PROBOSCIDEA FROM THE LEISEY SHELL PITS, HILLSBOROUGH COUNTY, FLORIDA S. David Webbl and Joseph P. Dudley2 ABSTRACT Leisey Shell Pits are remarkable for producing three species of Proboscidea representing three genera and indeed three separate families. Gomphotheres of the genus Cuvieronius are relatively rare at north temperate latitudes, and that is also true at Leisey lA Ai IEisey 38, however, Cuvieronius fropicus is relatively common. Molars of Mammut amencanum, a presumed browser, are represented by about 12% as many molars as Mammuthus hayi, a presumed grazer, thus suggesting a predominance of grassland and savanna near the site of the bone bed accumulation. The Leisey sample of Mammurhus hayi provides the richest population sample of this early Pleistocene (Irvingtonian) mammoth species. It is one of the earliest North American samples of mammoths. The wide variation of molar characters in mammoths are discussed, and the names M. haroldcooki and M. sonoriensis art synonymized wilhM. hayi RESUMEN El dep6sito de conchuelas de L«eisey es sobresaliente por el hecho de hal,er producido tres especies de proboscideos los cuales a£len,as de representar tres g6neros distintos, tambi6n pertenecen a tres familias diferentes. Gomfoterios pertenecientes al g6nero Cuvieronius son relativamente raros en Lkisey lA y por lo general en latitudes temperadas del Hemisferio Norte. Sin embargo, Cuvieronius fropicus es relativamente comOn en Leisey 38. Molares pertenecientes a la est)ecie presumiblemente ramoneadora Mammuthus amencanum representan un 12% con respecto a los molares de Mammuthus hayi, especie que presumiblemente consumia hierbas lo que hace pensar en un predominio de pastizales y savana cerca del sitio de acumulaci6n de huesos. La muestra deMammuthus hayi proveniente de los dep6sitos de conchuelas de Leisey otorga la Inds rica muestra de esta especie petteneciente al Pleistoceno temprano (Irvingtoniano). Esta es una de las mas tempranas muestras de mamuts en America del Norte. Se discute la amplia variacion en caracteristicas de los molares, sinonimiz~ndose los nombres M. haroldcooki yM. sonoriensis con M. hayi. The senior author is Cumtor of Vertebrate Paleontology, Depariment of Natural Sciences. Florida Museum of Natural History. University o f Flofida, Gainesville Fl 32611-2033. 2 The junior authoris Natural Resource Manager, Headquarters, U.S. Airforce, Environmental Planning, Washington DC 20330-501. WEBB, S.D., and J. P. DUDLEY. 1995. Proboscidea from the I.~isey Shell Pits, Hillsborough County, Florida. Bull. Florida Mus. Nat Hist. 37 PL 11(20):645-660. 646 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL- 37, PT. 4 No.20 INTRODUCTION One of the remarkable features of the Leisey mammalian fauna is the abundance and diversity of its Proboscidea. Both Leisey lA and 3B produce three species, representing three distinct families. The mammoths represent by far the largest early Pleistocene sample of mammoths in North America. The abundant mammoth remains are accompanied by somewhat rarer mastodons and gomphotheres. The Leisey fauna thus has the rare distinction (in the New World) of producing three apparently sympatric families of Proboscidea. The primary purpose of this chapter is to place on record these proboscidean occurrences, with relevant discussions of their systematics, biogeography, and paleoecology. A secondary purpose, with respect to the early mammoth record at Leisey, is to compare its geochronologic age with that of other Irvingtonian mammoth records in North America. For convenience, the following systematic account begins with the families Mammutidae and Gomphotheriidae. The systematic account of Elephantidae thus precedes the discussion of its geochronology. And finally there is a brief ecological discussion indicating the distinct adaptive zones that may have allowed the Leisey representatives of these three families to coexist in ecological