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1. Introduction
The capybaras (Rodentia: Caviidae: Hydrochoerinae) are large rodents that lived in North and South America from the Miocene to the recent. Only two genera are known from the late Pleistocene, Hydrochoerus and Neochoerus (Kurtén and Anderson, 1980). Hydrochoerus is represented by two living species: H. hydrochaeris and H. isthmius. Today, Hydrochoerus hydrochaeris inhabits Venezuela, Brazil, Paraguay, Uruguay, and eastern Colombia. It also inhabits the Amazon basin of Ecuador, Peru, and Bolivia, as well as northeastern to southern Argentina (Mones and Ojasti, 1986). The species has a late Pleistocene fossil record from Curaçao, Uruguay, Brazil, and Argentina (Mones, 1991; Kerber and Ribeiro, 2011) and Hydrochoerus isthmius inhabits Panama, western Colombia, and western Venezuela (Woods and Kilpatrick, 2005) and does not have a fossil record. Only two species of Hydrochoerus are represented in the fossil record: H. ballesterensis from late Pliocene to early Pleistocene of the Villa Ballester, Argentina (Mones, 1991), and H. gaylordi from late Pliocene to early Pleistocene of Grenadines Bank, island of Grenada, Lesser Antilles island-arc (MacPhee et al., 2000).
Neochoerus is an extinct genus closely related to Hydrochoerus (Vucetich et al., 2014), with a fossil record throughout the late Pliocene to the late Pleistocene of North and South America (Mones, 1991). Neochoerus was erected by Hay (1926) for the species Hydrochoerus pinckneyi, which he described based on a single M3 (third upper molar) from the Pleistocene of South Carolina (Hay, 1923).
Currently, six species are recognized: (i) Neochoerus occidentalis from Blancan-Irvingtonian (late Pliocene-early Pleistocene) of Sonora and Jalisco (Carranza-Castañeda, 2016); (ii) N. cordobai from Blancan III (early Pliocene) of Guanajuato (Carranza-Castañeda, 2016), referred as Phugatherium dichroplax by Vucetich et al. (2015); (iii) N. tarijensis from Ensenadian (middle Pleistocene) of Tarija, Bolivia; (iv) N. fontanai from late Pliocene to early Pleistocene of Villa Ballester, Buenos Aires, Argentina (although Mones [1991] considered it a nomen dubium); (v) N. sulcidens from the Lujanian (late Pleistocene) of Brazil and Uruguay; and (vi) N. aesopi from the Rancholabrean/Lujanian (late Pleistocene) of North, Central, and South America (Mones, 1991; Lucas et al., 2008). Occasionally, N. pinckneyi from South Carolina, USA (Hay, 1923, 1926) has been considered valid by some authors (e.g., Álvarez, 1969; Kurtén and Anderson, 1980; Rufolo, 1998; Carranza-Castañeda, 2016), but it was considered a synonymy of N. aesopi by Mones (1991), because both taxa came from the same locality.
The only North American Rancholabrean species, N. aesopi, has been described in Mexico from Tlapacoya, Mexico State (referred to as N. pinckneyi; Álvarez, 1969); La Cinta-Portalitos locality, on the border of Michoacán and Guanajuato; and Chapala lake, Jalisco (Lucas, 2008; Eng-Ponce, 2018). Other records of the genus include N. cordobai from the Blancan to Irvingtonian of Guanajuato (Carranza-Castañeda and Miller, 1988), and N. occidentalis from Irvingtonian of Jalisco and Sonora (Carranza-Castañeda et al., 1981; Shaw, 1981; Shaw and McDonald, 1987; Carranza-Castañeda, 2016). In addition, specimens referred to Hydrochoerus from the late Pleistocene of Media Luna lagoon, San Luis Potosí; Térapa, Sonora; Chapala lake, Jalisco; and Valsequillo, Puebla (Hernández-Junquera, 1977; Pichardo, 1997; Mead et al., 2006; Carranza-Castañeda, 2016), and indeterminate hydrochoerids from Los Tanques, Zacatecas (Lozano-Ramos et al., 2006) have been reported. The fossil record of capybaras in Mexico is poorly known. Therefore, the aim of this work is to formally describe the capybaras specimens recovered from Chiapas state, adding the first locality with these rodents in south-southeastern Mexico. We also comment on the taxonomic identity of the late Pleistocene capybara specimens from other localities in Mexico.
