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Journal of Vertebrate Paleontology e928305 (10 pages)
! by the Society of Vertebrate Paleontology
DOI: 10.1080/02724634.2014.928305
ARTICLE
THE FIRST SKULL OF SIVAMERYX AFRICANUS (ANTHRACOTHERIIDAE,
BOTHRIODONTINAE) FROM THE EARLY MIOCENE OF EAST AFRICA
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JOHN ROWAN,*,1 BRENT ADRIAN,2 and ARI GROSSMAN1,2
School of Human Evolution and Social Change, Arizona State University, Tempe, Arizona 85287, U.S.A., [email protected];
2
Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555 N. 59th Avenue, Glendale,
Arizona 85308, U.S.A., [email protected], [email protected]
1
ABSTRACT— Here we describe the first known skull and associated postcrania of the small bothriodontine anthracotheriid
Sivameryx africanus, which fills an important gap in the current knowledge of morphological diversity within the
Anthracotheriidae of Africa. The skull was recovered from the latest early Miocene sediments of the Kalodirr Member in the
Turkana Basin of Northern Kenya, and the age is well constrained between two tephra dated to 17.5 § 0.2 and 16.8 § 0.2
Ma. A partial mandible of Sivameryx from Kalodirr is also described because it may belong to the same individual. The new
anatomical data were incorporated into a genus-level phylogenetic analysis of Bothriodontinae that reveals that Sivameryx is
the sister taxon to Hemimeryx and belongs to a clade of advanced bothriodontine anthracotheriids alongside the genera
Merycopotamus, Libycosaurus, and Afromeryx. The new material of Sivameryx from Kalodirr greatly expands our
knowledge of the cranial anatomy of the genus, because the skull of Sivameryx does not reveal any specializations for aquatic
habitats, such as those seen in Libycosaurus. Here we suggest, based on the preserved cranial and postcranial evidence, that
Sivameryx may have been a small browser that inhabited denser stands of vegetation at Kalodirr based on evidence from its
narrow snout and well-developed labial musculature. However, its masticatory muscles were also relatively well developed,
suggesting repetitive loading of the jaw when chewing tough vegetation.
INTRODUCTION
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The early Miocene site of Kalodirr (Fig. 1) in the OmoTurkana Basin, Kenya, is famous for its rich mammalian
fauna that includes three sympatric genera of early hominoids: Afropithecus, Simiolus, and Turkanapithecus (Leakey
and Leakey, 1986a, 1986b). The Kalodirr fauna, ca. 17 Ma, is
critical to interpreting broader patterns of mammalian evolution and biogeography during the early to mid-Miocene of
Africa because it contains a variety of artiodactyl taxa that
are likely Eurasian immigrants, including listriodontine suids,
giraffoids, and anthracotheriids (Grossman, 2008; Orliac,
2009). At the same time that various artiodactyl taxa were
entering Africa, hominoids likely dispersed to Eurasia along
with other taxa of African origin, thus initiating the ‘hominoid
experiment’ in Eurasia (Pickford, 1991; Agusti et al., 2003).
Consequently, clarifying the biogeographic and paleoecological links between the early Miocene sites of Africa and Eurasia, and the timing of faunal exchange between the two
continents, is of great interest to both paleontologists and
paleoanthropologists.
Here we describe the first known cranium and partial mandible of Sivameryx africanus, which fills an important gap in
our knowledge of the morphological diversity within Anthracotheriidae. The skull was recovered from the latest early
Miocene sediments of Kalodirr in the Turkana Basin of
Northern Kenya, and although Kalodirr is best known for its
hominoid primates, the site has also produced a rich vertebrate fauna that improves our knowledge of terrestrial mammal communities during the Miocene of East Africa (Leakey
et al., 2011).
*Corresponding author.
GEOLOGIC SETTING
KNM-WK 18129 comes from the early Miocene Kalodirr Member of the Lothidok Formation in West Turkana, Kenya
(Boschetto, 1988; Boschetto et al., 1992). The Kalodirr Member
has been dated to the latest early Miocene, and its age is well con- 55
strained by the underlying Kalodirr tuff (17.5 § 0.2 Ma) and the
overlying Naserte tuff (16.8 § 0.2 Ma) (Boschetto et al., 1992).
