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Boletín del Museo Nacional de Historia Natural, Chile, 69 (1): 5-31 (2020) 5
FIRST MESOZOIC MAMMAL FROM CHILE: THE SOUTHERNMOST RECORD OF
A LATE CRETACEOUS GONDWANATHERIAN
Francisco J. Goin1, Agustín G. Martinelli2, Sergio Soto-Acuña3, Emma C. Vieytes4*, Leslie M.E. Manríquez5, Roy
A. Fernández3**, Juan Pablo Pino6, Cristine Trevisan6***, Jonatan Kaluza3,7, Marcelo A. Reguero8****, Marcelo
Leppe6*****, Héctor Ortiz3******, David Rubilar-Rogers9 and Alexander O. Vargas3*******
1CONICET-División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n,
B1900FWA La Plata, Argentina. E-mail: fgoin@fcnym.unlp.edu.ar
2CONICET-Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”,
Av. Ángel Gallardo 470, C1405DJR, CABA, Argentina. E-mail: agustin_martinelli@yahoo.com.ar
3Red Paleontológica U-Chile, Laboratorio de Ontogenia y Filogenia, Departamento de Biología, Facultad de
Ciencias, Universidad de Chile. Las Palmeras 3425, Ñuñoa, Santiago, Chile. E-mail: sesotacu@ug.uchile.cl
4CONICET-División Zoología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA La Plata,
Argentina. E-mail: cvieytes@fcnym.unlp.edu.ar
5Programa de Pós-Graduação em Geologia, Universidade do Vale do Rio dos Sinos, Av. UNISINOS 950, 93022- 000
São Leopoldo, Rio Grande do Sul, Brasil. E-mail: less.manriquez@gmail.com
6Laboratorio de Paleobiología de Antártica y Patagonia, Instituto Antártico Chileno, Plaza Muñoz Gamero, 1055,
Punta Arenas, Chile. E-mail: juanpablo.pinomorales@gmail.com
7Fundación de Historia Natural Félix de Azara, Universidad Maimónides, Hidalgo 775, C1405BCK, CABA,
Argentina Email: yojonatan@hotmail.com
8Área de Paleontología, Museo Nacional de Historia Natural. Interior Parque Quinta Normal s/n, Santiago, Chile.
E-mail: david.rubilar@mnhn.cl
* cvieytes@fcnym.unlp.edu.ar / ** rofer87@gmail.com / *** ctrevisan@inach.cl / **** regui@fcnym.unlp.edu.ar
***** mleppe@inach.cl / ****** hctros@gmail.com / ******* thearchosaur@gmail.com
urn:lsid:zoobank.org:pub:3C68664D-C7A1-42C0-9D62-D0ACAB0B3F8C
ABSTRACT
We describe Magallanodon baikashkenke gen. et. sp. nov., a new gondwanatherian mammal from
the Late Cretaceous of the Magallanes Region in southern Chile (Río de Las Chinas Valley, Estancia
Cerro Guido, north of Puerto Natales city, Última Esperanza Province). The mammal-bearing layer is
placed within the Late Campanian-Early Maastrichtian levels of the Dorotea Formation (Magallanes/
Austral Basin). The new remains constitute the southernmost record of a Mesozoic gondwanatherian
mammal, as well as the rst Mesozoic mammal from Chile. This taxon is comparable in size to the
hypsodont-toothed Gondwanatherium (Late Cretaceous) and Sudamerica (Early Paleocene) but with
noticeably brachyodont molariforms supported by four to ve roots. As in other gondwanatherians, it
has at least one hypertrophied, rodent-like incisor in the upper jaw. The new taxon is here diagnosed
and described, and is regarded as a possible ferugliotheriid (?Ferugliotheriidae). If conrmed, it would
represent the largest known taxon for this family. Its molariform occlusal crown pattern, after wear,
resembles that of other gondwanatherians, particularly ferugliotheriids and that of the sudamericid
Gondwanatherium. This adds new evidence on the phylogenetic proximity of ferugliotheriid and
sudamericid gondwanatherians. An analysis of the enamel microstructure of the upper incisor of
Magallanodon was performed demonstrating several crucial similarities with the pattern shown by
Gondwanatherium (Sudamericidae). We discuss the signicance of Magallanodon for understanding
the acquisition, within gondwanatherians, of a lophed molariform pattern. Finally, we discuss the
signicance of the new nding in the context of southern biotas, including those of Patagonia and
Antarctica.
Keywords: Gondwanatheria, Mammalia, Molariforms, Campanian-Maastrichtian, Dorotea
Formation, Magallanes/Austral Basin, Chile.
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
6
RESUMEN
Primer mamífero Mesozoico de Chile: el registro más austral de un gondwanaterio del Cretácico
tardío. Se describe a Magallanodon baikashkenke gen. et. sp. nov., un nuevo mamífero gondwanaterio
del Cretácico tardío de la Región de Magallanes, en el sur de Chile (Valle del Río de Las Chinas,
Estancia Cerro Guido, norte de Puerto Natales, Provincia de Última Esperanza). Las capas portadoras
se ubican entre los niveles del Campaniano tardío-Maastrichtiano temprano de la Formación Dorotea
(Cuenca de Magallanes/Austral). Los nuevos restos constituyen el registro más austral de un mamífero
gondwanaterio del Mesozoico, como así también el primer mamífero Mesozoico conocido para Chile. El
nuevo taxón es comparable en tamaño a las formas hipsodontes Gondwanatherium (Cretácico tardío) y
Sudamerica (Paleoceno temprano), pero con molares notoriamente braquidontes soportados por cuatro
a cinco raíces. Como en otros gondwanaterios, posee al menos un incisivo superior rodentiforme en la
serie superior. Se diagnostica y describe brevemente el nuevo taxón, considerado tentativamente como
un ferugliotérido (Ferugliotheriidae). De conrmarse esta asignación, este nuevo taxón representaría el
miembro de mayor tamaño para la familia. El patrón oclusal de los molariformes, con el desgaste, se
semeja también al de otros gondwanaterios, en particular al de los ferugliotéridos y al del sudamerícido
Gondwanatherium, agregando en consecuencia más evidencias en favor de la proximidad logenética
entre ambas familias. Se llevó a cabo un análisis de la microestructura del esmalte del incisivo superior
de Magallanodon; como resultado, se encontraron varias similitudes importantes con el patrón
existente en Gondwanatherium (Sudamericidae). Se discute la signicación de Magallanodon en la
adquisición, entre los gondwanaterios, de un patrón molariforme caracterizado por la presencia de
lofos transversos. Finalmente, se discute la signicación del nuevo hallazgo en el contexto de las biotas
australes, incluyendo aquellas de Patagonia y Antártica.
Palabras clave: Gondwanatheria, Mammalia, Molariformes, Campaniano-Maastrichtiano, Formación
Dorotea, Cuenca de Magallanes/Austral, Chile.
INTRODUCTION
Even though South America has an impressive fossil record of Cretaceous terrestrial vertebrates (e.g.,
Bonaparte 1996, Martinelli and Forasiepi 2004, Novas 2009, Bittencourt and Langer 2011, Rubilar-Rogers
et al. 2015), mammals are still sparse components of these assemblages. Their remains are known from few
localities in the Argentinian Patagonia (e.g., Bonaparte 1986a, 1987, 1990, Pascual et al. 2000, Rougier et
al. 2009a, b, 2011a, b, Forasiepi et al. 2012), as well as from isolated and extremely fragmentary records
in Bolivia, Brazil, and Peru (Mourier et al. 1986, Bertini et al. 1993, Gayet et al. 2001, Castro et al. 2018).