2. Study area
The material described in this work was collected from the Los Mangos locality, near downtown Villaflores, at 16°14ʹ25ʺN and 93°13ʹ28ʺW (Figure 1A). A sequence of 4 m thick lacustrine sediments crops out there (Figure 1B). The base of the section is composed of 1 m of coarse to fine sand with granular gravel. Over the base section, there is a 0.50 m layer of light brown silty clay where Neochoerus aesopi material reported here was collected, in association with Glyptotherium floridanum, Odocoileus virginianus, Equus mexicanus, E. conversidens, and Bison sp. remains (Gómez-Pérez and Carbot-Chanona, 2012; Carbot-Chanona and Gómez-Pérez, 2014). Stratigraphically above this bed is a 1.50 m layer composed of alternating beds of brown silt and reddish-brown fine sand. In this section, G. floridanum remains have been collected. The next layer is composed of sandy silt and fine sand, 1 m thick. The upper part of the sequence consists of soil with organic matter. The presence of Bison sp. is indicative of the Rancholabrean NALMA (North American Land Mammal Ages biochronology, late Pleistocene) for the bearing deposits (Bell et al., 2004).
3. Materials and methods
3.1. ANALYZED MATERIAL
Specimens used in this study include: IHNFG4865, a fragment of maxilla with complete right M3; IHNFG-4866, an almost complete lower jaw, with left and right p4-m3 tooth rows and both incisives preserved; IHNFG-4873, left hemi-mandible with an incisive, p4 and m1; IHNFG-5760, occipital part of the skull; and IHNFG-5761, a pelvic girdle. Specimens were recovered using the traditional vertebrate paleontology methods, and cleaned with needles, airscribe, and soft bristle brushes to remove sediment. The broken parts were joined with commercial glue insoluble to water, and the fissures were filled with epoxy clay. Specimens are housed at Paleontological Collection of the Paleontological Museum “Eliseo Palacios Aguilera”, Secretaría de Medio Ambiente e Historia Natural, Chiapas, Mexico.
3.2. NOMENCLATURE
We use the nomenclature for upper and lower dentition of capybaras (Figure 2) proposed by Mones (1975a, 1991), adapted and used by other authors (e.g. Kerber and Ribeiro, 2011; Vucetich et al., 2015; Carranza-Castañeda, 2016). Upper and lower dentition are identified by uppercase and lowercase letters, respectively (e.g., M1, m1). For the cranial, mandibular and postcranial elements the nomenclature was based on König and Liebich (2007), Bode et al. (2013) and Brombini et al. (2018). In the text, we employ the name Neochoerus cordobai because it is the first name used in the original description (see Carranza-Castañeda and Miller, 1988). Carranza-Castañeda (2016) used the name N. cordobae and did not explain the reason for the change of the taxonomic name, and there is no previous work where modifications in the nomenclature are discussed.
Figure 2 Nomenclature of the lower (A) and upper teeth (B), modified from Mones (1991), and some mandible measurements (C) taken from Carranza-Castañeda (2016). Dental abbreviations: i, lower incisor; p4, fourth lower premolar; m1, first lower molar; m2, second lower molar, m3: third lower molar; M3, third upper molar; h.1-5i., first-fifth internal fissure; h.1-3e., first-third external fissure; c.1-3e., first-third external column; c.1-3i., fist-third internal column; h.s.e., secondary external fissure; h.f.e., fundamental external fissure; h.t.i., tertiary internal fissure; h.s.i., secondary internal fissure; h.s.i.a., anterior secondary internal fissure; h.s.i.p., principal secondary internal fissure; h.p.i., primary internal fissure; HFI, fundamental internal fissure; H2-12I, second-twelveth internal fissure; HPE, principal external fissure; Pr.I, first prism; Pr.II, second prism; Pr.V, fifth prism; Pr.XII, twelfth prism; Pr.XIII, thirteenth prism; Pr.s.a., secondary anterior prism of p4; Pr.Ia-Pr.Ia’, anterior plate of first prism; Pr.Ib-Pr.Ib’, posterior plate of first prism; Pr.IIa-Pr.IIa’, anterior plate of second prism; Pr.IIb-Pr.IIb’, posterior plate of second prism. Measurements abbreviation: L, length; W, width; DL, diastema length; TL, toothrow length; IDA, internal distance between the alveoli of p4; DMF, distance of the masseteric fossa through the Pr.I of the m1.
