GRAVIGRADE XENARTHRANS FROM THE EARLY PLEISTOCENE LEISEY SHELL PIT lA, HILLSBOROUGH COUNTY, FLORIDA H. Gregory McDonaldi ABSTRACT Two tan of ground sloths are present at Lcisey Shell Pit 1 4 Nothrotheriops texanus and Paramylodon harlani. The Irvingtonian sample of Nothrotheriops is sufficiently distinct morphologically to warrant separation from the Rancholabrean species, N. shastensis, and is referred to Nothrotheriops texanus (Hay) (new combination). Individuals of the Irvingtonian P. harlani average smaller than those of the Rancholabrean and there is a general size increase in the lineage from the Blancan to Rancholabrean with only minor morphological changes. Use of Paramylodon instead of Glossotherium for the species P. harlaniis nomenclaturally correct RESUMEN En la fauna local de la Excavaci6n de Conchuelas de Leisey se encuentran dos tan de perezosos terestres: Nothrotheriops texanus y Paramylodon hartani. La muestra Irvingtoniana de Nothrotheriops es suficientemente diferente ent6rminos morfol6gicos como para permitir separarla de la bien conocida especie Rancholabreana N. shastensts y es referida como Nothrother,ops teranus (Hay) (nueva combinaci6n). Los Paramylodon del Irvingtoniano son mas pequefios que los del Rancholabreaense, existiendo un incremento general de tamaho en el linaje desde Blancano a Rancholabraense, con 5610 pequenos cambios morfol6gicos. El uso del nombre Paramylodon en vez de Glossotherium, en el case de la especie P. harlani, es correcto en 16rminos de nomenclatura 1 The author is a Paleontologist at the Hagerman Fossil Beds National Monument, P. O. Box 570, HageT·man, ID 83332-0570, U.S.A. MCDONALD, H. G. 1995. Gravigrade Xenarthrans from the early Pleistocene 1-£isey Shell Pit 14 Hillsborough County, Florida Bull. Florida Mus. NaL Hist. 37 PL Il(11):345-373. 346 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, PT. 4 No. 11 INTRODUCTION Among the diverse faims from Leisey lA are two ground sloths, Paramylodon hariani and Nothrotheriops texanus. P. hariani has long been known as a member of the Pleistocene fauna of Florida. By contrast, the presence of Nothrotheriops has only recently been recognimt in the state (McI)onald 1985). Rancholabrean records of both genera are common, but Irvingtonian age records are rare. Thus the recovery of a large sample of both taxa from the Leisey lA locality adds significantly to our understanding of the evolution and biogeography of these two animals. ABBREV[ATIONS The following abbreviations are used: AMNH - American Museum of Natural History, New York, CI - Albertson College of Idaho, Caldwell, FMNH - Field Museum, Chicago, IMNH - Idaho Museum of Natural History, Pocatello, LACM - Natural HiStOfy Museum of Los Angeles County, Los Angeles, UF - Florida Museum of Natural History, Gainesville, USNM - National Museum of Natural History, Washington D.C., mm - millimeters, cm - centimeters, M - mean, n- number. ACKNOWLEDGEMENTS 1 would like to thank S. David Webb ofthe Florida Muacum of Natural History for the opportunity to study the sloths of the Lcisey Shell Pit fauna and 16, his guidance and help in this and other projects. Gary S. Morgan aided in ways during my visits to the Florida Museum of Natural History. George Jefferson and Chris Shaw have greatly aided my work during my visits to the Page Museum to examine the collections from Rancho La Brea. Larry Barnes and David Whistler have graciously provided access to the collections housed at the Natural History Museum of Los Angeles County. Clayton E. Ray kindly permitted me to stu* specimens in his care at the Smithsonian. Mary Ellen Ahearn photographed the specimens, and Wendy 7nmiefer prepared the illustrations. The efforts of both are greatly appreciated 15 R Kleinberg greatly helped by meneuring mandibles ofParamytodon from Rancho La Brea. Elaine A -1-104 Gerry de Iuliis, Richard C. Hulbelt, Jr., and Gary S. Morgan kindly reviewed the manuscript A special word of thanks is extended to C. R "Bud" I£isey,Jr., and Eric Hunter who gencrously aided the project in many way£ Excavation of the site was conducted by numerous members of the Tampa Bay Gem and Mineral Society, without whose help this important fauna could not have been saved JoAnn Norris typed the manuscript Partial funding for the study of the sloths was provided by a grant from Leisey Shell Pit Inc. to the Florida Museum ofNatural History. MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL Prr lA 347 SYSTEMATIC PALEONTOLOGY Order XENARTHRA Cope 1889 Family MEGATHERm}AE Owen 1843 Subfamily NOTHROTHERINAE Kraglievich 1923 No~brotheriops texanus (Hay 1916) new combination Nothrotherium texanum Hay 1916. Nothrotherium shastense Sinclair 1905. Lull 1929 (in part). Nothrotheriops shastensis (Sinclair 1905) McDonald 1985 (in part). Type Specimen.- USNM 8353, incomplete cranium. Type Ikcality.- Wheeler County, Texas (see Hay 1916). Referred Leisey lA Specimens.- UF 86885, 80108, 84464, 86119, 86120, 86980, 86981, 86982, 86983, crania; 64348, 64349, 86899, 86121, 84626, 80314, 83100, 83594, 83900, 86984, 86985, mandible; 86185, 86987, 86989, 86990, 86991, humerus; 65821, 84463, 86996, 86999, 86997, 87000, ulna; 65821, 86168, 86992, 86993, 86994, 86995, radius; 87003 coossified third and fourth metacarpals; 87010, fifth metacarpal; 81500, 86733, 80038, 64350, 84931, 86355, 80211, 81362, 87012, femur, 67354, 64353, 86973, 87013, 87014, tibia; 87017, patella; 65824, 82938, 84449, 87028, calcaneum; 64335, 86891, 84448, 87026, 87027, astragalus; 86837, 87018 83688 coossified entocuneiform and first metatarsal; 65822, 64367, 81502, 87020, 87019, metatarsal II; 65823, 84287, 87021, 87022, metatarsal III; 87882, 86969, 87023, 87024, 86306, 86882, metatarsal IV; 87025, metatarsal V; 86952, 86870, 67127, 87035 coossified proximal and second phalanx, digit 3 pes. Emended Diagnosis.