Journal of Vertebrate Paleontology 34(2):444–464, March 2014 © 2014 by the Society of Vertebrate Paleontology

ARTICLE

FOSSIL OF THE WEST ATLANTIC AND CARIBBEAN REGION. IX. ALBIFONTANUM, SP. NOV.

∗ JORGE VELEZ-JUARBE´ ,1,† and DARYL P. DOMNING1,2 1Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A., [email protected]; 2Laboratory of Evolutionary Biology, Department of Anatomy, Howard University, Washington, D.C. 20059, U.S.A., [email protected]

ABSTRACT—We describe a new of the halitheriine dugongid Metaxytherium fromthelateOligoceneof Florida and South Carolina. The new species is represented by cranial and postcranial material, including parts of the axial and appendicular skeleton. Metaxytherium albifontanum, sp. nov., differs from other species of Metaxytherium by the follow- ing unique combination of plesiomorphic and derived characters: posterior end of nasal process of premaxilla broad and flat relative to what is observed in most other members of the genus (somewhat resembling M. subapenninum); ventral extremity of jugal under posterior edge of orbit (character 85[1]) (shared with M. krahuletzi); exoccipitals separated in dorsal midline (character 66[1]) (shared with all other species in the genus, except some M. krahuletzi); and innominate with acetabulum (nearly lost or lost in M. crataegense, M. floridanum, M. serresii). This new species was sympatric with two dugongines, Cre- natosiren olseni and Dioplotherium manigaulti. The small tusks and cranial morphology of M. albifontanum, sp. nov., indicate that it was likely a consumer of small seagrasses. Our phylogenetic analysis is consistent with previous ones in placing Hydro- damalinae within a paraphyletic Metaxytherium spp. and placing the Metaxytherium spp. + Hydrodamalinae clade as the sister group to Dugonginae. Metaxytherium albifontanum, sp. nov., is the oldest known member of its genus; this might indicate that the group originated in the West Atlantic and Caribbean region and later dispersed to the Old World Tethys region.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP.

INTRODUCTION Aguilera (2008), Bajpai et al. (2010), and/or Velez-Juarbe et al. (2012); e.g., (c. 6[0]) refers to state 0 of character 6; ChM Dugongid sirenians of the genus Metaxytherium are commonly PV, Charleston Museum, Charleston, South Carolina; M., mus- found in shallow marine deposits in the western At- cle; SC, South Carolina State Museum, Columbia, South Car- lantic, Caribbean, eastern Pacific, and Mediterranean regions olina; UF, Florida Museum of Natural History, University of (Domning, 1996; 2010, and references therein). The geochrono- Florida, Gainesville, Florida; USNM, Department of Paleobiol- logically oldest and most plesiomorphic species currently re- ogy, National Museum of Natural History, Smithsonian Institu- ferred to this genus is Metaxytherium krahuletzi Deperet,´ 1895, tion, Washington, D.C. from the early of the north Tethys and western and cen- tral Paratethys regions (Domning, 1994; Domning and Pervesler, 2001; Sorbi, 2008). This has led authors to the conclusion that the genus originated in the Tethys region (Domning and Pervesler, 2001; Sorbi, 2008). The subsequent appearance of members of SYSTEMATIC PALEONTOLOGY this genus in the late early Miocene of the Americas (Simpson, Class MAMMALIA Linnaeus, 1758

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 1932; Kellogg, 1966; Varona, 1972; Muizon and Domning, 1985; Order SIRENIA Illiger, 1811 Toledo and Domning, 1991) has seemed to support this view as Family Gray, 1821 well as call for an east-west trans-Atlantic dispersal of the group Subfamily HALITHERIINAE (Carus, 1868) Abel, 1913 (Domning, 1988). METAXYTHERIUM Christol, 1840 New material from the Oligocene of the West Atlantic and Caribbean region challenges these ideas. It is the aim of this pa- Metaxytherium Christol, 1840:323, September 24, 1840. per to describe some of this material, which represents a new Hesperosiren Simpson, 1932:426, September 6, 1932. species of Metaxytherium from the late Oligocene of the east (For additional synonyms based on Old World material, see coast of . The material described includes well- Domning, 1996, 2010). preserved cranial and postcranial material. This new species was sympatric, at least in part of its range, with two other dugongids, Type—Metaxytherium medium (Desmarest, 1822). Crenatosiren olseni (Reinhart, 1976) and Dioplotherium mani- Included Species—Metaxytherium arctodites Aranda-Manteca, gaulti Cope, 1883 (Domning, 1989a, 1989b, 1997; Velez-Juarbe Domning, and Barnes, 1994; Metaxytherium crataegense (Simp- et al., 2012). son, 1932) Aranda-Manteca, Domning, and Barnes, 1994; Abbreviations—c., character state as described and numbered Metaxytherium floridanum Hay, 1922; Metaxytherium krahuletzi by Domning (1994), Bajpai and Domning (1997), Domning and Deperet,´ 1895; Metaxytherium medium (Desmarest, 1822) Hooi- jer, 1952; Metaxytherium serresii (Gervais, 1847) Deperet,´ 1895; Metaxytherium subapenninum (Bruno, 1839) Fondi and Pacini, *Corresponding author. †Current address: Florida Museum of Natural 1974; Metaxytherium albifontanum Velez-Juarbe´ and Domning, History, University of Florida, Gainesville, Florida 32611, U.S.A. sp. nov. 444 VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 445

Range—Late Oligocene, southeastern United States; early- etabulum (nearly lost or lost in M. crataegense, M. floridanum, M. late Miocene, , North , North and , serresii). and Caribbean; , Europe and North Africa. Etymology—Latin albus = white + fontanus = of a spring; in Emended Diagnosis—Dugongidae based on loss of alisphe- reference to the type locality near White Springs, Florida. noid canal (c. 101[1]), loss of permanent premolar 5 (c. 146[1]), squamosal reaching temporal crest (c. 76[1]), and open foramen ovale (c. 103[1]). ‘Halitheriinae’ based on retention of the follow- DESCRIPTION ing plesiomorphies: nasal process of premaxilla thin and taper- ing (c. 6[0]); tusks small (c. 140[0]); frontal skull roof convex to Skull flat (c. 42[0]); and nasal incisure at posterior end of mesorostral Description of the skull is based on the holotype (UF 49051) fossa small or absent (c. 37[0]). Differs from most other halitheri- (Figs. 1–5, 7; Table 1), which is a subadult individual (based ines by loss of permanent premolars 1–4 (c. 157[2]), shared with on recently erupted M3 and unfused basioccipital/basisphenoid Caribosiren turneri Reinhart, 1959, and an undescribed early suture). Oligocene halitheriine (USNM 542417); supraorbital process of Premaxilla—An alveolus for a mediolaterally compressed frontal reduced (c. 36[1]); posterior part of zygomatic-orbital tusk, about 20 × 8 mm in diameter, extends much less than half bridge of maxilla usually elevated >1 cm above alveolar mar- the length of the symphyseal part of each premaxilla (c. 140[0]). gin (c. 11[1]); nasals separated in midline (c. 31[1]), shared with christolii Fitzinger, 1842, Caribosiren, and USNM 542417; supraoccipital wider ventrally than dorsally (c. 64[1]); ex- TABLE 1. Measurement of skulls (in mm) of Metaxytherium albi- occipitals usually not meeting along a midline suture above fora- fontanum sp. nov., following Domning (1978). men magnum (c. 66[1]); and ventral border of horizontal ramus of dentary strongly concave (c. 122[3]), shared with dugongines. Dimension UF 49051 METAXYTHERIUM ALBIFONTANUM, sp. nov. AB Condylobasal length 374e (Figs. 1–14; Tables 1–11) ab Height of jugal below orbit 39 AH Length of premaxillary symphysis 121 Metaxytherium sp., Velez-Juarbe et al., 2012:3, February 3, 2012. BI Rear of occipital condyles to anterior end of 230e interfrontal suture Holotype—UF 49051, subadult individual (based on recently CC’ Zygomatic breadth 179e erupted M3 and unfused basioccipital/basisphenoid suture); skull cc’ Breadth across exoccipitals 116 and mandible, ear bones, atlas, axis, cervicals 3–4 and 6, two de Top of supraoccipital to ventral side of occipital 102 condyles anterior thoracic vertebrae, and parts of 19 poorly preserved ribs. F Length of frontals—level of tips of supraorbital 138 Collected by G. Morgan, A. Pratt, R. Franz, and C. Puckett, processes to frontoparietal suture November 28, 1982 (photos of excavation shown in Domning, FF’ Breadth across supraorbital processes 115e 1989b:fig. 1). ff’ Breadth across occipital condyles 84 Type Locality—Suwannee River about 1100 feet upstream of GG’ Breadth of cranium at frontoparietal suture — the U.S. Highway 41 bridge, in the NE 1/4 SW 1/4 Sec. 8, T. 2 S, gg’ Width of foramen magnum 39 HI Length of mesorostral fossa 110e R. 16 E, White Springs East 7.5’ Quadrangle (1961), Columbia hi Height of foramen magnum 40 County, Florida, U.S.A. JJ’ Width of mesorostral fossa 48e Formation—Porters Landing Member, Parachucla Formation. KL Maximum height of rostrum 59 Age—Late Oligocene (Domning, 1997; Velez-Juarbe´ et al., LFr Length of interfrontal suture 120e 2012). MM’ Posterior breadth of rostral masticating surface 64 no Anteroposterior length of zygomatic-orbital — Referred Specimens—SC 89.115, subadult individual; den- bridge taries, cervical vertebrae 1–7, about 18 thoracic vertebrae, OP Length of zygomatic process of squamosal 120 15 right and 16 left ribs, left scapula, humerus, radius, OT Anterior tip of zygomatic process to rear edge of ulna, scaphoid-lunar-centrale, metacarpals ?III and IV, sternum squamosal below mastoid foramen (manubrium, intermediate sternebra, xiphisternum); collected P Length of parietals—frontoparietal suture to 75 from beds of the late Oligocene Chandler Bridge Formation, ex- rear of external occipital protuberance pq Length of row of tooth alveoli DP5 to M3 85 posed during the construction of Crowfield Plantation, Goose QR Anteroposterior length of root of zygomatic 54e Creek, Dorchester County, South Carolina, U.S.A. process of squamosal Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 ChM PV4757, young adult individual; skull fragments, Minimum width of skull roof between squamosal 55 mandible, scapula, humerus, radius-ulna, xiphisternum, verte- notches brae, ribs; collected from beds of the late Oligocene Chandler Maximum width of braincase at level of middle — Bridge Formation, exposed during excavation for a pillar of part of parietal-squamosal suture rr’ Maximum width between labial edges of left and 67e the Mark Clark Expressway, between Attaway Street and the right alveoli Seaboard Coast Line Railroad, Charleston County, South Car- ST Length of cranial portion of squamosal — olina, U.S.A. Collected by Alan and Jane Hopkins, 12 March ss’ Breadth across sigmoid ridges of squamosal — 1988. T’ Dorsoventral thickness of zygomatic orbital — Range—Known from the late Oligocene of southeastern bridge tt’ Anterior breadth of rostral masticating surface 30 United States. UV Height of posterior part of cranial portion of — Diagnosis—Small species of Metaxytherium (estimated body squamosal length 2–3 m), with the following unique combination of char- WX Dorsoventral breadth of zygomatic process 39 acter states among members of the genus: posterior end of nasal yy’ Maximum width between pterygoid processes — process of premaxilla broad and flat relative to what is observed YZ Length of jugal 152 in most other members of the genus (somewhat resembling M. HSo Height of supraoccipital 52 WSo Width of supraoccipital 75 subapenninum); ventral extremity of jugal under posterior edge RD Rostral deflection (degrees) 60e of orbit (c. 85[1]) (shared with M. krahuletzi); exoccipitals sepa- rated in dorsal midline (c. 66[1]) (shared with all other species in Abbreviations: e = estimate; l = left; r = right; +=measurement on the genus, except some M. krahuletzi); and innominate with ac- incomplete element. 446 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

