498Sullivan et al., eds., 2011, Fossil Record 3. New Mexico Museum of Natural History and Science, Bulletin 53.

DESCRIPTION OF A NEWBORN GOMPHOTHERE SKULL (MAMMALIA,GOMPHOTHERIIDAE) FROM LAKE CHAPALA, JALISCO, MEXICO

RICARDO H. AGUILAR

Museo de Paleontología de Guadalajara, “Federico A. Solórzano Barreto,” 520 Dr. Roberto Michel, Guadalajara, Jalisco 44460 MEXICO

Abstract—Few descriptions of juvenile skulls of fossil proboscideans have been published. Here, a skull of anewborn gomphothere from the Pleistocene of Lake Chapala, Jalisco, Mexico, is described and compared withpreviously published material. Based on these comparisons, the skull is best assigned to Cuvieronius hyodon.Some paleobiological and taxonomic implications are discussed.

INTRODUCTION

The family Gomphotheriidae Cabrera, 1929 has a well-documentedfossil record from North America. It first appeared in the Barstovian anddisappeared in the late Rancholabrean (Fisher, 1996). This subcontinenthas previously been considered a center for major autochthonous evolu-tion for this family (Lambert, 1996).

In Mexico, reports of gomphothere finds have occurred since thenineteenth century. However, in most cases, remains are limited to iso-lated molars and tusks that lack stratigraphic information, or even a well-defined locality (Alberdi and Corona-M, 2005). Nevertheless, in recentyears, systematic studies of this family have been augmented. The gen-era with a recognized presence in Mexico include: GomphotheriumBurmeister, 1837 (Ferrusquia-Villafranca, 1990; Carranza-Castañeda andAguirre-Díaz, 2000); Rhynchotherium Falconer, 1868 (Ferrusquia-Villafranca and Torres-Roldán, 1980; Miller and Carranza-Castañeda,2002; Alberdi and Corona-M, 2005); Cuvieronius Osborn, 1923 (Lucasand González-León, 1997; Montellano-Ballesteros, 2002; Alberdi andCorona-M, 2005); and Stegomastodon Pohlig, 1912 (Lucas, 2003; Alberdiand Corona-M, 2005). In Lake Chapala, only Cuvieronius and Stego-mastodon have been reported (Lucas, 2003; Alberdi and Corona-M.,2005).

The aim of this paper is to describe the skull of a newborngomphothere from Lake Chapala, Jalisco, Mexico, and to make a com-parative analysis with previous publications. A study of this nature willhelp to increase knowledge about ontogenetic variation in fossil probos-cideans, especially those of the family Gomphotheriidae. Moreover, asrecognized by Frick (1926), knowledge of the morphology of the premolarscan help in solving taxonomic problems.

In recent years, some papers describing juvenile gomphothereremains have been published (e.g., Valerio and Laurito, 2008; Mothé etal., 2010); however, these studies are based on isolated molars and do notdescribe skulls. Among the few published works that have describedjuvenile skulls are Simpson and Paula Couto (1957), in which two skullsfound in the state of Minas Gerais in Brazil are described, one of themfrom the locality of Lagoa Santa and the other from the locality of Lapado Caetano. They assigned both skulls to Haplomastodon. The first ofthese skulls had previously been described by Winge (1906) and hadbeen assigned to “Mastodon andium,” currently named Cuvieroniushyodon. Subsequently, Alberdi et al. (2002), in their revision of someBrazilian gomphothere skulls, described in greater detail those same ju-venile skulls and reassigned them to Stegomastodon, as they considerHaplomastodon to be a junior synonym of Stegomastodon, and do notbelieve that Cuvieronius was ever present in Brazil.

PROVENANCE

The skull studied in this work is housed at the Museo dePaleontología de Guadalajara "Federico A. Solórzano Barreto" in Jalisco,Mexico and is cataloged with the number MPG-R-0061.

