First record of Ischyodus (Chondrichthyes, Holocephali) from the Upper Jurassic of southwestern Gondwana

Full text

Acta Palaeontol. Pol. 66 (3): 623–630, 2021 https://doi.org/10.4202/app.00859.2020
First record of chimaeroid fish Ischyodus from
the Upper Jurassic of southwestern Gondwana
RODRIGO A. OTERO, CONSTANZA FIGUEROA BRAVO, PAULA SOTO-HUENCHUMÁN,
SARA FERNÁNDEZ-COLLEMANN, ANA M. VALENZUELA-TORO, and CAROLINA S. GUTSTEIN
Otero, R.A., Figueroa Bravo, C., Soto Huenchumán, P., Fernández-Collemann, S., Valenzuela-Toro, A.M., and Gutstein,
C.S. 2021. First record of chimaeroid fish Ischyodus from the Upper Jurassic of southwestern Gondwana. Acta Palaeonto-
lo gica Polonica 66 (3): 623–630.
This study presents two specimens of Chimaeriformes from Upper Jurassic strata of central Chile. The material was
recovered from Tithonian levels of the Baños del Flaco Formation and includes two different individuals, one preserving
two articulated mandibular plates, and the second, a fragment of an isolated palatine plate. Morphologic traits allow us to
refer the material to Ischyodus townsendi and Ischyodus sp., respectively. These are the oldest Chimaeriformes known to
date in the Southern Hemisphere and the first Late Jurassic record from Gondwana. The presence of I. townsendi in the
Tithonian of central Chile evidences this taxon as part of the proposed faunal interchange between the northern Tethys
and the southeastern Pacific during the Late Jurassic.
Key words: Chondrichthyes, Holocephali, Callorhinchidae, cartilaginous fishes, paleobiogeo graphy, Mesozoic, Jurassic,
Tithonian.
Rodrigo A. Otero [otero2112@gmail.com], Consultora Paleosuchus Ltda. Huelén 165 Oficina C, Providencia, Santi-
ago, Chile; Red Paleontológica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de Biología, Facultad
de Ciencias, Universidad de Chile. Las Palmeras 3425, Santiago, Chile; Museo de Historia Natural y Cultural del
Desierto de Atacama. Inferior Parque El Loa s/n, Calama, Chile.
Constanza Figueroa Bravo [constanza.figueroa@paleoconsultores.cl] and Sara Fernández Collemann [sara.fernan-
dez@paleoconsultores.cl], Consultora Paleosuchus Ltda. Huelén 165 Oficina C, Providencia, Santiago, Chile.
Paula Soto-Huenchumán [paula.soto@paleoconsultores.cl], Consultora Paleosuchus Ltda. Huelén 165 Oficina C,
Providencia, Santiago, Chile; Red Paleontológica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de
Biología, Facultad de Ciencias, Universidad de Chile. Las Palmeras 3425, Santiago, Chile; Corporación Laguna de
Taguatagua, Av. Libertador Bernardo O’Higgins 351, Santiago, Chile.
Ana M. Valenzuela-Toro [avalenzuela.toro@gmail.com], Consultora Paleosuchus Ltda. Huelén 165 Oficina C, Prov-
idencia, Santiago, Chile; Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 130
McAllister Way, Santa Cruz, CA 95060, USA; Department of Paleobiology, National Museum of Natural History, Smith-
sonian Institution, 10th & Constitution NW, Washington, DC 20560 USA.
Carolina S. Gutstein [carolina.sg@paleoconsultores.cl], Consultora Paleosuchus Ltda. Huelén 165 Oficina C, Prov-
idencia, Santiago, Chile; Red Paleontológica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de Bi-
ología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile.
Received 13 January 2020, accepted 7 January 2021, available online 2 August 2021.
Copyright © 2021 R.A. Otero et al. This is an open-access article distributed under the terms of the Creative Commons
Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original author and source are credited.
Introduction
Chimaeriformes (Chondrichthyes, Holocephali) is a clade
of cartilaginous fishes that appeared in the fossil record
during the Paleozoic, reaching a high diversity during the
Mesozoic and onwards (López-Arbarello et al. 2008). During
the Jurassic, the group is well-recorded in the Northern
Hemisphere and represented by several genera and species
(López-Arbarello 2004; López-Arbarello et al. 2008).
The oldest austral fossil Chimaeriformes are known
from the Lower Cretaceous of Australia (represented by the
Ischyodus Egerton, 1843 and Pyctoptychion Lees, 1986), be-
coming abundant during the Upper Cretaceous with records
in New Zealand, South America, and Antarctica (e.g., Otero
et al. 2013a, b). Then, during the Cenozoic, Chimaeriformes
have been recorded globally (Stahl 1999). However, prior to
the Cretaceous, there are no records of this clade along the
Southern Hemisphere. This contribution presents the oldest

624 ACTA PALAEONTOLOGICA POLONICA 66 (3), 2021
Chimaeriformes known to date in the Southern Hemisphere
and the first Upper Jurassic record from Gondwana. The
material consists of two specimens which preserve enough
diagnostic features for a taxonomic identification, being
identified as Ischyodus townsendi (Buckland, 1835), while
the second specimen is referred to as Ischyodus sp. The
coeval occurrence of I. townsendi during the Tithonian in
the northern Tethys, and now in southwestern Gondwana, is
discussed here.