FIGURE 1. Dorsal view of the holotype skull of Metaxytherium albifontanum, sp. nov. (UF 49051). Abbreviations: eo, exoccipitals; fr, frontal; j, jugal; mf, mastoid foramen; mx, maxilla; n, nasal; np, nasal process of the premaxilla; pmx, premaxilla; sop, supraorbital process of frontal; sq, squamosal; sr, sigmoid ridge; tc, temporal crest; zps, zygomatic process of squamosal. Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015

Each alveolus creates a slight bulge in the lateral surface of the posterior to its front end. The nasal process of the premaxilla bone. The dorsal and palatal sides of the rostrum are parallel in is mediolaterally broad and relatively flat posteriorly (Fig. 1), a lateral view except anteriorly, where the dorsal outline abruptly condition similar to that in Metaxytherium subapenninum (Sorbi becomes concave and then again convex at the tip of the snout et al., 2012), but scored as (c. 6[0]) because it does not approach (Fig. 3). The dorsal surface of the symphysis is slightly convex the more derived conditions observed in dugongines (e.g., Dio- posteriorly, broad and flat more anteriorly, and narrows forward plotherium manigaulti [Domning, 1989]). The part of it in con- to a keel less than 7 mm thick above the tusks (c. 10[1]). The tact with the lacrimal, nasal, and frontal extends less than half the incisive foramen lacks a well-defined anterior end. The nasopala- length of the mesorostral fossa. tine canal is slightly flattened dorsoventrally. The masticating sur- Nasal—The nasals are reduced (c. 32[1]); their dorsal exposure face of the rostrum is trapezoidal in outline and deeply concave is about 35 mm long and 20 mm wide, broad anteriorly and nar- (Fig. 2). Fractures and displacement of the bones prevent exact rowing posteriorly (Fig. 1). The nasals are separated in the mid- measurement of the rostral deflection, but it was approximately line by thin processes of the frontals (c. 31[1]), and together with 60◦. The anterior part of the mesorostral fossa is minimally con- these processes they form a dorsally convex arch. Anterolater- stricted by a pair of small (∼1 cm in length) bumps about 3 cm ally, the nasals are overlapped by the premaxillae. VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 447 Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015

FIGURE 2. Ventral view of the holotype skull of Metaxytherium albifontanum, sp. nov. (UF 49051). Abbreviations: as, alisphenoid; bo, basioccip- ital; bs, basisphenoid; dP, deciduous upper premolar; eo, exoccipital; fm, foramen magnum; hf, hypoglossal foramen/canal; if, incisive foramen; ioc, infraorbital canal; j, jugal; M, upper molars; mx, maxilla; oc, occipital condyle; pgp, postglenoid process; pl, palatine; pmx, premaxilla; pp, paroccipital process; pr, processus retroversus; pt, pterygoid; ptp, posttympanic process; sq, squamosal; tc, temporal condyle; zpj, zygomatic process of the jugal.

Ethmoidal Region—A large (of about the same height as blunt hook. The remainder of the nasal cavity is still filled with the nasal cavity) ethmoturbinal forms a thick vertical plate matrix. on either side of the dorsal part of the nasal cavity. Its ru- Vomer—Forms a delicate ‘V’-shaped trough as in other sireni- gose anterior end is about 2 cm high and 4 mm thick, and ans, and extends forward to about the middle of the mesorostral curves backward and inward ventrally as if to form a short, fossa. 448 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

FIGURE 3. Lateral view of the holotype skull of Metaxytherium albifontanum, sp. nov. (UF 49051). Abbreviations: as, alisphenoid; bo, basioccipital; eam, external auditory meatus; eo, exoccipital; fr, frontal; I, upper incisor; j, jugal; la,lacrimal;oc, occipital condyle; pa, parietal; pmx, premaxilla; M, upper molar; mf, mastoid foramen; mx, maxilla; pp, paroccipital process; pt, pterygoid; ptp, posttympanic process; sop, supraorbital process of frontal; sq, squamosal; sr, sigmoid ridge; zps, zygomatic process of squamosal. Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015

Lacrimal—A large (extending for more than half of the length bosses (c. 45[0]). The anterior border between the nasals is thin of the anterior orbital margin), somewhat crescentic bone mea- and broken but seems to have extended nearly the full length of suring 30 mm dorsoventrally and 15 mm anteroposteriorly; a na- the nasals, the nasal incisure thus being small or absent (c. 37[0]). solacrimal foramen is absent (c. 91[1]). It is in contact with the The anterior extremity of the frontoparietal suture lies about premaxilla anterodorsally (c. 93[1]), the maxilla anteriorly and 6 cm abaft the nasals. The temporal wall of the frontal is recessed medially, and the jugal anteroventrally (Figs. 1, 3). Its ventral end ventral to the crista orbitotemporalis, which is a smooth ridge, in- projects laterad as a low knob. distinct anteriorly, that extends posteroventrad from the supraor- Frontal—The supraorbital process has a blunt, rounded ante- bital process. The lamina orbitalis of the frontal, which forms this rior end, a poorly developed posterolateral corner (c. 36[1]), no recessed part of the wall, is thin (c. 38[0]) and extends forward division in its lateral margin (c. 44[0]), and no orbicular apophysis as a thin (<1 cm) plate to a level about 2 cm abaft the postero- (Figs. 1, 3). Its dorsal surface slopes laterally rather steeply, and lateral corner of the supraorbital process; its anterior border is is separated from the nearly horizontal frontal roof by a low but falciform. distinct temporal crest that extends straight forward across the Parietal—The cranial vault is nearly rectangular in frontal sec- base of the supraorbital process. The edges of the frontal roof do tion anteriorly. The roof is 13 mm thick in the anterior mid- not overhang. The central portion of the roof, including the in- line, and nearly flat; no sagittal crest is present (c. 51[1]) (Fig. ternasal processes, is gently convex (c. 42[0]) without knob-like 1). The posterolateral corner of the roof is slightly indented by VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 449

FIGURE 4. Posterior view of the holotype skull of Metaxytherium albifontanum, sp. nov. (UF 49051). Abbreviations: eo, exoccipital; eop, external occipital protuberance; fm, foramen magnum; oc, occipital condyle; pmx, premaxilla; pp, paroccipital process; scf, supracondylar fossa; so, supraoccip- ital; sq, squamosal; sr, sigmoid ridge; zps, zygomatic process of squamosal.

the squamosal. The temporal crests are low, barely rising above but the latter is shallow and lacks deep lateral pits. The anterior the level of the roof and confined to its lateral edges (temporal end of the bony falx is flattened and indistinct. crest type A [Domning, 1988]). Endocranially, the internal occip- Supraoccipital—Forms an angle of 112◦ with the posterior part ital protuberance is conical and extends well below the rest of the of the parietals. The external occipital protuberance does not internal surface. The tentorium and transverse sulcus are distinct, project above the parietal roof, and the median ridge below it

