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Croft, D.A., L.R. Heaney, J.J. Flynn, and A.P. Bautista. Fossil remains of a new, diminutive Bubalus (Artiodactyla: Bovidae: Bovini) from Cebu Island, Philippines. Journal of Mammalogy

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We describe a partial skeleton of a new species of Bubalus (Bubalus) from soft karst near Balamban, Cebu Island, Philippines. The specimen is likely Pleistocene or Holocene in age and includes left and right humeri, a left metatarsal, 2 posterior thoracic vertebrae, 2 left lower molars, and a pair of ungual phalanges. Bubalus sp. nov. differs from all previously described Bubalus in both the size and proportions of the skeleton and in possessing a unique combination of discrete character states. Possible autapomorphies for Bubalus sp. nov. evident in the metatarsal include a very broad dorsal longitudinal sulcus; a broad, triangular anterior cubonavicular facet; and a sulcus that bisects a small tuberosity on the proximolateral surface. Limb elements of Bubalus sp. nov. are less than two-thirds the length of corresponding elements of the Asiatic water buffalo, B. (Bubalus) bubalis, and are about 80% the length of those of the tamaraw, B. (Bubalus) mindorensis; they are similar in length to limb bones of the lowland anoa, B. (Anoa) depressicornis, but are more robust. Mass estimates based on regression equations for modern bovids suggests a mass of 150-165 kg for Bubalus sp. nov.; this is approximately 25% smaller than B. mindorensis (180-220 kg) and at least 15% larger than B. depressicornis (approximately 135 kg). The small size of Bubalus sp. nov. relative to other B. (Bubalus) is likely attributable to island dwarfing; this is supported by a consistent relationship between body size and island size in Bubalus sp. nov., B. mindorensis, and B. bubalis, and by the relatively larger dentition of B. sp. nov. relative to body size. Bubalus sp. nov. is the 1st fossil mammal to be reported from Cebu Island and is the only nonproboscidean documented from the Negros-Panay Philippine Faunal Region. In conjunction with the presence of Bubalus on Mindoro Island (and potentially Luzon), this specimen suggests that Bubalus may once have ranged throughout the Philippines.
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FOSSIL REMAINS OF A NEW, DIMINUTIVE BUBALUS
(ARTIODACTYLA: BOVIDAE: BOVINI) FROM
CEBU ISLAND, PHILIPPINES
DARIN A. CROFT,* LAWRENCE R. HEANEY,JOHN J. FLYNN, AND ANGEL P. BAUTISTA
Department of Anatomy, Case Western Reserve University School of Medicine, 10900 Euclid Avenue,
Cleveland, OH 44106-4930, USA (DAC)
Department of Zoology, The Field Museum, 1400 S Lake Shore Drive, Chicago, IL 60605, USA (LRH)
Division of Paleontology, The American Museum of Natural History, Central Park West at 79th Street,
New York, NY 10024-5192, USA (JJF)
Archaeology Division, National Museum of the Philippines, P. Burgos Street, Manila, Philippines (APB)
We describe a partial skeleton of a new species of Bubalus (Bubalus) from soft karst near Balamban, Cebu
Island, Philippines. The specimen is likely Pleistocene or Holocene in age and includes left and right humeri,
a left metatarsal, 2 posterior thoracic vertebrae, 2 left lower molars, and a pair of ungual phalanges. Bubalus sp.
nov. differs from all previously described Bubalus in both the size and proportions of the skeleton and in
possessing a unique combination of discrete character states. Possible autapomorphies for Bubalus sp. nov.
evident in the metatarsal include a very broad dorsal longitudinal sulcus; a broad, triangular anterior
cubonavicular facet; and a sulcus that bisects a small tuberosity on the proximolateral surface. Limb elements of
Bubalus sp. nov. are less than two-thirds the length of corresponding elements of the Asiatic water buffalo,
B. (Bubalus) bubalis, and are about 80% the length of those of the tamaraw, B. (Bubalus) mindorensis; they are
similar in length to limb bones of the lowland anoa, B. (Anoa) depressicornis, but are more robust. Mass
estimates based on regression equations for modern bovids suggests a mass of 150–165 kg for Bubalus sp. nov.;
this is approximately 25% smaller than B. mindorensis (180–220 kg) and at least 15% larger than
B. depressicornis (approximately 135 kg). The small size of Bubalus sp. nov. relative to other B. (Bubalus)is
likely attributable to island dwarfing; this is supported by a consistent relationship between body size and island
size in Bubalus sp. nov., B. mindorensis, and B. bubalis, and by the relatively larger dentition of B. sp. nov.
relative to body size. Bubalus sp. nov. is the 1st fossil mammal to be reported from Cebu Island and is the only
nonproboscidean documented from the Negros–Panay Philippine Faunal Region. In conjunction with the
presence of Bubalus on Mindoro Island (and potentially Luzon), this specimen suggests that Bubalus may once
have ranged throughout the Philippines.
Key words: Anoa, body size, Bovini, Bubalus, dwarfism, fossil, island biogeography, Philippines, Pleistocene, tamaraw
The Philippines comprise more than 7,000 islands situated
between Borneo and Taiwan in the northeastern corner of the
Malay Archipelago. The vast majority of these islands are tiny
(only 1–2 km
2
) but the 2 largest (Luzon and Mindanao) are
each approximately 100,000 km
2
in area (Fig. 1). Although
a few of the islands (the Palawan group) are continental, most
are oceanic in origin, and their current configuration is the
result of complex tectonic interactions among the Eurasian
continental plate, the Philippine oceanic plate, and various
microcontinental blocks (e.g., Hall 1998, 2002; Yumul et al.
2000; Zamoras and Matsuoka 2004).
The fractured geography of the Philippine islands and their
variable degrees and timing of connection and separation have
given rise to a diverse fauna of terrestrial vertebrates. At least
172 species of native mammals have been recorded, of which
111 (64%) are endemic (Heaney et al. 1998). This degree of
endemism is exceeded only by Madagascar, an island of nearly
twice the total area; on a per-area basis, the Philippines may
harbor the greatest number of endemic mammals in the world
(Heaney 1993). Because of this endemism, the Philippines has
been recognized both as one of the most ‘‘megadiverse’’
countries and as one of the ‘‘hottest’’ biological hotspots,
making it a top priority for conservation efforts (Ricketts et al.
2005; Shi et al. 2005). Newly discovered mammals continue to
* Correspondent: dcroft@case.edu
Ó 2006 American Society of Mammalogists
www.mammalogy.org
Journal of Mammalogy, 87(5):1037–1051, 2006
1037
be described from the region (e.g., Rickart et al. 2002, 2003,
2005), indicating that the true species richness of the country is
still unknown.
The large number of Philippine islands and their diverse
mammal faunas make the archipelago particularly amenable to
studies of island biogeography and the relative effects of
colonization, extinction, and speciation (Heaney 1986, 2000).
Such investigations have been aided by the recognition that the
present configuration of islands is a geologically recent event.