Institutional abbreviations.—MHNC, Museo de Historia
Natu ral de Concepción, Chile; MJSN, Jurassica Mu seum (for-
merly Musée Jurassien des Sciences Naturelles), Porrentruy,
Switzerland; NHMUK, Natural History Museum, London,
UK.
Geological setting
The studied material was recovered in the facilities of Mina
Del Fierro (Del Fierro Mine), owned by Minera Río Teno S.A.,
located in the Cajón del Fierro locality, High Andes, west of
Curicó city, Región del Maule, Chile (Fig. 1). Rocks cropping
out in this area belong to the Baños del Flaco Formation
(Klohn 1960). This sedimentary unit overlies the Río Damas
Formation through a concordant contact. The Baños del Flaco
Formation is overlain through a discordant contact by a volca-
noclastic sequence known as the Brownish-Red Clastic Unit
(BRCU; Charrier et al. 1996; Salazar 2012), and through a
concordant contact with the Colimapu Formation. The Baños
de Flaco Formation was recently divided in two formal units,
the Lower and the Upper Member (Salazar 2012). The unit
comprises limestone, sandy limestone, and calcareous sand-
stone mostly grey-colo red, with occasional glauconitic sand-
stone, limestone, and conglomerate. Salazar (2012) estimated
thickness of 369 m in the studied locality.
The age of the Baños del Flaco has been debated over the
years. In this sense, the abundant and diverse fauna of marine
invertebrates (including ammonoids, belemnoids, bivalves,
gastropods, scaphopods, echinoderms, bryozoans, porifera,
foraminifera, algae, cyanobacteriae, and ichnofossils) pres-
ent in the Baños del Flaco Formation was useful for increas-
ing the precision of its age. Firstly, Klohn (1960) assigned a
lower Valanginian–Hauterivian age, based on marine mol-
luscs (mostly ammonoids) present in different outcrops of the
unit. After, Covacevich et al. (1976) referred it to the lower
Tithonian–Hauterivian? based on the invertebrate assem-
blage. Later, in more comprehensive studies, Salazar (2012)
and Salazar and Stinnesbeck (2015) constrained the age of
the unit to the lower middle Tithonian–lowermost Berriasian
interval, based on the biostratigraphy of ammonoids.
For the Cajón del Fierro locality, Klohn (1960) described
outcrops of Baños del Flaco Formation as fossiliferous ma-
rine sediments with N8E/30W strike and dip strike, being
represented by a thick succession of limestone and marl
with intercalated cross-bedded calcareous sandstone, and
conglome rate levels, both concordantly overlying to breccias
and conglomerates with andesitic clasts from the Río Damas
Formation. Particularly, in the studied locality, Maldonado
(2016) described the basal part of the Lower Member of
Baños del Flaco Formation, conformed by conglomerate,
conglomeratic limestone, sandy limestone, calcareous sand-
stone, inter calated tuff, calcirudite, and calcareous shale.
For this section, the fossil content is abundant (Quinzio and
Varela 2015), being present in most levels of the section
and comprising bioturbation and marine invertebrates (am-
monoids, belemnoids, gastropods, inoce ramids, nautiloids,
and trigoniids) all of which indicate a Tithonian age. The
nature of this assemblage, in addition to the stratigraphic
section described by Quinzio and Varela (2015), allows
to assess the stratigraphic position of the two vertebrate
specimens studied here. These are detailed in Fig. 2. Both
specimens were recovered from upper levels of the Lower
Member of the Baños del Flaco Formation, thus, having a
Tithonian age.
Material and methods
The material is included in a single sandstone block with
two articulated mandibular plates; no other skeletal portions
were found nearby. This specimen was discovered in 2019
by personnel of Mina Del Fierro as part of a monitoring
policy for mitigation of the mining operation, following
the Chilean heritage law. Therefore, as the fossil-bearing
geologic unit (Baños del Flaco Formation) is known to host
frequent marine invertebrates, the area was the subject of
a periodic paleontological survey, as requested by the lo-
cal Chilean heritage authority (Consejo de Monumentos
Nacionales) which was carried out under a paleontological
excavation permit of the Chilean authority for one of the
authors (CFB; Ord. CMN N° 2275/17).
Fig. 1. A. Map indicating location of the studied area in central Chile.
B. Enlarged map of Mina Del Fierro area where the material was collected.

OTERO ET AL.—JURASSIC CHIMAERAS FROM CHILE 625
The site of the finding was firstly inspected by two of the
authors (SFC and PSH) during the paleontological survey
of the mining activities, recognizing the stratigraphic prov-
enance of the material. The block was originally removed
from its natural occurrence by mine blasting, together with
several large blocks of calcareous rocks.
Among the rescued material, a single sandstone block
was recovered, originally showing a partial broken dental
plate and part of a second, likely complete and articulated
plate. The articulated plates were later prepared by one of
the authors (RAO) during December 2019 and January 2020
in facilities of the Red Paleontológica U-Chile, Laboratorio
de Ontogenia y Filogenia, Departamento de Biología, Uni-
versidad de Chile (Santiago, Chile). The extraction of the
sediment was carried out with a 9100 air scribe, while the
fragile specimen was consolidated with Paraloid B-76 us-
ing different concentrations, and cyanoacrylate for bonding.