The fossil remains that make up this collection, in most cases, lackstratigraphic data or even a specific locality (Lucas, 2003; Schreiber,2004; Alberdi and Corona-M., 2005). Still, for much of the collection atleast the approximate provenance is known (cf. Solórzano, 1977). Mate-rial presented here was found in Lake Chapala by the founder of theMuseo de Paleontología de Guadalajara, Federico Solorzano (F. Solorzano,personal communication, 2002). The skull MPG-R-0061 has a generalgray color with shiny black premolars. This dark coloration distinguishesthe fossil material of Lake Chapala from that of other fossil localities inthe state of Jalisco. This type of staining is characteristic of a low-energylacustrine environment (Schreiber, 2004).

Previous geological studies in Lake Chapala have established thatsome of the fossils recovered from this basin come from a stratigraphicunit called the Chapala Formation (Rosas-Elguera et al., 1997), locatedon the north side of the lake, considered to be of Blancan age (Lucas,2008b). The rest of the material apparently comes from the lake bottom,collected during the decline in the water level. Determining the age of theremains of the lake bottom is problematic because no lithostratigraphicstudy of this part of the lake has been done. However, the fossil assem-blage identified in this area (e.g., Bison sp., Mammuthus imperator,Camelops hesternus) suggests a Rancholabrean age with possible mix ofBlancan material (e.g., Nannipus peninsulatus) (Lucas, 2008b).

In this paper, descriptions and nomenclature have been used ac-cording to Gregory (1903), Todd (2010) and Ferretti (2010) for the skull.For the molars, terminology follows Tassy (1996). Measurements weretaken according to Alberdi et al. (2002).

Data from the skull of Chapala MPG-R-0061 will be comparedwith previously published information on Brazilian juvenile skulls; theLagoa Santa specimen, labeled with the number ZMK-193 that is pre-served in the Zoologisk Museum in Copenhagen, Denmark; and the Lapado Caetano skull, labeled with the number P2-MHN-33, which is pre-served in the Museo de Historia Natural de la Universidad de MinasGerais in Belo Horizonte, Brazil.

SYSTEMATIC PALEONTOLOGY

Order PROBOSCIDEA Illiger, 1811Family GOMPHOTHERIIDAE Cabrera, 1929

Genus Cuvieronius Osborn, 1923Cuvieronius hyodon Fischer, 1814

Skull

The specimen is an incomplete skull without the mandible (Fig.1). The deciduous tusks, and DP2 and DP3 are present on both sides ofthe maxilla. The cranial vault is almost completely absent.

Antero-dorsal view (Fig. 1A): For the maxilla, the alveoli of theincisors are quasi-parallel, although a slight distal divergence between thetusks can be observed; this was confirmed by an X-ray image. Theincisive fossa is rectangular in shape. The incisura dentalis, though re-markable, do not diverge significantly between the tusk sheaths.

499

FIGURE 1. Newborn gomphothere skull from Chapala, MPG-R-0061, in A, antero-posterior, B, ventral, C, right lateral, D, left lateral (diagonal barcrossing the skull indicates the angle and position of the respiratory axis), E, ventro-lateral (showing the eruption stage of deciduous premolars) and F,posterior views. Abbreviations: apc, anterior palatine canal; DP2, second deciduous premolar; DP3, third deciduous premolar; ena, external nasalaperture; FR, frontal; id, incisura dentalis; if, incisive fossa; ina, internal nasal aperture; MX, maxilla; mzp, maxillary zigomatic process; Ob, olfactorybulb space; OF, orbital fossa; opf, orbital process of frontal. Scale bar = 50 mm.

500The nasal bone is absent. The external nasal aperture is oval and is

located above and slightly posterior to the orbit. The respiratory axis andthe occlusal plane form an angle of 67° (Fig. 1D).

The left frontal is well preserved, but the right one is absent. Thepost-orbital process of the left frontal is complete.

Lateral view (Fig. 1C and 1D): The left side of the skull is thebest preserved, although only a fragment of the left maxillary zygomaticprocess is still present. The orbital fossa is very large and its anteriormargin is located at the level of the first loph of the DP3.