During the last glacial maximum of the late Pleistocene
(approximately 20,000 years ago), the great quantity of water
trapped in polar and continental ice sheets lowered sea levels
worldwide, exposing areas of land that had previously been
submerged (e.g., Bird et al. 2005; Meijaard 2003). In the
Philippines, these exposed areas connected many previously
isolated islands, resulting in 6 major Philippine faunal regions
(Heaney 1991; Heaney et al. 1998; Fig. 1). Although these
islands once again became isolated after the Pleistocene,
disparities in faunal resemblance between intraregional and
interregional island pairs are still dramatic (Heaney 1986;
Heaney and Regalado 1998; Heaney et al. 1998) and may differ
from those that existed before that event.
Unfortunately, the terrestrial fossil record of the Philippines
is poor and has provided few insights into the development of
the country’s unique fauna. Thus far, only a few Pleistocene
and Holocene ungulates have been reported (Bautista 1991;
Beyer 1957; Koenigswald 1956; Table 1), although increased
efforts to collect and study microvertebrate fossils could
considerably expand knowledge of the recent biotic history of
the islands (Reis and Garong 2001). The present report
describes fossil remains of a new species of bovid that lived
on Cebu Island, perhaps as recently as a few thousand years
ago. The specimen was discovered in 1958 by Michael Armas,
a mining engineer, during exploration for phosphate (Fig. 2). In
1995, it was brought to the attention of Dr. Hamilcar Intengan,
who subsequently brought the bones to The Field Museum for
TABLE 1.—Extinct and extant Philippine ungulates listed by faunal
region (Bautista 1991; Heaney et al. 1998). Animals obviously
brought to the Philippines by the Spaniards (e.g., Equus) are not
included.
Extinct species Extant species
Luzon
Artiodactyla Artiodactyla
cf. Antilope Cervus mariannus
Bubalus Sus philippensis
Cervus
Perissodactyla
Rhinoceros philippinensis
Proboscidea
Elephas beveri
Elephas cf. namadicus
Paleoloxodon
Stegodon luzonensis
Stegodon cf. sinensis
Stegodon cf. trigonocephalus
Mindanao
Proboscidea Artiodactyla
Stegodon mindanensis Cervus mariannus
Sus philippensis
Mindoro
(None) Artiodactyla
Bubalus mindorensis
Sus philippensis
NegrosPanay
Artiodactyla Artiodactyla
Bubalus cebuensis sp. nov. Cervus alfredi
Proboscidea Sus cebifrons
Elephas
Stegodon
Palawan
(None) Artiodactyla
Axis calamianensis
Sus barbatus
Tragulus napu
Sulu
(None) (None)
FIG.1.—The Philippines. Areas that were exposed as dry land
during the last glacial maximum are shown by gray shading; faunal
regions are labeled in capital letters. Location where fossil specimen
was found on Cebu Island is indicated by a star.
1038 JOURNAL OF MAMMALOGY Vol. 87, No. 5
initial identification by our late colleague, Steven McCarroll,
and JJF. Armas and LRH visited the site in April 1999; it is an
area of soft karst, formed from poorly consolidated coral reef.
The fossil was found at the end of an approximately 10- to 11-
m horizontal tunnel that had been dug into the side of a ridge
for the purpose of phosphate mining. The sediments in which
the fossil was found likely represent fissure-fill (i.e., sediments
that had accumulated within a crack or crevice in the
limestone). All elements of the specimen were found on
a single day, in close proximity to each other, within loose
matrix. No other fossils were found at this site or in other
similar mining tunnels dug in the vicinity. This is the 1st fossil
mammal reported from Cebu Island, and the only non-
proboscidean fossil described from the entire Negros–Panay
Faunal Region of the Philippines.
MATERIALS AND METHODS
The descriptions below are based on direct observations of the
original material (left humerus, vertebrae, teeth, and unguals) or casts
of the original material (right humerus and left metatarsal) that are now
housed at the National Museum of the Philippines (PNM).
Morphological comparisons were made with osteological specimens
from the Recent mammal collections of the Division of Mammalogy at
The Field Museum of Natural History (FMNH) and the University of
Michigan Museum of Zoology (UMMZ); a list of these specimens is
provided in Appendix I.
All measurements were made to the nearest 0.5 mm, using a digital
caliper. Estimated measurements (e.g., for articulated specimens) are
indicated by parentheses. Statistical analyses were performed using
SPSS (SPSS Inc., Chicago, Illinois) on an Apple G4 computer
(Capertino, California). The dagger symbol () is used to designate
extinct species.
SYSTEMATICS
Mammalia Linnaeus, 1758
Artiodactyla Owen, 1848
Bovidae Gray, 1821
Bovinae Gray, 1821
Bovini Gray, 1821
Bubalina Pilgrim, 1939
Bubalus Hamilton-Smith, 1827
Type species.— Bubalus (Bubalus) bubalis (¼ B. arnee).
Included species.— Bubalus (Bubalis) bubalis, B. brevicor-
nis, B. (Anoa) depressicornis, B. guzhensis, B. mephistoph-
eles, B. (Bubalus) mindorensis, B. murrensis, B.
palaeindicus, B. palaeokerabau, B. platyceros, B. (Anoa)
quarlesi, B. sivalensis, B. teilhardi, B. tingi, B. triangu-
latus, B. wansijocki, B. youngi.
Comments.—As is evident from the list above, in addition to
the extant species, a large array of fossil species have been
referred to Bubalus. The majority of these species are in-
completely known, however, and are differentiated primarily
by horn core characters (e.g., Geraads 1992; Xue and Li 2000;
Young 1936). The new species described herein is represented
by 2 teeth and various postcranial elements and therefore
cannot be directly compared to most fossil taxa. Of necessity,
therefore, the diagnosis below focuses on character states that
distinguish the new Cebu Island species from extant species of
Bubalus, the only taxa for which sufficient postcranial speci-
mens are available for diagnostic differentiation. The new
species can only be stated with certainty to differ from all fossil
species of Bubalus by its dramatically smaller size.
Four extant species of Bubalus are currently recognized
(Grubb 2005; Nowak 1999). The most widespread of these is
Bubalus bubalis, the Asiatic water buffalo; domestic B. bubalis
is found virtually throughout the world (Kierstein et al. 2004),
but wild populations have declined and are considered
endangered (Nowak 1999). Water buffaloes are the largest
Bubalus, with wild males weighing more than 1,000 kg
(Popenoe 1983). Some authorities distinguish between the wild
and domestic forms, using the name B. arnee for the former
and reserving B. bubalis for the latter (e.g., Geraads 1992;
Groves 1969). We do not make this distinction in the present
report because the 2 species cannot be readily distinguished
from one another by anatomical differences. Bubalus mind-
orensis, the tamaraw or tamarau, is endemic to the Philippine
island of Mindoro (Custodio et al. 1996). It is much smaller
than B. bubalis (see below) and is highly endangered because
of a variety of factors, including hunting and habitat destruction
(Heaney and Utzurrum 1991; Oliver 1993). B. bubalis and B.
mindorensis are generally grouped together in the subgenus
Bubalus (Grubb 2005). The subgenus Anoa includes 2 very
similar species of dwarf buffalo endemic to Sulawesi,
Indonesia: B. depressicornis, the lowland anoa, and B.
quarlesi, the mountain anoa (Burton et al. 2005; Dolan 1965;
Groves 1969). They are the smallest Bovini, but the largest
endemic mammals of Sulawesi, and are also endangered
(Burton et al. 2005).
