from the Late Oligocene (Early Arikareean) of Florida

368

Chapter 15

New Oreodont (Mammalia, Artiodactyla) from theLate Oligocene (Early Arikareean) of Florida

BRUCE J. MACFADDEN1 AND GARY S. MORGAN2

ABSTRACT

Exceptionally well-preserved partial skeletal remains representing a minimum of six indi-viduals of an oreodont are described from the White Springs Local Fauna, Columbia County,northern Florida. Although oreodonts are very common from classic Oligocene and earlyMiocene deposits in the western United States, this group is poorly represented from Florida.The White Springs oreodont pertains to a new species, Mesoreodon floridensis, and is derived,particularly in the development of the auditory bulla, relative to more primitive, closely relatedspecies such as Merycoidodon culbertsoni, the latter of which is well known from the badlandsof the western United States. Mesoreodon floridensis differs from most other species assignedto this genus in the relative development of the nasal region, possible presence of a facialvacuity, configuration of the preorbital fossa, relatively simple occipital and zygomatic mor-phology, and imbricated premolar morphology. Based on the associated faunal remains andage determinations, M. floridensis is late early Arikareean (Ar2) in age, ca. 25–24 millionyears old, and occurs in an interval not well represented in the classic Arikareean sequenceof western Nebraska. A mounted skeleton of M. floridensis, on exhibition, is also described.

1 Research Associate, Division of Paleontology, American Museum of Natural History; Associate Director of Ex-hibits and Public Programs, Curator of Vertebrate Paleontology, Florida Museum of Natural History, University ofFlorida, Gainesville, FL 32611.

2 Curator of Vertebrate Paleontology, New Mexico Museum of Natural History, 1801 Mountain Road, Albuquerque,NM 87104.

INTRODUCTION

Oreodonts were very abundant and wide-spread throughout western North Americaduring the middle Cenozoic. Fossil oreodontremains, particularly from the badlands ofNebraska and South Dakota, are conservedin most U.S. natural history collections andtheir skeletons are widely exhibited. Thus,the discovery of a new oreodont from west-ern North America, even several individualswith associated and well-preserved skeletalmaterial, is unlikely to be considered impor-tant. On the other hand, the fossil record oforeodonts from the otherwise rich middleCenozoic sequence in Florida is heretoforeexceptionally poor.

Much of our perceived knowledge of or-eodont evolution comes from species that

lived during the earlier Oligocene, particu-larly as represented by the ubiquitous Mer-ycoidodon culbertsoni, a primitive and rela-tively unspecialized member of this group.Thereafter, however, oreodonts underwent anextensive adaptive radiation, and in the earlyMiocene (Arikareean-Hemingfordian) arerepresented by an array of morphologies, in-cluding a broad diversity of body sizes, withsome clades (Merychyus) becoming verysmall and others becoming very large (Mer-ycochoerus). The new Florida oreodont de-scribed here is from this part of the oreodontradiation. Oreodonts declined in diversity af-ter the early Miocene (Hemingfordian), andlate-surviving Clarendonian oreodonts (Us-tatochoerus, sensu lato) became high-crowned, rivaling the degree of hypsodonty

2003 369MACFADDEN AND MORGAN: NEW OREODONT FROM LATE OLIGOCENE

seen in other clades of middle Cenozoic un-gulates.

Since the late 1980s, a collection of rela-tively well-preserved oreodonts and associ-ated marine and terrestrial fossil vertebrateshas been made by the Florida Museum ofNatural History (FLMNH) from the WhiteSprings Local Fauna (Morgan, 1989), locat-ed in northern Florida. As of the end of 2000,the White Springs oreodonts consist of par-tial skeletons representing six individuals, in-cluding four skulls and five mandibles thatall pertain to the same taxon. The purpose ofthis paper is to describe this sample, whichrepresents a new species and includes a skel-etal reconstruction on exhibition, and to dis-cuss its biostratigraphic, morphological, andphylogenetic significance.

MATERIALS, METHODS,AND ABBREVIATIONS

The new Florida oreodont sample wascompared to relevant specimens housed inthe collections at the American Museum ofNatural History and University of Florida, inparticular, species within the subfamily Mer-ycoidodontinae (sensu Stevens and Stevens,1996), including the genera originally namedas, or currently allocated to, Eporeodon, Des-matochoerus, Merychyus, Merycoidodon,Mesoreodon, Paradesmatochoerus, Phena-cocoelus, and Pseudodesmatochoerus. Tocompare species, we used the 18 morpho-metric parameters presented in Stevens andStevens (1996). To these measurements, weadded the greatest skull length (GSL), widthof the nuchal crest (NUCW), and three mea-surements of the astragalus (fig. 15.1). Themeasurements were analyzed using Micro-soft Excel.

In some instances below we refer to cer-tain named taxa, for example, ‘‘Desmatocho-erus monroecreekensis’’ sensu Schulz andFalkenbach (1954), when we realize that sub-sequently these have been considered invalidjunior synonyms by workers such as Stevensand Stevens (1996). Nevertheless, we usethese previous names when discussing par-ticular morphologies, but do not imply thatthey are considered valid taxa in this study.

The following abbreviations are used inthe text:

INSTITUTIONS:

AMNH American Museum of Natural History,Division of Paleontology, New York

F:AM Frick American Mammals, part of theAMNH as above

UF Vertebrate Paleontology, Florida Mu-seum of Natural History, University ofFlorida, Gainesville

MORPHOLOGY:

AP or ap Upper or lower anteroposterior toothlength, respectively

I or i Upper or lower incisor, respectivelyL Left sideM or m Upper or lower molar, respectivelyP or p Upper or lower premolar, respectivelyR right sideT or t Upper or lower transverse tooth width,

respectively

Abbreviations for the cranial and dentalmeasurements, including those used by Ste-vens and Stevens (1996), are presented in ta-ble 15.2.

OTHER:

L.F. Local fauna, a geographically and strati-graphically restricted vertebrate assem-blage

Ma Megannum, in reference to millions ofyears on the geological time scale.

PREVIOUS STUDIES OFFLORIDA OREODONTS

Despite the existence of numerous sites ofsuitable age, oreodont remains are character-istically rare in the Oligocene and Mioceneof Florida. Patton (1969) presented a faunallist from the I-75 L.F., of probable Whitney-an age, that includes two oreodont taxa rep-resented by several poorly preserved toothfragments. Based on the quality of the spec-imens, it is currently impossible to assign amore specific identification to the I-75 or-eodonts. Also based on a few isolated teeth,Hayes (2000) reported the presence of or-eodonts from the early Arikareean Brooks-ville 2 L.F. in Hernando County, and Al-bright (1998) mentioned an oreodont fromthe early Arikareean Cowhouse Slough L.F.in Hillsborough County. Two late Arikareeanoreodont occurrences are known from Flor-ida, that is, a phenacocoeline, closest toPhenacocoelus stouti, from the Buda L.F.

370 NO. 279BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY

Fig. 15.1. Additional measurements used in this study. A, Cranial (using oreodont illustrations fromSchultz and Falkenbach, 1954): GSL, greatest skull length from anterior-most part of premaxillary toposterior-most part of nuchal crest; NUCW, greatest width of across the occipital region (nuchal crest).B, Astragalus: GRTL, greatest proximal-distal length; TWDTH, greatest transverse width; BRDTH,greatest breadth.

(Frailey, 1979) in Alachua County, and amaxilla of Phenacocoelus luskensis from amarine limestone at the Martin-Anthonyroadcut in Marion County (MacFadden,1980). Maglio (1966) described remains ofcf. Merychyus from the HemingfordianThomas Farm L.F. in Gilchrist County. Land-er (1998) noted the presence of an indeter-minate oreodont from the Hemingfordian(?)Shark Tooth Ravine site in Alachua County.Bryant (1991) described a RM3 of Ticholep-tus cf. T. hypsodus from the early BarstovianWillacoochee Creek Fauna, from GadsdenCounty in the Florida panhandle. With theexception of the maxilla described byMacFadden (1980), all of these oreodont oc-

currences are represented by isolated teeth,tooth fragments, and fragmentary isolatedpostcranial remains.