FIGURE 5. Bones of the ear region

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 of Metaxytherium albifontanum, sp. nov. (holotype, UF 49051). Terminology follows Robineau (1969). Left periotic in dorsal (A), medial (B), posterior (C), and ventral (D) views. Right tympanic in medial (E) and lateral (F) views. Left stapes in ventral view (G). Abbreviations: aa,anteriorarm; ap, apex; ar,areteˆ du rocher; cs, commisura suprafacialis; ef, endolymphatic foramen; ff, facial foramen; fmm, fossa muscularis minor; fo, foramen ovale; ft, fovea triangu- laris; gr, groove separating pars mastoidea from tegmen tympani; iaf, inferior acoustic foramen; la, lamella; pa, posterior arm; pc, pars cochlearis; pca, pars canalicularis; pi, pillar; pf, perilymphatic foramen; pm,pars mastoidea; pr, promontory; saf, superior acoustic foramen; sb, stapedial base; sf, stapedial foramen; sh, stapedial head; st, sulcus tympanicus; tt, tegmen tympani; tvp, attachment area for M. tensor veli palatini. 450 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

FIGURE 6. Mandibles of Metaxytherium albifontanum, sp. nov. Left ramus of holotype (UF 49051) in lateral (A) and medial (B)views.Left(C, D) and right (E, F) rami of SC 89.115 in lateral (C, E) and medial (D, F)views.Abbreviations: a, alveolus; an,angle;cc, coronoid canal; m, lower molar; Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 mc, mandibular condyle; mef, mental foramen; mnf, mandibular foramen; ms, mandibular symphysis.

is only moderately developed, reaching a thickness of only a few extends below the paramastoid process; its articular surface sub- millimeters (Fig. 4). The M. semispinalis insertions extend about tends an arc of about 120◦. halfway to the bone’s ventral border. The nuchal crest is dam- Basioccipital—Bears a pair of convex rugosities for the longus aged. The bone has a uniformly wide outline, without overhang- capitis muscles. It had not yet fused with the basisphenoid ing dorsolateral corners (c. 64[1]). (Fig. 2). Exoccipital—The exoccipitals are separated in the dorsal mid- Basisphenoid—The sella turcica is deeper than the surround- line by about 7 mm (c. 66[1]) (careful examination of the type ing dorsal surface of the bone, with a strong, posteriorly over- by both of us confirms that this region has been restored er- hanging tuberculum sellae. roneously in the holotype, giving the false impression that they Presphenoid—No elevated shelf (orbitosphenoidal crest) were joined); the foramen magnum has an acute dorsal peak and overhangs the chiasmatic grooves, nor are distinct grooves reaches the supraoccipital (Fig. 1). The dorsolateral border of the present. exoccipital is rounded and about 10 mm thick, without any pos- Orbitosphenoid—The optic foramen lies at the level of the teriorly projecting flange (c. 70[0]). The supracondylar fossa is dorsal side of the sphenorbital foramen. fairly deep and wide (c. 67[2]). The hypoglossal foramen is single Alisphenoid—The lateral side of the pterygoid process is and surrounded by bone (c. 72[0]) (Fig. 2). The occipital condyle ridged ventrally (Fig. 3). A smooth horizontal ridge continues VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 451

cheektooth row (Fig. 2). The edges border a moderately deep palatal gutter; each consists of a pair of ridges separated by a slight groove. Two canals open anteriorly into the palatal gutter at the level of the front of the tooth row. The palatal and ros- tral surfaces meet in a smooth curve. The posterior opening of the premaxillary canal on the side of the maxilla is about 6 mm in diameter. The zygomatic-orbital bridge was probably elevated 1 cm or less above the alveolar margin (11[0?]). The bridge is badly fragmented, but was some 4 cm long fore-and-aft (c. 14[0]), with a thin, sharp anterior and a thicker, rounded posterior edge (c. 22[0]) (Fig. 2). The infraorbital foramen is poorly preserved, but seems to have been large (c. 13[1]). The infraorbital canal is unobstructed (c. 20[0]). A thin (<5 mm) plate ascends from the dorsal side of the massive alveolar process, helping to form the wall of the temporal fossa; where it meets the lamina orbitalis of the frontal, a prominent, thin, horizontal shelf is formed. The edge of this shelf bears a groove for the optic nerve. Squamosal—The sigmoid ridge is prominent (projecting later- ally ∼1 cm), with a rugose surface, and almost semicircular in outline in posterior view (c. 74[2]) (Figs. 3, 4). The mastoid in- dentation is deep. The surface of the cranial portion dorsal to the zygomatic root is not inflated or bulging. The postglenoid pro- cess and postarticular fossa have well-defined edges. The tem- poral condyle is oval, with well-defined edges. The processus retroversus is not strongly turned in ventrally (c. 77[1]); it lacks distinct dorsal and ventral posterior terminations, in contrast to what is often observed in Metaxytherium floridanum (Domning, 1988). The zygomatic process is dorsoventrally narrow anteriorly and posteriorly, and broad in the middle; its posterodorsal edge is irregularly concave in outline and convex laterad; its medial surface is slightly concave (c. 84[0]). Its anterior portion has a sharper lateral than medial edge. The external auditory meatus is mediolaterally short (c. 75[1]) and about as high as it is wide (c. 82[1]). The posttympanic process projects anteroventally, bearing a facet for M. sternomastoideus (c. 73[0]) (Figs. 2, 3). The cranial portion of the squamosal reaches the temporal crest (c. 76[1]). Jugal—The preorbital process contacts the maxilla and lacrimal (c. 87[0]) and is relatively flat and thin (c. 88[0]) (Fig. 3). The ventral rim of the orbit does not overhang the lateral surface (c. 90[0]). The ventral-most point lies beneath or just anterior to FIGURE 7. Occlusal view of upper left cheek teeth (DP5–M3) of the rear edge of the orbit (c. 85[1]). This ventral tip is formed by Metaxytherium albifontanum, sp. nov. (holotype, UF 49051). Abbrevia- a rounded process somewhat distinct from, and displaced slightly tions: a, alveolus; ac, anterior cingulum; dP, deciduous upper premolar; lateral from, the border behind it. The latter is somewhat irregu- hy, hypocone; M, upper molar; mcl, metaconule; me, metacone; pa, para- larly ridged and beveled. The zygomatic process is long (c. 89[0]), cone; pc, posterior cingulum; pr, protocone; prl, protoconule; tv,trans- and tapers to a dorsoventrally flattened tongue that reaches the verse valley. level of the middle of the temporal condyle. Periotic—The lateral surfaces are smooth; no clear boundary exists between the pars temporalis (= tegmen tympani) and pars mastoidea; the anteroventral notch at the intersection of these

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 the forward edge of the zygomatic root anteriorly, overhanging two parts is semicircular, as in Metaxytherium floridanum (Fig. the anterior opening of the sphenorbital foramen. No alisphenoid 5A–D). The anteromedial end of the pars temporalis is pro- canal is present (c. 101[1]). longed, gradually tapering, and terminates in an abruptly down- Pterygoid—The pterygoid fossa is deep and broad, extending turned flange that appears to be curled laterally at its ventral above the roof of the internal nares (c. 102[1]); its lateral and edge. The raised area (processus fonticulus) on the posterolateral medial edges converge dorsally and intersect at a small protuber- surface of the pars mastoidea forms less of a triangular protuber- ance (Figs. 2, 3). The medial edge projects farther aft than the lat- ance than a sharp, thick, vertical ridge that is inserted into the eral edge. The ventromedial tip is formed by a thickened, smooth mastoid foramen. This ridge has a roughly semicircular outline trochlea (hamulus) for the M. tensor veli palatini tendon. in posterior view. The endolymphatic foramen is covered with Palatine—Forms the rounded anteromedial side and ventral sediment but seems to be narrow and slit-like. The cavity above tip of the pterygoid process. Dorsally it forms part of the lateral the aquaeductus vestibuli extends somewhat laterad over the me- wall of the internal naris, and anteriorly it reaches forward to the dial shelf of the pars temporalis. The medial outline of the pars level of the rear edge of the zygomatic-orbital bridge (c. 99[0]). petrosa bears two convexities, the posterior much larger; its edges The palatal incisure is very deep and narrow (c. 97[1]) (Fig. 2). are fairly thin and sharp. The dorsal side of the pars petrosa is The palatines appear to join anteriorly in a suture, which is at more or less flat; the ventral end of the promontory is bluntly most 1.5 cm in length. pointed. The fossa muscularis minor for the origin of M. stapedius Maxilla—The edges of the palatal surface are lyriform, or more is distinct. precisely, ‘mandolin-shaped’ sensu Kobayashi et al. (1995); i.e., Tympanic—Bulbous, with anterior and posterior borders curv- not pushed anterolaterad by a large tooth at the front of the ing somewhat irregularly towards a sharp ventral point (Fig. 5E, 452 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

