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First evidence of Lower–?Middle Ordovician (Floian–?Dapingian)
brachiopods from the Peruvian Altiplano and their
paleogeographical significance
Jorge Colmenar1and Eben Blake Hodgin2
1
Centro de Geociências, Universidade de Coimbra, Coimbra 3000-272, Portugal <jorgecolmenarlallena@gmail.com>
2
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA hodgin@fas.harvard.edu
Abstract.—The lower strata of the Umachiri Formation from the Altiplano of southeast Peru haveyielded a brachiopod-
dominated assemblage, containing representatives of the brachiopod superfamilies Polytoechioidea, Orthoidea, and
Porambonitoidea, as well as subsidiary trilobite and echinoderm remains. Two new polytoechioid genera and species,
Enriquetoechia umachiriensis new genus new species and Altiplanotoechia hodgini n. gen. n. sp. Colmenar in Colmenar
and Hodgin, 2020, and one new species, Pomatotrema laubacheri n. sp., are described. The presence of Pomatotrema in
the Peruvian Altiplano represents the occurrence at highest paleolatitude of this genus, normally restricted to low-latitude
successions from Laurentia and South China. Other polytoechioids belonging to Tritoechia (Tritoechia) and Tritoechia
(Parvitritoechia) also occur. Identified species of orthoids from the genera Paralenorthis,Mollesella, and Panderina?
occur in the Peruvian Cordillera Oriental and in the Argentinian Famatina Range. The only porambonitoid represented
is closely related to Rugostrophia latireticulata Neuman, 1976 from New World Island, interpreted as peri-Laurentian.
These brachiopod occurrences indicate a strong biogeographic affinity of the Peruvian Altiplano with the Famatina and
western Puna regions, suggesting that the brachiopod faunas of the Peruvian Altiplano, Famatina, and western Puna
belonged to a well-differentiated biogeographical subprovince during the Early–Middle Ordovician on the margin of
southwestern Gondwana. Links with peri-Laurentian and other low-latitude terranes could be explained by island hop-
ping and/or continuous island arcs, which might facilitate brachiopod larvae dispersal from the Peruvian Altiplano to
those terranes across the Iapetus Ocean. Brachiopods from the lower part of the Umachiri Formation indicate a
Floian–?Dapingian age, becoming the oldest Ordovician fossils of the Peruvian Altiplano.
UUID: http://zoobank.org/9670a000-260d-4d75-9261-110854c7afb8
Introduction
The paleobiogeography of the Central Andes during the Ordovi-
cian has been extensively investigated using benthic fossil
groups such as brachiopods from Argentina (Benedetto et al.,
2009 and references therein), Chile (Benedetto et al., 2008),
Bolivia (Havlíc
ek and Branisa, 1980; Benedetto, 2013), and
Peru (Hughes et al., 1980; Gutiérrez-Marco and Villas, 2007;
Villas et al., 2015); trilobites from Argentina (Tortello and Este-
ban, 2003; Waisfeld and Vaccari, 2003 and references therein),
Bolivia (Pr
ibyl and Vane
k, 1980), and Peru (Hughes et al., 1980;
Gutiérrez-Marco et al., 2015); bivalves and rostroconch mol-
lusks from Argentina (Sánchez, 2003,2008, and references
therein) and Bolivia (Babin and Branisa, 1987; Sánchez and
Babin, 2005); sponges from Argentina (Carrera and Rigby,
1999; Carrera, 2003); and ostracods from Argentina (Salas,
2002a,b; Williams et al., 2003).
The Tremadocian–Floian brachiopod assemblages of the
Cordillera Oriental, including its Argentinian, Bolivian, and
Peruvian segments, show high endemism during this time, shar-
ing only one genus with the western Puna Region of Argentina
(Lipanorthis Benedetto in Benedetto and Carrasco, 2002),
suggesting proximity but a certain degree of isolation between
these two regions. The faunal affinity in the Cordillera Oriental
indicates a strong peri-Gondwanan influence (from both high
and low latitudes) as demonstrated by the occurrence of Kvania
Havlíc
ek, 1994,Gondwanorthis Benedetto and Muñoz, 2017,
Euorthisina Havlíc
ek, 1950, and Tarfaya Havlíc
ek, 1971. Celtic
genera (Astraborthis Williams, 1974 and Monorthis Bates,
1968) are also present in the assemblages of the Cordillera
Oriental, implying direct links with Avalonia during Tremado-
cian and Floian times.
The Argentinian western Puna and Famatina Lower Ordo-
vician assemblages have several taxa in common such as the
genera Hesperonomia Ulrich and Cooper, 1936,Tritoechia
Ulrich and Cooper, 1936, and Rugostrophia Neuman, 1971
and the species Monorthis transversa Benedetto, 2003 and
even share endemic genera such as Pinatotoechia Benedetto,
2001 and Trigonostrophia Benedetto, 2003. Faunal evidence
is consistent with the existence of a continuous Puna–Famati-
nian arc likely connecting with Avalonia (Benedetto, 1998;
Ramos, 2018) and retroarc foreland basin (Astini and Dávila,
2004) extending between these two regions along the proto-
Andean margin of Gondwana (Benedetto, 1998). Despite the
Journal of Paleontology, page 1 of 19
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0022-3360/20/1937-2337
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strong endemicity of the Puna–Famatinian brachiopod assem-
blages, certain faunal exchange with other regions occurred dur-
ing that time as suggested by associations of several Celtic and
low-latitude genera (Schizambon Walcott, 1884, Rugostrophia,
Ffynnonia Neuman and Bates, 1978, and Hesperonomia Ulrich
and Cooper, 1936), minor representatives of high-latitude peri-
Gondwana (Incorthis Havlíc
ek and Branisa, 1980), and
abundant cosmopolitan genera. The Celtic signature of the
Puna–Famatinian assemblages was also supported by multivari-
ate analysis (Benedetto, 2004; Benedetto et al., 2009). Faunal
exchange among the Central Andean Basin (comprising the
Altiplano/Puna, the Cordillera Oriental, and the Subandean
Ranges), the Famatina Basin, and the Cuyania Terrane (Precor-
dillera) likely started during the late Floian–Dapingian, slightly
before the estimated time for docking of the Cuyania Terrane
against Gondwana (Benedetto, 2004; Lavié and Benedetto,
2016,2019). At that time, the separation of this terrane from
the main continent could have been small enough to facilitate
fluid faunal exchange (Benedetto, 2004; Lavié and Benedetto,
2016,2019).
As stated in the preceding, the faunal affinities of the Early
Ordovician brachiopod assemblages of the Argentinian segment
of the Central Andes are well known. However, the biogeo-
graphic relations of the Peruvian Altiplano, which is the northern
continuation of the Bolivian Altiplano and Argentinian western
Puna, have remained obscured until now. The assemblages of
the Umachiri Formation described in this paper contain the
only Early–?Middle Ordovician fossils known in the Peruvian
Altiplano and, thus, could potentially shed light on the paleo-
geography of this region and its biogeographic affinity with
other terranes of the southwestern margin of Gondwana during
the Early–Middle Ordovician.
Geographical and geological setting
The Andean Altiplano (= high plains morphotectonic region)
extends from western Bolivia to southern Peru, comprising
base elevation ranging from 3,600 to 4,500 m (Fig. 1). Geologic-
ally, it is a structural block with a distinct tectonostratigraphic
history from the Eastern and Western Cordilleras of the Central
Andes (Carlotto, 2013). The basement of the Altiplano is inter-
preted as the Arequipa Terrane (for extent and boundaries of this
terrane, see Ramos, 2008). The partial detachment of this terrane
from the Amazonian Craton led to the development of a large
retroarc basin of Ordovician to Devonian strata known as the
Central Andean Basin (Sempere, 1995; Bahlburg et al., 2006;
Ramos, 2018).
Upper Ordovician siliciclastic rocks have been identified
near Lake Titicaca, an area known as the Calapuja Formation
(Laubacher, 1974,1977,1978; Laubacher et al., 1982). This
unit has yielded abundant brachiopods, trilobites, gastropods,
bivalves, echinoderms, bryozoans, cornulitids, cnidarians, and
sponge spicules, suggesting a Sandbian age for these strata (Lau-
bacher, 1977; Villas et al., 2015; Gutiérrez-Marco et al., 2016;
Vinn and Gutiérrez-Marco, 2016; Ebbestad and Gutiérrez-
Marco, 2019). Previously, outcrops identified as the Calapuja
Formation north of Ayaviri have been tentatively correlated
with the Sandia and San Gabán formations of the Peruvian
Cordillera Oriental (Díaz-Martínez et al., 2001). Older strata
crop out 15 km to the west of Ayaviri, near Umachiri village,
in a succession that has been referred to as the Serie Umachiri
(Flores and Rodríguez, 1999; Carlotto et al., 2004; Ibarra
et al., 2004), also known as the Umachiri beds (Bahlburg
et al., 2006,2011). These beds are currently being redefined
as the Umachiri Formation, and it comprises approximately
2,400 m of conglomerate, sandstone, greywacke, siltstone, and
rare limestone (Fig. 2). Preliminary results suggest a correlation
of this unit with the Lower to Middle Ordovician Verónica and
San José formations of southern Peru.