With the exception of two cladotherian mammals, Vincelestes neuquenianus (Early Cretaceous; Bonaparte
1986a) and Cronopio dentiacutus (earliest Late Cretaceous; Rougier et al. 2011b), most taxa are based on
isolated teeth and partial upper or lower jaws (Bonaparte 1986a, b, 1990, 1994, 2002, Pascual et al. 2000,
Chornogubsky 2011, Rougier et al. 2009a, b, 2011a).
For the Late Cretaceous, the peak of mammalian diversity is plainly represented by non-therian
species counting a dozen dryolestoids, including Laurasian-related dryolestids and South American
endemic, bunodont meridiolestids (Bonaparte 1986a,b, 1990, 2002, Rougier et al. 2009a, b, 2011a), a few
and poorly known taxa of Gondwanatheria, including sudamericids and ferugliotheriids (Bonaparte 1986a,
b, Mones 1987, Krause et al. 1992, Krause and Bonaparte 1993, Pascual and Ortiz-Jaureguizar 2007,
Gurovich and Beck 2009), and probable cimolodontan multituberculates (Kielan-Jaworowska et al. 2007).
The Order Gondwanatheria was recognized by Mones (1987) for the inclusion of two enigmatic
mammals described few years before: the rst one was Sudamerica ameghinoi from the Paleocene of the
“Banco Negro Inferior” of the Salamanca Formation, Punta Peligro locality (Chubut province, Argentina),
7GOIN et al. / First Mesozoic mammal from Chile
which was included in the family Sudamericidae (Scillato-Yané and Pascual 1985). The second one was
Gondwanatherium patagonicum from the Late Cretaceous Los Alamitos Formation, Los Alamitos locality
(Río Negro province, Argentina), included in the family Gondwanatheriidae (Bonaparte 1986b). The rst
studies on these taxa regarded them as therian mammals (Mones 1987, Bonaparte 1986a, b, 1987, 1988,
Bonaparte and Pascual 1987). They were either included among the Paratheria (i.e., a group that formerly
included xenarthrans, aardvarks, pangolins, taeniodonts, among others; Scillato-Yané and Pascual 1984,
1985), or as part of the Cohort Edentata, Superorder Xenarthra (sloths, anteaters, and cingulates; Mones
1987).
By the same time Bonaparte (1986b) also described a third, enigmatic taxon from the Los Alamitos
Formation, based on an isolated brachyodont molariform: Ferugliotherium windhauseni. The species
was placed in its own family, Ferugliotheriidae (Bonaparte 1986a), referred to the Allotheria, and, with
uncertainties, related to the Multituberculata. Later, Bonaparte (1990) named Vucetichia gracilis from the
same Formation, based on brachyodont teeth with an occlusal pattern similar to that of the hypsodont-
toothed Gondwanatherium. A few years later Krause (1993, see also Krause et al. 1992) regarded Vucetichia
gracilis as a junior synonym of Ferugliotherium windhauseni. By the late 1980s, the relationships of
Gondwanatherium and Sudamerica with xenarthrans were strongly criticized (e.g.,Van Valen 1988, Jenkins
1990). After new collections of specimens and new studies, Krause and Bonaparte (1990, 1993, see also
Sigogneau-Russell et al. 1991, Krause et al. 1992, Bonaparte et al. 1993) relocated Gondwanatherium
and Sudamerica (both regarded as Sudamericidae) within the non-therian clade Multituberculata. These
authors also stressed the multituberculate afnities of Ferugliotherium (Ferugliotheriidae; see also Krause
et al. 1992; Bonaparte 1990). Consequently, Krause and Bonaparte (1993) recognized the Superfamily
Gondwanatherioidea to include sudamericids and ferugliotheriids, as part of Allotheria: Multituberculata:
?Plagiaulacoidea. An informal phylogenetic tree was presented by Krause and Bonaparte (1993) with
Ferugliotherium as the sister taxon of Gondwanatherium and Sudamerica.
Few years later, Kielan-Jaworowska and Bonaparte (1996) described, from the Los Alamitos
Formation, a fragmentary left dentary with the distal wall of the alveolus of a large incisor and a worn
plagiaulacoid tooth, regarded by them as a fourth premolar. Due to their provenance and size, they referred
the specimen to Ferugliotherium. Based on all the evidence, the authors inferred a dentary with one large,
rootless incisor separated by a diastema from a plagiaulacoid pm4, and the presence of at least two molars
(Kielan-Jaworowska and Bonaparte 1996). This proposal was posteriorly followed by Gurovich and Beck
(2009), Rougier et al. (2009b), and Krause et al. (2020).
The nding of a partial right dentary with dentition (including a large incisor, two mesial molariforms
and the loci for two other molariforms distal to them) of Sudamerica ameghinoi was pivotal to interpret the
morphology and tooth variations of the upper/lower cheek teeth in this species, and the basis to interpret
other gondwanatherians (Pascual et al. 1999, Koenigswald et al. 1999, Gurovich 2008). Based on this
specimen and assuming the phylogenetic proximity of ferugliotheriids and sudamericids, Pascual et al.
(1999; see also Kielan-Jaworowska et al. 2004, Pascual and Ortiz-Jaureguizar 2007) predicted that both
families didn’t have a plagiaulacoid lower premolar but instead four molariform teeth (i.e., cheek teeth),
after the enlarged lower incisor. In consequence, the authors claimed that the jaw with a plagiaulacoid
tooth from the Los Alamitos Formation was inconsistent with the known lower jaw and dental morphology
of Sudamerica. However, if that jaw was effectively referable to Ferugliotherium, they inferred that
sudamericids may have lost this blade-like premolar (Pascual et al. 1999). In addition, Pascual et al. (1999;
see also Kielan-Jaworowska et al. 2004; Pascual and Ortiz-Jaureguizar 2007) stated that some of the isolated
premolariforms from the Los Alamitos Formation referred by Krause et al. (1992) to Ferugliotherium
could in fact represent actual multituberculates rather than gondwanatherians (as well as the dentary with
the plagiaulacoid tooth). On the basis of this hypothesis and on new specimens from the Los Alamitos
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
8
and La Colonia formations, Pascual and Ortiz-Jaureguizar (2007) reconstructed the mf1-mf4 series of
Ferugliotherium. In that reconstruction, the cheek tooth row includes four brachyodont molariforms, with
rectangular (mf1-mf2) to quadrangular (mf3-mf4) occlusal surfaces that decrease in size and complexity
to the rear (Pascual and Ortiz-Jaureguizar 2007: 96). Subsequent new reports on allotherians from the
Cretaceous of South America included the description of Argentodites coloniensis (Kielan-Jaworowska
et al. 2007), from the La Colonia Formation, based on an isolated plagiaulacoid tooth considered as a
?cimolodontan multituberculate (Kielan-Jaworowska et al. 2007); and the ferugliotheriid Trapalcotherium
matuastensis from the Allen Formation, based on a left rst molariform tooth (Rougier et al. 2009b).