The depositional environment at Kalodirr is characterized by
gentle fluvial systems, such as small meandering stream channels
(Boschetto et al., 1992). Evidence for permanent or semiperma- 60
nent bodies of water comes from the presence of crocodilian,
fish, and pelomedusid turtle fossils (Grossman and Holroyd,
2009). The mammalian fauna suggests that the site likely represents a woodland community characterized by both closed and
open patches of canopy and swampland (Grossman, 2008; 65
Leakey et al., 2011).
SYSTEMATIC PALEONTOLOGY
Class MAMMALIA Linnaeus, 1758
Order ARTIODACTYLA Owen, 1848
Family ANTHRACOTHERIIDAE Leidy, 1869
Subfamily BOTHRIODONTINAE Scott, 1940
Genus SIVAMERYX Lydekker, 1877
SIVAMERYX AFRICANUS (Andrews, 1914)
Diagnosis—Modified from Lihoreau and Ducrocq (2007).
Small- to medium-sized bothriodontines with pentacuspidate
upper molars exhibiting a markedly reduced paraconule (sometimes referred to as ‘quasi-pentacuspidate’); protocone with cingulum developed on the lingual side and two distal crests
descending from the protocone apex; loop-like mesostyles and
parastyles on the upper molars. The hypoconulid of m3 is in line
with the tooth’s buccal cusps. Differs from other bothriodontines
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Afromeryx, Hemimeryx, Libycosaurus, Merycopotamus, and Telmatodon by the presence of a paraconule on the upper molars.
Differs from Bothriogenys by its long preprotocristid and prehypocristid. Differs from Brachyodus by its much smaller size and 85
loop-like mesostyles. Sivameryx africanus differs from Sivameryx
moneyi by its larger size.
Other African Localities—Rusinga, Kenya; Oued Bazina,
Tunisia; Jebel Zelten, Libya.
Dental Nomenclature—Dental nomenclature follows Lihor- 90
eau and Ducrocq (2007). Incisors are indicated by I or i, canines
by C or c, premolars by P or p, and molars by M or m. Capital letters refer to upper teeth, whereas lower case letters indicate
lower dentition. Specific cusp terminology is illustrated in
Figure 2.
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Institutional Abbreviation—KNM, Kenyan National Museums, Nairobi, Kenya.
DESCRIPTION AND COMPARISONS
FIGURE 1. Map of Kalodirr in the Turkana Basin, Kenya.
KNM-WK 18129 consists of a partial cranium, mandibular
fragment, and radius attributed to the small bothriodontine 100
anthracotheriid Sivameryx africanus (Figs. 3, 4, 6). During the
fossilization process the skull was distorted, with the torsion
occurring just anterior to the jugal bones. The snout is short; it is
sheared anteriorly in a diagonal plane that extends from the
canine root on the left to roughly a centimeter anterior to 105
the canine crown on the right side. As a result, the premaxilla on
the right preserves only its posterior aspect and is completely
missing on the left side. The nasals are also unequally preserved,
extending further anteriorly on the right than on the left; neither
of the nasal bones preserves its most rostral edge. The choanae 110
are dorsoventrally crushed so that there is no continuity between
FIGURE 2. Dental terminology used in this
work.
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FIGURE 3. Cranium of Sivameryx (KNM-WK 18129). A, ventral view; B, dorsal view; C, lateral view; D, lateral view schematic; E, posterior view.
Occipital fragment of Sivameryx. F, dorsal view; G, ventral view; H, posterior view. Abbreviations: buc, buccinator; fr, frontal; j, jugal; l, lachrymal;
lab, levator labii; levr, levator rostri; mas, masseter; m, maxilla; n, nasal. Scale bar equals 10 mm.
the anterior and posterior nasal cavities. The right maxilla is fully
preserved and contains a broken canine, alveoli of P1–P3, and a
complete tooth row from P4 to M3. On the left maxilla, the
115 canine root is preserved, along with a complete P1, the alveolus
of P2, and the entire P3–M3 tooth row. The palatomaxillary
suture is not visible, and the posterior nasal spine of the palatine
is broken. Evidence of a large incisive foramen, as in Afromeryx,
is absent. There is a ca. 10 mm space between the palatine and
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FIGURE 4. Fragment of right anterior dentary of Sivameryx (KNM-WK 18129). A, buccal view; B, lingual view. Scale bar equals
10 mm.
