AMERICAN MUSEUM NOVITATES Number 3897, 41 pp. March 21, 2018 A New Species of Forstercooperia (Perissodactyla: Paraceratheriidae) from Northern China with a Systematic Revision of Forstercooperiines HAI-BING WANG,1, 2, 3 BIN BAI,1, 2, 4 JIN MENG,4, 1 YUAN-QING WANG1, 2, 3 ABSTRACT Forstercooperiines are a group of large, primitive rhinocerotoids that are commonly regarded as ancestral to later giant rhinos. However, the type genus of forstercooperiines, the Middle Eocene Forstercooperia, is one of the most poorly known rhinocerotoids, and is repre- sented only by fragmentary material. Here we name a new species, Forstercooperia ulanshire- hensis, based on five specimens, including a well-preserved cranium and a pair of complete mandibles. This new material was collected from the Ulan Shireh Formation in the western part of the Erlian Basin and the Irdin Manha Formation in the eastern part of the Erlian Basin, northern China. These specimens provide the most complete craniodental remains of Forster- cooperia sensu stricto (excluding Pappaceras), and on this basis the species-level taxonomy of forstercooperiines is thoroughly revised and six species of two genera are considered as valid. Specimens previously assigned to “Forstercooperia minuta” are reassigned to different species based on the revised diagnoses. All equivocal specimens that were thought to have an affinity with Forstercooperiinae are briefly discussed. Based on a new character matrix, phylogenetic analyses fully resolve the relationships of early rhinocerotoids, including the recovery of For- stercooperia and Pappaceras as sister groups. The occurrence of Forstercooperia ulanshirehensis in the eastern and western Erlian Basin is indicative of age correlation between the lower part of the Ulan Shireh Formation and the Irdin Manha Formation. 1 Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing. 2 CAS Center for Excellence in Life and Paleoenvironment, Beijing. 3 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing. 4 Division of Paleontology, American Museum of Natural History, New York. Copyright © American Museum of Natural History 2018 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3897 INTRODUCTION Forstercooperines are a group of primitive rhinocerotoids from the Asian Eocene that have a close affinity to paraceratheres (giant rhinos) (Lucas and Sobus, 1989; Qiu and Wang, 2007). Although this group has been studied since 1938 (Wood, 1938), the fossil record of forstercoo- periines is not so abundant as that of other rhinocerotoid groups. There have been a few revi- sions of the systematics of this group (Radinsky, 1967; Lucas et al., 1981; Lucas and Sobus, 1989), in which forstercooperiines were considered as monogeneric by these authors. For example, Pappaceras Wood, 1963, was synonymized with Forstercooperia Wood, 1939. How- ever, evidence showing distinct features between Pappaceras and Forstercooperia has cast doubt on this consideration (Qiu and Wang, 2007; Bai and Wang, 2012; Wang et al., 2016). In particu- lar, on the basis of a recently reported, well-preserved specimen of Pappaceras, the phylogenetic relationships of early rhinoceorotoids has been extensively explored and discussed, in which Pappaceras was shown not readily synonymous with Forstercooperia (Wang et al., 2016). None- theless, the phylogenetic relationships within forstercooperiines still remain open to discussion of the paraphyly of Pappaceras, primarily because of character conflicts and numerous missing character states for several taxa in the data matrix, particularly Forstercooperia, which is one of the most poorly known rhinocerotoids, represented by only a few fragmentary specimens (Wood, 1938; Chow et al., 1974; Qiu and Wang, 2007). The morphology ofForstercooperia is significant for further exploration of the phylogenetic relationships of early rhinocerotoids as well as forstercooperiines. Since Forstercooperia was established in 1938, four genera have been included in forstercoo- periines, including Cooperia Wood, 1938; Imequincisoria Wang, 1976; Forstercooperia Wood, 1939; and Pappaceras Wood, 1963. Cooperia was originally erected based on the type specimen AMNH 20116, which was already occupied by a nematode genus, so it was replaced by Forster- cooperia (Wood, 1938). The two species of Imequincisoria have been assigned to Forstercooperia and Juxia respectively, as proposed by Qiu and Wang (2007), and thus the generic name Imequin- cisoria should be abandoned. Wood (1963) established Pappaceras as a well-documented Eocene rhinocerotoid ancestral to later rhinocerotids. In contrast, Radinsky (1967) and Lucas et al. (1981) suggested that Pappaceras was a junior synonym