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Redescription of the argyrolagid Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) based on new remains from Northwestern Argentina

M. Judith Babot and Daniel A. García-López

Plain Language Abstract

This study deals with the anatomy and systematic of the species Microtragulus bolivianus found in Pliocene beds exposed in Bolivia and Northwestern Argentina. This taxon is part of the Family Argyrolagidae, small bipedal fossil mammals included in Metatheria, which inhabited South America between the Oligocene and the early Pleistocene. The species, formerly represented only by very incomplete remains recovered from the Bolivian Altiplano, is here redescribed in detail and its diagnostic features are revisited. Moreover mandibular anatomical features of the family are revisited and a revision of the nomenclatural changes of the name Argyrolagidae is presented.

Resumen en Español

Redescripción del argirolágido Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) basada en nuevos restos del noroeste argentino

Este trabajo se basa en nuevos restos dentales, craneales y postcraneales del argirolágido Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) y piezas dentales de Microtragulus sp. provenientes de niveles de edad pliocena tardía-pleistocena temprana de la Formación Uquía, aflorantes en San Roque, Humahuaca (provincia de Jujuy, Argentina). Fueron encontados en asociación con anfibios, lagartijas, aves, roedores y marsupiales didélfidos, constituyendo una asociación probablemente generada por la actividad trófica de lechuzas. Los especímenes fueron asignados a M. bolivianus en base a la siguiente combinación de características: M3 subcircular, con un flexo entre el lóbulo mesiolabial y el metacono, paracono y metacono no diferenciados en M4, ausencia de entofléxido en m1-2 y un entofléxido somero en m3, un talónido proporcionalmente grande en m4, con un fléxido distal distinguible. Microtragulus bolivianus, inicialmente registrado en sedimentos pliocenos del altiplano boliviano, se hallaba representado únicamente por un fragmento mandibular con un incisivo y m3-m4. En base a una muestra mucho más completa presentamos una descripción dental y postcraneal detallada de la especie. Desde 1904 el nombre de la familia Argyrolagidae y los nombres genéricos Microtragulus y Argyrolagus han sido sujetos a varios cambios nomenclaturales. También se presenta una revisión de estas modificaciones, principalmente aquellas de los últimos 40 años. A su vez, analizamos algunas características de los argirolágidos tales como el canal maxilar (canal retrodental), un atributo muy particular presente en todos los miembros de la familia, el cual podría estar relacionado con el pasaje de una conexión entre las venas alveolar inferior y orbital inferior, como en algunos mamíferos actuales.

Palabras clave: Argyrolagidae; Bonapartheriiformes;Marsupialia; Formación Uquía; Formación Umala; Edad Mamífero Marplatense

Traducción: Diana Elizabeth Fernández

Résumé en Français

Révision de l'argyrolagidé Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) d'après des nouveaux restes du nord-ouest de l'Argentine

Ce travail est basé sur des nouveaux restes dentaires, crâniens, et postcrâniens de l'argyrolagidé Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) et des restes dentaires de Microtragulus sp. provenant des niveaux du Pliocène récent-Pléistocène ancien de la formation d'Uquía qui affleurent à San Roque, Humahuaca (province de Jujuy, Argentine). Ils ont été trouvés en association avec des amphibiens, des lézards, des oiseaux, des rongeurs, et des marsupiaux didelphidés, formant un assemblage probablement accumulé par l'activité trophique de chouettes. Les spécimens ont été attribués à M. bolivianus d'après la combinaison de caractères suivante : une M3 subcirculaire avec un flexus entre le lobe mésiolabial et le métacône, le paracône et le métacône non différenciés sur la M4, une absence d'entoflexide sur la m1 et la m2, et un entoflexide peu profond sur la m3, un talonide relativement développé sur la m4 avec un flexide distal perceptible. Microtragulus bolivianus, espèce à l'origine connue dans les sédiments pliocènes affleurant dans l'Altiplano bolivien, n'était jusqu'à présent représenté que par un seul fragment de mandibule avec m3-m4. D'après un échantillon bien plus complet, nous présentons une description détaillée des restes dentaires et postcrâniens de cette espèce. Depuis 1904, le nom de famille Argyrolagidae et les noms de genre Microtragulus et Argyrolagus ont été le sujet de nombreux changements de nomenclature. Une révision de ces modifications, principalement celles des 40 dernières années, est également présentée. De plus, nous analysons certains traits mandibulaires des argyrolagidés, tels que le canal maxillaire (canal rétrodentaire), un caractère très curieux qui est présent chez tous les membres de cette famille et qui pourrait être lié au passage d'une connexion entre la veine ophtalmique inférieure et la veine alvéolaire inférieure, comme chez certains mammifères actuels.