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the ethmoid bone, the latter being almost entirely preserved. The
frontal bone is distorted and has collapsed to a level below the
dorsal margin of the orbits; there is a conical puncture posterior
to the nasofrontal junction that is ca. 10 mm wide and ca. 5 mm
deep. On the left side of the skull, the orbit is well preserved and
is composed externally of the frontal, lachrymal, and jugal bones;
the frontal composes the dorsal portion of the orbit, and the jugal
forms its ventral and lateral margins. The jugal is well preserved
and exhibits a long temporal process; on the right the process is
missing. Postorbital constriction is marked. Bones of the neurocranium are mostly missing; the majority of the sphenoid is missing, in addition to the vomer, temporal, and parietal bones. The
skull is broken right at the level of the sphenoid-palatine junction. Part of the dorsal-most occipital was recovered, but the posterior portion of the cranium is fragmentary and does not permit
a faithful reconstruction of skull length.
In anterior view, the anterior-most portion of the snout is
square in cross-section but widens slightly at the palate. The
jugals are mediolaterally wide and robust and are dorsoventrally
thick; they make contact with the maxillae just dorsal to P3. The
lateral margin of the jugal bone is angular and forms a moderate
anteroposterior keel for the origin of the masseter muscle; this
keel originates just above P3 and extends posteriorly along the
preserved length of the jugal. Ventrally, the maxillae have slight
lateral flare, giving the lateral walls of the snout a concave shape
in anterior view. The maxillary and nasal bones meet at a 90!
angle, forming a well-defined ridge that extends from P2 to the
anterior-most portion of the skull that was preserved, probably
terminating in front of the canine; however, this may be due to
the distorted nature of the snout. This maxillary-nasal ridge continues posteriorly as the jugal keel. No evidence of a facial tuberosity was preserved, although there is a roughened surface
anterior to the orbit that may have been the origin of the levator
rostri muscle.
The frontal bones are distorted. In lateral view, it appears
that the dorsal margin of the orbit would have been at the
same level as the top of the braincase. Thus, the orbits of Sivameryx sit level with the braincase, which contrasts to the condition seen in other bothriodontines such as Brachyodus and
Libycosaurus, where the dorsal orbital margin is elevated
above the braincase (Orliac et al., 2013; Lihoreau et al., 2014).
In lateral view, the anterior margin of the orbit is dorsal to
and in line with the distal side of M2. This differs from the
condition seen in Libycosaurus petrocchii, where the anterior
margin of the orbit is more posterior, because it is dorsal to
and in line with the mesial side of M2 in the complete cranium
from Toros Menalla, TM90-00-68. The orbit is circular in outline and was likely open posteriorly because there is no evidence of a postorbital process. There is a small angled boss at
the anterodorsal margin of the orbit. Due to the poor state of
preservation, no foramina inside the orbit could be identified
confidently. The perpendicular plate of the palatine forms the
ventromedial aspect of the bony orbit.
The outline of the nasofrontal suture is not well marked, but
it appears to have occurred just anterior to the orbits. The
nasals are flat and show no sign of a ‘domed’ condition. No
supraorbital foramina can be securely identified. The cranial
vault is only slightly elevated and forwardly inclined relative
to the snout in lateral view; braincase flexion is low. No welldefined temporal lines are apparent in dorsal view, unlike the
condition observed in other bothriodontines such as Afromeryx and Libycosaurus. In posterior view, the anterior portion of the brain case is preserved as a relatively small
depression; the cranial cavity is constricted anteriorly and
widens posteriorly, forming a conical depression in the skull in
posterior view. The posterior nasal spine of the palatine is partially preserved, because its dorsal-most portion is broken.
The ethmoid is present and its perpendicular plate is preserved, extending ventrally towards the palatines. The dorsalmost portion of the occipital was recovered and exhibits a
prominent crest across the dorsal nuchal line; the bone is
robust and exhibits a shallow nuchal fossa. A sagittal crest is
present. Evidence from the occipital and frontal bones suggests that the cranial vault was relatively dorsoventrally thick.
The upper dental formula is ?.1.4.3., and the postcanine teeth
increase in size distally. Dental metrics are given in Table 1. In
ventral view, the tooth rows are parallel and remain relatively
straight throughout their course. Overall, the entire palate is
shallow and flat and is widest posteriorly at the level of M3. The
ventral width of the snout just posterior to the canines is
39.4 mm. There is a slight depression of the palate between the
canines. The palatine bones are thin and what are likely the
greater palatine foramina are present just posterior to the third
molar. However, the posterior extension of the palatines is
unknown, because the specimen preserves little anatomy behind
the level of M3. The palatomaxillary suture is not visible. The
upper incisors are missing. The right maxilla is slightly distorted
but preserves C, P4, M1, M2, M3, and the alveoli of P1, P2, P3;
the right M3 is broken and missing most of its buccal surface.