The second isolated plate was not prepared, and it is shown
in its natural occurrence, which is enough for its anatomi-
cal interpretation. After, both specimens were included in
the formal repository of the Museo de Historia Natural de
Concepción, together with the rest of the fossil invertebrate
collection from the studied locality.
The studied material was compared with Late Jurassic
species within the Ischyodus, based on literature review.
The anatomical terminology used here follows Popov and
Machalski (2014), adding an anatomical topology (plm,
prominence of the labial margin) discussed in the diagnosis
of the Ischyodus by Stahl (1999).
Systematic palaeontology
Chimaeroidei Patterson, 1965
Callorhinchidae Garman, 1901
Callorhinchinae Stahl, 1999
Genus Ischyodus Egerton, 1843
Type species: Chimaera townsendi Buckland, 1835; Tithonian of En-
gland.
Ischyodus townsendi (Buckland, 1835)
Fig. 3A.
Material.—MHNC.35.444, two articulated mandibular pla-
tes from Mina Del Fierro, Andes Cordillera, Región del
Maule, Chile; Baños del Flaco Formation, Tithonian (Upper
Jurassic).
Description.—Both plates are visible in basal view
(Fig. 3A). The mandibular plates remain articulated in
nearly anatomical position. The right mandibular plate is
the most damaged by diagenesis or transport, with the basal
surface lost and a few tritors broken, being exposed in
different sections. This preservation allows us to observe
the tritor distribution. Its posterior occlusal surface is pre-
served as a thin bone layer attached to the matrix, which is
why this was not removed. The preserved surface indicates
a sudden mechanical break-up, judging by the fresh bone
exposed. This is consistent with damage derived from rock
blasting, discarding erosive agents. On the broken surface
(basal view) it can be recognized a larger tritor pad placed
medially, and therefore, being identified as the median tri-
Fig. 2. Stratigraphic section of the levels were the studied material was
recovered. Modified from Quinzio and Varela (2015).

626 ACTA PALAEONTOLOGICA POLONICA 66 (3), 2021
tor which covers two-thirds of the plate width. A cylindri-
cal tritor, identified as the posterior outer tritor (pot), flanks
labially to the median tritor (mt). Over the labial margin of
each plate there is a prominence. The broken right mandib-
ular plate shows the anterior outer tritor (aot) near to this
prominence. The left mandibular shows two marked ridges
(r) over the basal surface, which reflect the internal position
of the symphyseal tritor (syt) of laminated pleromin and the
median tritor, respectively. On its basal margin, the symph-
yseal tritor is broken, leaving a cavity. The median tritor is
visible, it is also partially broken, but prominent. Flanking
the latter, there is a posterior exposure of the posterior
outer tritor. The beak (bk) is preserved in both plates, being
prominent and slightly recurved laterally. Its anteriormost
tip is worn. Measurements of both specimens are provided
on Table 1.
Remarks.—MHNC.35.444 can be referred to the genus
Ischyo dus based on the possession of mandibular plates
with a large central median tritor flanked by a short an-
terior outer tritor, an elongate posterior outer tritor, and
the existence of a symphyseal tritor of laminated pleromin
at the mesial tip of the tooth plate (Stahl 1999; Popov
and Machalski 2014). The occurrence of two small tritors
exposed at the prominence on the wavy labial margin of
the mandibular plate has been considered as another di-
agnostic feature of the genus (Stahl 1999: 131); however,
this feature is not present in the holotype of Ischyodus
townsendi, which only has a single tritor (anterior outer) in
this position. Nevertheless, the absence of a second tritor
is related to the wearing suffered in larger/old mandibular
plates, being instead a consequence of the ontogeny rather
than being a diagnostic value (Ward and Grande 1991;
Popov and Machalski 2014).
Stratigraphic and geographic.—Baños del Flaco Formation,
Tithonian (Upper Jurassic). Mina Del Fierro, Andes Cor dil-
lera, Región del Maule, Chile.
Ischyodus sp.
Fig. 3B.
Material.—MHNC.35.445, an isolated, fragmentary right
palatine plate from Mina Del Fierro, Andes Cordillera,
Región del Maule, Chile; Baños del Flaco Formation,
Tithonian (Upper Jurassic).
Description.—MHNC.35.445 is an isolated and poorly pre-
served palatine plate attached to the matrix. The basal sur-
face is lost, allowing us to see the internal part of the tritors.
The labial and symphyseal contour are preserved as a cast in
the sandstone matrix, allowing us to observe the triangular
shape of the plate. The posterior inner tritor is suboval and it
is the larger tritor in the plate. The labial margin shows three
aligned tritors, identified as fragments of the median tritor,
the outer tritor, and the anterior inner tritor.
Remarks.—MHNC.35.445 possesses a large, oval posterior
inner tritor, a median tritor likely smaller, an outer tritor ax-
ially elongated, and an anterior inner tritor slightly rounded.
These features are present in different species of the
Ischyodus (Stahl 1999: fig. 138A, C; Popov and Machalski
2014: fig. 4D1). The incompleteness of this mandibular plate
precludes a more specific identification.
Fig. 3. Chimaeroid fishes from Mina Del Fierro, Andes Cordillera, Región del Maule, Chile; Baños del Flaco Formation, Tithonian (Upper Jurassic).