- Smaller than Nothrotheriops shastensis with more gracile cranium. Alveolar length of maxilla less than predental length of maxilla in contrast to N. shastensis in which the alveolar length of the maxilla is equal to or greater than the predental length of the maxilla. Total alveolar length of the jaw is less than 50% of the length of the mandibular spout (measured from the anterior edge of the first cheek tooth to the anterior edge of the spout) in contrast to N. shastensis in which total alveolar length is equal to or greater than 50% of the spout length. Description.- Comparison of both adults and juveniles from Lcisey 14 which contains a minimum number of eight individuals, was made with specimens of late Pleistocene (Rancholabrean) Nothrotheriops shastensis from San Josecito Cave, Nuevo Leon Mexico and Rancho La Brea, California. Since the skeletal anatomy of the Leisey lA N. texanus is essentially the same as N. shastensis, the 348 BULLETIN ELORIDA MUSEUM NATURAL HISTORY VOL 37, Pr. Il, No. 11 reader is reRrred to Stock (1925) or Lull (1929) for specific descriptions of bones and to Paula Couto (1974) for the manus. Rather than reiterate their excellent descriptions, references to specific bones will be made only in a general way. Crania of Nothrotheriops from Leisey l A display only a few differences from those from Rancho La Brea (Fig. 1). Overall length is similar in both species but the relative dimensions of other parts of the skull differ. One difference is the relationship between cheek tooth row length and predental length of the maxilla (Fig. 2). Alveolar length is shorter than the predental length in the Leisey 1 A sample (73, 79, 84, and 89%) whereas in the Rancho La Brea sample of N. shastensis alveolar length of the maxilla is greater than that of the predental length (100, 119, 128 and 129%). Alveolar length of the maxilla is 91% of predental length in the type ofNothrotheriops texanus (USNM 8353). In length and relative proportions, the skulls of the two samples are closely comparable in most respects. Nevertheless, the Leisey lA sample is consistently smaller than the Rancholabrean sample in many transverse dimensions. This combination of similar length but smaller transverse dimensions gives the skull of Nothrotheriops texanus from Leisey lA a more gracile appearance. These dimensions in the holotype ofN texanus are more similar to those from Rancho La Brea and San Josecito than to Leisey lA specimens except in the relative proportions of the maxilla discussed above. The intermediate size of the holotype of N. texanus suggests that it probably represents a later population than that from Leisey lA. Although the length of the predental portion of the maxilla is different in the two species, thewidth of this portion of the skull remains the same. This gives the anterior part of the skull of N. shastensis the appearance of having a shorter and stouter rostrum than N. texanus. The relative increase in the total alveolar length of the maxilla from N. texanus to N. shastensis has no affect on the width of the rostrum. Comparison of the Leisey lA Nothrotheriops mandibles (Fig. 3A) with those from Rancho La Brea and San Josecito Cave indicate some differences. Specimens from Leisey IA are smaller (Figs. 4,5) than those from later deposits. Despite the smaller size, the ratio of total alveolar length to maximum depth of the jaw (usually below the third molariform) is essentially the same (Leisey lA: 0.96-1.08, M = 1.01, N = 6; Rancho La Brea and San Josecito 0.83-1.06, M = 0.99, N = 8). The relationship between alveolar length and mandibular spout length differs between the two samples (Fig. 5). Three specimens from Leisey lA had total alveolar lengths of 39,45 and 46% ofthe mandibular spout. The combined sample from Rancho La Brea and San Josecito Cave (N = 7) had an alveolar length from 52 to 59% (M = 55%) of the length of the mandibular spout. This relative increase in the total alveolar length compared to the mandibular spout length parallels the relative increase in the total alveolar length of the maxilla compared to its predental length. One right juvenile maxilla (UF 83700) is interesting because of the presence of an atavistic caniniform (Fig. 6). Primitive nothrotheres such as Hapalops and MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 349 A C 10cm Figure 1. Skull of Nothrotheriopnexanus, UF 86883, m (A) dorsal, (B) lateral and (C) ventral views. 350 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL- 37, Fr. IL No. 11 70 PR ED EN TA L LE N G TH mm o PAEOENTAL LENGTH , 1 ALVEOLAR LENGTH 0 65 PREDENTAL LENGTH >1ALVEOLAR LENGTH 0~ 60 0 5 55 LL O 50 45 45 50 55 60 65 70 mm ALVEOLAR LENGTH OF MAXILLA Figure 2. Comparison of predental length of maxilla against total alveolar length of maxilla in Nothrotheriops teramis and Nothrotheriops shastensis. Open circle = Leisey, solid circle = type N. texanus, sol~d squate - N. shastensis. Pronothrotherium, are characterized by the presence of upper and lower caniniforms. Some of the later nothrotheres such as Nothrotherium and Nothrotheriops, have lost the caniniforms although another Pleistocene genus, Nothropus, retained them. The caniniform is separated from the cheek tooth by a diastema and is positioned halfway between the anteriormost cheek tooth and the anterior edge of the maxilla. The caniniform in UF 83700 