A late Furongian trilobite assemblage from the eastern Cordillera Oriental (Santa Rosita Formation; Jujuy, Argentina) and its biostratigraphic significance

2018·5.2 MB·English

by  Tortello, Franco

Rev. Mus. Argentino Cienc. Nat., n.s.
20(2): 271-282, 2018
ISSN 1514-5158 (impresa)
ISSN 1853-0400 (en línea)
A late Furongian trilobite assemblage from the eastern
Cordillera Oriental (Santa Rosita Formation; Jujuy, Argentina)
and its biostratigraphic significance
M. Franco TORTELLO1, Fernando J. ZEBALLO2 & Daniela S. MONTI3
1CONICET - Universidad Nacional de La Plata, División Paleozoología Invertebrados, Museo de Ciencias
Naturales, Paseo del Bosque s-n°, 1900 La Plata, Argentina. [email protected] 2Museo de Paleontología,
Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 299,
5000 Córdoba, Argentina. [email protected] 3CONICET - Universidad de Buenos Aires, Instituto de
Ecología, Genética y Evolución de Buenos Aires, Facultad de Ciencias Exactas y Naturales, UBA, Intendente
Güiraldes 2160, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina. [email protected]
Abstract: The trilobite Parabolina frequens argentina Zone is widely represented in the upper Furongian of
northwestern Argentina. A fossil assemblage from the lower Santa Rosita Formation at Quebrada de Abra Blanca,
Jujuy Province, is described herein. Parabolina frequens argentina (Kayser) and Parabolinella coelatifrons
Harrington & Leanza have previously been reported from other localities of the biozone, whereas Lotagnostus
hedini (Troedsson) is here described from South America for the first time. The latter provides high resolution
data on the age of the P. frequens argentina Zone in the eastern Cordillera Oriental, where conodont-bearing stra-
ta have not been found yet. L. hedini exhibits a short biostratigraphic range, restricted to the latest Furongian of
China (Xinjiang, Bulbolenus Zone; western Zhejiang, Lotagnostus hedini Zone), Kazakhstan (Euloma limitaris-
Taoyuania Zone) and ?Canada (western Newfoundland, Phylacterus saylesi Fauna). In China and Kazakhstan, it
occurs in association with, or a few meters below, the first appearance of the conodont Cordylodus proavus; a fact
that increases the potential for global correlation.
Key words: Trilobites, late Furongian, Santa Rosita Formation, Jujuy, Argentina.
Resumen: Una asociación de trilobites del Furongiano tardío del sector este de la Cordillera Oriental
(Formación Santa Rosita; Jujuy, Argentina) y su significado bioestratigráfico. La Zona de trilobites de
Parabolina frequens argentina está ampliamente representada en el Furongiano superior del noroeste argentino.
En este trabajo se describe una asociación fosilífera del tramo inferior de la Formación Santa Rosita aflorante
en la Quebrada de Abra Blanca, Provincia de Jujuy. Parabolina frequens argentina (Kayser) y Parabolinella
coelatifrons Harrington & Leanza fueron previamente citados en otras localidades de la biozona, mientras que
Lotagnostus hedini (Troedsson) es descripto aquí por primera vez para Sudamérica. Este último taxón aporta da-
tos precisos sobre la edad de la Zona de P. frequens argentina en el sector este de la Cordillera Oriental, en donde
aún no se han hallado rocas portadoras de faunas de conodontes. Lotagnostus hedini posee un rango bioestrati-
gráfico corto, limitado al Furongiano más tardío de China (Xinjiang, Zona de Bulbolenus; oeste de Zhejiang, Zona
de Lotagnostus hedini), Kazakstán (Zona de Euloma limitaris-Taoyuania) y ?Canadá (oeste de Newfoundland,
Fauna de Phylacterus saylesi). En China y Kazakstán se registra asociado a, o unos pocos metros por debajo de la
primera aparición del conodonte Cordylodus proavus, lo cual incrementa el potencial para realizar correlaciones
globales.
Palabras clave: Trilobites, Furongiano tardío, Formación Santa Rosita, Jujuy, Argentina.
_____________
INTRODUCTION original definition, it is currently regarded as
late late Cambrian (late Furongian) in age.