of Forstercooperia in the context of assigning forstercooperiines to Hyracodontidae. They assigned both Asian and North American materials to this subfamily (Radinsky, 1967; Lucas et al., 1981). Subsequently, this bulk assignment to for- stercooperiines was challenged by the erection of the genus Uintaceras to encompass most of the North American materials formerly assigned to forstercooperiines (Holbrook and Lucas, 1997), restricting the distribution and evolution of forstercooperiines to Asia. Furthermore, new strati- graphical and morphological evidence lend more support to separating Pappaceras from Forster- cooperia (Meng et al., 2007; Qiu and Wang, 2007; Wang et al., 2010, 2016). Recent field investigation clarifies that the specimens of Forstercooperia are mainly from the Irdin Manha Formation or equivalent deposits, whereas all specimens of Pappaceras to date have been unearthed in the Arshanto Formation or equivalent sediments. Moreover, there is still a distinct morphological gap between Forstercooperia and Pappaceras, as recently suggested (Qiu and Wang, 2007; Bai and Wang, 2012; Wang et al., 2016) and that will be discussed in detail in this study. 2018 WANG ET AL.: NEW SPECIES OF FORSTERCOOPERIA 3 Among forstercooperiines, Pappaceras is the earliest representative, appearing first in the late early Eocene (Wang et al., 2016). It has a fairly abundant fossil record, represented by three species known from fragmentary craniodental elements (Wood, 1963; Lucas et al., 1981; Wang et al., 2016). In contrast, the type genus Forstercooperia, which is Irdinmanhan in Asian Land Mammal Ages, has a poor fossil record and consists of F. totadentata (the type species) and F. mazhuangensis that are represented only by a cranial fragment and a few dental fragments, respectively (Wood, 1938; Wang, 1976; Qiu and Wang, 2007). In the present study, we erect a new species of Forstercooperia, based on five specimens unearthed from the Eocene sediments in Erlian Basin, Nei Mongol, China, including a well-preserved cranium and a pair of complete mandibles. The new finding is fundamental for the comparative study of tapiromorphs, filling the large gap of the craniodental morphology of Forstercooperia and narrowing the morpho- logical gap between forstercooperiines and paraceratheriines. Additionally, it has great poten- tial to further resolve the phylogenetic relationships of forstercooperiines. MATERIALS AND METHODS Three new specimens (IVPP V20154, V20155, V20156) were recovered from the Irdin Manha Formation in the Irdin Manha site in the expeditions of the Institute of Vertebrate Paleontology and Paleoanthropology over the last 15 years (fig. 1). This is the type locality for the holotype of F. totadentata (AMNH 20116) (Wood, 1938). The other two specimens (AMNH 21608, 22101) were collected from the Ulan Shireh Formation at the Wulantaolegai site (previ- ously known as “4 miles north of Tukhum”) and the Wulanhuxiu site (previously known as “8 miles north of Tukhum Lamasery”), respectively, by the Central Asian Expeditions of the American Museum of Natural History in the 1920s (fig. 1) (Wang et al., 2012). The five speci- mens are not directly associated with each other, the new specimens were recovered in equiva- lent sediments in East and West parts of Erlian Basin as suggested in recent studies that the upper part of the Ulan Shireh Formation likely correlative to Irdinmanhan sediments (Wang et al., 2012). Anatomical terminology follows Qiu and Wang (2007), in which the entolophid corresponds to the “hypolophid” of Bai et al. (2010) and Mihlbachler (2008), and the hypolo- phid corresponds to the “cristid obliqua.” A list of specimens examined for this study is pro- vided in the appendix (see also table 1). Measurements were taken using digital calipers and are given in millimeters. For phylogenetic analyses, we adopted the character list from Wang et al. (2016) and coded the character states of the new species based on the new specimens reported in the present study. Following that character list, two polymorphic characters (chars. 29 and 30) are set as additive (or ordered) in this study. The phylogenetic analyses were performed using TNT 1.1 with the New Technology search method (Goloboff et al., 2008), under equally weighted par- simony. As conventionally used for large data sets, 200 ratchet iterations (Nixon, 1999), 100 drift cycles, and 10 rounds of tree fusion (Goloboff, 1999) were applied to conduct compre- hensive searches in the phylogenetic analyses. The data matrix has been archived in Morpho- bank (http://morphobank.org/permalink/?P2535). 4 AMERICAN MUSEUM NOVITATES NO. 3897 Institutional abbreviations: AMNH, American Museum