is strongly curved with its base positioned above the root of the first cheek tooth. The tooth is small measuring only 4.0 by 2.8 mm. Orientation of the long axis is anteroposteriorly. The occlusal surface is broken so it is not possible to tell if there is any wear suggestive of a complimentary lower caniniform. None of the recovered jaws of juveniles have any indication of a lower caniniform. Coossification of adjacent bones of the manus and pes is a common feature in ground sloths, especially fusion between the entocuneiform and first metatarsal. Stock (1925) described two specimens from Rancho La Brea in which these two bones are fused, and the sample from San Josecito Cave contains 20 left and 8 right examples ofthis fusion. Three specimens from Leisey lA (UF 86837, 87018 and 83688), two left and one right, show the coossification of the entocuneiform and first metatarsal. These bones are also fused in the other late Pleistocene nothrothere genus, Nothrotherium (Paula Couto 1971), but they are separate in early nothrotheres, such as Hapalops. Since Nothrotheriops is unknown prior to its appearance in the Irvingtonian of North America, it is not possible to determine when the ungual and proximal phalanx were lost and the entocuneiform and first metatarsal coossified. A mounted skeleton of Pronothrotherium Opicum of ce MCDONALD: GRAVIGRADE XENARTHRANS FROMLEISEY SHELL PIT lA 351 . 5 A 48~L.~# EY hfull.. IMB.- B C f ./ 10 cm Figure 3. (A) Nothrotheriops texanus, UF 86899, lateral view of mandible. Paramylodon harlam, UF 80367, (B) occlusal view and (C) lateral view of mandible. Pliocene age in the Field Museum (FM 14503) has lost the ungual phalanx, but the entocunciform and vestigial first metatarsal are still unfused. Another common coossification of two bones is the proximal and middle phalanx of the third digit of the pes. The two phalanges are separate in Miocene Hapalops, but are fused in many later sloths. Four specimens from the Leisey lA locality exhibit the fused condition; UF 86952, 86870, 67127 and 87035. These 332 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, Fr. n, No. 11 u.1 65-immm 5 60 55 50 D EP TH O F M AN 45 0 0 oo4042 44 46 48 50 52 54 56 58 60 mm ALVEOLAR LENGTH OF MANDIBLE Figure 4. C „ ' of total alveolar length of mandible against depth ofmandible at third molariform in Nothrotheriops texamis #om'L-emey IA(open circle) and Nothrotheriops shastensis (open sepiase). two bones are also fused in Nothrotherium. This feature seems to have been established early in the nothrotheres as they are already coossified in Pronothrotherium Opicum (FM 14503) of Huayquerian and Montehermosan (early to middle Pliocene) age. In contrast these two bones do not fuse in the megalonychid, Megaionyx, until the late Pleistocene (McI)onald 1977). A pathological coossification of the right third and fourth metacarpals (UF 87003) is represented in the Leisey 1 A sample. The area of fusion is restricted to the proximal end and excess bone tissue is present on the dorsal surface of both bones. A single fifth metacarpal (UF 87010) was recovered. It differs from late Pleistocene forms in being more gracile. A similarly gracile lifth metacarpal was described from the Irvingtonian age Pool Branch, Florida locality by McI)onald (1985). Postcranially the skeleton of the Leisey lA Nothrotheriops and other Irvingtonian specimens tend to be smaller than those from the Rancholabrean. This is shown by various plots for the humerus (Fig. 7). This separation does not hold as well for the femur (Fig. 8). A major impediment to a more accurate analysis of size trends in the post-cranial skeleton is the absence of the same bone from the various localities, so comparable samples are small. In many of the localities listed in Table 1, Nothrotheriops is represented by a single bone. However, based on the sample available from Leisey 14 it does not appear that the size increase of Nothrotheriops from the Irvingtonian to Rancholabrean was as great as in Paramy/odon harhmi over the same period of time. MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 353 65r mm 1- 0 LU Z J w m 55 AL VE OL L Dr z << 545 LL 0 0 0 35 85 90 95 100 105 110 115 mm SPOUT LENGTH Figure 5. Comparison of length of mandibular spout anterior to first molariform Against total alveolar length of mandible in Nothrotheriops teranum (open circle) and Nothrotheriops shastensis (solid circle). Line represents ratio of 2: 1 for spout length against alveolar length. Figure 6. Nothrotheriops texanus right maxilla ofjuvenile, UF 83700, showing atavistic presence of caniniform (indicated by arrow). Scale bar 20 mm in length. Discussion.- Hay (1916) based Nothrotherium texanum on an incomplete cranium (USNM 8353) recovered from a well in Wheeler County, Texas. He distinguished it from Nothrotherium graciliceps (= N. shastense) (Stock 1913), also based on a skull, on a number of morphological features. No comparison was made with N. shastense Sinclair (1905), since it was based on an edentulous mandible and 14 isolated teeth. Stock (1925) made N. gracihceps a subspecies of N. shastense. Lull (1929) reviewed the genus in his study of a mummified specimen from New Mexico and considered Nothrotherium texanum to be 354 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, PT. 4 No. 11 TA L W ID TH 170 0 D IS TA L W ID TH O F FE M U R F H U M ER U S mm 160 0 0 ~ 0 150 0 140 340 360 380 400 420 440 mm LENGTH OF HUMERUS Figure 7. C , '' Nothrotheriops texanus (cirde) and Nothrotheriops shastensis (squam) 200mm 0 190 00 0180 0 170 0. . 