F). The sides are smooth, without marked irregularities except for M. krahuletzi; Domning and Pervesler, 2001:pl. 5). The region of a rough protuberance on the anteromedial surface where the M. the mental foramen is mostly broken in both referred specimens, tensor veli palatini probably took its origin. A faint, laterally posi- but it appears that there were no accessory foramina (c. 123[1?]). tioned ridge may indicate the attachment of the posterior part of In the holotype and SC 89.115, the mandibular condyle is ellip- the tympanic membrane; no distinct sulcus tympanicus is present. tical in outline, its surface being convex to flat. In UF 49051, Malleus—Anteroposterior length = 13 mm. The posterior end the pterygoid fossa has a rugose surface and well-delineated pos- (orbicular apophysis) is slightly convex. The processus muscularis teroventral border. The posterior border of the dentary descends is moderately large, and forms a distinct nipple-like protrusion smoothly from the condyle, becoming broadly convex beginning on the medial side of the bone. The dorsolateral surface bears at the level of the tooth row (c. 125[2]). The anterior border of a rounded longitudinal ridge that does not connect with the ex- the ascending ramus is broken at the base in all specimens. The ternal edge of the manubrium; they are instead separated by a coronoid canal is oriented anterodorsally-posteroventrally, and broad, ‘U’-shaped valley. The external edge of the manubrium is the dental capsule is exposed posteroventrally (c. 127[1]). In the 15 mm long, delicate, and strongly convex. The articulations with referred specimens, the horizontal ramus is dorsoventrally broad the incus are not prepared. (c. 128[1]). Incus—Not prepared. Stapes—10 mm long, with a prominent stapedial foramen Dentition 1 mm in diameter located 4 mm above its base and close to the anterior side of the bone (Fig. 5G). The head end is flattened UF 49051(Figs. 2, 3, 7), a subadult individual, has a single anteroposteriorly, the basal end dorsoventrally. The basal end is empty alveolus, presumably for a root of DP4, at the front of the offset backward slightly; the basal facet is curved, its anterior part upper cheek tooth row. Four upper molariform teeth (DP5–M3), facing mediad, its posterior part more ventromediad. A groove each three-rooted, are still present on each side, although the first for the facial nerve is present. two are worn out and the last has not quite come into wear. The Mandible—In the holotype (Fig. 6A, B; Table 2), the alveo- adult upper dental formula would be I 1, C 0, DP 1 or 0, M 3 lar portion, coronoid process, and anterodorsal part of the sym- (c. 139[0]; 143[1]; 145[2]; 146[1]; 151[0]; 155[1]; 157[2]). In the re- physis are missing. The distance between its anterior and pos- ferred mandible (SC 89.115) (Figs. 7C–F, 8), a heavily worn m2 terior ventral extremities (dimension DF) is 123 mm; the height and a lightly worn m3 are present, as well as empty alveoli for of the ventral arch (dimension MN) is 41 mm. The ventral edge m1; hence, the adult mandibular dental formula is presumed to of the horizontal ramus is strongly concave in the holotype and be i 0, c 0, dp 1 or 0, m 3. The alveolar region in ChM PV4757 is in ChM PV4757 (c. 122[3]) (Figs. 6A, B, 14B). The mandible incompletely preserved. of the referred specimen (SC 89.115) (Fig. 6C–F) is unfused at I1—The overall length of the tusk is 42 mm. The root is medi- the symphysis. It is smaller than the holotype and ChM PV4757 olaterally compressed, 13 × 8 mm in diameter, closed, and ta- (Table 2). The symphyseal masticating surface is incompletely pers toward the end. The root is intermediate in shape between preserved in SC 89.115, but it seems to have been broad with a the two specimens of Metaxytherium floridanum illustrated by nearly rectangular outline, as it is in the other referred specimen Domning (1988:fig. 7); the posteroventral margin is uniformly (ChM PV4757) (c. 121[3]). In contrast to the holotype, the ven- convex; the apical end of the root curves slightly anterodorsad; tral border of the horizontal ramus of SC 89.115 is moderately closer to the crown, the anterodorsal margin of the root bears and evenly concave (c. 122[2]) (Fig. 6C–F); the degree of concav- a distinct hump. The enameled crown is distinct from the root ity thus may vary individually and/or increase with life age (cf. (c. 137[0]), virtually unworn, smooth, subconical, 11 mm high,

TABLE 2. Measurement of mandible (in mm) of Metaxytherium albifontanum sp. nov., following Domning (1978).

Dimension UF 49051 SC 89.115 ChM PV4757 AB Total length — 220+(l)/225+(r) 288 AG Anterior tip to front of ascending ramus — 161+(r) 220 AP Anterior tip to rear of principal mental foramen — 83+(r) — AQ Anterior tip to front of mandibular foramen — 138+(l) 200e AS Length of symphysis — 55+(l)/52+(r) 101 BG Posterior extremity to front of ascending ramus — 91(r) —

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 BQ Posterior extremity to front of mandibular foramen — 152+(r) 100e CD Height at coronoid process — — — DF Distance between anterior and posterior ventral 123 116(l)/117(r) 141e extremities DK Height at mandibular notch — 140(l)/138(r) — DL Height at condyle — 152(l)/151(r) — EF Height at deflection point of mandible — 101(l)/108(r) 152 EU Deflection point to rear of alveolar row — 91(l)/94(r) 99 GH Minimum anteroposterior breadth of ascending ramus — 64(l)/63(r) 81 GP Front of ascending ramus to rear of principal mental — 77(r) — foramen IJ Maximum anteroposterior breadth of dorsal part of —— — ascending ramus MN Top of ventral curvature of horizontal ramus to line 41 34(l)/35(r) 48 connecting ventral extremities MO Minimum dorsoventral breadth of horizontal ramus — 67(r) 77 RR’ Maximum breadth of masticating surface — 54e 67 SQ Rear of symphysis to front of mandibular foramen — 89(l) 110e WW’ Minimum width between angles — 71e — XX’ Minimum width between condyles — 116e —

Abbreviations: e, estimate; l, left; r,right.+=measurement on incomplete element. VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 453

TABLE 3. Measurements (in mm) of atlases of Metaxytherium albi- fontanum sp. nov. (based on Domning, 1978).

Dimension UF 49051 SC 89.115 External height 72 71 Internal height 43 44 Total breadth 117 112 Width between processes for transverse ligament 36 31 Width across anterior cotyles 90 78 Width across posterior cotyles 70 68 Length in dorsal midline 20 21 Length in ventral midline 20 16

tine exposed. Hypoconulid lophule composed of two cusps; buc- cal cusp larger and higher than lingual cusp; talonid basin widely open lingually. Anterior root like that of m2; posterior root larger and triangular in cross-section.

Vertebrae Cervical vertebrae 1–4, parts of ?C5–6, and at least two tho- racics are preserved in UF 49051. The preserved vertebral col- FIGURE 8. Occlusal view of lower right cheek teeth (m2, m3) of umn of SC 89.115 includes seven cervicals, 18 thoracics, three Metaxytherium albifontanum (referred specimen, SC 89.115). Abbre- lumbars, one sacral, and 13 caudals (Figs. 9, 10; Tables 3–5). viations: a.m1, alveoli for m1; co, crista oblique; end, entoconid; hld, Atlas—The upper arch has no articular surface for the axis. hypoconulid lophule; hyd, hypoconid; med, metaconid; prd, protoconid. The spine is low and blunt; on its anterodorsal surface, there are two depressions separated by a midline ridge, likely for insertion of M. rectus capitis dorsalis minor. The lower arch has a small posteroventrally directed triangular process. The articular sur- and 8.3 × 6.3 mm in diameter at its base, which is suboval in face for the odontoid process is round and well developed, but cross-section (c. 141[0]). Incipient wear facets are developed on its lateral and posterior borders are not well defined. The ante- each tusk at and just posteroventral to its tip. This suggests there rior cotyles are irregularly semilunar to kidney-shaped in outline, might have been a backward and downward movement of the with flaring dorsal, lateral, and ventral edges; two small rugosities tusk through the substrate while feeding, as inferred for other are present on the medial borders in UF 49051. The processes for sirenian taxa (Domning and Beatty, 2007). the transverse ligament are located on the lateral borders of the DP5, M1—Heavily worn, cusp patterns obliterated. DP5: neural canal at about the midlevel of the anterior cotyles. Dor- length = 13 mm; anterior width = 15.1 mm; posterior width = sal to the anterior cotyles the notches for the passage of the first 13.8 mm. M1: length = 16.0 mm; anterior width = 18.0 mm; pos- cervical nerve are open anteriorly. The transverse processes are terior width = 14.3 mm. thick and blunt, with rough tips, and directed posterolaterally; M2—Moderately worn; displays the cusp pattern typical of in UF 49051, there is a low protuberance on the ventromedial Metaxytherium in its most basic form, without accessory cuspules. surface on both sides, and together with the transverse processes A smooth precingulum is connected lingually to the protocone it forms a shallow notch that is absent in SC 89.115; transverse but also closely appressed buccally to the paracone, thereby con- processes of SC 89.115 are dorsoventrally thicker. There are no stricting or blocking the buccal end of the anterior cingular valley. vertebrarterial canals. The posterior cotyles are similar in out- The protoloph is straight. The transverse valley is open, impinged line to the anterior ones, but are smaller and less concave; in SC on only slightly by the centrally located metaconule. The meta- 89.115, the dorsal borders of the posterior cotyles have a squared- conule and hypocone have become confluent through wear, and off outline. are continuous with a smooth postcingular ridge that descends Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 buccally from the hypocone. The posterior cingular valley is open = = TABLE 4. Measurements (in mm) of axes of Metaxytherium albi- buccally. Length 21.7 mm; anterior width 19.2 mm; posterior fontanum sp. nov. (Measurements based on Domning, 1978). width = 16.7 mm. M3—Unworn; differs from M2 only in that the postcingulum Dimension UF 49051 SC 89.115 consists of two small cuspules rather than a smooth ridge, and the posterior cingular valley is occupied by a large cuspule. Length Total height 72+ 79 = 21.3 mm; anterior width = 17.6 mm; posterior width = 14.3 Length—tip of odontoid process to rear of 44 42 mm. centrum Breadth across cotyles 66 65 m2—Heavily worn, cusp patterns obliterated. Anterior and Breadth of cotyle 21 25(l)/21(r) posterior roots mesiodistally compressed and recurved. Height of cotyle 30 27 m3—Anterior interdental wear facet present; anterobuccal in- Posterior breadth of centrum 47 46 dentation on protolophid (‘vorderes Basalband’ of Abel, 1904) Posterior height of centrum 27 27 absent; protolophid crescentic in outline, metaconid and proto- Width of neural canal 28 28 conid worn, forming a continuous lake of dentine. Transverse Height of neural canal 28 29 Length of neural arch in midline 20 22 valley blocked by crista obliqua and hypoconid accessory cusp. Breadth across postzygapophyses 52 54 Hypolophid crescentic; hypoconid with large accessory cusp near center of tooth, both well worn, forming a confluent lake of den- Abbreviations: l, left; r,right;+, measurement taken on incomplete tine; entoconid smaller than hypoconid, tip worn with some den- specimen. 454 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