3.3. MEASUREMENTS AND PHOTOGRAPHS
The measurements were obtained with a digital caliper with 0.01 mm accuracy following Mones (1991) and Carranza-Castañeda (2016), as shown in Figure 2. The measurements of Neochoerus pinckneyi, N. aesopi (mean), N. sulcidens (mean), N. tarijensis (mean), N. cordobai, N. occidentalis, and Hydrochoerus hydrochaeris used for comparison were obtained from the literature (Carranza-Castañeda and Miller, 1988; Mones, 1991; Sanders, 2002; Kerber and Ribeiro, 2011; Carranza-Castañeda, 2016). The measurements of N. occidentalis from Sonora were obtained from the figures presented in Carranza-Castañeda (2016) using ImageJ software (Rasband, 2012). The comparative bivariate plots were elaborated in JMP version 8 (SAS, 2008), using the measurements of Appendix 1 and 2 (Supplementary Material).
The photographs were taken with a digital camera Canon XS, using a lightbox and indirect lighting. Later, the images were processed in Adobe Illustrator to erase the background. The final figures were made in CorelDraw X8.
3.4. INSTITUTIONAL ABBREVIATIONS
AMNH, American Museum of Natural History, Ney York, USA; AWC, Arizona Western College, Arizona, USA; IHNFG, Instituto de Historia Natural, Fósil Geográfico, Chiapas, Mexico (historically is the acronym for the Paleontological Collection of the Secretaría de Medio Ambiente e Historia Natural, Chiapas, Mexico); INAH, Instituto Nacional de Antropología e Historia, Ciudad de Mexico, Mexico; MCN-D, Museu de Ciências da Pontifícia Universidade Católica do Rio Grande do Sul, Uruguaiana, Brazil; MCN-PV, Coleção de Paleovertebrados do Museu de Ciências da Pontifícia Universidade Católica do Rio Grande do Sul, Uruguaiana, Brazil; MCPU, Museu de Ciências da Pontifícia Universidade Católica do Rio Grande do Sul, Uruguaiana, Brazil; MCPU-PV, Coleção de Paleovertebrados do Museu de Ciências da Pontifícia Universidade Católica do Rio Grande do Sul, Uruguaiana, Brazil; MCPU-M, Coleção de Mastozoologia do Museu de Ciências da Pontifícia Universidade Católica do Rio Grande do Sul, Uruguaiana, Brazil; MLP, Museo de La Plata, La Plata, Argentina; MPGJ, Museo de Paleontología Geociencias, Querétaro, Mexico; TMM, Jackson School of Geosciences, Vertebrate Paleontology Laboratory, The University of Texas at Austin, Texas, USA.
4. Results
4.1. SYSTEMATIC PALEONTOLOGY
Class MAMMALIA Linnaeus, 1758
Orden RODENTIA Bowdich, 1821
Infraorder Hystricognathi Tullberg, 1899
Family Caviidae Fischer, 1817 sensu Waterhouse, 1839
Subfamily Hydrochoerinae (Gray, 1825) Gill, 1872
Genus Neochoerus Hay, 1926
Neochoerus aesopi (Leidy, 1853)
Holotype. Fragment of the incisive (position indeterminate), described as Oromys aesopi, collected by Prof. Holmes on the Ashley River, Charleston, South Carolina, USA (Leidy, 1853). Housed at the AMNH under the catalog number FM 485.
Synonymy. Oromys aesopi (Leidy, 1853); Hydrochoerus aesopi (Leidy, 1856); Hydrochoerus magnus (Gervais and Ameghino, 1880); Hydrochoerus robustus (Leidy, 1887); Hydrochoerus holmesi (Simpson, 1928); Neochoerus magnus (Kraglievich, 1930); Neochoerus robustus (Kraglievich, 1930); Prohydrochoerus sirasakae (Spillmann, 1941); Protohydrochoerus schirasakae [sic] (Spillmann, 1948); Neochoerus (Neochoerus) sirasakae (Hoffstteter, 1952); Neochoerus sirasakae (Mones, 1975b); Neochoerus pinckneyi (Mones, 1991).