Materials and methods
The material for this study was collected by one of us (EBH)
during field campaigns in 2017 and 2018. Five fossiliferous hor-
izons were identified in the Umachiri Formation (Figs. 1,2).
Four horizons (localities 1–4) are situated 100–150 m from the
base of the formation, yielding a brachiopod-dominated assem-
blage with scattered trilobite sclerites and a single columnal
plate of pelmatozoan echinoderms; another fossiliferous horizon
is located at about 1,700 m (locality 5), yielding poorly pre-
served graptolites (identified by Cerrón and Chacaltana,
2002). All fossil remains are preserved as internal and external
molds. Brachiopods occur in localities 1–4 and will be described
herein. Fossils have been prepared using mechanical methods in
the labs of the Universidad Complutense of Madrid. Latex casts
of the specimens were subsequently prepared for replicating the
internal and external features. Fossils and latex casts were whi-
tened using magnesium oxide smoke for photography and stud-
ied under binocular microscopes.
Repository and institutional abbreviation.—Original specimens
are deposited in the paleontological collection (prefixed CPI) of
the Instituto Geológico, Minero y Metalúrgico (INGEMMET)
in Lima, Peru.
Systematic paleontology
(by J. Colmenar)
The use of open nomenclature follows Bengtson (1988),
and the synonymy lists follow recommendations by Matthews
(1973).
Phylum Brachiopoda Duméril, 1806
Subphylum Rhynchonelliformea Williams et al., 1996
Class Strophomenata Williams et al., 1996
Order Billingsellida Schuchert, 1893
Suborder Billingsellidina Öpik, 1934
Superfamily Polytoechioidea Öpik, 1934
Family Polytoechiidae Öpik, 1934
Genus Enriquetoechia new genus
Type species.—Enriquetoechia umachiriensis n. gen. n. sp.,
from the lower part of the Umachiri Formation, Peruvian
Altiplano, Floian–?Dapingian (Lower–Middle Ordovician).
Diagnosis.—As for the species by monotypy.
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Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Etymology.—After Enrique Villas, brachiopod researcher, who
described the first Ordovician brachiopod species of Peru.
Remarks.—Phylogeny of Order Billingsellida has been recently
revised by Topper et al. (2013) suggesting that polytoechioids
are derived billingselloids, distinct from the clitambonitoids
that are a sister group.
There have been extensive discussions about which are the
key taxonomical characters for discriminating among the Billing-
sellida. Wright and Rubel (1996) suggested the use of structures
related with their vital functions as key features for superfamily
discrimination within this order. These criteria were followed sub-
sequently by several authors (Rubel andWright in Williams et al.,
2000;Popovetal.,2001;Vinn,2001; Topper et al., 2013,among
others). Of special significance are the spondylium/pseudospon-
dylium and related structures and the structures covering the
delthyrium and notothyrium.
Figure 1. (1) Geographical location of Umachiri village. (2) Detailed geological map of the study area. Numbered white stars indicate fossiliferous horizons and
localities: 1, samples B1799 and B1806; 2, samples K1708 and B1807; 3, sample B1808; 4, sample B1798; 5, graptolite locality from Cerrón and Chacaltana(2002,
2003).
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 3
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The delthyrium in the clitambonitine varies from open to
partially covered by chilidial plates to completely covered by
either a deltidium or a pseudodeltidium. However, the distinc-
tion between deltidium and pseudodeltidium is problematic
since details, unfortunately, are not preserved in all genera
(Wright and Rubel, 1996). The notothyrium in the Billingsellida
varies from totally open to partially covered by chilidial plates to
completely covered by the chilidium. The cladistic analysis per-
formed by Topper et al. (2013) suggested that the combined
presence of a well-developed pseudodeltidium and chilidial
plates/chilidium are distinct features shared by most billingsel-
loids and polytoechioids, while clitambonitoids are character-
ized by having a deltidium.
The spondylium has been described as a spoon-like ele-
vated platform formed by dental plates that coalesce to a varying
degree, supported by a median septum, accommodating the ven-
tral muscle field (Williams et al., 2000). However, Vinn and
Rubel (2000), studying this structure in several juvenile speci-
mens of genera ascribed to the suborder Clitambonitidina,
noted that the spondylium does not derive from the convergence
of dental plates but develops from the free plate in early ontogen-
etic stages. In the clitambonitidine brachiopods, three kinds of
spondylium are common: spondylium simplex, which is solely
supported by the median ridge; spondylium triplex, which is
freestanding and supported in early stages only by the median
ridge and afterward additionally by auxiliary lateral ridges grow-
ing on both sides of the median ridge, on the undersurface of the
spondylium that may or may not reach the valve floor; and pseu-
dospondylium, a structure that mimics the spondylium but is
developed instead by discrete, parallel dental plates that reach
the valve floor early in the ontogeny, being the muscle field rest-
ing, between them, on the valve floor at that time. During the
ontogeny, the muscle field is raised by shell thickening, forming
a sessile spondylium. In some cases, this raised muscle field is
undercut anterolaterally, in lesser or higher degree, becoming
even free anteriorly and supported medially and laterally by den-
tal plates simulating the spondylium triplex, as occurs in some
genera assigned to the superfamily Polytoechioidea such as
Polytoechia Hall and Clarke, 1892,Antigonambonites Öpik,
1934, and Raunites Öpik, 1939 (Wright and Rubel, 1996;
Vinn and Rubel, 2000; Topper et al., 2013; Benedetto, 2016).
Wright and Rubel (1996, p. 62) also stated that “the opposite
is also true: a well-developed spondylium triplex, with its lateral
septa reaching the valve floor, strongly simulates a pseudospon-
dylium.”Finally, the spondylium simplex characterizes all cli-
tambonitoids excepting the gonambonitids, which develop a
spondylium triplex, whereas the presence of a pseudospondy-
lium distinguishes the polytoechioids.
Thus, observations of the well-developed convex pseudo-
deltidium, the chilidial plates, and the pseudospondylium mim-
icking the spondylium triplex all suggest including the Peruvian
material within the Polytoechioidea. Two families of polytoe-
chioids are recognized: Polytoechiidae and Tritoechiidae. The
former is characterized by having a free pseudospondylium, sup-
ported medially by a median ridge and laterally by dental plates
resembling the spondylium triplex of gonambonitids (Vinn and
Rubel, 2000). However, the tritoechiids differ by displaying the
ventral muscle field resting directly on the valve floor or raised
by shell thickening on a pseudospondylium not undercut
Figure 2. Composite stratigraphy of the Umachiri Formation at Umachiri.
Numbered white stars indicate fossiliferous intervals: 1, samples B1799 and
B1806; 2, samples K1708 and B1807; 3, sample B1808; 4, sample B1798; 5,
graptolite sample from Cerrón and Chacaltana (2002,2003). si = silt; f = fine
sand; m = medium sand; c = coarse sand; gr = gravel.
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anteriorly (sessile). Thus, this material may be ascribed to the
Polytoechiidae. Among the genera included in this family, the
Peruvian taxon strongly resembles Antigonambonites by having
a free-anteriorly pseudospondylium, with a small, transverse
ridge separating posteriorly each socket in the dorsal valve,
and radial grooves in the ventral interarea at both sides of the
convex pseudodeltidium, which limit the external dental lamella
with the interarea; it differs in lacking ventral and dorsal periph-
eral rims and a more raised pseudospondylium. Antigonambo-
nites is considered in the Treatise (Williams et al., 2000)tobe
a gonambonitid, but since this genus has a pseudospondylium
and not a spondylium triplex, as many authors suggested
(Vinn and Rubel, 2000; Popov et al., 2001; Vinn, 2001), it is
now considered a polytoechiid (Topper et al., 2013). In my opin-
ion, another gonambonitid, Jaanussonites Neuman, 1976, also
has a pseudospondylium, with the muscle field resting directly
on the valve floor in early growth stages and becoming free
and elevated anteriorly. In addition, this genus displays chilidial
plates and radially arranged dorsal muscle scars, which are typ-
ical characters of the polytoechioids. This genus has not been
included in the cladistic analysis of Topper et al. (2013), but it
seems necessary to consider it a polytoechiid from now on.