Bubalus cebuensis, sp. nov.
Figs. 3–8; Tables 2–5
Holotype.— PNM 2006-A, an associated partial skeleton
including left and right humeri, left metatarsal, 2 thoracic
vertebrae (?T9 and ?T11), 2 unguals, and left m1–2. More of
the skeleton (including several ribs and additional teeth and
vertebrae) was present when the specimen was discovered (M.
Armas, pers. comm.), but these were given away or lost subse-
quently; the aforementioned elements were the only ones
available to us for study. The individual elements are partially
permineralized (i.e., ‘‘fossilized’’) but the degree of perminer-
alization varies both within and between elements. The original
specimen will be deposited at the National Museum of the
Philippines; casts of the bones will be retained in the geology
collections of The Field Museum (FMNH PM 61097) and
a duplicate set of casts will retained in the Recent mammal
collections.
Type locality.— The specimen was collected from the end of
a horizontal tunnel in soft karst at approximately 50 m
elevation in K-Hill near Balamban, Cebu Island, Philippines
(approximately 108519N, 1238729E; Fig. 2). No stratigraphic
data were recorded when the specimen was collected.
October 2006 1039CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
Diagnosis.— Bubalus cebuensis differs from all previously
described Bubalus in the size and proportions of the humerus
and metatarsal (and presumably the rest of the postcranial
skeleton). Based on linear dimensions, B. cebuensis is less than
two-thirds the size of modern B. bubalis and is about 80% the
size of modern B. mindorensis. B. cebuensis is similar in size to
members of the subgenus Anoa (within approx. 10% for limb
element lengths), but its skeleton is much more robust. The
humerus, metatarsal, and vertebrae differ noticeably from those
of B. (Anoa) and display a mixture of characters shared with B.
bubalis, B. mindorensis, or both (e.g., roughly spherical
humeral head, large greater tuberosity on humerus, low and
broad deltopectoral crest, elongate metatarsal relative to
humerus, straight metatarsal in medial view, small posterior
cubonavicular facet on articular surface of metatarsal, T9–11
spinous processes straight in lateral view, and mammillary
processes absent on T9–11; Table 2). The relative width of the
dorsal longitudinal sulcus on the metatarsal is greater than that
exhibited by any modern Bubalus and may be an autapomor-
phy for the new species. The unusual configuration of the
proximal end of the metatarsal (i.e., with a broad, triangular
anterior cubonavicular facet on the articular surface and
a sulcus that bisects a small tuberosity on the proximolateral
surface) may also be autapomorphic for B. cebuensis.
Age and distribution.—The specimen is likely Pleistocene or
Holocene in age, based on the geology of the region, but we
were unable to obtain an absolute date because of a lack of
preserved collagen (i.e., carbon dating was unsuccessful; Uni-
versity of Arizona, Tucson, Accelerator Mass Spectrometry
Laboratory sample AA57785). The species is known only from
the type locality.
Etymology.— After Cebu Island, the type locality and only
known locality for the species. The specific epithet is analogous
to that of the tamaraw, B. mindorensis, named in reference to
Mindoro Island, Philippines, and reinforces the insular nature
of this endemic species.
Humerus.— The humerus (Fig. 3) is very similar in length to
that of B. depressicornis but is much more robust, as evidenced
by all other humeral measurements (Table 3). The head of the
humerus is roughly spherical in shape, similar to the condition
in B. mindorensis and B. bubalis;inB. depressicornis the
proximal surface of the humeral head is flattened, and the
transition between the proximal and caudal surfaces is more
abrupt, approximating a right angle. As in other Bubalus, the
greater tubercle in B. cebuensis projects far above the humeral
head and arches medially over the intertubercular groove,
creating a tunnel. The greater tubercle is much larger and more
developed in B. cebuensis, B. mindorensis, and B. bubalis
compared to B. depressicornis. A well-defined pit is present in
the tubercular fossa (i.e., the area anterior to the humeral head
and medial to the base of the greater tubercle); this pit is
absent in B. depressicornis and is present but less defined in
B. mindorensis and B. bubalis. The greater tubercle extends
inferiorly beyond the articular surface of the humeral head
in B. cebuensis and B. bubalis; this contrasts with the condition
in B. mindorensis, in which the greater tubercle ends at
approximately the same level as the articular surface. A rugose
deltopectoral crest is present in B. cebuensis, but the deltoid
tuberosity is low and broad, strongly differing from the
conditions observed in B. depressicornis (in which it is a thin,
platelike process) and B. mindorensis
(in which it is a high
ridge). It resembles the condition in B. bubalis, but is less
developed. The scar marking the insertion of the teres minor
FIG.2.—Locality where fossil was found near Balamban, Cebu
Island, Philippines. A) Distant view of tunnel entrance (indicated by
white arrow) amid dense vegetation. B) Close-up of tunnel entrance
illustrating soft texture of soil and remains of poorly consolidated
coral reef. The discoverer of the fossil specimen, Michael Armas, is
pictured to the right of the entrance.
1040 JOURNAL OF MAMMALOGY Vol. 87, No. 5
muscle is large and broad in B. cebuensis, again more closely
resembling the condition in B. bubalis than in either
B. depressicornis or B. mindorensis (in which it is narrow).
B. cebuensis differs from both B. bubalis and B. mindorensis
in having a smaller lesser tubercle and in having a less-
pronounced medial ridge on the lesser tubercle for insertion
of the subscapularis muscle.
To investigate size and shape variation of the humerus in
Bubalus, a principal components analysis was performed using
the raw data for the 9 measurements presented in Table 3. The
factor loadings for the first 2 principal components (PCs) are
presented in Table 4 and the specimens are plotted against
these 2 factors in Fig. 4. As expected, PC1 clearly represents
size (all variables have high positive loadings), and B.
cebuensis plots closer to B. depressicornis on this axis than
to any other species. PC2 represents humeral robustness; mid-
shaft and distal anteroposterior diameters have high posi-
tive loadings, and length has a high negative loading. This
axis clearly distinguishes the robust humeri of B. cebuensis and
B. bubalis from the more gracile humerus of B. mindorensis,
TABLE 2.—Variation in selected morphological characters among species of Bubalus. Character states shared between B. cebuensis and other
species are underlined; character states that are autapomorphic for B. cebuensis are italicized. T9–11 ¼ 9th through 11th thoracic vertebrae.
