A New Occurrence of Toxodonts in the Pleistocene of México

Abstract

Toxodonts were South American rhinoceros-like mammals, belonging to the extinct group Notoungulata. Prior to 2004, the northernmost record of toxodonts was from Guatemala, in Central America (Woodburne, 1969); however, Polaco and coworkers reported the occurrence of toxodonts in two different localities from Mexico (Polaco et al. 2004). A right mandibular ramus was collected from Hihuitlán, Michoacán, western Mexico, and partial molars and an incomplete upper incisor were collected from la Estribera, Veracruz, eastern Mexico (Polaco et al. 2004). One of the authors (C.O.H.M.) collected fossil material from a Pleistocene locality in the Municipio of Pánuco, northern Veracruz (587592.48 m E, 2442482.10 m N). This material included at least four isolated toxodont molars, the subject of this report (Figure 1). However, the authors were recently informed about the existence of at least four other partial molars collected at the same locality. Two of the molars presented here are a right M 1 and a left M 2 ; the other two specimens are a right P 4 and a left M 1 (Figure 1). These specimens are slightly larger than the specimens reported by Polaco et al. (2004), suggesting a rather mature individual. The right M 1 is 54 mm long (as preserved), 110 mm tall, and 17.5 mm broad (at the level of the entonconid; the left M 2 is 52 mm long, 108 mm tall, and 23 mm broad (at the protoconid-paraconid level); the right P 4 is 131 mm tall, 39 mm at its widest portion of the crown, and 28 mm in anteroposterior breadth; the left M 1 is 114 mm tall (as preserved), 63 mm at its widest portion, and 29 mm in anteroposterior breadth. As noticed by Polaco et al. (2004), all Central American toxodont fossils have been assigned to Mixotoxodon larensis Van Frank (1957), a toxodont first reported from northern Venezuela (Laurito 1993; Lucas et al. 1997; Polaco et al. 2004; Webb and Perrigo 1984). The Mexican fossils show dental features similar to those present in Mixotoxodon larensis; however, there exist some subtle morphological differ-ences, such as the meta-entoconid folds in both right M1 and left M2. How-ever, more material is still needed to know if these features represent only 1 2 3 4 5 7 6 8 12 P R O O F CURRENT RESEARCH IN THE PLEISTOCENE Vol. 28, 2011 30 morphological variation within a single species or if the Mexican toxodont really represents a new taxon. Hulbert (2001) suggested the occurrence of toxodonts in Mexico; Polaco et al. (2004) confirmed their presence. The occurrence of toxodonts in western and eastern México strongly suggests the possibility of finding more toxodont remains in other Pleistocene deposits present in coastal states of the Country, thus favoring the idea of toxodont migration to northern areas of North America. Authors want to thank Dr. Enrique Ortega Lozano, who initiated the fossil collection at the locality.