Mots-clés : Argyrolagidae ; Bonapartheriiformes ; anatomie ; formation d'Uquía ; formation d'Umala ; Marplatien SALMA

Translator: Antoine Souron

Deutsche Zusammenfassung

Neubeschreibung des agryolagiden Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) ausgehend von neuen Überresten aus Nordwest-Argentinien

Diese Arbeit basiert auf neuen dentalen, cranialen und postcranialen Überresten des argyrolagiden Microtragulus bolivianus (Metatheria, Polydolopimorphia, Bonapartheriiformes) und Zahnstücken von Microtragulus sp. aus den spätpliozänen bis frühpleistozänen Stufen der Uquía Formation, die in San Roque, Humahuaca (Jujuy Provinz, Argentinien) aufgeschlossen sind. Sie wurden zusammen mit Amphibien, Eidechsen, Nagetieren und didelphiden Beuteltieren gefunden und bilden eine Assemblage, die möglicherweise durch trophische Aktivitäten von Eulen generiert wurde. Die Stücke wurden M. bolivianus zugeschrieben, basierend auf folgender Kombination von Merkmalen: M3 subzirkular, mit einem Flexus zwischen dem mesiolabialen Lappen und dem Metaconus, Paraconus und Metaconus nicht unterschiedlich in M4, kein Entoflexid in m1-2 und flaches Entoflexid in m3, proportional großes Talonid in m4, mit einem klar erkennbaren distalen Flexid. Microtragulus bolivianus, zunächst erfasst in pliozänen Sedimenten im bolovianischen Altiplano war nur durch ein Mandibelfragment mit m3-m4 vertreten. Anhand einer vollständigeren Probe präsentieren wir eine detaillierte dentale und postcraniale Beschreibung dieser Art. Seit 1904 waren der Familienname Argyrolagidae und die Gattungsnamen Microtragulus und Argyrolagus Gegenstand einiger nomenklatorischen Änderungen. Es wird ebenso eine Revision dieser Modifikationen - überwiegend solcher die in den letzten 40 Jahren vorgenommen wurden - vorgelegt. Darüber hinaus analysieren wir einige Merkmale von Argyrolagiden die Mandibel betreffend, wie den Maxillarkanal (Retrodentaler Kanal). Dies ist ein sehr merkwürdiges Merkmal, das bei allen Mitgliedern der Familie vorkommt und das mit der Verbindung zwischen den inferioren alveolaren und den inferioren orbitalen Venen zusammenhängen könnte, wie bei einigen heutigen Säugertieren.

Schlüsselwörter: Argyrolagidae; Bonapartheriiformes; Anatomie; Uquía Formation; Umala Formation; Marplatan SALMA

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

APPENDIX

Revision of the changes that occurred in the last century in the nomenclature of the Family Argyrolagidae and the genera Microtragulus and Argyrolagus.

