A new species of Forstercooperia (Perissodactyla, Paraceratheriidae) from northern China with a systematic revision of forstercooperiines

2018·2.1 MB·English

by  Wang, Hai-bing, author

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 of Forstercooperia 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 of Natural History; CMNH,
Carnegie Museum of Natural History; IVPP, Institute of Vertebrate Paleontology and Paleoan¬
thropology; PGM, Geological Museum of China (Peking Geological Museum); UCMP, Uni¬
versity of California Museum of Paleontology
SYSTEMATICS
Mammalia Linnaeus, 1758
Perissodactyla Owen, 1848
Rhinocerotoidea Gray, 1825
Paraceratheriidae Osborn, 1923
Forstercooperiinae Kretzoi, 1940
Type genus: Forstercooperia Wood, 1938.
Included genus: The type genus and Pappaceras Wood, 1963.
Revised diagnosis: Small paraceratheriid of medium to large body size. Skull length
about 390-455 mm and length of upper/lower molar series about 70-130 mm. Skull dolicho¬
cephalic. Premaxilla in contact with nasal; preorbital fossa shallow; maxilla high; facial expo¬
sure of lacrimal large; frontal wide between orbits and followed by a distinct flange overhanging
postorbital cavity; postglenoid foramen absent. Upper premolars primitive with weak meta-
lophs, P3-4 transversely wide; ribs of upper premolars distinct. Antecrochet of Ml usually
present; metastyle of M2 elongated. Lower premolars primitive with weak entoconid of p4
present in some species; protolophid of lower molars anterolingually extended. Loss of PI/pi
present in some species. Cingulum/cingulid of cheek teeth usually present at anterior, lingual,
and posterior bases. Differs from other rhinocerotoids in having combination of basicranial
features: postglenoid process massive; posttympanic process enlarged, partially fused with par-
occipital process; paroccipital process slender and slightly longer than posttympanic process.
Differs from other rhinocerotoids except paraceratheriines in having posterior portion of cra¬
nium (from the postglenoid process to the occipital condyle) long, about 25% of the whole
length of cranium. Differs from other rhinocerotoids with combination of features of anterior
dentition: three upper/lower incisors conical and subequal in size with tight arrangement;
canines stubby, distinctively larger than incisors; and diastema short.
Forstercooperia Wood, 1938
Type species: Forstercooperia totadentata Wood, 1938.
Included species: The type species, Forstercooperia mazhuangensis Qiu and Wang, 2007,
and Forstercooperia ulanshirehensis, sp. nov.
Revised diagnosis: Large forstercooperiines with skull length about 455 mm and
length of Ml-M3/ml-m3 about 105-130 mm (table 1-3). Differs from Pappaceras in hav-
2018 WANG ET AL.: NEW SPECIES OF FORSTERCOOPERIA 5
FIG. 1. Location of the main fossil localities in the Erlian Basin. Three localities (Irdian Manha, Wulantaolegai,
and Wulanhuxiu), where the new specimens of F. ulanshirehensis were unearthed, are marked by red solid
stars. Black solid circles represent other known fossil localities, solid squares denote cities or counties, and
open circles denote towns and villages. This figure is modified from Wang et al., (2010).
ing a larger body size (the length of molar series greater than 100 mm), a transversely nar¬
rower postglenoid fossa with a well-developed median ridge separating two articular facets,
sagittal crest distinct, occipital condyle comparatively more enlarged, dentition complete;
12 slightly larger than II and 13, canines stout and rounded at base; P2 premolarized with
protocone and hypocone slightly separated; M3 triangular in occlusal outline along with
the absence of metacone and ectoloph; tooth crowns of lower incisors nearly symmetric
with distinct mesial and distal flanges, i2 larger than il and i3; and talonids of p3-4 elongate
with the presence of entoconid.
Forstercooperia ulanshirehensis, sp. nov.
Holotype: A nearly complete cranium (AMNH 21608) (figs. 2-4).
Referred specimens: A pair of complete mandibles (IVPP V20155) (figs. 5, 6), a frag¬
mentary maxilla with P3-M3 (IVPP V20154) (figs. 7A, 7B); a fragmentary mandible with the
6 AMERICAN MUSEUM NOVITATES NO. 3897
TABLE 1. Measurements of cranium of Forstercooperia ulanshirehensis (mm). H = height; L = length;
Max = maximum; W = width.