CIRCUMSTANCES OF CURRENTDISCOVERIES AND

GEOLOGICAL BACKGROUND

LOCALITIES

Daryl Domning and Gary Morgan begancollecting vertebrate fossils in 1981 fromnearshore marine sediments of the Parachu-cla Formation along the banks of the Suwan-nee River in northern Florida. They madeseveral collecting trips during most yearsthroughout the 1980s and early 1990s. The


original purpose of these trips was to pros-pect for sirenian fossils that are well knownfrom these strata (Reinhart, 1976; Domning,1989a, 1989b, 1997). A rich and varied ma-rine vertebrate fauna occurs in associationwith the fossil sirenians; however, from abiostratigraphic perspective, the most signif-icant aspect of the fauna from these beds isthe rare, but regular, occurrence of landmammals.

Morgan (1989) named the White SpringsL.F. for the latest Oligocene (early Arika-reean) vertebrate fauna recovered from sed-iments exposed along the banks of the Su-wannee River in the vicinity of WhiteSprings. The White Springs L.F. includesvertebrate fossils collected from the Parachu-cla Formation along about 10 km of the Su-wannee River. Most of the fossils referred tothe White Springs L.F. were derived fromthree sites, designated White Springs 1A, 3A,and 3B (Morgan, 1989). Precise locality in-formation for these sites is on file in the UFVertebrate Paleontology Collection.

The White Springs 1A and 3B sites haveproduced diverse faunas of nearshore marinevertebrates (sharks, rays, bony fish, marinecrocodiles, and sirenians), along with small,but important, samples of terrestrial mam-mals. White Springs 1A (UF locality CO48)extends for several hundred meters along theeast bank of the Suwannee River near WhiteSprings. This site has produced two taxa ofdugongid sirenians, including a skull of Dio-plotherium manigaulti and a skull and partialskeleton of Metaxytherium sp., as well as anassociated fauna of both marine and terres-trial vertebrates (Domning, 1989a, 1989b;Morgan, 1989). Routine screenwashing ofsediments from the plaster jacket in whichthe Metaxytherium skeleton was collectedproduced an associated fauna of nearshoremarine vertebrates, as well as an isolated ro-dent tooth. The discovery of a terrestrialmammal at White Springs 1A was unex-pected and led to intensive screenwashing toaugment the terrestrial component of the fau-na. In addition to the marine taxa, the WhiteSprings 1A fauna now consists of a horse,shrew, small carnivore, rabbit, and at leastfive species of rodents.

White Springs 3B (UF locality CO61) is asmall site (,100 m2) located in the middle

of the Suwannee River near White Springs.This site also has produced a varied marinevertebrate fauna, but is better known for thepresence of articulated partial skeletons andisolated elements of the oreodont, Mesoreo-don floridensis, n. sp., described herein. Apartial skeleton of a medium-sized camelid(cf. Oxydactylus sp.) was the first fossil dis-covered at the White Springs 3B site. Twospecies of smaller camels, an equid, and asmall rhinoceros also have been recoveredfrom White Springs 3B, primarily represent-ed by fragmentary fossils. UF field crewsalso collected and screenwashed a largeamount of sediment from White Springs 3B,and recovered a fairly diverse sample ofsmall terrestrial vertebrates, including a ty-phlopid snake, two species of boid snakes, amarsupial, two species of bats, and sevenspecies of rodents.

The vertebrate-bearing strata of the Para-chucla Formation have been traced along thebanks of the Suwannee River for the entiredistance between White Springs 1A and 3B,confirming that these two sites are essentiallylateral equivalents, occurring stratigraphical-ly within 2 m of one another. These two sitesalso share several species of land mammals,including a horse and four rodents. There-fore, the vertebrate faunas from WhiteSprings sites 1A and 3B are combined intothe White Springs L.F. (Morgan, 1989).

STRATIGRAPHY

Morgan (1989) referred the stratigraphicinterval that produces the White Springs L.F.to the Porters Landing Member of the Para-chucla Formation (following Huddlestun,1988). The lithology of the bone-bearing unitis a light gray to buff to brown, slightly clay-ey, fine quartz sand with a minor percentageof fine phosphatic grains. At the two primaryvertebrate sites, White Springs 1A and 3B,invertebrate fossils are rare except for poorlypreserved silicified oysters and pectens.However, in some places along the Suwan-nee River in the White Springs area, laterallyequivalent beds of this same unit consist ofa lighter colored, grayish calcareous shellysand 1–2 m thick that contains a rich faunaof marine invertebrates (Portell, 1989; Zulloand Portell, 1991).


In his description of the Porters LandingMember of the Parachucla Formation at thetype locality at Porters Landing on the Sa-vannah River in Effingham County, Georgia,Huddlestun (1988) noted that the southern-most occurrence of this unit was an outcropcontaining fossiliferous shell beds on the up-per Suwannee River at White Springs innortheastern Florida. Portell (1989) pub-lished a stratigraphic section of these shellbeds measured about 2 km east of the WhiteSprings 3B site. The strata Portell referred tothe Parachucla Formation are about 3 m thickwhere his section was measured, but reach amaximum thickness of about 5 m in outcropelsewhere in the White Springs area. Morgan(1989) expanded Huddlestun’s concept of thePorters Landing Member of the ParachuclaFormation in the White Springs area to in-clude all strata exposed on the banks and inthe bed of the Suwannee River that uncon-formably overlie the Suwannee Limestoneand underlie Huddlestun’s (1988) unnameddolostone, clay, and sand of the HawthorneGroup. Geologic units that are laterallyequivalent, and at least in part temporallyequivalent, to the Parachucla Formation in-clude the Penney Farms Formation in north-ern Florida, the Chattahoochee Formation inthe Florida panhandle, and the Tampa Mem-ber (formerly the Tampa Limestone) of theArcadia Formation in central Florida (Hud-dlestun, 1988; Scott, 1988).

We follow previous lithostratigraphic stud-ies (Huddlestun, 1988; Scott, 1988, 1989)and place the fossil-bearing strata along theSuwannee River in the vicinity of WhiteSprings in the Parachucla Formation. How-ever, we suspect that detailed field work inthis region may show that these strata shouldinstead be placed in the Penney Farms For-mation of Scott (1988), a unit of similar li-thology to the Parachucla Formation. ThePenney Farms Formation is primarily a sub-surface unit, and has been identified fromtwo cores in the Suwannee River area, onein Columbia County about 10 km southeastof White Springs, and one in HamiltonCounty about 15 km northwest of WhiteSprings (Scott, 1988). Surface exposures ofthe Penney Farms Formation occur at theMartin-Anthony roadcut in Marion County(Scott, 1988), the site that produced the or-

eodont Phenacocoelus luskensis (Mac-Fadden, 1980). Differences in Sr-isotope ageestimates from mollusk shells led Jones et al.(1993) to question the placement of theWhite Springs strata in the Porters LandingMember of the Parachucla Formation. Stron-tium isotope age estimates derived from mol-lusks at White Springs and the Penney FarmsFormation at Martin-Anthony are very sim-ilar (24.4 Ma and 24.6 Ma, respectively), andboth are significantly older than strontiumages on mollusks (20.2 Ma) from the typelocality of the Porters Landing Member inGeorgia (Jones et al. 1993).

SYSTEMATIC PALEONTOLOGY

CLASS MAMMALIA LINNAEUS, 1758

ORDER ARTIODACTYLA OWEN, 1848

FAMILY †MERYCOICOCONTIDAE HAY, 1902

SUBFAMILY †MERYCOIDODONTINAE HAY, 1902

Mesoreodon Scott 1893

Mesoreodon floridensis, new speciesFigures 15.1–15.13; tables 15.1–15.3

Family Merycoidodontidae, genus and species un-det., Morgan, 1989: 32

Family Merycoidodontidae, genus and species in-det., Hulbert, 1993: 25

HOLOTYPE: UF 125416, cranium and man-dible with complete R & L dentition.