The trilobite Parabolina frequens argentina
The unit is principally characterized by ole-
Zone constitutes an emblematic biostratigraph-
nids and agnostoids, and is widely distributed
ic unit of the Lower Paleozoic of northwest-
throughout Jujuy and Salta Provinces (e.g.,
ern Argentina. It was erected by Harrington
& Leanza (1957) for the Cordillera Oriental- Harrington & Leanza, 1957; Esteban & Tortello,
Famatina and, after some amendments to its 2007; Waisfeld & Vaccari, 2008 and references).
272 Revista del Museo Argentino de Ciencias Naturales, n. s. 20(2), 2018
Parabolina frequens argentina (Kayser, 1876) Puncoviscana Formation (e.g., Harrington &
clearly dominates the assemblages of the Biozone, Leanza, 1957; Turner, 1960; Turner & Mon,
whereas the associated faunas are somewhat vari- 1979; Moya, 1988; Ramos, 1999, 2008; Astini,
able in different localities. Sections of the western 2003, 2008).
Cordillera Oriental (Lampazar Formation; Sierra The Santa Rosita Formation consists of
de Cajas, Angosto del Moreno, Quebrada de Jueya) a complex mosaic of late Furongian-late late
and the Iruya area (Santa Rosita Formation) Tremadocian shales and subordinate sandstones
contain various genera such as Gymnagnostus, that represent a wide variety of sedimentary en-
Micragnostus, Pseudorhaptagnostus, Lotagnos- vironments (Buatois & Mángano, 2003; Astini,
tus, Parabolinella, Plicatolina, Beltella, 2003). The unit displays fluvio-estuarine (Tilcara
Angelina, Akoldinioidia, Asaphellus and and Pico de Halcón Members), shoreface and
Onychopyge (Tortello & Esteban, 2003; Esteban offshore sediments (Casa Colorada, Alfarcito,
& Tortello, 2007, 2009), whereas other localities, Rupasca and Humacha Members) which accu-
especially around the Quebrada de Humahuaca mulated on a gently dipping shelf (Buatois &
(Santa Rosita Formation; Finca Soledad, Mángano, 2003; Moya et al., 2003; Buatois et al.,
Alfarcito, Purmamarca, Punta Corral, Volcán), 2006 and references; Esteban et al., 2015).
show lower biodiversity values (Harrington The trilobites studied herein come from the
& Leanza, 1957; Aceñolaza, 1996, unpub- discoloured siltstones and shales of the Casa
lished; Zeballo & Tortello, 2005; Buatois et al., Colorada Member exposed at the Abra Blanca
2006; Zeballo, 2010, unpublished) (Fig. 1.A). creek (Fig. 2.A, B), about 3 km southeast of
In addition, there are still some outcrops Huacalera village, Jujuy Province (Fig. 1.A, B).
that require further sampling and comprehen- There, a 110 m-thick section displays thinly bed-
sive systematic and biostratigraphic studies. In ded yellowish and light brown shales with inter-
this regard, the Huacalera region is of particu- calations of sandstones, which overlie the sand-
lar importance (Fig. 1.B). In Quebrada de La stones of the Tilcara Member and are overlain by
Huerta, Manca (1992) reported the occurrence Quaternary deposits.
of P. frequens argentina in association with frag-
mentary material of Lotagnostus Whitehouse, BIOSTRATIGRAPHIC IMPLICATIONS OF
1936, a key fossil of Furongian strata of differ- THE FAUNAS
ent continents. In addition, Di Cunzolo (2006)
and Zeballo (2010, unpublished) mentioned the The assemblage studied is clearly dominated
presence of P. frequens argentina in Quebrada de by Parabolina (Neoparabolina) frequens argen-
Abra Blanca, although detailed systematic study tina (Kayser, 1876), followed in abundance by
was not achieved. Based on new collections, the Parabolinella coelatifrons Harrington & Leanza,
present paper includes a description of the trilo- 1957 and Lotagnostus hedini (Troedsson,
bite assemblages from Quebrada de Abra Blanca 1937). Parabolina frequens argentina is a key
and a discussion on their biostratigraphic impli- taxon of the eponymous zone (cf. Harrington &
cations. The material studied provides precise Leanza, 1957); a unit that is widely exposed in
information on the age of the P. frequens argen- northwestern Argentina (Esteban & Tortello,
tina Zone, which correlates with late Furongian 2007; Waisfeld & Vaccari, 2008 and references).