330 350 370 390 410 mm LENGTH OF FEMUR Figure 8 Comparison of fen,„r length agninst nwliolateral width of proxim„i end in Nothrotherlops texanus (cirde) and Nothrotheriops shastensis (scluare) synonymous with N shastense. Since Lull's work it has generally been accepted that there is a single North American species, N. shastense. Hoffstetter (1954) proposed that the North American nothrothere was subgenerically distinct from the South American species and established the subgenus Nothrotheriops. Paula MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 355 Table l. Irv' J ' remrds ofP , ' ' ' ' ' ' " '* '' . Unpublished specimens are in the following collections: CI = College of Idaho; IMNH = Idaho Museum of Natural History, LACM = Los Angeles County Museum. UF = Florida Museum of Natural History; USNM - United States National Museum. Numbers in front ofeach locnlity refer to the localitics on the map in Figure 15. Paramylodon Nothrotheriops Locality harlani texanu) Reference California 1. Irvington X X Savage 1951 Alameda Co 2. Vallecito Creek X X Downs and White 1968 San Diego Co. Florida 3. Haile 16A X UF 4 Alachua Ca. 4. Inglis lA X Webb 1974 Citrus Co. 5. Leisey IA X X This paper Hillaborough Co. 6. Pool Branch X McDonald 1983 Polk Co. Idaho 7. Oreana X Cl Onyhee Co. Kansas 8. Adams X Hibbard and Taylor 1960 Meade Co. 9. Courtiand Canal X Eshelman and Hager 1984 Jewell Co. 10. Kanopolis X Hibbard et al. 1978 Ellsworth Co. 11. Sandahl X Sen*en 1966 McPherson Co. Nebraska 12. Angus X Schultz and Martin 1970 Nuckolls Co. 13. Gordon X Schultz and Stout 1948 Sheridan Co. 14. Hay Springs X Allen 1913; Brown 1903 Sheridan Co. (Type Locality for Paramytodon nebrascen:,s and Mylodon garmani) Oklahoma 15. Curtis X X Akerstenand McI)onald 1991 Woodward Co. 16. Holloman X Daiquest 1977 Tillman Co. Oregon 17. Rome X IMNH Matheur Co. Pennsylvania 18. Pod Kennedy Cave X Cope 1899 Montgomery Co. 356 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, rr. IL No. 11 Table l Continued. I.~cality Paramykdon Nothrotheriops Reference harlani texanus Texas 19. Gilliland X Hibbard and Dalquest 1966Baylor and Knox Cos 20. Rock Creek X Lu!11915Briscoe Co. 21. Wheeler Co. X Hay 1916(Type l,ocality Nothrotheriops texamis) Washington 22. Delight X Matthew 1902Adams Co. Mexico 23. El Gotfo X Shaw 1981 State of Sonon Canada 24. Medicine Hat Fauna 9 X Harington 1978Province of Alberta Couto (1971) reviewed the North and South American forms and raised Nothrotheriops to genedc status. There does not seem to be any reason to believe that there is more than a single lineage of North American nothrothere. They appear in the early Plcistocene (Irvingtonian) and culminate in the Rancholabrean speciesNothrotheriops shastensis. The question then arises as to the value of subdividingthis lineage and formally recognizing an earlier evolutionary stage as a separatespecies. In the continuum of an evolving lineage, it is difficult and somewhat arbitrary to demarcate the boundaries distinguishing two species. Smaller samples mayshow a marked separation in size or proportions which disappear as the samplesize increases. Three of the criteria used here to distinguish N. texanus from N.shastensis, size, ratio of alveolar to predental length of maxilla, and ratio ofalveolar length to length of mandibular spout--may blend as intermediate populations are found. However, since these criteria serve clearly to distinguishthe two forms, use of a distinct binomen serves the practical purpose of identifyingthe earlier evolutionary stage of the lineage and thus aiding in the identification ofthe age of the fauna with which it is associated. The type of Nothrotheriopstexanus is distinguishable from N. shastensis and falls easily within the range ofthe Leisey lA sample. Other Irvingtonian samples are also referred to N. fexanusbased primarily on their smaller size. At this time all referred material of N.texanus occurs in the Irvingtonian and N. shastensis is exclusively Rancholabrean.The timing of the transition of N. texanus to N. shastensis is currently unknown MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL Prr lA 357 and must await the recovery of intermediate cranial or mandibular material from known age faunas. Family MYLODONTIDAE Gill 1872 Genus Paramy/odon Brown 1903 Type Specia- P. nebrascensis Brown 1903 (= A*lodon hariani Owen 1840). Discussion.- There has been a common trend in the recent literature to refer the North American species harlani to the genus Glossotherium (Kurt6n and Anderson 1980). I have not followed this usage but rather have retained the older binomen, Paramy/odon hartani. A short synopsis of the history of these names will demonstrate the nomenclatural problems involved. Owen (1840) described Mylodon darwinii based on a complete mandible and Glossotherium based on a left temporal. Glossotherium originally was not used in a binomen. Owen (1842) described a second species of Mylodon, M. robusms. In a footnote in this same publication, Owen (1842:154) considered Glossotherium to be the same as Ady/odon darwinii, the type species for A*/odon. Harlan (1831) described and figured a mandible from Big Bone Lick, Kentucky which he referred to his previously described Megalonyx laqueatus. This paper was later republished by Harlan (1835). The mandible was that of a mylodont, not a megalonychid, and Owen (1840; 1843) recognizing its amnities, proposed the species harlani which he placed in his genus A*/odon. This resulted in three species being recognized for the genus A*/odon (Leidy 1855). One, and possibly two, of these species represented other genera. Recognizing that more than one genus