In this swing of discoveries and hypotheses concerning South American Late Cretaceous to Paleocene
gondwanatherians, the fossil record of the group was expanded through discoveries in Madagascar (Krause
2013, Krause et al. 1997, 2014a, b, c), Tanzania (Krause et al. 2003, O’Connor et al. 2019), India (Prasad
et al. 2007, Wilson et al. 2007, Verma et al. 2012), plus a handful of ndings in the Late Eocene of Peru
(Campbell et al. 2004, Goin et al. 2004), Patagonia (Goin et al. 2012), and the Antarctic Peninsula (Goin
et al. 2006). These ndings supported the persistence of the group during the Cenozoic as relic Mesozoic
lineages (Figure 1). Chimento et al. (2015) argued that the middle Eocene Groeberia minoprioi and G.
pattersoni, as well as the Miocene Patagonia peregrina are sudamericid gondwanatherians. However,
Zimicz and Goin (2020; see also Beck 2017) supported the metatherian afnities of Groeberia, as was
historically assumed (e.g., Patterson 1952, Pascual et al. 1994). The extremely specialized Patagonia was
Figure 1. Global records of gondwanatherian mammals. Late Cretaceous (~80Ma) map (modied from
Scotese 2013) including records from Chile, Argentina, Antarctic Peninsula, Peru, Tanzania, Madagascar
and India. Main references for each point: 1, this paper; 2, Bonaparte 1986b, Krause and Bonaparte 1993; 3,
Bonaparte 1986a, Krause et al. 1992, Pascual and Ortiz-Jaureguizar 2007; 4, Rougier et al. 2009a; 5, Scillato-
Yané and Pascual 1985, Pascual et al. 1999, Koenigswald et al. 1999, Gurovich 2008; 6, Goin et al. 2012; 7,
Goin et al. 2006; 8, Campbell et al. 2004, Goin et al. 2004, Antoine et al. 2012; 9, O’Connor et al. 2019; 10,
Krause et al. 1997, 2014a, 2020, Krause 2013; 11, Prasad et al. 2007, Wilson et al. 2007, Verma et al. 2012.
9GOIN et al. / First Mesozoic mammal from Chile
originally regarded as a marsupial, within its own Superfamily Patagonioidea (Pascual and Carlini 1987).
Posterior reviews (e.g., Goin and Abello 2013, Goin et al. 2016) included it within the Polydolopimorphia
(Bonapartheriiformes, Argyrolagoidea). Patagonia is such an aberrantly derived taxon that a specic
test on its afnities is still pending. Remarkable discoveries, in terms of completeness and quality of the
studied specimens, are those of Vintana sertichi and Adalatherium hui, from the Maastrichthian Maevarano
Formation of Madagascar (e.g., Krause et al. 2014a, b, c, 2020). Vintana is represented by a complete skull
(lower jaws are missing) and Adalatherium by an almost complete, articulated skeleton. Both display a
unique mosaic of plesiomorphic and derived features and are key to understand the complex evolutionary
history of this group of archaic Gondwanan mammals.
Summarizing, after an initial consideration as therian mammals, gondwanatherians were later referred
to the Multituberculata (Krause and Bonaparte 1990, 1993, Gurovich 2006, 2008, Gurovich and Beck 2009,
Rougier et al. 2009a, b), and later to its sister taxon within allotherians (Krause et al. 1997, 2014a, 2019,
2020, Pascual and Ortiz-Jaureguizar 2007, Goin et al. 2012). They were also included within Haramiyida
(Huttenlocker et al. 2018), or regarded as Mammalia incertae sedis (Pascual et al. 1999, Koenigswald et
al. 1999, Kielan-Jaworowska et al. 2004). More recently, the hypothesis of Gondwanatheria as allotherians
allied with (but not belonging to) multituberculates and euharamiyidans, has received much support from
new specimens and phylogenetic analyses (e.g., Krause et al. 2014a, 2020).
Here we describe a new gondwanatherian mammal from the Late Cretaceous of the Magallanes
Region of southern Chile, discovered in the context of a long-term project (starting in 2013) in the Chilean
Patagonia by the Chilean Antarctic Institute (Instituto Antártico Chileno) and the University of Chile. The
new mammal remains represent the southernmost record of the group for the whole Mesozoic and the rst
Mesozoic mammal from Chile. The new taxon is based on an upper incisor and three molariforms discovered
in a single quarry, namely Mammal Quarry, in the area known as Río de Las Chinas Valley, Estancia Cerro
Guido, located about ~100 km north from Puerto Natales City (Última Esperanza Province, Magallanes
Region). The mammal-bearing layer is located in late Campanian-early Maastrichtian levels of the Dorotea
Formation (Magallanes/Austral Basin). We comment on its afnities, morphological signicance, as well
as on the biotic and biogeographic context that framed its evolution in southernmost South America.
GEOLOGICAL AND PALEONTOLOGICAL CONTEXT
The Late Cretaceous units of Última Esperanza Province were deposited over the Magallanes
Basin (=Austral Basin), a foreland basin developed and active during the Late Cretaceous-Neogene lapse,
forming the internal and external domains of the Southern Patagonian Andes fold and thrust belt system
(Biddle et al. 1986, Macellari et al. 1989, Fildani et al. 2008, Romans et al. 2011, Cuitiño et al. 2019).
Three sedimentary units were recognized in the Río de Las Chinas valley. The oldest one is the Tres Pasos
Formation (Katz 1963) of Campanian-Early Maastrichtian age (Macellari 1988, Shultz et al. 2005, Romans
et al. 2011). It is conformably overlaid by the Dorotea Formation (Katz 1963) of Late Campanian-Danian
age (Gutiérrez et al. 2017, George et al. 2020). Finally, the youngest Man Aike Formation (Feruglio 1938),
of Lutetian-Bartonian age, unconformably overlies the Dorotea Formation in erosive contact (Gutiérrez
et al. 2017, Schwartz et al. 2017, Sickmann et al. 2018, Manríquez et al. 2019). The mammalian remains
described herein were discovered in a fossiliferous level of the Dorotea Formation (Katz 1963) (Figure 2).
The Dorotea Formation represents a marine to transitional succession of rocks (Fosdick et al. 2015,
Schwartz et al. 2016, George et al. 2020), cropping out in a N-S direction, along the international border
between Chile and Argentina (Sickmann et al. 2018) (Figure 2). The Chilean unit is equivalent to La Irene,
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
10
Chorrillo, Calafate, and Cerro Cazador formations in the Argentinian side (Nullo et al. 2006, Manríquez
et al. 2019). The depositional environment of the Dorotea Formation has been interpreted as a transitional
shallow marine shelf-edge to delta inuenced by tides (Covault et al. 2009, Hubbard et al. 2010, Schwartz
and Graham 2015, Manríquez et al. 2019, Rivera et al. 2020). The Dorotea Formation outcropping in
the eastern ank of the Río Las Chinas valley comprises 900 to 1200 m thick fossiliferous deposits of
sandstones (greenish-gray and reddish-brown), frequent conglomerate and siltstone lenses, thin beds of
sandy calcareous concretions and mudstones (Cecioni 1957, Katz 1963, González et al. 2015, Manríquez
et al. 2019) (Figure 2). Along the succession there are several fossil-bearing levels with abundant
pteridophytes, gymnosperms, angiosperms, bivalves, gastropods, ammonites, chondrichthyans, anurans,
plesiosaurs, mosasaurs, turtles, dinosaurs, and the mammals described here (Katz 1963, Cortés 1964, Soto-
Acuña et al. 2014, 2016a, b, Schwartz and Graham 2015, Leppe et al. 2016, Manríquez et al. 2019, Alarcón
et al. 2020, Trevisan et al. 2020) (Figure 2). The fossil-bearing mammal horizon corresponds to sandy
mudstone with ne-grained sandstone lenses (Figure 2), interpreted as oodplain facies associated to a
meandering uvial deposit (Manríquez et al. 2019). The presence of numerous bones and teeth of different
Figure 2. A, Location map of the Río de Las Chinas Valley, Estancia Cerro Guido, Última Esperanza Province,
Magallanes Region, southern Chile. B, Location of the Mammal Quarry. C, Representative stratigraphic prole
of the Late Cretaceous Dorotea Formation (Magallanes/Austral Basin), showing the level where the specimens of
Magallanodon baikashkenke gen. et sp. nov. were found, at ~30m above the base. The stars indicate the levels with
absolute radiometric dating.