TYPE LOCALITY, AGE, AND RANGE: WhiteSprings L.F., consisting of the fauna collectedfrom the White Springs 3B site (UF CO61)from the late Oligocene Parachucla Forma-tion, late early Arikareean (Ar2) land mam-mal age, Columbia County, Florida (Morgan,1989). Mesoreodon floridensis is only knownfrom the type locality. Detailed locality in-formation is on file in the UF Vertebrate Pa-leontology collection archives and computerdatabase.

ETYMOLOGY: florida-, Florida; -ensis, inthe place of, in reference to the geographiclocation.

REFERRED MATERIAL: UF 125417, L half-side of cranium with I2, I3, C, P1–M3, man-dible with R & L i1–i3, R & L c, R p1–m2,L p1–m1, associated postcranial elements in-cluding atlas, axis, other vertebra, proximalfragment of L humerus; UF 201856, cranium


Fig. 15.2. Dorsal view of cranium of Mesoreodon floridensis, new species, UF 125416, holotype,from the late Oligocene (Arikareean) White Springs L.F., Columbia County, Florida.

and mandible with complete R & L denti-tions, partial associated skeleton; UF 201869,L distal humerus, L proximal ulna, distalphalanx; UF 205721, cranium with completeR & L dentition; UF 205719, R & L man-dibles with complete dentition; UF 205720,L mandible with p2–m3; UF 205722,205723, astragalus; UF 205746, posteriorportion of articulated skeleton, including fourlumbar vertebrae, sacrum, R & L innomina-tes, and complete R & L hind limbs (femur,tibia, tarsals, metatarsals, and phalanges);206414, cranium with complete juvenile den-tition, associated R & L mandibles, atlas,miscellaneous vertebrae, and R radius andulna; composite mounted skeleton, includingcomplete catalogued specimen or cast, or in-dividual elements of UF 125416 (cast ofskull of holotype), 125417, 201856–201864,201866–201868.

DIAGNOSIS: Medium-sized merycoidodon-tine oreodont (SKL 5 206.3 mm, GSL 5231.5 mm, P1M3 5 97.7 mm, p1m3 5107.4; tables 15.1, 15.2). Skull transverselynarrow (SKL/SKW 5 1.9). Nasal notchmoderately retracted (SUBN/NASL 5 0.62,table 15.1), dorsal to P2/P3. Infraorbital fo-ramen dorsal to P4. Tear-drop-shaped facial

vacuity apparently developed at junction ofmaxillary, frontal, and lacrimal bones. Pre-orbital fossa relatively small, shallow, andpositioned on the lacrimal bone. Zygomaticarch thin and bladelike. Low and roundedsagittal crest. Kidney-bean shaped, moder-ately inflated auditory bulla. Nuchal crestbroad (GSL/NUCW 5 6.0) and does not ex-tend posterodorsal to foramen magnum(GSL/SKL 5 1.1). Premolars crowded andimbricated so that P3 and P3 are short andbroad with transverse width greater than an-teroposterior length. Mandible and incisorsrobust, incisiform c, caniniform p1, well-de-veloped angular process. Teeth brachydont(HTM3 5 12.5 mm, htm3 5 13.3 mm; table15.1), although moderately hypsodont rela-tive to other oreodonts.

Mesoreodon floridensis differs from Mer-ycoidodon culbertsoni because the latter isslightly smaller, lacks an inflated auditorybulla, and has a square, unreduced trapezoidin the carpus. M. floridensis differs fromPseudodesmatochoerus longiceps becausethe latter has a longer snout with less nasalretraction, infraorbital foramen positionedmore anteriorly, premolars not imbricating,skull longer (e.g., SKL 5 232.0, N 5 1) and


Fig. 15.3. Left lateral view of cranium of Mesoreodon floridensis, new species, from the late Oli-gocene (Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF125417 (fv, apparent location of facial vacuity dorsal to preorbital fossa).

postcranial elements (e.g., astragalus) about20% larger. M. floridensis differs from theMesoreodon cheeki complex (sensu Stevensand Stevens, 1996) because the latter has a10% larger and more elongated skull, lacksa facial vacuity, lacks an upper diastema,teeth are slightly larger, premolars moreelongated and not as imbricating, better de-veloped, bladelike, more continuous, andposteriorly directed sagittal crest, broader zy-gomatic arches, and rounder, more inflatedbulla. M. floridensis differs from Desmato-choerus monroecreekensis and D. wyomin-gensis (sensu Schultz and Falkenbach, 1954)

because the latter are larger (e.g., SKL 5231.8 mm, GSL 5 275.5 mm; N 5 4, versusfor M. floridensis SKL 5 206.3 mm, GSL 5231.5 mm [table 15.2]), have a better devel-oped and more continuous sagittal ridge,more posteriorly directed nuchal crest (GSL/SKL 5 1.2 vs. for M. floridensis 5 1.1 [table15.2]), and relatively narrower nuchal ridge(GSL/NUCW 5 8.9 vs. for M. floridensis 56.1 [table 15.2]). Although of generally sim-ilar size, M. floridensis differs from Eporeo-don because the latter has less nasal retrac-tion, deeper preorbital fossa, posteriorly di-rected and elongated occipital region (GSL/


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TABLE 15.2Measurement Abbreviations and Descriptions for Florida Mesoreodon floridensis, new species,

and Total Study SampleStudy sample also includes species within the merycoidodontine genera Eporeodon, Desmatochoerus, Merychyus,Merycoidodon, other Mesoreodon, Paradesmatochoerus, Phenacocoelus, and Pseudodesmatochoerus contained inthe AMNH and UF collections. Characters 1–18 from Stevens and Stevens (1996); 19–20 (fig. 15.1) added forthe current study.

SKL 5 1.2 vs. for M. floridensis 5 1.1 [table15.2]), and more inflated bulla. M. floridensisdiffers from Phenacocoelus because the skullof the latter is transversely broader (SKL/SKW 5 1.6 versus in M. floridensis 5 1.9[table 15.2]), the facial fossa is deeper, andM. floridensis is larger than P. luskensis andP. kayi (SKL 5 189.5 mm, GSL 5 215.5mm, N 5 2, versus for M. floridensis SKL5 206.3 mm, GSL 5 231.5 mm [table 15.2]).

DESCRIPTION: The skull is mesocephalicand relatively narrow (figs. 15.2–15.4). It isnot as elongated as in most Mesoreodon(e.g., ‘‘Desmatochoerus wyomingensis,’’ and‘‘D. monroecreekensis’’), but is longer thanspecies of Phenacocoelus. The zygomaticarches are generally thin, with the ventralmargin not thickened or rounded, and thearches are not expanded laterally. On theposterior zygomatic margin, there are nostrongly upturned processes; instead there isa thin dorsally projecting ridge that is low

compared to most Mesoreodon. The sagittalcrest is low and broad (not sharp and narrow)and the nuchal crest is broader than in mostMesoreodon and does not extend posteriorlymuch beyond the level of the occiptal con-dyles. In the occipital region, the fossae ven-trolateral to the nuchal crest are relativelysmall, shallow, and rounded, whereas this re-gion is deep and dorsoventrally elongated inmany Mesoreodon. Although the facial re-gions are crushed or otherwise distorted, andit is difficult to determine the original mor-phology, it seems like a facial vacuity is pre-sent on UF 125417 (fig. 15.3B) and UF201456 (the relevant facial regions in the ho-lotype, UF 125416, are not preserved) at thejunction of the premaxillary, frontal, and lac-rimal bones. The preorbital fossa is small andshallow, which is generally characteristic ofMesoreodon and different from the verydeep, pocketed fossa in Phenacocoelus. Thefossa is located principally on the lacrimal


TABLE 15.3Mammalian Faunal List from the White Springs

L.F. (CO61), Columbia County, Florida(see Morgan [1989] for an earlier compilation)

bone. The infraorbital foramen above the an-terior root of P4 is located more posteriorlythan in most Mesoreodon. The nasal notch isretracted to above P2, which is slightly great-er than in most Mesoreodon. The auditorybulla (e.g., in UF 125416) is kidney-beanshaped (i.e., anteroposteriorly elongated; fig.15.5). This structure is better developed thanin Merycoidodon, which lacks an ossifiedbulla, but not as well developed as in Epo-

reodon from Oregon, or the relatively verylarge bulla seen in leptaucheniine oreodonts.The postglenoid process is large, inflated,transversely elongated, and broad.