The left maxilla preserves P1, P3–M3, and the canine root.
There is a diastema present just anterior to the canine; however, due to the state of preservation, an accurate measurement
could not be taken. The canine is circular in cross-section at its
base but tapers ovately to become buccolingually compressed
distally. In midsection, the canine is oval and buccolingually
compressed. A diastema (ca. 8 mm) separates the canine from
the first premolar. On the left side, the crown of P1 is broken,
but the tooth appears to have been buccolingually compressed
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FIGURE 5. Fragmentary right lower jaw of
Sivameryx (KNM-WK 18124). A, occlusal
view; B, medial view; C, lateral view. Scale
bar equals 10 mm.
and mesiodistally long; its main cusp runs at a 45! angle with
respect to the long axis of the maxilla. The alveolus of P2 is
220 poorly preserved, and nothing can be said about its morphology.
P3 has a large central cusp with a buccodistally descending crest
and a much smaller cusp on the lingual side of the tooth; the
tooth is rectangular in occlusal view. P4 is bicuspidate and is
trapezoidal in occlusal view; the buccal cusp is slightly taller than
225 the lingual cusp and possesses two crests that descend distally
and one that descends buccally. There is no cingulum present on
any of the premolars.
The quasi-pentacuspidate upper molars are buccolingually
wider than mesiodistally long and are relatively brachyodont.
230 The selenodonty is advanced, and the tall cusps give the teeth
high relief. In all molars, the paraconule is significantly reduced.
The mesostyle forms a smooth loop towards the buccal side of
the teeth, and the parastyle is relatively more angular in its overall course. The metastyle is present and projects distally. The
preparacristule is shelf-like and wraps around the mesiolingual 235
side of the paracone; the rib of the paracone is bulbous and
descends buccally. The median transverse valley is narrow at its
base and is level with the cervix; it is open lingually but closed
buccally because of contact between the postparacrista and the
mesostyle. A shelf-like cingulum is present on M3 and covers the 240
mesial, lingual, and distal portions of the tooth; it is most prominent lingually. A prominent cingulum is also present on the palatal side of M2.
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FIGURE 6. Right radius of Sivameryx (KNM-WK 18129). A, B, anterior view; C, D, posterior view; E, distal view; F, proximal view. Scale bar equals
10 mm.
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The anterior portion of the right dentary bone was preserved
in association with the cranium (Fig. 4). This bone exhibits a
shallow and dorsoventrally long canine fossa, suggesting long
upper canines. The root of the lower canine is present, but
because of its fragmentary nature, nothing can be said about its
morphology except that it appears to have been buccolingually
compressed. The angle of the ventral margin of the dentary is
steep and suggests that the mandible deepened posteriorly.
Despite evidence of posterior deepening, the anterior dentary is
relatively mediolaterally thin.
A partial dentary bone (KNM-WK 18124; Fig. 5) may
belong to the same individual, although its association with
the skull KNM-WK 18129 is more tentative than the other elements. The hemimandible is from the right side and preserves
m2 and m3; the root of m1 is present, but the crown has been
broken off. Dental metrics are given in Table 2. The selenodonty is more advanced than the condition observed in teeth
of Afromeryx. The mandibular body is deep and robust, and it
is mediolaterally widest just below m3. Prominent shelving of
the mandibular body starts just anterior to m3 and widens posteriorly, a condition that is more pronounced relative to Afromeryx specimens from Jabal Zaltan that are comparable in
size, such as X-57 (Pickford, 1991:1504). There is a retromolar
space between the m3 and the anterior margin of the ascending ramus. In lateral view, the ventral margin of the mandible
exhibits gradual curvature from m1 to m3 and then becomes
depressed dorsally just posterior to the end of the tooth row.
Due to the state of preservation, nothing can be said about
the crown morphology of m1. On m2, the hypoconid projects
more buccodistally relative to the protoconid; both cusps are
equal in length and height. The m2 metaconid is the tallest
cusp on the tooth, whereas the entoconid is level with the
hypoconid and protoconid. A cingulum is present on the buccal surface of m3 extending from the metaconid to the entoconid. As in m2, the m3 hypoconid projects more buccodistally
relative to the protoconid. A hypoconulid is present and is
bulbous, sloping forward anterolingually but in line with the
buccal cusps. The entoconid is the tallest cusp of the m3. In
all lower molars, linguobuccal compression of the lingual
cusps is exhibited.
