First Central American Record of Anthracotheriidae (Mammalia, Bothriodontinae) from the Early Miocene of Panama

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FIRST CENTRAL AMERICAN RECORD OF ANTHRACOTHERIIDAE (MAMMALIA, BOTHRIODONTINAE) FROM THE EARLY MIOCENE OF PANAMA

ALDO F. RINCON,*,1 JONATHAN I. BLOCH,1 BRUCE J. MACFADDEN,1 and CARLOS A. JARAMILLO2 1Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611, U.S.A., arincon@ufl.edu; jbloch@flmnh.ufl.edu; bmacfadd@flmnh.ufl.edu; 2Smithsonian Tropical Research Institute, Box 0843-03092 No. 8232, Balboa-Ancon, Panama, [email protected]

ABSTRACT—A new species of bothriodontine anthracothere, Arretotherium meridionale, is described from the early Miocene (Arikareean North America Land Mammal Age) Las Cascadas fossil assemblage in Panama, Central America. Fossils of A. meridionale are the ﬁrst record of an anthracothere from the New World Tropics. Among anthracotheres, A. meridionale is most similar to A. acridens from the middle Arikareean from Texas in having a relatively deep and robust jaw, high and sharp cusps on the lower molars, short c–p1 diastema, and absence of a mesiolingual metacristid. A. meridionale differs from other species in being generally larger, two lower incisors (rather than three), prehypocristid never reaching the postprotocristid, more apical junction between postprotocristid and postmetacristid, mesiolingual entocristid transversely notching preentocrisitid, and transverse valley tapered lingually by prehypocristid. Although cladistic analysis of 28 anthracotheriids coded for 51 characters supports a relationship between A. meridionale and A. acridens, some presumably convergent dental characteristics are also similar to certain Oligocene-Miocene Eurasian bothriodontines. The presence of Arretotherium in the Las Cascadas Formation in Panama, and absence in the later Centenario Fauna, shows that primitive bothriodontines entered into Central America by the early Miocene before disappearing from the New World during the late early–middle Miocene. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

INTRODUCTION 2006; Boisserie et al., 2010, 2011). They dispersed widely during the early Neogene, reaching all continents except Australia Anthracotheriid artiodactlys likely split from helohyid ar- by the end of the Neogene. Although North American both- tiodactyls (Coombs and Coombs, 1977; Ducrocq et al., 1997) riodontines were probably derived from a primitive Eurasian in Eurasia (Suteethorn et al., 1988; Lihoreau and Ducrocq, form, such as Elomeryx or Bothriodon (Scott, 1940; Macdon- 2007) before representatives of this family dispersed into North ald, 1956; Macdonald and Shultz, 1956; Lihoreau and Ducrocq, America in the Eocene (Douglass, 1901; Troxell, 1921; Scott, 2007), distinguishing between Old and New World bothriodon- 1940; Macdonald, 1956; Macdonald and Shultz, 1956). Their tines has been one of the primary difﬁculties in clarifying the re- North American fossil record is restricted to the late middle lationships between American forms and their Eurasian coun- Eocene to middle Miocene of the Great Plains, with a few terparts (Kron and Manning, 1998; Lihoreau and Ducrocq, Oligocene and Miocene records from further south in Texas 2007). (Kron and Manning, 1998; Albright, 1999; Tedford et al., 2004). The early Miocene bothriodontines Arretotherium and North American anthracotheres are classiﬁed in two subfam- Kukusepasutanka are the last-known North American anthra-

Downloaded by [Yale University Library] at 06:42 05 March 2013 ilies (Scott, 1940; Kron and Manning, 1998): Anthracotheri- cotheres (Fig. 1). Although they are only known from a few inae Leidy, 1869, represented by the genus Heptacodon Marsh, specimens, these taxa are similar in lacking a paraconule on 1894a, from the Whitneyan of North America, and Bothriodon- the upper molars; however, Kukusepasutanka is larger, has a tinae Scott, 1940, which includes Aepinacodon Troxell, 1921, more invaded mesostyle, and has more strongly developed stylar from the late Eocene of South Dakota and Nebraska (mid- cusps (Macdonald, 1956). The only known species, K. shultzi, dle to late Chadronian), Arretotherium Douglass, 1901 (Fig. 1), was recovered from early Miocene sediments in the Drummond ranging from the late Oligocene–early Miocene of North Amer- Granite County in Montana. K. shultzi is characterized by ica (early Arikareean–early Hemingfordian), Kukusepasutanka an elongated and massive tubular snout and the presence of Macdonald, 1956, from the late Arikareean deposits of Montana well-developed anterior diastema (Macdonald, 1956; Kron and (Macdonald, 1956), and Bothriodon Aymard, 1846, from the Manning, 1998). Although no lower dentition of K. shultzi has Brule Formation in South Dakota (Orellan to early Arikareean) been recovered, making its relationship with Arretotherium and from the early Chadronian of Saskatchewan (Kron and Man- unclear, it is similar to Heptacodon in its development of ning, 1998). Bothriodontines, characterized by the presence of stylar cusps on the upper molars. In contrast to K. schultzi, more selenodont molars, a relatively shorter rostrum, upper mo- Arretotherium has a relatively short snout and a more robust lars with four or ﬁve cusps, and the upper molar mesostyle be- mandible (Macdonald, 1956). Distinguishing characteristics orig- ing variably invaded by the transverse valley (Scott, 1940; Mac- inally noted by Douglass (1901) for Arretotherium and further donald, 1956; Kron and Manning, 1998; Lihoreau and Ducrocq, discussed by Macdonald (1956) include (1) four-cusped upper 2007), have been recognized as possibly sharing a relationship molars; (2) teeth with sharp cusps or crescents; (3) small ﬁrst with Hippopotamidae (Simpson, 1945; Boisserie and Lihoreau, upper premolar; (4) upper premolars increasing rapidly in size posteriorly, composed of a simple cone and a cingulum-like cusp; *Corresponding author. (5) upper molars high and square with heavy cinguli; (6) upper

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FIGURE 1. Location and biochronology of early Miocene bothriodotines discussed in this study. A,cf.Arretotherium fricki from the early Heming- fordian Cypress Hill Formation in Saskatchewan (Storer and Bryant, 1993); B, A. fricki Macdonald and Shultz, 1956, from the early Hemingfordian Upper Marsland Formation in Nebraska and also present in the Hemingfordian Flint Hill L. F. from South Dakota (Macdonald and Shultz, 1956; Macdonald and Martin, 1987); C, A. leptodus (= Ancodon leptodus) Matthew, 1909, from the early Arikareean Lower Rosebud beds, South Dakota (Scott, 1940; Macdonald, 1956; Macdonald, 1963; Tedford et al., 2004); D, A. acridens Douglass, 1901, from the early Arikarrean Blacktail Deer Creek Fauna., Montana (Hibbard and Keenmon, 1950); E, Kukusepasutanka Macdonald, 1956, from the late Arikareean deposits of Montana (Macdonald, 1956); F, Arretotherium acridens Douglass, 1901, from the early Miocene Toledo Bend L. F., Texas (Albright, 1999); G, A. meridionale, sp. nov., from the Las Cascadas fossil assemblage, Panama. Chronostratigraphy and biochronology modiﬁed from Albright et al. (2008). Abbreviations: Ar, Arikareean Faunal Zone; E, early; L, late; L. F., Local Fauna.

