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Early Pliocene Leporids from the Gray Fossil Site of Tennessee

Joshua X. Samuels1,2* and Julia Schap1,2

1Department of Geosciences, East Tennessee State University, Johnson City, TN, USA. 2Don Sundquist Center of Excellence in Paleontology, East Tennessee State University, Johnson City, TN, USA. *Corresponding author.

Eastern Paleontologist, No. 8 (2021)

Abstract
The early Pliocene age Gray Fossil Site of Tennessee is one of the few late Neogene sites in eastern North America outside of Florida. Here, we describe two leporid species from the site: 1) a larger, less abundant Alilepus vagus and 2) a smaller, more abundant Notolagus lepusculus. Both species are well-known taxa with relatively broad geographic and limited stratigraphic ranges, making them useful in refining the age of the site. In contrast to the open habitats characteristic of the many other sites where these species occur, floral and faunal evidence from the Gray Fossil Site suggests it was a forested habitat with at least a partially-closed canopy. Forest-dwelling rabbits occur in much of the Eastern United States today, and the Gray Fossil Site rabbits were likely filling similar niches in the Pliocene. The cranial and dental morphology of the two species do not provide any evidence of niche partitioning, but the postcranial morphologies of the two taxa at the site are distinct, with the smaller taxon more cursorially-adapted than Alilepus.

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No. 8 2021 Early Pliocene Leporids from the Gray Fossil Site of Tennessee Joshua X. Samuels and Julia Schap Eastern Paleontologist EASTERN PALEONTOLOGIST The Eastern Paleontologist (ISSN # 2475-5117) is published by the Eagle Hill Institute, PO Box 9, 59 Eagle Hill Road, Steuben, ME 04680-0009. Phone 207-546-2821 Ext. 4, FAX 207-546-3042. E-mail: office@eaglehill.us. Webpage: http://www.eaglehill. us/epal. Copyright © 2021, all rights reserved. Published on an article by article basis. Special issue proposals are welcome. The Eastern Paleontologist is an open access journal. Authors: Submission guidelines are available at http://www.eaglehill.us/epal. Co-published journals: The Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, and Urban Naturalist, each with a separate Board of Editors. The Eagle Hill Institute is a tax exempt 501(c)(3) nonprofit corporation of the State of Maine (Federal ID # 010379899). Board of Editors Richard Bailey, Northeastern University, Boston, MA David Bohaska, Smithsonian Institution, Washington, DC Michael E. Burns, Jacksonville State University, Jacksonville, AL Laura Cotton, Florida Museum of Natural History, Gainesville, FL Dana J. Ehret, New Jersey State Museum, Trenton, NJ Robert Feranec, New York State Museum, Albany, NY Steven E. Fields, Culture and Heritage Museums, Rock Hill, SC Timothy J. Gaudin, University of Tennessee, Chattanooga, TN Russell Graham, College of Earth and Mineral Sciences, University Park, PA Alex Hastings, Virginia Museum of Natural History, Martinsville, VA Andrew B. Heckert, Appalachian State University, Boone, NC Richard Hulbert, Florida Museum of Natural History, Gainesville, FL Steven Jasinski, State Museum of Pennsylvania, Harrisburg, PA Chris N. Jass, Royal Alberta Museum, Edmonton, AB, Canada Michal Kowalewski, Florida Museum of Natural History, Gainesville, FL Joerg-Henner Lotze, Eagle Hill Institute, Steuben, ME ... Publisher Jim I. Mead, The Mammoth Site, Hot Springs, SD Roger Portell, Florida Museum of Natural History, Gainesville, FL Frederick S. Rogers, Franklin Pierce University, Rindge, NH Joshua X. Samuels, Eastern Tennessee State University, Johnson City, TN Blaine Schubert, East Tennessee State University, Johnson City, TN Gary Stringer (Emeritus), University of Louisiana, Monroe, LA Steven C. Wallace, East Tennessee State University, Johnson City, TN ... Editor ♦ The Eastern Paleontologist is a peer-reviewed journal that publishes articles focusing on the paleontology of eastern North America (ISSN 2475-5117 [online]). Manuscripts based on studies outside of this region that provide information on aspects of paleontology within this region may be considered at the Editor’s discretion. ♦ Manuscript subject matter - The journal w elcomes manuscripts based on paleontological discoveries of terrestrial, freshwater, and marine organisms and their communities. Manuscript subjects may include paleo - zoology, paleobotany, micropaleontology, systematics/ taxonomy and specimen-based research, paleoecology (including trace fossils), paleoenvironments, paleobio - geography, and paleoclimate. ♦ It offers article-by-article online publication for prompt distribution to a global audience. ♦ It offers authors the option of publishing lar ge files such as data tables, and audio and video clips as online supplemental files. ♦ Special issues - The Eastern Paleontologist welcomes proposals for special issues that are based on conference proceedings or on a series of invitational articles. Special issue editors can rely on the publis her’s years of experiences in efficiently handling most details relating to the publication of special issues. ♦ Indexing - The Eastern Paleontologist is a young journal whose indexing at this time is by way of author entries in Google Scholar and Researchgate. Its indexing coverage is expected to become comparable to that of the Institute's first 3 journals (Northeastern Naturalist, Southeastern Naturalist, and Journal of the North Atlantic). These 3 journals are included in full -text in BioOne.org and JSTOR.org and are indexed in Web of Science (clarivate.com) and EBSCO.com. ♦ The journal's staff is pleased to discuss ideas for manuscripts and to assist during all stages of manu - script preparation. The journal has a page char ge to help defray a portion of the costs of publishing manu - scripts. Instructions for Authors are available online on the journal’s website (http://www.eaglehill.us/epal). ♦ It is co-published with the Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, Urban Naturalist, Eastern Biologist, and Journal of the North Atlantic. ♦ It is available online in full-text version on the journal's website (http://www.eaglehill.us/epal). Arrangements for inclusion in other databases are being pur - sued. Cover Photograph: Selected leporid specimens from the Gray Fossil Site in Tennessee, including a lower 3rd premolar (ETMNH 20522) of Alilepus, lower 3rd premolar (ETMNH 20520) and partial dentary (ETMNH 21233) of Notolagus, and an astragalus (ETMNH 22421) and calcaneum (ETMNH 9708) of a small rabbit. Photograph © Joshua X. Samuels. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 1 2021 EASTERN PALEONTOLOGIST 8:1–23 Early Pliocene Leporids from the Gray Fossil Site of Tennessee Joshua X. Samuels1,2* and Julia Schap1,2 Abstract - The early Pliocene age Gray Fossil Site of Tennessee is one of the few late Neogene sites in eastern North America outside of Florida. Here, we describe two leporid species from the site: 1) a larger, less abundant Alilepus vagus and 2) a smaller, more abundant Notolagus lepusculus. Both species are wellknown taxa with relatively broad geographic and limited stratigraphic ranges, making them useful in refining the age of the site. In contrast to the open habitats characteristic of the many other sites where these species occur, floral and faunal evidence from the Gray Fossil Site suggests it was a forested habitat with at least a partially-closed canopy. Forest-dwelling rabbits occur in much of the Eastern United States today, and the Gray Fossil Site rabbits were likely filling similar niches in the Pliocene. The cranial and dental morphology of the two species do not provide any evidence of niche partitioning, but the postcranial morphologies of the two taxa at the site are distinct, with the smaller taxon more cursorially-adapted than Alilepus. Intoduction Rabbits and hares (Leporidae) are key components of nearly every terrestrial ecosystem in North America today, and have been so since the Eocene (Dawson 1958, 2008). The family is known for being successful, and despite often being considered biologically conservative over their history, they do exhibit some ecological and morphological variability (Chapman and Flux 2008, Kraatz et al. 2015). In North America, the diversity of Leporidae has