A near-complete right radius was found with the skull (Fig. 6).
The midshaft of the diaphysis is missing, but the proximal and
distal ends were recovered and are well preserved. In articular
view, the proximal end is rectangular in outline and has a wide
and shallow articulation posteriorly to accommodate the lateral
facet of the ulna. The neck is anteroposteriorly compressed, and
there is a prominent tuberosity on the anterior surface. The
diaphysis is oval in cross-section and is proximally mediolaterally
wide in its proximal end, but it tapers to become anteroposteriorly wide in its distal end. A broad posterolateral groove on the
diaphysis permits contact with the ulna. The distal surface is
roughly circular in articular view. A shallow scaphoid articular
surface is present on the medial side. The centrally placed lunar
articular surface is deep and well defined by its posterior margin.
A shallow extensor tendon groove is present anteriorly, with a
wide and robust lateral ridge; the medial ridge is less
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FIGURE 7. Consensus tree of Bothriodontinae based on 51 craniodental characters.
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pronounced, although this may be related to the preservation of
this particular fossil.
PHYLOGENETIC ANALYSIS
In order to determine the phylogenetic relationships of Sivameryx africanus, a Bayesian phylogenetic analysis of 12 anthra305 cotheriid genera was constructed in MrBayes version 3.2.2. using
the data set provided by Lihoreau and Ducrocq (2007) with the
recent character updates of Rincon et al. (2013). A representative species for each genus was chosen based on the completeness of data. New data from KNM-WK 18129 were coded for the
310 skull of Sivameryx and are given in Appendix 2; additional data
on the mandible of Sivameryx were collected from Pickford
(1991) and Holroyd et al. (2010). The data set contained 51
TABLE 1. Dental metrics for the skull of Sivameryx (KNM-WK
18129).
Tooth
Right P1
Right P2
Right P3
Right P4
Right M1
Right M2
Right M3
Left P1
Left P2
Left P3
Left P4
Left M1
Left M2
Left M3
Mesiodistal length
Buccolingual length
—
—
—
9.7
12.4
13.6
19.9
11.2
—
9.5
9.7
11.6
14.6
16.6
—
—
—
13.1
14.7
18.3
20.3
5.9
—
12.5
14.2
15.5
18.7
18.9
craniodental characters as given by Lihoreau and Ducrocq
(2007) and included the majority of bothriodontine genera. Preliminary analyses using the complete data set of all 27 taxa provided by Lihoreau and Ducrocq (2007) did not change the
topology of the tree, so only an analysis of Bothriodontinae is
presented here using a microbunodontine taxon as the outgroup.
Microbunodon was designated as the outgroup for the bothriodontine analysis presented here because its character matrix had
no missing data. The analysis was run for 2,500,000 generations,
and trees were sampled every 100 generations; the first 25% was
discarded as burn-in.
The consensus tree is shown in Figure 7. The basal split in
Bothriodontinae is between a clade uniting Bothriogenys C Brachyodus and all other bothriodontines; within the latter clade,
Aepinacodon and Bothriodon are sister taxa and are separate
from all other genera. Arretotherium is the next genus to diverge,
and the remaining phylogeny is a split between Elomeryx and a
clade of the other advanced bothriodontines Hemimeryx, Sivameryx, Merycopotamus, Libycosaurus, and Afromeryx. Afromeryx is the first to diverge within this clade of advanced
bothriodontines, followed by the divergence of two lineages, one
of which leads to Merycopotamus C Libycosaurus and the other
to Sivameryx C Hemimeryx. These results replicate the phylogeny of Bothriodontinae by Lihoreau and Ducrocq (2007); therefore, the inclusion of new cranial characters for Sivameryx does
not alter the tree topology.
TABLE 2. Dental metrics for Sivameryx lower jaw fragment (KNMWK 18124).