The teeth are relatively brachydont (upperhypsodonty index [HTM3/APM3] 5 0.52,lower hypsodonty index [htm3/apm3] 50.40; table 15.2), but they are moderatelyhypsodont relative to the oreodonts studiedhere (upper hypsodonty index 5 0.44, lowerhypsodonty index 5 0.36; table 15.2). I1 andI2 are similar in size, I3 is larger, and all arespatulate. C is large and robust, highlycurved, with a well-developed wear facet onthe posterior face. The cheek teeth are rela-tively smaller than in most Mesoreodon. Thisis most notable in the premolar series, espe-cially P1–P3 (figs. 15.3, 15.4, 15.6), wherein most Mesoreodon these teeth are long andnarrow (much longer than wide) and thereusually is a short diastema between P1 andP2. In M. floridensis there is a distinct im-brication of P1 and P2 so that these teethpartially overlap. The P2 and P3 are similarin morphology, triangular, and partially mo-larized. P3 of M. floridensis is broader thanlong. In P3 the ectoloph is V-shaped with acentral cusp at the apex. Each has three trans-verse crests (anterior, medial, and posterior).P4 is square and consists of a single selene.The molars are relatively square and havetwo subequal-sized selenes in M1 and M2,but in M3 the posterior selene is slightly re-duced transversely relative to the anterior se-lene. A distinct lingual cingulum is devel-oped on P4, M2–M3, but not M1; the labialcingulum is developed on P2–M3. As re-ported in Stevens and Stevens (1996), thegeneral proportions of the M3 are of taxo-nomic importance. In M. floridensis the meanAPM3/TM3 5 1.1; the mean APM3/HTM35 1.9 (table 15.2).

The mandibles are very robust with rela-tively deep horizontal ramus below the cheekteeth. There is a moderately developed pos-teroventral thickening on the posterior sym-physis (figs. 15.7, 15.8). Posteriorly, there isa large, rounded angular process. The coro-noid process is small, triangular, and only ex-tends slightly dorsal to the articular condyle.The incisors, i1–i3 are peglike and of similarsize; c is incisiform, triangular, and largerthan the incisors (about half the size of the


Fig. 15.4. Ventral view of cranium of Mesoreodon floridensis, new species, from the late Oligocene(Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF 201856.


Fig. 15.5. Basicranial region showing development of ear region. A, UF 191546, Merycoidodonculbertsoni, from the middle Oligocene (Orellan) of Sioux County, Nebraska. B, UF 125416, holotype,Mesoreodon floridensis, new species, from the late Oligocene (Arikareean) White Springs L.F., ColumbiaCounty, Florida. Abbreviations: fm, foramen magnum; gf, glenoid fossa; tb, tympanic bulla; oc, occipitalcondyle.

p1). The p1 is caniniform, conical, and trans-versely compressed, has a well-developedanterior wear facet for occlusion with the C,and lacks an external cingulum. The p2 andp3 are imbricated (partially overlap). The p2is transversely compressed. The p3 and p4are subtriangular and are shorter and broaderthan in most Mesoreodon. In particular, theanterior portion of the tooth is much shorterand more lingual (medial) in position than inmost Mesoreodon (fig. 15.9). The p4 is thelargest lower premolar, with the posteriorhalf of the tooth being more square than ei-ther p2 or p3. The internal (lingual) cingulumis very well developed on p1–p4. The m1 issmaller than m2, and m2 is smaller than m3.The m3 has a well-developed hypoconulidheel. The labial and lingual cingula on m1and m2 are weakly developed; these struc-tures are better developed on m3.

The general characters and proportions ofthe postcranial elements are described belowunder the discussion of the mounted skele-ton.

DISCUSSION

COMPARISONS WITH OTHER

FLORIDA OREODONTS

The earliest oreodonts known from Floridacome from the Whitneyan I-75 L.F. in Ala-chua County and are represented by threeteeth, including a lower canine (UF 97410),p2 (UF 97411), and upper canine (UF97409). The p2 of the I-75 oreodont is ofsimilar size to, but transversely narrowerthan, Mesoreodon floridensis. The overallcusp morphology of the I-75 oreodont andM. floridensis are similar. The upper caninefrom I-75 is much smaller than the otherspecimens from I-75 and M. floridensis, and,as previously noted (Patton, 1969), may rep-resent a second, much smaller species. Nev-ertheless, given the fragmentary materialfrom I-75, not much can be said about phy-logenetic affinities of these oreodonts relativeto M. floridensis.

Several Arikareean oreodonts occur inFlorida. Cowhouse Slough, located in Hills-


Fig. 15.6. Left upper dentition of Mesoreodon floridensis, new species, from the late Oligocene(Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF 201856.

borough County, contains one oreodont RP3,UF 40138. This tooth is significantly largerand, in particular, more anteroposteriorlyelongated than in M. floridensis. The Brooks-ville sites contain several oreodont teeth.Three canines, UF 163761–163763, are ofsimilar size, but more bladelike and com-pressed than in M. floridensis. A RM1, UF18480, is of similar size to M. floridensis; theformer also has a strong lingual cingulumwhereas in M. floridensis the lingual cingu-lum is poorly developed. After WhiteSprings, the Buda L.F. contains the secondbest sample of oreodont teeth and postcran-

ials from Florida. Upper canine UF 16902 isof generally similar size and morphology tothat of M. floridensis. A P3, UF 18424, issimilar in morphology to M. floridensis. AP4, 16903, is generally similar in morphol-ogy but about 10% longer than M. floriden-sis. Two M3s, UF 16931, are about 10%larger than M. floridensis. These Buda M3slack a lingual cingulum whereas there is acorresponding well-developed, continuouscingulum in M. floridensis. Both the Budaoreodont and M. floridensis have well-devel-oped anterior cingula. The Buda oreodontappears to be slightly higher crowned than


Fig. 15.7. Dorsal views of mandibles of Mesoreodon floridensis, new species, from the late Oligo-cene (Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF201856.

M. floridensis. Another site, the Martin-An-thony roadcut, produced an oreodont palatewith C, P1–P3, and M1–M2 referred toPhenacocoelus luskensis (MacFadden,

1980). M. floridensis is about 20% largerthan P. luskensis (including both the speci-men from Florida and the referred materialin the AMNH). The P1 and P2 of the P. lu-


Fig. 15.8. Left lateral views of mandibles of Mesoreodon floridensis, new species, from the lateOligocene (Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF201856.


Fig. 15.9. Left lower dentition of mandibles of Mesoreodon floridensis, new species, from the lateOligocene (Arikareean) White Springs L.F., Columbia County, Florida. A, UF 125416, holotype. B, UF201856. Note triangular and caniniform p1.

skensis sample are more transversely com-pressed and not as crowded (imbricated) asin M. floridensis.

Maglio (1966) described several fragmen-tary oreodont fossils from Thomas Farm. Al-though extremely rare, there is a small sam-ple of the Thomas Farm oreodont specimensin the UF collection that can be compared toMesoreodon floridensis, including an uppercanine (UF 173986), an upper molar (UF59027), and five astragali (UF 156231,157535, 175112, 180405, 181041). TheThomas Farm oreodont fossils are muchsmaller than comparable elements of M. flor-idensis. As Maglio (1966) noted, the ThomasFarm oreodont is of similar size to Mery-chyus minimus, best known from late Ari-kareean faunas of the Great Plains. This isdemonstrated by the comparative size of theastragalus (figs. 15.10, 15.11). The latest-known Florida oreodont is Ticholeptus sp.from the Barstovian Willacoochee CreekFauna in the Florida panhandle (Bryant,1991). Represented by a M3, UF 116823,Ticholeptus is about 10% smaller and lacksthe labial cingulum seen in M. floridensis.

The M3 anterior selene is of similar size,whereas the posterior selene of Florida Tich-oleptus is reduced relative to M. floridensis.In the midcontinent, oreodonts decline dra-matically in abundance after the Barstovian.The absence of oreodonts in Florida duringthe Clarendonian may result from a lack ofsites of that age.