The proximal-distal axis of the tusk alveolus and the occlusalplane of the premolars form an angle approximating 37°, the nasal planeand the occlusal plane form an angle approximating 62°, and the frontalplane and the occlusal plane form an angle approximating 44°. The unionof the maxilla and the premaxilla is wide and forms a very discrete angle,probably due to the incomplete emergence of the premolars.

Ventral view (Fig. 1B): The skull lacks the basioccipital regionand the basisphenoid is crushed.

The palatine is narrow and elongated; its posterior edge, adjacentto the opening of the inner nasal aperture, has a "V" form and is locatedat the poterior border of the DP3. The anterior palatine canal starts at theanterior border of the DP3. The internal nasal aperture perfectly commu-nicates with the external nasal aperture. The vomer is preserved butincomplete.

The tooth rows are parallel. The postrite cusps of the premolarsare more emergent than the pretrite cusps (Fig. 1E).

Posterior view (Fig. 1F): The cranial vault is partially preservedretaining a left antero-lateral fragment. This allows us to observe theinside anterior part of the braincase of this hemisphere. Here, a space forthe frontal lobe can be seen, and contains what appears to be a space fora large olfactory bulb, which seems to be located below the frontal lobeand slightly projected forward. The bones of the cranial vault (the fewpreserved) have an average thickness of 3 mm.

Dentition

Deciduous tusksBoth tusks are present and have a slightly oval shape in cross

section. The right one is more complete and slightly protrudes beyondthe level of the alveolar border. This tusk has an almost complete enamelcap broken at the tip. The enamel cap has a ventro-lateral ridge. The lefttusk has no tip and has almost completely lost the enamel cap, althoughit still retains some small fragments on the medial side. An X-ray image ofthe skull shows a large pulp cavity, open at the apex, and longitudinallyapproaching the level of the alveolar border. This image also allowed anapproximate measurement of the length of the tusks.

The general measurements taken on the right tusk are: approxi-mate length is 57 mm, dorso-ventral diameter of enamel cap is 11.8 mm,transverse diameter of enamel cap is 14 mm, and length of the enamel cap(crown of the tusk) is 13 mm (inferred, by absence of the tip of theenamel cap).

PremolarsOn both sides of the maxilla, the emerging DP2 and DP3 can be

observed. None of the four premolars show signs of attrition by wear,although slight erosion of the main cusps is observed, especially in themore erupted ones. The DP2 is bilophodont while the DP3 is trilophodont.However, the third loph is not as developed as the anterior ones. Inocclusal view, the cups show a clear tendency towards a double trefoilpattern, especially in the second and third loph of the DP3 where theanterior and posterior central conules of the postrites are well developed.The third loph has a well-developed pretrite half-loph, but very littledevelopment of the postrite half-loph. The premolars have a remarkableanterior cingulum made up by some cusps. Measurements of the premolarsare in Table 1.

DISCUSSION

Alberdi et al. (2002) consider Haplomastodon a junior synonymof Stegomastodon, on the basis of no significant differences between thegenera. However, Ferretti (2010) just recently has questioned the valid-ity of Stegomastodon for South America and reaffirms the validity ofHaplomastodon, based on the observation of new characters and a cla-distic analysis. This discussion requires a more detailed study.

The general morphology of the cranium studied in this work re-sembles that of the juvenile skulls of Stegomastodon or Haplomastodonfrom Brazil (see Introduction). The profiles are very similar in the threeskulls, so a comparable elevation of the cranial vault can be expected(even though there is no occipital region to make an observation of theelevation of the occipital condyles). However, the specimen ZMK-193has a more acute angle between the plane of the alveolar tusks and theocclusal plane of the premolars, approximating 28° vs. 37° in the othertwo specimens (Fig. 2). Boule and Thevenin (1920) and several subse-quent authors (e.g., Cabrera, 1929; Osborn, 1936, Simpson and PaulaCouto, 1957) believe the skull of Cuvieronius is depressed with respectto Haplomastodon and Stegomastodon, which have a more elephantineskull. This might be easily seen in the case of the Stegomastodon typespecies, S. mirificus. However, by looking at some of the different skullsfigured in the literature, not much difference can be observed among theskulls of North American Pliocene Stegomastodon, Haplomastodon,Cuvieronius, and South American Stegomastodon. This fact opens thepossibility that the three skulls that are discussed here, even though theyshow a similar pattern, may belong to different taxa. The two Brazilianskulls, though, look a little different in profile, but were both assigned toHaplomastodon by Simpson and Paula-Couto (1957), and toStegomastodon by Alberdi et al. (2002). They assigned these skulls to asingle taxon because both were found in nearby localities and, they con-cluded in their studies of adult individuals, that in Brazil there is no morethan one gomphothere genus.