canine laterally compressed; and (7) upper premolars reduced, stratigraphic position and the probable age of the fossil assem- with protocone not connected labially to cingulum. blage (Hibbard and Keenmon, 1950; Macdonald, 1963). Disre- Despite the fact that only a few fossils have been referred to garding the poorly understood relationship between A. leptodus Arretotherium, there are three described species: (1) A. acridens and A. acridens, A. fricki seems to represent the last appearance Douglass, 1901 (type species), from the early Arikareean Black- of Anthracotheriidae (Fig. 1) in the fossil record of North tail Deer Creek Fauna in Montana (Douglass, 1901; Hibbard America (Macdonald and Martin, 1987). Although it is beyond and Keenmon, 1950), thought to be equivalent to the Harri- the scope of the present study, a more detailed analysis of the son Formation in Nebraska (Tedford et al., 1987; Tedford et al., American Anthracotheriidae is clearly needed to further clarify 2004), and the middle to late Arikareean Toledo Bend Local the present taxonomic uncertainties associated with this family. Fauna (L. F.) in Texas (Albright, 1998, 1999); (2) A. leptodus Herein, we describe a new American bothridontine, Ar- (= Ancodon leptodus) Matthew, 1909, from the early Arika- retotherium meridionale, sp. nov., from the upper part of the reean Lower Rosebud beds that overly the White River Group in volcanoclastic early Miocene Las Cascadas Formation from the South Dakota and is presumably the oldest record of this genus Panama Canal area (Gaillard Cut) in Central America (Fig. 2). (Scott, 1940; Macdonald, 1956; Tedford et al., 2004); and (3) A. The new fossils represent the southernmost occurrence of Both- fricki Macdonald and Shultz, 1956, described from cranial mate- riodontinae, suggesting that it reached tropical habitats before its Downloaded by [Yale University Library] at 06:42 05 March 2013 rial from the early Hemingfordian Runningwater Formation in extinction in North America during the middle Miocene (Kron Nebraska, and is also present in the Hemingfordian Flint Hill L. and Manning, 1998; Lihoreau and Ducrocq, 2007). F. from South Dakota (Macdonald and Martin, 1987) and the early Hemingfordian Cypress Hill Formation in Saskatchewan Abbreviations—The biochronology follows late Oligocene– (Storer and Bryant, 1993). A. acridens and A. leptodus from the early Miocene biozonation developed in the Great Plains (Ted- early to middle Arikareean are characterized by a heavier, more ford et al., 1987, 2004; MacFadden and Hunt, 1998) and the sub- robust skull and a deeper mandible than that of A. fricki.In sequent recalibration proposed by Albright et al. (2008) for the contrast, although the Hemingfordian A. fricki might be derived Arikareean North America Land Mammal Age (NALMA). For from A. acridens (Macdonald and Martin, 1987), it is character- the most part, dental nomenclature (Fig. 3) follows Lihoreau and ized by a more slender and gracile cranium (Kron and Manning, Ducrocq (2007). We also use the descriptive system of crests and 1998). crescents deﬁned by Loomis (1925) for buno-selenodont denti- To date, there is no agreement about the relationships be- tions in artiodactyls. Additionally, we follow the tooth orienta- tween the North American early Miocene forms, which has tion terminology proposed by Smith and Dodson (2003) for the caused several taxonomic problems. For example, there is an incisors. overlap between the deﬁning molar characteristics of A. acridens Institutional Abbreviations—AMNH, American Museum of and A. leptodus. Macdonald (1956) discussed in detail this Natural History, New York, U.S.A; CM, Carnegie Museum, matter and suggested that A. leptodus could represent a nomen Pittsburgh, Pennsylvania, U.S.A.; F:AM, Frick: American Mam- vanum because of the poorly preserved holotype. However, mals collection at the AMNH; LSUMG-V, Louisiana State Macdonald later abandoned his argument, ratifying the validity University Museum of Geoscience; Baton Rouge, Louisiana, of this taxonomic entity, but transferring this taxon to the genus U.S.A; SDSM, South Dakota School of Mines, Rapid City, Arretotherium (A. leptodus Macdonald, 1963) based solely on its South Dakota, U.S.A; UCMP, University of California Museum RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 423

FIGURE 3. Diagram showing most of the dental cusp nomenclature applied to lower permanent dentitions of anthracotheres in this study. Abbreviations: dlmtcid, distolingal metacristid; Entd, entoconid; Hypd, hypoconid; Hypulid, hypoconulid; mletcid, mesiolingual entoconid; mlmtcid, mesiolingual metacristid; Metd, metaconid; poetcid, postento- conulid; pohypid, posthypoconid; pometid, postmetacristid; poptcid, postprotocristid; peetcid, preentocristid; pehypid, prehypocristid; pemtcid, premetacristid; peptcid, preprotocristid; Ptcd, protoconid. Modiﬁed from Lihoreau and Ducrocq (2007).

glomerates. Fossil-bearing lithologies are restricted to local flu- vial sequences in the uppermost part of the Las Cascadas For- mation. The fossils described here were found in the northern part of the Gaillard Cut and were associated with other ungulates, FIGURE 2. Location and stratigraphic position of fossil bothriodon- including protoceratids, equids, peccaries, and camelids (Rincon tines from the Gaillard Cut, Panama Canal area. A, map of North and et al., 2010, 2012). Although the better-preserved fossils are re- Central America showing the location of the Panama Canal area and the stricted to the fine-grained ash falls, additional fossils were also Gaillard Cut. B, stratigraphic position of the Las Cascadas fossil assemblage and the Centenario Fauna. Modified from Kirby et al. (2008), Mac- recovered from an overlying conglomeratic welded tuff. Fadden et al. (2010), and Montes et al. (2012). Although the shallow marine Culebra Formation unconformably overlies the upper part of Las Cascadas Formation in the northern part of the Gaillard Cut (Montes et al., 2012), in- Downloaded by [Yale University Library] at 06:42 05 March 2013 tense faulting and deformation obscures this contact in the Las Cascadas fossil locality (Lirio Norte). Fossil vertebrates from of Paleontology, Berkeley, California, U.S.A; UF, Vertebrate the Gaillard Cut (Whitmore and Stewart, 1965; Woodring, 1957, Paleontology Collection, Florida Museum of Natural History 1982; MacFadden and Higgins, 2004; MacFadden, 2006, 2009; (FLMNH), University of Florida, Gainesville, Florida, U.S.A; MacFadden et al., 2010; Uhen et al., 2010) have been formally UNSM, University of Nebraska State Museum, Lincoln, U.S.A. grouped into the Centenario Fauna (MacFadden et al., 2010). This fauna extends from the uppermost part of the Culebra For- mation and includes the transitional to continental Cucaracha AGE AND GEOLOGIC SETTING Formation (Fig. 2B), representing about 120 m of fossil-bearing The early Miocene Las Cascadas Formation represents the old- sediments that are widely distributed along the Gaillard Cut est continental sequence cropping out along the Gaillard Cut, (MacFadden et al., 2010). The Centenario Fauna includes mam- Panama Canal area (Fig. 2A, B). The basal part of the Las Cas- malian taxa known from the Arikareean to the Barstovian of cadas Formation unconformably overlies the welded and massive North America, but does not obviously fit within the biochrono- marine to shallow marine volcanic agglomerates of the middle to logical context of a specific Miocene NALMA (MacFadden and late Oligocene Bas Obispo Formation (Woodring and Thomp- Higgins, 2004; MacFadden, 2006, 2009; MacFadden et al., 2010). son, 1949; Woodring, 1957, 1982; Kirby et al., 2008; Montes et al., Attempts to independently determine the age of the Centenario 2012). Although the thickness of the Las Cascadas Formation is Fauna using geochronological analyses are currently in progress. still unknown, it is composed of a lower member with massive Despite the absence of a reliable isotopic date, the age of the agglomerates and an upper member that includes paleosols, ash upper part of the Las Cascadas Formation can be tentatively con- falls, lenticular bodies of conglomeratic sandstones, and purple to strained through its stratigraphic relationships with other forma- green mudstones interbedded with coarser-grained volcanic ag- tions from the Gaillard Cut (Fig. 2B). Consequently, the upper 424 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 33, NO. 2, 2013