successions of China, Kazakhstan and Canada. Although this biozone was originally assigned
to the Lower Tremadocian (see Harrington &
GEOLOGICAL SETTING Leanza, 1957), subsequent studies confirmed the
Cambrian aspect of the strata bearing P. frequens
The Cordillera Oriental is a high relief thrust argentina, below the first appearance of the tri-
system that is delimited to the east by the Sierras lobite Jujuyaspis keideli Kobayashi, 1936 and
Subandinas and to the west by the Puna. Lower the graptolite Rhabdinopora flabelliformis s.l.
Paleozoic rocks are well represented in the (Branisa, 1965; Benedetto, 1977; Rushton, 1982,
mountain ranges of this geological province, in- p. 46; Ludvigsen, 1982, p. 150; Aceñolaza, 1983;
cluding Cambrian quarzites of the Mesón Group Salfity et al., 1984; Shergold, 1988, p. 367).
and late Furongian–Early Ordovician shales and The first evidence of the genus Lotagnostus
sandstones of the Santa Victoria Group (Santa in the Cordillera Oriental was provided by
Rosita and Acoite formations and equivalents), Manca (1992), who described one cephalon and
which are juxtaposed on Neoproterozoic–early one fragmentary pygidium (Lotagnostus sp.)
Cambrian slates and meta-graywackes of the associated with Parabolina frequens argentina
Tortello et al.: A late Furongian trilobite assemblage from the eastern Cordillera Oriental 273
Fig. 1. Location map. A, Cordillera Oriental, northwestern Argentina. B, fossil locality (asterisk).
from Quebrada de la Huerta (Fig. 1). Because vus, C. andresi, Eoconodontus notchpeakensis,
Lotagnostus is a cosmopolitan key fossil of late Hirsutodontus hirsutus and Proconodontus
Furongian age, (e.g., Shergold & Laurie, 1997 and muelleri (Rao, 1999; Moya et al., 2003; Zeballo
references), its finding in the P. frequens argen- & Albanesi, 2013, fig. 2). Additionally, the low-
tina Zone provided strong evidence in favor of a est Ordovician index fossil Iapetognathus fluc-
pre-Tremadocian age for this unit. Subsequently tivagus Nicoll, Miller, Nowlan, Repetski and
Esteban & Tortello (2007) described new material Ethington occurs in the upper part of the overly-
of Lotagnostus (Lotagnostus shergoldi Tortello; ing Cardonal Formation at Sierra de Cajas, defin-
L. llamaensis Tortello), associated with P. fre- ing the Cambrian-Ordovician boundary in that
quens argentina and other species of the biozone, area (Albanesi et al., 2015).
from different localities of the western Cordillera The record of Lotagnostus hedini (Troedsson,
Oriental (Lampazar Formation; Sierra de Cajas, 1937) in the Quebrada de Abra Blanca provides
Angosto del Moreno, Quebrada de Jueya). new high resolution data on the age of the
In addition, studies of conodont faunas sup- Parabolina frequens argentina Zone within the
plied more precise information about the age of late Furongian. This information is novel for the
the P. frequens argentina Zone in the Lampazar eastern part (Eastern Belt sensu Astini, 2003)
Formation. At Sierra de Cajas and Angosto del of the Cordillera Oriental (lower Santa Rosita
Moreno, P. frequens argentina occurs in associa- Formation, Casa Colorada Member), where con-
tion with conodonts of the Cordylodus proavus odont-bearing strata have not been found yet
Zone (Hirsutodontus hirsutus Subzone), which (Zeballo & Albanesi, 2013). Lotagnostus hedini
include, in particular, C. proavus, C. primiti- is one of the youngest species of Lotagnostus
274 Revista del Museo Argentino de Ciencias Naturales, n. s. 20(2), 2018
Fig. 2. Lower part of the Santa Rosita Formation at Quebrada de Abra Blanca, Huacalera area, Jujuy. A,
stratigraphic section showing distributions of trilobites identified. B, photograph showing part of the outcrop.