COMPARISON OF MESOREODON FLORIDENSIS

WITH OTHER MERYCOIDODONTIDAE

The systematics of the Family Merycoi-dodontidae were reviewed by Thorpe (1937)and in a series of monographs published be-tween 1940 and 1968 (see Schultz and Fal-kenbach, 1968). The latter studies were ex-haustive in scope, and encompassed a tre-mendous number of important specimensfrom many relevant localities. The Schultzand Falkenbach monographs, however, arecharacterized by a typological approach tonomenclature, in which a plethora of specieswere named and in our opinion were grosslyoversplit (also see Stevens and Stevens,1996; Lander, 1998). Oreodont dentitions are


Fig. 15.10. Right astragali of selected oreodonts: A, UF 200627, Merycoidodon culbertsoni fromthe middle Oligocene (Orellan) of Sioux County, Nebraska. B, UF 205723, Mesoreodon floridensis,new species, from the late Oligocene (Arikareean) White Springs L.F., Columbia County, Florida. C,UF 181041, Merychyus cf. minimus, from the middle Miocene (Hemingfordian) Thomas Farm, GilchristCounty, Florida.

relatively conservative, and consequently, or-eodont systematics are based principally onskull characters. The problem with the use ofskull characters, however, is that availablesample sizes are usually small, and conse-quently population variation is poorly under-stood. Similarly, the effects of postmortemcrushing can distort the original cranial mor-phologies and result in a nonbiological com-ponent of variation.

Two recent studies have attempted to un-ravel the complex systematics of the Mery-coidodontidae. Lander (1998) presents a sys-tematic overview of this group, but seems toinclude in his species concepts previouslynamed species encompassing a broad scopeof morphologies. Relative to the Florida or-eodont described here, Lander’s (1998) con-cept of Eporeodon comes closest. However,based on our examination of relevant Epo-reodon specimens in the AMNH collections,particularly from the type area in the JohnDay basin of Oregon, and while of similarsize (e.g., SKL 5 208.4 mm, N 5 10, vs.206.3 mm for M. floridensis [table 15.2]),Eporeodon has numerous characters, includ-

ing less retracted nasal notch, relatively deeppreorbital fossa, transversely broader skull,much more inflated auditory bulla, and moreelongated occipital area than the Florida or-eodont.

We essentially follow Stevens and Stevens(1996) in determining the alpha-level tax-onomy of the Florida oreodont. (As men-tioned above, however, we refer to previousnamed taxa when discussing specific mor-phologies, e.g., ‘‘Desmatochoerus monroe-creekensis,’’ sensu Schulz and Falkenbach[1954].) Their suite of 18 skull, mandibular,and dental characters was particularly usefulin making morphological comparisons, andwe followed their scheme in our study. As afirst approximation, the Florida oreodont fitswithin the concept of ?Mesoreodon minor.During our studies of the AMNH collections,we found that ?M. minor as envisioned byStevens and Stevens (1996) encompasses abroad range of variation, which generallyfalls into two morphotypes. The first of theseis characterized by M. cheeki Schlaikjer andM. cheeki scotti Schultz and Falkenbach,which have a morphology generally similar


Fig. 15.11. Bivariate plot of GRTL versus TWDTH of astragali of Mesoreodon floridensis, newspecies, and selected specimens in the AMNH, F:AM, and UF collections. Pseudo. 5 Pseudodesma-tochoerus.

to Merycoidodon (although with well-devel-oped bullae) and are of moderate size. Thesecond group is characterized by speciessuch as Desmatochoerus monroecreekensisSchultz and Falkenbach and D. wyomingen-sis Schultz and Falkenbach. This group hasdistinctive characteristics such as a well-de-veloped sagittal ridge, constricted nuchalcrest, posteriorly directed occipital region,and expanded zygomatic arches. Of thesetwo morphotypes contained within Stevensand Stevens (1996) concept of ?Mesoreodonminor, the Florida oreodont is most similarto the first group, including M. cheeki (e.g.,F:AM 45430, also see Schultz and Falken-bach 1949) from the Arikareean of Goshen

Hole, Wyoming and Pseudodesmatochoeruslongiceps (AMNH 9732) from the late Ari-kareean (Harrison equivalent) of Montana.There are, however, a few exceptions to thesecomparisons that do not allow an unequivo-cal match for M. floridensis. With regard toM. cheeki, this species lacks a facial vacuity,whereas this feature appears to be developedin M. floridensis. With regard to P. longiceps,the associated postcranials (e.g., astragalus;see fig. 15.11) are about 10% larger than inM. floridensis. Although we use the genericallocation Mesoreodon and believe that thenew Florida oreodont is close to the overallmorphology demonstrated in the ‘‘M. cheekicomplex,’’ M. floridensis differs significantly


in the cranial and dental characters describedabove and hence a new species is justified.

Oreodont systematics have traditionallybeen based on the morphology and relativeproportions of crania, and to a lesser extent,dentitions and postcranial elements. One cra-nial character that has been generally over-looked as being of phylogentic significanceis the development of the facial vacuity. Us-ing extant artiodactyls as an analog, the facialvacuity in oreodonts probably served tohouse a scent gland (Webb, 1965). Whenpresent in oreodonts, this facial vacuity is lo-cated in the preorbital cheek region on vari-ous combinations of the nasal, premaxillary,maxillary, frontal, and/or lacrimal bones. Thepresence or absence, relative size, and shapeof these facial vacuities vary within the Mer-ycoidodontidae. Schultz and Falkenbach(1954) considered the development of the fa-cial vacuity to have no phylogenetic signifi-cance, whereas Stevens and Stevens (1996;personal commun., 2001) assert the contrarypoint of view. Thus, the discussion of thesystematic utility of oreodont facial vacuitiesis similar to that of the preorbital facial fos-sae in fossil Equidae, with schools of thoughtfor (e.g., MacFadden, 1982) and against(e.g., Forsten, 1982). As described above,Mesoreodon floridensis appears to have fa-cial vacuities. In this regard, M. flordensis issimilar to taxa such as Pseudodesmatocho-erus longiceps, and different from Mesoreo-don cheeki and M. chelonyx, the latter ofwhich are central to the revised concept ofthis genus (Stevens and Stevens, 1996). Iffuture studies of oreodonts indicate that thepresence of a facial vacuity is outside theconcept of Mesoreodon, then the species M.floridensis as currently envisioned may needto be reassigned to include it and similarforms such as Pseudodesmatochoerus longi-ceps in a new taxon. Resolution and furtherclarification of the taxonomic utility and dis-tribution of the facial vacuity in oreodontswould require a study outside the intendedscope of this paper. For the present time, weprefer to accept a broader, and taxonomicallymore conservative concept of Mesoreodonthat includes some species that lack the facialvacuity (e.g., M. cheeki) and others in whichthis structure is present (e.g., M. floridensisand Pseudodesmatochoerus longiceps).

BIOSTRATIGRAPHY, AGE, ANDPALEOECOLOGY OF THE WHITE

SPRINGS LOCAL FAUNA

One of the most significant aspects of theWhite Springs L.F. is that it contains landmammals preserved in nearshore marine sed-iments. Therefore, this fauna presents a rareopportunity for marine and terrestrial corre-lations (e.g., Tedford and Hunter, 1984; Mor-gan, 1993). The Parachucla Formation in thevicinity of White Springs can be dated bios-tratigraphically using terrestrial mammals(Morgan, 1989; this paper), sirenians (Domn-ing, 1989, 1991, 1997), and marine macro-invertebrates (Portell, 1989; Zullo and Por-tell, 1991). Supposedly correlative strata innorthern Florida (Scott, 1988) and Georgia(Huddlestun, 1988) have been dated usingplanktonic foraminifera. The Parachucla For-mation at White Springs and in Georgia andthe Penney Farms Formation at the Martin-Anthony roadcut have been dated usingstrontium isotope geochronology (Jones etal., 1993).

