THE EARLY HEMINGFORDIAN (EARLY MIOCENE) POLLACK FARM LOCAL FAUNA: FIRST TERTIARY LAND MAMMALS DESCRIBED FROM DELAWARE1 Robert J. Emry2 and Ralph E. Eshelman2 ABSTRACT Land mammal fossils were discovered in 1992 in the lower part of the Calvert Formation at the Pollack Farm Site, a tem- porary excavation for highway construction, between Smyrna and Dover, Delaware. During the short time the pit was open the collection grew to become the most diverse Tertiary land mammal fauna known in eastern North America north of Florida. The assemblage, termed the Pollack Farm Local Fauna, includes at least 26 species representing at least 17 families. The age estab- lished by the land mammals is early Hemingfordian (early Miocene), in good agreement with the mean strontium-isotope age estimate of 17.9±0.5 Ma on mollusk shells. The fauna shares the greatest homotaxial similarity with the Thomas Farm Local Fauna of Florida, but also has several taxa in common with the classic early Hemingfordian faunas of the Great Plains, such as those from Quarry A of northeastern Colorado, the Runningwater Formation of western Nebraska, and the Flint Hill Quarry of southwestern South Dakota. The Pollack Farm Local Fauna provides a direct and unambiguous correlation between the North American Land Mammal Age system and marine biochronologies based on diatoms, radiolarians, foraminifers, and molluscs. INTRODUCTION Order ERINACEOMORPHA Although terrestrial mammals of Tertiary age have Family ?ERINACEIDAE been known from eastern North America for well over a cen- Unidentified genus or genera tury (e.g., Leidy, 1860), the eastern record has remained poor Order CHIROPTERA compared to the rich faunas known from western North Family VESPERTILIONIDAE America. In eastern North America, Tertiary land mammals Unidentified genus are best represented in Florida, with faunas ranging from Order RODENTIA Arikareean (about 22 Ma) to Hemphillian (about 5 Ma) Family CASTORIDAE (MacFadden and Webb, 1982). North of Florida, Miocene Anchitheriomys sp. land mammals are known only from a few specimens from “Monosaulax” sp. each of a few localities: Ashley River in South Carolina Family HETEROMYIDAE (Leidy, 1860), the Kirkwood Formation in Monmouth Proheteromys magnus County, eastern New Jersey (Marsh 1870a, 1870b, 1893; Family ZAPODIDAE Wood 1939), the Chesapeake Group of Maryland (Gazin and Plesiosminthus sp. Collins, 1950; Wright and Eshelman, 1987), and near Statenville in extreme southern Georgia (Voorhies, 1974). Order CARNIVORA Only a few of these sites represent early Miocene. Recent Family URSIDAE discovery (Ramsey et al., 1992; Benson, 1993) near Smyrna, ?Hemicyon just north of Dover, Delaware, of the most diverse assem- Family PROCYONIDAE blage of Tertiary land mammals known from eastern North Unidentified genera America north of Florida is therefore of special importance. Family AMPHICYONIDAE The assemblage, described below as the Pollack Farm Local Amphicyon intermedius Fauna, is early Miocene; more precisely, it is early Cynelos sp. Hemingfordian in the system of North American Land Family CANIDAE Mammal Ages (Wood et al, 1941; Tedford et al, 1987). The Tomarctus cf. T. thomsoni land mammal fossils occur in nearshore marine deposits Tomarctus cf. T. canavus associated with rich marine faunas, vertebrate and inverte- Order PERISSODACTYLA brate, thereby affording direct, unambiguous comparison of Family EQUIDAE marine and nonmarine biochronologies. Archaeohippus cf. A. blackbergi The land mammals of the Pollack Farm Local Fauna Anchitherium sp. are represented predominantly by single teeth and parts of Parahippus leonensis postcranial elements. In just a few instances are more than Family CHALICOTHERIIDAE one tooth associated in a single specimen. The land mammal cf. Tylocephalonyx sp. fauna includes a minimum of 26 species representing at least Family RHINOCEROTIDAE 17 families in 7 orders, summarized as follows: Unidentified genus or genera Order SORICOMORPHA Order ARTIODACTYLA Family PLESIOSORICIDAE Family TAYASSUIDAE Plesiosorex cf. P. coloradensis Cynorca sociale 1 In Benson. R.N., ed., 1998, Geology and paleontology of the lower Miocene Pollack Farm Fossil Site, Delaware: Delaware Geological Survey Special Publication No. 21, p. 153–173. 