and exhibits a short biostratigraphic range, re- of the graptolite Rhabdinopora (Rushton, 1982).
stricted to the latest Furongian. It is known from Fragmentary material of P. frequens has also
the Bulbolenus Zone of Xinjiang, Northwest been described from the late Furongian of Mexico
China (Troedsson, 1937), the Lotagnostus hedi- (Tiñu Formation), from levels of the Cordylodus
ni Zone of western Zhejiang, China (Lu & Lin, proavus Zone (Robison & Pantoja-Alor, 1968;
1980, 1981, 1983a–c, 1984, 1989), the Euloma Landing et al., 2007).
limitaris-Taoyuania Zone of the Malyi Karatau As noted above, the trilobite assemblage
Range of Kazakhstan (Apollonov et al., 1984), of Quebrada de Abra Blanca is completed with
and, probably, the Phylacterus saylesi Fauna Parabolinella coelatifrons. To date, this species is
of western Newfoundland (Ludvigsen et al., restricted to the P. frequens argentina Zone. Type
1989; see Westrop et al., 2011). In Zhejiang and specimens were collected from Cerro Colorado
Kazakhstan, L. hedini is recorded with, or a in the Iruya Department in Salta Province, in
few meters below, the first appearance (FAD) of association with P. frequens argentina, the ole-
Cordylodus proavus. nid Plicatolina scalpta Harrington & Leanza,
The occurrence of L. hedini in the P. frequens 1957, and the agnostoids Pseudorhaptagnostus
argentina Zone is in line with the global upper (Machairagnostus) tmetus Harrington & Leanza,
Cambrian correlation chart of Shergold (1988, 1957 and Micragnostus vilonii Harrington &
fig. 2). Strata with L. hedini correlate with the Leanza, 1957 (Harrington & Leanza, 1957). In
Acerocare Zone of Avalon and the Baltic region. addition, Parabolinella coelatifrons is part of si-
Rushton (1982) and (2001) recognized milar assemblages in Orán, Salta (Harrington &
Żylińska
olenid faunas including Parabolina frequens in Leanza, 1957), Iruya, Salta (Esteban & Tortello,
Wales and Poland, respectively, below the record 2009), Sierra de Cajas and Quebrada de Jueya,
Tortello et al.: A late Furongian trilobite assemblage from the eastern Cordillera Oriental 275
Jujuy (Tortello & Esteban, 2003; Esteban & clearly delimited by conspicuous basal furrows,
Tortello, 2007). length (exs.) equal to about 35–40% of glabellar
length (sag.), with anterior tip reaching F2; gla-
SYSTEMATIC PALEONTOLOGY bellar rear rounded; F1 almost imperceptible; F2
shallow but better developed than F1, directed
The material is housed in the Museo de inward from the axial furrows and then curved
Paleontología, Facultad de Ciencias Exactas, strongly forward exsagittally, delimiting two lat-
Físicas y Naturales, Universidad Nacional de eral lobes (M3); median node posterior to the gla-
Córdoba (CORD-PZ), and the Museo de La bellar midpoint, elongate (sag.), better defined
Plata, Facultad de Ciencias Naturales y Museo, posteriorly (between F1 and F2); transglabellar
Universidad Nacional de La Plata (MLP). furrow (F3) well-defined, curved forward exsag-
Specimens were whitened with magnesium oxide ittally; anteroglabella ogival, occupying about
vapors before photographing. TThhee mmoorrpphhoollooggii-- 42–43% of glabellar length. Gena smooth (Fig.
cal terms used below have been mostly defined 3.B) or with weak indications of scrobiculation
by Robison (1964), Shergold et al. (1990) and (Fig. 3.E), somewhat narrower (sag.) in front of
Whittington & Kelly (1997). the glabella; median preglabellar furrow slightly
Abbreviations: sag sagittally; exs exsagittally. shallower than axial furrows, extending fully
from the anterior tip of the glabella to the border
Order Agnostida Salter, 1864b furrow. Cephalic border narrow (sag.) and con-
Family Agnostidae M‘Coy, 1849 vex, separated from the gena by a well-defined
Subfamily Agnostinae M‘Coy, 1849 border furrow; sagittally, the border and border
furrow combined occupy about 7–8% of the total
Genus Lotagnostus Whitehouse, 1936 length of the cephalon; posterior border with a
tiny intergenal spine.