been relatively low and stable throughout the Cenozoic (Dawson 2008, Samuels and Hopkins 2017), but there was a substantial increase in leporid diversity in the latest Miocene and early Pliocene. In the late Pliocene, the family reached its current level of species diversity (Nowak 1999), and also had greater generic diversity and morphological disparity (as indicated by p3 pattern, Dawson 2008, Moretti 2018) than today. The few species present in fossil faunas are often particularly abundant components, just as they are in modern communities (Hibbard 1969). Two of the most notable adaptations of leporids today, hypselodont dentition and saltatory/cursorially-adapted postcrania, appear very early in the family’s history, suggesting their general ecology has changed little since the Oligocene (Dawson 1958, 2008; Samuels and Hopkins 2017). In general, most late Cenozoic rabbits likely occupied small generalist-browsing, running-adapted niches (Armstrong et al. 2010, Bittner et al. 1982, Dalke and Sime 1941, Peers et al. 2018). Six leporid species currently live in eastern North America, including three in the southern Appalachian Mountains region (Sylvilagus floridanus, S. obscurus, and Lepus americanus). While abundant and relatively diverse now, there are few records of leporids from eastern North America prior to the late Pleistocene. There is a single archaeolagine leporid, Hypolagus cf. H. fontinalis, known from the early Pliocene (early Blancan) age Pipe Creek Sinkhole in Indiana (Farlow et al. 2001). The archaeolagines Hypolagus ringoldensis and Hypolagus cf. H. tedfordi and the leporine Nekrolagus progressus have been noted from the late Miocene (Hemphillian) Palmetto Fauna of Florida (Hulbert 2001, Webb et al. 2008; White 1987, 1991a). Several species of Sylvilagus (specifically S. floridanus, S. palustris, and S. webbi) are known from a number of early Pleistocene (late Blancan and early Irvingtonian) sites in Florida (Dawson 2008, Hulbert 2001,White 1991b). 1Department of Geosciences, East Tennessee State University, Johnson City, TN, USA. 2Don Sundquist Center of Excellence in Paleontology, East Tennessee State University, Johnson City, TN, USA. *Corresponding author: samuelsjx@etsu.edu Manuscript Editor: Richard Hulbert Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 2 Lepus has also been noted in Florida at Inglis 1A and Leisey Shell Pit, which are the and early Pleistocene (late Blancan and Irvingtonian) in age (Hulbert 2001) Here, we describe the leporids from the Early Pliocene (latest Hemphillian or early Blancan) age Gray Fossil Site of Tennessee. The specimens described here represent the only Neogene records of lagomorphs from the Appalachian region and the first reported occurrences of the genera Alilepus and Notolagus in the eastern part of North America. Both of the leporids at the Gray Fossil Site are particularly useful for biostratigraphic age assignment and conteribute to the recently revised estimate of age of the site (Samuels et al. 2018). Materials and Methods Fossil rabbit specimens are typically identified and diagnosed based on the pattern of enamel reentrants in the lower third premolar (p3) (e.g., Dawson 1958, 2008; Dice 1929, White 1987, 1991a), and the upper second premolar (P2) is also taxonomically informative. Upper teeth are indicated by capital letters (e.g., M1) and lower teeth by lower case letters (e.g., m1). Dental nomenclature used here follows several sources (Čermák et al. 2015, White 1987, 1991a). Abbreviations of terms commonly used to describe the morphology of the p3 are as follows: AER = anteroexternal reentrant, AIR = anterointernal reentrant, AR = anterior reentrant, PER = posteroexternal reentrant, PIR = posterointernal reentrant. Measurements of the teeth, to the nearest 0.01 mm, were made using Mitutoyo Absolute digital calipers. Measurements of upper teeth include anteroposterior length and transverse breadth; for lower teeth they include anteroposterior length and transverse breadth of the trigonid (Wtri) and talonid (Wtal). Additional measurements, based on White 1991a, were taken from photographs using ImageJ (Rasband 2007). Measurements and dental terminology used are illustrated in Figure 1. Postcranial measurements include the following: HEW = epicondylar width of the humerus, HartW = maximum distal articular width of the humerus, TibDW = maximum mediolateral width of the distal tibia , TibDD = maximum anteroposterior depth of the distal tibia, TibSW = minimum width of the tibia shaft near the distal end, AstL = maximum length of astragalus, AstW = maximum mediolateral width of astragalus, CalL = maximum length of calcaneus, CalW = maximum mediolateral width of calcaneus at the level of the sustentaculum, CalTL = maximum length of calcaneal tuber from proximal tip of the tuber to the proximal end of the ectal prominence, CalTW = maximum width of the calcaneal tuber at its proximal end, CalBL = maximum length of the calcaneal body from the distal end of the ectal prominence to the distal-most point of the body; hindlimb were modified from those presented in Fostowicz−Frelik (2007). Fossil specimens were photographed using either a DinoLite Edge AM4815ZT digital microscope camera or a Nikon D810 DSLR camera with a AF-S Micro Nikkor 60mm lens. All specimens described here are housed at the East Tennessee State University Museum of Natural History (ETMNH), Gray, Tennessee. Material was compared to modern leporid specimens in the ETMNH collection, including: Sylvilagus audobonii (ETVP CC255, 2540, 5101, 10363, 10433), S. floridanus (ETVP 5767, 7021), Lepus californicus (ETVP 134, 2563, 11667), and Brachylagus idahoensis (ETVP 2586, 2589). Fossil specimens examined include Hypolagus and Alilepus from the Glenns Ferry Formation in several collections (National Museum of Natural History - NMNH, Hagerman Fossil Beds National Monument - HAFO, Natural History Museum of Los Angeles County - LACM), and specimens of Notolagus in the LACM collection. Material was also compared to specimens and measurements in a wide range of publications (including Averianov 1995, Campbell 1969, Čermák et al. 2015, Hibbard 1969, Moretti 2018, White 1991a, White and Morgan 1995). Complete measurement data for all leporids studied are included in Supplemental Tables 1 and 2 (available online at https://eaglehill.us/epalonline/suppl-files/epal-008-samuels-s1.pdf and https://eaglehill.us/epalonline/suppl-files/epal-008-samuels-s2.pdf). Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 3 Geological Setting The Gray Fossil Site of northeast Tennessee was formed as an ancient sinkhole with a small, deep lake that filled with sediment over approximately 4,500 to 11,000 years (Shunk et al. 2006, 2009). The sediments in the upper lacustrine strata include a series of rhythmites, with alternating layers of fine-grained silty clay and coarse-grained, organic rich sediments (Shunk et al. 2006, 2009). The site includes an amazingly diverse and well-preserved fauna and flora (e.g., Mead et al. 2012, Parmalee et al. 2002, Ochoa et al. 2012, 2016; Worobiec et al. 2013, Wallace and Wang 2004, Zobaa et al. 2011). The flora includes both macro- and microfossils that indicate the presence of a forest dominated by oak (Quercus), hickory (Carya), and pine (Pinus), accompanied by variety of herbaceous taxa (Ochoa et al. 2016, and references therein). Multiple palynology studies (Ochoa et al. 2012, 2016; Zobaa et al. 2011) have found almost no grass (Poaceae) pollen at the site, strongly indicating grass-dominated habitats were not present in close proximity. Presence of tupelo (Nyssa) and bald cypress (Taxodium) leaves and pollen at the site also suggest humid riparian or wetland areas occurred at the site (Brandon 2013, Worobiec et al. 2013). Based on the flora, Ochoa et al. (2016) interpreted the site as a woodland or woodland savanna environment with frequent disturbance. Carbon and oxygen isotopic analyses from ungulate and proboscidean teeth from the site support the presence of relatively dense forest, but a single proboscidean specimen suggested more open grassdominated habitats occurred nearby, at least within the dispersal range of an individual, which might have been hundreds of kilometers (DeSantis and Wallace 2008). Isotopic analyses also suggest the climate had little seasonal variation in temperature and precipitation (DeSantis and Wallace 2008). The fauna includes multiple taxa that indicate the presence of aquatic environments, specifically fish, neotenic salamanders, aquatic turtles, Alligator, and beavers (Boardman and Schubert 2011, Bourque and Schubert 2015, Jasinski 2018, Mead et al. 2012, Parmalee et al. 2002). The site also Figure 1. Schematic illustration of a leporid p3 indicating measurements taken for each specimen. Measurements follow White, 1987. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 4 has several vertebrate taxa that are intolerant of freezing conditions (Alligator, Heloderma) (Mead et al. 2012, Parmalee et al. 2002), and others characteristic of forested habitats (tree squirrels, flying squirrels, Tapirus, Bassariscus, and Pristinailurus) (Crowe 2017, Hulbert et al. 2009, Samuels et al. 2018, Wallace and Wang 2004). Combined, the flora and fauna at the site present a truly unique combination among North American biotas (Hulbert et al. 2009, Wallace and Wang 2004). The estimated age of the Gray Fossil Site was recently revised based on a number of newly identified taxa, which have good fossil records and limited stratigraphic ranges (Samuels et al. 2018). Of the genera at the site, none is restricted to the Miocene or the Hemphillian NALMA and multiple taxa are characteristic of Blancan faunas. Based on the presence of the rhino Teleoceras, dromomerycid Pediomeryx, mephitid Buisnictis breviramus, leporids Alilepus and Notolagus (described here), and the cricetids Neotoma, Repomys, and Symmetrodontomys, the age of the site is estimated to be Early Pliocene, between 4.9 and 4.5 Ma, near the Hemphillian-Blancan transition (Samuels et al. 2018). Previous records of the species described here, and the associated geographic and chronologic data were derived from the MIOMAP/FAUNMAP Databases (Carrasco et al. 2007, Graham and Lundelius 2010, www.ucmp.berkeley.edu/neomap/), NOW Database (Fortelius 2013, pantodon.science.helsinki. fi/now/), and recent publications (e.g., Moretti 2018), these records are outlined in Supplemental Table 3 (available online at https://eaglehill.us/epalonline/suppl-files/epal-008-samuels-s3.pdf). Results Systematic Paleontology Class MAMMALIA Linnaeus 1758 Order LAGOMORPHA Gidley 1912 Family LEPORIDAE Gray 1821 Subfamily LEPORINAE Trouessart 1880 Genus ALILEPUS Dice 1931 Alilepus vagus Gazin 1934 (Figure 2, Tables 1–2, Supplemental Tables 1 and 2) Referred Specimens—ETMNH 9765, left dentary with m2; ETMNH 20522, 22423, p3; ETMNH 9698, 9699, 9702, 20521, 21240, lower molariform teeth (p4–m2); ETMNH 9691, 13809, P2; ETMNH 9672, 9701, 9703, 9706, 18431, 18438, 20505, 20513, 20603, 21239, upper molariform teeth (P3–M2). Locality—Gray Fossil Site, Washington County, Tennessee. Age—Early Pliocene (earliest Blancan). Description—The dentary (ETMNH 9765) is incomplete and bears only a single tooth, the m2; the incisor and all other premolars and molars are missing (Figure 2 E–F). The preserved portion of the dentary is fairly complete, with alveoli for the incisor and all of the cheek teeth preserved. The horizontal ramus is complete and preserves the anterior portion of the masseteric fossa, but the mandibular angle, coronoid process, and articular (condyloid) process are all missing. The mandibular symphysis is clearly defined, with a highly rugose portion directly adjacent to the incisor alveolus and a subtle, but distinct ridge running posteriorly along the ventral margin of the diaphyseal portion of the horizontal ramus, ending below the anterior margin of the p3. The lower incisor root terminated just above and posterior to that ridge, below the p3, and a bulging capsule surrounding the root is evident despite breakage. The lateral surface of the diaphysis bears multiple mental foramina, including prominent foramina along the dorsal and ventral margins of the diaphysis anterior to the p3. The masseteric fossa has a clearly defined margin, though only the ventral portion of the fossa is delimited by an elevated ridge. The anterior margin of the masseteric fossa is curved and somewhat angular. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 5 While the p3 is not preserved in this dentary, aspects of its morphology allow referral of the specimen to Alilepus. The preserved alveolus for the p3 has a prominent ridge marking the location of the PIR (Fig. 2E, F), which matches the size and position of that structure in other specimens of Alilepus. In contrast, for the few specimens of Notolagus with the PIR preserved it is more anteriorly placed and in that taxon there is also a similar ridge for the AIR. Archaeolagines, like Hypolagus, lack internal reentrants on the p3 entirely, and other leporines studied lack ridges marking the location of internal reentrants. The m2 in ETMNH 9765 does not have the prominent crenulations present in Pratilepus (Hibbard 1939, 1969). Additionally, the dimensions of the dentary are similar to smaller specimens of Alilepus (Table 2). The size of the m2 within the dentary, as well as the alveolus of the p3 and other teeth, are consistent with the size of the other teeth referred here to Alilepus vagus. In the p3 (ETMNH 20522, 22423, Figure 2 A–B) the anteroconid is relatively triangular and pointed. There is not a distinct paraflexid (AIR) or anteroflexid (AR) present. In both specimens, very shallow depressions along the anterior and lingual margins of the anteroconid, which extend to the base of the tooth, suggest an incipient paraflexid (AIR) and anteroflexid (AR) are present; these structures are more distinct in ETMNH 22423 highlighted in Figure 2B. The protoflexid (AER) is shallow and crosses about 1/3 of the tooth. The hypoflexid (PER) crosses about half of the tooth in both specimens, but in ETMNH 20522 its medial portion curves posteriorly and the enamel along its posterior margin is somewhat crenulated, while it is straight and not crenulated in ETMNH 22423. The mesoflexid (PIR) is straight and crosses about 1/3 of the tooth in both specimens. The protoflexid (AER), hypoflexid (PER), and mesoflexid (PIR) all contain cementum. Figure 2. Specimens of Alilepus vagus from the Gray Fossil Site, Tennessee. A. ETMNH 20522, R p3; B. ETMNH 22423, L p3; C. ETMNH 9691, L P2; D. ETMNH 13809, L P2; E-F. ETMNH 9765, L dentary with m2: E, lateral view; F. occlusal view. Scale bars equal 1 mm for A-D and 5 mm for E-F. In Figure 2B, the incipient paraflexid (AIR) and anteroflexid (AR) a re indicated by arrows. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 6 Under the system utilized by Čermák et al. (2015, and sources cited therein), ETMNH 20522 has the A0/PR1/Pa0 p3 morphotype, though if the paraflexid (AIR) and anteroflexid (AR) in ETMNH 22423 are considered distinct reentrants then that specimens is the A1/PR1/Pa1 p3 morphotype. In addition to the dentary and p3 specimens, five lower molariform teeth are also referred to this taxon. As in the m2 in the dentary of ETMNH 9765, these other referred lower molariform teeth (p4–m2) lack crenulations. The widths of these teeth are similar to the widths of the two described p3 specimens from GFS, as well as the alveoli for p4–m2 within ETMNH 9765. In the P2 (ETMNH 9691, 13809, Figure 2 C–D) the lingual portion (hypercone) is roughly triangular in shape, and the labial portion (lagicone) is rounded. The tooth has two anterior reentrants, a deep paraflexus (MAR) and shallow, but distinct mesoflexus (EAR) (morphotype B, Čermák et al., 2015). Neither reentrant is crenulate, but both are filled with cementum, and that cementum actually covers most of the anterior surface of the tooth. The distal portion of the paraflexus curves strongly labially. There is no hypoflexus, but the anterolingual portion of the hypercone is flattened (morphotype III, Čermák et al., 2015). In addition to the P2 specimens, ten upper molariform teeth are referred to this taxon based primarily on their size, with widths proportionate to the P2 specimens and similar to p3 specimens from GFS. Remarks—The sizes of ETMNH 20522 and 22423 (Table 1) fall within the range of variation for the p3 of Alilepus vagus documented previously (Hibbard 1969, White 1991a). The morphology of the p3 is also consistent with A. vagus, showing distinct similarity to well-documented samples like those from the Hagerman local fauna in Idaho (Gazin 1934, Hibbard 1969, Ruez 2009). Large samples