Las Cascadas fossiliferous sequence represents an interval older lected in the upper part of the Las Cascadas Formation (Fig. 2B), than the lower part of the Culebra Formation, for which several likely equivalent to the late Arikareean NALMA (Rincon et al., dates have been published, including 20.62 ± 0.58, 23.07 ± 0.53 2012). (Kirby et al., 2008), and 19.3 ± 0.4 (Montes et al., 2012) Ma. Etymology—From the Latin ‘meridionale’ (southern). Corre- The lower boundary of the Las Cascadas Formation can also be sponding to the southernmost record of Anthracotheriidae in the constrained using an Ar40/Ar39 age of 25.37 ± 0.13 Ma derived New World. from the andesitic water-saturated arc lavas of the underlying Bas Referred Material—The following were found in association Obispo Formation (Rooney et al., 2010). Therefore, the duration with the holotype: UF 245609, right upper incisor; UF 244295, of the Las Cascadas Formation may span the late Oligocene to left upper C1 (broken); UF 244181, right astragalus; and UF early Miocene (<25 to ∼19 Ma), likely representing the middle 244290, distal right metacarpal. Additionally, the following speci- to late Arikareean NALMA sensu MacFadden and Hunt (1998), mens were found in association in a different horizon of the same Tedford et al. (2004), and Albright et al. (2008). Based on the locality: UF 244174, partial left M3; UF 246821, partial skull frag- stratigraphic position and available biochronology, fossil verte- ment; and UF 244177, right distal femur. Although it is possible brates from the Las Cascadas fossil assemblage likely represent that associated specimens are from the same individuals (mini- the late Arikareean and represent the oldest mammalian fauna mum number of individuals = 2), the lack of any sort of articu- so far found in the Gaillard Cut, indicating the arrival of north- lation makes this ambiguous and they are thus cataloged sepa- ern populations into a recently emerged continental area (Rincon rately. et al., 2012). Diagnosis—Differs from all other species of Arretotherium in having overall larger size, two lower incisors, lower molars with SYSTEMATIC PALEONTOLOGY prehypocristid never reaching postprotocristid, more apical junction between postprotocristid and postmetacristid, mesiolingual Class MAMMALIA Linnaeus, 1758 entocristid transversely notching preentocrisitid, and transverse Order ARTIODACTYLA Owen, 1848 valley lingually tapered by prehypocristid. Further differs from Family ANTHRACOTHERIIDAE Leidy, 1869 A. acridens in having incisors with stronger and more cylindrical Subfamily BOTHRIODONTINAE Scott, 1940 roots and an upper canine with a serrated anterior edge pinched ARRETOTHERIUM Douglass, 1901 into a carina. Further differs from A. fricki in having a deeper Type Species—Arretotherium acridens (Douglass, 1901) and more robust jaw, and more sloping mandibular symphysis. Holotype—CM 704. Right and left partial maxillae, with Further differs from A. leptodus in having a more laterally com- RI1–P2, M1–M3, and isolated LP3–P4 and LM1–M2. pressed upper canine. Generic Diagnosis—Short rostrum without diastema, upper cheek teeth as in Elomeryx except molars have lost protoconule, cusps of upper and lower cheek teeth extremely high and pointed Description (Macdonald, 1956). Mandible—A single juvenile partial dentary is referred to Ar- Included Species—Arretotherium acridens Douglass, 1901, retotherium meridionale, sp. nov., from the Las Cascadas For- from the early Arikareean Blacktail Deer Creek from Montana mation fossil assemblage (UF 244187, holotype). The mandible (Douglass, 1901; Hibbard and Keenmon, 1950; Tedford et al., is deep, with short diastemata in front of, and behind, the p1 2004) and the middle to late Arikareean Toledo Bend L. F. (Fig. 4A–C). The anterior part is partially broken but exhibits in Texas (Albright, 1999); A. leptodus (= Ancodon leptodus) two preserved incisor alveoli. The jaw is relatively narrow and Matthew, 1909, from the early Arikareean Lower Rosebud beds deep, with no evidence of constriction at the level of the canine. in South Dakota; A. fricki Macdonald and Shultz, 1956, from The mandible posterior to the m2 is not preserved in this speci- the early Hemingfordian Upper ‘Marsland Formation’ in Ne- men. The labial surface of the horizontal ramus is uniformly con- braska, the Hemingfordian Flint Hill L. F. from South Dakota vex along the jaw, whereas the lingual segment is convex below (Macdonald and Shultz, 1956; Macdonald and Martin, 1987), the molars and concave anterior to the dp3 (Fig. 4). An atten- and the early Hemingfordian Cypress Hill Formation in uated transverse constriction is present between the p1 and the Saskatchewan (Storer and Bryant, 1993); A. meridionale, sp. nov., dp2 and coincides with the position of the anterior mental fora- from the Las Cascadas fossil assemblage in Panama. men (Fig. 4C). A second smaller posterior foramen is located just

Downloaded by [Yale University Library] at 06:42 05 March 2013 Remarks—Although only a single partial upper molar has below the anterior root of the dp3. The anterolingual surface of been referred to Arretotherium meridionale, sp. nov. (see below), the mandible is characterized by a relatively straight and oblique it lacks the distinctive strongly developed stylar cusps and deeply symphysis that ends ventrally with a distinct genial spine that ex- invaded mesostyle considered diagnostic for the similarly sized tends posteriorly from the posteroventral end of the symphysis monospecific genus Kukusepasutanka (Macdonald, 1956:fig. 16). (Fig. 4A, B). Both the ventral and dorsal borders of the sym- In all other comparable features, A. meridionale, sp. nov., is most physis are subparallel and slightly convex dorsally. The symph- similar to species classified in Arretotherium (see also Douglass, ysis has a broader anterior segment that ends in a flattened ven- 1901; Scott, 1940; Macdonald, 1956; Macdonald and Shultz, 1956; tral surface just below the genial spine. The symphysis is broad, Kron and Manning, 1998; Albright, 1999; Lihoreau and Ducrocq, long, and V-shaped in cross-section, with no evidence of fusion. 2007). Although description of this new taxon could result in an A short diastema is present between the single-rooted p1 and expanded concept of Arretotherium, we are reluctant to emend a the dp2. A relatively well-developed vascular groove is partially generic diagnosis that is based solely on the morphology of the preserved at the posterior ventral end of the ramus, correspond- upper dentition (Macdonald, 1956) without more complete fos- ing to a change in curvature of the ventral mandibular notch sils of A. meridionale, sp. nov. (Fig. 4B, C). ARRETOTHERIUM MERIDIONALE, sp. nov. Lower Deciduous Dentition—The preserved deciduous den- (Figs. 4–6; Table 1) tition includes the left dc1 and dp2–dp4 (Fig. 4). The crown of the dc1 is very worn. It is elongated and posteriorly recurved. Holotype—UF 244187, juvenile left dentary with associated The posterior part of crown has an elongated constriction that deciduous canine, partially erupted c1, p1, dp2–dp4, m1–m2, and is evident even in intense wear stages. The dp2 is double-rooted associated right i1–i2 and mandibular symphysis. (Fig. 4A–C). The crown of dp2 consists of an anterior crest, a Locality and Horizon—Lirio Norte (site key YPA-024 in Uni- large primary cusp, and a relatively elongated posterior crest with versity of Florida Vertebrate Paleontology Collection), Panama a small but distinct cingular segment enclosing a small, conical Canal area, Panama, Central America (Fig. 2A). Fossils were col- cuspule. These structures form the talonid of the tooth and the RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 425 Downloaded by [Yale University Library] at 06:42 05 March 2013