In specimens ZMK-193 and MPG-R-0061, the anterior marginof the orbital fossa is located at the level of the anterior margin of theDP3. Contrasting these is P2-MHN-33, which has a much more for-wardly projecting anterior margin, situated at the level of the borderbetween the maxilla and premaxilla. A forward position (anterior to theupper tooth rows) of the anterior margin of the orbit is considered aderived character in brevirostrine gomphotheres, implying a trend to-ward an elephantine skull (Ferretti, 2010). However, it is expected thatthese skulls in an adult would suffer a change in the position of the orbitby development of cranial pneumatization, not present in newborn pro-boscideans (Shoshani et al. 2006), and by the development of subse-quent molars.

The distal divergence between the alveoli of the upper tusks haslong been recognized as an important character to separate the skulls ofStegomastodon, Cuvieronius and Haplomastodon. Frassinetti and Alberdi(2005) mentioned that Cuvieronius has a marked divergence whileStegomastodon (including Haplomastodon) has a slight divergence. Ferretti(2010) agrees with these authors, in regard to the extreme divergence ofCuvieronius tusks, and emphasizes the slight distal divergence inHaplomastodon chimborazi (suggested by him as type species ofHaplomastodon). However, Boule and Thevenin (1920) had previouslyconsidered that Cuvieronius has only a slight divergence of the alveoli. Inthe three skulls compared here, a slight divergence can be observed,maybe even slighter in the skull from Chapala.

The comparison of skull measurements (Table 2) allows us toobserve a much smaller general size in the Chapala skull than in theBrazilian specimens; in some measurements the difference is more than50%. It should be noted that the Brazilian specimens are ontogeneticallyolder, as indicated by the complete eruption of the DP2 and DP3 and thepresence, at least in P2-MHN-33, of the DP4 in an embryonic stage.

The dimensions of the premolars coincide with the remains ofCuvieronius from Tarija figured by Boule and Thevenin (1920). They

501

also show some similarity with isolated molars that Valerio and Lauritodescribed and assigned to Rhynchotherium. In this regard, Lucas andAlvarado (2010) have argued that in Central America only Cuvieroniusand Gomphotherium were present, so perhaps the remains mentionedby Valerio and Laurito may actually belong to Cuvieronius. The premolarsof the Chapala skull are separated clearly from Mammut by the morphol-ogy of the occlusal pattern and the overall proportion of the premolars,being squarer in Mammut than in gomphotheres.

Among juvenile remains of gomphotheres at the Museo dePaleontologia de Guadalajara, there is an associated jaw and an uppermaxilla, cataloged under the number MPG-R-5099 (Fig. 3), also fromLake Chapala. This material has the same anatomical and fossilizationcharacteristics of MPG-R-0061 discussed in this article. It is in a similarontogenetic stage, but a little more advanced in age. The taxonomic asso-ciation of this material and the main skull described in this paper is clearand allows us to infer the shape of the jaw that the MPG-R-0061 wouldhave had. The mandibular symphysis of MPG-R-5099 is long and de-flects downward, but has no lower tusks (Fig. 3A). Such deflection of themandible’s symphisis is a character seen in the jaws of Cuvieronius fromTarija (Boule and Thevenin, 1920, pl. 6). This character, according toFerretti (2010), has not been recognized in Stegomastodon orHaplomastodon of South America. Like the upper premolars, the man-

TABLE 1. Measurements (in mm) of DP2s and DP3s of juvenile gomphotheres and mastodonts from different localities in the Americas made forcomparison with the Chapala specimen. * Approximate measurement.