from the Glenns Ferry Formation show some variation in morphology, particularly in the structure of the mesoflexid (PIR), which is in some cases a deep, distinct reentrant (as in both ETMNH specimens) and in others a closed mesofossettid (enamel lake). That variation, with some p3s displaying a mesoflexid and others a mesofossettid is even apparent within a single individual, as Hibbard (1969) described for the left and right p3 in a fused mandible from Hagerman (USNM 23574). The GFS P2 specimens (ETMNH 9691, 13809) have two anterior reentrants, a deep paraflexus (MAR) and shallow mesoflexus (EAR), as is characteristic of Alilepus (White 1991a). As in described specimens of A. vagus (Hibbard 1969), the paraflexus (MAR) of the GFS specimens curves strongly labially. The reentrants are filled with cement, as is the anterior surface of the tooth. These features are all in contrast to the only other P2 in the sample from GFS, which is described below. While two or three reentrants are variably observed in several fossil and extant leporine genera (White 1991a), several are only known from specimens with three anterior reentrants, including both Pratilepus (Hibbard 1939) and Nekrolagus (White 1991a). It is worth noting that the morphologies of the GFS p3 and P2 specimens are consistent with other samples of A. vagus, but they are differentiable from other late Miocene and Pliocene leporine species. The A0/PR1/Pa0 morphotype of the p3, as in the GFS sample, is also seen in most Late Miocene members of the genus from North America (A. hibbardi), Eurasia (A. annectens, A. elongatus, A. hungaricus, A. laskarewi, A. ucranicus), and Africa (A. sp.) (Čermák et al. 2015, White 1991a, Winkler et al. 2011). It is important to note that the cranial and dental morphology of A. hibbardi and A. vagus overlap, and the two species are also the same size (White 1991a, Tables 1 and 2). White (1991a) indicated A. vagus was distinguished by a more deeply incised PER than A. hibbardi (PER depth 51% or less width of p3). Ruez (2009) noted that feature is variable in the large sample of A. vagus from Hagerman. In the GFS sample one of the two p3 specimens (ETMNH 20522) does have a PER that is incised more than 51% the width of the p3 (Supplemental Table 2), indicating it should be referred to A. vagus based on the most recent diagnoses of these species (White 1991a). As was noted by Ruez (2009), the only other character that has been used to distinguish between A. hibbardi and A. vagus is the Eastern Paleontologist J.X. Samuels and J. Schap 2021 7 No. 6 Table 1. Dental measurements (in mm) of Alilepus vagus and Notolagus lepusculus from the Gray Fossil Site, and a comparative sample of Neogene leporid species. Note that measurements of unworn teeth are excluded from the table below. Measurements for other related taxa from White (1991). Complete listing of measurements for all individuals in Supplemental Tables 1 and 2. Taxon Source P2L P2W P3-M2L P3-M2W p3L p3W p4-m2L p4-m2Wtri p4-m2Wtal Alilepus vagus Gray Fossil Site, TN Mean (n) Minimum Maximum (2) 1.25 1.60 (2) 2.46 3.05 2.06(10) 1.77 2.47 3.66(10) 3.01 4.9 (2) 3.31 3.33 (2) 2.80 2.88 2.47(6) 2.27 2.91 2.87(6) 2.72 3.17 2.30(6) 1.95 2.73 Alilepus vagus White, 1991a Mean (n) Minimum Maximum 3.2 (22) 2.4 3.8 3.0 (22) 2.1 3.7 Alilepus hibbardi White, 1991a Mean (n) Minimum Maximum 3.3 (7) 3.0 3.4 3.0 (7) 2.6 3.3 Alilepus wilsoni White, 1991a Mean (n) Minimum Maximum 2.6 (11) 2.4 2.7 2.3 (11) 2.0 2.4 Pratilepus kansasensis White, 1991a Mean (n) Minimum Maximum 3.0 (25) 2.8 3.4 2.6 (25) 2.3 3.2 Notolagus lepusculus Gray Fossil Site, TN Mean (n) Minimum Maximum (1) 0.87 (1) 1.64 1.40(10) 1.22 1.69 2.49(9) 1.82 3.12 2.68(5) 2.36 3.01 2.26(5) 1.94 2.63 1.80(5) 1.63 2.12 2.01(5) 1.75 2.27 1.61(5) 1.45 1.76 Notolagus lepusculus White, 1991a Moretti, 2018 Mean (n) Minimum Maximum Mean (n) Minimum Maximum 2.5 (27) 2.2 2.9 2.3 (12) 2.0 2.5 1.9 (28) 1.6 2.4 1.8 (12) 1.5 2.0 Notolagus velox White, 1991a Mean (n) Minimum Maximum 3.0 (8) 2.3 3.4 2.4 (8) 1.7 2.6 Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 8 Table 2. Dentary measurements (in mm) of Alilepus vagus and Notolagus lepusculus from the Gray Fossil Site, and a comparative sample of Neogene leporid species. Measurements for other related taxa from White (1991) and Moretti (2018). Taxon Source Mean/Range iW i – p3 Diastema L Cheek Toothrow L (p3 – m3) Dentary Depth at m1 Alilepus vagus ETMNH 9765 Gray Fossil Site, TN 2.60 12.54 14.61 10.67 Alilepus vagus White, 1991a Mean Minimum Maximum 15.6 14.1 16.9 16.5 15.4 17.3 12.5 12.0 13.0 Alilepus hibbardi White, 1991a Mean Minimum Maximum 17.5 18.0 12.4 Alilepus wilsoni White, 1991a Mean Minimum Maximum 12.0 11.7 12.2 Pratilepus kansasensis White, 1991a Mean Minimum Maximum 14.2 13.6 15.0 13.5 13.2 13.8 13.5 13.2 13.8 Notolagus lepusculus ETMNH 20524 Gray Fossil Site, TN 1.00 7.42 Notolagus lepusculus White, 1991a; Moretti, 2018 Mean Minimum Maximum 9.7 10.7 9.3 11.6 Notolagus velox White, 1991a Mean Minimum Maximum 14.4 13.8 15.0 11.6 11.6 11.7 Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 9 presence of an enamel lake on the P3 of A. hibbardi (White 1991a), but the occurrence of enamel lakes in the upper premolars and molars is something that varies through wear of the tooth in some leporids. Without large samples for study and assessment of intraspecific variability in that trait, it may not be appropriate for use in differentiation of species. The other species of Alilepus known from the latest Hemphillian and Blancan of North America, A. wilsoni, is rather different from other members of the genus, with the mesoflexid (PIR) absent and the hypoflexid (PER) extended across the tooth, resulting in the A0/PR0/Pa0 morphotype being present in all described specimens (White 1991a, White and Morgan 1995). Ruez (2009) stressed how A. wilsoni bears strong similarity to Aluralagus virginiae, as noted by White (1991a) in the original description, and as such its taxonomy should be reassessed. The GFS specimens can be readily differentiated from the Blancan age Pratilepus kansasensis, which has a much deeper protoflexid (AER) on the p3 and more highly crenulate enamel in all reentrants (Hibbard 1939, Ruez 2009, White 1991a). Several other leporine genera (Nekrolagus, Lepus, and Sylvilagus) are easily distinguished from A. vagus by the lack of a PIR and presence of a much deeper PER (or adjacent enamel island) and possession of a distinct cement-filled AR. Additionally, in contrast to the P2 of A. vagus from GFS, the P2 of Pratilepus and Nekrolagus have three reentrants, including a shallow IAR (White 1991a). The morphology of the dentary (ETMNH 9765, Fig. 2 E–F) is consistent with other described specimens of Alilepus vagus (Hibbard 1969) and A. hibbardi (White 1991a), but it is smaller in every measurement (Table 2) than any of the specimens reported by White (1991a). Smaller body size in a population of rabbits living in a relatively densely forested environment is not particularly surprising, as some leporids have previously been shown to follow Bergmann’s rule (Ashton et al. 2000, Davis 2019, Meiri and Dayan 2003). cf. Alilepus sp. (Figure 3, Table 3) Referred Specimens—ETMNH 20502, distal left humerus; ETMNH 18440, distal left tibiofibula; ETMNH 18434, left astragalus; ETMNH 8054, right calcaneum. Locality—Gray Fossil Site, Washington County, Tennessee. Age—Early Pliocene (earliest Blancan). Description—The left humerus (ETMNH 20502) consists only of the distal extremity of the bone, including the trochlea and medial epicondyle (Fig. 3A). There is no evidence of an epiphyseal plate, indicating the specimen is from an adult individual, but some weathering/erosion is evident on the margins of the trochlea and medial epicondyle. Overall, size and morphology of the element are similar to that of larger specimens of Sylvilagus (Table 3), but there are some notable differences. The distal articulation (trochlea) is like that of other studied leporids, with a prominent central groove flanked by a pair of raised splines, though they are somewhat weathered in the fossil specimen. The groove in ETMNH 20502 is shallower than in extant leporids studied and the lateral portion of the articular surface is also relatively broader. Similarly, the medial epicondyle of ETMNH 20502, though worn, was clearly relatively larger than in extant