Morphological character B. depressicornis B. cebuensis B. mindorensis B. bubalis
Shape of humeral head With abrupt angle
Roughly spherical Roughly spherical Roughly spherical
Size of greater tuberosity Small
Large Large Large
Pit in trochanteric fossa Absent Well developed Slight Slight
Deltopectoral crest Thin and platelike Low and broad High ridge Low ridge
Teres minor scar Narrow Broad Narrow Broad
Metatarsal length/humeral length 65%
70% 60% 65–75%
Metatarsal shape in medial view Slightly bowed
Straight Straight Straight
Metatarsal posterior cubonavicular facet Mediolaterally elongate
?Small Small and circular Mediolaterally elongate
Metatarsal anterior cubonavicular facet Narrow Broad, triangular Broad, quadrangular Broad, quadrangular
Proximolateral sulcus on metatarsal Absent Bisects tuberosity Medial to tuberosity Medial to tuberosity
T911 spinous processes Curved
Straight Straight Straight
T911 mammillary processes Well developed
Absent Absent Absent
Molar length/humeral length ,7.2%
.7.9% ,7.2% .7.9%
FIG.3.—Left humeri of Bubalus mindorensis (FMNH 18817, left) and Bubalus cebuensis (PNM 2006-A, right) in A) anterior and B) posterior
views. Scale bars ¼ 5 cm.
October 2006 1041CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
whereas the humeral morphology of B. depressicornis is
intermediate between these 2 groups.
Metatarsal.— In contrast to the humerus, the metatarsal of
B. cebuensis is more similar in length to that of B. mindorensis
than B. depressicornis (Fig. 5; Table 3). As in both
B. mindorensis and B. bubalis, it is straight in medial view;
in B. depressicornis, this bone is slightly bowed (concave
dorsally) and is much more gracile. The most conspicuous
feature of the metatarsal in dorsal view, the dorsal longitudinal
sulcus (i.e., the sulcus for the extensor digitorum longus
tendon), is quite broad in B. cebuensis. It is absolutely wider
than that of the larger B. mindorensis and B. depressicornis,
and is equal in width to that of the much larger B. bubalis (and
thus proportionally is much wider). The sulcus also differs
from that of B. mindorensis and B. depressicornis in lacking
overarching sides, although this may be an artifact of
preservation.
A triangular process projects cranially from the posterior
edge of the tarsal articular surface of the metatarsal in
B. cebuensis. Although it is incompletely preserved, it is lon-
ger than that of B. depressicornis and is more similar in form to
that of B. mindorensis and B. bubalis. In extant Bubalus, this
process supports various facets for articulation with the
posterior portions of the cubonavicular (¼ centroquartal) and
fused tarsals II and III. In B. depressicornis and B. bubalis, the
posterior cubonavicular facet is mediolaterally elongate; in
B. mindorensis, it is small and circular. The size and position of
this facet cannot be discerned precisely in the fossil cast, but it
appears it would have more closely resembled the condition in
B. mindorensis than in B. bubalis or B. depressicornis. The
remaining tarsal facets are much broader in B. bubalis, B.
mindorensis, and B. cebuensis than in B. depressicornis.InB.
cebuensis, the anterior cubonavicular facet tapers slightly
anteriorly; in both B. mindorensis and B. bubalis it is more
constant in breadth. The facet for tarsals II and III is relatively
larger in B. bubalis than in B. mindorensis; the condition in B.
cebuensis more closely resembles that in B. mindorensis.
The tuberosity on the proximomedial end of the planter
surface of the metatarsal is proportionately broader in
B. cebuensis than in
B. depressicornis, B. mindorensis,and
B. bubalis. This tuberosity is proximodistally elongate in
both B. mindorensis and B. bubalis, but extends further
proximally in the former. In B. cebuensis, the tuberosity is
broad proximally, resembling a triangle with its apex pointed
distally. In both B. mindorensis and B. bubalis,asulcus
delimits the medial edge of the tuberosity from the plantar
surface; no sulcus is present in B. depressicornis.InB.
cebuensis, the feature that appears to be the homologous
sulcus is positioned more laterally, essentially bisecting the
tuberosity; this condition strongly contrasts with that present
in all extant species of Bubalus.
In B. cebuensis, a slight crest extends distally from the
proximomedial tuberosity of the metatarsal along its plantar
surface; it is similarly developed in B. mindorensis. This crest
is more strongly developed in B. bubalis, and is essentially
absent in B. depressicornis. The heads of the metatarsal of B.
cebuensis are reminiscent of those of modern Bubalus.
A principal component analysis was performed to explore
size and shape variation in the metatarsal among different
Bubalus. Seven of the measurements presented in Table 3 were
used in this analysis; breadth of the dorsal longitudinal groove
was excluded because the condition in B. cebuensis differs so
dramatically from that of other Bubalus. The factor loadings
for PC1 and PC2 are presented in Table 4 and the specimens
are plotted against these 2 factors in Fig. 4. Again, PC1 clearly
represents size (all variables have high positive loadings), but
TABLE 3.—Humeral and metatarsal measurements (mm) for selected specimens of Bubalus. Measurements at proximal and distal ends are
greatest diameters. Humeral trochlear diameter was measured in a proximodistal orientation. FMNH ¼ The Field Museum of Natural History;
PNM ¼ National Museum of the Philippines; UMMZ ¼ University of Michigan Museum of Zoology; AP ¼ anteroposterior; ML ¼ mediolateral.
Measurement
B. depressicornis
FMNH 98791
B. cebuensis
PNM 2006-A
B. mindorensis
FMNH 18817
B. mindorensis
UMMZ 84106
B. bubalis
FMNH 92912
B. bubalis
UMMZ 157862
Humerus
Length 210.5 207.0 279.5 280.0 320.0 289.0
Proximal ML diameter 61.0 62.5 88.0 90.0 99.5 99.5
Proximal AP diameter 60.0 68.0 94.0 93.5 120.0 108.0
Teres minor ML diameter 35.5 44.5 54.0 52.0 74.0 72.0
Midshaft ML diameter 22.5 25.0 33.0 32.5 42.0 36.5
Midshaft AP diameter 27.5 30.5 41.5 41.0 48.0 45.0
Distal ML diameter 46.0 52.5 65.0 62.5 90.0 87.0
Distal AP diameter 47.0 53.5 67.0 65.0 87.5 77.5
Trochlear diameter 26.0 30.5 39.0 39.5 52.0 45.5
Metatarsal
Length 137.5 148.0 (165) 167.0 232.0 196.0
Proximal ML diameter 30.5 37.0 44.0 43.5 59.5 52.5
Proximal AP diameter 26.0 33.5 38.5 38.0 55.1 42.0
Midshaft ML diameter 20.0 23.5 31.0 28.0 32.5 31.5
Midshaft AP diameter 17.5 22.0 23.5 24.0 33.0 27.0
Distal ML diameter 32.5 42.0 49.5 49.5 69.0 61.0
Distal AP diameter 19.5 24.5 28.0 26.5 39.0 34.0
Dorsal longitudinal groove breadth 7.5 11.0 8.5 9.0 11.0 10.5
1042 JOURNAL OF MAMMALOGY Vol. 87, No. 5
in contrast to the humeral results, B. cebuensis is positioned
between B. depressicornis and B. mindorensis on this axis,
reflecting the relatively larger size of the metatarsal in the new
species compared to the humerus. PC2 represents metatarsal
robustness to some degree—midshaft mediolateral diameter
has a high positive loading and length has a high negative
loading—but proximal and midshaft anteroposterior diameters
also exhibit somewhat higher negative loadings. There is less
discrimination along this axis than in the same axis in the
principal component analysis of humeral measurements,
reflecting a greater amount of individual or ontogenetic shape
variation, or both, in the Bubalus metatarsal than in the
humerus. Both B. mindorensis and B. bubalis vary greatly in
their scores on PC2, but show surprisingly little overlap;
B. cebuensis and B. depressicornis are within the range of
variation of B. bubalis, distinct from B. mindorensis.