A. Ischyodus townsendi (Buckland, 1835) (MHNC.35.444); two articulated mandibular plates in basal view. B. Ischyodus sp. (MHNC.35.445); ventral
view of the bony contour of a right palatine attached to the matrix, preserving the occlusal surface of the tritors. Abbreviations: ait, anterior inner tritor; aot,
anterior outer tritor; bk, beak; lm, left mandibular; mt, median tritor; out, outer tritor; pit, posterior inner tritor; plm, prominence of the labial margin; pot,
posterior outer tritor; r, ridges; rm, right mandibular; syt, symphyseal tritor. Photographs (A1, B1), schematic illustrations (A2, B2).
Table 1. Measurements (in mm) of the two studied specimens. Mesio-
distal length definition follows Popov and Machalski (2014).
Taxon Specimen
number Plate Mesiodistal
length
Ischyodus townsendi MHNC.35.444 left mandibular 995
Ischyodus sp. MHNC.35.444 right mandibular 102
MHNC.35.445 right palatine 721

OTERO ET AL.—JURASSIC CHIMAERAS FROM CHILE 627
Discussion
Late Jurassic records of Ischyodus and comparison
with the studied specimen.—Twenty-two nominal species
within Ischyodus have been described from the Jurassic of
Europe, with eight species known in the Tithonian (Table 2).
However, more recent reviews (Stahl 1999; Duffin 2004;
Lauer et al. 2019) have reduced this initial great diversity.
Tithonian species from Germany initially included Ischyodus
schuebleri Quendstedt, 1858, Ischyodus suevicus Philippi,
1897, Ischyodus quendstedti Wagner, 1857, Ischyodus ros-
tratus Meyer, 1859, and Ischyodus acutus Meyer, 1859. From
these, Ischyodus rostratus and I. suevicus were synonymized
to I. schuebleri by Riess (1887) and by Heimberg (1949),
respectively. The most informative Tithonian species from
Germany is represented by I. quendstedti, which is based in a
complete holotype and several referred specimens, including
well preserved mandibular plates (Leuzinger et al. 2017).
Duffin (in Stahl 1999) considered I. rostratus, I. suevi-
cus, and I. schuebleri to be synonyms of I. quendstedti.
Besides the latter, the remaining species I. acutus was
based in a unique known vomerine (Meyer 1859), making
any direct comparison to the Chilean specimen impossible.
Finally, Ischyodus avitus (Meyer, 1862) from the Tithonian
of Solnhofen, Ger many, is known by several fairly complete
specimens, but their dentition was not sufficiently exposed
for a good description (Stahl 1999). This species was later
referred to Ischyo dus avitus (Riess, 1887). More recently,
Duffin (2004) and Lauer et al. (2019) transferred the species
to the genus Elasmodectes Newton, 1878. Therefore, the
currently valid known Ischyodus species from the Tithonian
of Germany can be reduced to only two species, Ischyodus
quendstedti and I. acutus, the latter known by a single vome-
rine, rising reasonable doubts about its eventual synonymy
with I. quendstedti.
Additional Tithonian records of Ischyodus are known
from France and England, represented by Ischyodus dutertrei
Egerton, 1843, and Ischyodus townsendi (Buckland, 1835),
respectively. Agassiz (1837, tome III) mentioned I. duter trei
“as very similar to I. townsendi, but being one third smaller.
The exterior [= labial margin] of the lower mandible [= man-
dibular plate] is not strongly grooved as in Ischyodus town-
sendi; [...] the most evident difference lays in the obtuse angle
formed by the tooth crown [= beak] with the upper board of
the mandible [= posterior part of the labial margin]. In other
words, the tritorial surfaces are used in a more obliquous po-
sition in its mandibles [= mandiblar plates]”.
The description of Agassiz (1837, tome III) indicated that
the occlusal curvature of the plate was more pronounced in
I. townsendi than in I. dutertrei. This feature, plus the larger
size of the former, could be better explained by the different
ontogenetic stages of each specimen. Otherwise, the topol-
ogy of the tritors is very similar in both species (see Sauvage
1896: pl. 21: 1, 2).
Comparison of MHNC.35.444 with the I. town sendi
(holo type, BMNH P474; currently under acronym and nu-
meration NHMUK 010039966 PV), I. quendstedti (referred,
MJSN SCR010 -10 0 0), and I. dutertrei (holotype, specimen
number 3402, Musée Bou logne-sur-le-mer, France) revealed
a very similar topology of the tritorials in all cases (Fig. 4).
Different plate outlines are explainable due to their respective
ontogenetic stages. Ward and Grande (1991: fig. 4) brilliantly
Table 2. List of Jurassic species within the Ischyoudus Egerton, 1843. Modified from Stahl (1999).