FIGURE 4. Lower dentition of Arretotherium meridionale, sp. nov. A, UF 244187, juvenile left dentary with left dc1, partially erupted left canine, p1, dp2–dp4, m1–m2, and associated right i1–i2 and mandibular symphysis, occlusal view; B, lingual view; C, labial view; D, associated right i1, lingual view; E, labial view; F, associated right i2, lingual view; G, labial view; H, detailed view of the anterior part of UF 244187 showing the erupting Lc1. Abbreviations: pehypid, prehypocristid; postlgF, posterolingual furrow; antlgF, anterolingual furrow. 426 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 33, NO. 2, 2013

cingulid extends from the posterior end of the principal cusp TABLE 1. Summary of dental measurements (in mm) of A. merid- along the labial and the lingual segment. Two small furrows are ionale, sp. nov., from the Las Cascadas Formation. present lingual to the principal cusp; the anterior is deeper and elongated, whereas the posterior is shorter (Fig. 4B). Despite in- Tooth position MDL LLL APL TW tense wear, an additional anterior cusp is evident, occupying the Ri1 13.06 9.01 — — position of the paraconulid, and an anterior crest connects this Ri2 15.70 8.99 — — cusp with the primary cusp (paraconid). The paraconid is more Lp1 — — 10.08 5.93 separated from the posterior crest, resulting in a trenchant over- Ldp2 — — 17.04 7.91 all shape with a higher paraconid. The crown of dp3 is longer and Ldp3 — — 22.05 8.90 Ldp4 — — 31.25 14.13 larger than that of dp2 but preserves a similar trenchant mor- Lm1 — — 26.90 18.25 phology. The anterior crest is well developed and proportion- Lm2 — — 31.76 19.74 ally longer than that of the dp2. A lingually opened invagination LIx 15.07 9.41 — — of the enamel is present along the anterolingual segment of the LC1, partial — — 25.33 14.84 paraconid (Fig. 4A). A deep enamel valley separates the princi- LM3 — — 28.55 30.25 pal cusp from the posterior crescent, which is completely worn and exposes the posterior root below the cervix (enamel-dentine Abbreviations: MDL, mesiodistal length; APL, anterior–posterior length; LLL, labiolingual width; TW, transversal width. junction). The anterior crest is high, and, like that of dp2, has an anterolingual ridge located in the position of the paraconulid. The crown of dp4 is molariform and trilobed. The anterior lobe is A partially erupted canine is replacing an extremely worn de- similar in size to the intermediate lobe and both are slightly nar- ciduous canine in the holotype (Fig. 4H). Although c1 is only rower than the posterior lobe (Fig. 4A). The tooth is worn almost partially erupted, an X-ray image (Fig. 5) shows it to be large to the base of the crown, especially its anterior-most lobe. The and robust, which is characteristic of male anthracotheres. The anterior-posterior length of the dp4 exceeds that of m1 or m2. crown of p1 is small and single-rooted and is isolated by short an- Even though intensive wear is present, a fully selenodont poste- terior and posterior diastemata. The p1 is oval, recurved, and has rior lobe is perceptible. A distinctive cingular segment forms the a well-defined main cusp that projects posteriorly. Two separate posterolingual part of the dp4. The metaconid is separated from ridges extend from the crown apex. The anterior ridge is lingually the entoconid by a lingual notch that is visible even in advanced inflected and extends lingually from the apex toward the cervix wear stages. A strong, shelf-like cingulid is evident anterior to forming a small furrow (Fig. 4A–C). In contrast, the posterior the hypoconid in the labial side (Fig 4A, C). The presence of a ridge extends uniformly along the posterior edge of the crown metastylid could not be evaluated due to strong wear on the lin- until it reaches the cervix. This ridge defines two small posterior gual segment of the dp4. concavities located along the lingual and labial sides of the tooth Lower Permanent Dentition—The permanent dentition in- that extend upwards from the cervix (Fig. 4A, B). cludes Ri1–2, Lp1, and Lm1–m2 (UF 244187). Additionally, two The lower molars of A. meridionale are bunoselenodont, with incisor alveoli are preserved in the anterior part of the left den- four somewhat sectorial, well-defined, high, sharply pointed, and tary. Both incisors have long, deep cylindrical roots and procum- strongly crenulated cusps. The two external cusps are crescen- bent broad and acutely pointed crowns (Fig. 4D–G). The second tic and the two internal ones relatively conical (Figs. 4A, C and incisor is considerably larger than the first (Table 1), and both 5A, B). The apex of each transverse pair of cusps is widely sep- are characterized by having a spatulate appearance. The basal arated, similar to those of the longitudinal pairs. The lingual and part of the crown of i2 is extremely elongated, suggesting that labial cusps have almost the same transverse width in occlusal it was located more distally than the smaller i1 (Fig. 4D, F). The view (Fig. 5B). The anterior and posterior lingual basal segments lingual surface of each incisor is concave, the labial surface is con- of each molar have strongly crenulated anterolabial cingulids that vex, and both surfaces are heavily crenulated (Fig. 4E, G). There are more developed on the labial side, but incomplete lingually is a distinctive cingular segment along the lingual surface at the (Fig. 5B). The lower molars increase in size posteriorly, with m1 enamel-dentine junction, which is more developed on i2 than on smaller than m2 (Table 1). The lower molars have a metaconid i1 (Fig. 4D, F). Downloaded by [Yale University Library] at 06:42 05 March 2013

FIGURE5.Detailedviewofthelowerper- manent dentition of Arretotherium meridionale, sp. nov. A, UF 244187, left m1–m2, lingual view; B, occlusal view; C, X-ray detailed image of the anterior part of UF 244187 showing the erupting permanent Lc1. Abbreviations: pehypid, prehypocristid; mlmtcid, mesiolingual metacristid; peetcid, preentocristid; pometid, postmetacristid; hypulid, hypoconulid. RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 427