Vertebrae.—Two thoracic vertebrae of B. cebuensis are
preserved but they differ in several respects from thoracic
vertebrae of modern Bubalus (Fig. 6); because of this, their
precise positions within the thoracic series are uncertain. Both
preserved vertebrae exhibit relatively small costal articular
facets (both on the vertebral body and transverse process),
which suggests they pertain to the caudal half of the thoracic
region (i.e., T7–13). They differ from vertebrae in this region
of B. depressicornis in being larger, more robust, and lacking
well-developed mammillary processes on the dorsal surfaces
of the transverse processes. Both vertebrae exhibit lateral
vertebral foramina, a feature present in most Bubalus vertebra.
The more complete of the 2 vertebrae (Fig. 6A) is likely
the more anterior; its spinous process is less vertical (posi-
tioned at an angle of just under 458 to the horizontal), its
transverse costal facets are slightly larger and directed more
cranially, and its vertebral body is longer and narrower. It
compares reasonably well with T9 of B. mindorensis in
having a spinous process that is long and straight and
mediolaterally expanded at its distal end (although the
epiphysis is not preserved in the fossil vertebra). The caudal
articular facets are positioned at approximately the same
angle as the spinous process (458) and are elliptical. The
vertebra differs from the T9 of B. mindorensis, however, in
having the transverse costal facets oriented more laterally (as
opposed to cranially). In this respect, it is more similar to T10
of B. mindorensis. The vertebra differs dramatically from
both T9 and T10 of B. depressicornis; in those vertebrae, the
spinous processes arch caudally (i.e., they are concave
caudally) and the caudal costal facet is positioned more
dorsally on the vertebral body than the cranial costal facet
(they are at the same level in B. cebuensis). In anterior view,
the neural arch more closely resembles that of B. bubalis than
B. mindorensis; the transverse processes do not extend as far
FIG.4.—Bivariate plot of the first 2 factor scores from principal
components analyses of 9 humeral measurements (above) and 7
metatarsal measurements (below) for selected specimens of Bubalus.
Factor loadings for each principal component (PC) axis are listed in
Table 4.
TABLE 4.—Factor loadings and proportion of variation for first
2 principal components (PCs) from principal component analyses of
Bubalus humeral (H) and metatarsal (MT) measurements. PC1
accounts for 96.8% of the variation in the data; PC2 accounts for
2.3%. AP ¼ anteroposterior; ML ¼ mediolateral; NA ¼ not available.
Measurement PC1 (H) PC2 (H) PC1 (MT) PC2 (MT)
Length 0.971 0.226 0.981 0.162
Proximal ML diameter 0.971 0.173 0.998 0.0215
Proximal AP diameter 0.999 0.029 0.984 0.0959
Teres minor ML diameter 0.995 0.021 NA NA
Midshaft ML diameter 0.989 0.128 0.914 0.403
Midshaft AP diameter 0.970 0.228 0.988 0.123
Distal ML diameter 0.992 0.089 0.997 0.0214
Distal AP diameter 0.972 0.225 0.994 0.0371
Trochlear diameter 0.995 0.035 NA NA
Variation explained (%) 96.8 2.3 96.0 3.1
October 2006 1043CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
superiorly as in B. mindorensis. The vertebra is intermediate
in length between that of B. depressicornis and B. mind-
orensis and the vertebral body is wider than tall, more closely
resembling the condition in B. mindorensis than in either B.
depressicornis or B. bubalis (Table 5).
The less-complete vertebra (Fig. 6B) appears to represent
T11. It possesses caudal articular facets that are directed
inferiorly from the base of the spinous process, precluding the
possibility of its referral to T12 or T13 (both of which have
facets that are oriented more vertically and laterally, as in the
lumbar vertebrae). The vertebra also exhibits a more vertical
spinous process than typical T12 and T13 of modern Bubalus.
It cannot represent T10, however, if the identification of the
more complete vertebra described above is correct; when
placed in approximate articulation, the 2 vertebrae do not
appear to represent consecutive positions. The vertebra is more
similar to T11 of B. mindorensis than of B. depressicornis,
although the transverse processes are less well developed than
in B. mindorensis. The vertebral body is very robust; it is
intermediate in length between that of B. depressicornis and B.
mindorensis, but is similar in breadth to the latter, making it
relatively broader than in any modern material of Bubalus
examined (Table 5). The within-species variability in this
character is not known. The relative height of the vertebral
body approximates that of B. bubalis.
Unguals.— The morphology of the unguals of B. cebuensis
is similar to that of other Bubalus (Fig. 5D). The most
conspicuous feature is a large, anteroposteriorly elongate
depression on the posterolateral surface, an area that normally
exhibits 1 or more large nutrient foramina in extant taxa. In B.
cebuensis, it appears that several of these nutrient foramina
might have coalesced. Whether this is a constant, discriminat-
ing feature of the taxon is unknown. This more closely
resembles the condition seen in some individuals of B. bubalis
than of B. mindorensis (no comparative specimens of B.
depressicornis were available).
FIG.5.—Left metatarsals of Bubalus mindorensis (FMNH 18817, left) and Bubalus cebuensis (cast of PNM 2006-A, right) in A)
plantar (posterior), B) dorsal (anterior), and C) proximal (with dorsal toward the top) views. D) Paired unguals of Bubalus cebuensis in dorsal
view. Scale bars ¼ 5 cm in A and B, 2 cm in C and D. The extra foramina in FMNH 18817 are the result of its previously having been articulated
with wires and screws.
1044 JOURNAL OF MAMMALOGY Vol. 87, No. 5
It is unclear whether these elements represent manual or
pedal unguals. In B. mindorensis, the manual unguals appear to
circumscribe a larger arc than the pedal ones. Additionally, the
medial sides of the plantar surfaces are flatter in manual
unguals; they are slightly upturned in the pedal unguals. The B.
cebuensis unguals display an intermediate morphology be-
tween the anterior and posterior, precluding a confident
identification of homology and suggesting a slightly different
relationship between the ungual and pedal phalanges in this
extinct taxon. The left ungual measures 50 mm (anteroposte-
rior) 25 mm (mediolateral); the right measures 49.5 mm
(anteroposterior) 23 mm (mediolateral).