Cranium AMNH 21608
Basilar L 420a
Profile L (= total length) 455 a
Occipital-postorbital process, L 236.0
Premaxilla-postorbital process, L 225 a
PI-condyle, L 376.0
Postglenoid process-condyle, L 96.5
Anterior end of orbital-nasal notch, L 117.3 a
Premaxilla-anterior end of orbital, L 185.5a
Zygomatic, Max W 182a
Palatine at PI, W 53.2a
Palatine at Ml, W 51.8 a
Palatine at M3, W 52.8a
Postglenoid processes, Max W 131.5
Parocciptal processes, Max W 99.1
Occipital, H 120.5 a
Foramen magnum, Max W 24.9
Occipital condyles, Max W 76.3
Occipital condyle, H 42.9
Occipital condyle, W 35.9
a Approximate measurements.
lower canine and pl-4 (IVPP V20156) (figs. 7C, 7D), and a fragmentary mandible with p3-m3
(AMNH 22101) (fig. 8).
Etymology: The specific name ulanshirehensis refers to the Ulan Shireh Formation, in
which AMNH 21608 was collected.
Horizon and locality: AMNH 21608 (field number, 613), Ulan Shireh Formation, Wul-
anhuxiu site (previously known as 8 miles north of Tukhum Lamasery) of Erlian Basin, Nei
Mongol, China; AMNH 22101 (field number, 602), Ulan Shireh Formation, Wulantaolegai site
(previously known as 4 miles north of Tukhum) of Erlian Basin, Nei Mongol, China; IVPP
V20154, V20155, and V20156, Irdin Manha Formation, Irdin Manha site, Erlian Basin, Nei
Mongol, China. Middle Eocene.
Diagnosis: Small species of Forstercooperia, the length of upper premolar series about 81
mm, about 25% smaller than that of Forstercoopeia totadentata (-108 mm), about 20% smaller
than that of Forstercooperia mazhuangensis (-103 mm) (see appendix, tables 2-3). Upper pre¬
molars transversely slightly narrower. Protocone and hypocone of P2 barely separate, metaloph
of P2 narrow and posterolingually oriented. Metalophs (metaconules) of P3-4 short. Entoconid
of p4 present.
2018 WANG ET AL.: NEW SPECIES OF FORSTERCOOPERIA 7
TABLE 2. Measurements of upper dentition of Forstercooperia ulanshirehensis (mm). L = length;
W = width.
AMNH 21608 IVPP V20154
Left Right Right
PI L 17.6
PI W 11.9
P2 L 18.0 19.0a
P2 W 17.3
P3 L 24.6 23.4 a 21.3a
P3 W 25.8 27.0a 29.2a
P4L 25.4 23.8a 26.8
P4 W 31.3 34.4
Ml L 36.5 36.1a 38.5
Ml W 35.9 34.8
M2 L 39.9 39.3a 47.0
M2 W 43.3 41.3a 42.6
M3 L 33.3 32.6 41.1
M3 W 41.0 38.5a
P1-4L 81.4
Ml-3 L 106.7 104.2 a 123.0
PI-M3 L 177.8
Diastema between C-Pl, L 30.2 29.7a
a Approximate measurements.
Description
AMNH 21608 is well preserved except for the anterior portion of premaxilla and nasal,
and the zygomatic arch (figs. 2-4). In lateral view (fig. 2), the dorsal profile is fairly flat, char¬
acteristic of a dolichocephalic cranium. The premaxilla is nearly completely damaged, and the
alveoli of the upper canines represent the anterior tip of the preserved cranium. The rostral
portion of the nasal is not preserved, and in anterior view, the nasal is dorsoventrally thin
with the cross section platelike. The lateral border of the nasal smoothly curves lateroventrally
to meet the maxilla with the facial exposure of the nasal narrow. The suture of the nasal and
maxilla is almost horizontal. The maxilla is large and high, and trapezoidal in outline in lateral
view. Above the maxillary diastema (between the alveoli of the upper canines and upper pre¬
molars), the lateral surface of the maxilla is slightly concave. The preorbital fossa is present,
shallow and smooth on the lateral surface. The infraorbital foramen is a distinctive and large
opening, situated above P3. The maxilla posteriorly contacts the zygomatic and lacrimal by
forming a nearly vertical suture on the lateral surface. The postorbital process of the frontal
is well developed, situated above the posterior border of M3. The dorsal roof of the orbital
region is formed by the nasal extended posterolaterally and the wide frontal. The lacrimal has
AMERICAN MUSEUM NOVITATES NO. 3897
TABLE 3. Measurements of mandible and lower dentition of Forstercooperia ulanshirehensis (mm). H =
height; L = length; W - width.