Type species. Agnostus trisectus Salter, 1864a. Pygidium en grande tenue, subelliptical in
outline in dorsal view, slightly wider than long;
Remarks. The diagnosis of Lotagnostus was dis- axis long, trilobed, slightly constricted at M2, oocc--
cussed in detail by Shergold & Laurie (1997 and cupying about 85% of the total pygidial length
references) and Westrop et al. (2011). Westrop (excluding articulating half-ring), clearly delim-
(1995) and Westrop et al. (2011) regarded the ited by narrow, deep axial furrows; M1 and M2
partially effaced taxon Distagnostus Shergold, divided into a pair of subquadrate lateral lobes
1972, as a junior synonym of Lotagnostus, a deci- and a central, elongate tubercle; F1 and F2 of
sion that is accepted herein. similar width and depth, continuous across axis;
M3 long, semiovate to ogival in outline, occupying
62–64% of the total length of the axis (excluding
Lotagnostus hedini (Troedsson, 1937)
articulating half-ring), smooth or with faint indi-
Fig. 3.A, B, E, H
cations of an intranotular axis and a delicate ter-
1937. Agnostus hedini sp. nov. Troedsson, p. 20, pl. 1, minal node. Acrolobe gently constricted; pleural
figs. 6–8. fields smooth, confluent, narrower (sag.) behind
2011. Lotagnostus hedini (Troedsson). Westrop, Adrain the axis. Border narrow (sag.) and slightly con-
& Landing, p. 584, 586 (see for further synonymy). vex, separated from the pleural fields by a shal-
low border furrow of variable width; sagittally,
Material. Three complete specimens and one the border and border furrow combined occupy
fragmentary thoracopygon (MLP 35824–35826, about 6–7% of the total length of the pygidium
CORD-PZ 32189). (excluding articulating half-ring); posterolateral
Description. Exoskeleton of large size. Cephalon spine vestigial, with base opposite posterior third
en grande tenue, subcircular to subelliptical in of axis.
outline in dorsal view, slightly wider than long Remarks. The specimens studied are preserved
(maximum width at the posterior part of ac- in siliciclastic rocks and are partially compacted,
rolobe). Glabella long, parallel-sided to gently so that they do not exhibit their original con-
tapered forward, faintly constricted at F2 and vexity. Nevertheless, the state of preservation
F3, pointed anteriorly, clearly defined by nar- of the material is quite good. Specimens are
row, deep axial furrows, occupying about 73-74% characterized by the presence of a proportion-
of cephalic length (sag.); basal lobes large, en- ately long glabella, a broad V-shaped F3 glabel-
tire, subtriangular in outline, longer than wide, lar furrow, conspicuous basal lobes, a smooth to
276 Revista del Museo Argentino de Ciencias Naturales, n. s. 20(2), 2018
weakly scrobiculate gena, a pygidial F1 that is ous F1 pygidial furrow, an unconstricted pygid-
connected across the axis, a long posteroaxis oc- ial acrolobe, and a border lacking posterolateral
cupying more than 60% of the total length of the spines. Lotagnostus shergoldi has, in addition, a
axis, and a slightly constricted pygidial acrolobe. less constricted pygidial M2, and L. llamaensis
This combination of characters indicates direct exhibits a semicircular cephalon and a more deli-
morphological affinities with Lotagnostus hedini cate pygidial axial node.
(Troedsson, 1937), from the uppermost Cambrian
Lotagnostus hedini is similar to L. peladen-
of Xinjiang, Northwest China (Troedsson, 1937,
sis (Rusconi, 1951), from the upper Furongian
pl. 1, figs. 6–8), western Zhejiang, China (Lu &
of the Argentine Precordillera (e.g., Shergold et
Lin 1980, pl. 1, figs. 8, 9; 1983a, pl. 1, figs. 5-6;
al., 1995, pl. 1, figs. 1–9; Tortello, 2014, figs. 2.1–
1983b, pl. 2, figs. 4, 5; 1984, pl. 3, figs. 12, 13;
2.28, 3.1–3.7), but the exoskeleton of the latter
1989, pl. 7, figs. 4–8), Kazakhstan (Apollonov et
differs by having variably effaced dorsal furrows,
al., 1984, pl. 14, figs. 1–8) and, possibly, western
a proportionately shorter (sag.) pygidial axis, and
Newfoundland (Ludvigsen et al. 1989, pl. 1, figs.