that is high and conical and is surrounded by a labial anterior the deep cylindrical roots are mesially recurved. There is no no- continuous crest (preprotocristid) that reaches the lingual mar- ticeable lingual cingulum on the tooth (Fig. 6D). gin of the tooth (Fig. 5B, C). A premetacristid extends from the An isolated LM3 (UF 244174) has a square-shaped crown in summit of the metaconid and reaches the preprotocristid at its occlusal view (Fig. 6E) and is posteriorly transversely reduced. midpoint, whereas a small postmetacristid extends to the post- The crown is heavily worn and its anterior crest is badly bro- protocristid, blocking the anterior longitudinal valley (Fig. 5B). ken. The protocone and metaconule are crescentic and almost The mesiolingual metacristid is very reduced and restricted to completely worn. A strong cingulum surrounds the protocone, the basal part of the crest, making the anterior portion of the whereas a weaker but strongly crenulated posterolingual cingu- metaconid conical in shape (Fig. 5A). The protoconid is selen- lum encircles the posterior part of the metaconule. The lingual odont with two cristids. The preprotocristid reaches the lingual opening of the transverse valley is characterized by a stronger part of the lower molar crowns, whereas the postprotocristid cingulum, resulting from the connection of the anterior and pos- reaches the postmetacristid, forming a distinctive shallow longitu- terior cingula (Fig. 6E). dinal valley apically isolated from the main transversely oriented Discussion and Comparisons—Although there are some dis- valley. The labial opening of the transverse valley is blocked by similarities, the well-preserved lower molars of A. meridionale a well-defined cingular segment formed by the junction of small clearly resemble those of A. acridens (LSUMG V-2270) from the cuspids issuing from the hypoconid and protoconid. Small cus- Toledo Bend L. F., suggesting a close relationship with this late pids are partially blocking the lingual part of transverse valley middle Arikareean form. They share several characteristics, such (Fig. 5B). as a relatively deep and strong jaw morphology, four high and The lower molars of A. meridionale are composed of a well- sharp cusps in the lower molars, the absence of a mesiolingual defined selenodont hypoconid located posterior to the transverse metacristid, the presence of a relatively short c–p1 diastema, the valley, a relatively elongated entoconid, and a relatively high and presence of a small hypoconulid on m1 and m2, and the pres- conical hypoconulid located distally between the postentocristid ence of spurs blocking the labial segment of the transverse valley. and the posthypocristid. Two main cristids are attached to the en- The general morphology of the cingula on the M3 resembles the toconid. The preentocristid is continuous and well defined close robust morphology present in the holotype of A. acridens from to the summit of the entoconid, but diverges into two anterior Montana (Douglass, 1901:pl. IX), whereas this cingulum is more cristids, the mesiolingual entocristid and the preentocristid, at reduced in A. acridens from the Toledo Bend L. F. (LSUMG V- the same level of the junction between the postprotocristid and 2269; Albright, 1999:52). The overall shape of the partial upper the postmetacristid in the anterior part of the molar. This diver- canine of A. meridionale (Fig. 6A, B) is also similar to that of gence is responsible for a distinctive notch anterior to the ento- the holotype of A. acridens (Douglass, 1901:270) and A. acridens conid that is clearly visible in the lingual view (Fig. 5A, B). The (LSUMG V-2351) from the Toledo Bend L. F., only differing in hypoconid is selenodont. The prehypocristid runs anteriorly but the presence of a lingually inflected carina and the absence of it does not reach the postprotocristid, partially closing the trans- convexities on the labial surface of the canine. The upper incisor verse valley at its base. The postentocristid stretches posteriorly (Fig. 6C, D) closely resembles incisors referred to Elomeryx cris- and does not reach the posthypocristid, leaving the posterior lon- pus crispus (Hellmund, 1991:pl. 2) in having a serrated distal ridge gitudinal valley opened. Both cristids are separated by a conical and generally mesially recurved shape. and small hypoconulid. A small posthypocristulid runs labially The partially preserved dentition of A. meridionale has a num- from the hypoconulid, redirecting the posterior longitudinal val- ber of diagnostic bothriondontine characters, including (1) a ley labially (Fig. 5B). transversely compressed C1 with a posterior serrated margin; (2) Upper Dentition—A partial C1 (UF 244295) and a right upper a shelf-like lingual cingula on upper molars; (3) distinctly cres- incisor (UF 245609) were found in association with the dentary centic cusps on upper and lower molars (Scott, 1940; Macdonald, (UF 244187) and might be the same individual (Fig. 6A–D). The 1956; Macdonald and Shultz, 1956; Macdonald, 1963); and (4) re- C1 is robust and transversely compressed into the shape of a flat- duced hypoconulids on m1–m2 (Kron and Manning, 1998). Addi- tened cone. Despite lacking the apical part of the tooth, the lin- tionally, it shares characteristic features with Arretotherium that gual side is relatively flat, whereas the labial side is more convex. include (1) lower cheek teeth with high and sharp cusps; (2) ro- The posterior part of C1 is more constricted (Fig. 6B), with an bust jaw; (3) reduced anterior diastemata; (4) selenodont cristids edge that is pinched lingually into a carina (Fig. 6A) that leads to associated with the protoconid; (5) absence of a premetacristid; the concave anterolingual side of the tooth. The lingual side an- (6) a relatively deep transverse valley partially blocked by spurs Downloaded by [Yale University Library] at 06:42 05 March 2013 terior to the carina is convex (Fig. 6B). The posterior basal part from the hypoconid and protoconid; (7) anterior and posterior of the carina has small cuspules, giving it a serrated appearance cingulids restricted to the labial part of the metaconid and en- (Fig. 6A). The right upper incisor (UF 245609) is caniniform and toconid; (8) lingual outlet of the transverse valley tapered by has strongly crenulated enamel (Fig. 6C, D). It has a distinctive the junction of cingulids issued to the metaconid and entoconid; serrated pattern along the mesial and distal edges. The crown and (9) single-rooted p1; (10) overall morphology of the mandibular

FIGURE 6. Upper dentition of Arretotherium meridionale, sp. nov. A, UF 244295, left upper canine, lingual view; B, occlusal view; C,UF 245609, right upper incisor (Ix), labial view; D, lingual view; E, UF 244174, partial left M3, occlusal view. 428 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 33, NO. 2, 2013

TABLE 2. Summary table of the anterior–posterior length (APL) and maximum transverse width (MTW) of m1 and M3 for relevant specimens of Arretotherium.

Taxon Biostratigraphic/lithostratigraphic unit Tooth position Catalog number APL (mm) MTW (mm) A. acridens Toledo Bend L. F. (Texas) Rm1 LSUMG V-2270 19.612.5 A. acridens Toledo Bend L. F. (Texas) Lm1 LSUMG V-2347 19.112.65 A. fricki Flint Hill L. F. (South Dakota) Lm1 SDSM 53440 19.811.3 A. meridionale, sp. nov. Las Cascadas fossil assemblage (Panama) Lm1 UF 244187 26.53 18.1 A. fricki Flint Hill L. F. (South Dakota) Lm1 SDSM 6826 20.311 A. fricki Flint Hill L. F. (South Dakota) Rm1 UCMP 32373 18.210.5 A. acridens Toledo Bend L. F. (Texas) RM3 LSUMG V-2366 28.10 26.80 A. acridens Toledo Bend L. F. (Texas) LM3 LSUMG V-2367 26.50 26.20 A. acridens Toledo Bend L. F. (Texas) LM3 LSUMG V-2365 27.50 26.50 A. acridens Blacktail Deer Creek Fauna (Montana) M3 CM 704 28.30 29.40 A. leptodus Monroe Creek Formation (South Dakota) RM3 AMNH 13005 24.90 26.60 A. leptodus Monroe Creek Formation (South Dakota) LM3 AMNH 13005 25.80 28.70 A. leptodus Monroe Creek Formation (South Dakota) RM3 F:AM 132055 27.60 27.00 A. leptodus Monroe Creek Formation (South Dakota) LM3 F:AM 132055 27.40 27.00 A. fricki Flint Hill L. F. (South Dakota) M3 UNSM 5764 25.70 24.90 A. fricki Flint Hill L. F. (South Dakota) RM3 UCMP 32369 25.90 26.10 A. fricki Flint Hill L. F. (South Dakota) LM3 UCMP 32369 25.30 24.75 A. fricki Flint Hill L. F. (South Dakota) RM3 F:AM 132053 25.50 27.00 A. fricki Flint Hill L. F. (South Dakota) LM3 F:AM 132053 25.50 26.90 A. meridionale, sp. nov. Las Cascadas fossil assemblage (Panama) LM3 UF 244174 33.29 28.96

Compiled from Douglass (1901), Macdonald (1956), Macdonald and Shultz (1956), Macdonald and Martin (1987), and Albright (1999).