The Peruvian material strongly resembles Jaanussonites in its
pseudospondylium with the lateral ridges/teeth growing toward
the valve floor merging with two vascular ridges posteriorly, by
having a convex pseudodeltidium, the same arrangement and
shape of dorsal muscle field, and bisected sockets in the dorsal
valve; it clearly differs from this genus by its multicostellate
ornament without spines in the intercostal spaces and aditicules
in the costellae and by lacking peripheral rims in both valves.
The Peruvian taxon also strongly recalls Polytoechia but differs
from it by its bigger size, ornamentation, more elongate outline,
wider interarea, undifferentiated ventral adductor scars, and not
deeply concave spondylium. Given all these differences, we pro-
pose a new genus, Enriquetoechia, to include the Peruvian
material.
Enriquetoechia umachiriensis new species
Figure 3
Holotype.—Internal and external mold of a ventral valve (CPI–
9913) (Fig. 3.1–3.6) from the lower part of the Umachiri
Formation at locality 2, Floian–?Dapingian (Lower–Middle
Ordovician).
Paratypes.—Internal and external mold of a dorsal valve (CPI–
9923) (Fig. 3.7–3.12); internal mold of a ventral valve
(CPI–9944); internal mold of a fragmented dorsal valve (CPI–
9953); internal and external mold of a dorsal valve (CPI–9958).
Diagnosis.—Polytoechioid of large size, biconvex,
multicostellate with well-developed concentric irregular fila
giving a zig-zag aspect to the ribs when eroded;
pseudodeltidium convex; pseudospondylium formed very
early in the ontogeny, elevated on the valve floor, supported
posterolaterally by the two dental plates arising below the
deltidiodont teeth, which grow toward the valve floor, fusing
with two of the radially arranged ovarian vascular ridges and
supported medially by a strong, high median ridge reaching its
anterior edge and continuous anteriorly, decreasing in height
until mid-valve length, where it disappears; ventral and dorsal
peripheral rims absent; notothyrial platform small, restricted to
the notothyrial cavity, elevated on the valve floor, strongly
undercut in its frontal edge, continuous anteriorly in a median
ridge; cardinal process ridge-like, swollen anteroventrally;
chilidial plates leaving the notothyrium partially open
medially; dorsal transmuscle septa and adductor scars radially
arranged.
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Description.—Shells of large size, up to 25 mm wide and 28
mm long; longitudinal profile equally biconvex; elongate in
outline; cardinal extremities with obtuse angles; maximum
shell width located slightly anteriorly of hinge line;
rectimarginate anterior commissure.
Ventral valve about 110% as long as wide and 12% as deep
as long; convex umbonal region, subplanar anteriorly. Ventral
interarea slightly curved, apsacline, about 12% as long as
valve length, with radial grooves marking the boundaries of
the interarea with the dental lamella; deltiodont teeth strong,
medially grooved; delthyrium covered by convex pseudodelti-
dium; pedicle foramen not visible. Dorsal valve about 85% as
long as wide and 11% as deep as long; maximum depth near
the umbo. Dorsal interarea planar, anacline, about 9% as long
as valve length, with growth lines subparallel to hinge line;
notothyrium partially covered by chilidial plates, diverging
anteriorly, forming an angle of about 90°.
Radial ornament multicostellate with 12 ribs per 5 mm at
15 mm anteromedianly from umbo, all of them with rounded
tops; costellae arise by intercalation at different growth stages;
intercostal spaces as wide as ribs. Concentric ornament consist-
ing of well-developed concentric irregular fila, when intersect-
ing with the ribs generating a zig-zag pattern, more visible
when the shell is abraded; strongly marked growth lines become
more frequent anteriorly.
Ventral interior with a pseudospondylium formed very
early in the ontogeny, as long as the interarea, elevated on the
valve floor, supported posterolaterally by the dental plates,
reaching the anterior edge of the spondylium, arising below
the deltidiodont teeth, which grow toward the valve floor fusing
with two of the radially arranged vascular ridges; spondylium
also supported medially by a strong, high median ridge reaching
its anterior edge and continuous anteriorly, decreasing in height
until mid-valve length, where it disappears; ovarian vascular
ridges radially arranged, evenly spaced, as long as median
ridge, counting six at each side of this structure; subperipheral
rim absent; mantle canal system pinnate; shell substance
unknown.
Dorsal valve with short, anchor-shaped, highly elevated
notothyrial platform, undercut in its frontal edge and restricted
to the notothyrial cavity, it continues anteriorly into a high
and thin median septum about 30% as long as valve; cardinal
process ridge-like, swollen anteroventrally; dental sockets
transversely elongated, bisected posteriorly by a transverse
thin ridge originated in the interarea; sockets bounded anteri-
orly by strong socket ridges forming an angle of about 23°
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 5
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with hinge line; dorsal muscle field large, radially arranged,
extending anteriorly slightly beyond median septum; adductor
scars with rounded, strongly impressed anterior ends; periph-
eral rim absent; mantle canal system and shell substance
unknown.
Etymology.—After the Umachiri Inlier of the Peruvian
Altiplano, where this species occurs.
Remarks.—Enriquetoechia umachiriensis is the only species
included so far within genus Enriquetoechia. See preceding
remarks of Enriquetoechia n. gen.
Genus Altiplanotoechia new genus
Type species.—Altiplanotoechia hodgini n. gen. n. sp.
Colmenar in Colmenar and Hodgin, 2020, from the lower part
Figure 3. The polytoechioid brachiopod Enriquetoechia umachiriensis Colmenar n. gen. n. sp. from the Umachiri Formation at locality 2. (1–6) Holotype, external
and internal molds of a ventral valve (CPI–9913); (1) latex cast of exterior, (2, 3) internal mold in (2) upper and (3) posterior views; (4–6) latex cast of interior in (4)
ventral, (5) lateral oblique, and (6) anterior oblique views. (7–12) Paratype, external and internal molds of a dorsal valve (CPI–9923); (7) latex cast of exterior, (8)
internal mold, (9) latex cast of interior, (10) detail of external ornamentation, (11) magnification of the cardinalia and dorsal interarea, (12) anterior oblique view of
dorsal interior showing the adductor scars, median ridge, and median septum. Scale bars = 2mm.
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of the Umachiri Formation, Floian–?Dapingian (Lower–Middle
Ordovician).
Other species.—Billingsella dice Walcott, 1905, from loose
boulders at St. Albans, Vermont, USA, likely belonging to
the Luke Hill Formation (Lower Ordovician) of the
Philipsburg sequence; Antigonambonites sp. (in Neuman,
1976, pl. 4, fig. 24) from the Dapingian–lower Darriwilian
Calcareous Tuff at Virgin Arm in the New World Island,
Newfoundland; Jaanussonites? sp. (in Benedetto, 2001,fig.
2V, W) from the upper Floian–lower Dapingian Aguada de
la Perdiz Formation of the western Puna region of
northwest Argentina.
Diagnosis.—Ventribiconvex shells with hemipyramidal ventral
valves and unisulcate commissure; ventral interior with sessile
pseudospondylium during early stages, becoming slightly free,
undercut anteriorly and supported laterally and medially by
septa; radially arranged vascular septa usually present; dorsal
interior with ridge-like cardinal process located in a small,
triangular notothyrial platform, deeply undercut in its frontal
edge, continuous anteriorly into a thin, long median ridge;
dorsal adductor scars radially arranged.
Etymology.—After the Altiplano (= high plains) morphotectonic
region of Peru where the Umachiri Formation crops out.
Remarks.—The presence of a pseudospondylium in the
Peruvian material clearly relates it with the Polytoechioidea.
Currently, two families are recognized within the
Polytoechioidea: Tritoechiidae and Polytoechiidae (Popov
et al., 2001,2007; Topper et al., 2013; Benedetto, 2016). In
the former, the entire ventral muscle field rests directly on the
floor of the delthyrial cavity or is raised on a
pseudospondylium, not undercut anteriorly. By contrast, in the
Polytoechiidae, the pseudospondylium is free anteriorly and
supported medially and laterally by septa resembling the
spondylium triplex of gonambonitids (Vinn and Rubel, 2000).