4.2. DESCRIPTION
IHNFG-4866 is a nearly complete mandible. However, the right condylar and angular process are missing (Figures 3A and 3B). Both tooth rows are complete and included the p4-m3. The diastema length (DL) is shorter (nearly 90 mm) than the toothrow length (TL: 100.5 mm in the left toothrow, 110 mm in the right toothrow). The internal distance between the alveoli of the p4 (IDA) in its lingual portion is 34 mm. The masseteric crest is robust and more retracted than in Hydrochoerus hydrochaeris and begins below the Pr.I (first prism) of p4. The masseteric fossa in the two portions of the mandible is located below the Pr.I of the m1 and the distance of the masseteric fossa (DMF) through the Pr.I of the m1 is 97 mm.
Figure 3 IHNFG-4866, nearly complete mandible from Los Mangos locality, Villaflores, Chiapas, in occlusal (A) and left lateral (B) view. Detail of the left toothrow in occlusal view (C); the red circle indicates the unusual union between the Pr.IIa’ and Pr.IIb’. Abbreviations: apr, angular process; conpr, condylar process; corpr, coronoid process; mcr, masseteric crest; mfo, masseteric fossa. Dental abbreviations as in Figure 2.
Like in all rodents, the lower incisors lack enamel in their lingual portion (Hillson, 2005). They are robust and have an anteromedial canal with longitudinal grooves in the labial portion. The alveolus of the incisors extends below the h.s.i. (secondary internal fissure) of the m1. Both p4 show the Pr.s.a. (secondary anterior prism), Pr.I and Pr.II are joined by a small enamel bridge. The h.4i. (fourth internal fissure) is not present and the h.2e. (second external fissure) extends to more than 90% of the total width of the prism. The junction of Pr.I and Pr.II is flanked by h.1e. (first external fissure) in the labial portion and in the lingual portion by the h.s.i.p. (principal secondary internal fissure) leaving a narrow enamel bridge. The Pr.s.a. has a Y shape like the Pr.I, while Pr.II has a V shape. The length of the p4 is greater than the length of the m2, this feature is characteristic of N. aesopi (Mones, 1991).
The m1 presents the Pr.IIa joined to Pr.IIb in the labial portion by a thin bridge of enamel; the h.p.i. (primary internal fissure) is deep, exceeding 90% of the width of the prisms but does not separate them. The Pr.I and Pr.IIb are Y shape, while the Pr.IIa are V shape. Both m2 possess complete Pr.Ia and Pr.IIb. On the left molar the h.t.i. (tertiary internal fissure) does not divide the Pr.IIa into Pr.IIa’ (anterior plate of the second prism) and Pr.IIb’ (posterior plate of the second prism) and maintain the union of the enamel bridge in the labial portion (Figure 3C). This feature has been observed in juveniles and young adults of H. hydrochaeris, but it is a rare feature in adults (Mones, 1975a) and cannot be seen in the right m2 because that area is damaged. The right m3 has the Pr.I divided into two plates; the Pr.IIb has an abnormal widening making the h.s.e. shorter. The left m3 has a complete Pr.I; the h.s.i. exceeds 90% of the total width and the h.s.e. is deep, exceeding 90% of the width of the molar. The complete prisms have a V shape.
IHNFG-4865 is a right maxillary fragment with the M3 (Figure 4A). It is composed of 16 prisms of which Pr.I is incomplete in its mesial portion and Pr.XVI is represented only by a fragment of enamel laminae. The length of the M3 is 59.12 mm and the width is 20.67 mm. The prisms in the mesial portion are robust and tend to thin out at their distal portion.
Figure 4 Dental, cranial and postcranial material of Neochoerus aesopi from Los Mangos locality, Villaflores, Chiapas. IHNFG-4865, right M3 in occlusal view (A); IHNFG-4873, left hemimandible in lateral (B) and occlusal (C) views; IHNFG-5760, parietal (D); IHNFG-5761, pelvic girdle (E and F). Bar scale in all cases equal to 50 mm. Abbreviations: ac, acetabulum; an, acetabular notch; co, condyle; fmg, foramen magnum; mcr, masseteric crest; o, occipital bone; pcp, paracondylar process; stu, sacral tuberosity; tmrf, tuberosity for the m. rectus femoris. Dental abbreviations as in Figure 2.