11GOIN et al. / First Mesozoic mammal from Chile
taxonomic groups in these layers together with the mammal teeth suggests a terrestrial environment with
more limited marine inuence than other levels, lacking typical marine fauna and traces. The deposits result
of the accumulation of silt, clay, and ne sand and then increased accumulation of coarse sand with cross-
stratication near to the coastline. The associated taphoora is inferred from macrofossil compression of
stems, sterile and fertile fronds, leaves and a few reproductive structures. The assemblage is dominated by
ferns and angiosperms (Trevisan et al. 2020), the last ones including large and well-preserved leaves of
Lauraceae and Rosaceae. Among pteridophytes, there are fossils belonging to Equisetum, Cladophlebis,
Dicksoniaceae and Cyatheaceae, typical understory of humid forests, but with the record of aquatic forms,
such as Marsileaceae ferns, indicating the inuence of lacustrine and riparian freshwater environments.
Endorsing this interpretation, the nding of monocot imprints of Poales (cf. Typhaceae), complete the
scene with aquatic plants, perennial, hydrophytic to helophytic. Horsetails are very frequent indicating the
transition among freshwater low-energy environment to land sandy conditions.
U-Pb maximum depositional age above and below the mammal-bearing horizon provides values
between 71.7±1.2Ma and 74.9±2.1Ma (Gutiérrez et al. 2017), respectively, which allow us to refer it to a
Late Campanian-Early Maastrichtian age for the fossil-bearing levels. These levels are equivalent to the
Chorrillo Formation (Furque and Camacho 1972) exposed at the south of Lago Argentino, Santa Cruz
Province, Argentina (Nullo et al. 2006), which has also provided a taxonomically diverse and abundant
fossil record (Novas et al. 2019).
MATERIAL AND METHODS
Field work and specimen recovery: The holotype and referred specimens herein described were
collected by both picking at the outcrop and at the lab after dry- and screen-washing of sediments collected
during the 2017 to 2019 eld seasons.
Specimens imaging: Scanning electron microscope (SEM) images were made for specimens
CPAP 5906 and CPAP 5916. CPAP 5906 was scanned at the Laboratorio de Microscopía Electrónica y
Microanálisis of the Facultad de Ciencias Físicas y Matemáticas of the Universidad de Chile, and CPAP
5916 at the Unidad de Microscopía Avanzada of the Ponticia Universidad Católica de Chile, both at
Santiago, Chile. For the enamel microstructure imaging, due to the unique nature of the specimen collected
(CPAP 5906, an upper right mesial incisor), we opted to polish the distal portion of the specimen; thus,
we were able to obtain only transverse views of its enamel. After polishing, the enamel was exposed a few
seconds to a 10% HCl solution.
Dental descriptive terminology: We used the dental terminology employed by Krause (2014) for
the dentition of Vintana. Figure 3 shows a detail of the dental anatomy here employed. The dental formula
for gondwanatherians is a problematic issue (e.g., Pascual et al. 1999, Krause 2014, Krause et al. 2014a)
due to the lack of complete dental sequences in most species, and the lack of different ontogenetic stages
to evaluate replacement and morphological changes. The lower jaw of Sudamerica ameghinoi supports a
lower dental formula of one incisor, no canine, and four cheek teeth (Pascual et al. 1999). Based on isolated
teeth, four upper cheek teeth were inferred for this same taxon (Koenigswald et al. 1999, Gurovich 2008).
Due to the homology problem, upper and lower cheek teeth of Sudamerica were regarded in the literature
as “molariforms” (e.g., Koenigswald et al. 1999, Gurovich 2008, Gurovich and Beck 2009). The skull of
Vintana indicates the existence, in the upper dentition, of 2I, 0C, 1PMF, 4MF (Krause 2014, Krause et al.
2014a). The skull and jaws of Adalatherium indicates 2I/1i, 1C/0c, 5/4 cheek teeth. The rst upper cheek
tooth was considered a premolariform due to its small size and less complex morphology (Krause et al.
2020), similar to the condition of Vintana, while the remaining were considered as postcanine teeth. The four
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
12
lower cheek teeth of Adalatherium show an increased posterior complexity, but the premolar/molar nature
for these teeth was not further discussed. Summarizing, available evidence suggests ve upper cheek teeth
for gondwanatherians, with the rst one reduced and premolariform in gross morphology, based on Vintana
and Adalatherium, as well as four lower cheek teeth, based on Sudamerica and Adalatherium; however, the
bizarre morphology of the dentition of Adalatherium precludes a clear identication of premolariforms and
molariforms.
Dental abbreviations: I, upper incisor; MF/mf, upper/lower molariforms; PMF, upper premolariforms.
The numbers indicate the suggested position of each tooth in the series. All measurements are in mm.
Enamel microstructure abbreviations: EDJ, enamel-dentine joint; IPM, interprismatic matrix, OES,
outer enamel surface, P, prism; PLEX, prismless enamel.
Institutional Abbreviations: CPAP, Paleontological Collection of Antarctica and Patagonia, Instituto
Antártico Chileno, Punta Arenas, Chile. MACN-PV-RN, Colección Río Negro, Sección Paleontología
Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, Argentina.
SYSTEMATIC PALEONTOLOGY
MAMMALIA Linnaeus 1758
GONDWANATHERIA Mones 1987
?FERUGLIOTHERIIDAE Bonaparte 1986a
Genus Magallanodon nov.
urn:lsid:zoobank.org:act:06DA7596-509A-4FA8-A5FA-811377C879DBType
Species: Magallanodon baikashkenke sp. nov.
Diagnosis: As for the species, by monotypy.
Magallanodon baikashkenke sp. nov.
urn:lsid:zoobank.org:act:7A0C2687-9C46-408D-9D90-9AEB475A3583
Derivation of name: The generic name comes from the Magallanes Region in Southern Chile, and odontos,
Greek for “tooth”. The specic name derives from the Tehuelchian terms bai (grandfather) and kashkenke
(valley). Grandfather’s Valley is the aboriginal name for the current valley of the Río de Las Chinas, where
the type locality is placed.
Holotype specimen: CPAP5916, rst lower left molariform (mf1; Figs. 3, 4).
Hypodigm: The type and specimens CPAP 5906, an upper right mesial incisor (Figure 5), and the
molariforms CPAP 3223 and CPAP 3224, a left and a right ?MF4, respectively (Figure 6).
