Journal of Vertebrate Paleontology 34(2):444–464, March 2014 © 2014 by the Society of Vertebrate Paleontology ARTICLE FOSSIL SIRENIA OF THE WEST ATLANTIC AND CARIBBEAN REGION. IX. METAXYTHERIUM 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 species of the halitheriine dugongid genus 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 Neogene 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 Miocene 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 DUGONGIDAE 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 North America. 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, Europe, North Africa, North and South America, serresii). and Caribbean; Pliocene, 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 Halitherium 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