IHNFG-4873 corresponds to the anterior portion of the left hemimandible of a juvenile with incisor, p4, m1, and an associated unidentified upper molar fragment (Figures 4B and 4C). The specimen preserves the distal portion of the masseteric crest and the masseteric fossa is located below the Pr.II of m1. It retains most of the incisor, which presents the anteromedial groove and poorly marked longitudinal striations. The p4 shows the Pr.s.a. and Pr.I in Y shape while Pr.II has V shape. The Pr.s.a. is similar to the adult specimen with the exception of the h.5i. (fifth internal fissure), which is deeper. The h.4i. is little marked and, like the adult, the union between Pr.I and Pr.II is very thin. Only the shape of the prisms can be observed in the m1 and, unlike the adult specimen, the Pr.I and Pr.IIa have a V shape and Pr.IIb has a Y shape.
IHNFG-5760 is an occipital portion of the skull (Figure 4D) and is similar to the occipital of Hydrochoerus hydrochaeris. The occipital bone is almost flat, with a smooth depression in each side of the foramen magnum. The condyles are thin and border the lower part of the foramen magnum. The foramen magnum is oval in shape. The paracondylar processes are small and are at the level of the upper end of the occipital condyle.
IHNFG-5761 is a pelvic girdle partially conserved and resembles the pelvis of the extant capybara H. hydrochaeris. In ventral view, the hip bones are elongated and narrow and with an Y shape. The ilium is straight. The distal part of both ilium is missing but it is notorious that the ilium wing lay in a sagittal plane. The upper side of the body of the right ilium preserves the proximal part of the sacral tuberosity, which is thin in lateral-medial direction. The body of the ilium bears a prominent tuberosity for the m. rectus femoris. Only the iliopubic eminence of the ilium is preserved. The pubis is not preserved and is only observed as part of the branch of the pubis. The acetabulum is deep and circular in shape, with a smooth acetabular notch located in the posterior margin (Figure 4E).
5. Discussion
5.1. TAXONOMIC ASSESSMENT
The Neochoerus genus can be distinguished from the close relative Hydrochoerus by the following: Neochoerus is almost twice as large; the rostrum is longer; the anterior portion of the zygomatic arc is more rounded and oriented backward; the anterorbital bar and lacrimal are more robust; the skull roof is wider; the supraoccipital is wider and more excavated; the masseteric crest is retracted; the coronoid process is greatly reduced; and the M3 has 14 to 17 prisms, while Hydrochoerus has 12-13 prisms (Mones, 1991; Flynn, 2008). In the mandible IHNFG-4866, the masseteric crest is retracted and the coronoid process is slightly elevated, while in the M3 IHNFG-4865 16 prisms are observed. In addition, the measurements of IHNFG-4865 and IHNFG-4866 fall within the observed range of Neochoerus (Figures 5A and 5B). All these characteristics allow us to assign the fossil material from Chiapas to the genus Neochoerus.
Figure 5 Bivariate plot of M3 and p4 measurements. Black asterisks: Neochoerus aesopi from Villaflores, Chiapas; red dots: N. aesopi from Chapala Lake, Jalisco (INAH, Mexico City, not catalogued); black dot: N. aesopi from Valsequillo, Puebla (INAH CDMX, “66-I; Y-I”); purple dot: N. pinckneyi (= N. aesopi, Sanders, 2002); blue dots: N. aesopi mean (Mones, 1991); pink dots: N. sulcidens mean (Mones, 1991); gray dot: N. tarijensis mean (Mones, 1991); yellow dot: N. cordobai (Carranza-Castañeda and Miller, 1988); orange dots: N. occidentalis (Carranza-Castañeda, 2016); green triangles: Hydrochoerus hydrochaeris (Kerber and Ribeiro, 2011). Red lines: trend of the genus Neochoerus; green lines: trend of the genus Hydrochoerus.
The North American species in the genus Neochoerus can be differentiated by its size and dental morphology. In the oldest species, N. cordobai and N. occidentalis, the central laminas of the M3 bear small invaginations in the labial side (Carranza-Castañeda and Miller, 1988; Carranza-Castañeda, 2016), called extraordinary external fissures (Mones, 1991). Apparently, this feature is a primitive dental character in the capybaras, because it is also present in the M3 of the Pliocene taxa Phugatherium, “Chapalmatherium” and Hydrochoeropsis (Deschamps et al., 2013; Vucetich et al., 2014). This dental morphological characteristic is not present in the M3 of N. aesopi. Another difference between N. cordobai, N. occidentalis, and N. aesopi is observed in the DL. The DL in N. cordobai and N. occidentalis is between 60 and 70 mm, while in N. aesopi it is 70-90 mm. In specimen IHNFG-4865, the M3 does not have the extraordinary external fissures on the laminas like N. aesopi. In the same way, the mandible of IHNFG-4866 has a DL of 90.05 mm, longer than the DL of N. cordobai and N. occidentalis, falling into the range of N. aesopi.