Author and year of publication and erected family and species or used names

Comments
Ameghino, 1904
Family Tragulidae
Microtragulus argentinus
This taxon was founded on the base of metatarsal and tarsal bones
Ameghino, 1904
Family Argyrolagidae
Argyrolagus palmeri
A. palmeri is the type species of the genus Argyrolagus. Microtragulus argentinus and A. palmeri were published in the same year, but Microtragulus has priority because was published in an earlier issue of the same volume
Kraglievich, 1931
Family Argyrolagidae
Microtragulus catamarcensis
This author named a small dentary coming from Catamarca Province as Argyrolagus catamarcensis. Posteriorly Simpson (1970a) proposed the new combination Microtragulus catamarcensis
Rusconi, 1936
Family Argyrolagidae
Microtragulus = Argyrolagus
This author suggested the synonymy but he did not consider the priority of Microtragulus under Argyrolagus and continued the use of Argyrolagus and Argyrolagidae (See also Rusconi, 1967)
Reig, 1955, 1958
Family Microtragulidae
Microtragulus = Argyrolagus
This author established this synonymy after he and Kraglievich studied the then new specimen referred as Microtragulus sp. (probably the holotype of Argyrolagus scagliai) and began the use of Microtragulidae with Microtragulus as the only valid genus
Ringuelet, 1966
Family Microtragulidae
Microtragulus = Argyrolagus
M. argentinus = A. palmeri
This author established the priority of Microtraguidae over Argyrolagidae, Microtragulus under Argyrolagus, and M. argentinus  under A. palmeri. The material there figured (but not catalogued; see p. 58) was referred as M. argentinus but later assigned to the neotype of A. parodii (Simpson, 1970b) and catalogued as MLP 62-VII-27-81
Simpson, 1970a
Family Argyrolagidae
Microtragulus (including M. argentinus, M. catamarcensis, M. reigi)
This author made the first comprehensive attempt in order to resolve the nomenclatural problems in the family (see text for a complete explanation)
Hoffstetter and Villarroel, 1974
Family Microtragulidae
Microtragulus (including M. reigi, M. catamarcensis, and M. bolivianus
They validated the genus Microtragulus (including Argyrolagus) and proposed tentatively the erection of the subgenus Microtragulus and Argyrolagus. Microtragulus bolivianus is presented as Microtragulus ( Argyrolagus ?) bolivianus in the original publication. The authors did not formalize the taxonomic status of the genera included in Argyrolagus
Tonni et al., 1992
Family Microtragulidae
Argyrolagus palmeri
These authors included these taxon names in a taxomic list of the mammals recovered at Monte Hermoso (Buenos Aires) and included in the Montehermosan SALMA. No explanation was given in relation to the exclusion of M. argentinus from this list
Cione and Tonni, 1995
Family Microtragulidae
Microtragulus (including M. reigi)
Argyrolagus (including A. palmeri, A. scagliai)
M. argentinus is not included among the taxa recovered at Monte Hermoso, Buenos Aires
Goin, 1995
Family Argyrolagidae
Microtragulus (including M. argentinus, M. reigi)
Argyrolagus (including A. palmeri, A. scagliai)
The author followed the proposal of Simpson (1970a)
Vizcaíno et al., 2004
Family Microtragulidae
Microtragulus reigi
Argyrolagus scagliai
The authors followed Tonni et al. (1992)
Sanchez-Villagra, 2001; Goin et al., 2000; Zimicz, 2011; Ortiz et al., 2012; Goin and Abello, 2013; Tomassini et al., 2013; García López and Babot, 2015.
Family Argyrolagidae
Microtragulus (including M. argentinus, M. reigi, M. bolivianus)
Argyrolagus (including A. palmeri, A. scagliai)
These authors followed the proposal of Simpson (1970a)
 

FIGURE 1. 1. Location map of the fossiliferous levels of the Uquía Formation exposed at San Roque, Humahuaca (Jujuy Province, Argentina). Relative location of the prospected area in: 2, Jujuy Province; and 3, Northwestern Argentina. Modified from Ortiz et al. (2012).

figure1

FIGURE 2. Line drawings (occlusal view) of Microtragulus bolivianus showing the anatomical nomenclature used in the text. 1. Right M3-4. 2. Right m1-4 (image reflected). Abbreviations: cf, central fossa; cfd, central fossid; ectf, ectoflexid; ectd, ectostylid; ent, entoconid; entd, entostylid?; entf, entoflexid; gr, groove; hyp, hypoconid; hypd, hypoconulid; mesl, mesiolabial lobe; met, metacone; metd, metaconid; metl, metaconule; prt, protocone; prtd, protoconid.