symphysis; and (11) strongly crenulated enamel in the permanent not only provides a test for the position of the new species from dentition. Even though there is overlap in the dimensions of the Panama, but also offers an opportunity to evaluate its specific molars of A. acridens and A. leptodus (Douglass, 1901; Macdon- designation and its relationship to the A. acridens holotype from ald, 1963; Albright, 1999), there are enough differences between Montana. these two forms and the molar dimensions of A. meridionale Morphologic data were compiled from the study of specimens (Table 2) to warrant a specific differentiation. and a literature review. Despite the fact that A. meridionale is The general morphology of the lower deciduous dentition only known from a juvenile partial lower dentition, we retained of A. meridionale does not differ substantially from the juve- the 51 characters suggested in Lihoreau and Ducrocq (2007) for nile dentition referred to from Elomeryx armatus Marsh, 1894b both taxa, A. acridens from the Toledo L. F. (Albright, 1999) and (SDSM 4084; Macdonald, 1956). However, compared with E. ar- A. meridionale, sp. nov., from Panama (Appendix 2 and Supple- matus (SDSM 4084), A. meridionale has a distinctly more re- mentary Data). The data matrix includes cranial and dental char- duced p1 and more selenodont lower molars, with no mesiolin- acters that are unordered and weighted equally. Characters not gual metacristid on the m1 (Macdonald, 1956:626). known for a taxon were coded as missing. Data were compiled in Mesquite version 2.72 (Maddison and Maddison, 2009) and the data set was analyzed under the parsimony criterion using the PHYLOGENETIC ANALYSIS ‘branch and bound’ algorithm of PAUP version 4.0b10 (Swof- To evaluate the phylogenetic relationships of Arretotherium ford, 2003) with zero-length branches not collapsed. The analysis meridionale, sp. nov., within a sample of Anthracotheriidae, we resulted in six equally most parsimonious trees (MPTs) with tree performed a cladistic analysis of 28 anthracotheriid taxa, with lengths of 120 steps, a consistency index (CI) of 0.583, a retention the most primitive anthracothere, Siamotherium krabiense Su- index (RI) of 0.829, and a homoplasy index (HI) of 0.414 (Fig. 7). teerthorn et al., 1988, as the outgroup (Lihoreau and Ducrocq, Despite the large amount of missing data for the upper den- Downloaded by [Yale University Library] at 06:42 05 March 2013 2007). Fifty-one dental and mandibular characters (Appendix 1) tition of A. meridionale, our results support the allocation of were scored and used in the analysis using a revised version of a A. meridionale, sp. nov., with Arretotherium (node 17) in the previously published matrix (Lihoreau and Ducrocq, 2007:table strict consensus tree (Fig. 7). This association is based on the 7.1). In our analysis (Appendix 2), Bothriogenys fraasi Schmidt, dimensions of the lower incisors (4[1]), on the presence of only 1913, Bothriodon velaunus von Meyer, 1832, Elomeryx crispus one postprotocrista (18[0]), and partially on the presence of a Gervais, 1849, and Elomeryx armatus Marsh, 1894b, are scored as mesial cusp in the lower premolars in A. acridens from the Toledo 1 (instead of 0) for character 20 (number of cristules issued from Bend L. F. (9[0]). Following our resulting topology, A. acridens the metaconule) and Libycosaurus petrocchii Bonarelli, 1947, is from the Great Plains, equivalent to A. acridens in Lihoreau and scored as 1 (instead of 2) for character 15, which only presents Ducrocq (2007), is consistently the sister taxon of A. acridens two states: three roots for P4 (0) and fused roots of P4 (1) (Li- from the Toledo Bend L. F. and A. meridionale. The Toledo Bend horeau, pers. comm., August, 2011). form of A. acridens falls out from the holotype of A. acridens The ingroup (Fig. 7) includes taxa classified in three anthra- (node 18) based on the relative dimension of the labial and lin- cotheriidae subfamilies: (1) Anthracotheriinae Leidy, 1869, is gual cusp on the lower molars (24[0]) and the presence of a strong represented by five species; (2) Microbunodontinae Lihoreau and laterally compressed upper canine (6[1]). Furthermore, A. merid- Ducroqc, 2007, is represented by four species; and (3) Bothri- ionale differs from both forms of A. acridens with the presence of odontinae is represented by 19 species. To assess the relation- a postentocristid not reaching the posthypocristid and leaving the ship between Arretotherium meridionale and A. acridens from longitudinal valley open (23[0]) and the reduction of one incisor the Toledo Bend L. F. (Albright, 1999), A. acridens from Texas (1[2]). was scored as a distinct taxon from A. acridens Douglass, 1901, Results from our analysis support A. meridionale as a bothri- reported by Lihoreau and Ducrocq (2007). We believe that the odontine attributable to the genus Arretotherium; Arretotherium inclusion of this Gulf Coast species in our preliminary analysis acridens from the Toledo Bend L. F. and A. meridionale as RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 429

FIGURE 7. Biogeographic distribution and hypothesized phylogenetic relationships (cal- culated in PAUP 4.0b10) of Anthracotheri- idae including Arretotherium meridionale,sp. nov., and A. acridens from the Toledo Bend L. F. (Albright, 1999). Data matrix includes 51 characters and 28 ingroup taxa; Siamoth- erium krabinese as the outgroup (modiﬁed from Lihoreau and Ducrocq, 2007). Pictured here is the strict consensus tree of the six most parsimonious trees resulted from the equally weighted Downloaded by [Yale University Library] at 06:42 05 March 2013 branch-and-bound search (tree length = 120; CI = 0.583, RI = 0.829, HI = 0.41). At each node (bold numbers), the supporting unam- biguous synapomorphies are 1, Antracotheri- idae (20[1]); 2, Anthracotheriinae (7[1], 19[1]); 3, (18[1], 25[1], 35[1]); 4, (36[1]); 5, (16[1], 34[1], 38[1]); 6, Microbunodontinae (5[1], 6[1], 33[1]); 7, (26[1], 27[1], 32[1], 39[1], 40[1]; 8, (20[0], 37[1]); 9, Bothriodontinae (6[2], 17[1], 23[1], 39[2]); 10, (26[1], 27[1]); 11, (1[2], 2[2], 3[1], 4[2], 14[1], 20[0], 28[1], 44[2]); 12, (17[2], 18[1], 29[1], 35[1]); 13, (4[1], 33[1]); 14, (6[0], 7[1], 8[3], 24[1], 38[2], 39[1]); 15, (12[1]); 16, (20[0], 45[1]); 17, (4[1], 18[0]); 18, (6[1], 24[0]); 19, (11[1], 14[1], 23[0], 35[0], 44[1]); 20, (13[1], 21[1]); 21, (41[1]); 22, (18[0], 28[1]); 23, (39[0]); 24, (17[3], 40[2]); 25, (1[1], 9[2], 10[1], 11[2], 30[1], 31[1], 42[1], 49[1]. 430 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 33, NO. 2, 2013