Species Age Geographic occurrences References
Ischyodus aalensis Bajocian Württemberg, Germany Quendstedt 1858; Riess 1887
Ischyodus personati Bajocian Württemberg, Germany Quendstedt 1858
Ischyodus colei Bathonian England Agassiz 1837, tome III
Ischyodus curvidens Bathonian England Egerton 1843
Ischyodus ferrugineus Bathonian Württemberg, Germany Riess 1887
Ischyodus emarginatus Bathonian England Egerton 1843
Ischyodus obruchevi “Middle Jurassic” Russia Averianov 1992
Ischyodus egertoni Callovian–Kimmeridgian south England Buckland 1835
Ischyodus dufrenoyi Kimmeridgian Boulogne, France Egerton 1843
Ischyodus baeumonti Kimmeridgian Boulogne, France Egerton 1843
Ischyodus beaugrandi Kimmeridgian Boulogne, France Sauvage 1867
Ischyodus bouchardi Kimmeridgian Boulogne, France Sauvage 1867
Ischyodus suprajurensis Kimmeridgian Boulogne, France Sauvage 1867
Ischyodus sauvaugei Kimmeridgian Boulogne, France Hamy 1866
Ischyodus schuebleri Tithonian Württemberg, Germany Quendstedt 1858
Ischyodus suevicus Tithonian Württemberg, Germany Philippi 1897
Ischyodus quendstedti Tithonian Bavaria, Germany Wagner 1857; Riess 1887
Ischyodus rostratus Tithonian Hannover, Germany Meyer 1859
Ischyodus acutus Tithonian Hannover, Germany Meyer 1859
Ischyodus dutertrei Tithonian Boulogne, France Egerton 1843
Ischyodus avitus Tithonian Solnhofen, Germany Meyer 1862
Ischyodus townsendi Tithonian south England Buckland 1835

628 ACTA PALAEONTOLOGICA POLONICA 66 (3), 2021
illustrated how wearing by occlusion and growth define the
outline of the mandibular plates of the Ischyodus. The strictly
ontogenetic changes reported by these authors are reflected
in the enlargement of each tritor pad and the separation
between tritors coupled to the plate growth. Wearing can
explain the reduction or even the loss of the small tritors
located close to the labial margin and the reduction of the
beak sharpness.
With all these considerations, MHNC.35.444 shares
with I. townsendi, I. dutertrei, and I. quendstedti the pres-
ence of a large median tritor, flanked labially by the poste-
rior outer tritor. It differs from I. dutertrei, which lacks the
anterior outer tritor (although, this could be a consequence
of the wearing). Based on the referred specimen (MJSN
SCR010-1000; Leuzinger et al. 2017), the anterior outer
tritor of I. quendstedti is placed anterolateraly to its median
tritor. In I. townsendi (holotype) and in the Chilean spec-
imen, the anterior outer tritor is placed laterally to their
respective median tritor. This condition cannot be assessed
in I. dutertrei (holotype) because the anterior outer tritor is
not present. Also, the posterior outer tritor of I. quendstedti
(referred specimen) is well-exposed in occlusal view. Older
individuals of the genus show this tritor embedded within
the plate, which is the case of the Ischyodus spp. mandib-
ular plates compared on Fig. 4. On the lingual margin, the
Chilean specimen, I. dutertrei (holotype) and I. townsendi
(holotype) have partial exposition of the posterior outer
tritor, seen in cross-section, and closely placed lateral to
the median tritor.
Under these considerations, I. dutertrei and I. townsendi
could likely belong to the same species, as first pointed
out by Agassiz (1833–1843) himself. However, a review
of the valid species of the genus elsewhere is out of the
scope of this study. Nevertheless, the completeness of the
I. townsendi holotype compared with other Tithonian spe-
cies, allows us to establish more detailed comparisons. The
presence in I. townsendi of an anterior outer tritor laterally
placed relative to the median tritor (contrary to the anterior
outer tritor placed anterior to the median tritor in I. quend-
stedti) in effect occurs in the Chilean specimen. Following
Grande and Ward (1991), the ontogenetic stage can cause
lateral separation of the tritors, but a rostral migration seems
more unlikely. Based on these traits, we refer MHNC.35.444
to the species I. townsendi.
Records of Austral Mesozoic Chimaeriformes.—T he
studied material represents the first Late Jurassic Chimaeri-
formes recorded in South America. Previous to this re-
search, the oldest austral Callorhinchidae were represented
by Aptian–Albian records from Queensland, Australia, in-
cluding Ischyodus cf. thurmanni Pictet and Campiche, 1858
(Popov 2011; Popov and Machalski, 2014); Ptyktoptychion
tayyo Lees, 1986, and Pyctoptychion wadeae Bartholomai,
2008. In addition, Albian–Cenomanian records from west-
ern Australia include material referred to Callorhinchus
cf. borealis and Ischyodus sp. (Popov 2011; Popov and
Machalski 2014). During the Late Cretaceous, the genus
Ischyodus was recorded in the Campanian–Maastrichtian
of New Zealand (Pictet and Campiche 1858), and in the
upper Maastrichtian of Seymour Island, Antarctica (Stahl
and Chatterjee 2002). It is also documented during the
Paleogene of Antarctica and southern South America (Ward
Fig. 4. Comparison of mandibular plates of Tithonian species within Ischyodus Egerton, 1843. All in occlusal view. A. Ischyodus quendstedti, MJSN
SCR010-1000), Tithonian of Switzerland; right mandibular, mirrored for comparison (modified from Leuzinger et al. 2017). B. Ischyodus townsendi
(MHNC.35.444), Tithonian of central Chile; outline of the left mandibular (only visible in basal view) is overlapped in dashed lines for a better under-
standing of the complete plate outline. C. Ischyodus dutertrei (holotype, specimen number 3402, Musée Boulogne-sur-le-mer, France), Kimmeridgian–
Tithonian of France (modified from Sauvage 1896). D. Ischyodus townsendi (holotype, BMNH P474; currently NHMUK 010039966 PV), Tithonian of
England (modified from Natural History Museum, London, Data Portal, data.nhm.ac.uk, https://doi.org/10.5519/0002965). Abbreviations: act, accessory
tritor; aot, anterior outer tritor; mt, median tritor; pot, posterior outer tritor; syt, symphyseal tritor.