The Peruvian material displays mixed characters between the
Polytoechiidae and Tritoechiidae. The Peruvian taxon shows
similar pseudospondylium development to the polytoechiid
Pinatotoechia, which displays a sessile pseudospondylium
until adult stages when it becomes slightly undercut and free
anteriorly, but clearly it differs from that genus in its
ornamentation consisting of hollow tubular spines developed
on the ribs. It also resembles the genera Polytoechia Hall and
Clarke, 1892 and Tritoechia Ulrich and Cooper, 1936. Hall
and Clarke (1892, p. 240) described the pseudospondylium of
Polytoechia as “supported by a stout median septum, and two
smaller lateral septa […], the former of these extends for the
entire length of the plate, while the latter is free from the
accessory septa near its anterior edge. The umbonal cavity of
the valve is thus divided into five chambers […]”, which
means that those three septa are discrete from early
ontogenetic stages. Tritoechia, however, exhibits a sessile
pseudospondylium that can be elevated onto the valve floor in
higher or lesser extent by secondary shell thickening, leaving
only three chambers in the umbonal cavity. Some gerontic
specimens of few Tritoechia species, such as the type species
Tritoechia typica (Schuchert and Cooper, 1932) and T.
curvirostris Sando, 1957, develop obscure ridges at the
anterior margins of the ventral muscle field, which tend to
elevate the muscular platform slightly above the floor of the
valve (see Ulrich and Cooper, 1938, pl. 33B, fig. 19 and
Sando, 1957, pl. 14, fig. 3). The pseudospondylium of the
Peruvian material is similar to the sessile spondylium of
Tritoechia only in young stages, but it differs from Tritoechia
since in the Peruvian specimens this structure becomes free,
strongly undercut anteriorly, and supported laterally and
medially by septa, in a similar way to Polytoechia, but only in
adult stages. It also differs from Tritoechia in lacking radial
lines in the interarea, which is another diagnostic character of
that genus. Another character that differentiates this material
from Polytoechia is the anterior commissure, unisulcate in the
Peruvian specimens and uniplicate in Polytoechia. The
Peruvian material also resembles Antigonambonites by having
a sessile pseudospondylium becoming slightly raised
anteriorly in gerontic specimens but differs from this genus in
having a more convex ventral valve and a more raised
pseudospondylium from early stages and in lacking a
peripheral rim.
Material with pseudospondylium development similar to
the material described here can be found in the literature,
e.g., Tritoechia dice (Walcott, 1905) (see Ulrich and Cooper,
1938, pl. 31B) from the Floian Luke Hill Formation of Can-
ada, Antigonambonites sp. (in Neuman, 1976, pl. 4, fig 24)
from the Dapingian–lower Darriwilian Calcareous Tuff at
Virgin Arm in Newfoundland, Jaanussonites? sp. (in Bene-
detto, 2001,fig. 2V, W) from the upper Floian–lower Dapin-
gian Aguada de la Perdiz Formation of the western Puna
region of northwest Argentina, and Pomatotrema jiangsuense
Wang and Xu (1966, pl. II, figs. 4–7) from the Floian–lower
Darriwilian part of the Lunshan Formation at Tangshan,
Nanjing. However, the latter clearly differ from the Peruvian
material by having peripheral rims, which is a character only
displayed by Pomatotrema within the Polytoechioidea. The
mixed characters of the Chinese species suggest that it
may belong to a new genus yet to be described. Dorsal
valves attributable to this new genus display typical polytoe-
chioid features such as chilidial plates, ridge-like cardinal
process, small notothyrial platform continuous anteriorly in
a median septum, widely divergent socket ridges, and radi-
ally arranged dorsal adductor scars. However, the dorsal
valves studied here show a dorsal sulcus. This character is
unique within the polytoechioids, given that the only folded
genera in the superfamily are Polytoechia and Martellia
Wirth, 1936, but both genera are uniplicate and not unisul-
cate as the Peruvian shells.
From the previous discussion, we propose here the estab-
lishment of a new genus, Altiplanotoechia, to embrace all the
species with questionable generic determination mentioned in
the preceding (except P. jiangsuense), with similar pseudospon-
dylium development and without spinose ornamentation. The
family assignment of the new genus is more complicated since
it shares characteristics of both Polytoechiidae and Tritoechii-
dae, but we tentatively place it here within the Polytoechiidae
until further investigations have been made in the suprageneric
taxonomy of this superfamily.
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 7
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Altiplanotoechia hodgini new species
Figure 4.1–4.13
Holotype.—Internal and external mold of a ventral valve (CPI–
9929) (Fig. 4.6–4.10) from the lower part of Umachiri
Formation at locality 2, Floian–?Dapingian (Lower–?Middle
Ordovician).
Paratypes.—Internal and external mold of a ventral valve (CPI–
9921) (Fig. 4.1–4.5); internal and external mold of a dorsal valve
(CPI–9930) (Fig. 4.11–4.13).
Diagnosis.—Altiplanotoechia species with hemipyramidal
ventral valve, slightly unisulcate commissure and small
notothyrial platform, extremely undercut in its frontal edge,
highly elevated on the valve floor, and continuous anteriorly
in a long and thin median ridge.
Occurrence.—Lower part of Umachiri Formation at locality 2,
Floian–?Dapingian (Lower–?Middle Ordovician).
Description.—Shells of medium size up to 18 mm wide and 14
mm long; longitudinal profile ventribiconvex; subcircular in
outline; cardinal extremities acute in early growth stages, right
to obtuse in adult stages; maximum shell width approximately
at mid-valve length; slightly unisulcate anterior commissure.
Ventral valve hemipyramidal, about 104% as long as wide
and 50% as deep as long; maximum convexity at umbonal
region. Ventral interarea slightly curved, apsacline, about 52%
as long as valve length, with strong, triangular deltiodont
teeth; delthyrium covered by strongly convex pseudodeltidium
apically perforated by a large, ovate pedicle foramen.
Dorsal valve about 92% as long as wide and 22% as deep as
long; maximum depth near the umbo; dorsal interarea planar,
anacline, about 8% as long as valve length; notothyrium almost
totally covered by chilidial plates, which nearly touch the poster-
ior part of the cardinal process, diverging anteriorly forming an
angle of about 99°.
Radial ornament multicostellate with 18 ribs per 5 mm at
anterior commissure, all of them with rounded tops; costellae
arise by branching at different growth stages; intercostal spaces
narrower than ribs. Concentric ornament consisting of weakly
marked fila and strong growth lines becoming more frequent
anteriorly; in abraded parts of the shell, the intersection of cost-
ellae and fila is more visible (Fig 4.11).
Ventral interior with strong dental plates arising from
the teeth and growing toward valve floor forming a pseudos-
pondylium elevated on the valve floor by shell thickening,
sessile during early stages, becoming free, undercut anteri-
orly and supported laterally and medially by septa in adult
stages, medium septum extending anteriorly almost until
the commissure; ventral muscle field elongate, with diductor
scars separated from adductor scars by strong, subparallel
ridges, adductor scars deeply impressed in the pseudospon-
dylium; ovarian vascular ridges radially arranged, shorter
than median ridge; mantle canal system pinnate; shell sub-
stance unknown.
Dorsal interior with ridge-like cardinal process, slightly
thickened anteriorly, located on a small notothyrial platform,
extremely undercut in its frontal edge, highly elevated on the
valve floor, and continuous anteriorly in a long and thin median
ridge reaching less than half of the valve length; divergent socket
ridges forming an angle of about 28° with hinge line; sockets
big, triangular in outline, fairly deep; adductor scars radially
arranged, poorly impressed; shell substance and mantle canal
system unknown.
Etymology.—After Eben Blake Hodgin (Harvard University),
who found the Umachiri Formation fossil localities.
Remarks.—Some of the taxa included within this new genus are
in open nomenclature; however, they will be included here for
comparison with the Peruvian species. Altiplanotoechia
hodgini is here proposed as type species since the type
material of Tritoechia dice (Walcott, 1905) comes from loose
boulders of uncertain origin within the Philipsburg sequence
of St. Albans, Vermont, northeastern USA. A. hodgini differs
from Tritoechia dice by having a more subcircular outline,
slightly unisulcate anterior commissure, a more convex ventral
valve, deeper impressed adductor scars, and longer ventral
median and vascular septa. Antigonambonites sp. (in Neuman,
1976) differs from the new species in having a much shorter
ventral median septum and a more convex dorsal valve with
dorsal muscle scars strongly impressed anteriorly. Only one
poorly preserved ventral interior of Jaanussonites? sp. (in
Benedetto, 2001,fig. 2V, W) is known. It displays internal
characters very similar to those in A. hodgini, e.g., the deeply
impressed ventral adductor scars and length of median and
vascular septa. Additional and better-preserved material of the
Argentinian taxon could perhaps confirm its synonymy with
A. hodgini.
Family Tritoechiidae Ulrich and Cooper, 1936
Genus Pomatotrema Ulrich and Cooper in Schuchert and Coo-
per, 1932
Type species.—Pomatotrema murale Ulrich and Cooper in
Schuchert and Cooper, 1932 from the West Spring Creek
Formation, Arbuckle Group, Oklahoma, Dapingian–lower
Darriwilian (Middle Ordovician).