9–11-only-). Westrop et al. (2011, p. 584, 586) a pygidial F1 that is not continuous across the
provided a diagnosis of L. hedini and updated axis. Another species from the Precordillera, L.
information about its synonymy, distribution atenuatus (Rusconi, 1955), is also distinguished
and affinities with allied species (see also Peng by its discontinuous pygidial F1 and, also, by its
et al., 2015, p. 299–300). Lotagnostus hedini usu- relatively shorter glabella, pygidial axis and pos-
ally possesses smooth genae, but some specimens teroaxis (Westrop et al., 2011; Tortello, 2018). As
from W. Zhejiang (Lu & Lin, 1983, pl. 2, fig. 4), indicated by Westrop et al. (2011) and Peng et al.
Kazakhstan (Apollonov et al., 1984, pl. 14, fig. (2015, p. 299–300), the transaxial F1 furrow and
6) and Argentina (Fig. 3.E) show faint signs of the large size of the pygidial axis are two of the
genal scrobiculation. Similarly, the posteroaxis is
most diagnostic characters of L. hedini.
generally smooth, with the exception of certain
cases from China (see Lu & Lin, 1989, p. 216;
Order Ptychopariida Swinnerton, 1915
Peng et al., 2015) and the Argentinian Cordillera
Suborder Olenina Burmeister, 1843
Oriental (Fig. 3.B), which exhibit indications of
Family Olenidae Burmeister, 1843
notular furrows. Intraspecific variability also
Subfamily Oleninae Burmeister, 1843
involves proportions of axial characters. The py-
gidial axis of small holaspides seems to be a lit-
Genus Parabolinella Brøgger, 1882
tle shorter (sag.) than that of larger specimens
(compare Fig. 3.A with Fig. 3.E).
As stated above, Manca (1992) described Type species. Parabolinella limitis Brøgger,
scarce material of Lotagnostus sp. from Quebrada 1882.
de La Huerta, consisting of one cephalon and one
incomplete pygidium. The latter apparently dif- Parabolinella coelatifrons Harrington & Leanza,
fers from L. hedini in having a discontinuous F1 1957
and a much shorter (sag.) posteroaxis; however, Fig. 3.C, D, F, G, I–L
the deficient state of preservation of this speci-
men prevents a proper comparison. Lotagnostus 1957 Parabolinella coelatifrons sp. nov. Harrington &
shergoldi Tortello in Esteban & Tortello (2007, Leanza, p. 109, fig. 39.3a, b, d–f, h (non fig. 39.3c,
fig. 8A–I, L) and L. llamaensis Tortello in g).
Esteban & Tortello (2007, fig. 8J–K, M–Q), from 2007 Parabolinella coelatifrons Harrington & Leanza.
the western Cordillera Oriental, are clearly dis- Esteban & Tortello, p. 49, fig. 11B–D, L (top) (see
tinguished from L. hedini because the former for further synonymy).
have a partially effaced exoskeleton, a more an- 2009 Parabolinella cf. coelatifrons Harrington &
teriorly positioned glabellar node, a discontinu- Leanza. Esteban & Tortello, p. 148, fig. 11.C, D, H, J.
Fig. 3. (Next page) Trilobites from the Parabolina frequens argentina Zone of Quebrada de Abra Blanca,
Huacalera area, Jujuy. A, B, E, H, Lotagnostus hedini (Troedsson, 1937); A, fragmentary exoskeleton, MLP
35825; B, complete specimen, CORD-PZ 32189; E, complete specimen, MLP 35824; H, pygidium and fragmentary
thorax, latex mould, MLP 35826. C, D, F, G, I–L, Parabolinella coelatifrons Harrington & Leanza, 1957; C,
complete specimen, CORD-PZ 32182; D, fragmentary cranidium and thorax, MLP 35827; F, complete specimen,
CORD-PZ 32190a; G, cephalon and fragmentary thorax, CORD-PZ 32153; I, cranidium and fragmentary thorax,
CORD-PZ 32173; J, complete specimen, MLP 35828; K, axial shield, MLP 35831; L, cranidium, MLP 35829.