Diagnosis: Large-sized gondwanatherian (mesio-distal length of mf1=8.34 mm; see Table 1) which can
be distinguished from other gondwanatherians by the following combination of features: brachyodont
molariforms with four to ve roots; molariforms with distinct transverse lophs which in unworn condition
are formed by multiple rounded adjacent cuspules; mesial lower molariform crown with four main lobes,
the mesial one D-shaped, the second formed by a longitudinal ridge, and the third and fourth V/U-shaped
in occlusal view, all of them separated by continuous labio-lingual grooves that open on the lingual wall
13GOIN et al. / First Mesozoic mammal from Chile
of the crown as deep furrows; the lobes dene seven cuspules on the labial margin of the crown of mf1;
distalmost upper molariforms with two lobes divided by a transverse groove that starts in the labial edge
and does not reach the lingual side; presence of islets on the worn occlusal surface of the lobes; distalmost
upper molariforms with crown distal width ¾ smaller than the mesial width.
Comment: Magallanodon baikashkenke is tentatively referred to the family Ferugliotheriidae as it shares
the same occlusal pattern observable in worn molariforms of ferugliotheriids (e.g., specimens MACN-PV-
RN 20 and MACN-PV-RN 174), as well as on its brachyodont condition (Krause and Bonaparte 1993). The
remaining gondwanatherians have hypsodont cheek teeth (e.g., Bonaparte 1986b, Krause et al. 1997, 2014a,
2020, Pascual et al. 1999, Wilson et al. 2007, O’Connor et al. 2019) or an unique cheek teeth dentition
(i.e., Adalatherium hui; e.g., lower cheek teeth with four major cusps arranged in a diamond pattern and
connected by four perimetric crests, bearing a prominent mesio-labial basin on the two distalmost teeth;
Krause et al. 2020). If its family referral is conrmed by further studies (e.g., new material under preparation
and phylogenetic studies), the new species would represent the largest known ferugliotheriid (around ve
times larger than Ferugliotherium and Trapalcotherium).
Locality, horizon and age: The holotype and referred specimens come from a small quarry, named Mammal
Quarry, located in the Río de Las Chinas valley (50° 42’S /72° 32’W), Estancia Cerro Guido, ~100 km
north from Puerto Natales, Última Esperanza Province, 12th Region (Magallanes and Chilean Antarctica),
Chilean Patagonia (Figure 2); base of the Dorotea Formation, Late Campanian to Early Maastrichtian, Late
Cretaceous. (Measurements--See Table1).
Figura 3. Dental terminology for the lower molariforms of Magallanodon baikashkenke gen. et sp. nov. Specimen
CPAP 5916 (holotype), a rst lower left molariform (mf1) in occlusal view.
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14
Figure 4. Magallanodon baikashkenke gen. et sp. nov., holotype specimen CPAP 5916, rst lower left
molariform. SEM image in occlusal view (A) and photographs in occlusal (B), radicular (C), labial (D),
lingual (E), mesial (F), and distal (G) views.
Table 1: Measurements of Magallanodon baikashkenke gen. et sp. nov.
Number Specimen Mesio-distal length
(mm)
Labio-lingual width
(mm)
Crown height
(mm)
CPAP 3223 Left MF4? 6.19 5.05 2.28
CPAP 3224 Right MF4? 6.55 5.13 2.32
CPAP 5906 Upper right incisor 4.40 5.40 13.69
CPAP 5916 Left mf1 8.34 6.31 4.42
15GOIN et al. / First Mesozoic mammal from Chile
DESCRIPTION
Upper mesial incisor: Specimen CPAP 5906 has preserved its apical portion (Figure 5). The
tooth is strongly curved (labially convex, lingually concave) and is subelliptical in section (it is slightly
compressed mesio-distally). Its thickness is not homogeneous, as it gets thinner at its apical end (the tip is
broken). The cross section is subcircular all along the tooth. One of its lateral faces lacks enamel; we infer
that this is the mesial face of the tooth, thus being an upper right mesial incisor. The lingual face has a thin
stripe of enamel covering only less than half of this face. Along the incisor extension a series of enamel
ribs can be observed on the labial and distal faces, being most prominent on the distal face. Dentine also
contributes to the formation of these ribs. The rst two ribs are close to each other. A third one is clearly set
apart from the former two, while the remaining ribs are aligned at regular intervals.
Comment: The size of specimen CPAP 5906 is clearly compatible with that of the molariforms of
Magallanodon baikashkenke. This, together with the absence of other mammalian specimens even remotely
similar in size to it, led us to condently assign the specimen to this species. From previous works on much
more complete gondwanatherian specimens (e.g., Krause 2014, Krause et al. 2014a, 2020) it is clear that
the upper mesial incisor is strongly curved (arch-shaped), more than the lower incisor and the upper distal
one. Specimen CPAP 5906 displays a curvature similar to that of the upper mesial incisor of the skull of
Vintana (Krause 2014). This, and the presence of enamel ribs on its labial surface, supports the assignment
of this tooth to an upper mesial incisor.
Lower molariform: CPAP 5916 is a left mf1, which was chosen as the holotype specimen (Figure
4). It is a large and relatively elongated tooth, and it barely shows any wear at all. The presence of a low
crown, together with a clear cervix and distinctive roots, dene a typical brachyodont pattern. The crown
is subquadrangular in occlusal view, with the mesial face somewhat rounded and the distal one at (Figure
4 A, B). It does not show cementum in any of its faces. The mesial face lacks an interdental contact facet,
as expected for a rst lower cheek tooth (some gondwanatherians lack a tooth anterior to the rst lower
molariform; e.g., Pascual et al. 1999); instead, there is a small facet on the distal face, semilunar in shape,
developed at its labial half. The crown base shows a distinct interruption of the enamel layer at the cervix
that denes a conspicuous neck. The mesial and distal faces of the tooth are subvertical; the labial face
is subvertical in its lower two-thirds, curving gently at the upper third. Finally, the lingual face is not
subvertical but instead is inwardly curved. The labial face of the tooth is just slightly higher than the lingual
one. There are seven distinct cusps in the labial face of the crown, separated by small valleys that descend
just a fth of the crown height. In turn, on the lingual face of the crown there are four main cusps that are
larger than the labial cusps. The main lingual cusps have a strongly convex lingual wall and a labial at
surface, where most of the wear is initially produced. The main lingual cusps are split by deep furrows that
run down more than half of the crown height. These deep lingual furrows and their transverse grooves that
continue over the crown to the labial side dene four lobes (Figs. 3, 4 A-B).
In occlusal view, the four lobes are separated by transverse grooves, which on the lingual wall are
deeper than in the labial face. The rst lobe (mesial) is externally outlined as D-shaped. It has three slightly
oblique ridges: the mesial ridge has two cuspules, the central ridge has two central cuspules and a crest-like
cusp, which corresponds to the rst labial cusp, and the distal ridge has at least two middle cuspules and
the second labial cusp. The second lobe is formed only by a transversal ridge with the main second lingual
cusp, two central cuspules and the third labial cusp. The third lobe is V-shaped, with three central cuspules
and the fourth and fth labial cusp. The fourth lobe is U-shaped; the mesial ridge has at least four central
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
16
cuspules and the sixth labial cusp, while the distal ridge has two central cuspules (laying on the distal wall
of the crown) and the seventh (last) lingual cusp (Figure 4 A). The unworn nature of CPAP 5917 clearly
demonstrates how the transverse ridges (lophs) are formed by tiny, aligned cuspules.