Other species.—Pomatotrema semiconvexum (Poulsen, 1927)
(Nunatami Formation, northwest Greenland, Dapingian–lower
Darriwilian), P. magnum Ulrich and Cooper, 1938 (Arbuckle
Limestone, Oklahoma, Dapingian–lower Darriwilian), P.
oklahomense Ulrich and Cooper, 1936 (West Spring Creek
Formation, Oklahoma, Dapingian–lower Darriwilian), P.
transversum Ulrich and Cooper, 1936 (West Spring Creek
Formation, Oklahoma, Dapingian–lower Darriwilian), P.
inconspicuum Williams and Curry, 1985 (Tourmakeady
Limestone, Ireland, Dapingian–lower Darriwilian), Pomatotrema
sp. (upper Fenxiang Formation., China, Tremadocian–lower
Floian, Lower Ordovician).
Pomatotrema laubacheri new species
Figure 4.14–4.19
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Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 9
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Holotype.—Internal mold of a ventral valve (CPI–9916)
(Fig. 4.14–4.17) from the lower part of the Umachiri
Formation at locality 2, Floian–?Dapingian (Lower–Middle
Ordovician).
Paratype.—Internal and external mold of a ventral valve
(CPI–9914) (Fig. 4.18,4.19).
Diagnosis.—Pomatotrema species with hemipyramidal ventral
valve, extremely high interarea, and ventral muscle scars
raised on the valve floor by shell thickening.
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Description.—Hemipyramidal ventral valves of medium size,
up to 15 mm wide and 13 mm long; transversely oval in
outline; cardinal extremities rectangular; maximum shell width
located at hinge line; rectimarginate anterior commissure.
Ventral valve about86% as long as wide and 50% as deep as
long; maximum convexity at umbonal region. Ventral interarea
slightly curved, apsacline, about 50% as long as valve length,
with horizontal, subparallel growth lines; deltiodont teeth strong;
delthyrium covered by convex pseudodeltidium, longer than
wide, apically perforated by a big, oval pedicle foramen.
Radial ornament multicostellate with 14 ribs per 5 mm at
anterior commissure, all of them with rounded tops; costella
arise by branching at different growth stages; intercostal spaces
narrower than ribs. Concentric ornament consisting of strongly
marked growth lines becoming more frequent and lamellose
anteriorly.
Ventral interior with strong dental plates, slightly conver-
gent toward valve floor forming a pseudospondylium and
bounding laterally the muscle field that is resting on the thick-
ened valve floor; ventral muscle field strongly impressed, diduc-
tor scars about 30% shorter than adductor scars, diductor scars
elongated, subparallel, undercutting the pseudospondylium pos-
teriorly, adductor scars lanceolate, separated from each other by
a narrow, weak ridge and from the diductor scars by strong
ridges; strongly marked pedicle callist present in the posterior
part of the delthyrial cavity; radially arranged ovarian vascular
ridges present posterolaterally; mantle canal system pinnate.
Etymology.—After Gérard Laubacher, French geologist, who
devised the first stratigraphic scheme for the Altiplano and the
first Ordovician fossil findings in the region.
Remarks.—The curved pseudodeltidium, apically perforated,
and the sessile pseudospondylium, formed by the dental plates
extending toward the valve floor, justify the inclusion of this
material within the family Tritoechiidae. The presence of a
peripheral rim and the absence of radial lines in the interarea
are diagnostic characters of Pomatotrema Ulrich and Cooper
in Schuchert and Cooper, 1932. Only two ventral internal
molds and an associated external mold are available. However,
the ventral muscle field raised on the valve floor by shell
thickening allows differentiation from all species included in
this genus. Among all described species, P. laubacheri is
morphologically closest to the genotype P. murale Ulrich and
Cooper in Schuchert and Cooper, 1932 by showing strong
radial ovarian vascular ridges and strong dental plates,
converging toward the valve floor, bounding laterally the
ventral muscle field, but P. laubacheri clearly differs from the
type species in having a more convex ventral valve and higher
ventral interarea and lacking the median ridge in the ventral
valve.
Genus Tritoechia Ulrich and Cooper, 1936
Subgenus Tritoechia (Tritoechia) Ulrich and Cooper, 1936
Type species.—Deltatreta typica Schuchert and Cooper, 1932
from the Arbuckle Limestone of Oklahoma, USA, Dapingian–
lower Darriwilian (Middle Ordovician).
Tritoechia (Tritoechia) sp.
Figure 4.20–4.23
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Description.—Ventral valve of medium size about 20mm wide
and 19 mm long; subquadrate in outline; cardinal extremities
rounded with obtuse angles; maximum shell width slightly
anterior to hinge line; anterior commissure rectimarginate.
Ventral valve hemipyramidal, about 95% as long as wide
and 60% as deep as long; maximum depth near the umbo; ven-
tral interarea planar, apsacline; delthyrium covered by a convex
pseudodeltidium.
Radial ornament multicostellate with 11 ribs per 5 mm at
10 mm anteromedianly, all of them with rounded tops; costellae
arise by branching at different growth stages; intercostal spaces
as wide as ribs.
Ventral interior with thin dental plates, almost subparallel,
slightly convergent toward valve floor forming a sessile pseu-
dospondylium and bounding laterally the muscle field, which
is resting on the thickened valve floor; dental plates extending
anteriorly beyond muscle field scars as low, narrow ridges;
ventral muscle field elongated, about twice as long as wide,
Figure 4. Polytoechioid brachiopods from the Umachiri Formation. (1–13)Altiplanotoechia hodgini n. gen. n. sp. Colmenar in Colmenarand Hodgin, 2020 (1–5)
Paratype, external and internal molds of a ventral valve (CPI–9921); (1–3) latex cast of exterior in (1) upper, (2) lateral, and (3) posterior oblique views; (4) internal
mold and (5) latex cast of interior. (6–10) Paratype, external and internal molds of a ventral valve (CPI–9929); (6, 7, 10) latex cast of exterior in (6) upper, (7) lateral,
and (10) posterior views; (8) internal mold and (9) latex cast of interior. (11–13) Paratype, external and internal molds of a dorsal valve (CPI–9930); (11) latex cast of
exterior, (12) internal mold and (13) latex cast of interior. (14–19)Pomatotrema laubacheri Colmenar n. sp. (14–17) Holotype, internal mold of a ventral valve (CPI–
9916); (14, 15) internal mold in (14) upper and (15) lateral oblique views; (16, 17) latex cast of interior in (16) upper and (17) posterior oblique views; (18, 19)
paratype, external and internal molds of a ventral valve (CPI–9914); (18) latex cast of exterior and (19) internal mold. (20–23)Tritoechia (Tritoechia) sp. (20–
23) External and internal molds of a ventral valve (CPI–9915); (20) latex cast of exterior, (21–23) internal mold in (21) upper and (23) lateral oblique views,
(22) latex cast of interior. (24, 25) Polytoechioidea indet., dorsal valve (CPI–9932); (24) internal mold and (25) latex cast of interior. Scale bars = 2 mm.
Journal of Paleontology:1–1910
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muscle scars strongly impressed, each diductor as wide as both
adductor scars altogether, diductor scars separated from the
adductors by strong, subparallel ridges, low and thin median
ridge growing anteriorly from the adductor scars until approxi-
mately two-thirds of valve length; radiallyarranged ovarian vas-
cular ridges present posterolaterally; mantle canal system
pinnate.
Materials.—One ventral interior and exterior (CPI–9915)
(Fig. 4.20–4.23).
Remarks.—The curved pseudodeltidium and the sessile
pseudospondylium formed by the dental plates extending
toward the valve floor justify the inclusion of this material
within the family Tritoechiidae. The extremely convex ventral
valve, the non-undercut anteriorly ventral muscle field, and
the median ridge extending in front of ventral muscle field are
characters typically displayed by Tritoechia. More than 40
species have been included in this genus. Among the species
with hemipyramidal ventral valve, the Peruvian species
resembles T. delicatula Ulrich and Cooper, 1936 from the
Tremadocian Kindblade Formation of Oklahoma in having
narrow, almost subparallel ventral muscle scars with
subparallel ridges separating diductor from adductor scars.
However, the Peruvian species differs from T. delicatula in
being almost double the size of the largest specimen attributed
to that species and by having a much narrower median ridge.
The Peruvian species also resembles the type species T. typica
(Schuchert and Cooper, 1932) from the same formation in
having the dental plates extending anteriorly beyond the
muscle field as low ridges. However, the Peruvian material
clearly differs from T. typica in lacking the aditicules/hollow
costellae characteristic of the type species and by having a
subparallel muscle field, anteriorly widely divergent in
T. typica. The dental plates extending anteriorly beyond the
elongated muscle field as low ridges is a character also shared
with Tritoechia sp. from the upper member of the Suri
Formation from the Famatina Range of northwest Argentina
(Benedetto, 2003), but the Peruvian species differs from the
Argentinian species in having a slightly thicker ornamentation
and having ridges separating diductor from adductor scars.