compatability. ACKNOWLEDGEMENTS We thank John F. Eisenberg. Ernest L Lundelius, Jr., David Lamben, and Louise Roth for helpful discussions ofproboscidean history and valuable comments on this paper. This work was pastly supported by National Science Foundation grant BSR 8918065 to S.D. Webb. We appreciate the cooperation of Ralph -Tonf Estevez of Tampa and James L and Susan Pendergraft of Large. Florida. for letting us measure kisey mammoth jaws in their private collections SYSTEMATIC PALEONTOLOGY Order PROBOSCIDEA Illiger 1811 Family MAMMUTIDAE Cabrera 1929 The mammutids are distinguished from other Late Cenozoic proboscidean families by simple cross crests on their cheek teeth and by their vestigial lower tusks. In North America the transition between Pliocene mammutids, usually referred to the genus Pliomastodon, and their presumed Pleistocene descendants of the genus Mammut is not well-defined; nonetheless, there is general agreement that Irvingtonian samples can be referred to Mammut. WEBB & DUDLEY: LEISEY SHELL PIT PROBOSCIDEA 647 A 4 »1 3 ez,< . ad! B Figure 1. Mammut amencanum juvenile dentitions from LEisey Shell Pit lk (A) UF 80286, left maxillary with DP2 and DP3; (B) UF 80286, rightmandible with dp2-4. Scale bar = 40 mm Genus Mammut Blumenbacl, 1799 Mammut americanum Kerr 1791 Referred Specimens.-Leisey Shell Pit IA: UF 80286, DP2-3 and mandible with dp2-4 (Fig. 1); UF 82255, Ml; UF 86826, Ml; UF 81453, mandible with dp4-ml; UF 84751, mandible with broken tooth; UF 84443, broken dp4; UF 84444, broken dp4; UF 80691, broken ml; UF 81936, di}4; UF 82373, dp3; UF 85138, broken m2; UF 80004, fragmentary cheektooth. Unlisted are a number of other fragmentary mandibles, as well as skull fragments, tusk fragments and limb bones. Discussion.-The Leisey sample of American mastodon in the UF collection consists primarily of 11 fairly complete cheek teeth. As indicated by dental 648 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL- 37, Fr. II, No.20 morphology and in some localities by stomach contents, Mammut represents a browsing habitus, whereas Mammuthus presumably preferred grazing in open environments. This suggests that Leisey consisted predominantly of grassland and coastal savanna. Mammut cheek teeth occur 12 percent as abundantly as Mammuthus cheek teeth in the Leisey Kample. A striking feature of the m~todont wmple is the large number ofjuvenile teeth and heavily waterworn tusks and tusk fragments. Family GOMPHOTHERm}AE Cabrera 1929 The gomphotheriids are distinguished by complex cusps (wearing to a trefoil pattern) on their cheek teeth and, in most generg elaborate lower as well as upper tusks. The loss of lower tusks, however, came to characterize the progressive Pleistocene gomphotheriids, including Cuvieronius, which radiated in the American tropics and spread throughout South America (Webb 1985). Genus Cuvieronius Osborn 1923 Cuvieronius tropicus (Cope 1884) (=Cordilierion oligobunis in Osborn 1936) Referred Specimens.-Leisey Shell Pit lA: five fragmentary cheek teeth: UF 40073, 40074, 65061, 88005, and 88006; and an upper tusk fragment, UF 88008. Leisey 38: well-preserved left M3, UF 129033 (Fig. 2). Discussion.-The rarest proboscidean taxon at Lcisey, Cuvieronius tropicus, nonetheless occurs at both Leisey lA and 3B. The Leisey material is similar in all respects to the much richer sample (as yet undescribed) from the approximately contemporaneous site at Punta Gorda (Webb 1974). Cuvieronius evidently had its origin in North America in the Ptiocene and ranges through both American continents until about the end of the Pleistocene. An early plesiomorphous (or transitional) form of Cuvieronius occurs in the late Blancan of Florida, e.g. at Macasphalt Pit in Sarasota Co, Florida (Jones et al. 1991). Webb and Perrigo (1984) provided evidence from the late Miocene of Honduras in support of the hypothesis that Rhynchotherium is the primitive sister group of Cuvieronius (Tobien 1973; May and Repenning 1982; Webb and Perrigo 1984; Miller 1990), as suggested by the presence of spiral enamel bands on the upper tusks and by the downturned and progressively abbreviated mandibles in Rhynchotherium. A practical definition of Cuvieronius, distinguishing it from Rhynchotherium, can be based on the loss of its lower tusks. Improved samples of Cuvieromus and/or Rhynchotherium from Blancan faunas are needed to clarify the transition. WEBB & DUDLEY: LEISEY SHELL PIT PROBOSCIDEA 649 Figure 2. Cuvieronius tropicus. UF 129033, M3 from Leisey 3 B. Scale bar = 50 mm During the Pleistocene Cuvieronius tropicus ranged from Florida (e.g. at Punta Gorda and in the early Rancholabrean at the Daytona Beach site), around the Gulf Coastal Plain and southward through Mesoamerica. The species was named by Cope from Mexico; it is also known in Honduras, El Salvador, and Costa Rica (Freudenberg 1922; Webb and Perrigo 1984; Laurito 1988). Cuvieronius is also the earliest known proboscidean to enter South America, appearing in the Uquian at a time roughly equivalent to the early Irvingtonian (Webb 1985). It is best known in the middle and late Pleistocene from the Andes. Its South America sister genera are Haplomastodon and Notiomastodon (Simpson and Paula Couto 1957; Webb 1992). Family ELEPHANTIDAE Gray 1821 Genus Mammuthus Brookes 1828 Mammuthus hayi Barbour 1915 (=M scotti Barbour 1925) (=Al haroldcooki Hay 1928) (=Ai sonoriensis Osborn 1929) Referred Specimens.-Leisey IA: UF 80664, right m3 with associated jaw fragments (Fig. 3C); UF 81748, mandible with right and left p4 and ml; UF 81749, M2; UF 82211, partial M2; UF 87201, partial M2; UF 85326, partial maxilla with right and left M2, and Ml fragments;UF 87451, m3; UF 85325, juvenile mandible with right and left dp3, d4, and part of ml (Fig. 4); UF 86974, 630 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, Fr. 4 No.20 m3; UF 86975, partial m3; UF 65395, m3; UF 81750, m2; UF 86825, dp4; UF 81707, m3; UF 84185, Ml; UF 84476, ml; UF 85326, DP4; UF 83549, partial maxilla with DP3; UF 64686, 81708, 81570, 83550, 86748, 80064, 86748, 81347, 88017, deciduous premolars; UF 86978, left and right M3's in maxilla (Fig. 3A); UF 67200, mandible with m3; UF 85324, left and right M3's in maxilla; UF 86976, partial mandible with m3 (Fig. 3B); and about 60 limb elements not cited. Description.- As the richest collection of early Pleistocene mammoths in North America, the Leisey sample of Mammuthus hayi warrants thorough characterization. Fortunately the sample of cheek teeth spans the entire ontogenetic range of the mammoth population, and has especially strong representation of deciduous teeth. Tables 1 and 2 present measurements of 16 upper and 10 lower molars from Leisey. The most diagnostic features traditionally used to separate mammoth species are the number of lamellae (LN) in the last upper and lower molars and also the lamellar frequency (LF) (i.e. the average number of lamellae in 100 mm of occlusal length). For the Leisey sample of 10 lower third molars, the mean for lamellar frequency is 5.1. In upper third molars, based on four complete specimens, this figure is 5.6. These lamellar frequencies, among the lowest observed in North American mammoths, result partly from the large spacing between lamellae and partly from the very thick, crenulated enamel making up the grinding battery of each molar. Although the full lamellar number, ranging up to 17 in m3 and 19 in M3, is given for each molar, it should be noted that typically there are only about 10 plates in wear at any given stage, leaving the equivalent of 30% of an ultimate molar in reserve. Figure 3C illustrates a left m3 in early wear with each anterior plate partly integrated by wear, but with many cuspids still distinct with the next seven plates unworn, and with an estimated four posterior plates absent. Another very important feature of each molar is its