153 ?Desmathyus or Hesperhys For permission to collect at the Pollack Farm Site, and ?Family ANTHRACOTHERIIDAE for other courtesies and assistance that facilitated access to Family OREODONTIDAE the site, we thank David Duke of the Department of ?Unidentified genus Transportation of the State Of Delaware, Ed Adams of Family MOSCHIDAE Century Engineering, and Gordon Simonson of Pierson Blastomeryx galushai Engineering. Family uncertain Frederick Grady of the National Museum processed Unidentified genera (probably 2) and picked the washed matrix to recover the micromammals, which added substantially to the diversity of the collection. Acknowledgments Peter Kroehler did the photography for the plates and assist- From the first discovery of land mammal fossils at the ed with preparing and curating the material. Pollack Farm Site through the completion of this report, an For access to collections and assistance in identifying unusually large number of people have made direct and specimens we thank David Webb and Gary Morgan at the important contributions. First and foremost were the special Florida Museum of Natural History, and Richard Tedford at efforts of Gordon Simonson, supervisor at the site for the American Museum of Natural History. Pierson Engineering. Clearly two-thirds of the terrestrial Major funding for the field portion of this study was mammals known to us from the site are the direct result of provided by the National Geographic Society (grant 4778- his efforts. Not only did he personally find many of the spec- 92). The Remington and Marguerite Kellogg Memorial Fund imens, but with his contagious enthusiasm and spirit of vol- provided support for initial trips to the site by Smithsonian unteerism, he encouraged his fellow workers at the site to personnel. either donate their finds to the National Museum of Natural We thank Clayton Ray and Peter Kroehler for their History, or to loan them for making replicas. comments on the manuscript prior to submission. Careful The following persons donated land mammal fossils to critical reviews by Richard H. Tedford and S. David Webb the National Museum of Natural History: David Crew, John led to improvements in this report, for which we thank them. Danner, Mike Derieux, Stuart Derrow, David Duke, Evelyne Eshelman, Keith Glunt, Michael Miskofsky, Thomas METHODOLOGY O’Hagan, Mark Power, Deborah Paruszewski, Mark Though some of the vertebrate fossils reported herein Rikerson, Sandy Roberts, Gordon Simonson, Grace were collected in situ, most were collected from the surface, Simonson, Albert Snelson, Cheryl Snelson, Scott Walters, either of freshly exposed in situ sediment, of stockpiled sed- and Kenneth Webb. iment at the site, or at places where the sediment had been The following persons loaned their specimens for used as road bed or embankment fill. We are confident that study and casting: Mike Derieux, David Duke, Majdi El- all of the specimens used in this study were derived from the Taher, Ron Ford, Terry Fulmer, Keith Glunt, W. Hester, lower shell bed of the Cheswold sands of the lower Calvert Sarah Jones, Wayne Miller, Michael Miskofsky, Thomas Formation (Benson, 1993, 1998; Ramsey, 1998). This con- O’Hagan, John O’Neal, Krisin Pleasanton, Mark Power, clusion is supported by the fact that all fossils that were dis- Kelvin Ramsey (Delaware Geological Survey), John Ricard, covered in situ were from this lower shell bed, all specimens Mark Rickerson, Greg Turner, Tom Vos, Scot Walters, and have similar preservation, and all are consistent with a very Larry Yucht. The Virginia Museum of Natural History also restricted age assignment.3 loaned specimens for study. Most of the material was recovered by walking or In the field aspects of this study, Dave Bohaska crawling over the exposed pit surfaces, spoil piles, and road deserves special mention; he made a number of collecting bed fill surfaces. The best collecting conditions were after trips to the site, and was the National Museum’s primary con- rains on newly stockpiled shell bed material. On some occa- tact with Pierson Engineering and Century Engineering and sions buckets and shovels were used to toss water from the their employees, and with the many amateurs who collected pit (constant pumping of the pit was necessary to keep it much of the material. The following people from various from filling with water) onto the outcrop faces or surfaces of institutions assisted in collecting: Betty Ashby, Wally Ashby, spoil piles to wash matrix from fossils. Pumps with hoses, George Fonger, Vivian Marsh, Sandy Roberts, Albert and even buckets of front end loaders, were similarly Snelson, Cheryl Snelson, Curry Snelson, and Verna Muir, all employed with good results. When a potentially good lens of the Calvert Marine Museum Fossil Club; Joann Austin, was encountered in place, a tool such as an oyster knife was Ruth Bowman, Diane Crow, Stephen Curtis, Allison Elterich, used to carefully scrape away the surface a thin layer at a Charles Fithian, Libby Gregg, Alice Guerrant, Ann Horsey, time to expose fossils. Clydia Melson, Heather Patton, and James Stewart, all asso- Virtually all of the teeth of small mammals such as the ciated with Delaware State Museums; Lauck Ward and heteromyid rodent and bat were recovered by screening and Cheryl