Despite showing differences from all published Tritoechia
species, it is preferable not to define a new species
until additional and more abundant material of this taxon is
available.
Subgenus Tritoechia (Parvitritoechia) Benedetto, 2003
Type species.—Tritoechia (Parvitritoechia)preandina
Benedetto, 2003 (in Benedetto et al., 2003) from the lower
part of the San Juan Formation, Precordillera, Argentina,
upper Tremadocian–lower Floian (Lower Ordovician).
Tritoechia (Parvitritoechia) sp.
Figure 5.1–5.4
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Description.—Dorsal valve of medium size up to 17 mm wide
and 10 mm long; transversely oval in outline; cardinal
extremities rounded with obtuse angles; maximum shell width
located slightly before mid-valve length; slightly unisulcate
anterior commissure.
Dorsal valve about 60% as long as wide and 11% as deep as
long; maximum depth near the umbo; dorsal interarea planar,
anacline, about 11% as long as valve length; notothyrium par-
tially covered by chilidial plates, diverging anteriorly forming
an angle of about 93°.
Radial ornament unequally parvicostellate with up to 12
prominent costae and up to six costellae arising by intercalation;
some of the costellae become more marked near the anterior
margin. Both costae and costellae with rounded tops. The only
dorsal exterior available shows evidence of shell damage
reflected as discontinuities in shell ornament (Fig. 5.1).
Dorsal interior with ridge-like cardinal process, located in a
small notothyrial platform, undercut in its frontal edge, elevated on
the valve floor, and continuous anteriorly in a short and thin
median ridge restricted to notothyrial cavity; widely divergent
socket ridges forming an angle of about 13° with hinge line; sock-
ets triangular in outline, fairly shallow; dorsal muscle field not
impressed; shell substance and mantle canal system unknowns.
Materials.—One dorsal interior and exterior (CPI–9920)
(Fig. 5.1–5.4).
Remarks.—This material is assigned to Polytoechioidea on the
basis of its typical cardinalia. The only genera in this
superfamily with unequally parvicostellate ornament are
Acanthotoechia Williams and Curry, 1985,Raunites Öpik,
1939, and Tritoechia (Parvitritoechia) Benedetto, 2003. The
Peruvian material clearly differs from Acanthotoechia by not
having rows of spines peripherally and by lacking peripheral
rims in the interior. The Peruvian material differs from
Raunites in lacking concentric fila and in having thicker ribs,
rounded cardinal angles, better-marked and fewer costae over
the disc, smaller, more elevated notothyrial platform, and
thinner median ridge. Benedetto (in Benedetto et al., 2003)
described Tritoechia (Parvitritoechia) to encompass all
Tritoechia species with clearly unequal parvicostellate
ornament. The Peruvian material perfectly fits within the
diagnosis of this subgenus, so we propose to include our
material within Tritoechia (Parvitritoechia). This material
differs from the type species T. (Parvitritoechia)preandina
from the lower part of the San Juan Formation of the
Precordillera in having rounded cardinal extremities, a smaller
size, a non-thickened anteriorly cardinal process, and a thinner
median ridge. It differs from T.(P.) pyramidalis (Bates, 1968)
from the Treiorwerth Formation of Anglesey in having much
thinner ribs and lacking growth lines. The Peruvian material is
morphologically closer to the material assigned to this genus
from the volcaniclastic rocks of the Aguada de la Perdiz
Formation of the Argentinian western Puna, Tritoechia sp.
A and Tritoechia sp. B (Benedetto, 2001), later reassigned to
T. (Parvitritoechia) by Benedetto (2003). The material from
the western Puna also displays rounded cardinal extremities, a
similar number of costae, and costellae between them, but
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 11
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differs from the Peruvian material in having a low median
septum dividing the dorsal muscle field. Even though the
material from the Umachiri Formation shows differences with
all the known species of T. (Parvitritoechia), it is too scarce
and fragmentary to define a new species.
Polytoechioidea indet.
Figure 4.24, 4.25
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Materials.—One dorsal interior (CPI–9932) (Fig. 4.24–4.25).
Remarks.—The dorsal valve available can clearly be ascribed to
the Polytoechioidea on the basis of its cardinalia. However, it
does not seem to correspond to any of the taxa belonging to
that superfamily described in this paper in either external or
internal features. Pomatotrema laubacheri and Tritoechia sp.
lack dorsal valves in the collection, so this dorsal valve could
potentially belong to any of those taxa. However, the absence
of a peripheral rim precludes its attribution to Pomatotrema,
and the subcircular outline does not match Tritoechia species
described in the preceding. So it is plausible to think that other
polytoechioids might be present in the Umachiri associations.
Order Orthida Schuchert and Cooper, 1932
Suborder Orthidina Schuchert and Cooper, 1932
Superfamily Orthoidea Woodward, 1852
Family Orthidae Woodward, 1852
Genus Paralenorthis Havlíc
ek and Branisa, 1980
Type species.—Paralenorthis immitatrix Havlíc
ek and Branisa,
1980; Floian (Lower Ordovician) siltstones at San Lucas,
Bolivia.
Paralenorthis cf. P. carlottoi Villas in Gutiérrez-Marco and
Villas, 2007
Figure 5.5–5.10
cf. 2007 Paraleonorthis carlottoi Villas in Gutiérrez-Marco and
Villas, p. 555, fig. 6A–6M
2
.
Holotype.—External mold of a ventral valve (MGM 5973X−1)
from the Horizon A of the San José Formation, Cordillera
Oriental, Peru; upper Floian (uppermost Lower Ordovician).
Diagnosis.—Paralenorthis species with rectangular cardinal
angles, costate and capillate, with 18–20 costae in adult dorsal
valves, only two median costae occupying median sulcus, ventral
muscle field 26%–33% as long as valve, notothyrial platform
restricted to notothyrial cavity and 14%–22% as long as valve,
blade-like divergent brachiophores, and low median ridge.
Occurrence.—Lower part of the Umachiri Formation at
localities 1, 2, and 4, Floian–?Dapingian (Lower–Middle
Ordovician).
Materials.—Thirty-one specimens; figured: CPI–9917, 9922,
9927, 9928 (Fig. 5.5–5.10); non-figured: CPI–9931, 9933–
9943, 9945–9952, 9954–9957, 9959–9961.
Remarks.—The material from the Umachiri Formation strongly
resembles, both externally and internally, Paralenorthis
carlottoi Villas (in Gutiérrez-Marco and Villas, 2007)from
the middle–upper Floian San José Formation of the Peruvian
Cordillera Oriental. The material studied here commonly
displays rectangular cardinal angles, about 18 costae in adult
dorsal valves, with only two median costae in the median
sulcus, a ventral muscle fieldabout32%aslongasvalve,a
notothyrial platform about 18% as long as valve, continuous
anteriorly in a low median ridge. These values are within the
variability range of the species P. carlot toi .However,this
material displays differences in the dorsal muscle field, showing
wider posterior adductor scars than the species described by
Villas (in Gutiérrez-Marco and Villas, 2007). Given this
difference displayed by the population of the Umachiri
Formation, it is assigned here only tentatively to this species.
Family Hesperonomiidae Ulrich and Cooper, 1936
Genus Mollesella Benedetto, 2003
Type species.—Mollesella planiventralis Benedetto, 2003 from
the uppermost Floian–lower Dapingian Molles Formation,
Famatina, northwest Argentina.
Mollesella cf. M. planidorsalis Benedetto, 2003
Figure 5.14–5.19
cf. 2003 Mollesella planidorsalis Benedetto, p. 233, fig. 11.13–
11.28.
Holotype.—Internal mold of a ventral valve (CEGH-UNC 19649)
from the Molles Formation, Famatina Range, Argentina; middle
Floian-Dapingian (Lower–Middle Ordovician).
Diagnosis.—Medium-sized to large shells with planar ventral
valve and moderately convex sulcate dorsal valve.