figure2

FIGURE 3. Microtragulus bolivianus. 1-3. JUY-P-0065, fragment of right maxilla with M3-M4 in: 1, lateral; 2, medial; and 3, occlusal views. 4-5. JUY-P-0066, right mandibular body with i1, alveoli of i2 and p3, and complete m1-4 in: 4, medial; and 5, lateral views. 6-7. JUY-P-0067, right mandibular body with complete i1 and i2, alveolus of p3, and complete m1-4 in: 6, medial; and 7, lateral views. 8-9. JUY-P-0068, anterior fragment of right mandibular body with i1 and alveoli of i2 and p3 in: 8, medial; and 9, lateral views. Scale bar equals 5 mm.

figure3

FIGURE 4. Microtragulus bolivianus, right lower dentition in occlusal view. 1. JUY-P-0066, detail of i1. 2. JUY-P-0066, m1-4. 3. JUY-P-0067, m1-4. Scale bar equals 5 mm.

figure4

FIGURE 5. Microtragulus bolivianus, fore and hindlimb bones. 1-4. JUY-P-0069, right humerus almost complete except the proximal third in: 1, anterior; 2, posterior; 3, medial; and 4, lateral views. 5-8. JUY-P-0070, left humerus almost complete except the proximal third in: 5, anterior; 6, posterior; 7, medial; and 8, lateral views. 9-12. JUY-P-0071, distal half of left humerus in: 9, anterior; 10, posterior; 11, medial; and 12, lateral views. 13-16. JUY-P-0072, distal end of right humerus in 13, anterior; 14, posterior; 15, medial; and 16, lateral views. 17-19. JUY-P 59, proximal half of right ulna in: 17, anterior; 18, lateral; and 19, medial views. 20-22. JUY-P 60, proximal half of left ulna in: 20, anterior; 21, lateral; and 22, medial views. 23. JUY-P 61, proximal fragment of radius. 24-25. JUY-P 52, distal end of right tibiofibula in: 24, anterior; and 25, posterior views. Scale bar equals 10 mm.

 figure5 new

FIGURE 6. Microtragulus bolivianus, astragalus and calcaneus. 1-5. JUY-P-0075, complete right astragalus in: 1, dorsal; 2, plantar; 3, medial; 4, lateral; and 5, distal views. 6-10. JUY-P-0073, complete left calcaneus in: 6, dorsal; 7, plantar; 8, medial; 9, lateral; and 10, distal views. Scale bar equals 5 mm.

figure6

FIGURE 7. Microtragulus bolivianus, metatarsal III and IV and phalanges. JUY-P 55, complete right metatarsal III and JUY-P 56, distal portion of right metatarsal IV (not associated) in: 1, anterior; and 2, posterior views. Scale bar equals 10 mm. 3-5. JUY-P 58, ungual phalanges in lateral view. Scale bar equals 5 mm.

figure7

FIGURE 8. Microtragulus sp., upper and lower molars in occlusal views. 1. JUY-P 53, isolated left M3. 2. JUY-P 54, isolated left m2 or m3. Scale bar equals 2 mm.

figure8

FIGURE 9. Argyrolagus sp. MACN 17590, left mandibular fragment with m1-4. 1-4. Photograph and line drawing in: 1-2, medial; and 3-4, dorsal views. The arrow points the maxillary canal. Scale bar equals 5 mm.

figure9

 

 

TABLE 1. List of the genera and species included in the Family Argyrolagidae and their temporal and geographic distribution. Abbreviations: AR, Argentina; BO, Bolivia.

Species Temporal distribution Geographic distribution References
Proargyrolagus bolivianus Wolf, 1984 Late Oligocene (Deseadan) Salla-Luribay Basin (BO) Wolf (1984); Sánchez-Villagra and Kay (1997)
Proargyrolagus argentinus Goin and Abello, 2013 Early Miocene (Colhuehuapian) Puesto Almendra, Chubut (AR) Goin and Abello (2013)
Anargyrolagus primus Carlini et al., 2007 Early Miocene (Colhuehuapian) Lower Chubut River valley, Chubut (AR) Carlini et al. (2007); Goin and Abello (2013)
Hondalagus altiplanensis Villarroel and Marshall, 1988 Middle Miocene (Laventan) Quebrada Honda (BO) Villarroel and Marshall (1988); Sánchez-Villagra et al. (2000)
Microtragulus argentinus Ameghino, 1904 ?Early Pliocene (Montehermosan) Monte Hermoso, Buenos Aires (AR) Ameghino (1904); Simpson (1970a); Tomassini et al. (2013)
M. catamarcensis (Kraglievich, 1931) ?Early Miocene - Early Pliocene 25 de Mayo, Mendoza (AR)