FIGURE 9. Cervical vertebrae of holotype (UF 49051) (A–G) and referred specimen (SC 89.115) (H–M)ofMetaxytherium albifontanum, sp. nov. Atlas in anterior, (A, H) and posterior (C, J) views. Axes in anterior (B, I), posterior (D, K), and right lateral (F, M) views. C3 and C4 in anterior (E, G) view. C7 in posterior (L)view.Abbreviations: ac, anterior cotyle; c,centrum;c1, notch for passage of cervical nerve 1; da, dorsal arch; fop, facet for odontoid process; ft, foramen transversarium; nc, neural canal; op, odontoid process; pc, posterior cotyle; pd, posterior demifacet; pozp, postzygapophysis; ptl, process for attachment of transverse ligament; tp, transverse process; va, ventral arch.

Axis—The odontoid process is circular in outline, ∼2 cm long, Thoracics—Only two anterior thoracics are preserved in UF with an irregularly pointed tip in UF 49051. On the ventral sur- 49051, of which only one is sufficiently preserved. The neural face of the odontoid process, near its base, there is an oval, flat spine slopes strongly aft; the outline of its summit forms a straight surface for articulation with the corresponding facet on the at- line parallel to the body axis. Anterior and posterior costal demi- las. The cotyles are triangular (SC 89.115) to kidney-shaped (UF facets are present; the anterior demifacets face anterolaterally, Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 49051) in outline, with well-demarcated borders; their articular the posterior demifacets face posterolaterally and are larger. surfaces are convex to nearly flat. The vertebrarterial canals are The transverse processes are robust and have ventrolaterally open laterally and are bounded dorsally and ventrally by short, directed tubercular facets. Anterior to the postzygapophyses laterally directed processes. The posterior surface of the cen- there are two mediolaterally elongate depressions that serve as trum is concave and kidney-shaped in outline. The pedicles are attachment sites for the ligamentum flavum. The postzygapophy- triangular in cross-section, with their lateral surfaces oriented ses are not separated from the laminae; therefore, they do not anteromedial-posterolateral. The neural canal is nearly square in project farther aft than the transverse processes. The epiphyses outline. The postzygapophyses are short and stout, with articular of the centra are not fused. surfaces oriented ventrolaterad. Medial to each postzygapophysis At least 18 thoracic vertebrae are present in SC 89.115 (Ta- is a small posteroventrad-oriented process, likely for attachment ble 5). With the exception of the first three and the last vertebrae, of the ligamentum flavum. The neural spine is incompletely pre- we are uncertain of their exact positions within the vertebral served on UF 49051; in SC 89.115, it is robust, rounded, with con- column; we have arranged them in as precise an order as possible vex anterior and dorsal surfaces and a flat posterior surface; no based on comparisons with Metaxytherium krahuletzi (Domning articular surface for the atlas is present on the neural spine; the and Pervesler, 2001) and jordani (Domning, 1978), and midline suture is unfused in SC 89.115. have assigned them letters a–l. Cervicals 3–7—The vertebrarterial canals on these cervicals In T1–3, the spinous processes are inclined aft; their centra are small, about 5 mm in diameter. The transverse process of ?C6 are subrectangular in outline. The prezygapophyses are antero- projects ventral to the centrum. posteriorly short, with their articular surfaces facing dorsally; the VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 455 Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015

FIGURE 10. Elements of the axial skeleton of referred specimen (SC 89.115) of Metaxytherium albifontanum, sp. nov. First right rib in anterior (A) and posterior (B) views. First thoracic vertebra in anterior (C) view. Middle thoracic vertebrae in anterior (D, F) and right lateral (E, G)views. Posterior thoracic vertebra in anterior (H) and right lateral (I) views. Last thoracic vertebra (T18) in anterior (J) and right lateral (K) views. Second lumbar (L), sacral (M), and second and ninth caudal (N, O) vertebrae, in anterior views. Lumbar (L1–3), sacral (S1) and caudal (Ca1–13) series in dorsal (P)view. 456 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

TABLE 5. Measurements (in mm) of thoracic, lumbar, sacral, and caudal vertebrae of Metaxyterium albifontanum sp. nov. (SC 89.115) (based on Domning 1978).

Vertebra TH BTP ABC PBC HC TC WNC HNC ML T1 — — — — — — — — 36 T2 134 — 40+ 40+ 31 27 34 32 40 Ta — 128 45e 54 32 33 30 27 — Tb 134 123 49 57 36 37 27 29 53 Tc — — 39+ 49+ 37 38 — — — Td — 111 52 61 38 42 28 32 55 Te 137 101 55 69 42 44 27 32 63 Tf 139 100 59 68 44 46 27 32 62 Tg 140 96 67 64+ 50 47 29 26 47 Th — 96 62 67 52 48 28 26 67 Ti 148 97 67 72 54 49 27 39 65 Tj 144 99 62 68 50 47 26 32 63 Tk 141 99 75 72+ 51 50 — 25 68 Tl — — 71 69+ 51 50 — 24 — T18 138 97 71 74 48 51 — 24 69 L1 131 260 67+ 82 48 51 35 22 69 L2 — — 71+ 78 47 52 — — — L3 — — 68+ 79 49 51 — — — S — — — 75 48 53 — — — Ca1 — 175 65 70 50 47 — — — Ca2 107 153 68 68 48 44 22 14 55 Ca3 — 136 64 66 47 44 — — — Ca4 108 119+ 64 65 47 43 — 15 53 Ca5 88+ —61624542181350 Ca6 69+ 91+ 60 63 44 41 17 15 — Ca7 — — 58 60 41 39 — — — Ca8 — — 55 60 43 40 16 — — Ca9 — 88+ 56 58 40 37 — — — Ca10 — — 57 52 37 36 13 — — Ca11 — — 52 48e 35 33 11 — — Ca12 — — 44 42 29 27 6 — — Ca13 — — 40 39 26 26 4 — —

Abbreviations: ABC, anterior breadth of centrum; BTP, breadth across transverse processes; HC, height of centrum; HNC, height of neural canal; ML, maximum length, front of prezygapophysis to rear of postzygapophysis; PBC, posterior breadth of centrum; TC, thickness of centrum in midline; TH, total height; WNC, width of neural canal; +, measurement taken on incomplete specimen.

postzygapophyses are not separated from the laminae and thus peak as in some of the anterior thoracics, but are more dorsoven- do not project posteriorly beyond the spinous processes, and their trally compressed overall. articular surfaces are oriented posteroventrally. In Ta–f (anterior Lumbars—Three lumbar vertebrae are present in SC 89.115. thoracics), the outlines of the centra are dorsoventrally flattened, The centrum of L1 has a ventral keel similar to posterior thoracic as in T2, but become more cardiform in outline posteriorly. vertebrae. The transverse processes extend slightly posteriorly Anterior and posterior costal demifacets are present, oriented and are nearly uniform in anteroposterior width with nearly anterolaterally and posterolaterally, respectively; demifacets are straight edges, tapering in their distal 3 cm. The distal ends of deep on the more anterior vertebrae, becoming shallow and the transverse processes of L1 are rugose and dorsoventrally nearly indistinct by Tf. The transverse processes are robust, with thickened. In L2, the neural spine is vertical, with its pos- tubercular facets oriented ventrolaterally. Their prezygapophy- terodorsal extremity thickened. The prezygapophyses are thick ses are anteroposteriorly short, with dorsally oriented articular surfaces in Ta and b, becoming more elongate with dorsome- Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 dially oriented articular surfaces on succeeding vertebrae. The postzygapophyses are anteroposteriorly elongated, with articular surfaces oriented ventrolaterally; anterior to the bases of the postzygapophyses there are semilunar depressions that served for the attachment of ligamenta flava. The spinous processes are nearly vertical with thickened ends; their anterior edges are sharp, and their posterior surfaces are concave with a midline ridge. The neural canals are nearly round in the more anterior thoracics, and become more acute dorsally in the more posterior ones. Posterior thoracics (Tg–l, T18?) are overall similar to anterior thoracics. Faint indications of posterior costal demifacets are still visible on Tg and h. The centra are more triangular in outline than in the anterior thoracics, mostly due to the presence of a ventral FIGURE 11. Sternum of referred specimen (SC 89.115) of keel. The transverse processes are shorter and less robust than in Metaxytherium albifontanum, sp. nov., in dorsal (A) and ventral anterior thoracics and are greatly reduced in what is interpreted (B)views.Abbreviations: cf, costal facet; m, manubrium; s, intermediate as the last thoracic (T18?). The costal facets on the transverse sternebra; sf, sternal foramen; ssc, surface for sternal cartilage; x, processes face laterally. The neural canals have an acute dorsal xiphisternum. VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 457