Full text

PROOF
CURRENT RESEARCH IN THE PLEISTOCENE Vol. 28, 2011
29
A New Occurrence of Toxodonts in the
Pleistocene of México
Rubén A. Rodríguez-de la Rosa, José Rubén Guzmán-Gutiérrez,
and Carlos Ortega-Hurtado de Mendoza
➤➤
➤➤
➤Keywords: Toxodonts, Pleistocene, Veracruz, México
Toxodonts were South American rhinoceros-like mammals, belonging to the
extinct group Notoungulata. Prior to 2004, the northernmost record of
toxodonts was from Guatemala, in Central America (Woodburne, 1969);
however, Polaco and coworkers reported the occurrence of toxodonts in two
different localities from Mexico (Polaco et al. 2004). A right mandibular
ramus was collected from Hihuitlán, Michoacán, western Mexico, and partial
molars and an incomplete upper incisor were collected from la Estribera,
Veracruz, eastern Mexico (Polaco et al. 2004).
One of the authors (C.O.H.M.) collected fossil material from a Pleistocene
locality in the Municipio of Pánuco, northern Veracruz (587592.48 m E,
2442482.10 m N). This material included at least four isolated toxodont
molars, the subject of this report (Figure 1). However, the authors were
recently informed about the existence of at least four other partial molars
collected at the same locality.
Two of the molars presented here are a right M1 and a left M2; the other two
specimens are a right P4 and a left M1 (Figure 1). These specimens are slightly
larger than the specimens reported by Polaco et al. (2004), suggesting a rather
mature individual. The right M1 is 54 mm long (as preserved), 110 mm tall,
and 17.5 mm broad (at the level of the entonconid; the left M2 is 52 mm long,
108 mm tall, and 23 mm broad (at the protoconid-paraconid level); the right
P4 is 131 mm tall, 39 mm at its widest portion of the crown, and 28 mm in
anteroposterior breadth; the left M1 is 114 mm tall (as preserved), 63 mm at its
widest portion, and 29 mm in anteroposterior breadth.
As noticed by Polaco et al. (2004), all Central American toxodont fossils
have been assigned to Mixotoxodon larensis Van Frank (1957), a toxodont first
reported from northern Venezuela (Laurito 1993; Lucas et al. 1997; Polaco et
al. 2004; Webb and Perrigo 1984).
The Mexican fossils show dental features similar to those present in
Mixotoxodon larensis; however, there exist some subtle morphological differ-
ences, such as the meta-entoconid folds in both right M1 and left M2. How-
ever, more material is still needed to know if these features represent only
Rubén A. Rodríguez-de la Rosa, Unidad Académica de Ciencias Biológicas, Universidad Autónoma
de Zacatecas, Campus 2, Zacatecas, México; e-mail: ruben_raptor@yahoo.com
José Rubén Guzmán-Gutiérrez, Secretaria del Medio Ambiente, Gobierno del Estado de
Aguascalientes, Aguascalientes; e-mail: paleovert@yahoo.com
Carlos Ortega-Hurtado de Mendoza, Protenek, Ciudad Victoria, Tamaulipas; e-mail: protenek@
hotmail.com
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PROOF
CURRENT RESEARCH IN THE PLEISTOCENE Vol. 28, 2011
30
morphological variation within a single species or if the Mexican toxodont
really represents a new taxon.
Hulbert (2001) suggested the occurrence of toxodonts in Mexico; Polaco et
al. (2004) confirmed their presence. The occurrence of toxodonts in western
and eastern México strongly suggests the possibility of finding more toxodont
remains in other Pleistocene deposits present in coastal states of the Country,
thus favoring the idea of toxodont migration to northern areas of North
America.
Authors want to thank Dr. Enrique Ortega Lozano, who initiated the fossil collection at the locality.
References Cited
Hulbert, R. C., Jr. 2001 Florida’s Fossil Vertebrates: An Overview. In The Fossil Vertebrates of
Florida, edited by R. C. Hulbert Jr., pp. 25–33. University Press of Florida, Gainesville.
Laurito, C. A. 1993 Análisis Topológico y Sistemático del Toxodonte de Bajo de los Barrantes,
Provincia de Alajuela, Costa Rica. Revista Geológica de América Central 16:61–8.
Lucas, S. G., G. E. Alvarado, and E. Vega 1997 The Pleistocene Mammals of Costa Rica. Journal of
Vertebrate Paleontology 17(2):413–27.
Polaco, O. J., A. F. Guzmán, and G. Tapia-Ramírez 2004 Occurrence of Toxodonts in the
Pleistocene of México. Current Reseacrh in the Pleistocene 21:113–14.
Van Frank, R. 1957 A Fossil Collection from Northern Venezuela 1. Toxodontidae (Mammalia,
Notoungulata). American Museum Novitates 1850:1–38.
Webb, D. S., and S. C. Perrigo 1984 Late Cenozoic Vertebrates from Honduras and El Salvador.
Journal of Vertebrate Paleontology 4(2):237–54.
Woodburne, M. O. 1969 A Late Pleistocene Occurrence of the Collared Peccary, Dicotyles tajacu,
in Guatemala. Journal of Mammalogy 50(1):121–25.
Figure 1. Occlusal and labial views of Toxodont molars from Pánuco, northern Veracruz,
México: A, right M1; B, left M2; C, right P4 ; D, left M1 shown in lingual and occlusal views. A–C
shown in labial view.
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