Figure 5. Polytoechioid, orthoid, and porambonitoid brachiopods from Umachiri Formation. (1–4)Tritoechia (Parvitritoechia) sp., external and internal molds of a
ventral valve (CPI–9920); (1) latex cast of exterior, (2) internal mold, (3) latex cast of exterior and (4) magnification of the cardinalia. (5–10)Paralenorthis cf. P.
carlottoi.(5) Latex cast of exterior of a ventral valve (CPI–9917); (6, 7) ventral valve (CPI–9927), (6) internal mold and (7) latex cast of interior; (8) latex cast of
exterior of a dorsal valve (CPI–9922); (9, 10) dorsal valve (CPI–9928), (9) internal mold, and (10) latex cast of interior. (11–13)Panderina? sp. (11) Latex cast
of exterior of a dorsal valve (CPI–9926); (12, 13) ventral valve (CPI–9911); (12) internal mold and (13) latex cast of interior. (14–19)Mollesellacf. M. planidorsalis.
(14, 15) Internal mold of a fragmented ventral valve (CPI–9925); (14) internal mold and (15) latex cast of interior; (16–19) dorsal valve (CPI–9924); (16) latex cast of
exterior, (17) internal mold, (18) latex cast of interior, and (19) magnification of the cardinalia. (20–23)Rugostrophia cf. R. latireticulata.(20) Latex cast of exterior
dorsal valve (CPI–9918); (21–23) dorsal valve (CPI–9912); (21) internal mold; (22, 23) latex cast of interior in (22) dorsal and (23) anterior oblique views. Scale bars
= 2 mm.
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 13
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Ornamentation finely multicostellate. Ventral valve with
triangular muscle field and proximal half of vascula media
subparallel. Notothyrial platform strongly raised, continued
anteriorly as high, rounded median ridge bearing simple,
anteriorly thickened cardinal process, which becomes bulbous
and prominent in full-grown specimens.
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Materials.—One dorsal interior and exterior (CPI–9924)
(Fig. 5.16–5.19) and one fragmentary ventral interior (CPI–
9925) (Fig. 5.14,5.15).
Remarks.—The finely costellate ornament, the open delthyrium,
the triangular and relativelyshort ventral muscle field impressed
directly on the valve floor, the short dorsal interarea, the simple
cardinal process, and the quadripartite dorsal muscle field allow
assigning this material to the family Hesperonomiidae. The
dental plates laterally and anterolaterally bounding the ventral
muscle field, the cardinal process becoming bulbous
anteriorly, the absence of chilidial plates, the relatively raised
notothyrial platform, and the posterolateral, radially arranged
ovarian vascular ridges warrant its inclusion within the
monospecific genus Mollesella Benedetto, 2003 from the
Famatina Range of northwest Argentina. The Peruvian
material shows some differences from M. planiventralis, such
as having wider notothyrial platform and median ridge. Since
these features seem to vary within the Argentinian species and
given that the Peruvian material is fragmentary and poorly
preserved, we decided to assign it tentatively to that species.
Family Productorthidae Schuchert and Cooper, 1931
Subfamily Productorthinae Schuchert and Cooper, 1931
Genus Panderina Schuchert and Cooper, 1931
Type species.—Productus abscissus Pander, 1830 from the
Leetse Formation of northwest Russia, Dapingian (Middle
Ordovician).
Panderina? sp.
Figure 5.11–5.13
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Materials.—One ventral interior (CPI–9911) (Fig. 5.12–5.13)
and one dorsal exterior (CPI–9926) (Fig. 5.11).
Remarks.—Short and thick dental plates continued as a ridge
around the front margin of the oval, small, ventral muscle
field, forming a pseudospondylium, closely resembling the
genus Panderina Schuchert and Cooper, 1931. However, in
this genus the pseudospondylium usually continues anteriorly
into a median ridge, absent in the Peruvian material.
Benedetto (2003) described a new species, Panderina?
ambigua from the Argentinian Famatina Range with similar
features in the ventral valve. He also noted that this species
showed mixed characters from other productorthid genera,
making the generic classification problematic. Mixed
characters include the strongly lamellose ornament in the
whole shell surface, shared with the material described here.
We agree with Benedetto (2003) that the generic assignment
of the Argentinian species is doubtful, and we consider our
material congeneric. Further investigation must be done to
clarify the generic classification of the Argentinian and
Peruvian taxa. Due to small differences in the ventral muscle
field outline and the lack of dorsal interiors in the Peruvian
collection, it is preferable to leave this material in open
nomenclature.
Order Pentamerida Schuchert and Cooper, 1931
Suborder Syntrophiidina Ulrich and Cooper, 1936
Superfamily Porambonitoidea Davidson, 1853
Family Tetralobulidae Ulrich and Cooper, 1936
Subfamily Punctolirinae Andreeva, 1982
Genus Rugostrophia Neuman, 1971
Type species.—Rugostrophia sylvestris Neuman, 1971 from the
Lower Birch Island Member of the Turnbull Mountain
Formation. (Dapingian–lower Darriwilian) at Newfoundland,
Canada.
Rugostrophia cf. R. latireticulata Neuman, 1976
Figure 5.20–5.23
cf. 1976 Rugostrophia latireticulata Neuman, p. 41, pl. 7, figs.
1–8.
Holotype.—Dorsal valve, internal mold, and counterpart
external mold (GSC 35085) from the ‘calcareous tuff’at
Virgin Arm, New World Island, Newfoundland; lower
Dapingian–lower Darriwilian (Middle Ordovician).
Diagnosis.—Large, transversely elliptical Rugostrophia having
a coarse reticulate ornament, the costellae more widely spaced
than the concentric laminae.
Occurrence.—Lower part of the Umachiri Formation at locality
2, Floian–?Dapingian (Lower–Middle Ordovician).
Materials.—One dorsal external (CPI–9918) (Fig. 5.20) and
internal (CPI–9912) (Fig. 5.21–5.23) molds.
Remarks.—The only ventral interior available is identical to
R. latireticulata Neuman, 1976 (pl. 7, fig.7) from the
Dapingian–lower Darriwilian of New World Island. Neuman
(1976) stated that differences between R. sylvestris and
R. latireticulata lie essentially in the ornamentation. The
Peruvian material differs from Rugostrophia sp. from the
Dapingian–lower Darriwilian Treiorwerth Formation (Neuman
and Bates, 1978, pl. 67, figs. 15–18) in displaying flattened
posterolateral extremities. In addition, it clearly differs from
the Argentinian Rugostrophia species, R. protoandina
Benedetto, 2003 and Rugostrophia sp. in having a much
deeper notothyrial cavity and strongly raised anterior ends of
adductor scars. Since no exteriors are available in the Peruvian
collection that enable differentiating between the Canadian
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species, it is preferable to assign this material tentatively to
R. latireticulata.
Paleobiogeographical remarks
Most of the brachiopod taxa occurring in the Umachiri Forma-
tion belong to the superfamilies Orthoidea and Polytoechioidea
with the exception of a porambonitoid. Among the orthoids, the
most abundant genus is Paralenorthis. Even though it is a
cosmopolitan genus, the species occurring in the Umachiri For-
mation strongly resembles Paralenorthis carlottoi Villas (in
Gutiérrez-Marco and Villas, 2007) from the middle–upper
Floian rocks of the San José Formation in the Carcel Puncco
Canyon (Inambari River) section of the Peruvian Cordillera
Oriental. Another orthoid brachiopod at Umachiri is very similar
to the type species of Mollesella Benedetto, 2003, previously
known only in the uppermost Floian–lower Dapingian rocks
of the Molles Formation from the Famatina Range of northwest
Argentina (Benedetto, 2003). The similarity of the Peruvian
assemblage with those of the Famatina Range is also strength-
ened by the co-occurrence of specimens referable to the brachio-
pod genus Panderina. Although this genus is typical from
Baltica and China, Benedetto (2003) described a new species
from the upper volcaniclastic member (Loma del Kilómetro
Mb) of the Suri Formation that he tentatively ascribed to Pander-
ina.Panderina?ambigua Benedetto, 2003 shows mixed charac-
teristics from other productorthid genera, making the generic
classification problematic. The material from the Umachiri For-
mation shows some of the same mixed characteristics, suggest-
ing that the species are strongly related. All these occurrences
highlight the resemblance of the Peruvian assemblage to those
of the Argentinian Famatina Range.
The brachiopod-dominated assemblage described here con-
tains numerous polytoechioids. One of them, Enriquetoechia,is
endemic to the Peruvian Altiplano. The other new genus
described here, Altiplanotoechia, is likely present in the Argen-
tinian western Puna, the Ganderia and Monian composite
(including Anglesey) terranes (both likely located west of Ava-
lonia forming an island arc at intermediate latitudes between
Gondwana and Laurentia), and the Dashwoods (New World
Island) and Moretown (St. Albans, Vermont) terranes (both
likely located near Laurentia) (see Domeier, 2016 and Liljeroth
et al., 2017, for estimated position of these island arcs during the
Cambrian–Ordovician times). Pomatotrema is a genus previ-
ously known only in the Laurentian realm and South China.