and robust, with articular surfaces oriented dorsomedially; the TABLE 6. Measurements (in mm) of sterna of Metaxytherium albi- postzygapophyses are more slender than the prezygapophyses fontanum sp. nov. (based on Domning, 1978). and have articular surfaces oriented ventrolaterally. The anterior surface of the lamina, at the base of the prezygapophysis, is Dimension SC 89.115 rugose and concave. The neural canal is wider than high, with Manubrium a slit-like dorsal peak. The ventral surface of the centrum is Length 104 keeled as in L1, but to a lesser degree; the posterior outline of Maximum breadth (at anterior rib 62 the centrum is hexagonal. The transverse processes are oriented articulation) laterally, constricted anteroposteriorly proximally, widening Breadth of anterior process near midline of its length towards midlength and tapering distally. The distal ends are Length of anterior process in midline similar to those of L1. The centrum of L3 has a hexagonal Posterior thickness 14 outline; its ventral surface is not keeled, being flat to concave Anteroposterior distance between rib 34(l)/29(r) overall. The transverse processes extend slightly posteriorly, articulations with their anterior and posterior edges sigmoidal when viewed SC 89.115 ChM PV4757 dorsally, being widest anteroposteriorly at about midlength; their Xiphisternum distal ends are as in the other lumbar vertebrae. Length 161 159+ Sacral—The centrum has a hexagonal outline, its ventral Minimum breadth 24 38 surface being concave as in L3. The transverse processes extend Maximum breadth posteriorly 49+ — laterally and ventrally, with distal ends lower than the ventral + surface of the centrum. The anterior edges of the transverse Abbreviations: l, left; r,right; , measured on incomplete specimen. processes are straight, the posterior edges are convex; the distal ends are rugose and expanded dorsoventrally, more so than in the lumbars. The expanded ends of the transverse processes likely served for ligamentous attachment to the ilia. whereas in ChM PV4757 only the xiphisternum is preserved. The Caudals—The neural spines are vertical in more anterior cau- anterior end of the manubrium is not preserved. The manubrium dals (Ca2), becoming more posteriorly oriented distally (Ca4, is flat, dorsally concave with a low, inconspicuous ventral keel. Ca6). The transverse processes are oriented laterally on the first The anterolateral surface bears a rugose, flat, elongate surface three caudals, and progressively become shorter and more poste- for the sternal cartilage. The costal facets for rib 1 are oval and riorly oriented caudally; by Ca9 the transverse processes extend oriented dorsolaterally; they are asymmetrically located on the beyond the posterior surface of the centrum. The transverse pro- manubrium, with the left one more anterior than the right. The cesses are dorsoventrally flattened up to Ca6, then become more posterior surface of the manubrium is subrectangular in outline triangular and almost rod-like in some of the more distal verte- with a rugose surface. The single intermediate sternebra is ir- brae. The centra are hexagonal in outline, with their ventral sur- regularly hexagonal in outline, dorsoventrally flat, and concave faces bearing two pairs, one anterior and one posterior, of demi- dorsally. The xiphisternum is straight overall, with convex dor- facets for the hemal arches; on each side the anterior and poste- sal and ventral surfaces. Anteriorly the xiphisternum is wide, be- rior demifacets are connected by a keel, with the surface between coming narrower posteriorly, then widening again where it bi- the keels being concave. The transverse processes on Ca12 and 13 furcates and becomes dorsoventrally flat. Only the left posterior seem to be more laterally oriented than the preceding ones, indi- extremity is completely preserved in SC 89.115; it is long and cating the presence of a -like fluke (Brandt, 1868:pl. 8, fig. bowed laterally, with a length of ∼6.5 cm; a foramen is present 4; Domning, 1978; Zalmout and Gingerich, 2012) (Fig. 10P). at about its midlength with a posteromedial-anterolateral orien- Ribs—Only the distal ends of 19 ribs are preserved in UF tation; a shallow groove on the dorsal surface is continuous with 49051. They are relatively slender, mediolaterally flattened, and the foramen. Both posterior extremities are incomplete in ChM pachyosteosclerotic; the largest has cross-sectional dimension of PV4757, but it seems to have been similar to the other referred about 41 × 22 mm. In SC 89.115, there are about 15 right and 16 specimen. left ribs preserved; however, except for R1, we are uncertain of Scapula—Not preserved in the holotype and poorly preserved their individual positions within the ribcage. in ChM PV4757; the description is based on the left scapula of SC R1—The capitulum and tuberculum lie dorsal to the neck 89.115 (Fig. 12; Table 7). The scapula is somewhat sickle-shaped, (Fig. 10). On the ventral surface of the neck there is a prominent with a broad supraspinous fossa and shallower infraspinous fossa. anteroventrally oriented process for M. longus capitis. The shaft Its medial surface is poorly preserved, anteroposteriorly convex

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 is subtriangular in cross-section, becoming flatter distal to the an- and dorsoventrally concave. The vertebral border is mostly bro- gle. A low ridge extends along most of the length of the posterior ken, but where preserved it is rugose for attachment of a scapu- surface of the shaft. The shaft is narrower at about midlength; lar cartilage. The spine of the scapula is not preserved. The an- anteriorly, just distal to this point, there is a protuberance for M. terior border of the blade is thinner than the posterior border. sternocostalis. The shaft tapers distally and turns inward; its end Posterodorsally on the lateral surface of the blade, a low crest forms an oval rugose surface for attachment of cartilage. marks the origin of M. teres major. The neck of the scapula is The ribs are pachyosteosclerotic; only a small amount of long and narrow with a broad suprascapular notch. The surface cancellous bone is present at proximal and distal ends. Two on the posterior edge of the neck is rugose, marking the origin of distinct facets can be observed on the capitulum in more anterior the long head of M. triceps brachii. The coracoid process is me- ribs, whereas only one facet is present in posterior ones. The dially inflected; its anteromedial surface is rugose, marking the distance between the capitulum and the tuberculum diminishes origin of M. coracobrachialis. The glenoid is oval in outline, with posteriorly, but these never merge. The shafts are elliptical in its anterior end narrower than the posterior; the articular surface cross-section; their distal ends taper and are turned inward and is concave, more so anteroposteriorly. posteriorly. Nearly all ribs have a large, oval depression for M. Humerus—Not preserved in the holotype; the description is iliocostalis on the lateral surface distal to the angle. based on the left humeri of SC 89.115 and ChM PV4757 (Figs. 12, Sternum—Not preserved in the holotype; the description is 14D; Table 8). The proximal epiphysis is detached, indicating based on the sterna of SC 89.115 and ChM PV4757 (Figs. 11, a young age for the specimens. The humerus is robust and 14C; Table 6). The sternum in SC 89.115 comprises three dumbbell-shaped; the shaft is triangular in cross-section. The parts: manubrium, an intermediate sternebra, and xiphisternum, greater tubercle extends farther proximal than the humeral head; 458 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014 Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 459

TABLE 7. Measurements (in mm) of left scapula of Metaxytherium alb- TABLE 8. Measurements (in mm) of left humerus of Metaxytherium ifontanum sp. nov. (SC 89.115) (based on Domning, 1978). albifontanum sp. nov. (SC 89.115) (based on Domning, 1978).

Maximum length 254+ Maximum length, greater tubercle to distal end 174 Mediolateral width of glenoid fossa 39 Maximum breadth, greater to lesser tubercle 67 Lateral border of glenoid to inside of distal end of spine 37e Maximum breadth, ectepicondyle to entepicondyle 57 Maximum breadth of blade dorsally 170 Maximum thickness, posterior side of head to 70 Minimum anteroposterior breadth of neck 40 anterior side of greater tubercle Maximum anteroposterior breadth of distal end 53 Maximum thickness, posterior to anterior ends of 22 Anteroposterior length of glenoid fossa 48 medial rim of trochlea Length of teres major origin 60e Mediolateral breadth of head 48 Proximodistal breadth of head 43 Abbreviations: e, estimated measurement; +, measurement based on in- Breadth of anterior side of trochlea 40 complete specimen. Length, saddle between head and greater tubercle 160 to saddle of trochlea