The two distal lingual cusps, as well as (at least) the last three labial cusps of CPAP 5916 show
on their worn surfaces a series of striations that run roughly parallel to the dental axis, although slightly
oblique to it, in a mesio-lingual to disto-labial direction. These striations are indicative of the masticatory
movements of Magallanodon, which in turn are congruent with the inferred palinal movements of other
gondwanatherians (e.g., Krause and Bonaparte 1993). The tooth has four subequal roots of relatively large
size, as well as a tiny, fth one near the mesial face; all roots are broken at their bases (Figure 4 C). The
four large roots are placed at each corner of the tooth: mesio-labial, mesio-lingual, disto-labial, and disto-
lingual.
Comment: We refer the holotype CPAP 5916 as a rst lower left molariform following comparisons
with other gondwanatherians. First, it is similar in shape and proportions to other lower molariforms referred
to mf1 as for example for Ferugliotherium, Trapalcotherium, and Gondwanatherium (e.g., Krause et al.
1992, Gurovich 2006, Rougier et al. 2009a). Second, the rst molariform is the longest of the upper and
lower series in Sudamerica (Koenigswald et al. 1999: table 1, Pascual et al. 1999). Taking in account the
differences in size with the specimens here referred to ?MF4 (the holotype is quite mesio-distally longer; see
Table 1), it is reasonable to assume that it corresponds to a mf1. Third, as it happens in several caviomorph
rodents, it is quite possible that in gondwanatherians an inverse relation of furrows in the upper and lower
molariforms occurs, opening labially in the upper ones (Krause 2014, Krause et al. 2014a) and lingually
in the lower ones. Fourth, the mesial wall of the crown lacks an interdental contact facet, as expected for
a rst lower cheek tooth, as in other gondwanatherians (e.g., Pascual et al. 1999), and the distal wall bears
this facet, indicating a subsequent tooth. For this reason we infer that the holotype of Magallanodon is a left
mf1 (Figures 3, 4).
Figure 5. Magallanodon baikashkenke gen. et sp. nov. Specimen CPAP 5906, an upper right mesial incisor, in
distal (A) and mesial (B) views. C, SEM image of the transverse section of the tip of the incisor showing the
analyzed region of the enamel layer. D, SEM image of the distal end of the enamel band showing the different
types of enamel. E, SEM image with detail of the enamel layer showing the path of the prisms. Abbreviations:
EDJ, enamel-dentin junction; IPM, interprismatic matrix; P, prism; PLEX, prismless enamel; RE, radial
enamel; TE, tangential enamel.
17GOIN et al. / First Mesozoic mammal from Chile
?Upper molariforms: Specimens CPAP 3223 and CPAP 3224 are tentatively referred to last upper
molariforms (MF4; see below); the former, a left one, and the latter, a right one (Figure 6). In occlusal
view, CPAP 3223 is subrectangular in shape, wider than long; with the height of the crown about half the
mesio-distal length of the tooth. It has a well-dened neck between the crown and the roots. Four roots are
observable: two labial and two lingual. The occlusal surface is not at, as the lingual third is higher than the
central and labial parts, gently sloping towards them. The mesial face of the tooth shows a wide interdental
facet, while the distal face does not (as expected in a last MF). The mesial half of the crown is wider than the
distal half. A deep syncline (transverse groove) runs from the labial face almost reaching the lingual edge of
the tooth, and divides the tooth in two lobes. This syncline is not straight but instead is mesially directed in
its rst third (from the labial face) to almost transverse in its remaining length. The syncline ends in a deep
furrow directed posteriorly at the labial face. Anterior to the syncline there is a mesio-distally compressed
islet, and posterior to it there are two islets, also mesio-distally compressed. Both islets are surrounded by
enamel (Figure 6A, B).
Specimen CPAP 3224 is very similar in morphology and dimensions but opposite in shape to
CPAP 3223. We interpreted it as a slightly more worn right ?MF4 (Figure 6). It has an interdental wear
facet at the mesial face, lacking one at the distal face. Probably due to its more intensive wear, distal to the
syncline there are two (Figure 6 C) instead of a single larger islet surrounded by enamel, as occurs in CPAP
3223 (Figure 6 A).
Comments: There are several interesting resemblances when comparing specimens CPAP 3223
and CPAP 3224 to the last upper molariform of Vintana sertichi (see Krause 2014, Krause et al. 2014a):
(1) molariform proportions, with the distal half narrower than the mesial one; (2) a deep furrow oriented
backwards on the labial face; (3) a central syncline dividing the molariform in halves (however, the MF4
of Vintana has two furrows, while Magallanodon shows only one). Also, only one transverse groove with a
labial furrow, which denes two lobes is a feature similar to the condition inferred in the distal molariforms
of ferugliotheriids (e.g., Krause and Bonaparte 1993). Additionally, the presence of only one interdental
wear facet indicates that the molariform locus is at an extreme end of the series (i.e., either a MF1 or a
MF4). Taking in account all these aspects, we provisionally refer both molariforms (CPAP 3223 and CPAP
3224) to MF4.
Besides their obvious differences in crown height, there are remarkable similarities between the
specimens CPAP 3223 and CPAP 3224 of Magallanodon and MACN-PV-RN 1025 of Gondwanatherium
patagonicum, regarded by Gurovich (2006) as a lower left molariform. Even though, as it happens in
Vintana, Gondwanatherium has two labial furrows instead of a single one, the overall proportions of the
molariform, as well as the lophs, syncline and islet morphology, are suggestive of a similar locus in the
upper molar series. Thus, we provisionally refer MACN-PV-RN 1025 of Gondwanatherium to a ?MF4.
We also wonder if specimen MACN-PV-RN 20 of Ferugliotherium, regarded by Krause et al. (1992) as a
second (and last) lower molar, actually constitutes a last upper molariform, as its morphology and overall
proportions closely match those of specimens CPAP 3223 and CPAP 3224.
ENAMEL MICROSTRUCTURE
Description: In cross section, the enamel layer of the upper incisor (CPAP 5906) reaches 160
microns in the thickest portion, which is very thick compared to other gondwanatherians (e.g., Koenigswald
et al. 1999, Koenigswald and Krause 2014). Three enamel zones can be distinguished, two of radial enamel
and one of tangential enamel between them (Figure 5). Towards the distal end of the enamel, the tangential
enamel occupies the entire thickness of the band. The orientation of the tangential enamel prisms shows a
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
18
lateral inclination on the distal side. Unfortunately, there is a single photographic record of the enamel band
on the distal side, which does not allow the recognition of a neutral zone (see, e.g., Koenigswald et al. 1999),
nor the mesial portion of the enamel. A neutral band is observable in sudamericids, such as Sudamerica
(Koenigswald et al. 1999). Enamel microstructure is unknown for the incisors of Ferugliotherium or
Trapalcotherium.
In the innermost zone of the enamel layer the upward inclination of the prisms regarding the dental
axis is very slight, but in the next zone the prisms change direction in a simultaneous prism deviation, to
nally rise abruptly towards the occlusal surface (Figure 5). Prisms are small, of 4 to 5 microns in diameter,
and some have incomplete prism sheaths. They are surrounded by a thick interprismatic matrix (IPM)
whose crystals are arranged at an angle of 45º with respect to the prisms, at the level of the tangential
enamel. The prisms are organized into ordered and aligned rows, as is evident in the outermost radial
enamel area. However, the IPM does not form interrow sheets but instead is anastomosed. No decussation
of prisms was observed. In the outermost portion of the enamel, a thin area (around 15 um) is recognized,
in which the prisms lose denition (fade away) until they disappear so that the IPM becomes dominant
towards the outer enamel surface (OES).