Benedetto (1987) described two species of this genus from
material of the San Juan Formation of the Precordillera; how-
ever, they were subsequently reassigned to Martellia (Popov
et al., 2001). The occurrence of Pomatotrema in the Peruvian
Altiplano represents the highest paleolatitudinal occurrence of
this genus so far and indicates connections of this region with
the Laurentian realm and South China during Floian times.
The links with Laurentia, the peri-Laurentian terranes, and
other low-latitude terranes during the Floian–Dapingian are
strengthened by the presence of Tritoechia (Tritoechia), with
several species described from localities of the Dashwoods Ter-
rane, Laurentia, Siberia, Kazakhstan, and Tasmania (Schuchert
and Cooper, 1932; Ulrich and Cooper, 1936,1938; Sando,
1957; Neuman, 1976; Laurie, 1980; Popov et al., 2001; Hansen
and Harper, 2003). Species of Tritoechia (Tritoechia) have also
been described from the Argentinian Precordillera, western
Puna, and Famatina regions, as well as in the Ganderia Terrane.
The subgenus Tritoechia (Parvitritoechia) is known from the
Dapingian–lower Darriwilian assemblages of the Treiorwerth
Formation of the Midland Valley–Mayo Terrane (Williams
and Curry, 1985), located in peri-Laurentian settings, from the
San Juan Formation of the Precordillera (Benedetto, 2003),
and from the Aguada de la Perdiz Formation of the Argentinian
western Puna (Benedetto, 2001). The Peruvian material
assigned to Tritoechia (Parvitritoechia) seems morphologically
related to the species described from the upper Floian–lower
Dapingian Aguada de la Perdiz Formation of the Argentinian
western Puna.
The productorthid present in the Umachiri Formation,
assigned here to the brachiopod genus Rugostrophia, strongly
resembles Rugostrophia latireticulata Neuman, 1976 from the
‘calcareous tuff’at Virgin Arm, New World Island, Newfound-
land. This genus normally occurs in localities belonging to the
Ganderia (e.g., Maine, New Brunswick) and Monian composite
(Anglesey) terranes, located at intermediate latitudes between
Gondwana and Laurentia, and on the Dashwoods Terrane
(New World Island), located close to Laurentia, during early
Dapingian–early Darriwilian times (Neuman, 1976; Neuman
and Bates, 1978). However, species assigned to this genus
also occur in the substantially older (uppermost Floian–lower
Dapingian) volcaniclastic rocks of the Aguada de la Perdiz For-
mation of the Argentinian western Puna (Benedetto, 2001,
2003) as well as in the Darriwilian part of the San Juan Forma-
tion of the Precordillera (Herrera and Benedetto, 1991).
All these occurrences highlight the strong biogeographic
affinity of the Peruvian Altiplano during the Early–?Middle
Ordovician with the Famatina and western Puna regions of
northwest Argentina. The brachiopod fauna of the Peruvian Alti-
plano could be integrated, together with their homologues from
Famatina and western Puna, into a well-differentiated biogeo-
graphical subprovince (in the sense of Servais et al., 2013) dur-
ing the Early–Middle Ordovician within the South American
margin of Gondwana.
As discussed in the preceding, the Peruvian assemblage
studied here also shows clear links with several terranes, of prob-
able Gondwanan origin (Murphy et al., 1999; Zagorevski et al.,
2015; Reusch et al., 2018), located at intermediate (Ganderia
and Monian composite terranes) and low (Moretown, Dash-
woods, and Midland Valley–Mayo terranes) latitudes between
Gondwana and Laurentia (see Johnson et al., 1991 and Cutts
et al., 2011 for paleogeographic position of Dashwoods Terrane)
during Floian-Dapingian times. Villas et al. (2015) proposed the
existence during Sandbian times (early Late Ordovician) of
intermediate islands in the Rheic Ocean between the Peruvian
Altiplano and Avalonia, permitting dispersal following the
Southern Westerlies currents (Pohl et al., 2016) and island hop-
ping of brachiopod species with low dispersal potential (short
larval period) to overcome the presumably large distances
between those terranes. Several of these islands/terranes
(known as Ganderian terranes) likely detached from Gondwana
and drifted toward Laurentia and Baltica during the late Cam-
brian–Early Ordovician, triggering the opening of the Rheic
Ocean (van Staal et al., 1996; Ayuso and Schulz, 2003;
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 15
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Ayuso et al., 2003; Schulz and Ayuso, 2003; Wilson, 2003;
Valverde-Vaquero et al., 2006; Zagorevski et al., 2007,2010;
Dennis et al., 2020). It is also important to consider that these
islands were likely connected to continuous, emergent arcs
that may have been oblique, consuming oceanic crust and
migrating physically across the greater Iapetus realm (see Dome-
ier, 2016, for estimated position of these island arcs during the
Cambrian–Ordovician times). These tectonic processes and
the resultant island arcs would have facilitated faunal migration
from Gondwana to Laurentia (Nowlan et al., 1997; Fortey and
Cocks, 2003; Harper et al., 2009). The same method of faunal
migration is proposed here, during Floian to Dapingian times,
facilitating faunal exchange between the Peruvian Altiplano
and the Ganderia and Monian Composite terranes. In addition,
Ganderian and Monian composite terranes could have acted as
intermediate island arcs allowing subsequent faunal swapping
of Gondwanan and Celtic faunas with peri-Gondwanan and
peri-Laurentian terranes (Moretown, Dashwoods, and Midland
Valley–Mayo terranes). These island arcs collided with Lauren-
tia in the Taconic Orogeny and may have closed the main tract of
the Iapetus Ocean in the Floian (Macdonald et al., 2014,2017;
Karabinos et al., 2017), much earlier than previous estimates
(i.e., Late Ordovician, van Staal et al., 2012 and references
therein). After their docking with Laurentia, faunal transfer
with the Scoto-Appalachian Province might have been facili-
tated (Neuman, 1984; Neuman and Harper, 1992; Harper
et al., 1996; Liljeroth et al., 2017). The faunal dispersal mechan-
isms discussed in the preceding may also explain the slight
diachronism existing among the Peruvian, Celtic, and peri-
Laurentian faunas, with younger occurrences in the latter.
Age of the fossil assemblages
Given the similarities of the Peruvian brachiopods recorded from
the lower strata of the Umachiri Formation, especially with the
volcaniclastic uppermost Loma del Kilómetro Mb of the Suri For-
mation and the Molles Formation of the Central Famatina Range
and with those of the volcaniclastic Aguada de la Perdiz Forma-
tion from the western Puna of northwest Argentina, a similar
Floian to ?middle Dapingian (475–468 Ma) age range has been
inferred. The age of correlated strata is constrained by the occur-
rence of conodonts of the Prioniodus elegans,Oepikodus evae,
and ‘Baltoniodus navis’zones in the Famatinian strata (Albanesi
and Vaccari, 1994; Lehnert et al., 1997; Albanesi and Astini,
2000) and by associated trilobite and graptolite occurrences in
equivalent western Puna strata (Koukharsky et al., 1996; Mon-
teros et al., 1996; Brussa et al., 2003; Toro et al., 2015).
The youngest identifiable fossils in the Umachiri Formation
are graptolites from the upper part of the Umachiri Formation at
locality5(Figs. 1,2), previously reported by Cerrón and Chacal-
tana (2002). The preservation of these graptolites is poor, but pre-
liminary data suggest a Middle–?Upper Ordovician age for this
horizon (J.C. Gutiérrez-Marco, personal communication, 2020).
Acknowledgments
We thank J.L. Benedetto (CONICET) and an anonymous
reviewer for their constructive review of the manuscript. We
are grateful to J. Newmann (UC Santa Barbara), K. Butler
(Western Washington University), and M. Huancca (Universi-
dad Nacional San Antonio Abad del Cusco) for field assistance;
to C. Chacaltana (INGEMMET, Lima) for information regard-
ing a graptolite locality southwest of Umachiri; to J.C.
Gutiérrez-Marco (Instituto de Geociencias CSIC-UCM,
Madrid) for helping in the preparation of the samples, for fruitful
discussions, and for critical reading of an earlier version of the
manuscript; to C. Alonso (Universidad Complutense de Madrid)
and A. Brenner (Harvard University) for fossil photography; to
L. Tejada and A. Ticona (INGEMMET, Lima) for curatorial
work of the specimens. EBH was funded by Harvard University
and JC by the Spanish Ministry of Science and Innovation (Pro-
ject CGL2017-87631-P). This is also a contribution to the Inter-
national Geoscience Programme (IGCP) Project 653 ‘The Onset
of the Great Biodiversification Event.’
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Accepted: 11 August 2020
Colmenar and Hodgin—Ordovician brachiopods Peruvian Altiplano 19
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