OTERO ET AL.—JURASSIC CHIMAERAS FROM CHILE 629
and Grande 1991; Kriwet and Gaździcki 2003; Otero et al.
2013a; Otero and Soto-Acuña 2015). The material from cen-
tral Chile studied here represents the oldest Chimaeriformes
known to date in the Southern Hemisphere and the oldest
known occurrence of the group in Gondwana.
Paleobiogeography.—The presence of the Ischyodus in
the Tithonian of central Chile adds to a growing body of
evidence regarding the interchange of marine vertebrates
between the northern Tethys and the southeastern Pacific.
Gasparini et al. (2007) synthesized the Middle and Late
Jurassic record of ichthyosaurs, thalattosuchians, plesiosau-
rians, and Testudines from the Neuquén Basin (Argentina
and Chile), suggesting that the common occurrence of sev-
eral genera in the northern Tethys and the southeastern
Pacific are likely explained as the result of an interchange
through the Caribbean Seaway (sensu Iturralde-Vinent
2003). In addition, Arratia (1994, 2015) reviewed the os-
teichthyan fossil record from Chile, where phylogenetic
analyses endorse a narrow relationship between the oste-
ichthyan faunas from Europe, Cuba, and northern Chile,
pointing out the Caribbean Seaway as the main path for such
interchange. In this sense, the material here studied rep-
resents the first paleobiogeographically valuable evidence,
now including chondrichthyans to the proposed connection.
Previously, there was a single known record of an indeter-
minate neoselachian from the Tithonian of central Chile,
likely representing a palaeospinacid or a hybodontid (Suárez
and Otero 2011). Its still unsolved generic status precludes a
palaeobiogeographic approach.
Conclusions
We present two new specimens of the Ischyodus (Chimaeri-
formes) from Tithonian levels of the Baños del Flaco
Formation of central Chile. Available elements include one
partial specimen comprising two articulated mandibular
plates of a single individual, preserving enough diagnostic
traits for an alpha-taxonomic identification. The specimen
is here referred to Ischyodus townsendi (Buckland, 1835),
a species previously restricted to the Tithonian of England.
The common presence of this taxon in the northern Tethys
and now in the southeastern Pacific reinforces the Caribbean
Seaway as a fully functional path of marine faunal inter-
change, at least during the Late Jurassic. Evidence of this
interhemispheric marine faunal interchange was already
noted during the Middle and Late Jurassic on several groups
of marine vertebrates (i.e., thalattosuchians, ichthyosauri-
ans, plesiosaurians and osteichthtyes), although, previous to
this research, no evidence of such interchange was verified
among chondrichthyans. The studied material represents
the first record of I. townsendi in the Southern Hemisphere,
the first find of a Chimaeriformes in the Upper Jurassic of
Gondwana, and the oldest known callorhinchid from South
America.
Author’s contributions
PSH, survey of the collecting site, detailed stratigraphy,
stratigraphic column, geologic setting, manuscript writing;
SFC, survey of the collecting site, manuscript writing and
review; CFB, survey of the collecting site, data processing,
manuscript writing and review. AVT, data processing, man-
uscript writing and review; CSG, survey of the collecting
site, complementary stratigraphy, data processing, manu-
script writing; RAO, preparation of the material, conceptu-
alization of the research, methods, anatomical identification
and taxonomic determinations, elaboration of pictures and
schemes, manuscript writing and review.
Acknowledgements
The authors thank Sergio Bogan (Universidad Maimónides, Buenos
Aires, Argentina), to Jaime Villafaña (University of Vienna, Austria)
and to Editor Daniel Barta (Oklahoma State University, Tahlequah,
USA) for their valuable reviews and comments which improved our
manuscript. Fieldwork resulting in this research was supported by
Minera Río Teno S.A. Authorization for paleontologic management in
Chile was granted by Consejo de Monumentos Nacionales (National
Monuments Council, Chile) on Ord. CMN N° 2275/17. Access to
laboratory and research for RAO, CSG, and PSH was supported by
the project “New data sources on the fossil record and evolution of
vertebrates”, Anillos de Ciencia y Tecnología-ACT-172099, ANID
(formerly Conicyt)-Chile. AVT was funded by ANID PCHA/Becas
Chile, Doctoral Fellowship; Grant No. 2016-72170286 and a Peter
Buck Predoctoral Fellowship, National Museum of Natural History,
Smithsonian Institution. All fieldwork and research was permanently
supported by Consultora Paleosuchus Ltda.
References
Agassiz, L. 1833–1843. Recherches sur les Poissons fossiles. Tome III.
448 pp. Petitperriere, Neuchâtel.
Arratia, G. 1994 Phylogenetic and paleobiogeographic relationships of the
varasichthyid group (Teleostei) from the Late Jurassic of central and
South America. Revista Geológica de Chile 21: 119–161.
Arratia, G. 2015. Los peces osteíctios fósiles de Chile y su importancia en
los contextos paleobiogeográfico y evolutivo. In: D. Rubilar-Rogers,
R.A. Otero, A. Vargas, and M. Sallaberry (eds.), Vertebrados Fósiles
de Chile. Publicación Ocasional del Museo Nacional de Historia Nat-
ural (Chile) 63: 35–83.