FIGURE 2. Comparison of the lateral profiles of the juvenile gomphothere skulls mentioned in the text. A, MHN-33, Lapa do Caetano. B, MPG-R-0061,Chapala. C, MZK-133, Lagoa Santa, modified from Simpson and Paula-Couto (1957).

TABLE 2. Measurements (in mm) of skulls mentioned here. Data of Brazilianspecimens, taken from Alberdi, et al. (2002). * Measure inferred by duplicatingthe distance between the maximal point and the sulcus of the premaxilla.

502

FIGURE 3. Upper left tooth row and hemimandible of MPG-R-5099, showing DP2 and DP3. A, Left lateral view showing occlusion of upper and lowertooth rows. B, Left hemimandible, occlusal view. C, Upper left tooth row, occlusal view. Scale bars = 50 mm.

503dibular premolars show a tendency towards a double-trefoil pattern inthe DP3s (Fig. 3B and 3C)

Evidence of the internal cranial cavity in posterior view indicatesthe presence of an eminent olfactory lobe in a lower position relative tothe frontal lobe and slightly projected forward. In this regard, the mor-phology of the anterior part of the brain in this species should be similarto that of Mammut americanum and different from modern elephants,which reflects a plesiomorphic feature (Shoshani et al., 2006).

CONCLUSIONS

MPG-R-0061 is a newborn individual as indicated by the state oferuption of the DP2 and DP3 (Tassy, 1987). This eruption stage isassigned to Class I of the dental ages by several authors (e.g., Tassy,1987, 1996; Moss, 1996) and is based on the presence of deciduoustusks and the premolars emergence phase.

The general morphology of the skull does not allow accurate taxo-nomic designation of MPG-R-0061. The only reliable character to sepa-rate Stegomastodon, Haplomastodon and Cuvieronius is the presence, inadult individuals, of a band of enamel in spiraled tusks of the latter. Theslight divergence of the tusks would suggest that the skull from Chapalacould be assigned to Haplomastodon or Stegomastodon. However, thosecharacters that can be useful for assigning adults to various taxa may notapply in juvenile gomphotheres. For this reason, it is necessary to havemore data on juvenile gomphothere skulls at different ontogenetic stagesto enable a clearer understanding of the ontogeny of gomphotheres. Thus,it is not possible at this time to make a very reliable taxonomic assign-ment.

The morphology of the premolars, even tending to form a doubletrefoil pattern in occlusal view, falls within the range of variation ob-served in Stegomastodon, Cuvieronius and Haplomastodon (v. Simpsonand Paula Couto, 1957, Frassinetti and Alberdi, 2005, Lambert andShoshani,1998, Ferretti, 2010), so the premolars themselves are notenough to recognize the genus.

The jaw cataloged with the number MPG-R-5099, which has amandibular symphysis very similar to the specimens of Tarija, which iswidely recognized as Cuvieronius (Prado et al., 2005), can be assignedtogether with the skull described here, to this genus.

The small size of the skull and premolars of MPG-R-0061, con-trasted with the materials used for comparison, could confirm its assign-ment to Cuvieronius, since several authors suggest that this genus wassmaller in size (e.g., Prado et al, 2005). However, we must recognize thatthe Brazilian skulls belonged to individuals of a little more advanced agethan the skull from Chapala. Another aspect to be taken into account, inassessing the size of this skull, is the different environmental conditionsof the places where these individuals lived that may have affected theirgrowth (Tassy, 1996)

The Chapala skull is here tentatively assigned to Cuvieroniushyodon, but also possesses some similarities to Stegomastodon (sensuAlberdi et al., 2002; Frassinetti and Alberdi, 2005; Prado et al., 2005) andHaplomastodon (sensu Ferretti, 2010).

ACKNOWLEDGMENTS

I am grateful to S.G. Lucas and M.T. Alberdi for encouragmentand bibliographical support. M. Pasenko and S.G. Lucas provided veryhelpful comments that improved the original manuscript.

REFERENCES

Alberdi, M.T. and Corona-M., E., 2005, Revisión de los gonfoterios en elCenozoico Tardío de México: Revista Mexicana de Ciencias Geológicas,v. 22, p. 246-260.