Dentition.— The only dental elements preserved are 2
isolated lower molars, left m1–2 (Fig. 7; Table 6). In overall
form, they closely resemble the corresponding teeth of modern
Bubalus. In size, they are most similar to B. mindorensis; they
are slightly smaller mesiodistally but are comparable buccolin-
gually (Fig. 8). Both teeth exhibit moderate wear, suggestive of
a mature individual; only the talonid fossette is present in m1,
whereas in both trigonid and talonid fossettes are present in m2.
They closely resemble the state of wear exhibited by UMMZ
157862 (B. bubalis).
The enamel is thick relative to tooth size in both m1 and m2,
but this may be a function of wear stage. In m1, the crown
height is 14.8 mm labially and 17.2 mm lingually. The
corresponding values for m2 are 12.0 mm and 12.8 mm. A
well-developed labial projection is present between the trigonid
and talonid in both teeth. The presence or absence of this
feature appears to vary individually and with wear in extant
Bubalus. The enamel islands approximate a figure eight in B.
cebuensis; enamel island shape also appears to vary with wear
state in extant Bubalus, and a larger sample size of both B.
FIG.6.—Vertebrae of Bubalus cebuensis (PNM 2006-A) in left lateral (left) and cranial (right) views. A) ?T9. B) ?T11. Scale bars ¼ 5 cm.
October 2006 1045CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
cebuensis and other Bubalus would be required to test the
taxonomic significance of this character.
?Radius.— One other long bone (lacking epiphyses) origi-
nally was found with the holotype, but we were unable to
examine it firsthand. Based on study of a plaster cast preserving
little detail, it most likely represents a ?right radius, potentially
referable to B. cebuensis. It certainly represents an individual
distinct from that of the holotype, however, in which all
appendicular epiphyses are solidly fused (i.e., any sutures have
been obliterated). The element measures 136 mm in length; the
proximal end measures 47.5 24.5 mm and the distal end
measures 34.5 28 mm.
PHYLOGENETIC AFFINITIES
Only a single cladistic analysis has examined relationships
within Bovini. Geraads (1992) performed a phylogenetic
analysis of 32 fossil and extant taxa based on 57 morphological
characters. The monophyly of Asiatic buffaloes (the tradition-
ally recognized Bubalina clade) was not supported in the
consensus tree, but Geraads (1992) favored a slightly longer
tree that included a monophyletic Bubalina (including Bubalus,
Hemibos, Anoa, and Proamphibos). All but one of the
characters used in this analysis were craniodental, however,
precluding testing of the phylogenetic position of B. cebuensis
using this data set. Xue and Li (2000) examined relationships
among Chinese fossil Bubalus, but that analysis also was based
exclusively on craniodental (especially horn core) characters.
Rautian et al. (2000) examined morphological and molecular
differentiation within the Bovini (including a few fossil
species), but did not perform a phylogenetic analysis nor
include any extinct genera. Among extant taxa, Rautian et al.
(2000) advocated a common ancestry of Bubalus and Anoa
exclusive of other taxa. The same association was favored by
Geraads (1992) among extant Bovini.
In sum, the few studies that have examined relationships
among fossil Bovini have relied almost exclusively on
craniodental characters and thus cannot be used to directly
test the phylogenetic affinities of B. cebuensis. The lack of
postcranial data in those analyses is due to the paucity of
associated postcrania for fossil taxa. Although a comprehensive
revision of fossil bovine postcrania would likely help identify
postcranial characters useful for phylogenetic analysis, such an
undertaking is well beyond the scope of the present report of
this single new endemic island taxon.
Among extant Bubalus for which postcranial data are
available, B. cebuensis much more closely resembles B.
(Bubalus) than B. (Anoa); B. cebuensis shares a variety of
discrete morphological character states with both B. bubalis
and B. mindorensis, but shares none with B. depressicornis
TABLE 5.—Measurements of 9th (T9) and 11th (T11) thoracic vertebrae for selected specimens of Bubalus. FMNH ¼ The Field Museum of
Natural History; PNM ¼ National Museum of the Philippines; UMMZ ¼ University of Michigan Museum of Zoology; AP ¼ anteroposterior.
Measurement
B. depressicornis
FMNH 98791
B. cebuensis
PNM 2006-A
B. mindorensis
FMNH 18817
B. mindorensis
UMMZ 84106
B. bubalis
UMMZ 157862
T9
Length of body 33.0 42.0 47.0 51.0 58.0
Anterior width of body 20.0 27.5 34.0 31.5 36.5
Anterior height of body 20.5 25.0 27.0 28.0 38.5
Spinous process length 58.5 89.5 84.0 98.0 107.5
Spinous process AP width 18.0 20.0 24.5 24.5 35.5
T11
Length of body 33.5 39.0 46.0 49.0 57.5
Anterior width of body 20.5 30.0 30.0 31.5 38.0
Anterior height of body 20.0 26.0 26.5 28.0 38.5
Spinous process length 30.5 49.0 47.0 66.0
Spinous process AP width 16.0 18.5 25.5 28.5 30.5
FIG.7.—First (left) and 2nd (right) lower molars of Bubalus
cebuensis (PNM 2006-A) in occlusal (above) and lingual (below)
views. Scale bar ¼ 1 cm.
1046 JOURNAL OF MAMMALOGY Vol. 87, No. 5
(Table 2). Given the greater similarity in size between B.
cebuensis and B. (Anoa) than between the former and B.
(Bubalus), the character states common to B. cebuensis and B.
(Bubalus) cannot be attributed to allometry and are more likely
indicative of phylogenetic relationship. Based on these
resemblances, B. cebuensis can reasonably be referred to B.
(Bubalus). Within B. (Bubalus), B. cebuensis shares more
character states with B. bubalis than with B. mindorensis. The
latter 2 species share several traits not observed in B. cebuensis,
however, which may indicate a closer relationship between
them than between either and B. cebuensis. The relationships
among these 3 species are probably best considered unresolved
until additional material of B. cebuensis is discovered and
a thorough cladistic analysis (incorporating postcranial fea-
tures, as well as living and fossil taxa) can be performed.
BODY MASS
Long-bone lengths for B. cebuensis suggest an animal
roughly similar in stature (i.e., limb length) to B. depressi-
cornis; in contrast, the breadths of these bones suggest a more
massive animal. To test this assertion, we estimated the body
mass of B. cebuensis using postcranial regression equations for
modern bovids published by Scott (1983). Eleven humeral and
metatarsal measurements examined by Scott (1983) were
preserved in the available material of B. cebuensis and 10 of
these were used to estimate body mass; metatarsal length was
excluded because it is poorly correlated with body mass in
modern bovids (Scott 1983). The remaining 10 variables
produced mass estimates of approximately 115–215 kg with
X
¼ 157.2 kg and SD ¼ 36.6 kg (Table 7). Humeral mass
estimates exhibited a much greater range than metatarsal mass
estimates, but the average values were quite similar (154.0 kg
and 162.0 kg, respectively). A reasonable mass estimate for this
particular specimen of B. cebuensis is roughly 150–165 kg.