Comparisons: The composition in terms of enamel types of the gondwanatherian incisors show
signicant variations between the distal and mesial sides of the enamel band, unlike other groups of
mammals (e.g., rodents) where this does not occur. In gondwanatherians, the incisor schmelzmuster is made
by a combination of radial and tangential enamel; in the latter, prisms are oriented in opposite directions
between the distal and the mesial sides. Normally, between both elds of tangential enamel there is a
“neutral area” of radial enamel. Contrary to what was observed in Magallanodon, the incisor enamel of
Sudamerica ameghinoi has an inner layer of radial enamel, one of tangential enamel and a thick outer
Figure 6. Magallanodon baikashkenke gen. et sp. nov., left upper molariform (?MF4) CPAP 3223
(A, B) and right upper molariform (?MF4) CPAP 3224 (C, D), in occlusal (A, C) and labial (B, D)
views.
19GOIN et al. / First Mesozoic mammal from Chile
layer of PLEX (Koenigswald et al. 1999). The prisms are separated by incomplete prism sheaths from an
unusually thick IPM. A neutral area of somewhat mesial position separates the two tangential enamel elds
in which its opposite-oriented prisms converge towards it. Towards the distal end of the enamel, the enamel
band thins, being only formed by radial enamel. Goin et al. (2006) studied the enamel of a gondwanatherian
incisor from the Middle Eocene of Antarctica, tentatively referred to as cf. Sudamerica ameghinoi. Its
enamel microstructure differs in part from that of Magallanodon in that the schmelzmuster is made up of
two layers of tangential enamel, divided into two elds, one mesial and one distal, by a neutral area which
is similar to that observed in Sudamerica (close to the mesial inection of the enamel band). The authors
were able to observe that the prisms of the inner layer of tangential enamel diverge from the neutral area
while the prisms of the outer layer of tangential enamel converge towards the neutral area (coincident with
the outer tangential enamel layer of Sudamerica). As in Sudamerica, in the Antarctic specimen the prisms
are surrounded by a thick layer of IPM and have incomplete prism sheaths.
The enamel of Gondwanatherium patagonicum shows several features similar to those of
Magallanodon. Gondwanatherium shows a neutral area of radial enamel much more extensive than in
Sudamerica, which is located on the distal side (Koenigswald et al. 1999). In both elds the tangential enamel
is seen as a central layer of increasing thickness towards the distal end of the enamel, between two layers
of radial enamel. The tangential enamel prisms show opposite directions in both elds, diverging from the
neutral area and opposite to that observed in Sudamerica. In Magallanodon, the pattern coincides with this
three-layer pattern, with the tangential enamel prisms tilted laterally towards the distal side. Unfortunately,
the complete enamel band of the later was not available; therefore, the “neutral area” and the inclination of
the tangential enamel prisms in the mesial eld could not be identied. In Gondwanatherium patagonicum,
the enamel layer thins towards the end of the enamel, being made only of tangential enamel; the same is
observed in the most distal lip of the enamel of Magallanodon. These similarities suggest a common pattern
between ferugliotheriids, if Magallanodon is effectively a ferugliotheriid, and other gondwanatherians. As
previously mentioned, no enamel microstructure analysis has been perfomed in Ferugliotherium’s incisor
(also, no incisors are known for Trapalcotherium).
DISCUSSION
Magallanodon baikashkenke represents the rst Mesozoic mammal for Chile and the southernmost
record of a Mesozoic gondwanatherian (the paleolatitude of the Las Chinas valley was ~54º South, van
Hinsbergen et al. 2015; see Figure 1). The integration of geological and geophysical data, together with
tectonic frameworks from well-studied once-conjugate continents have improved the knowledge of
the paleogeography of the southern part of the South America/West Antarctica area prior to the break-
up of these blocks (Jordan et al. 2020). The plate tectonic reconstruction map by the Late Cretaceous
(Late Campanian, ~80 Ma; Jordan et al. 2020) shows one of the West Antarctica blocks, Antarctic
Peninsula (AP) was very near the current Magallanes Region. The Magallanodon-bearing horizon of the
Dorotea Formation at Río de Las Chinas valley constricted on ~75 Ma probably represents a terrestrial
paleoenvironment similar to that depicted for the Late Campanian-Early Maastrichtian of the James Ross
Basin (Vega Island, Cape Lamb Member, Snow Hill Island Formation; Reguero et al. 2013). Consequently,
the presence of gondwanatherians is expected at even more southern latitudes than reported here. Antarctic
gondwanatherians are known for the Eocene (Goin et al. 2012), so early arrival at this region is expected
and supports this biogeographic scenario.
The age of Magallanodon is constrained as Late Campanian-Early Maastrichtian, similar to the
inferred age of Los Alamitos and Allen formations of northern Patagonia (Río Negro Province, Argentina),
where a diverse mammal assemblage was recovered, including gondwanatherians and dryolestoids
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
20
(e.g., Bonaparte 1986a, b, 1987, 1990, Pascual et al. 2000; Rougier et al. 2009a, 2011b). Amongst the
mammalian assemblage of Los Alamitos Formation there are two gondwanatherians, the relatively
large-sized and hypsodont toothed Gondwanatherium patagonicum (Sudamericidae) and the small-sized
brachyodont toothed Ferugliotherium windhauseni (Ferugliotheriidae) (Bonaparte 1986a, b, Krause et al.
1992, Gurovich 2008). In the Allen Formation, there is only one taxon, Trapalcotherium matuastensis
(Rougier et al. 2009a), with a roughly similar size and gross dental morphology to that of Ferugliotherium.
La Colonia Formation (Chubut Province) has also provided Cretaceous mammals (e.g., Pascual et al. 2000,
Rougier et al. 2009b, Harper et al. 2019), including a preliminary report of Ferugliotherium (Pascual
and Ortiz-Jaureguizar 2007). Nonetheless, the faunal assemblage of this unit was considered as younger
than that of Los Alamitos and Allen formations (e.g., Martinelli and Forasiepi 2004, Pascual et al. 2000,
Rougier et al. 2011b). A large sized brachyodont-toothed gondwanatherian taxon like Magallanodon is
yet unknown in these Cretaceous assemblages of northern Patagonia. As a consequence, considering a
roughly similar age between the Dorotea Formation and the Los Alamitos/Allen formations, the presence
of Magallanodon in high southern latitudes likely highlights distinctive ecological strategies for Late
Cretaceous gondwanatherians, including large sized/brachyodont toothed forms, small-sized/brachyodont
toothed forms, and large-sized/hypsodont toothed forms. Similarly, they all share enlarged, rodentiform
incisors. Further studies on the whole faunal and oral associations of these units will elucidate the diverse
ecologic dynamic by the Late Cretaceous, which resulted in taxonomically diverse and morphologically
disparate non-therian mammal morphotypes.
Is Magallanodon a ferugliotheriid gondwanatherian?--Magallanodon baikashkenke is a Late
Cretaceous mammal, that can be condently referred to Gondwanatheria. Within this clade, it shares
more features with ferugliotheriids than other gondwanatherians (e.g., sudamericids, adalatheriids). As a
consequence, it is tentatively referred to the Ferugliotheriidae until new material and studies are provided.