VERTEBRATE BIOSTRATIGRAPHY

There have been significant advances re-cently in the biostratigraphy of Arikareeanvertebrate faunas. Precision in dating thesefaunas has improved through the use of high-resolution geochronology, specifically argon-argon (40Ar/39Ar) radioisotopic dates (e.g.,Woodburne and Swisher, 1995), magneticpolarity stratigraphy (MacFadden and Hunt,1998), detailed biochronologic data fromArikareean sites in both the Great Plains(Tedford et al., 1987, 1996) and the GulfCoastal Plain (Albright, 1998; Hayes, 2000),and correlation with marine units, principallyin the southeastern United States (Tedfordand Hunter, 1984; Morgan, 1993, 1994). Ted-ford et al. (1987) and Woodburne and Swish-er (1995) subdivided the Arikareean into four‘‘subages’’ as follows: early early Arikareean(Ar1); late early Arikareean (Ar2); early lateArikareean (Ar3); and late late Arikareean(Ar4). These ‘‘subages’’ and their abbrevia-tions are followed here.

Morgan (1989, 1993, 1994) reviewed thevertebrate fauna from White Springs andmade preliminary biochronologic compari-sons with other Arikareean faunas from Flor-


ida and the Great Plains. Albright (1998) re-viewed all Arikareean vertebrate faunas fromthe Gulf Coastal Plain of Florida and Texas,including White Springs. Hayes (2000) madecomparisons of several taxa of small mam-mals from White Springs with similar taxafrom the Arikareean Brooksville 2 L.F. Thevertebrate fauna from White Springs is herecompared to the faunas from other Arika-reean localities in the northern peninsularFlorida. The location, age, and references forFlorida Arikareean faunas are: Brooksville 2L.F., Hernando County (Ar2; Hayes, 2000);Cowhouse Slough L.F., Hillsborough County(Ar2; Morgan, 1993; Albright, 1998; Hayes,2000); SB-1A/Live Oak L.F., SuwanneeCounty (Ar2; Frailey, 1978; Hayes, 2000;Frailey named the SB-1A L.F.; however, thesame site previously had been collected andrecorded in the UF locality files as the LiveOak L.F., and both names are used here toeliminate any confusion); Buda L.F., AlachuaCounty (Ar3; Frailey, 1979; Albright, 1998);and Franklin Phosphate Pit Number 2, Ala-chua County (Ar3; Albright, 1998). TheWhite Springs L.F. consists of 57 vertebratespecies, including 14 Chondrichthyes (fiverays and nine sharks); 10 Osteichthyes; sixReptilia (a land tortoise, three snakes, andtwo crocodilians); and 27 mammals (table15.3). The following discussion on the bio-stratigraphy of the White Springs L.F. coversall age diagnostic vertebrates, in particularterrestrial mammals.

A single upper cheek tooth (UF 121427)from White Springs 1A is identified as a pa-laeolagine rabbit based on the presence of acrescentic valley on the upper cheek teeth, aprimitive character not found in the more ad-vanced archaeolagines (e.g., Archaeolagus).Compared to Arikareean species of Palaeo-lagus, the White Springs tooth is lowercrowned, lacks cement, has a buccal root,and is thus identified as a small species ofMegalagus. Although smaller, the WhiteSprings tooth is morphologically similar, par-ticularly in the well-developed hypostria andcrescentic valley and presence of a buccalroot, to the upper cheek teeth of the recentlydescribed species Megalagus abaconis fromtwo Florida early Arikareean sites, Brooks-ville 2 and Cowhouse Slough (Hayes, 2000).Both Megalagus and Palaeolagus became

extinct at the end of the early Arikareean(Dawson, 1958).

Seven sciurid teeth representing two gen-era occur in White Springs 3B. Three teethrepresent the large sciurid Protosciurus.Frailey (1978) described and illustrated aProtosciurus mandible with p4 from the SB-1A/Live Oak L.F. Lower p4s of the WhiteSprings and SB-1A/Live Oak Protosciurusare similar in size and morphology, but nei-ther has been identified to species. Korth(1992) reported an undescribed species ofProtosciurus from the Ar2 McCann CanyonL.F. in Nebraska. Protosciurus is restricted toChadronian through early Arikareean faunas.Four teeth of a tiny sciurid are referred toNototamias. The type species of Nototamias,N. hulberti, is from the early HemingfordianThomas Farm L.F. in northern Florida (Prattand Morgan, 1989). Korth (1992) describedthe species Nototamias quadratus from theMcCann Canyon L.F. in Nebraska, and alsomentioned the occurrence of N. quadratus inthe Ar2 Monroe Creek Fauna.

Morgan (1989) referred three species ofgeomyoid rodents from White Springs to theHeteromyidae, including small, medium, andlarge species. More detailed study of thissample (A. Pratt, personal. commun.) hasshown that these three species may representtwo families, including Heteromyidae andHeliscomyidae. The Heliscomyidae is repre-sented at White Springs by a small speciesreferred to the genus Heliscomys. The WhiteSprings Heliscomys is similar in size andmorphology to species of Heliscomys fromthe Orellan (early Oligocene) of the westernUnited States. The range of Heliscomys isfrom the Chadronian (late Eocene) throughthe early Arikareean (late Oligocene), withthe possible exception of several isolatedteeth from the Hemingfordian of Saskatche-wan (Korth et al., 1991). Two other rodentspecies previously referred to the Hetero-myidae (Morgan, 1989) occur at WhiteSprings, neither of which has been identifiedto genus. The medium-sized species is sim-ilar to a species from SB-1A/Live Oak andthe largest is similar to a species from Buda.

Five teeth of a large eomyid rodent, threefrom White Springs 1A and two from WhiteSprings 3B, are referred to the genus Arika-reeomys, which is known outside of Florida


only by the type species A. skinneri from theArikareean McCann Canyon L.F. in Nebras-ka (Korth, 1992). Arikareeomys is a largeeomyid with high crowned teeth in whichboth the upper and lower cheek teeth arecharacterized by two enamel lakes that areseparated by a central, transverse valley. TheWhite Springs sample is clearly referable toArikareeomys, as no other similar largeeomyid is known from North America. How-ever, the Florida teeth differ in minor detailsfrom A. skinneri from Nebraska and appearto represent an undescribed species. Arika-reeomys occurs in four Florida Arikareeanfaunas, including White Springs, CowhouseSlough, SB-1A/Live Oak, and Buda. WhiteSprings, Buda, and SB-1A/Live Oak all havethe same Arikareeomys, whereas the Cow-house Slough taxon is a distinct species.

A large, brachydont ‘‘cricetid’’ rodent ofthe genus Leidymys is represented at WhiteSprings 3B by more than 10 isolated molars.Leidymys generally is referred to the subfam-ily Eucricetodontinae, Family Cricetidae(e.g., Martin, 1980; Korth, 1992). The M1 ofthe White Springs Leidymys is similar to L.cerasus from the McCann Canyon L.F. inNebraska (Korth, 1992), although it differsfrom the latter species in slightly smaller sizeand several dental details, and almost cer-tainly represents an undescribed species. Lei-dymys is typical of Whitneyan and early Ari-kareean faunas (Martin, 1980). L. cerasusfrom McCann Canyon is the youngest knownspecies in the genus (Korth, 1992).

Compared to oreodonts and camels, equidsand rhinoceroses are very rare in the WhiteSprings L.F. Morgan (1989) reported severalpartial teeth of a primitive Parahippus-gradehorse from White Springs 1A. Albright(1998) later referred these teeth to Anchippustexanus, a species also known from two otherArikareean sites on the Gulf Coastal Plain,the Franklin Phosphate Pit Number 2 site inFlorida, and the Ar3 Toledo Bend L.F. fromeasternmost Texas. A partial upper tooth (UF206417) from White Springs 3B is tentative-ly referred to the Arikareean rhinoceros Di-ceratherium.

There are three species of camelids in theWhite Springs L.F., all of which were foundonly at White Springs 3B. A partial articu-lated hind limb (UF 205725), seems referable

to the large, long-limbed camelid Oxydacty-lus based on its large size compared to otherArikareean camelids, elongation of the tibia(total length 460 mm), and unfused metatar-sals. An intermediate-sized camelid is rep-resented by two associated lower premolars(UF 205724), associated distal hind limb (UF205728), and isolated astragalus (UF205727). This species is similar to a camelidtentatively referred to Gentilicamelus fromthe Buda L.F. (Frailey, 1979). A small cal-caneum (UF 205729) is similar in size andcharacters to those of the tiny camelid No-thokemas waldropi from SB-1A/Live Oak(Frailey, 1978).