height or degree of hypsodonty. The maximum unworn height of m3 in the mandible, UF 86976, is 185 mm (Fig. 313). A fourth commonly used measure in comparing elephantid taxa is the enamel thickness (ET). Mean enamel thickness in ultimate molars from the entire Leisey sample is 2.5 mm for both upper and lower third molars. In addition to very thick enamel, the cheek teeth of the Leisey mammoth are characterized by the strongly crenulated or corrugated surface of the enamel crests, presumably an adaptation for cutting and tearing fibrous vegetation. It is not uncommon, especially in early wear stages, for the cheek teeth to develop a "loxodont sinus," i.e. a separate median loop of enamel in the lamella. In three dimensions a loxodont sinus may be viewed as an enamel cusp that broadens beyond the normal anteroposterior width of the lamella during a 'particular wear stage. This WEBB & DUDLEY: LEISEY SHELL PIT PROBOSCIDEA 651 04 4 4, B * 1 Figure 3. Mammuthus hayi from Leisey lA (A) UF 86978, palate with left and right M3 in early wear stage; (B) UF 86976, mandible with left m3 and right m2-3; (C) UF 80664, left m3 in early wear stage, showing six weakly worn anterior plates, seven unworn plates, and missing an estimated four posterior plates. Scale bars = 100 mm in length. 652 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, Fr. IL No.20 Table 1. 1' Catalog # Tooth LN L W* H• LF ET UF 83324 RM3 19+ 242+ 954 - 6.50 3.10 Pendergralt a LM3 - - 924 . 6.00 2.89 UF 86978 RM3 12+ 265(e) 964 - 5.00 2.21 Pendergraft b LM3 12+ 265(0) 97'1 - 5.00 2.30 UF 87201 LM2 12+ 184+ 992 1589 5.75 2.28 UF 86137 RM2 x15 246+ 923 1487 6.00 2.50 UF 81749 RM2 13+ 248+ 836 10810 4.75 2.90 UF 81750 LM2 x13 286 866 12810 5.00 2.69 UF 83326 RM1 14 187 793 1817 7.50 2.33 Pendergraft c LM 1 13 179 784 1787 7.50 2.35 UF 86979 RMl 11+ 215+ 727 118+10 5.75 2.18 UF 84185 RMt 8+ 182+ 683 51+3 5.60 2.70 UF 85309 RMl 10+ 186+ 784 784 6.00 1.87 UF 81748 RM 1 13 185 725 - 7.00 2.55 PendergraR d LMl 12(e) . 704 - 7.00 2.73 UF 84476 LMl 11+ 175+ 807 803 6.75 2.62 •r. phenomenon is especially common in primitive elephantids with very 1hick enamet, as in living African elephants of the genus Loxodonta. Other teeth form irregular lamellar patterns based on unusual temporary unions between individual enamel cusps. Similar statistics for the penultimate molars are also valuable for comparisons, although they are based on smaller samples. In the Leisey mammoth sample the following means are found: M2 has a lamellar number of 12, a frequency of 5.8, and enamel thickness of 2.4; while m2 has equivalent data of 12, 4.9, and 2.4. A number of complete mammoth tusks were collected at Leisey lA. They vary considerably in length and diameter, but all are nearly straight, with only slight spiral curvature noticeable in the longest specimens. When viewed from above the tusks would have converged somewhat anteriorly, giving a subtly lyrate pattern. WEBB & DUDLEY: LEISEY SHELL PIT PROBOSCIDEA 653 Table 2. M ·third molan from Lcisey 1 A Catalog # Tooth LN L W* H* LF ET UF 65395 rm3 4++ 102+ 77+4 102+4 4.00 2.66 UF 67200 nn3 9++ 205+ 885 - 4.00 2.56 UF 80664 In13 15+ 284+ 754 1436 6.25 2.58 UF 81707 nn3 10+ 185+ 783 141+6 6.25 2.00 UF 86974 nn3 12+ 254+ 907 135+3 4.50 3.29 UF 86975 Im3 8+ 171+ 965 132+8 4.50 2.80 UF 86976 im) 8+ 197+ 87~ - 4.75 2.18 ESTEVEZa Im3 8+ 138+ 984 95+3 5.25 2.13 ESTEVEZ b rm3 15+ 218+ 963 1639 5.75 2.28 UF 67451 Im3 17+ 322+ 1084 1899 3.50 2.21 •r. ... Elephantidae have six cheek teeth in each jaw half, three deciduous premolars and three molars. Uppers and lowers for all these positions are represented in the Leisey gample. A series of three relatively complete mandibles represents three distinct growth stages. This series extends from UF 85325, with both left and right dp3 and *4(Fig. 4), through UF 81748, with left dp4 and right and left ml, to UF 86976, a mature individual with left and right m3 in full wear (Fig. 3B). Another mandible, UF 67200, is somewhat more worn and somewhat less complete than UF 86976. The length of the symphysis evidently grew from more than 53 mm in the juvenile to about 115 mm in the adolescent, of which nearly 30 mm formed a prominent "chin" which was not downturned (Fig. 3B). With just tlgee symphyses at hand, the significance of this variation in symphyseal prominence length cannot be determined. The depth in these mandibles progressed from 69 mm below dp3, to 148 below ml, to 185 below m3. The width between opposite cheek teeth increased from 57 between dp2's, to about 65 between dp4's, to 75 at the anterior end of m2, to 120 at the anterior end of m3. The coronoid process reached only slightly above the alveolar border in the adult. In UF 81748, with ml in wear, the coronoid reaches about 250 mm above the jaw base and the articular process 654 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL 37, PT. II, No.20 about 430 mm above. In UF 67200, these features are 240 mm and 420 mm respectively. About 60 postcranial elements of the Leisey mammoth were preserved. These limb bones show the characteristically long-limbed proportions of elephantids, but were somewhat smaller than typical Rancholabrean skeletons of Mommuthus columbi from Florida. For example, an adult ulna (albeit with weakly fused epiphyses) from Leisey has an overall length of 995 mm and an articular length of 825 min, as compared with a younger (unfused) stage in M columbi from the Aucilla River (UF 14779) which measures 1055 mm and 940 mm respectively. Discussion.--The wide range of molar variation documented in the Leisey mammoth sample (Tables 1 and 2) suggests that early Pleistocene mammoths in North America may all represent a single relatively primitive species. Observed plate counts in third lower molars from Leisey ranged from 8 to 17 plates. It is inappropriate to develop any statistical profile other than observed range under these circumstances. On the other hand, the enormous variability to be found in a population of elephantid teeth was recently stressed in a detailed meristic study of Elephas maximus. In that study Roth and Shoshani (1989, p. 26) noted that "recognition of this variability will demand a re-evaluation of the status of many fossil species named within the Elephantidae." More recently, Roth (1992) showed that many samples of fossil elephantid teeth express even greater sample variability than in other mammals. When applied to the early mammoths in North America this warning clearly places an immense burden of proof on anyone splitting species on the basis of minor meristic differences. The extraordinary variation seen in the Leisey sample, briefly described above, fully encompasses the quantitative and qualitative variation seen in much more limited samples of early Pleistocene Mammuthus elsewhere in North America. These include the types of four nominal species, as discussed below. The oldest available name for a primitive mammoth in North America is Mommuthus hayi Barbour 1915. The type specimen (UNSM 1301) is a fully mature mandible with very shallow depth (241 mm below coronoid process), and only 11 lamellae on each of its last molars (Barbour 1915; Osborn 1942). The last molars are 229 mm long by 76 mm maximum width with a plate frequency just over 4. Unfortunately the type was discovered as an isolated specimen at Crete, Nebraska, with no associated fauna nor any clear basis for dating the surrounding sediments, although they were said to be "Aftonian" gravels. Its morphology alone must serve as the evidence for its probable early Pleistocene age. We accept this type as the appropriate name-bearer for the early North American mammoth species that is more fully sampled and dated at Leisey. Madden (1981) has referred several specimens from other western sites to this species. WEBB & DUDLEY: LEISEY SHELL PIT PROBOSCIDEA 655 A , FZ>iiI-f r sYMAE.1116&