Tooth
Right m2
Right m3
Mesiodistal length
Buccolingual length
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DISCUSSION
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The Anthracotheriidae are a diverse family of artiodactyls
with a fossil record spanning the Eocene to the Pliocene throughout Eurasia, Africa, and the Americas (Holroyd et al., 2010; Rincon et al., 2013). We attribute the Kalodirr specimens to
Sivameryx and not to Afromeryx, Libycosaurus, and other quadricuspidate bothriodontines based on the presence of a paraconule, making the upper molars pentacuspidate, and not to
Brachyodus based on its much smaller size and loop-like styles
on the upper molars. KNM-WK 18129 further differs from Afromeryx by possessing a cingulum that extends onto the metaconule and a median transverse valley that is level with, instead of
elevated above, the cervix of the upper molars. KNM-WK 18129
further differs from Brachyodus by molars that are considerably
more selenodont. Additionally, the Kalodirr specimen possesses
four upper premolars, whereas Libycosaurus possesses five. The
paraconule is markedly more reduced than in specimens of Elomeryx from Eurasia and secures the generic identification as
Sivameryx.
We follow the most recent taxonomic revision of African
Anthracotheriidae (Holroyd et al., 2010) and attribute the
Kalodirr specimen to Sivameryx africanus. Earlier classifications of Lihoreau (2003) and Lihoreau and Ducrocq (2007)
supported the synonymy of S. africanus with S. palaeindicus
by noting that the Asian and the African specimens of Sivameryx are morphologically and metrically similar in dental
characters and may represent a single, widely dispersed species. Given the lack of cranial material for Asian specimens
of Sivameryx, the cranial evidence is too scanty to bear on
this issue in the present work, and we follow Holroyd et al.
(2010) in recognizing Sivameryx africanus as a valid taxon.
The recovery of KNM-WK 18129 from the latest early Miocene of Kenya clarifies the anatomy of Sivameryx africanus
and permits inferences about the paleoecology of the genus
during the early Miocene of East Africa.
A semiaquatic niche has historically been suggested for
anthracotheriids based on contextual and morphological evidence. For example, Pickford (1983) noted that anthracotheriids
were among the most common fossils recovered from fluvial and
lacustrine deposits, particularly those representing lake margins,
in association with fish and aquatic reptiles, and suggested that
this revealed a semiaquatic lifestyle analogous to modern hippopotamids. Similarly, with respect to cranial anatomy, elevation
of the dorsal rims of the orbits above the frontal bone is often
taken as evidence for partial submersion of the skull, an aquatic
adaptation similar to the condition seen in the skull of Hippopotamus (Orliac et al., 2013). In contrast to the condition of taxa
such as Brachyodus, Merycopotamus, and Libycosaurus (Orliac
et al., 2013; Lihoreau et al., 2014), the dorsal rim of the orbits
are level with the braincase in the Kalodirr specimen of Sivameryx, suggesting a primarily terrestrial lifestyle.
The Kalodirr skull is robust, and the muscle markings on it
suggest that the individual possessed equally robust musculature, despite the small size of the specimen. For example, the
widely flared and keeled jugals offer a large origin area for
the masseter muscles. The well-developed sagittal crest, as
evinced in the occipital fragments, reveals strong posterior
fibers of the temporalis muscle. Both masseter and temporalis
are chewing muscles; thus, the relatively large insertion and
origin areas on the skull of Sivameryx suggest that the taxon
engaged in repetitive loading of the jaw musculature when
chewing vegetation. There is a deep groove along the lateral
surface of the snout where buccinator would have run anteroposteriorly along the skull. The anterior portion of the snout
preserves evidence of relatively large insertion areas for the
muscles of labial elevation, suggesting that the lips of Sivameryx were suited to selectively crop vegetation, presumably
browse. Evidence for a narrow anterior snout also suggests
selective feeding and a browsing niche.
The canine fossa of the Kalodirr skull is deep, and from this it
can be inferred that the specimen most likely represents a male,
because Sivameryx is known to be sexually dimorphic in canine
size (Holroyd et al., 2010). Furthermore, poorly defined sutures
and a fully erupted M3 suggest that the specimen is an adult individual; however, assessment of suture morphology may be
affected by the state of preservation. Despite the fact that the
Kalodirr skull most likely represents an adult male, the associated radius indicates a small and relatively gracile postcranial
skeleton. Unfortunately, the fragmentary nature of the radius
prevents any detailed ecomorphological comparisons that would
permit inferences of locomotion. However, what is clear is that
the limb elements of Sivameryx clearly differed from other taxa
such as Merycopotamus and Libycosaurus, both of which possess
massive limb bones (Lihoreau and Ducrocq, 2007).
The early Miocene habitats of Kalodirr have been reconstructed as a mosaic of woodlands characterized by both
closed and open patches of canopy, with the presence of
some swampland (Grossman, 2008; Leakey et al., 2011).