One of the most important mammals bear-ing on the age of White Springs is the newlydescribed oreodont Mesoreodon floridensis.This species is endemic to Florida, but thegenus Mesoreodon is otherwise restricted tolate Whitneyan and early Arikareean (Ar1and Ar2) faunas in the western United States(Stevens and Stevens, 1996). Mesoreodon ismore typical of the early Arikareean, includ-ing faunas from the Gering Formation inWyoming and Nebraska, the Cabbage PatchFormation in Montana, and the John DayFormation in Oregon. Of the two westernspecies referred to Mesoreodon by Stevensand Stevens (1996), the early Arikareean M.minor is most similar to M. floridensis.

Three genera of sirenians, Crenatosiren,Dioplotherium, and Metaxytherium, co-occurin the White Springs L.F. (Domning 1988,1989a, 1989b, 1991, 1997). Crenatosiren ol-seni, originally described from WhiteSprings 3A (Reinhart, 1976; Domning, 1997)has since been reported from the Ashley andChandler Bridge formations in South Caro-lina, both of which are late Oligocene (Chat-tian) in age (Domning, 1997). Domning(1989a) reported a nearly complete skull ofthe sirenian Dioplotherium manigaulti fromWhite Springs 1A, a species that also occursin the Oligocene Ashley and ChandlerBridge formations in South Carolina. Thethird sirenian from White Springs, Metaxy-therium, has the longest stratigraphic rangeof the three genera, occurring in the NewWorld from the late Oligocene through thelate Miocene (Domning, 1988).

Morgan (1989) referred two teeth of thelarge shark Carcharodon from the Parachu-


cla Formation near White Springs to the Ol-igocene and early Miocene species C. an-gustidens. The White Springs record of C.angustidens is one of the youngest occur-rences of this species, and indicates that thefauna is no younger than early Miocene. Themost common shark in the White SpringsL.F., a small undescribed species of Car-charinus, is known elsewhere only from theOligocene (Whitneyan) I-75 L.F. in Gaines-ville, Alachua County, Florida (Tessman,1969).

In summary, the biochronology of theWhite Springs L.F. clearly establishes an Ari-kareean age for this assemblage. Certain ofthe genera and species allow for a more pre-cise placement within the Arikareean, whichis important because the Arikareean is about10 million years long (29–19 Ma; Tedford etal., 1987; MacFadden and Hunt, 1998). Al-most all of the age-diagnostic mammals fromWhite Springs indicate a ‘‘medial’’ Arika-reean age, either late early Arikareean (Ar2;28–24 Ma) or early late Arikareean (Ar3;24–22 Ma). This time range is significant be-cause it includes the Oligocene-Mioceneboundary at 23.8 Ma (Berggren et al., 1995)and is not well represented in the midconti-nental sequence.

Mammalian taxa from White Springs thatindicate an early Arikareean age are: Meso-reodon floridensis; the lagomorph Megala-gus sp.; the rodents Arikareeomys new spe-cies, Heliscomys sp., Leidymys new species,and Protosciurus sp.; and the sirenian Cren-atosiren olseni. Among these genera, Meso-reodon, Megalagus, Arikareeomys, Leidy-mys, and Protosciurus do not occur after theearly Arikareean, and Crenatosiren is foundelsewhere only in late Oligocene (Chattian)marine faunas. With the exception of a Hem-ingfordian record from Canada (Korth et al.,1991), Heliscomys is otherwise restricted toearly Arikareean and older sites, and theWhite Springs Heliscomys resembles Oligo-cene (Orellan) species of the genus. Korth(1992) reported three of these genera, Ari-kareeomys, Leidymys, and Protosciurus,from the McCann Canyon L.F. of Nebraska,which he regarded as Ar3 in age. However,Korth noted the similarity of certain of thesmall mammals from McCann Canyon tothose from the somewhat older Ar2 Monroe

Creek Fauna of Nebraska and South Dakota.We follow Tedford et al. (1996), who con-sidered the McCann Canyon L.F. to be cor-relative with the Monroe Creek Fauna, andthus early Arikareean, rather than late Ari-kareean.

First appearances of either immigrant orautochthonous taxa are generally consideredto be more important in establishing the ageof faunas than are last appearances. There-fore, it would be significant from a biostrati-graphic standpoint if the White Springs L.F.contained genera or species that had theirfirst appearance in the late Arikareean. Onlytwo genera of mammals from White Springsappear to be late Arikareean first occurrences(Tedford et al., 1987; Albright, 1998), thehorse Anchippus and the camel Oxydactylus.However, the presence of these two generaat White Springs must be considered tenta-tive, as Anchippus is represented by two par-tial teeth and Oxydactylus is known onlyfrom postcranial material. The remainder ofthe White Springs mammalian fauna includessix genera (Arikareeomys, Crenatosiren, Lei-dymys, Megalagus, Mesoreodon, and Protos-ciurus) that are unknown after the early Ari-kareean, and a seventh genus (Heliscomys)that is most typical of early Arikareean andolder faunas but may persist into somewhatyounger faunas. In summary, the weight ofthe biochronologic evidence indicates thatthe White Springs Local Fauna is late Ar2 inage, probably between 25 and 24 Ma (latestOligocene, Chattian equivalent), given evi-dence cited below. Correlative faunas fromthe Great Plains are the Monroe Creek Faunaand the McCann Canyon L.F.

INVERTEBRATE BIOSTRATIGRAPHY

Among the 65 taxa of marine invertebratesfrom the Porters Landing Member of the Par-achucla Formation in the vicinity of WhiteSprings, Portell (1989) identified severalbiostratigraphically diagnostic species ofmollusks, including Chlamys acanikos andOstrea normalis. Both of these bivalves havebeen identified from localities in Florida andGeorgia that are considered to be early Mio-cene in age, including the Penney Farms For-mation in the Devils Millhopper and at theMartin-Anthony roadcut in northern Florida,


the lower part of the Torreya Formation inthe Florida Panhandle, and the type localityof the Porters Landing Member in Georgia(Portell, 1989). Zullo and Portell (1991) re-ported three species of barnacles from thePorters Landing Member at White Springs.They also identified these same three barna-cle taxa from the laterally equivalent PenneyFarms Formation from a core in ColumbiaCounty, Florida, about 18 km east of WhiteSprings. One of these barnacles, referred tothe genus Solidobalanus, belongs to a com-plex of species that ranges from the middleEocene through the early Oligocene on theeastern Gulf Coastal Plain. They referred an-other species to Concavus crassostricola, abarnacle known elsewhere only from the ear-ly Miocene (Aquitanian) of North Carolina.

Cores from the Penney Farms Formationin Nassau County, Florida, about 80 kmnortheast of White Springs (Scott, 1988), andthe Porters Landing Member of the Parachu-cla Formation in southeastern Georgia, about300 km northeast of White Springs (Hud-dlestun, 1988), both contain planktonic fo-raminifera. Comparison with subtropicalplanktonic foraminifera results in a correla-tion of these two units to either upper ZoneN4 (upper Globorotalia kugleri Zone) orlower Zone N5 (lower Catapsydrax dissimi-lis Zone). This correlation suggests an earlyMiocene (late Aquitanian) age of about 22–21 Ma based on the time scale of Berggrenet al. (1995). This is considerably youngerthan the age for White Springs L.F. suggestedby the mammalian biostratigraphy. The cor-relation of the foraminifera-bearing stratafrom Penney Farms Formation in NassauCounty and the type locality of the Parachu-cla Formation in Georgia is not questioned.However, the correlation of these units withthe Parachucla Formation at White Springs,which has not produced diagnostic plankton-ic foraminifera, is open to question, particu-larly considering the age discrepancy indi-cated by both the mammalian fauna and thestrontium isotope analysis below.

