the body. It differs from M.?
Figure 5. Mepygurus? andinus new. comb.; 1, 2, MOZ-PI 5580, in oral
(1) and aboral (2) views; 3, 4, MOZ PI 1099, in oral (3) and aboral (4)
views. Both specimens from Picún Leufú locality, Col. J. Garate Zubillaga.
Scale bars equal 10 mm.
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AMEGHINIANA - 2023 - Volume 60(6): 522–534
author as Pygurus (Mepygurus) sp., are preserved with the
1978; Ventura & Pintos de Oliveira, 2021). This allows
identification (Fig. 5). However, the specimens have the
within their digestive tract while maintaining a directionality
oral region covered by sediment, which complicates their
periproct with a similar subtriangular shape within a
surrounding fossa and the test has a morphology similar to
that described in this paper both in the subpentagonal form
of the test and the arrangement of the apical system (i.e.,
tetrabasal, Fig. 6). In addition, the ambulacra are continuous
individuals to maintain a continuous movement of sediment
of grain transport from the anterior region of the body to
the peristome (Gladfelter, 1978).
The burrowing activity of cassiduloids has been
hypothesized to be limited by grain size, though this was
never tested. Kier (1962) proposed that the space located
up to the margin and have the characteristic petaloid shape.
below the petaloids on the aboral region of the test could
comb. nov.
the substrate.
Therefore, this material is herein attributed to M.? andinus
ECOLOGY AND PALEOECOLOGY OF CASSIDULOIDS
define the limit to which the organism could bury itself in
In Apatopygus recens (Milne Edwards, 1836), the ambu-
lacra are long and reach the ambitus, and the burrowing is
Very little is known about cassiduloid behavior. Some
complete in coarser grain size, including the apical system
limited lateral displacement of adults and the movement of
bulacra than both A. recens and Mepygurus? andinus new
modern cassiduloid species present endemism due to the
larvae almost exclusively by the action of currents and tides
(Emlet et al., 1987; Contins & Ventura, 2011). The larvae
(Higgins, 1974). Cassidulus mitis Krau, 1954 has shorter amcomb. and it lives in coasts with coarse sand substrates
showing a complete burrowing habit (Ventura & Pintos de
have cilia in their pre-metamorphic stage that allow them
Oliveira, 2021).
2011). Also, some living cassiduloids present a gregarious
morphological features that would allow categorizing the
Current species of cassiduloids are depositivorous,
reach the thecal margins. Additionally, both in the Picún
to rotate on their axis but not to “swim” (Contins & Ventura,
habit (Caballero-Ochoa et al., 2021).
consuming the organic films on sand grains and moving
them with the podia towards the peristome (Gladfelter,
Mepygurus? andinus new comb. presents some
species as semi-infaunal, as a low test and petaloids that
Leufú and the Baños del Flaco formations (Bed 85, Larrain &
Biró-Bagóczky, 1985), the Mepygurus-bearing deposits have
Figure 6. 1, close-up of the apical system of Mepygurus? andinus new. comb., CPBA 21815.4. 2, schematic representation of 1. Scale bars equal 1 mm.
530
CACCIA ET AL.: JURASSIC CASSIDULOIDS FROM ARGENTINA
a fine granulometry, i.e., fine (calcareous) sandstones. In any
CONCLUSIONS
M.? andinus new comb. and living species are very limited,
straight anterior margin and longer lateral margins on the
case, the ecological comparisons that can be made between
Based on the subpentagonal outline of the test, the
and no serious conclusions can be drawn.
anterior region of the body, and the petaloids that are con-
M.? andinus new comb. represent juvenile stages of the
the Picún Leufú Formation of the Neuquén Basin herein
It is difficult to verify whether the smaller specimens of
species, given the loss of reproductive structures (Smith,
tinuous up to the margin of the test, the specimens from
studied were attributed to a cassiduloid species previously
1984; Contins & Ventura, 2011). The small specimen CPBA
described from the Tithonian of Central Chile. This is, there-
to the presence of gonal plates with the opening correspon-
study has allowed establishing the new combination
21815.4 likely represents a reproductively active adult due
ding to the gonopore (Smith, 1984; Contins & Ventura,
2011). Unfortunately, not all the smaller specimens preserve
the apical region.