leporids. The ratio of epicondylar width of the humerus relative to distal articular breadth in ETMNH 20502 (HEW/HartW = 1.245) is greater than in any of the extant taxa studied (HEW/HartW range from 1.152 to 1.218), as well as the humeri of the smaller leporine present at the site (HEW/HartW = 1.162 and 1.169). The tibiofibula (ETMNH 18440) has the distal portion preserved and there is no evidence of an epiphyseal plate, indicating the specimen is from an adult individual (Figure 3G). Overall, the morphology and proportions of the tibia closely resembles that of the specimens of A. vagus described from Idaho (Campbell, 1969), as well as studied specimens of Sylvilagus audoboni and S. floridanus. The distal articular facets of the tibiofibula are like those of extant leporines studied, with a distally extended medial astragalar articular facet, deeply depressed lateral astragalar articular Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 10 facet, and distally extended calcaneal articular facet. The articular facets are the same width and capable of articulation with the referred astragalus of cf. Alilepus sp. (ETMNH 18434). The medial malleolus has a deep sulcus for the tibialis posterior muscle. The lateral malleolus is prominent and the sulcus for the peroneus longus tendon is clear and prominent. The left astragalus (ETMNH 18434) is incomplete, with the entirety of the astragalar head and neck missing and some weathering/erosion evident on the anteroventral margin of the trochlea (Figure 3C, D). The morphology of the trochlea is typical of extant leporids studied, with the medial articular surface larger and longer than the lateral articular surface, a deep groove running between the articular surfaces, and prominent splines running anteroposteriorly along each. Only the posterior calcaneal articular facet is preserved, it is triangular in shape with its apex extending laterally approximately half-way across the bone; that shape is similar to extant leporines like Sylvilagus, Lepus, and Brachylagus, but is not typical of archaeolagines, where the facet is more restricted to the medial aspect of the bone (Fostowicz-Frelik 2007). Figure 3. Selected postcranial specimens of leporids from the Gray Fossil Site, Tennessee. Humerus: A. ETMNH 20502, cf. Alilepus sp.; B. ETMNH 20518, Leporinae indeterminate. Astragalus: C-D. ETMNH 18434, cf. Alilepus sp., C. dorsal view, D. ventral view; E-F. ETMNH 22421, Leporinae indeterminate, E. dorsal view, F. ventral view. Tibia: G. ETMNH 18440, cf. Alilepus sp.; H. ETMNH 13805, Leporinae indeterminate. Calcaneum: I. ETMNH 8054, cf. Alilepus sp.; J. ETMNH 9708, Leporinae indeterminate. Scale bar equals 2 mm. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 11 Table 3. Postcranial measurements (in mm) of leporines from the Gray Fossil Site, and a comparative sample of Neogene leporid species. Measurements of Lepus californicus, Sylvilagus floridanus, Sylvilagus obscurus, and Brachylagus idahoensis directly measured from specimens in the ETMNH collection. Measurements for Alilepus vagus from Campbell (1969), Trischizolagus dumitrescuae from Averianov (1995), and Hypolagus beremdensis, Oryctolagus cuniculus, Pentalagus furnessi, and Lepus europaeus from Fostowicz-Frelik (2007). Taxon Source Specimen # HEW HartW TibDW TibDD TibSW AstL AstW CalL CalW CalTL CalTW CalBL cf. Alilepus sp. Gray Fossil Site, TN ETMNH 20502 8.18 6.57 ETMNH 18440 9.05 4.92 4.91 ETMNH 18434 5.05 ETMNH 8054 23.57 8.54 10.72 5.55 9.20 Alilepus vagus Campbell 1969 Various 8.6-9.3 10.5- 13.2 6.2-7.5 11.4- 11.9 5.6-6.1 23.5- 24.5 5.8-6.6 Leporinae Indeterminate Gray Fossil Site, TN ETMNH 9709 6.90 5.94 ETMNH 20497 5.82 ETMNH 20498 5.05 ETMNH 20518 6.57 5.62 ETMNH 13805 8.37 4.36 4.61 ETMNH 9700 6.51 6.56 4.07 ETMNH 9708 17.23 6.74 7.43 4.18 6.77 Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 12 Taxon Source Specimen # HEW HartW TibDW TibDD TibSW AstL AstW CalL CalW CalTL CalTW CalBL ETMNH 21229 6.39 6.65 3.99 ETMNH 22421 9.42 4.14 Trischizolagus dumitrescuae Arverianov 1995 14.4 6.4 28.0 Hypolagus beremendensis Fostowicz- Frelik 2007 13.1 6.6 6.8 14.1 6.4 26.4 9.5 12.4 6.3 10.2 Oryctolagus cuniculus Fostowicz- Frelik 2007 12.4 5.3 5.9 11.9 6 23.0 8.1 11.2 6.2 8.5 Pentalagus furnessi Fostowicz- Frelik 2007 15.9 6.8 7.6 13.7 8.1 27.0 11.8 13.0 7.6 9.0 Lepus europaeus Fostowicz- Frelik 2007 16.4 8.8 7.6 17.3 8.1 34.5 11.7 17.4 8.3 12.6 Lepus californicus Various (n=2) 10.70- 10.90 8.89- 9.16 13.65- 14.25 7.67- 7.91 6.45- 6.65 13.55- 14.00 6.79- 6.96 29.21- 30.20 9.24- 10.75 13.59- 15.08 7.11- 7.52 10.80- 10.99 Sylvilagus audobonii Various (n=5) 6.67- 7.22 5.52- 6.19 8.61- 10.42 4.23- 4.94 4.47- 4.93 8.08- 9.69 4.21- 4.54 16.67- 19.59 6.21- 7.26 7.27- 8.28 4.06- 4.71 6.07- 7.73 Sylvilagus floridanus Various (n=2) 7.68- 7.83 6.37- 6.53 10.52- 11.11 5.18- 5.31 4.64- 5.1 10.11- 10.47 4.90- 5.18 20.4- 22.06 6.80- 7.43 8.87- 8.99 4.63- 5.31 7.79- 7.85 Brachylagus idahoensis Various (n=2) 5.49- 5.76 4.73- 4.75 7.29- 7.45 3.58- 3.96 3.43- 3.56 7.31- 7.36 3.48- 3.60 13.37- 13.46 4.87- 5.49 4.93- 5.25 2.97- 3.27 5.35- 5.54 Table 3, continued. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 13 The right calcaneum (ETMNH 8054) is complete (Figure 3I), and similar in both size and morphology to extant leporines studied. Notable differences between the calcaneum of ETMNH 8054 and extant taxa studied can be seen in the ectal prominence, ectal facet, and cuboid facet. The ectal prominence of ETMNH 8054 is relatively larger than in extant taxa studied. In ETMNH 8054, the ectal facet is relatively mediolaterally narrow and ovoid in shape, which is actually fairly similar to specimens of Brachylagus, and distinct from studied specimens of Sylvilagus and Lepus where the ectal facet is rather triangular and broad. The cuboid facet of Sylvilagus and Lepus is more concave (has a smaller radius of curvature) and the cuboid facet of Brachylagus is more broad than that of ETMNH 8054. As in other leporids, there is a clear calcaneal canal, though in ETMNH 8054 it has two medial openings adjacent to and proximal to the sustentaculum, and a single lateral opening adjacent to the lateral surface of the ectal prominence. Interestingly, the calcaneum from GFS falls within the range of lengths for the specimens of A. vagus described from Idaho (Table 3), but the element is generally more elongate and slender than the specimens noted by Campbell (1969). Remarks—Postcranial remains of leporids from GFS are fairly abundant, including multiple elements that clearly come from two distinctly different size taxa (Figure 3). The sizes of these postcranial remains (Table 3) are consistent with observed dental material, with a clearly larger taxon distinct from the smaller one. The fact that two of the larger specimens, the tibiofibular (ETMNH 18440) and astragalus (ETMNH 18434) are capable of articulation with one another, despite originating from different samples at GFS suggests they are from the same taxon. Based on both size and morphology, we refer larger specimens to cf. Alilepus sp.; the overall size of these specimens are comparable to larger specimens of Sylvilagus floridanus studied (Table 3). The morphologies of the bones referred to cf. Alilepus sp. are consistent with the postcrania of Alilepus vagus described from the Glenns Ferry Formation of Idaho (Campbell, 1969), though, with the exception of the calcaneum, the GFS specimens are all slightly smaller than those from Idaho (Table 3). We consider it likely that these specimens are actually from Alilepus vagus, but the absence of associated cranial and postcranial elements at the site prevents definitive attribution. There are several interesting features of the referred postcranial specimens that warrant discussion. The distal humerus (ETMNH 20502) has several features that suggest slightly different locomotor habits in cf. Alilepus sp. than those of extant leporids like Lepus and Sylvilagus. While the morphology of this taxon is still clearly consistent with cursoriality, the larger medial epicondyle of the humerus reflects relatively larger areas of muscle attachment for the wrist and digital flexors (Reese et al. 2013, Samuels and Van Valkenburgh 2008) and the more shallow groove in the trochlea indicates less resistance to dislocation of the elbow joint (Hildebrand and Goslow 2001, Winkler et al. 2016), features that may suggest more terrestrial or burrowing habits. The apparent lesser degree of cursoriality in A. vagus was previously recognized by Campbell (1969). The presence multiple of calcaneal canal openings (as is seen in ETMNH 8054) has been noted for extant leporids, but not in any described fossil taxa (Bleefeld and Bock 2002). Genus NOTOLAGUS Wilson 1937 Notolagus lepusculus Hibbard 1939 (Figure 4, Tables 1–2, Supp. Tables 1 and 2) Referred Specimens—ETMNH 20524, right dentary with incisor, unerupted p3, dp4, unerupted p4, m1; ETMNH 13808, 20520, 20523, 21071, 21072, 21228, 21233, 22422, p3; ETMNH 9693, 9705, 20509, 20602, 20606, lower molariforms (p4–m2); ETMNH 21232, L dp3, dp4; ETMNH 9697, P2; ETMNH 9696, 12289, 12292, 18429, 20605, 20607, 21226, 21227, 21230, upper molariforms (P3–M2). Locality—Gray Fossil Site, Washington County, Tennessee. Age—Early Pliocene (earliest Blancan). Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 14 Description—There are only two dentaries of this taxon from the GFS sample; ETMNH 21233 is a small jaw fragment with the p3 (Figure 4 E–F) and ETMNH 20524 is a fairly complete specimen from a relatively young individual, and bears a small incisor, an unerupted p3 with little wear, a heavily worn and loose dp4, an unerupted p4, and slightly worn m1 (Figure 4 G–H). In ETMNH 20524, the masseteric fossa extends anteriorly to below the trigonid of the m2. In both specimens, the diastema does not dip strongly anterior to the p3, and bears a relatively gentle curvature. The incisor is relatively narrow, dorsally flattened, and enamel extends about halfway onto its lateral surface. All p3 specimens from the GFS sample are distinctly anteroposteriorly elongate and mediolaterally narrow (Figure 4 A–E). The enamel reentrants of all specimens are cement filled. In worn p3 specimens (ETMNH 20520, 20523, 21071) the paraflexid (AIR) is deep and curves distally, the protoflexid (AER) is shallow, the hypoflexid (PER) crosses about half the tooth, and the mesoflexid (PIR) is absent or shallow. The paraflexid (AIR) is crenulated and its posterior margin is adjacent the hypoflexid (PER) in nearly all specimens, though it is variably forked. The Figure 4. Specimens of Notolagus lepusculus from the Gray Fossil Site, Tennessee. A. ETMNH 20520, R p3; B. ETMNH 21071, L p3; C. ETMNH 20523, R p3; D. ETMNH 21228 L p3, E-F. ETMNH 21233, L dentary with p3: E, occlusal view; F. lateral view; G-H. ETMNH 20524, L dentary with m1, unerupted p3 and p4: G, occlusal view; H. lateral view; I. ETMNH 21232, L dp3, dp4; J. ETMNH 9697, R P2. Scale bars equal 1 mm for A-D and I-J and 2 mm for E-H. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 15 paraflexid and protoflexid nearly meet in ETMNH 20520, but in other specimens (ETMNH 20523, 21071, 21072) the two flexids are fairly widely separated. In ETMNH 20523 the paraflexid (AIR) is not crenulated at the occlusal surface, but it is at the base of the tooth. Both the protoflexid (AER) and hypoflexid (PER) are variably crenulated, with pronounced crenulation evident in ETMNH 20520 and 21071, and subtle crenulation in ETMNH 20523. The mesoflexid (PIR) is absent in some specimens (ETMNH 20520, 21071), but it changes with wear in others, it is very shallow at the occlusal surface of the crown and absent from the base of ETMNH 20523. In the relatively unworn p3 specimens (ETMNH 13808, 21228, 22422) there are distinct differences between the reentrant pattern on the occlusal surface of the tooth and the tooth base. On the occlusal surface, the protoflexid (AER) and paraflexid (AIR) meet (in ETMNH 13808) or nearly meet (ETMNH 21228) in some specimens, which isolates the anteroconid; in the completely unworn ETMNH 22422 the two reentrants do not meet, as they seem to actually originate slightly below the apex of the trigonid. The hypoflexid (PER) is deep, crossing more than halfway across the tooth in all specimens. The mesoflexid (PIR) is shallow (in ETMNH 13808, 20523, 22422) or absent (ETMNH 21228). At the base of each of these teeth, the paraflexid (AIR) is deep, crenulated and forked, the protoflexid (AER) is shallow, the hypoflexid (PER) is deep and crosses more than halfway across the tooth, and the mesoflexid (PIR) is missing and only evident from some cementum on the posterolingual surface of the tooth. In addition to the juvenile dentary and eight p3 specimens, five lower molariform teeth are referred to this taxon. As in the m1 in the dentary of ETMNH 20524, these other referred lower molariform teeth (p4–m2) lack crenulations. The widths of these teeth are similar to the widths of the sample of p3 specimens from GFS, as well as m1 of ETMNH 20524. Two deciduous teeth found associated with one another, a dp3 and dp4 (ETMNH 21232, Figure 4I), are also referred to this species. Though deciduous teeth have not been described for Notolagus previously, the size and morphology of the dp4 in ETMNH 21232 closely matches that of the worn dp4 associated with ETMNH 20524, which also includes an unworn p3 that allows identification of the specimen. The dp3 (ETMNH 21232) has a prominent anteroconid that is separated from and larger than either the metaconid or protoconid, which are about the same size. The trigonid of the dp3 is centrally joined to the talonid by a narrow ridge of enamel. The dp4 (ETMNH 21232) has subtle anteroconid along the anterior margin of the trigonid, a large protoconid, and slightly smaller metaconid. The trigonid of the dp4 is separated from the talonid at the current level of wear (no “bridge” of enamel is present). The only P2 (ETMNH 9697, Figure 4J) in the sample has two anterior reentrants, the lingual portion (hypercone) is triangular in shape and particularly broad anteroposteriorly, and the labial portion (lagicone) is rounded and narrower. The paraflexus (MAR) is particularly deep (extends over half the length of the tooth) and is oriented primarily anteroposteriorly, curving only slightly laterally. The mesoflexus (EAR) is very shallow. No internal anterior reentrant (IAR) is evident on the P2, though there is a subtle concavity to the anterointernal surface of the lingual portion of the tooth. While the paraflexus is cement-filled, the mesoflexus is not, and the rest of the anterior surface of the tooth completely lacks cementum. In addition to the single P2, nine upper molariform teeth are referred to this taxon. The widths of these upper teeth are similar to the widths of the sample of p3 and lower molariform teeth from GFS. Remarks—The specimens of Notolagus from GFS are referred to N. lepusculus based on having a p3 with a posteriorly deflected AIR, AIR and AER not merged in any worn specimens, and variably present PIR (White 1991a). The p3 of N. velox has a relatively laterally oriented AIR, the AIR and AER are fused in most specimens, and the PIR is absent (Moretti 2018, White 1991a). It is important to note that the AIR and AER do merge in the unworn crown of ETMNH 13808 and isolate the anteroconid, though the two reentrants are clearly separate at the base of the tooth. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 16 Another difference of the GFS sample from the diagnosis of N. lepusculus by White (1991a) is that the P2 (ETMNH 9697) has two anterior reentrants, whereas previously reported P2 specimens of the species had 3 reentrants. The GFS sample of Notolagus lepusculus is characterized by considerable variability in size and p3 morphology (Figure 4 A–E). Overall, the GFS sample (Table 1) is comparable to and broadly overlaps with the range of p3 sizes for N. lepusculus reported by White (1991a) and Moretti (2018). The largest and most worn p3 specimens in the GFS sample are over 25% larger than the smallest worn specimens. The cheek toothrow length of ETMNH 20524 is smaller than in previously reported specimens of N. lepusculus (Table 2), but this is not surprising given the young age of this individual and the fact that dental dimensions of lagomorphs can change dramatically through the course of wear (Bair 2007, Kraatz et al. 2010). Several morphological features used to distinguish Pronotolagus from Notolagus, like lack of crenulation on the paraflexid (AIR) and presence of a mesoflexid (PIR), are variably present among specimens in the GFS sample. White (1991a) actually noted that the PIR was present in two of the specimens of N. lepusculus