Tortello et al.: A late Furongian trilobite assemblage from the eastern Cordillera Oriental 277
278 Revista del Museo Argentino de Ciencias Naturales, n. s. 20(2), 2018
Material. Five complete specimens, four cephala Parabolina (Neoparabolina) frequens argentina
and thoraces, one cranidium, one cranidium and (Kayser, 1876)
fragmentary thorax, two axial shields and one Fig. 4.A–K
thoracopygon (CORD-PZ 32153, 32156, 32171,
32173, 32182, 32187, 32190, 32440a; MLP Synonymy. See Tortello & Clarkson (2008) and
35827–35832). references therein.
Remarks. Parabolinella coelatifrons Harrington
& Leanza is well represented in the Parabolina Material figured. One complete specimen, one
frequens argentina Biozone (Harrington & cephalon, three cephala and thoraces, two axial
Leanza, 1957; Tortello & Esteban, 2003; Esteban shields, and five thoraces and pygidia (CORD-PZ
& Tortello, 2007). This species is characterized 32152, 32163b, 32176, 32177a, 32192a,b; MLP
by the presence of a well-developed, faintly stri- 35833–35837).
ated preglabellar field; a sub-squared glabella
having three pairs of lateral glabellar furrows; a Remarks. Parabolina frequens argentina is an
facial suture with sub-parallel anterior branches emblematic late Cambrian trilobite of northwest-
and straight posterior branches, defining sub-tri- ern Argentina and southern Bolivia (Harrington
angular fixigenae; and a pygidium with two axial & Leanza, 1957; Waisfeld & Vaccari, 2003). As
rings. Specimens from Quebrada de Abra Blanca stated by Harrington & Leanza (1957) and
combine all of these characters, but also display Tortello & Clarkson (2008), this olenid exhibits
some intraspecific variability which broadens the a relatively high morphologic variability. In the
scope of P. coelatifrons. Variations involve the de- material from Quebrada de Abra Blanca, vari-
gree of development of the preglabellar field (Fig. ations are especially evident in the width (sag.)
3.I, L), the shape of the anterior glabellar margin of the cephalic anterior border (Fig. 4.A, G), and
(Fig. 3.D, G, J), and the width of the posterior the degree of expression of the thoracic axial
margin of the fixigenae (Fig. 3.D, F, I). nodes, which are better developed in small adults
Esteban & Tortello (2009, fig. 11.C, D, H, J) (e.g., compare Fig. 4.F with Fig. 4.K). It is inter-
assigned to Parabolinella cf. coelatifrons several esting to note that some late holaspid specimens
cranidia from the Iruya area, pointing out that studied herein reach large sizes (largest observed
their preglabellar furrows are more curved than exoskeleton –excluding 12th thoracic axial spine-:
those of the typical representatives of P. coelati- 43mm in length).
frons. However, according to the variability re-
ported above, these cranidia are now regarded ACKNOWLEDGEMENTS
confidently as belonging to this species.
Some specimens from Quebrada de Abra We thank Gladys Ortega, Guillermo Albanesi,
Blanca show the librigenae displaced back- Susana Esteban and Eric Hasselrot for assistance
wards below the axial shield (Fig. 3.C, F, G). in the field. The journal reviewers, Adrian Rushton
This configuration is common among olenids and Steve Westrop, made valuable comments on
(e.g. Henningmoen, 1957; Clarkson et al., 2003; the manuscript. FFiinnaanncciiaall ssuuppppoorrtt wwaass pprroovvii--
Tortello & Clarkson, 2003) and is interpreted as ded by the Consejo Nacional de Investigaciones
the result of the molting process (Harrington, Científicas y Técnicas (CONICET), the Instituto
1959; Henningsmoen, 1975). Superior de Correlación Geológica (CONICET
– Universidad Nacional de Tucumán) and the
Genus Parabolina Salter, 1849 Universidad Nacional de La Plata, Argentina.
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