was represented, Reinhardt (1879) proposed the genus Grypotherium to replace Mylodon for the binomen Mylodon darwinii. Additional confusion arose from considering the species robustus to be the type species for Adylodon and placing darwinii in the genus Glossotherium (Ameghino 1889; Lydekker 1894). Kraglievich (1928), assuming that Glossotherium had no species attached to it, proposed the name Glossotherium uruguayense as the type species for G/ossotherium, utilizing the temporal described by Owen as the type. Brown (1903) established the genus Paramylodon, with the type species, P. nebrascensis. Unfortunately, many workers considered harlani to be the type species ofA*/odon rather than darwinii (Stock 19144 b, 1917, 1925) and felt that there were two North American mylodonts; Mylodon harlani and Paramylodon nebrascensis. Eventually the convention of recognizing a distinct genus for each species developed; Mylodon danvinii, Glossotherium robustum and Paramylodon harlani (Kraglievich 1928). During this time other species had been described for each of these genera or under a genus proposed as a substitute for an earlier name; for example, Eumy/odon chapadmatensis (Kraglievich 1925) which later became Glossotherium chapadmalense (Kraglievich 1928). Hoffstetter (1952) used 358 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, PT. 4 No. 11 Paramy/odon as a subgenus of G/ossotherium. Cartelle (1980) and Cartelle and Fonseca (1981) resurrected the name Ocnotherium Lund 1842 as a subgenus of Glossotherium. Given the date of publication of this name, Ocnotherium may be the next available name for South American species currently placed in Glossotherium should the name Glossotherium be considered invalid. Despite this n„72 of nomenclatural proposals, there has been very little discussion of the morphological features that distinguish the various genera or the various species grouped within a particular genus. There has certainly been little consideration of evolutionaq or phylogenetic relationships of the various taxa and the change in relationships implied by the changing of names. None of the previous studies have demonstrated that Paramy/odon should be considered a junior synonym of Glossotherium. Using the genus Glossotherium for the North American species hariani is of dubious value (I would even question retaining it as a valid genus). I recommend continued use of the name Paramylodon harlani for Iningtonian and Rancholabrean specimens of North American mylodonts. Use of the genus Paramy/odon recognizes the geographic isolation and separate evolution of this lineage from the South American mylodonts. In an attempt to avoid further nomenclatural confusion I have followed Robertson (1976) in recognizing the North American Blancan mylodont as "Glossotherium" chapa&nalense. This usage recognizes the ancestor-descendant relationship of the two forms and is with the full realization that further study of the relationships between the North and South American mylodonts is needed. Paramylodon harlani (Owen 1840) Mplodon hariani Owen 1840. Owen 1842 1843; Leidy 1855; Stock 19148. 1914b, 1917,1925. Oryctotherium missouriense Harlan 1841. Perkins 1843. Oryctotherium oregonense Perkins 1843. Eubra*s antiquus Leidy 1853 Megaionyx potens Leidy 1853 Mylodon sodalis Cope 1818 Mylodon renidens Cope 1%95 Mylodon sulcidens Cope 1895 Paramylodon nebrascensis Brown 1903 Mylodon garmani Allen 1913 Adylodon tenuceps Stock 1917 A*/odon har/ani tenuceps Stock. Stock 1925 Paramylodon harlani (Owen). Kraglievich 1928 Glossotherium (Paramy/odon) harhmi (Owen).. Hoffstetter 1952 Glossotherium hariani Kurt6n and Anderson 1980 Type Specimen.- Partial right mandible, New York Lyceum, now missing. MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL Prr lA 359 Type Locality.- Big Bone Lick, Boone County, Kentucky (see Harlan 1831). Referred Specimens.- Leisey lA: UF 83769, 64400, 64373, crania; 87039- 87042, 67426, 80215, 80911, 83791, 83983, 84077, 86158, 80215, isolated upper caniniform; 87051, 87070, 87058, 67427, 86379,86739, 86738, 83337, 80778, 80779, M2; 80367, 83335, 87048, 87047, 87037, 84750, 64357, 87046, 87038, 87045, 87044, 87043, 80912, 84848, 80214, mandibles; 67436, 87054, 67437, 80895, 80531, 81216, 87063, 86767, 87065, 95880, isolated lower first molariform; 86846, 87045, 87044, 87043, 80912, 82004, 67446, isolated lower fourth molariform; 84136, 82933, 65851, 65855, 65856, 64364, humerus; 65857, ulna; 80163, radius; 65830, 65828, 65829, metacarpal I; 64368, 81791, metacarpal II; 65831, metacarpal III; 87024, met~rpal IV; 82245, metacarpal V; 80109, 81716, 64361, 80776, 63859, 80039, 80164, 87087, femora; 65860, 64365, 65862, 65861, 80176, 86930, tibiae; 64366, 87100, astragali; 65832, 82658, metatarsal II and mesocuneiform; 87105, 83986, metatarsal III; 65833, 83984, metatarsal V. Description.