Averianov, A.O. 1992. New Jurassic chimeroids of Russia. Paleontologi-
cal Journal 3: 57–62.
Bartholomai, A. 2008. Lower Cretaceous chimaeroids (Chondrichthyes:
Holocephali) from the Great Artesian Basin, Australia. Memoirs of the
Queensland Museum 52: 49‒56.
Buckland, W. 1835. A notice on the fossil beaks of four extinct species
of fishes, referrible to the genus Chimaera, what occurs in the oolitic
and Cretaceous formations of England. Proceedings of the Geological
Society of London 2: 205‒206.
Charrier, R., Wyss, A., Flynn, J., Swisher, C., Norell, M., Zapatta, F.,
McKenna, M., and Novaceck, M. 1996. New evidence for late Me-
sozoic–early Cenozoic evolution of the Chilean Andes in the upper
Tinguiririca valley (35º S), Central Chile. Journal of South American
Earth Sciences 9: 1–30.
Covacevich, V., Varela, J., and Vergara, M. 1976. Estratigrafıa y Sedi-

630 ACTA PALAEONTOLOGICA POLONICA 66 (3), 2021
mentación de la Formación Baños del Flaco al sur del Rıo Tinguiririca,
Cordillera de los Andes. Provincia de Curicó, Chile. Actas I Congreso
Geologico Chileno, 191‒211. Santiago.
Duffin, C.J. 2004. Plattenkalk Late Jurassic chimaeroids. In: F.J. Poyato-
Ariza (ed.), Fourth International Meeting on Mesozoic Fishes—Sys-
tematics, homology, and nomenclature, 83‒86. Miraflores de la Sierra,
Madrid.
Egerton, P.M.G. 1843. On some new species of fossil chimaeroid fishes,
with remarks on their general affinities. Proceedings of the Geological
Society of London 4: 153–157.
Garman, S. 1901. Genera and families of the chimaeroids. Proceedings of
the New England Zoological Club 2: 75–77.
Gasparini, Z., Fernández, M., De La Fuente, M., and Salgado, L. 2007.
Reptiles marinos jurásicos y cretácicos de la Patagonia Argentina: su
aporte al conocimiento de la herpetofauna mesozoica. Asociación Pale-
ontológica Argentina. Publicación Especial Ameghiniana 50º aniversa-
rio 11: 125‒136.
Hamy, M.E.T. 1866. Note sur une nouvelle espece d’Ischyodus de l’argile
kimmeridgienne de Chatillon, pres de Boulogne-sur-Mer. Bulletin del-
la Societé Geológiqué de France 2 (Series XXIII): 654‒657.
Heimberg, G. 1949. Neue Fischfunde aus dem Weissen Jura von Wurttem-
berg. Palaeontographica 97: 75‒98.
Iturralde-Vinent, M. 2003. The conflicting paleontologic versus strati-
graphic record of the formation of the Caribbean Seaway. In: C. Barto-
lini, R.T. Buffler, and J. Blickwede (eds.), The Circum-Gulf of Mexico
and the Caribbean: Hydrocarbon Habitats, Basin Formation, and Plate
Tectonics. American Association Petroleum Geology, Tulsa OK, Mem-
oire 79: 75–88.
Klohn, G. 1960. Geología de Santiago, O’Higgins, Colchagua y Curicó.
Instituto de Investigaciones Geologicas Chile. Boletin 8: 1‒95.
Kriwet, J. and Gaździcki, A. 2003. New Eocene Antarctic chimaeroid fish
(Holocephali, Chimaeriformes). Polish Polar Research 24: 29‒51.
Lauer, B., Lauer, R., Bernard, E., Duffin, C., Popov, E., and Ward, D. 2019.
Observations on the Mesozoic chimaeroid, Elasmodectes Newton,
1878. In: A. Farke, A. MacKenzie, and J. Miller-Camp (eds.), 79th
Annual Meeting of the Society of Vertebrate Paleontology, Meeting
Program, 138. Society of Vertebrate Paleontology, Brisbane.
Lees, T.A. 1986. A new chimaeroid Ptyktoptychion tayyo gen. et sp. nov.
(Pisces: Holocephali) from the marine Cretaceous of Queensland. Al-
cheringa 10: 187‒193.
López-Arbarello, A. 2004. The record of Mesozoic fishes from Gondwana
(excluding India and Madagascar). In: G. Arratia and A. Tintori (eds.),
Mesozoic Fishes 3—Systematics, Paleoenvironments and Biodiversity.
597‒624. Verlag Dr. Friedrich Pfeil, München.
Lopez-Arbarello, A., Rauhut, O.W.M., and Moser, K. 2008. Jurassic fish-
es of Gondwana. Revista de la Asociacion Geologica Argentina 63:
586‒612.
Leuzinger, L., Cuny, G., Popov, E., and Billon-Bruyat, J.P. 2017. A new
chondrichthyan fauna from the Late Jurassic of the Swiss Jura (Kim-
meridgian) dominated by hybodonts, chimaeroids and guitarfishes.
Papers in Palaeontology 3: 471‒511.
Meyer, H. 1859. Fossile chimaeriden aus dem Portland von Hannover.
Palae ontographica 7: 14‒18.