sister taxa with a common ancestor shared with A. acridens from of A. meridionale, allowing us to better address some of these the Great Plains. Our results also suggest that Elomeryx Marsh, remaining questions. 1894b (probably E. armatus, the American species), is the sister taxon of Arretotherium, and therefore sister taxon of the ACKNOWLEDGMENTS other more derived American bothriodontines (Arretotherium and probably Kukusepasutanka). However, the resolution of our We thank J. Bourque at FLMNH, who prepared the speci- analysis was not clear enough to clarify the relationship between mens in the laboratory; J. Schiebout and S. Ting at the Louisiana the more primitive American anthracotheres (Aepinacodon and State University Department of Geology for access to relevant Bothriodon). research collections; M. Warren at C.A. Pound Human Identi- ﬁcation Laboratory (University of Florida) for access to the X- ray equipment; C. Montes, S. Suarez, M. Vallejo, and F. Moreno DISCUSSION AND CONCLUSIONS (STRI) who helped in the collection of the specimens; R. Hulbert Arretotherium meridionale, sp. nov., represents the southern- Jr. for help with anatomical terminology and taxonomic nomen- most occurrence of Anthracotheriidae in the New World. The clature; F. Lihoreau and B. Shockey for help with the phyloge- inferred early Miocene (late Arikareean) age for the Las Cas- netic character matrix; and C. Manz, L. Oviedo, K. Cummings, cadas fossil assemblage (Kirby et al., 2008; Montes et al., 2012; E. Woodruff, F. Herrera, A. Hastings, and J. Pardo, who edited Rincon et al., 2012) places A. meridionale as one of the last an- an earlier version of the manuscript and made helpful com- thracotheres reported in North America and the only occurrence ments for its improvement. We thank the Panama Canal Author- of the family in Central America (Fig. 1). Although its relation- ity (ACP) and the Ministerio de Comercio e Industria (MICI) ship with other American bothriodontines is still unresolved, re- for assess to relevant fossil sites. This research was supported sults from our cladistic analysis suggest a relationship with A. by University of Florida Research Opportunity Grant; the U.S. acridens from The Toledo Bend L. F. These tropical to subtropi- National Science Foundation Partnerships in International Re- cal forms share several plesiomorphic characters with coeval an- search and Education grant 0966884 (OISE, EAR, DRL), EAR thracotheres from different continents, such as Merycopotamus 0824299, and EAR 0418042; STRI-Tupper Paleontological Fund; Falconer and Cautley, 1847, from the middle to late Miocene STRI-Panama Canal Authority Fund; and Ricardo Perez Toyota, of Asia (Douglass, 1901; Troxell, 1921; Scott, 1940), Brachyudus Panama. This is a University of Florida Contribution to Paleobi- Deperet, 1895, from the early Miocene of Eurasia, and Liby- ology number 643. cosaurus from the late Miocene of Libya. In addition, some plesiomorphic characters in the lower dentition are also present in A. LITERATURE CITED meridionale and Elomeryx. These characters include (1) canini- Albright, L. B., III. 1998. The Arikareean Land Mammal Age in Texas form upper incisors; (2) the presence of a partially reduced mesi- and Florida: southern extension of the Great Plains and Gulf olingual entocristid that diverges from the preentocristid; (3) a Coastal Plain endemism; pp. 167–183 in D. O. Terry Jr., H. E. relatively enlarged prehypocristid that does not reach the lingual LaGarry, and R. M. Hunt Jr. (eds.), Depositional Environments, margin of the lower molars; (4) a shallow junction between the Lithostratigraphy, and Biostratigraphy of the White River and postmetacristid and the postprotocristid, and (5) similar trans- Arikaree Groups (Late Eocene to Early Miocene, North America). Geological Society of America Special Paper 325. verse widths of the labial and lingual cusps. In fact, A. meridionale Albright, L. B., III. 1999. Ungulates of the Toledo Bend Local Fauna seems to be less derived than other early Miocene forms, which (late Arikareean, early Miocene), Texas Coastal Plain. Bulletin of are characterized by more conical inner posterior cusps on the the Florida Museum of Natural History 42:1–80. lower molars, as well as the disappearance of the mesiolingual en- Albright, L. B., III, M. Woodburne, T. Fremd, C. Swisher, B. J. tocristid by the middle to late Arikareean (e.g., A. acridens from MacFadden, and G. R. Scott. 2008. Revised chronostratigraphy and the Toledo Bend L. F.). biostratigraphy of the John Day Formation (Turtle Cove and Kim- The differences in morphology and geographic distribution berly Members), Oregon, with implications for updated calibration during the late Arikareean early Hemingfordian (Fig. 1) between of the Arikareean North American Land Mammal Age. Journal of A. meridionale and similarly aged A. fricki suggest that the two Geology 116:211–327. Aymard, A. 1846. Essai monographique sur un nouveau genre de mam- species occupied two separate ecosystems during the earliest mifere´ fossile trouve´ dans la Haute-Loire, et nomme´ Entelodon, Miocene. A. acridens fron the Toledo Bend L. F. and A. merid- Annales de la Societe´ d’Agriculture, Sciences, Arts et Commerce

Downloaded by [Yale University Library] at 06:42 05 March 2013 ionale occupied a distinctive biogeographic area connecting the du Puy 12:227–267. Gulf Coast with southern Central America (Albright, 1998, 1999; Boisserie, J. R., and F. Lihoreau. 2006. Emergence of Hippopotamidae: Kirby and MacFadden, 2005), whereas A. fricki was restricted new scenarios. Comptes Rendus Palevol 5:749–756. to more temperate and open habitats in the northern and central Boisserie, J. R., R. E. Fisher, F. Lihoreau, and E. M. Weston. 2011. Great Plains (Stromberg,¨ 2002, 2006). We also note that there Evolving between land and water: key questions on the emer- is a remarkable difference in the dimensions of the molars in gence and history of the Hippopotamidae (Hippopotamoidea, the later forms of Arretotherium. The Hemingfordian A. fricki Cetancodonta, Cetartiodactyla). Biological Reviews 86:601–625. doi: 10.1111/j.1469-185X.2010.00162.x. from the Great Plains is relatively smaller than A. acridens from Boisserie, J. R., F. Lihoreau, M. Orliac, R. E. Fisher, E. M. Weston, and Montana (Douglass, 1901) and A. acridens from the Toledo Bend S. Ducrocq. 2010. Morphology and phylogenetic relationships of L. F. (Albright, 1999), whereas A. meridionale seems to indicate the earliest known hippopotamids (Cetartiodactyla, Hippopotami- an increase in overall body size (Table 2). This interpretation dae, Kenyapotaminae). Zoological Journal of the Linnean Society should be reevaluated in the light of more complete material 158:325–366. to avoid possible bias due to sexually dimorphic morphologies. Bonarelli, G. 1947. Dinosauro fossile del Sahahra Cirenaico. Rivista Bio- It is also possible that the morphological differences in A. logica Colonial Roma 8:23–33. meridionale could be explained by insular isolation (Eisenberg, Coombs, M. C., and W. P. Coombs. 1977. Dentition of Gobiohyus and a 1981; Gould and MacFadden, 2004) in Panama due to a rapid revaluation of the Helohyidae (Artiodactyla). Journal of Mammal- ogy 58:291–308. emergence of new tropical volcanic terrains (Las Cascadas Deperet,´ C. 1895. Uber¨ die Fauna von miocanen¨ Wirbelthieren aus Formation) and rapid changes in the relative sea level during the der ersten Mediterranstufe von Eggenburg. Sitzungsberichten der late Oligocene–earliest Miocene (Zachos et al., 2001). It is our Osterreiche¨ Akademie der Wisssenschaften 4:395–416. hope that ongoing excavation associated with the expansion of Douglass, E. 1901. Fossil Mammalia of the White River Beds of Mon- the Panama Canal and continued ﬁeld activities in the Gaillard tana. Transactions of the American Philosophical Society, New Se- Cut will reveal new fossil material and add to our knowledge ries, 20:237–279. RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 431