facets for the infra- and supraspinatus mm. on the greater tu- bercle are poorly defined. A flange of the greater tubercle ex- tends anteromedially over the bicipital groove, which is deep and coming triangular distally. Distally, there are two grooves on the narrow. The head is elliptical and oriented obliquely to the long lateral surface of the shaft. The first, on the posterolateral sur- axis of the shaft. A suboval rugose area on the posterolateral sur- face, is a shallow groove for the M. extensor pollicis tendon; the face of the head marks the origin for the lateral head of M. tri- second, on the anterolateral surface, is shallow, but broader than ceps brachii. The lesser tubercle does not rise above the humeral the other, and was likely for the M. extensor carpi radialis ten- head. The deltoid crest is prominent and recurved; distally, it is don. The distal epiphysis is partially unfused in ChM PV4757; the continuous with the deltopectoral crest, ending in an elongated, distal articular surfaces do not differ from those of other species shallow, pitted depression, which marks the insertion of M. pec- of Metaxytherium. toralis major. Distally, the trochlea is canted obliquely to the long axis of the shaft; a shallow circular notch subdivides the antero- Manus proximal surface. A shallow groove on the posterolateral corner of the trochlea marks the insertion of a humeroulnar ligament. Not preserved in the holotype; the description is based on pre- The olecranon fossa is deep, with well-defined borders; the coro- served elements of SC 89.115 (Fig. 12; Table 10), consisting of the noid fossa is shallow. The entepicondyle extends distally as far as left scaphoid-lunar-centrale and metacarpals ?III and IV. the trochlea. Scaphoid-Lunar-Centrale—The proximal articular surface is Radius-Ulna—Not preserved in the holotype; the description roughly hourglass-shaped; the posteromedial one-fourth of its is based on the left radii-ulnae of SC 89.115 and ChM PV4757 surface is concave, the rest being flat to convex. The anterior (Figs. 12, 14E; Table 9). The tip of the olecranon and the distal surface is convex. The posterior surface of the bone has a shal- epiphyses of the ulna and radius are not preserved in SC 89.115. low median convexity. The medial half of the posterior surface The radius and ulna are unfused proximally in SC 89.115, but has a suboval facet and the lateral half has a smaller mediolat- contact each other over a flat and rugose surface, which would erally elongated facet; these two facets are for articulation with have prevented pronation or supination; in ChM PV 4757, they the cuneiform-pisiform. The distal articular surface has two facets are fused proximally and unfused distally. The shafts are both for the trapezium-trapezoid-magnum; the anterior of these two nearly straight, only slightly bowed anteriorly, with little torsion facets is mediolaterally elongated, oval, and flat; the posterior one between them. The olecranon is deflected posteriorly ∼50◦ from is concave, triangular in outline, with its apex pointed anteriorly. the long axis of the shaft; the tip is oval in outline and rugose. An Metacarpal ?III—The proximal articular surface is nearly elongate shallow depression, ∼2.5 cm long, on the medial surface rectangular in outline; it has two articular surfaces, one of the olecranon posterior to the semilunar notch, possibly marks canted anteriorly and the other posteriorly, which are sep- the insertion of the long head of M. triceps brachii. An indenta- arated by a mediolaterally oriented ridge; the surfaces on tion on the lateral portion of the ulnar surface of the semilunar both facets are flat to slightly convex. Proximally, the notch marks the insertion of a humeroulnar ligament. The cross- anterior, medial, and posterior surfaces of the shaft are section of the ulnar shaft is triangular, distally becoming more rugose; the posteromedial corner has a raised knob. The lateral oval and elongated anteroposteriorly. A shallow groove for the surface of the shaft is flat, whereas its medial surface has a low Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 tendon of M. extensor digiti quinti is located distally on the lat- ridge that extends proximodistally, beginning from the anterome- eral surface of the ulna. The proximal end of the radius has a dial corner and going to the midline. The distal end of the shaft is concave, mediolaterally elongate surface that forms part of the oval in outline, with its long axis oriented anteroposteriorly. The semilunar notch. The radial tuberosity, located on the medial sur- distal epiphysis is not preserved. face about 2 cm distal to the proximal end, marks the insertion of Metacarpal IV—The proximal articular surface is trapezoidal M. brachialis. The shaft of the radius is oval in cross-section, be- in outline and its surface is mediolaterally convex. Proximally,

← FIGURE 12. Left forelimb of referred specimen (SC 89.115) of Metaxytherium albifontanum, sp. nov. Articulated bones in lateral view (A). Scapula in lateral view (B). Humerus in anterior (C), lateral (D), posterior (E), and medial (F) views. Radius and ulna in medial (G), lateral (H), and anterior (I) views. Scaphoid-lunar-centrale in proximal (J), distal (K), and posterior (L) views (anterior toward the top for J and K). Metacarpals ?III andIVinproximal(M, P), lateral (N, Q), and medial (O, R)views.Abbreviations: bg, bicipital groove; cp, coracoid process; dc, deltoid crest; dpc, deltopectoral crest; ecr.g, groove for tendon of M. extensor carpi radialis; edq.g, groove for tendon of M. extensor digiti quinti; en, entepicondyle; ep.g, groove for M. extensor pollicis; g, glenoid; gt, greater tubercle; h, head; hu, humerus; hul.n, notch for humero-ulnar ligament; inf.i, insertion for M. infraspinatus; isf, infraspinous fossa; lt, lesser tubercle; mc, metacarpal; o, olecranon; of, olecranon fossa; pma.i, insertion for M. pectoralis major; ra, radius; rf, radial fossa; rt, radial tuberosity; sc, scapula; sc.a, attachment area for scapular cartilage; slc, scaphoid-lunar-centrale; sln, semilunar notch; sn, suprascapular notch; ss, spine of scapula; ssf, supraspinous fossa; tm.o, origin for M. teres major; tr, trochea; trla.o, origin for lateral head of M. triceps brachii; trlo.i, insertion of long head of M. triceps brachii; ul,ulna. 460 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

TABLE 9. Measurements (in mm) of left radii and ulnae of Metaxytherium albifontanum sp. nov. (based on Domning, 1978).

Dimension SC 89.115 ChM PV4757 Total length of ulna 147+ 184 Total length of radius, anterior lip of 126+ 147 semilunar notch to distal end Height of semilunar notch, anterior tip 27e 24 of olecranon to anterior radial lip of notch Thickness of olecranon, anterior to 31+ 27 posterior side Distal thickness, anterior side of radius 58+ 59 to posterior side of ulna Maximum mediolateral breadth, radial 36+ 42 portion of semilunar notch Maximum mediolateral breadth, ulnar 30+ 34 portion of semilunar notch Minimum mediolateral breadth of 19 21 semilunar notch (at midsection) Minimum thickness of olecranon, 13 24 FIGURE 13. Lateral views of right (A)andleft(B) innominates of re- posterior side to semilunar notch ferred specimen (SC 89.115) of Metaxytherium albifontanum, sp. nov. Ab- breviations: ac, acetabulum;il, ilium; is, ischium; ist, ischial tuberosity; pu, Abbreviations: e, estimated measurement; +, measurement based on in- complete specimen. pubis.

the anterior, medial, and posterior surfaces of the shaft are ru- gose. The lateral surface of the shaft is flat and its medial sur- Halitherium christolii Fitzinger, 1842, and Metaxytherium sub- face is rounded. The distal end of the shaft is anteroposteriorly apenninum Bruno, 1839, and using Phosphatherium escuilliei expanded, subtriangular in outline with its apex posterior. The Gheerbrant et al., 1996, and Cornwallius sookensis (Corn- distal epiphysis is not preserved. wall, 1922) as outgroup taxa representing Proboscidea and Innominate—Not preserved in the holotype; the description is Desmostylia, respectively, for a total of 38 taxa. We chose Phos- based on the left and right innominates of SC 89.115 (Fig. 13; Ta- phatherium over Moeritherium (used in previous analyses, e.g., ble 11). The ilium is long and rod-like; the cross-section of the Domning, 1994) because it is now the basal-most proboscidean shaft is oval. The proximal end of the ilium is flat mediolater- for which good comparative cranial material is known; char- ally and expanded dorsoventrally, with its dorsomedial surface acter states were scored based on the description by Gheer- rugose but not forming an auricular surface. This rugose surface brant et al. (2005). We used Cornwallius as a representative was likely in contact with or, more likely, connected by ligaments of Desmostylia because it is one of the oldest members (late to the expanded end of the transverse process of the sacral verte- Oligocene) of the group that is known from good cranial material bra. An iliac spine is absent. The acetabulum is shallow, oriented (see Beatty, 2009). Character states for Cornwallius were scored posteroventrad, and oval in outline with no acetabular notch. The using Beatty (2009) and direct observations of the specimens re- surface medial to the acetabulum is concave. A short pubis seems ferred to in that publication. Character states for sirenians were to have been present, but this area is broken on both innomi- scored from direct observation of specimens by one or both of us. nates. The obturator foramen is absent. The ischium is medio- The characters and states used follow Domning (1994), Domning laterally flattened, with its distal end (ischial tuberosity) rugose et al. (1994), Bajpai and Domning (1997), Domning and Aguil- and thicker posteroventrally, giving it a triangular cross-section. era (2008), Bajpai et al. (2010), and Velez-Juarbe et al. (2012), ∼ ◦ The ischium forms an angle of 129 with the long axis of the with the addition of characters 21, 23, 76, 81, and 118 and mod- ilium. Based on the morphology of the innominate, it seems this ification of others for a total of 69 characters (Supplemental specimen was a male (cf. Domning, 1991; Zalmout and Gingerich, Data S1, S2). All characters were left as unordered. The ma- 2012). trix was analyzed with TNT (Goloboff et al., 2008a) by doing a traditional search using the tree bisection-reconnection (TBR) Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 PHYLOGENETIC ANALYSIS The choice of taxa used in the phylogenetic analysis fol- lows that of Velez-Juarbe et al. (2012), with the addition of TABLE 11. Measurements (in mm) of innominates of Metaxytherium albifontanum sp. nov. (SC 89.115) (based on Domning, 1978). TABLE 10. Measurements (in mm) of left manus elements of Metaxytherium albifontanum sp. nov. (SC 89.115) (based on Domning, Dimension Left Right 1978). Total length 190 191 Height, proximal end 27 27 Scaphoid-lunar-centrale Breadth, proximal end 13 12 Length (anteroposterior) 24 Minimum dorsoventral thickness, ilium 15 15 Breadth (mediolateral) 22 Minimum mediolateral thickness, ilium 11 11 Metacarpals III? IV Length, proximal end to acetabular area (center 108 108 Total length (proximodistal) 56+ 60+ of acetabulum) Length (anteroposterior), proximal end 15 17 Thickness at acetabular area 22 24 Breadth, proximal end 17 16 Maximum dorsoventral breadth, ischium 37+ 45 Length (anteroposterior), distal end 18+ 21+ Thickness, mediolateral, distal end 16 19 Breadth, distal end 14+ 13+ Length ilium (center of acetabulum to distal end) 89 91