5.2. HYDROCHOERUS IN MEXICO?
Material of capybaras from Chapala lake, Jalisco; Terapa, Sonora; Media Luna lagoon, San Luis Potosí; and Valsequillo, Puebla, have been referred to Hydrochoerus (Álvarez, 1971; Hernández-Junquera, 1977; Pichardo, 1997; Mead et al., 2006; Carranza-Castañeda, 2016).
5.2.1. SPECIMENS FROM CHAPALA LAKE
Álvarez (1971) referred the specimens from Chapala lake as Hydrochoerus. Recently, Carranza-Castañeda (2016) reviewed this material and mentioned that some specimens have characteristics of Hydrochoerus, and referred the specimens labeled with the numbers 78 and 126 as Hydrochoerus sp. (fig. 9, p. 310). Nevertheless, a review of these specimens from Chapala (housed at the Laboratorio de Arqueozoología, INAH), by one of the authors (JEP) showed that these specimens have the Neochoerus mandibular characteristics mentioned by Mones (1991) that allows the differentiation of Neochoerus from Hydrochoerus. Such differences are more evident in the DL and the TL. In H. hydrochaeris the range of the DL is 35-52.1 mm, while in H. isthmius it is 34.6-41.7 mm (Mones, 1991). In Neochoerus the DL has a longer range (60-90 mm).
In the same way, in the Neochoerus species, the TL range is between 90 and 112 mm (N. cordobai = 112 mm, N. aesopi = 90-110 mm, N. sulcidens = 102.6 mm, N. tarijensis = 101 mm), while in Hydrochoerus the TL range is 61.5-91.4 mm (H. hydrochaeris = 64-91.4 mm, H. isthmius = 61.5-71.5 mm) (Mones, 1991). Specimen 78 from Chapala has a DL of 71.97 mm and a TL of 99.26 mm, measurements within the range of Neochoerus. Additionally, the masseteric crest begins between the Pr.s.a and the Pr.I (like in Neochoerus), while in Hydrochoerus it begins in the anterior part of the Pr.s.a. On the other hand, specimen 126 has a DL of 40.3 mm and a TL of 89.87 mm, measurements within the range of Hydrochoerus. However, the p4 length is greater than the m2 length, and the masseteric crest begins in the posterior part of the Pr.s.a, characteristics of N. aesopi (Mones, 1991). The DL and TL measurements of the specimen are indicative of one young individual.
The M3 also exhibits differences between Neochoerus and Hydrochoerus. Although the general morphology is similar, the number of prisms varies. In Neochoerus, the number of prisms is 14 to 17, while in Hydrochoerus it is 12 to 13 (Mones, 1991; Flynn, 2008). In some individuals from Chapala, the M3 has 14 prisms (also mentioned by Carranza-Castañeda, 2016), which allows assigning the specimens to Neochoerus. The size of the M3 in some specimens from Chapala falls into the range of Hydrochoerus, whereas the taxonomic assignation to Neochoerus or Hydrochoerus is difficult (Figure 5A).
However, the variation in the size of the teeth of capybaras is a consequence of age, which does not affect significantly the morphological characteristics (Vucetich et al., 2005). Therefore, the small size of some individuals is the result of age, and not due to specific differentiation.
The bivariate plot of the p4 (Figure 5B) shows that the size of this molar is more informative and a better indicator for Neochoerus to Hydrochoerus differentiation, although it is the most morphologically variable tooth (Álvarez, 1971).
Finally, the presence of Hydrochoerus in Chapala lake is rejected, because the coexistence of two or more species with the same ecological requirements within the same area is not possible.
5.2.2. THE CAPYBARA FROM VALSEQUILLO, PUEBLA
Hydrochoerus remains have been reported from Valsequillo, Puebla (Pichardo, 1997). However, these remains have not been illustrated. Later, Pérez-Crespo et al. (2014, 2019) mentioned the presence of Neochoerus sp. in Valsequillo. However, they are not specific on the basis of the taxonomic assignment.