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Tedford, R. H., M. F. Skinner, R. W. Fields, J. M. Rensberger, D. (13) p1 roots: one (0); two (1). P. Whistler, T. Galusha, B. E. Taylor, J. R. Macdonald, and (14) Mesial crests on P1–P3: one (0); two (1). S. D. Webb. 1987. Faunal succession and biochronology of the (15) Number of P4 roots: three (0); two (1); one (2). Arikareean through Hemphillian interval (Late Oligocene through (16) Accessory cusp on distolingual margin of P3: one (0); none Earliest Pliocene Epochs) in North America; pp. 153–210 in M. O. (1). Woodburne (ed.), Cenozoic Mammals of North America. Univer- sity of California Press, Berkeley, California. (17) Upper molar mesostyle; simple (0); V-shaped and invaded Tedford, R. H., L. B. Albright III, A. D. Barnosky, I. Ferrusquia- by a transversal valley (1); loop-like (2); divided into two Villafranca, R. M. Hunt Jr., J. E. Storer, C. C. Swisher III, M. (3). R. Voorhies, S. D. Webb, and D. P. Whistler. 2004. Mammalian (18) Number postprotocristae: one (0), two (1). biochronology of the Arikareean through Hemphillian interval (19) Accessory cusp on upper molar mesial cingulum: no (0); yes (late Oligocene through early Pliocene epochs); pp. 169–231 in (1). M. O. Woodburne (ed.), Late Cretaceous and Cenozoic Mammals (20) Number of cristules issued from the metaconule: two (0); of North America: Biostratigraphy and Geochronology. Columbia three (1). University Press, New York. (21) Preprotocristids and prehypocristids on lower molars: do Troxell, E. L., 1921. The American bothriodonts. American Journal of Science 3:325–339. not reach the lingual margin of the tooth (0); reach the lin- Uhen, M. D., A. G. Coates, C. A. Jaramillo, C. Montes, C. Pimiento, gual margin (1). A. Rincon, N. Strong, and J. Velez-Juarbe. 2010. Marine mammals (22) Hypoconulid on m3: loop-like (0); single cusp (1). from the Miocene of Panama. Journal of South American Earth Sci- (23) Postentocristid on lower molars: does not reach the ences 30:167–175. posthypocristid and leaves the ling. valley open (0); reaches Whitmore, F. C., and R. H. Stewart. 1965. Miocene mammals and Central the posthypocristid and closes the long valley (1). American seaways. Science 148:180–185. (24) Dimension of the lingual and labial cusps: equal (0); differ- Woodring, W. P. 1957. Geology and paleontology of Canal Zone and ent (1). State (1): labial cusps twice as large at their basis as adjoining parts of Panama; description of Tertiary mollusks; gas- the lingual cusp. tropods; Trochidae to Turritellidae. US Geological Survey Profes- sional Paper 306-A:1–239. (25) Entoconulid on m3: absent (0); present (1). Woodring, W. P. 1982. Geology and paleontology of Canal Zone and ad- (26) Number of cristids issued to from the hypoconulid: three joining parts of Panama; description of Tertiary mollusks; pelecy- (0); two (1). pods, Propeamussiidae to Cuspidariidae; additions to families cov- (27) Position of the preentocristid on lower molars: reaches the ered in P306-E; additions to gastropods; cephalopods. US Geologi- hypoconid summit (0); reached the prehypocristid (1). cal Survey Professional Paper 306-7:541–759. (28) Premetacristid on lower molars: present (0); absent (1). Woodring, W. P., and T. F. Thompson. 1949. Tertiary formations of (29) Mesial part of looplike hypoconulid: open (0); pinched (1). Panama Canal Zone and adjoining parts of Panama. American As- (30) Entoconid fold on lower molars: absent (0); present (1). sociation of Petroleum Geologists Bulletin 33:223–247. (31) Ventral vascular groove on mandible: slightly marked (0); Zachos, J. C., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. absent (1); strongly marked (2). Science 292:686–693. (32) Morphology of mandibular symphysis cross-section: ‘U’- shaped (0); ‘V’-shaped (1). Submitted October 22, 2011; revisions received June 19, 2012; (33) Transverse constriction of mandible at Cp1 diastema: no accepted August 4, 2012. (0); yes (1). Handling editor: Jessica Theodor. (34) Cp1 diastema: absent (0); present (1). (35) p1-p2 diastema: absent (0); present (1). (36) Lateral mandibular tuberosity: absent (0); present (1). APPENDIX 1. Description of dental characters used in the (37) Dentary bone fussion at the symphysis: no (0); yes (1). phylogenetic analysis. All characters are treated as unordered. (38) Morphology of the symphysis is sagittal section: elliptic (0); Modiﬁed from Lihoreau and Ducrocq (2007). dorsally concave (1); ventrally concave (2). (1) Lower incisors: three (0); from two to three (1); two (2). (39) Maximal thickness of the symphysis in sagittal section: in (2) Upper incisors: three of equal size (0); three with i3 reduced the middle part (0); in the anterior part (1); in the posterior (60% or less) (1); two (2). part (2). (3) Lower incisor morphology: not caniniform (0); at least one (40) Number and position of main external mandibular foram- Downloaded by [Yale University Library] at 06:42 05 March 2013 caniniform (1). ina: only one foramen, below the anterior part of the pre- (4) Relative dimension of lower incisors: all equal size (0); i2 molar row (0); two foramina, one below the anterior part of larger (1); i3 larger (2). the premolar row, the other below its posterior part (1); one (5) Wear on lower canine: distal wear facet caused by the con- foramen, below the posterior part of the premolar row (2). tact with upper C (0); mesial wear facet cause by contact (41) Tuberosity on the dorsal border of the mandible at c–p1 di- with I3 (1). astema: no (0); yes (1). (6) Upper canine morphology: strong with subcircular cross- (42) Palatine depression between the canines: no (0); yes (1). section (0); strong and laterally compressed (1); premolari- (43) Canine fossa: short (0); long (1). form (2). (44) Aperture of the main palatine foramen: between M3 and (7) Lower canine in males: premolariform (0); large (1); ever- P3; between P2 and P1 (1); between P1 and C. growing (2). (45) Morphology of the frontonasal suture: V-shaped (0); (8) Lower canine cross-section at cervix: subcircular (0); ellipti- rounded or straight (1). cal with rounded mesial margin and distal keel (1); elliptical (46) Lachrymal extension: separated from the nasal by the with a mesial and distal crest (2); elliptical with a concave frontal (0); in contact with the nasal (1). buccal margin and a distal keel (3). (47) Supraorbital foramina on the frontal: one (0); several (1). (9) Accessory cusps on the mesial crest of lower premolars: (48) Facial crest: horizontal (0); oblique (1). none (0); only one (1); several (2). (49) Anterior border of premaxillary in lateral view: concave (0); (10) Presence of ﬁve upper premolars: no (0); yes (1). convex (1). (11) Distolabial crest on upper premolars: simple (0); with a (50) Postglenoid foramen position: posterior to the styloid pro- maximum of two accessory cusps (1); with more than two cess of the tympanic bulla (0); anterior to the styloid process (2). of the tympanic bulla (1). (12) Accessory cusp on p4: no (0); yes (1). (51) Opening of internal choanes: at M3 (0); behind M3 (1). RINCON ET AL.—NEW EARLY MIOCENE ANTHRACOTHERE FROM PANAMA 433

APPENDIX 2. Character-taxon matrix used in the phylogenetic analyses of Anthracotheriidae. See Appendix 1 for character descriptions. 10 20 30 40 50 S. krabiense 000??00?00000000000000000000000000000000000?00?00?0 M. minimun 000011010000000100000000011000011100111100001000000 M. silistrensis 0?001?0100000?010000000001100001110011110?????????? A. magnum 00000010000000?00111000010000000001110010000????0?0 A. mosvialense 00000010000000?001110000100000000011100?0000???00?0 A. chaimanei 0?00?0?00000?0?001110000100000000?10?00?00000?00??0 A. pangan ???0?01?0?00000001110000100000???0?00???0?????????? A. thailandicus 0?001?01000000?10001000001100001110001110?000?0???0 A. ulnifer 000011010000000101010000000000001110010000000000000 H. occidentalis 0?0000140000000000110010000000?00000100?000000000?0 B. fraasi 00??0202000000?110010010000000000100012000?00?000?1 B. aequatorialis 22120202000001?110000010011100000100112000020000001 B. onoideus 22120202000001?110000010011100000100112000020??0001 A. americanus 0001020200000001210000100110100011101120000000000?0 B. velaunus 0001020200000001210100100110100011101120000?0000000 E. crispus 000000130001000121010011011010000110021000000000001 E. armatus 000000130000000121010011011010000110021000000000001 E. borbonicus 00000013100100012100001101101000011002100000??000?? A. acridens 00010013000000?120000011011010000110021000001?1?001 A. zelteni 10000013101101?121000001011010000100021100?11?1?0?1 S. palaeindicus 0?000?13101111012100100101101000010002111?????????? H. blandfordi ??0???132??11???2200100101101000010002101?????????? M. pusillus 000000131011110120001001011110000100020000110111011 M. dissimilis 000000231011110130001101011111200100020200111111011 M. medioximus 000000131011110130001001011110000100020200111111011 L. anisae 1?00001321211111200010010111111001000211011????11?1 L. petrocchii 110000132121112120001101011111100100021101121111111 A. acridens(TBend) 0?0101100?0100113000001011101?0?011?0200??????????? A. meridionale 2?0??11?????0?????0?0?00???0??0??11?0210??????????? Downloaded by [Yale University Library] at 06:42 05 March 2013