Given the variability in estimates derived from individual
measurements in living taxa, this estimate is probably within
15% of the true mass of this fossil animal (Scott 1983).
As discussed by Scott (1983), accurate individual or species
body masses are difficult to obtain for extant large herbivores;
this type of information is rarely recorded in the field, and body
masses listed for these mammals frequently include only trophy
or zoo animals (which are not representative of the species in
general). In the case of rare ungulates such as B. mindorensis
and B. (Anoa), even poor mass estimates are comparably
scarce. Only 2 independent body masses have been published
for B. mindorensis: Talbot and Talbot (1966) estimated the
mass of a female zoo animal at 600 lb (¼ 275 kg) and Roth and
Montemayor-Taca (1971) estimated the mass of a female zoo
animal at 180–220 kg. Although sexual dimorphism is evident
in the skull of B. mindorensis, body mass and limb proportions
do not vary with sex (Custodio et al. 1996), and so these
estimates also should apply to male B. mindorensis. Using the
regression equations of Scott (1983), an average body mass of
approximately 210 kg was obtained for the 2 male specimens
examined in the present study; this accords well with the
TABLE 6.—First (m1) and 2nd (m2) lower molar measurements for selected specimens of Bubalus. FMNH ¼ The Field Museum of Natural
History; PNM ¼ National Museum of the Philippines; UMMZ ¼ University of Michigan Museum of Zoology; L ¼ length (measured
mesiodistally); W ¼ width (measured buccolingually).
Measurement
B. depressicornis
FMNH 98791
B. cebuensis
PNM 2006-A
B. mindorensis
FMNH 18817
B. mindorensis
FMNH 43300
B. mindorensis
FMNH 43301
B. bubalis
FMNH 92912
B. bubalis
FMNH 31711?
B. bubalis
FMNH 31711?
B. bubalis
UMMZ 157862
Wear Heavy Medium Medium Medium Light Medium Light Medium Medium
Side Right Left Right Right Right Right Right Right Right
m1 L 12.3 16.5 18 17.4 22.4 28.1 33.1 29.5 24.2
m1 W 9.8 12.7 12.7 12.3 11.5 15.5 17.8 18.4 16.1
m2 L 15.1 18.3 19.8 20.9 25.1 30.1 37.6 32.8 29.5
m2 W 10.9 12 12.3 12.3 11.2 16.4 16.9 19.3 18
FIG.8.—Bivariate plots of log-transformed measurements for m1 (left) and m2 (right) for selected specimens of Bubalus. Length is measured
mesiodistally; width is measured buccolingually.
October 2006 1047CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
estimate of Roth and Montemayor-Taca (1971) and highlights
the lack of sexual dimorphism in this species.
Groves (1969) reported a body mass of 56 kg for an adult B.
quarlesi and indicated it was the only body mass for B. (Anoa)
that he was aware of; this same mass was used by Scott (1983)
for B. depressicornis, presumably because no better data were
available. Burton et al. (2005) estimated the body mass of B.
quarlesi as ,150 kg, but provided no data for individual
specimens; they estimated the body mass of B. depressicornis
as ,300 kg, but noted that no specimen has ever been recorded
at more than 150 kg. Based on skull length (Groves 1969),
there does not appear to be dramatic sexual size dimorphism in
B. (Anoa). Using the regression equations of Scott (1983),
a body mass of approximately 135 kg was obtained for the
single female specimen of B. (A.) depressicornis examined in
the present study. Therefore, this suggests that a mass estimate
of ,150 kg for B. depressicornis may be more accurate than an
estimate of ,300 kg.
The data considered above indicate that B. cebuensis was
intermediate in body mass between B. depressicornis and B.
mindorensis, being about 15% larger than the former and 25%
smaller than the latter. This contrasts with long-bone lengths,
which suggest a stature more similar to that of B. depressi-
cornis than B. mindorensis. The prominent muscle scars on the
humerus and the breadth of the dorsal longitudinal sulcus of the
metatarsal support the interpretation of relatively large
appendicular muscles in B. cebuensis, indicative of its larger
body mass (relative to B. depressicornis). Together, these
observations paint a picture of a short, heavy-bodied Bubalus,
perhaps similar in stature to an anoa, but certainly of greater
mass; the structure of the skull is unknown, but the animal may
have resembled a small tamaraw.
INSULAR DWARFING
The phenomenon of insular ‘‘dwarfing’’ has been observed
in many groups of large mammals, including proboscideans
(Hooijer 1970; Roth 1990; Vartanyan et al. 1993), hippopot-
amids (Burney et al. 2004; Simmons 1988), cervids (Lister
1989), and possibly hominids (Brown et al. 2004; Morwood et
al. 2005). Together with its converse—insular gigantism—
insular dwarfing has been the subject of many studies over the
past 40 years (e.g., Anderson and Handley 2002; Case 1978;
Foster 1964; Heaney 1978; Lawlor 1982; Lomolino 1985,
2005; Meiri et al. 2004; Melton 1982; Michaux et al. 2002;
Sondaar 1977; Van Valen 1973). Although the causes (and
patterns) of insular body-size change are still being debated,
certain cases continue to be exemplars of how a major life-
history trait can evolve rapidly, over a geologically brief period
of time, after isolation (e.g., Lister 1989).
Given the much larger size (in terms of both stature and
mass) of the closest relatives of B. cebuensis, both fossil and
extant, it is clear that this Cebu Island form represents another
case of insular dwarfing. In fact, the long fossil record of
Bubalus in Asia suggests that both B. mindorensis and
B. cebuensis may be dwarf forms of B. bubalis that arose by
dispersal to and within the Philippines. Given the rarity of
fossils in the Philippines and the lack of a secure phylogeny for
the species of B. (Bubalus), details of such a scenario must
remain provisional. However, certain independent aspects of
the distribution and morphology of these taxa do support this
general interpretation.
Heaney (1978) examined body-size variation in the tri-
colored squirrel, Callosciurus prevostii, and found a significant
correlation between body size and island size. Based on this
correlation and patterns of variation in other mammals, he
constructed a model predicting that the effects of food
limitation, predation, and interspecific competition on body
size would vary depending on the body size of the species in
question and the area of the island. In some cases, these factors
would be expected to produce insular dwarfs; in others, giants
would result. For large mammals, food limitation was proposed
as the most significant factor affecting insular body size, and
a direct correlation between body size and island size was the
expected result. In support of this model, Heaney (1978) noted
such a correlation in Pleistocene populations of Elephas
falconeri, where increasingly smaller-bodied taxa are found
on progressively smaller Mediterranean islands (Maglio 1973).
Although this pattern may not apply to carnivorans (Heaney
1978; Meiri et al. 2004) or tree sloths (Anderson and Handley
2002) it does seem to be generally applicable to large
ungulates, including Bubalus.