STRONTIUM ISOTOPE GEOCHRONOLOGY

Jones et al. (1993) used strontium isotopes(87Sr/86Sr) to determine the age of macroin-vertebrate fossils from the type locality of the

Porters Landing Member of the ParachuclaFormation in Georgia and from supposedlycorrelative strata exposed at White Springs,which are directly correlative with the stratathat produced the White Springs L.F. Stron-tium isotopic analyses of two shells of theoyster Ostrea normalis from White Springsgive an age estimate of 24.4 Ma (latest Oli-gocene, Chattian). The strontium isotopic agecalculated for a specimen of Ostrea normalisfrom Porters Landing, Georgia yielded a sig-nificantly younger date of 20.2 Ma (earlyMiocene, Burdigalian). The errors associatedwith these strontium isotopic age estimates,which range from 60.5 m.y. to 61.0 m.y.,are not nearly large enough to account forthe 41 Ma difference in age (Jones et al.,1993) between correlative units in Georgiaand White Springs. Strontium isotopic ageson the bivalves Ostrea normalis and Chla-mys acanikos from the Penney Farms For-mation at the Martin-Anthony roadcut inMarion County yielded an age estimate of24.6 Ma, very similar to the age of the Par-achucla Formation at White Springs. Themollusks dated from the Martin-Anthonyroadcut were collected from the same marinelimestone (unit 9) that produced a partialskull of the oreodont Phenacocoelus lusken-sis (see MacFadden, 1980).

PALEOECOLOGY

Of the 57 vertebrate species in the WhiteSprings L.F., 27 species are marine (five rays,nine sharks, nine bony fish, one crocodilian,and three sirenians), two species are fresh-water (one gar and one alligator), and 28 spe-cies are terrestrial (a land tortoise, threesnakes, and 24 mammals). The terrestrialmembers of the vertebrate fauna are concen-trated at two sites, White Springs 1A andWhite Springs 3B. The fauna from the re-mainder of the Parachucla Formation alongthe Suwannee River between these two sitesconsists primarily of marine taxa, includingboth vertebrates and an extensive inverte-brate fauna (Portell, 1989).

The vertebrate fauna from White Springs1A is predominantly marine, with the mostabundant fossils consisting of isolated teethof sharks, dasyatid rays, and bony fish. Themost complete mammals from this site are


Fig. 15.12. Mounted skeleton of Mesoreodon floridensis, new species, on exhibition at the FloridaMuseum of Natural History. This is a composite of UF 125416 (cast of skull of holotype), 125417,201856–201864, 201866–201868 and ribs and vertebrae of Merycoidodon culbertsoni.

sirenians, including a skull and partial artic-ulated skeleton of Metaxytherium and a com-plete skull of Dioplotherium. The terrestrialcomponent of White Springs 1A mostly con-sists of isolated teeth and postcranial ele-ments of small mammals, often heavily wa-terworn. Several partial teeth of the horseAnchippus are the only large land mammalsfrom this site. The marine fauna from WhiteSprings 1A consists of nearshore taxa. De-position probably occurred in a marginal ma-rine habitat such as delta or coastal lagoon,with the terrestrial taxa transported into ashallow marine depositional environment bya coastal river.

The vertebrate fauna from White Springs3B includes a larger sample of terrestrialmammals than does White Springs 1A. Fur-thermore, the most completely and best pre-served specimens are from the terrestrialcomponent of White Springs 3B, including

partial articulated skeletons of the oreodontMesoreodon floridensis and a large camelid.The presence of partial skeletons of landmammals at White Springs 3B suggests thatthe carcasses were not transported far andwere buried rather quickly. This site alsocontains several partial jaws and maxillaeand numerous well-preserved isolated teethof small mammals, further indicating quiet-water depositional conditions and limitedtransport. Several of the small mammalsfrom White Springs 3B, including two spe-cies of squirrels, suggest forested habitat.White Springs 3B also has a diverse marinevertebrate fauna of sharks, rays, and bonyfish, similar to the fauna from White Springs1A. Most of the marine vertebrate fossils alsoare well preserved and indicate limited trans-port and waterwear. The predominantly ma-rine nature of the Parachucla Formation andthe difficulty in explaining how a diverse ma-


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rine fauna could be transported and depositedinland under freshwater conditions indicatesa marine depositional environment for WhiteSprings 3B as well. A quiet coastal lagoonsurrounded by deciduous forests with smallfreshwater streams emptying into it is a pos-sible depositional environment that could ex-plain the diverse and well-preserved faunasof both terrestrial mammals and marine ver-tebrates.

MOUNTED SKELETON AND RECONSTRUCTION

OF MESOREODON FLORIDENSIS

During preparations for the opening of the‘‘Hall of Florida Fossils’’ at the Florida Mu-seum of Natural History, a mounted skeletonof Mesoreodon floridensis was articulated forexhibition (fig. 15.12). The skull, jaws, somevertebrae, and limbs consist of a compositeof White Spring specimens (see ‘‘ReferredMaterial’’) and most of the axial skeletonconsists of vertebrae from Merycoidodonculbertsoni from western Nebraska, or recon-structed ribs. Merycoidodon culbertsoni is aclose relative of M. floridensis, similar inmorphology and overall size, and was there-fore appropriate to fill in the missing skeletalelements.

Mesoreodon floridensis is a medium-sizedmammal, with a head-body length of 1070mm and a mean shoulder height (base of foot[distal-most tip of ungual phalanx], withflexed limb [not extended], to top of scapula)of 475 mm (R 5 470 mm, L 5 480 mm).Like other oreodonts, the cranium is robustand large relative to overall body size. In thefront limb the humerus, radius, and ulna ofM. floridensis are all about the same length,but more robust than, Merycoidodon. Themean length of the humerus is 170 mm (R5 170 mm, L 5 170 mm) and the meanlength of the radius is 125 mm (R 5 120mm, L 5 130 mm). In the hind limb, thefemur of M. floridensis is of similar lengthas, but more robust than, Merycoidodon. Thetibia of M. floridensis is of similar proportionto Merycoidodon. The mean length of the fe-mur of M. floridensis is 184 mm (R 5 187mm, L 5 180 mm) and the mean length ofthe tibia is 166 mm (R 5 167 mm, L 5 165mm). The mean ratio of the forelimb (hu-merus and radius measured as a unit) com-

pared to that of the hindlimb (femur and tib-ia) is 0.82. In the fore- and hind foot of M.floridensis, the carpals and tarsals are moreelongated, whereas the metacarpals andmetatarsals are generally more slender andslightly shorter than in Merycoidodon. Thecarpus of Mesoreodon floridensis contains atrapezoid that is triangular and positionedproximal to both MC I and II, whereas inMerycoidodon this bone is rectangular andpositioned directly proximal to MC II. Themetatarsals (MT II, III, and IV) of M. flori-densis are more slender and slightly shorterthan those of Merycoidodon. The lifelike re-construction of M. floridensis (fig. 15.13) isgenerally similar to that of Merycoidodon.

Given the associated fauna and interpretedpaleoecology of the White Springs sites, thelocal habitat of Mesoreodon floridensis prob-ably was a scrub or woodland located nearan estuary or lagoon, very close to a full ma-rine environment. The dental morphology ofM. floridensis, being relatively short-crowned, indicates a principally browsingdiet. Given these parameters, little or no ap-parent sexual dimorphism, and an estimatedbody size of 25 kg, M. floridensis probablylived in mixed-sex feeding herds (Janis,1982).

ACKNOWLEDGMENTS

We thank E. Dotson, S. Emslie, R.C. Hul-bert, A. Poyer, A. Pratt, and E. Simons forassistance collecting the White Springs spec-imens in the field. R. McCarty coordinatedthe fossil preparation, A. Poyer assisted withthe research, and E. Simons and J. Gage pho-tographed the specimens described here. Wethank S. Hutchens for his expertise in recon-structing the skeletal mount, and for bringingto our attention certain interesting aspects ofthe morphology of Mesoreodon floridensis.Dale Johnson prepared the line drawings andIan Breheny prepared the lifelike reconstruc-tion illustrated in figure 15.13. R.M. Hunt,M.S. Stevens, and R.H. Tedford provided ad-vice and helpful information that improvedthis study. This study was partially supportedby the Vertebrate Paleontology Fund of theFlorida Museum of Natural History. This isUniversity of Florida Contribution to Paleo-biology number 513.


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from the Late Oligocene (Early Arikareean) of Florida