Meyer, H. 1862. Chimaera (Ganodus) avita aus dem Lithographischen
Schiefer von Eichstadt. Palaeontographica 10: 87‒95.
Newton, E.T. 1878. The chimaeroid fishes of the British Cretaceous rocks.
Memoirs of the Geological Survey of the United Kingdom 4: 1‒62.
Otero, R.A. and Soto-Acuña, S. 2015. New chondrichthyans from Barto-
nian–Priabonian levels of Río de Las Minas and Sierra Dorotea, Ma-
gallanes Basin, Chilean Patagonia. Andean Geology 42: 268‒283.
Otero, R.A., Oyarzún, J.L., Soto-Acuña, S., Yury-Yáñez, R., Gutierrez, N.,
Le Roux, J., Torres, T., and Hervé, F. 2013a. Neoselachians and Chi-
maeriformes (Chondrichthyes) from the Upper Cretaceous–Paleogene
of Sierra Baguales, southernmost Chile. Chronostratigraphic, paleo-
biogeographic and paleoenvironmental implications. Journal of South
American Earth Sciences 48: 13‒30.
Otero, R.A., Rubilar-Rogers, D., Yury-Yañez, R.E., Vargas, A.O., Gutstein,
C.S., Mourgues, F.A., and Robert, E. 2013b. A new species of chimae-
riform (Chondrichthyes, Holocephali) from the uppermost Cretaceous
of the López de Bertodano Formation, Isla Marambio (Seymour Is-
land), Antarctica. Antarctic Science 25: 99‒106.
Patterson, C. 1965. The phylogeny of the chimaeroids. Philosophical
Transactions of the Royal Society of London B249: 101‒219.
Philippi, E. 1897. Ueber Ischyodus suevicus nov. sp. Ein Beitrag zur Ken-
ntnissder fossilen Holocephalen. Palaeontographica 44: 1‒10.
Pictet, F.J. and Campiche, G. 1858. Description des fossiles du terrain
Crétacé des environs de Sainte-Croix. Matériaux pour la Paléonto-
logie Suisse: 1–380.
Popov, E.V. 2011. New data on chimaeroid fishes (Holocephali; Chimae-
roidei) from the Cretaceous and Neogene of Australia. In: O. Lebedev
and A. Ivanov (eds.), II International Obruchev Symposium “Paleozoic
Early Vertebrates”, Russia, Abstract Volume, 40–41. Alexander Ivanov
Publisher, Saint Petersburg.
Popov, E.V. and Machalski, M. 2014. Late Albian chimaeroid fishes (Ho-
locephali, Chimaeroidei) from Annopol, Poland. Cretaceous Research
47: 1‒18.
Quenstedt, F.A. 1858. Der Jura. 842 pp. Laupp, Tübingen.
Quinzio, L.A. and Varela, N. 2015. Caracterización Paleontológica Mina
del Fierro. Proyecto Mina del Fierro de Minera Río Teno S.A. Región
del Maule. Report for the Consejo de Monumentos Nacionales (Na-
tional Heritage Council, Chile), ingreso CMN Nº5287-25/08/2015.
19 pp. Santiago.
Riess, J. 1887. Ueber einige fossile Chimeriden-Reste im Münchenerpa-
laeontologischen Museum. Palaeontographica 34: 1‒27.
Salazar, C. 2012. The Jurassic–Cretaceous Boundary (Tithonian–Hau te-
rivian) in the Andean Basin, Central Chile: Ammonite fauna, Bio- and
Sequence Stratigraphy and Palaeobiogeography. 388 pp. Doctoral
Thesis, Universität Heidelberg.
Salazar, C. and Stinnesbeck, W. 2015. Redefinition, stratigraphy and fa-
cies of the Lo Valdés Formation (Upper Jurassic-Lower Cretaceous) in
central Chile. Boletín del Museo Nacional de Historia Natural, Chile
64: 41–68.
Sauvage, H.E. 1867. Poissons fossiles des formations secondaires du Bou-
lonnais. Mémoires de la Société Académique de l’Arrondissement de
Boulogne-sur-Mer 2: 53–152.
Sauvage, H.E. 1896. Les Ischyodus des terrains Jurassiques superieurs du
Boulonnais. Bulletin de la Societé Geológiqué du France 24: 456‒465.
Stahl, B.J. 1999. Handbook of Paleoichthyology, Vol. 4: Chondrichthyes
III. Holocephali. 164 pp. Verlag Dr. Friedrich Pfeil, München.
Stahl, B.J. and Chatterjee, S. 2002. A Late Cretaceous callorhinchid (Chon-
drichthyes, Holocephali) from Seymour Island, Antarctica. Journal of
Vertebrate Paleontology 22: 848‒850.
Suárez, M.E. and Otero, R.A. 2011. First record of a neoselachian shark
in the Jurassic of Chile. Resúmenes del IV Congreso Latinoamericano
de Paleontología de Vertebrados, San Juan Argentina. Ameghiniana 48
(Suplemento): R213.
Wagner, J.A. 1857. Charakteristik neuer Arten von Knorpelfischen aus den
lithographischen Schiefern der Umgegend von Solnhofen. Gelehrte
Anzeigen der königlich bayerischen Akademie der Wissenschaften 44
(35–36): 288–293.
Ward, D.J. and Grande, L. 1991. Chimaeroid fish remains from Seymour
Island, Antarctic Peninsula. Antarctic Science 3: 323‒330.