The preserved remains are consistent with it being a gondwanatherian: hyperthropied, rodent-like rst
upper incisor, molariform teeth with transverse ridges (lophs) and furrows (labial in MFs, lingual in mfs),
and evidences of palinal masticatory movements (e.g., striations made by wear in the molariform cusps,
which are more or less aligned with the dental row). Our referral of Magallanodon, with doubts, to the
?Ferugliotheriidae (see a revised diagnosis in Krause and Bonaparte 1993) is supported by a molariform
occlusal pattern that is similar to that of Ferugliotherium (e.g., specimens MACN-PV-RN 20, MACN-
PV-RN 174) in conjunction with brachyodont crowns supported by transverse pairs of roots (in the case
of the holotype, there are two pairs of large, transverse roots and a minute, additional one at the mesial
edge of the crown; Figure 4 C). The only feature that disagrees with Krause and Bonaparte’s (1993)
diagnosis of Ferugliotheriidae is its size, as members of this family were regarded as small compared to the
Sudamericidae. Magallanodon is comparable in size to the largest members of this last family.
With the exception of Adalatherium, which exhibits extremely bizarre cheek teeth dentition
(Krause et al. 2020), all other non-ferugliotheriid gondwanatherians (sudamericids plus gondwanatherians
of uncertain afnities, such as enamel-less toothed Galulatherium; O’Connor et al. 2019) show some
degree of hypsodoncy (e.g., Bonaparte 1986b, Krause et al. 1997, 2014a, b, Pascual et al. 1999, Krause
2003, 2014, Wilson et al. 2007, Goin et al. 2012). In this regard, Magallanodon presents a brachyodont
pattern with crowns that functionally work as those of sudamericids, including a system of lobes, with
transverse lophs separated by furrows, palinal jaw movements during chewing, and distinctive dental roots.
This also characterized the already known brachyodont ferugliotheriids (e.g., Krause and Bonaparte 1993).
Vintana sertichi, from the Late Cretaceous of Madagascar, was considered to have hypsodont cheek teeth
(Krause 2014, Krause et al. 2014a), however, we think that this is debatable: its molariforms have several
roots, a distinctive crown/root division, and relatively low crowns (although they are strongly worn). As no
other specimens of Vintana are known, the precise height of its unworn molariforms cannot be assessed. We
suggest that a brachyodont to mesodont condition could better dene their crown pattern.
21GOIN et al. / First Mesozoic mammal from Chile
Further studies and new specimens are certainly essential to improve the understanding of
morphological variation and homologies along the tooth rows in poorly known gondwanatherian species,
which in the last years have produced disparate opinions, especially regarding ferugliotheriids (e.g., Pascual
et al. 1999, Kielan-Jaworowska et al. 2004, Pascual and Ortiz-Jaureguizar 2007, Gurovich 2008, Gurovich
and Beck 2009, Rougier et al. 2009b, Krause 2014, Krause et al. 2014a). Better knowledge of these species
will support or refute the taxonomic and phylogenetic hypotheses for the members of this specialized
group of non-therian mammals. With the available evidence on the clade and the set of features known in
Magallanodon, we opt to consider it as tentatively allied to the Ferugliotheriidae.
Signicance of the molariform pattern of Magallanodon--One of the most outstanding aspects
of the molariform morphology of Magallanodon baikashkenke is that it sheds light on how the transverse
lophs (ridges) of gondwanatherians did evolve: not as crests joining opposite cusps but instead by a series
of minute, labial-lingual aligned cuspules that developed between major opposite cusps (Figures 3, 4).
This feature was partially evident in Ferugliotherium (Krause et al. 1992, Krause and Bonaparte 1993)
and some sudamericid gondwanatherians, such as Gondwanatherium (Bonaparte 1986b, 1988, Gurovich
2008). Specimen MACN-PV-RN 22 of Gondwanatherium, for example, shows at least three small cusps
which are aligned forming the lingual half of the second ridge. However, due to the worn nature of most
collected sudamericids, this feature is not observable in most of the known specimens. The holotype of
Magallanodon baikashkenke indicates that all lophs/ridges developed following the same pattern.
Another relevant aspect that deserves further comment is the strong degree of wear seen in the
molariforms of Magallanodon, as revealed by specimens CPAP 3223 and CPAP 3224, which is unusual
in a brachyodont mammal. It seems clear the ecological context must have favored the development of
hypsodonty among gondwanatherians, as revealed by the relatively high diversity of hypsodont toothed
sudamericid taxa from the Late Cretaceous. Both the molar morphology and the inferred masticatory
movements of gondwanatherians are suggestive of herbivorous feeding habits that probably included hard
plant materials, as those inferred for Vintana sertichi (Schultz et al. 2014), including roots, seeds, twigs,
and/or nut-like fruits.
CONCLUSION
We describe the rst Mesozoic mammal for Chile, discovered in the Upper Cretaceous Dorotea
Formation (Magallanes/Austral Basin) at the Río de Las Chinas Valley, Estancia Cerro Guido, Última
Esperanza Province, Magallanes Region, southern Chile. It is based on isolated teeth (one incisor and
three molariforms) that represent a new genus and species, Magallanodon baikashkenke, included into the
allotherian clade Gondwanatheria. Based on its gross occlusal morphology and brachyodont molariforms
it is tentatively referred to ?Ferugliotheriidae, which at the moment was endemic for northern Patagonia,
Argentina. The relatively large size of this species coupled with its large, hypsodont incisors and
brachyodont molariforms highlight the ecological disparity of this group during the Late Cretaceous. This
new gondwanatherian record also represents the southernmost for the Cretaceous, but the occurrence of
members of this clade in the Antarctic Peninsula during the middle to late Eocene, supports a long-lasting
presence in southern latitudes since at least the near end of the Mesozoic.
ACKNOWLEDGMENTS
We thank Jhonatan Alarcón, Héctor Mansilla, José A. Palma, Vicente Muñoz, Sara Davis, Valentina Poblete,
Luna Núnéz, Daniel Bajor, Verónica Milla, Felipe Suazo, Rodrigo Otero, Guillermo Aguirrezabala and Marcelo
Miñana, for their valuable eld assistance. Special thanks to Bárbara Aravena for her help collecting specimens in the
BOLETÍN DEL MUSEO NACIONAL DE HISTORIA NATURAL
22
eld and laboratory assistance. Thanks to INACH and Estancia Cerro Guido for their logistic support. We also thank the
technicians of the Electron Microscopy and Microanalysis Laboratory of the Universidad de Chile and the Advanced
Microscopy Unit of the Ponticia Universidad Católica de Chile (PUC) for allowing the access to their equipment,
and also to Joao Botelho (PUC) for assistance during the process. Marcela Tomeo designed the gures of the incisor
and the enamel microstructure of Magallanodon. This research was supported by an Anillo grant ACT-172099 (PIA-
ANID Chile) and a FONDECYT grant N° 1151389 “Paleogeographic patterns v/s climate change in South America
and the Antarctic Peninsula during the latest Cretaceous: ¿A possible explanation for the origin of the Austral biota?”.
We specially thank the reviewers Analía Forasiepi, Alfredo Carlini and J. Enrique Bostelmann for providing useful
comments that substantially improved this work.
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Recibido: 01/jun/2020; Aceptado: 06/jun/2020; Administrado por Jhoann Canto H.