- The large sample from Leisey 14 like that from Rancho La Brea, permits an evaluation of the morphological variation that may be encountered in North American mylodonts. When compared with the Rancho La Brea and other samples, it permits the evaluation of evolutionary trends. Except for its smaller size and a few minor differences, the skeletal anatomy of P. har/ani from Leisey lA resembles that of the sample from Rancho La Brea, which is well described in Stock's (1925) classic monograph. Discussion of the sample from Leisey lA is restricted here to variation and evolutionary trends. One evolutionary trend in Paramy/odon harlani is the tendency to reduce or lose the anterior tooth of the upper dentition (= caniniform). Loss of this tooth parallels a similar loss in Mylodon darwinii. Loss of the upper caniniform was used by Brown (1903) in the diagnosis of the genus Paramylodon. Stock (1925) noted that in a sample of 45 skulls from Rancho La Brea, 21 had the first tooth on both sides, 14 had the tooth absent on both sides, 7 had the tooth on either the right or left side and 3 were doubtful regarding the condition. The Leisey lA sample has six specimens which preserve the anterior portion of the palate where this tooth is located (Fig. 9). Some have the tooth in place, and others have an open alveolus. Twelve isolated upper caniniforms were recovered. Unlike the Rancho La Brea sample all of these caniniforms are large with well developed occlusal surfaces. Based on the Leisey lA sample it appears that the caniniforms had not experienced any reduction in the early Pleistocene. This observation is confirmed in several other early Pleistocene samples. Prominent caniniforms are also present in Paramy/odon harlani from the earlier Inglis lA and Haile 16A faunas of Florida. Unfortunately, neither of these samples is as large as that from Leisey lA. Specimens from Irvingtonian localities outside of Florida, such as Rock Creek, Texas (Lull 1915), and Hay Springs, 360 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL- 37, PT. II, No. 11 48'~WI#..t - B *- i C 10 cm Figure 9. Skull ofParamylodon hartani, UF 83769, in (A) dorsal, (B) lateral and (C) ventral views. MCDONALD: GRAVIORADE XENARTHRANS FROM LEISEY SHELL PIT lA 361 Nebraska (the type locality for Mylodon garmani [= P. harlanil [Allen 1913] also have prominent caniniforms. A partial palate from Rome, Oregon has alveoli for both caniniforms. The holotype of Paramylodon nebrascensis (AMNH 2780) is one possible exception to the pattern that all Irvingtonian Paramylodon have both upper caniniforms. Brown's (1903) diagnosis of Paramylodon was based panially on the absence of the first upper tooth (=caniniform). However, the holotype was actually found near Hay Springs. Thus, it may not be part of the Hay Springs fauna proper, but from younger deposits. Supporting evidence for the presence of a caniniform in all the individuals of Paramylodon from the Leisey lA fauna is provided by the first lower cheek tooth. All specimens (12), both isolated and those still in the mandible, display a double wear surface reflecting occlusion against the upper caniniform anteriorly and the first upper molariform posteriorly. Specimens lacking the upper caniniform, such as the holotype of P. nebrascensis, have a lower first molariform with a wear surface only on the posterior side of the tooth. There are two morphs of the upper caniniform represented in the sample from Leisey lA (Fig. 10). The first form develops an occluml surface at an angle oblklue to the long axis of the tooth. The occlusal surface of the second morph develops perpendicular to the long axis of the tooth, so that the occlusal end of the tooth appears truncated. In the second morph the occlusal surface reflects the shape of the tooth's cross-section. The radius of curvature of the two morphs is the same, but the dimensions of the tooth anteroposteriorly and mediolaterally are larger in the first morph (Fig. 11). The occlugal surface of both morphs bear prominent dorsoventral striae and less prominent mediolateral striae. Caniniforms from Inglis lA (3 specimens) and Haile 16A (1 specimen) include only the larger morph with the obliquely worn occlusal surface. The type ofAnalensis, and that this digit may have born an ungual, a feature lost in later species such as P. hariani and G. robustum. There is a noticeable size difference between "Glossotherium" chapad,nalense in the Blancan and Paramy/odon harlani in the Rancholabrean. The gap is bridged by a graded series of specimens ofP. harlani in the Irvingtonian. Samples MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 365 120 D EP TH O F M A N D IB LE mm 110 100 90 .. O 80 00 70 El 6090 100110 120 130 140 150 160 170mm ALVEOLAR LENGTH OF MANDIBLE Figure 13. Comparison of alveolar length and depth of mandible in Rancholabrean, Irvingtonian and Blancan mylodents. Blancan "Glossothenum" chapadmatense (open square), Irvingtonian Paramylodon hariani (open circle), and Rancholabrean P. harlani (solid circle). of Irvingtonian P. har/ani are not large enough to quantify the size change. It can nevertheless be indicated in a simplistic way for certain abundant elements. A series of astragali (Fig. 14) from different Florida faunas demonstrate the gradual increase in size. The sequence of these faunas was independently determined using the biochronology of other species present (see Morgan and Hulbert this volume). This gradational sequence blurs the distinction between "G." chapadmalense and P. hartani when based on size alone. A careful reevaluation of the morphological features which distinguish the two taxa is therefore needed. Such a reevaluation, however, must await a larger sample of Blancan and very early Irvingtonian mylodonts. PALEOECOLOGY Juvenile Representation.