he examined. Some of these features are even variable between the occlusal surface and base of teeth in the GFS sample (ETMNH 13808, 20523). Overall, the teeth show a pattern of increasing complexity through wear, with: 1) the protoflexid (AER) and hypoflexid (PER) clearly evident in all individuals, 2) the paraflexid (AIR) highly variable and becoming deeper, more crenulated, and variably forked through wear, and 3) the mesoflexid (PIR) present in some specimens, primarily those with lower wear. That variability has important implications for the taxonomic placement of the genus and for identification of fossil leporid specimens. Wilson (1937) originally described Notolagus as an archaeolagine based on the fact that the p3 bore an AIR rather than PIR. Later White (1991a) assigned the genus to the Leporinae because of the presence of an AIR, an assignment which was followed by Moretti (2018) among others. However, Dawson (2008) suggested that it be considered a highly derived archaeolagine since leporines are characterized by possession of a PIR or remnant thereof (Hibbard 1963). Given the fact the PIR is variably present among specimens the GFS sample, this supports assignment of the genus to Leporinae, placing it among the most primitive members of the subfamily along with Pronotolagus (Dawson 2008, White 1991a). The large degree of dental variability observed here suggests caution should be used when studying isolated specimens of fossil leporids, and points to risk of incorrect identifications if only small samples are examined. For example, a specimen like ETMNH 20523 (Figure 4C) could be incorrectly referred to Pronotolagus based on the reentrant pattern if only its occlusal surface were preserved or examined, which could easily happen if that tooth were preserved sitting within a dentary or as an isolated tooth with its base missing. The P2 referred to Notolagus from GFS (ETMNH 9697, Figure 4J) is clearly distinct from the other GFS leporid, based on the structure of its anterior reentrants and lack of cementum on its anterior surface. The size of ETMNH 9697 is also fairly similar in width to the smaller and less worn p3 specimens of N. lepusculus in the sample (Supplemental Table 1). ETMNH 9697 has two anterior reentrants, in contrast to the three reentrants noted by White (1991a) in his diagnosis of N. lepusculus. While there is no internal anterior reentrant (IAR) evident on the P2, the presence of a subtle concavity to the anterointernal surface of the lingual portion of the tooth suggests it may have been evident at a lower stage of wear, or variably present. Other species of Notolagus, namely N. velox, have been described as having only two anterior reentrants (Wilson 1937). White (1991a) also described N. lepusculus as having “MAR deeper than EAR” and N. velox as having “MAR slightly deeper than EAR”; in ETMNH 9697 the paraflexus (MAR) is particularly deep and the mesoflexus (EAR) is very shallow, which resembles N. lepusculus. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 17 Leporinae Indeterminate (Figure 3, Table 3) Referred Specimens—ETMNH 9709, 20497, 20498, 20518, distal humeri; ETMNH 13805, distal left tibiofibula; ETMNH 22421, left astragalus; ETMNH 9700, 9708, 21229, calcaneum. Locality—Gray Fossil Site, Washington County, Tennessee. Age—Early Pliocene (earliest Blancan). Description—The referred humeri (ETMNH 9709, 20497, 20498, 20518) are all from the left side and preserve only the distal end of the bone (Figure 3B); the only specimen that includes more than the distal extremity is ETMNH 20498. Each of the fossil specimens have morphology similar to studied specimens of Sylvilagus, similar in size to smaller specimens of S. audobonii and substantially smaller than extant S. floridanus. The distal articulation (trochlea) is like that of extant leporids studied, with a prominent and deep central groove flanked by a pair of raised splines, which contrasts with the shallower groove described for the referred specimen of cf. Alilepus sp. (ETMNH 20502). The epicondyles of the distal humerus are small (HEW/HartW = 1.162 and 1.169), similar in morphology and size to smaller individuals of S. audobonii studied. The left tibiofibula (ETMNH 13805) only has its distal-most portion preserved; there is no evidence of an epiphyseal plate, indicating the specimen is from an adult individual (Figure 3H). Overall, the morphology of the tibia closely resembles that of studied specimens of Sylvilagus, slightly smaller than S. audobonii and substantially smaller than S. floridanus, and larger than Brachylagus. The distal articular facets of the tibiofibula are like those of extant leporines studied, with a distally extended medial astragalar articular facet, deeply depressed lateral astragalar articular facet, and distally extended calcaneal articular facet. The articular facets are the same width and capable of articulation with the astragalus to this taxon (ETMNH 22421), but much smaller than in the astragalus referred to cf. Alilepus sp. (ETMNH 18434). The medial malleolus has a deep sulcus for the tibialis posterior muscle, and that sulcus extends more proximally on the diaphysis than in Sylvilagus, Lepus, or Brachylagus. The lateral malleolus is prominent and the sulcus for the peroneus longus tendon is clear and prominent, but narrower than in Sylvilagus or Lepus, more similar to that of studied specimens of Brachylagus. The left astragalus (ETMNH 22421) is complete (Figure 3E, F), and the morphology is similar to that of extant leporines studied. The overall morphology and size of the bone is similar to that of Sylvilagus audobonii. As described in the astragalus of cf. Alilepus sp. above, the posterior calcaneal articular facet is triangular in shape with its apex extending laterally approximately half-way across the bone, similar to extant leporines. The neck of the astragalus does not show a deep and prominent constriction, contrasting with archaeolagines like Hypolagus (Campbell 1969, Fostowicz-Frelik 2007). The neck of the astragalus in ETMNH 22421 is relatively long, and the ratio of width of the astragalus relative to its length for this specimen (AstW/AstL = 0.439) is smaller than in any of the extant taxa studied (AstW/AstL range from 0.461 to 0.531). Three calcanea are referred to this taxon, one right (ETMNH 9708) and two left (ETMNH 9700, 21229). The most anterior portions of both ETMNH 9700 and 21229 are missing, thus the only specimen with a complete cuboid facet is ETMNH 9708. These are similar in morphology to extant leporines studied, in the range of size of studied specimens of Sylvilagus audobonii, but smaller than Sylvilagus floridanus. Unlike the calcaneum of cf. Alilepus sp. (ETMNH 8054), the ectal prominence of these specimens is similar in proportions to that of extant taxa studied, and the ectal facet is relatively broad and either round or triangular. The cuboid facet of these specimens has a relatively smaller radius of curvature, like that of Sylvilagus and Lepus. As in other leporids studied, there is a clear calcaneal canal, with a single medial opening adjacent to and proximal to the sustentaculum, and a lateral opening adjacent to the lateral surface of the ectal prominence. Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 18 Remarks—As mentioned above, leporid postcranial remains at GFS are from two distinctly different size taxa (Figure 3, Table 3), consistent with observed dental material, and have some differences in aspects of their morphology. The larger specimens, here referred to cf. Alilepus sp., are quite similar to previously described material of Alilepus, but there are quite a few smaller and morphologically distinct specimens from GFS. Those smaller remains are similar in size to S. audobonii, smaller than S. floridanus and larger than Brachylagus idahoensis (Table 3). It is important to point out that among those smaller specimens, the tibiofibula, astragalus, and calcaneum described above all are capable of articulation with one another, despite originating from different samples at GFS. Consequently, these specimens are considered to be from a single leporine species. The smaller postcranial remains have a number of morphological features that distinguish them from the specimens of cf. Alilepus sp. and extant leporines studied (Sylvilagus, Lepus, Brachylagus), indicating they are from a leporine distinct from any of those taxa. In particular, the lateral and medial malleolus of the tibia and the neck of the astragalus are distinct from extant and fossil leporines studied, and the ectal prominence and ectal facet of the calcaneum are distinct from the described specimen of cf. Alilepus sp. Based upon their size, abundance, and morphological differences from other studied taxa, the smaller GFS leporine remains are considered to most likely belong to Notolagus. Since there are no associated cranial and postcranial specimens yet recovered from GFS, we cannot confidently make a more precise attribution than Leporinae here. These specimens do represent the first postcranial remains described as possibly attributed to that genus. Several aspects of the morphology of the smaller GFS leporine suggest it had a locomotor ecology similar to relatively cursorial extant members of the family. The prominent splines and deep groove in the trochlea of the humeri and the relatively small epicondyles indicate the smaller GFS leporine was relatively cursorial, with an elbow morphology adapted to resist dislocation and lacking prominent muscle attachments for wrist and digital flexors. Similarly, the relatively elongate astragalus in the smaller GFS leporine would yield a relatively high velocity ratio for the muscles responsible for plantar flexion of the foot, which is a morphology characteristic of more cursorial leporids (Fostowicz-Frelik 2007). Discussion The two leporids known from the Gray Fossil Site are well-known taxa with limited stratigraphic ranges (Supplemental Table 3); Alilepus vagus was previously known to have a broad geographic range, within the Pacific Northwest (WA and ID), Great Basin (NV), and Great Plains (NB), and now into the southern Appalachian region. With the specimens described here, the range of Notolagus lepusculus is also much broader, extending from the Southwest (AZ and NM), to the Great Plains (KS and TX), and now into Appalachia. These are the first records of both species east of the Mississippi River. Several extant rabbits in North America have particularly expansive ranges; for example, the respective ranges of Lepus americanus and Sylvilagus floridanus today encompass the fossil distributions of A. vagus and N. lepusculus, and more (Bittner and Rongstad 1982, Chapman et al. 1980, Chapman and Ceballos 1990, Murray 2003). These two taxa are biostratigraphically useful and were recently used to help refine the interpreted age of the Gray Fossil Site (Samuels et al. 2018), prior records of these species are listed in Supplemental Table 3. The earliest records of Alilepus vagus are from the Santee Local Fauna of Nebraska (White 1987), which has recently been discussed as representing the early Pliocene (latest Hemphillian NALMA), likely between 5.3 and 5.0 Ma (Martin et al. 2017). The most abundant and well-dated records of this species are from the Hagerman Local Fauna, between 4.18 and 3.11 Ma, from the Glenns Ferry Formation of Idaho (Ruez 2009). The latest records of A. vagus are Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 19 from the early Pleistocene (late Blancan) age Grand View Fauna in Idaho, dating to between 2.6 and 2.1 Ma (White 1987, White and Morgan 1995). All known records of Notolagus lepusculus are from the Blancan NALMA (Moretti 2018), with the earliest being the early Pliocene age Truth or Consequences fauna of New Mexico (White 1991a). Most other records of N. lepusculus are from the late Pliocene, though the record from Roland Springs Ranch in Texas is early Pleistocene in age (Moretti 2018). Based on the inferred age of the Gray Fossil Site, between 4.9 and 4.5 Ma (Samuels et al. 2018), the record of N. lepusculus there may be the earliest record of the species. While both GFS leporids are relatively well-known in the fossil record of North America, the forest ecosystem preserved at the site is in sharp contrast to that of other sites where they occur. Floral evidence from the site along with the abundance of arboreal mammals point to the presence of an oak, hickory, pine forest habitat (Ochoa et al. 2016), likely densely wooded with at least a partially-closed canopy. Rabbits do commonly occur in such habitats today (Chapman et al. 1980, Chapman and Ceballos 1990, Murray 2003), but every other site that records these fossil taxa represent much more open environments, as evidenced by the abundance of large cursorial mammals. The lack of records of these Neogene rabbits from sites that preserve forest habitats is at least, in part, a consequence of the biases in the late Cenozoic fossil record of North America, which is characterized by the presence of many arid sites from the western and central US and relatively few eastern sites (Bell et al. 2004, Tedford et al. 2004). It is important to point out that while most of the specimens from GFS described here are isolated teeth and fragmentary postcranial bones, very few show evidence of pitting or erosion consistent with digestion by predators. Fragmentation of bones may indicate predation and transport of specimens (Hockett 1989, 1995; Lloveraas et al. 2008a, b; Schmitt and Juell 1994). However, the compacted sedimentary deposits in the sinkhole at GFS are also characterized by complete fragmentation of nearly everything preserved at the site, thus fragmentation of specimens alone is not good evidence of predation. Only a few of the GFS leporid specimens, like ETMNH 18434 and 20502, show taphonomic modification like pitting and erosion consistent with digestion by predators (Lloveras et al. 2008a, 2008b; Schmitt and Juell 1994). The majority of leporid specimens recovered at GFS were likely from individuals that lived in the local area around the site, rather than having been transported to the site from another area by predators. This suggests the GFS leporids were actually inhabiting the oak, hickory, pine forest habitat preserved at the site, rather than some more open habitat farther afield. As was noted by Dawson (1958), there seem to be two size classes of leporids present at many fossil sites and in recent faunas. The two rabbits at GFS represent a larger, less abundant Alilepus and smaller, more abundant Notolagus; this is similar to the co-occurrence of the larger Lepus and smaller Sylvilagus observed in many modern communities (Dawson 1958). In the southern Appalachian region today, two different cottontails (Sylvilagus floridanus and S. obscurus) cooccur with snowshoe hares (Lepus americanus) at higher elevations (Bittner and Rongstad 1982). Based on their morphological similarity to extant leporines studied, the two GFS leporids likely filled similar niches in the past. While the cranial and dental morphology of the two species do not provide any evidence of apparent niche partitioning, the postcranial morphology of the two taxa preserved at the site are somewhat different. Despite being limited to a few fragmentary specimens, they can offer some interesting insights into how these extinct rabbits may have lived. Living lagomorphs vary substantially in their degree of cursoriality and in some aspects of their limb morphology, with the limbs of the more cursorially-specialized Lepus generally showing elongation of elements and reduced mechanical advantage of joints relative to those of the somewhat less-cursorial Sylvilagus (Young et al. 2014). The smaller rabbit at GFS (possibly Notolagus) displays features that suggest it was relatively cursorial, including elbow joint morphology characteristic of preventing dislocation Eastern Paleontologist J.X. Samuels and J. Schap 2021 No. 8 20 (Hildebrand and Goslow 2001) and a smaller medial epicondyle of the humerus, along with a particularly elongate neck of the astragalus. In contrast, the larger cf. Alilepus sp. has an elbow joint morphology reflecting less specialization for resisting dislocation and larger wrist and digital flexors, suggesting greater mobility and power at the elbow joint, as is typical of burrowers (Reese et al. 2013, Samuels and Van Valkenburgh 2008, Winkler et al. 2016). This sort of difference in running adaptation among co-occurring leporids in the Pliocene was also previously observed in rabbits from the Hagerman Local Fauna (Campbell 1969), and is evident in many modern communities. 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