Based on the Kalodirr anthracotheriid’s relatively small size
and apparent terrestrial adaptations, Sivameryx africanus
may have filled an ecological niche similar to modern tragulids or duikers during the early Miocene of East Africa, a suggestion previously made by Lihoreau and Ducrocq (2007).
Thus, Sivameryx, at least in Africa, might have been a relatively small and cryptic animal that foraged and sought refuge in denser stands of vegetation. The puncture present on
the top of the braincase is likely the result of predation from
a Kalodirr crocodilian, or a member of Kalodirr’s particularly
rich carnivore guild that includes amphicyonids (e.g., Cynelos), barbourofelids (e.g., Afrosmilus), and hyaenodontids
(e.g., Hyainailouros) (Grossman, 2008).
CONCLUSIONS
We describe new material of a bothriodontine anthracotheriid
from the early Miocene of Kalodirr, Kenya, and attribute the
specimen to the genus Sivameryx based primarily on its small
size and its upper molar structure. We use the species Sivameryx
africanus and not S. palaeindicus for the Kalodirr specimen
based on the most recent revision of African Anthracotheriidae.
A phylogenetic analysis with new data for the skull of Sivameryx
does not change the tree topology recovered by Lihoreau and
Ducrocq (2007) because Sivameryx is recovered as the sister
taxon to Hemimeryx. The new material of Sivameryx from
Kalodirr greatly expands our knowledge of the cranial anatomy
of small African representatives of Bothriodontinae, because the
skull of Sivameryx does not reveal any specializations for aquatic
habitats, such as those seen in other African taxa, such as Libycosaurus. Here we suggested that Sivameryx may have been a
small browser that inhabited denser stands of vegetation at
Kalodirr based on evidence from its narrow snout and welldeveloped labial musculature. However, its masticatory muscles
were also relatively well developed, suggesting repetitive loading
of the jaw when chewing tough vegetation.
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ACKNOWLEDGMENTS
We thank E. Mbua and staff at KNM for access to specimens
in their care, M. G. Leakey for encouragement and information
about the Kalodirr fauna, and H. Glowacka and E. R. Miller for
helpful comments on earlier versions of the manuscript. We 465
thank JVP technical editor J. M. Harris, JVP editor G. W. Rougier, and the reviewers of this manuscript, S. Ducrocq and M.
Pickford, for their most helpful comments.
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JOURNAL OF VERTEBRATE PALEONTOLOGY
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Submitted March 15, 2014; revisions received May 12, 2014;
accepted May 19, 2014.
Handling editor: Guillermo Rougier
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Citation for this article: Rowan, J., B. Adrian, and A. Grossman. 2015.
The first skull of Sivameryx africanus (Anthracotheriidae, Bothriodontinae) from the early Miocene of East Africa. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2014.928305.
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APPENDIX 1. Characters and character states for 51
craniodental characters of Anthracotheriidae from Lihoreau and
Ducrocq (2007) and Rincon et al. (2013).
(1) Lower incisors: three (0); from two to three (1); two (2).
(2) Upper incisors: three of equal size (0); three with I3
reduced to 60% or less (1); two (2).
(3) Lower incisor morphology: not caniniform (0); one caniniform incisors (1).
(4) Relative dimension of lower incisors: all equal size (0); i2
larger (1); i3 larger (2).
(5) Wear on lower canine: distal wear facet caused by the contact with upper C (0); mesial wear facet cause by contact
with I3 (1).
(6) Upper canine morphology: strong with subcircular crosssection (0); strong and laterally compressed (1); premolariform (2).
(7) Lower canine in males: premolariform (0); large (1); evergrowing (2).
(8) Lower canine cross-section at cervix: subcircular (0); elliptical with rounded mesial margin and distal keel (1); elliptical
with a mesial and a distal crest (2); elliptical with a concave
buccal margin and a distal keel (3).
(9) Accessory cusps on the mesial crest of lower premolars:
none (0); only one (1); several (2).
(10) Presence of five upper premolars: no (0); yes (1).
(11) Distolabial crest on upper premolars: simple (0); with a maximum of two accessory cusps (1); with more than two (2).
(12) Accessory cusp on p4: no (0); yes (1).
(13) p1 roots: one (0); two (1).
(14) Mesial crests on P1–P3: one (0); two (1).
(15) Number of P4 roots: three (0); two (1); one (2).
(16) Accessory cusp on distolingual margin of P3: one (0); none (1).
(17) Upper molar mesostyle; simple (0); ‘V’-shaped and invaded
by a transversal valley (1); loop-like (2); divided into two (3).