- The samples of both Nothrotheriops and Parmnylodon include juveniles as indicated by limb bones lacking epiphyses, incompletely fused cranial bones, or isolated teeth that are conical. The juvenile characteristics of the Paramylodon sample are more strikingly displayed than those of the Nothrotheriops sample. This is indicated·in Paramy/odon by the presence of mandibles with conical teeth. Sloth teeth are markedly expanded basally during early stages of their eruption. They generally have become parallel-sided, 366 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 37, PT. It, No. 11 A i f 4. C Fipre 14. Ina &*aplus of (A) "Glossotherium" chapadmalense and (»C) Paramylodon harlani showing increase in size. (A) Haile 15A (Blancan), UF 10922; (B) Leisey lA (early Irvinglonian), UF 64366; and (C) Hornsby Sprinp (Rancholabrean), UF 4033. Scale bar 50 mm in length. however, prior to fusion of the epiphyses of the limbs and the presence of conical teeth indicates an extremely young individual. In the Leisey sample there are a number of juvenile Paramy/odon jaws with conical teeth. On the other hand, juvenile mandibles of Nothrotheriops are recognized on the basis of their smaller size and porous texture of the bone, but all specimens have parallel-sided teeth. It is not clear whether nothrothere teeth progress more rapidly that those of mylodonts, or whether there is some taphonomic bias against younger nothrotheres at the Leisey site. At the time of deposition of Leisey 14 four species of ground sloth were present in Florit. Megalonyx wheatleyi, Eremotherium n. sp., Nothrotheriops MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 367 texanus and Paramylodon harlani. Yet only the latter two species were recovered from this deposit, and they were quite richly sampled. Their abundance, as well as the absence of Megalonyx and Eremotherium, reflects the local environment and is not an artifact of small sample size. Distribution of Eremotherium in the United States is restricted to the Gulf and southern Atlantic coastal plains. The few inland records of this species are from riverine deposits, suggesting that the invasion inland was facilitated by the river, but limited to gallely forests. A similar distribution pattern occurs in South America where the genus is found along the coast or lowlying coastal plains. Eremotherium has generally been interpreted as a browser. This is confirmed by the recovery from the tar seeps of Peru and Ecuador of cut twigs, whose length matches the distance between the transverse lophs of eremothere teeth (A.G. Edmund pen. comm.). Absence of Eremotherium from the deposit cannot be attributed to its antiquity, since the genus is present in the older Inglis 14 DeSoto Shell Pit, and Haile 7C faunas (Webb 1974; Morgan and Hulbert this volume). Specimens of Eremotherium were collected at the Leisey Shell Pit (but not the Leisey lA site). In fact, Eremotherium was the most common ground sloth from the Leisey Shell Pit 3 quarry, located only 0.5 km north of Leisey lA. Megalonyx is the most ubiquitous of the North American ground sloth genera. The Irvingtonian species, M. wheatleyi did not range as widely as the Rancholabrean M. je#rsonii, but is known from numerous localities in Florida (McDonald 1977). Two of these, Inglis 14 which is earlier than the Leisey lA fauna, and the younger McLeod fauna produced large numbers of individuals of Megalonyx indicating that the genus was common in Florida. Megalonyx, in fact, can be considered the most common ground sloth in Florida having been found in deposits ranging in age from late Hemphillian to late Rancholabrean. Like Eremotherium, it is hypothesized to be a browser and an inhabitant of forests. Although commonly found in deposits along rivers, unlike Eremotherium, it was not restricted to gallery forests. Given its widespread distribution, its absence from the Leisey lA fauna must reflect local ecological conditions which prevented it from living close to the area of deposition. However, a few specimens of M wheatleyi are known from Leisey Shell Pit 3. More is known of the ecology and food preferences of Nothrotheriops shastensis, the descendent species of N. texanus than any other ground sloth, except possibly Mylodon darwinii. The preserved dung balls of both N. shastensis and M danvinii have been collected and analyzed, although more so for Nothrotheriops (Hansen 1978; Martin, Sabels and Shutler 1961). Cave deposits preserving the dung of N. shastensis are chronologically and geographically restricted to the late Rancholabrean of the Southwest, so caution must be exercised in extrapolation from these data. Although the primary food resource was desert shrubs ies. Sphaeralcea, Ephedra, Atriplex and Acacia), N. shastensis was catholic in its tastes and an opportunistic feeder (Hansen 1978). As pointed out by McDonald (1985) the plant types in Florida available to Nothrotheriops are similar enough to their western relatives that they were probably utilized by the genus. 368 BULLETIN FLORIDA MUSEUM NATURAL. HISTORY VOL- 37, Fr. IL No. 11 Nothrotheriops and Megalonyx in the late Pleistocene seem to be ecologically incompatible. There are a few faunas in the western United States which contain both genera, but there is a mafked difference in the number of individuals of each genus. At Rancho La Brea in Los Angeles, numerous individuals of Nothrotheriops have been recovered but only parts of a single individual of Megaionyx (Stock 1925). Likewise a similar pattern is seen in the fauna from San Josecito Cave-numerous individuals of Nothrotheriops, but a single individual of Megaionyx (Stock 1943). The only other locality in Florida at which Nothrotheriops has been found, Pool Branch, did not include Megalon,or (McI:)onald 1985). This generally consistent pattern of exclusion suggests that the few localities where both genera have been recovered are probably near an ecotone that provided a small area of overlap between their preferred habitats. Paramy/odon har/ani is as common as Nothrotheriops in the Leisey lA fauna (9 and 8 individuals respectively). Irvingtonian records of the species are rare, as