IVPP V20155 IVPP V20156 AMNH
22101
il -condyle, L 421.0
pi-mandibular angle, L 364.0
Mandible at the condyle, H 178.0
Mandible at the coronoid process, H 217.0a
Horizontal ramus at pi, H 88.5
Horizontal ramus at ml, H 97.3
Symphysis, L 96.4
Left Right Left Right Left
il L 11.7 11.6
il W 16.0 17.1
i2 L 13.7 13.7
i2 W 18.5 16.7
i3 L
i3 W 14.6 a
cL 20.0 19.6 20.0 20.4
c W 14.3 15.0 16.6 16.9
pi L 19.0 19.4 17.0 17.2
pi W 10.4 10.6 10.6 11.0
p2 L 18.6 19.0 20.0 19.6
p2 W 11.0 10.8 13.8 13.6
p3 L 25.2 25.0 24.0 21.5a 23.3a
p3 W 14.5 14.2 15.0a 16.8a 15.4a
p4L 29.0 28.6 27.3 29.4
P4 W 17.2 16.8 20.0 17.4
ml L 35.3 35.5 31.0
ml W 22.6 22.4 22.2
m2 L 43.3 42.8 37.4
m2 W 26.0 27.2 25.4
m3 L 46.1 44.1 37.9
m3 W 27.5 25.5 24.8
pl-4 L 92.8 91.6 85.0
ml-3 L 129.5 a 125.4a 110.5
pl-m3 L 219.0a 218.0
Diastema between c-pl, L 34.9 35.2a 33.9a
Approximate measurements.
2018 WANG ET AL.: NEW SPECIES OF FORSTERCOOPERIA 9
FIG. 2. Cranium of F. ulanshirehensis (AMNH 21608) in lateral view. Abbreviations: for, foramen orbitale; fr,
frontal; fro, foramen rotundum; iof, infraorbital foramen; ju, jugal; lc, lacrimal; mr, median ridge of postgle¬
noid process; mx, maxilla; na, nasal; oc, occipital condyle; opf, optic foramen; pa, parietal; pf, preorbital fossa;
pgp, postglenoid process; pop, postorbital process; pocp, paroccipital process; ppf, posttympanic-paroccipital
foramen; ptp, posttympanic process; sc, sagittal crest; sq, squamosal; tc, temporal crest.
a rough surface with some damages and its anterior and ventral sutures are identified, nearly
forming a right angle. The zygomatic contacts the lacrimal nearly at the middle point of the
anterior orbital margin. The zygomatic is flat on the lateral surface, rough on the ventral sur¬
face, and shows a well-developed ridge along the ventrolateral margin. The zygomatic arch is
not preserved, and rises slightly posteriorly. The poor preservation of the orbital region makes
it hard to accurately identify particular foramina and fissures, except the one regarded as the
optic foramen on the left side (fig. 2). Ventral to the optic foramen is the foramen orbitale and
the foramen rotundum, but the boundary of the two openings is not preserved. Laterally, the
zygomatic process of the squamosal is dorsoventrally thin. The zygomatic arch is badly dam¬
aged on the both sides. The glenoid fossa is widely open. The squamosal ventrally bears the
postglenoid process, which possesses two articular facets divided by a ridge, the medial facet
facing anteriorly and the lateral facet facing anterolaterally. Posteriorly, the posttympanic pro¬
cess is widely separated from the postglenoid process. The posttympanic process is partially
fused with the paroccipital process posteriorly, and the former is robust and anteroposteriorly
10 AMERICAN MUSEUM NOVITATES NO. 3897
FIG. 3. Cranium of F. ulanshirehensis (AMNH 21608) in dorsal view. Abbreviations: fr, frontal; iof, infraorbital
foramen; ju, jugal; mx, maxilla; na, nasal; nf, nutrient foramen; pa, parietal; sc, sagittal crest; sq, squamosal.
thickened, whereas the latter is more slender, slightly longer and nearly vertically directed.
Lateral to the posttympanic process and the paroccipital process is the posttympanic-paroc-
cipital foramen with a large opening at the dorsal extremity (equivalent to mastoid foramen)
(fig. 2) (Holbrook, 2001). The occipital extends posteriorly beyond the level of the occipital
condyle.
In dorsal view (fig. 3), the tip of the nasal might extend anteriorly more than the level of
the upper canine, judging from the width of the posterior part of the nasal. The nasal increases
in width posteriorly, and extends lateroposteriorly to the anterior part of the postorbital pro¬
cess, contacting the frontal at the level of the anterior border of the orbit. The frontal contrib¬
utes to the widest part of the cranium at the level of the postorbital process, and decreases in
width posteriorly. The frontoparietal crests gradually rise from the postorbital process posteri¬
orly, and fully merge together slightly anterior to the suture of the frontal and parietal (~10 cm