(18) Number postprotocristae: one (0), two (1).
(19) Accessory cusp on upper molar mesial cingulum: no (0); yes
(1).
(20) Number of cristules issued from the metaconule: two (0);
three (1).
(21) Preprotocristids and prehypocristids on lower molars: do
not reach the lingual margin of the tooth (0); reach the lingual margin (1).
(22) Hypoconulid on m3: loop-like (0); single cusp (1).
(23) Postentocristid on lower molars: does not reach the posthypocristid and leaves the lingual valley open (0); reaches the
posthypocristid and closes the lingual valley (1).
(24) Dimension of the lingual and labial cusps: equal (0); different (1). State (1): labial cusps twice as large at their base as
the lingual cusp.
(25) Entoconulid on m3: absent (0); present (1).
(26) Number of cristids issued from the hypoconulid: three (0);
two (1).
(27) Position of the preentocristid on lower molars: reaches the
hypoconid summit (0); reaches the prehypocristid (1).
(28) Premetacristid on lower molars: present (0); absent (1).
(29) Mesial part of looplike hypoconulid: open (0); pinched (1).
(30) Entoconid fold on lower molars: absent (0); present (1).
(31) Ventral vascular groove on mandible: slightly marked (0);
absent (1); strongly marked (2).
(32) Morphology of mandibular symphysis cross-section: ‘U’shaped (0); ‘V’-shaped (1).
(33) Transverse constriction of mandible at Cp1 diastema: no
(0); yes (1).
(34) Cp1 diastema: absent (0); present (1).
(35)
(36)
(37)
(38)
(39)
(40)
(41)
(42)
(43)
(44)
(45)
(46)
(47)
(48)
(49)
(50)
(51)
p1‒p2 diastema: absent (0); present (1).
Lateral mandibular tuberosity: absent (0); present (1).
Dentary bone fusion at the symphysis: no (0); yes (1).
Morphology of the symphysis is sagittal section: elliptic (0);
dorsally concave (1); ventrally concave (2).
Maximal thickness of the symphysis in sagittal section: in the
middle part (0); in the anterior part (1); in the posterior part
(2).
Number and position of main external mandibular foramina: only one foramen, below the anterior part of the premolar row (0); two foramina, one below the anterior part of
the premolar row, the other below its posterior part (1);
one foramen, below the posterior part of the premolar row
(2).
Tuberosity on the dorsal border of the mandible at c–p1
diastema: no (0); yes (1).
Palatine depression between the canines: no (0); yes (1).
Canine fossa: short (0); long (1).
Aperture of the main palatine foramen: between M3 and
P3 (0); between P2 and P1 (1); between P1 and C (2).
Morphology of the frontonasal suture: ‘V’-shaped (0);
rounded or straight (1).
Lachrymal extension: separated from the nasal by the frontal (0); in contact with the nasal (1).
Supraorbital foramina on the frontal: one (0); several (1).
Facial crest: horizontal (0); oblique (1).
Anterior border of premaxillary in lateral view: concave
(0); convex (1).
Postglenoid foramen position: posterior to the styloid process of the tympanic bulla (0); anterior to the styloid process of the tympanic bulla (1).
Opening of internal choanae: at M3 (0); behind M3 (1).
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APPENDIX 2. Character matrix of 51 craniodental characters
for 12 anthracotheriid genera with commands for MrBayes
version 3.2.2.
Microbunodon_minimum
000011010000000100000000011000011100111100001000000
Bothriogenys_fraasi
00??0202000000?110010010000000000100012000?00?000?1
Brachyodus_aequatorialis
22120202000001?110000010011100000100112000020000001
Aepinacodon_americanus
0001020200000001210000100110100011101120000000000?0
Elomeryx_crispus
000000130001000121010011011010000110021000000000001
Bothriodon_velaunus
0001020200000001210100100110100011101120000?0000000
Hemimeryx_blanfordi
??0???132??11???2200100101101000010002101??????????
Afromeryx_zelteni
10000013101101?121000001011010000100021100?11?1?0?1
Sivameryx_africanus
0?0001131011110121001001011010000100021111?????0??1
Aretotherium_acridens
00010013000000?120000011011010000110021000001?1?001
Merycopotamus_dissimilis
000000231011110130001101011111200100020200111111011
Libycosaurus_petrocchii
110000132121111120001101011111100100021101121111111
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640
645
650
655