Alberdi, M.T., Cartelle, C. and Prado, J.L., 2002, El registro de Stegomastodon(Mammalia, Gomphotheriidae) en el Pleistoceno superior de Brasil:Revista Española de Paleontología, v. 17, p. 217-235.

Boule, M. and Thevenin, A., 1920, Mamiféres fossiles de Tarija: Paris,Soudier, 256 p.

Cabrera, A., 1929, Una revisión de los mastodontes argentinos: Revista delMuseo de la Plata, v. 32, p. 61-194.

Carranza-Castañeda, O. and Aguirre-Díaz G.J., 2000, Bioestratigrafía de lascuencas sedimentarias del Terciario tardío en el centro de México: 2ªReunión Nacional de Ciencias de la Tierra, Octubre: Sociedad GeofísicaMexicana, A.C. GEOS, Abstract, v. 20, p. 301-302.

Ferretti, M.P., 2010, Anatomy of Haplomastodon chimborazi (Mammalia,Proboscidea) from the late Pleistocene of Ecuador and its bearing on thephylogeny and systematic of South American gomphotheres: Geo-diversitas, v. 32, p. 663-721.

Ferrusquia-Villafranca, I., 1990, Biostratigraphy of the Mexican continen-tal Miocene, Pt II, the Southestern (Oaxacan) faunas: PaleontologíaMexicana, n. 56, p. 57-109.

Ferrusquia-Villafranca, I. and Torres-Roldan, V., 1980, El registro demamíferos terrestres del Mesozoico y Cenozoico de Baja California:Universidad Nacional Autónoma de México, Revista del Instituto deGeología, v. 4, p. 56-62.

Fisher, D.C., 1996, Extinction of probosideans in North America; in Shoshani,J. and Tassy, P., eds., The Proboscidea: evolution and paleoecology ofelephants and their relatives: Oxford, Oxford University Press, p. 296-315.

Frassinetti, D. and Alberdi, M.T., 2005, Presencia del género Stegomastodonentre los restos fósiles de mastodontes de Chile (Gomphotheriidae),Pleistoceno superior: Estudios Geológicos, n. 61, p. 101-107.

Frick, C., 1926, Tooth sequence in certain trilophodont tetrabelodont mast-odons and Trilophodon (Serridentinus) pojoaquensis, new species: Bul-

letin of the American Museum of Natural History, v. 56, p. 123-179.Gadens-Marcon, G.T., 2008, Contribution to the study of the proboscidean

(Mammalia, Gomphotheriidae) of Quaternary from Rio Grande do SulState, Brazil: Revista UNG-Geociencias, v. 7, n. 1, p. 93-109.

Green, J.M. and Hulbert, R.C., Jr., 2005, The deciduous premolars of Mammutamericanum (Mammalia, Proboscidea): Journal of Vertebrate Paleon-tology, v. 25, p. 702-715.

Gregory, W.K., 1903, Adaptive significance of the shortening of theelephant’s skull: Bulletin of the American Museum of Natural History, v.19, p. 387-394.

Lambert, W.D., 1996, The biogeography of the gomphotheriid proboscide-ans of North America; in Shoshani, J. and Tassy, P., eds., The Proboscidea:evolution and palaeoecology of elephants and their relatives: Oxford,Oxford University Press, p. 143-148.

Lambert, W.D. and Shoshani, J., 1998, Probsocidea; in Janis, C., Scott, K.and Jacobs, L.L., eds., Evolution of Tertiary mammals of North America.Volume I. Terrestrial carnivores, ungulates and ungulate-like mammals:Cambridge, Cambridge University Press, p. 606-621.

Lucas, S.G., 2003, Pleistocene proboscideans from Lago de Chapala, Jalisco,Mexico: Current Research in the Pleistocene, v. 20, p. 105-107.

Lucas, S.G. 2008a, Cuvieronius (Mammalia, Gomphotheriidae) from theNeogene of Florida: New Mexico Museum of Natural History and Sci-ence, Bulletin 44, p. 31-38.