The examination of the incomplete skull from Valsequillo (housed at Laboratorio de Arqueozoología, INAH, labeled with the number “66-I; Y-I”) allow us to assign this specimen to Neochoerus aesopi. The taxonomic assignation is based on the morphological characteristics of the skull and the M3. The skull roof is wider than Hydrochoerus, with the supraoccipital wider and more excavated; lacrimal more robust and higher, and the M3 with 15 laminae, and these without extraordinary external fissures. The size of M3 indicates that this specimen is from a juvenile (Figure 5A).
5.2.3. HYDROCHOERUS FROM TÉRAPA AND MEDIA LUNA LAGOON
Fossil remains of capybaras from Térapa have been referred to Hydrochoerus sp. (Mead et al., 2006) and Hydrochoeridae indeterminate (Nunez et al., 2010). However, this material has never been described or illustrated. Unfortunately, the repository of these fossils is not mentioned and therefore a revision is not possible. Further, the fossil of capybaras from Media Luna lagoon, San Luis Potosí, assigned as Hydrochoerus sp. (Hernández-Junquera, 1977), was never formally deposited in a museum and is now missing (Ferrusquía-Villafranca, 2018, pers. com.). Nevertheless, we do believe that the capybaras from Térapa and Media Luna lagoon are Neochoerus, and, considering the temporal range (late Pleistocene, Rancholabrean) assigned for both faunas, it is possible to refer this material as N. aesopi.
Such affirmation is based upon two assumptions: (1) Mones (1984) considered that the reports of Hydrochoerus in North America are misidentifications of Neochoerus, and (2) the review of the specimens from Chapala and Valsequillo, identified as Hydrochoerus, showed that they are actually Neochoerus.
5.3. PALEOECOLOGICAL SIGNIFICANCE
The paleoecological aspects of the extinct capybaras have been inferred by comparison with the extant species of Hydrochoerus. Recent capybaras are semiaquatic and live within lowlands habitats in the proximity of water, like forested riverbanks, former riverbeds, brackish wetlands, and mangrove swamps (Mones and Ojasti, 1986).
Fossil capybaras are usually recovered from fluvial, lacustrine or swampy deposits (Vucetich et al., 2013), so the lifestyle related to water is supported. Therefore, the presence of Neochoerus aesopi in Los Mangos locality indicates the existence of permanent water bodies in the area during the late Pleistocene, which is consistent with the lithology of the outcrops in the study locality. The feeding habits of Neochoerus can also be inferred through comparison with feeding habits of H. hydrochaeris. Hydrochoerus hydrochaeris consumes grasses, aquatic plants, and occasionally bark, stems, and leaves (Ojasti, 1973). Recent observations show that H. hydrochaeris has preference for Hymenachne amplexicaulis (an aquatic grass) during the wet season, and feeds on Eleocharis interstincta (a reed) and Paratheria prostrata (a grass) during the dry season (Barreto and Quintana, 2013).
Based on the feeding habits of H. hydrochaeris, it is possible to infer that N. aesopi from Los Mangos locality fed on different types of grasses, reeds, and shrubbery. This assumption is supported by the microwear and stable isotopes analyses of δ13C and δ18O on N. aesopi from La Cinta-Portalitos, Michoacán-Guanajuato and Valsequillo, Puebla, and shows that some individuals have a mixed feeder diet based on C3/C4 plants and other individuals were C4 grazers (Pérez-Crespo et al., 2014; Eng-Ponce et al., 2017; Eng-Ponce, 2018). These data are similar to that obtained from N. tarijensis from Bolivia, species referred to as a C3/ C4 mixed feeder (MacFaden and Shockey, 1997).
6. Conclusions
The formal description of the capybara fossil remains from Villaflores, Chiapas, allows us to confirm the specific taxonomy assignation as Neochoerus aesopi, which adds a new locality for this taxon in Mexico. It also documents the southernmost record, until now, for North America, and increases the spatial range of Neochoerus in the late Pleistocene.
The historical presence of Hydrochoerus in Chapala lake, Jalisco, and Valsequillo, Puebla, is rejected based upon the review of the specimens housed in Laboratorio de Arqueozoología, INAH, and confirms that the only species present in both areas is Neochoerus aesopi. In the same way, we refer the capybaras from Térapa and Media Luna lagoon as N. aesopi. The presence of N. aesopi from Sonora to Chiapas allows us to hypothesize that this was the only capybara species present in the late Pleistocene of Mexico.