?Andalhuala, Catamarca (AR)

Kraglievich (1931); Simpson (1970a); Garrido et al. (2014); García-López and Babot (2015)
Microtragulus sp. ?Late Miocene North of Tucumán (AR) García-López and Babot (2015)
M. reigi Simpson, 1970a Middle Pliocene - Early Pleistocene; Chapadmalan - Marplatan Punta San Andrés, Buenos Aires (AR) Simpson (1970a); Cione and Tonni (2005)
M. bolivianus Hoffstetter and Villarroel, 1974 ?Early Pliocene - Early Pleistocene

Montehermosan - Marplatan

Vizcachani (BO)

San Roque, Jujuy (AR)

Hoffstetter and Villarroel (1974); Ortiz et al. (2012)
Argyrolagus palmeri Ameghino, 1904 Early Pliocene; Montehermosan Monte Hermoso, Buenos Aires (AR) Ameghino (1904); Tomassini et al. (2013)
A. scagliai Simpson, 1970a Middle Pliocene; Chapadmalalan Miramar, Buenos Aires (AR) Simpson (1970a)
A. parodii Rusconii, 1933 Middle Pliocene; Chapadmalalan Chapadmalal, Buenos Aires (AR) Rusconi (1933); Simpson (1970a, b)
A. rusconii (Goin, Montalvo, and Visconti, 2000) Late Miocene Bajo Giuliani, La Pampa (AR) Goin et al. (2000); García-López and Babot (2015)
Argyrolagus sp. ?Late Miocene Caleufú, La Pampa (AR) Abello et al. (2002)

 

 

TABLE 2. Measurements of the lower dentition of Microtragulus bolivianus (in mm). * Measures taken from Hoffstetter and Villarroel (1974).

  i1 i2 m1 m2 m3 m4 m1-m4 i1-m4
  L W L W L W L W L W L W L L
                             
Holotype* 1.3 .6 - - - - - - 1.5 1.3 1.4 1.0 - 10.3
JUY-P-0066 1.35 0.59 - - 1.50 1.14 1.53 1.49 1.44 1.34 1.14 1.08 5.77 11.01
JUY-P-0067 1.66 0.70 0.92 0.63 1.68 1.27 1.88 1.61 1.68 1.47 1.49 1.19 6.44 12.50
 

babotM. Judith Babot. Fundación Miguel Lillo, Miguel Lillo 251, 4000, San Miguel de Tucumán, Tucumán, Argentina; This email address is being protected from spambots. You need JavaScript enabled to view it.
and CONICET-Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina

Judith Babot is mainly interested in cranial and postcranial anatomy, phylogeny and morphofunctional studies of South American fossil metatherians, specially Sparassodonta. At present, her research is focusing on Paleogene small metatherians of Northwestern Argentina and their morphological and evolutionary responses in relation to the climatic changes that affected South America during this period.

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garcia-lopezDaniel A. García-López. CONICET-Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina, Facultad de Ciencias Naturales, Miguel Lillo 205, 4000, San Miguel de Tucumán, Tucumán, Argentina; This email address is being protected from spambots. You need JavaScript enabled to view it., and Instituto Superior de Correlación Geológica-INSUGEO (CONICET)

Daniel García-López was graduated in biology at the Universidad Nacional de Tucumán, Argentina. He continued as a PhD student, focusing his research in the study of paleogene mammals, particularly notoungulates, and obtained a PhD degree in Biology in 2009. Nowadays he teaches paleontology in the Facultad de Ciencias Naturales e Instituto Miguel Lillo, in the mentioned University and, since 2012, he is a researcher of the Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet). Now, his work is intended to increase the knowledge regarding the mammalian communities that developed during the Cenozoic in northern Argentina.