in the case of Nothrotheriops so it is difficult to evaluate the degree of overlap in their habitat preference. Both are known from Rancho La Brea but P. harlani is the more abundant. P. har/ani is similarly abundant at American Falls Reservoir, Idaho in which MegalonJor is also common but Nothrotheriops is absent. The ecological requirements of P. harlani apparently were such that it could co-exist with either Nothrotheriops or Megalonyx with equal probability. Stock (1925) suggested that P. harlani was a grazer, and this interpretation has been followed by most subsequent workers. It could also be argued that the powerful forelimbs, with the expanded distal end of the humerus, short radius, ulna with an enlarged olecranon process and dorsoventrally flattened unguals permitted Paramylodon to dig up roots and tubers. Both interpretations permit us to view Paramylodon as primirily an inhabitant of scrub or open country habitat. BIOSTRATIGRAPHY Compared to other North American ground sloth genera, Nothrotheriops along with Eremotherium, was a relatively recent addition to the North American fauna. The first ground sloth in North America is the megalonychid, Pliometanastes, from the early Hemphillian (Late Miocene) (Hirschfeld and Webb 1968). Ptiometanastes is replaced by Megalonyx in the late Hemphillian. The mylodont lineage also first appears in the early Hemphillian and is represented by the genus Thinobadistes (Webb 1989). A second invasion of mylodonts occurred in the Blancan with the appearance of *Glossotherium" chapadmalense (Robertson 1976). It is presumed, but not yet demonstrated, that Paramylodon harlani is derived from "G." chapa&nalense and does not represent a third immigration of mylodonts into North America Webb and Marshall (1982) recognized three phases to the Great American Faunal Interchange, with the third phase subdivided into two parts. The first MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL PIT lA 369 rance of Nothrotheriops is considered to be indicative of Phase 3B, and Leisey lA appears to be the earliest fauna which includes Nothrotheriops. Eremotherium is present in four Florida late Blancan sites (Morgan and Hulbert this volume) and thus entered Florida much earlier. The slightly younger El Golfo fauna State of Sonora, Mexico is the earliest west coast record of Nothrotheriops. It is considered to be early Irvingtonian in age (Shaw 1981). A supposed Blancan record of Nothrotheriops (Gok et al. 1974) has since been determined to be a megalonychid, probably Megalonyx (Akersten and McDonald 1991). BIOGEOGRAPHY The wide coast to coast distribution of Nothrotheriops (Fig. 15) at the time of its earliest appearance in North America suggests a fairly rapid dispersal and integration into the North American fauna. This widespread distribution in the Irvingtonian is in marked contrast to its range in the later Rancholabrean in which it is confined to the western United States and northern Mexico (Akersten and McDonald 1991). Assuming that the ecological requirements of Nothrotheriops did not change during this time, the observed range reduction may represent the animal's response to changes in available habitat. McDonald (1985) has already suggested that its disappearance from Florida was due to the onset of more mesic conditions in the early Rancholabrean. Whether this pattern holds in other parts of its range can only be determined by the recovery of additional specimens with associated pollen or flora. Unlike Nothrotheriops, there does not appear to bean appreciable difference in the Irvingtonian and Rancholabrean distribution of Paramylodon. During the Irvingtonian, the northern edge of its range was at Rome, Oregon; Hay Springs, Nebraska and Port Kennedy Cave, Pennsylvania. Northernmost records of Paramylodon in the Rancholabrean include the Olympic Peninsula, Washington; American Falls, Idaho; Tecumseh, Nebraska; and Big Bone Lick, Kentucky. Such differences that do exist more likely reflect the relative paucity of Irvingtonian faunas compared to those of the Rancholabrean. McNab (1985) suggested that the northern expansion of Paramylodon was facilitated by the combination of its large size and long hair. This permitted it to tolerate climates with seasonally cool to cold periods. Another factor which may have contributed to heat retention is its relatively short and compact limbs which would have had a low ratio of surface area to volume. Nothrotheriops too was covered with long hair but had a smaller body volume and its limbs were long and slender. Studies of amino acid ratios in the bone indicate that Nothrotheriops had a core body temperature lower than expected for an animal of its size (McNab 1985). Northernmost records of Nothrotheriops are from southern Oregon, southern Utah, and Oklahoma. Comparison of Paramylodon to the similar sized South American genus, A*/odon, by McNab showed that A*lodon and by 370 B U LLE TIN FLO R ID A M U SEU M N ATU R A L H IS TO R Y V O L 37, P r. Il, No. 11 ~24 22 i 17 7 12~*3 18~ :00) Ais21~ /16 20~ A19 A23 3 4 5 Figure 15. Distribution of'Nothrothenops recanus and Paramylodon harlam in the Irvingtonian Symbols are: triangles = localities with onlyNothrotheriops tcranus, circles = localities with only Paramylodon harlam, squares = localities with both tan Numbers refer to the localities listed in Table 1. MCDONALD: GRAVIGRADE XENARTHRANS FROM LEISEY SHELL Prr lA 371 inference Paramylodon had a lower thermal conductance than Nothrotheriops, thus permitting a greater tolerance to colder environments. 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