Lucas, S.G., 2008b, Late Cenozoic fossil mammals from the Chapala riftbasin, Jalisco, Mexico: New Mexico Museum of Natural History andScience, Bulletin 44, p. 39-50.

Lucas, S.G. and Gonzalez-León, C.M., 1997, Cuvieronius (Mammalia,Proboscidea) de Oquitoa, Sonora: Geología del Noroeste, v. 2, p. 12-13.

Miller, W.E. and Carranza-Castañeda, O., 2002, Importance of Mexico’slate Tertiary mammalian faunas; in Montellano-Ballesteros, M. andArroyo-Cabrales, J., eds., Avances en los Estudios Paleomastozoológicos,Instituto Nacional de Antropología e Historia, p. 83-102

Montellano-Ballesteros, M., 2002, New Cuvieronius finds from the Pleis-tocene of Central Mexico: Journal of Paleontology, v. 76, p. 578-583.

504Moss, C., 1996, Getting to know a population; in Kandwana, K., ed., Study-

ing elephants: African Wildlife Foundation Technical Handbook Series,n. 7, p. 58-74.

Mothé, D., Avilla, L.S. and Winck, G.R., 2010, Population structure of thegomphothere Stegomastodon waringi (Mammalia: Proboscidea:Gomphotheriidae) from the Pleistocene of Brazil: Anais da AcademiaBrasileira de Ciencias, v. 82, n. 4, p. 983-996.

Osborn, H.F., 1936, Proboscidea. A monograph of the discovery, evolution,migration and extinction of the mastodons and elephants. 1:Moeritherioidea, Deinotherioidea, Mastodontoidea: New York, Ameri-can Museum of Natural History, p. 1-802.

Prado, J.L., Alberdi, M.T., Azanza B., Sánchez, B. and Frassinetti, D., 2005,The Pleistocene Gomphotheriidae (Proboscidea) from South America:Quaternary International, v. 126-128, p. 21-30.

Rosas-Elguera, J., Ferrari, L., Garduño-Monroy, V.H. and Urrutia-Fucugauchi,J., 1997, Continental boundaries of the Jalisco block and their influencein the Pliocene-Quaternary kinematics of western Mexico: Geology, v.24, p. 921-924.

Schreiber, D., 2004, Faunal characterisation of Neogene and Pleistocenelocalities of the state Jalisco, Mexico: Carolinea, v. 62, p. 63-68.

Shoshani, J., Kpsky, W.J. and Marchant, G.H, 2006, Elephant brain Part I:gross morphology, functions, comparative anatomy, and evolution: Brain

Research, Bulletin 70, p. 124-157.Simpson, G.G. and Paula-Couto, C., 1957, The mastodonts of Brazil: Bulle-

tin of the American Museum of Natural History, v. 112, p. 125-190.Solórzano, F.A., 1977, Catálogo de sitios y localidades fosilíferos en el

occidente de México: Unpublished.Tassy, P., 1987, A hypothesis on the homology of proboscidean tusks based

on paleontological data: American Museum Novitates, n. 2895, p. 1-18.Tassy, P., 1996, Growth and sexual dimorphism among Miocene elephantoids:

the example of Gomphotherium angustidens; in Shoshani, J. and Tassy,P., eds., The Proboscidea: evolution and palaeoecology of elephants andtheir relatives: Oxford, Oxford University Press, p. 143-148.

Todd, N.E., 2010, Qualitative comparison of the cranio-dental osteologyof the extant elephants, Elephas maximus (Asian elephant) andLoxodonta africana (African elephant): The Anatomical Record, v.293, p. 62-73.

Winge, H., 1906, Jordfundne og nulevende Hovdyr (Ungulata) fra LagoaSanta, Minas Geraes, Brasilien: Copenhagen, E. Mus. Lundii, v. 1, 230p., pl. 1-9.

Valerio, A.L. and Laurito, C.A., 2008, Dental remains of immature individu-als of Rhynchotherium blicki (Frick, 1930) of San Gerardo de Limoncito,Coto Brus, Costa Rica: Revista de Geología de América Central, v. 39, p.87-91.