fore, a novel record for the basin. The performed taxonomic
Mepygurus? andinus (Larrain & Biró-Bagóczky, 1985) for the
species based on the subpentagonal test outline, the morphology of its bourrelets (i.e., rounded and poorly developed),
the shape and length of its phyllodes (i.e., straight and con-
DEPOSITIONAL ENVIRONMENT AND DISTRIBUTION
tinuous up to the margin), and the position and outline of
Specimens of Mepygurus? andinus new comb. from the
tends the stratigraphic range of the genus Mepygurus to at
OF MEPYGURUS? ANDINUS
Picún Leufú Formation have been found associated with
other marine invertebrates, such as ramous corals,
the periproct (i.e., submarginal and subtriangular). This exleast the Tithonian. Additionally, comparisons of Mepygurus
with the genus Astrolampas led to the conclusion that a
ammonoids, bivalves, and gastropods. The facies and
thorough revision of both genera is needed to better differ-
the type locality of the Picún Leufú Formation allowed them
morphology and disposition of the phyllodes is crucial.
microfacies analyses performed by Armella et al. (2007) in
to define a carbonate platform environment with the
entiate them, in particular, more information about the
There is morphological variability within the species,
development of lagoonal facies. Water was temperate,
evidenced by the presence of a fossa surrounding the
It is worth mentioning that, overall, the Baños del Flaco
5580. The lack of more and better-preserved specimens
shallow, and well-oxygenated (Armella et al., 2007).
Formation (the bearing unit of the holotype of M.? andinus
new comb.) represents a similar setting to that of the Picún
Leufú Formation, interpreted as a coastal marine environment
periproct in specimen CPBA 21815.2 and specimen MOZ PI
precludes further assessment of the meaning of this
variability.
The presence of M.? andinus new comb. in the Neuquén
with predominance of lower shoreface deposits and upper
Basin expands our knowledge on irregular echinoids in
Based on the biozonation of ammonoids, the age of the
the presence of the species in both southern Neuquén
shoreface and transition zone deposits (Salazar, 2012).
Baños del Flaco Formation is between the Tithonian and the
lower Berriasian, according to Salazar and Stinnesbeck
(2015). Thus, the roughly concomitant (upper Tithonian)
shallow coastal systems during the Late Jurassic. Besides,
province and Central Chile during the latest Jurassic provides
further evidence to the interpretation of the spatial
continuity of shallow-water platforms in the Mesozoic of
presence of M.? andinus new comb. in the Picún Leufú
the Andean region.
the relative continuity of the shallow-water platform
ACKNOWLEDGMENTS
and Baños del Flaco formations adds further evidence to
environments in the Neuquén-Aconcagua Basin. These are
necessary for the spread of cassiduloid larvae transported
by ocean currents and the formation of successive
population nuclei (e.g., Buitrón-Sánchez et al., 2019;
Caballero-Ochoa et al., 2021).
This article is part of the degree thesis of PEC developed in the
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos
Aires, Argentina. Andreas Kroh (Naturhistorisches Museum Wien) is
gratefully acknowledged for providing essential bibliography and
for his help with the systematics of cassiduloids. Marian Tanuz
(Colección de Paleontología de la Universidad de Buenos Aires) and
Belén Boilini (Museo Provincial de Ciencias Naturales “Dr. Prof. Juan
A. Olsacher”) kindly facilitated access to repository material under
531
AMEGHINIANA - 2023 - Volume 60(6): 522–534
their care. The thorough and constructive reviews by Andrew Smith
(Natural History Museum, London) and Camilla Alves Souto
(National Museum of Natural History, Smithsonian Institution,
Washington, DC) are greatly appreciated. This is the contribution
R-455 of the IDEAN.
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Editorial Note: Both this work and the nomenclatural act it contains have
been registered in the ZooBank. The work is permanently archived in the Online
Archives LOCKSS and Portico.
LSID urn:lsid:zoobank.org:pub:828EDA5B-DEE0-49D0-A4CD-51695A3A278F
doi: 10.5710/AMGH.28.08.2023.3565
Submitted: 15 May 2023
Accepted: 28 August 2023
Published: 18 September 2023