Abbreviation: +, measured on incomplete element. Abbreviation: +, measurement on incomplete element. VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 461

algorithm with the following parameters: 1000 replicates and between the more basal M. krahuletzi and other species within keeping 10 trees per replicate. This was followed by an analysis the genus, despite its earlier geological age. using the implied weight method (Goloboff, 1993; Goloboff et al., The sternum gives a similar impression. M. krahuletzi and M. 2008b) set to K = 3.00. albifontanum (as well as M. arctodites) retain the tripartite condi- Results—The phylogenetic analysis resulted in 2205 most par- tion of the sternum seen in Halitherium schinzii (Lepsius, 1882:pl. simonious trees (MPTs), 185 steps long with consistency index 6, figs. 73–75; cf. Domning and Pervesler, 2001:pl. 14), whereas of (CI) = 0.5205 and retention index (RI) = 0.7578. The strict no other species of Metaxytherium for which the sternum is suf- consensus was 271 steps but had very poor resolution. Analyzing ficiently known (M. floridanum, M. medium, M. serresii, M. sub- those results using the implied weighting method resulted in one apenninum), nor any hydrodamaline, has been found to exhibit MPT, 187 steps long with CI = 0.5348 and RI = 0.7521 (Fig. 15). more than two separate elements, termed the manubrium and The topology of the tree is largely consistent with that of Velez-´ xiphisternum. A notable difference between M. krahuletzi and Juarbe et al. (2012). Some of the main differences are that (1) the M. albifontanum, however, is the latter’s greater width of the polytomies between an undescribed halitheriine (USNM 541417) manubrium relative to the posterior parts of the sternum. Three and Caribosiren turneri as well as that among the different species sterna of M. krahuletzi (a young adult and two mature adults) are of Metaxytherium have been resolved; and (2) Halitherium chris- quite uniform in their long, narrow shapes, with the manubrium tolii is no longer the sister taxon to the Metaxytherium spp. + Hy- not appreciably wider than the intermediate sternebra or the an- drodamalinae + Dugonginae clade (as in Domning, 1994). The terior part of the xiphisternum. None of these has the propor- position of Metaxytherium albifontanum among other species of tions seen in M. albifontanum. In the holotype of M. arctodites, Metaxytherium confirms its generic affinities. the manubrium (not yet published) is intermediate in shape, be- ing long relative to the rest of the sternum as in M. krahuletzi but expanded at its anterior end as in M. albifontanum. DISCUSSION Given the wide range of variation in sirenian sterna generally, Comparisons and the inadequate sampling of individual and ontogenetic vari- ability of this element in the taxa at issue, it would be prema- Among species of Metaxytherium, UF 49051 is most similar, in ture to conclude that these characters of the sternum are (or are size and overall morphology, to M. crataegense. However, M. alb- not) of phylogenetic value. The evidence suggests patterns that ifontanum retains the plesiomorphic condition of having the ven- are interesting, but too complex to decipher from the available tral extremity of the jugal under the posterior edge of the orbit data. (c. 85[1]), a characteristic that it shares with M. krahuletzi, more basal halitheriines, and some basal dugongines (Fig. 3). M. albi- Paleoecology fontanum differs from some M. krahuletzi by having exoccipitals that do not meet in a suture dorsal to the foramen magnum (c. Metaxytherium albifontanum lived sympatrically with Cre- 66[1]) (Fig. 4; this area has been partially reconstructed in the natosiren olseni and Dioplotherium manigaulti (Domning, 1989b; holotype, giving the false impression that they did), a derived Velez-Juarbe et al., 2012). These three species differed, most condition that is polymorphic in M. krahuletzi and present in all notably, in tusk size, which are hypothesized, together with other Metaxytherium, hydrodamalines, and some dugongines. In other cranial characters, to serve as proxies for their feed- this respect, UF 49051 seems to be a morphological intermediate ing preferences. Metaxytherium albifontanum with its small Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015

FIGURE 14. Cranial and postcranial elements of referred specimen (ChM PV4757) of Metaxytherium albifontanum, sp. nov. Left zygomatic process of the squamosal in lateral view (A). Mandible in left lateral view (B). Xiphisternum in dorsal view (C). Left humerus in posterior view (D). Left radius-ulna in lateral view (E). Abbreviations: an,angle;h, head; mef, mental foramen; o, olecranon process; of, olecranon fossa; sln, semilunar notch. 462 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 34, NO. 2, 2014

FIGURE 15. Single most parsimonious tree obtained using the implied weight method (Goloboff, 1993; Goloboff et al., 2008b) set to K = 3.00.

Downloaded by [Society of Vertebrate Paleontology ] at 09:07 17 April 2015 Length = 187 steps; CI = 0.5348; RI = 0.7521. Open circles identify node-based clades; arcs indicate stem-based taxa.

tusks was most likely less well suited for uprooting larger bosiren, although the right age, shows derived features not seen seagrasses than the other two species. A much more detailed de- in any of the later ‘halitheriines,’ such as extreme rostral de- scription of the paleoecology of Metaxytherium albifontanum was flection and possible loss of tusks. Previous assumptions for the recently published by Velez-Juarbe´ et al. (2012). origins of Metaxytherium have been in favor of either a Euro- pean origin from Halitherium christolii or a New World origin (Domning, 1994). Based on our results, we argue in favor of a Discussion West Atlantic–Caribbean origin for Metaxytherium around the The more basal position of Metaxytherium krahuletzi with late early Oligocene. However, the more basal position of M. respect to M. albifontanum (Fig. 15) indicates that the diver- krahuletzi likely points to a more complicated history in this gence between the two occurred prior to the late Oligocene. In- group. deed, the sister taxa to the Metaxytherium + Hydrodamalinae + Dugonginae clade include two early Oligocene taxa from Puerto ACKNOWLEDGMENTS Rico, an undescribed genus and species of halitheriine (USNM 542417), and Caribosiren turneri. Of these, USNM 542417 is We thank R. Hulbert and K. Auffenberg (FLMNH), J. Knight the most fitting, morphologically and chronologically, to be the and D. Cicimurri (SCSM), and A. Sanders (ChM) for access ancestor of the Metaxytherium + Hydrodamalinae clade. Cari- and loans of specimens under their care. J.V.J. was partially VELEZ-JUARBE´ AND DOMNING—METAXYTHERIUM ALBIFONTANUM (SIRENIA) 463

supported by the WBHR-LSAMP Bridge to the Doctorate Pro- Domning, D. P. 1994. A phylogenetic analysis of the Sirenia. Proceedings gram at Howard University, a predoctoral fellowship from the of the San Diego Society of Natural History 29:177–189. National Museum of Natural History, Smithsonian Institution, Domning, D. P. 1996. Bibliography and index of the Sirenia and and the Remington Kellogg Fund, Smithsonian Institution. On- Desmostylia. Smithsonian Contributions to Paleobiology 80:1– going work by D.P.D. and J.V.J. is supported by NSF Earth 611. Domning, D. P. 1997. Fossil Sirenia of the West Atlantic and Caribbean Sciences grant no. 0929117. We wish to thank N. D. Pyenson region. VI. Crenatosiren olseni (Reinhart, 1976). Journal of Verte- (USNM) for comments on the morphology of the specimens and brate Paleontology 17:397–412. guidance to J.V.J. during his fellowship at NMNH. Alan and Jane Domning, D. P. 2010. Bibliography and index of the Sirenia and Hopkins are gratefully acknowledged for the collecting of ChM Desmostylia. Available at www.sirenian.org/biblio/. Accessed De- PV4757. This work benefited from the comments and corrections cember 2012. of I. Zalmout (King Saud University, Riyadh, Saudi Arabia) and Domning, D. P., and O. A. Aguilera. 2008. Fossil Sirenia of the West At- an anonymous reviewer. lantic and Caribbean region. VIII. garciae, gen. et sp. nov. and Nanosiren sanchezi, sp. nov. Journal of Vertebrate Paleontology LITERATURE CITED 28:479–500. Domning, D. P., and B. L. Beatty. 2007. Use of tusks in feeding Abel, O. 1904. Die Sirenen der mediterranen Tertiarbildungen¨ Osterre-¨ by dugongid sirenians: observations and tests of hypotheses. The ichs. Abhandlungen der Geologischen Reichsanstalt 19:1–223. Anatomical Record 290:523–538. Abel, O. 1913. Die eocanen¨ Sirenen der Mittelmeerregion. Erster Domning, D. P., and P. Pervesler. 2001. 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