Based on body mass, B. cebuensis is some 25% smaller than
B. mindorensis; B. mindorensis is itself less than half the size of
wild (mainland) B. bubalis. Such a pattern in body size would
be predicted based simply on the relative sizes of Cebu Island
(5,088 km
2
), Mindoro Island (10,243 km
2
), and mainland Asia,
if island size were a major factor in body-size evolution. This
pattern does not hold if one substitutes the entire area of the late
Pleistocene Negros–Panay Faunal Region for that of Cebu
Island—a region probably 10 times larger—but this is a moot
TABLE 7.—Humeral (H) and metatarsal (MT) variables used to
predict body mass of Bubalus cebuensis using measurements from the
holotype and predictive equations from Scott (1983). Predictive
equations are in the form: log(body mass) ¼ b log(variable) þ a.
The mean of the predicted body masses for B. cebuensis is 151.4 kg
and SD ¼ 40.0. For more detailed explanations of variables, see Scott
(1983). AP ¼ anteroposterior; ML ¼ mediolateral.
Variable Value (mm) b a Mass (kg)
Humerus
H1 (headtrochlea length) 180.5 3.4556 2.4150 217.6
H2 (tubercletrochlea length) 205.0 3.3696 2.4709 204.1
H3 (head breadth) 46.5 2.7311 0.2334 120.0
H4 (anterior distal
articular width) 51.0 2.5499 0.4078 117.0
H5 (maximum distal width) 53.5 2.6246 0.2756 123.0
H6 (posterior trochlear
width) 20.0 2.7630 1.3617 142.1
Metatarsal
MT2 (proximal ML diameter) 37.0 2.9220 0.6162 181.0
MT3 (proximal AP diameter) 33.5 3.0306 0.5755 180.8
MT4 (distal ML diameter) 42.0 2.7421 0.5614 150.3
MT5 (distal AP diameter) 18.5 2.9763 1.1416 136.1
1048 JOURNAL OF MAMMALOGY Vol. 87, No. 5
point if B. cebuensis evolved during the Holocene; given the
numerous other examples of post-Pleistocene dwarfing in large
mammals, B. cebuensis certainly could have undergone the
observed changes in body size subsequent to Cebu’s isolation.
No well-preserved Bubalus have been discovered on other
islands that might permit testing of this scenario; although
isolated teeth from Luzon have been referred to B. mindorensis
(Beyer 1957), they have not been critically examined (Custodio
et al. 1996), and probably are not useful for estimating body
size in bovids except in very general terms (Scott 1983; see
also below).
Size reduction in insular dwarfs is not generally isometric
across all parts of the body; allometric relationships have been
noted both for the dentition (Fortelius 1985; Lister 1989) and
distal limb elements (Ko¨hler and Moya`-Sola` 2001; Sondaar
1977), among other structures. In dentition, island dwarfs tend
to have relatively larger teeth, an attribute apparently exhibited
by B. cebuensis; although much less massive than B.
mindorensis, the teeth of these 2 species are similar in size
(Fig. 8). Based on this pattern of positive dental allometry, it
has been suggested that paedomorphosis is the mechanism of
insular dwarfing in some lineages (Fortelius 1985).
In contrast to the dentition, the metatarsal of B. cebuensis
does not exhibit the pattern of size reduction typical of island
dwarfs; it is 71.5% the length of the humerus in B. cebuensis,
a value comparable to that of B. bubalis examined (68–
72.5%). However, the metatarsal does appear to be reduced in
B. mindorensis, being only 59–60% the length of the humerus.
Whether such reductions in distal limb elements are attribut-
able to paedomorphosis or simply are locomotor adaptations
(e.g., Sondaar 1977) may depend on the mosaic pattern of
insular evolution in the particular species in question; the
metatarsal of B. mindorensis more closely resembles an
osteologically mature B. bubalis than a slightly less mature
one (Fig. 4), but testing for such an ontogenetically driven
trend would certainly require examining much younger
individuals of B. bubalis.
CONCLUSIONS
The new taxon described above is the 1st fossil mammal of
any age to be reported from Cebu Island and the only
nonproboscidean to be documented from the Negros–Panay
Faunal Region. In conjunction with the presence of Bubalus on
Mindoro Island (and potentially Luzon), discovery of this
specimen suggests that Bubalus may once have ranged
throughout the Philippines—a hypothesis that hopefully will
be tested by future paleontological sampling across the islands.
Similarly, this discovery, combined with the exceptionally high
endemism and diversity of the extant mammal fauna of the
Philippines, suggest that many more new late Cenozoic to
Holocene fossil species remain to be recovered from this
region. B. cebuensis is clearly referable to the subgenus
Bubalus, and is diagnostically differentiated from B. mind-
orensis and B. bubalis by metric and morphological character-
istics. In life, B. cebuensis was probably similar in stature to the
lowland anoa, B. depressicornis, but regression equations from
modern bovids suggest that it was approximately 15% more
massive. The overall small size of B. cebuensis relative to other
B. (Bubalus) appears to be attributable to island dwarfing, an
explanation that is supported by the consistent relationship
between body size and island size in B. cebuensis, B.
mindorensis, and B. bubalis. Although the relatively large
dentition of B. cebuensis suggests paedomorphosis as a possible
mechanism of body-size reduction in this lineage, this is not
supported by the relatively large (i.e., normal for this clade)
size of the metatarsal relative to the humerus. Additional
material of B. cebuensis would facilitate testing of paedomor-
phosis as a mechanism for dwarfing in these bovids, as would
a detailed study of the postcranial osteology of B. mindorensis.
Although the exact age of B. cebuensis is unknown, the
condition of the material and its small size suggest it is no older
than Pleistocene, and possibly Holocene. Further study of B.
cebuensis and other island dwarfs may provide insights into the
evolution of small-bodied hominins such as Homo floresiensis,
yet another reason to be interested in dwarf mammals on
oceanic islands in Indo-Australia.
ACKNOWLEDGMENTS
We thank M. Armas and H. Intengan for their generosity and sense
of curiosity in recognizing the scientific value of the specimen. At
The Field Museum of Natural History, S. McCarroll, W. Simpson,
and W. Stanley gave valuable assistance with the preliminary
identification and accessioning of the specimen; J. Weinstein and
M. Widhalm skillfully executed the photographs; and A. Shinya
graciously made the molds and casts. P. Myers and S. Hinshaw
provided access to specimens at the University of Michigan Museum
of Zoology. Carbon isotope analyses were conducted by the
Accelerator Mass Spectrometry Laboratory at the University of
Arizona. We thank 2 anonymous reviewers for providing construc-
tive assessments of this manuscript.
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Associate Editor was Eric A. Rickart.
APPENDIX I
List of specimens examined from the Recent mammal collections of
the Division of Mammalogy at The Field Museum of Natural History
(FMNH) and the University of Michigan Museum of Zoology
(UMMZ).
Bubalus (Anoa) depressicornis.—FMNH 98791, mature female,
skull and skeleton, from Lincoln Park Zoo, Chicago, Illinois.
Bubalus (Bubalus) mindorensis.—FMNH 18817, mature male, skull
and skeleton, from Mindoro Island, Philippines; FMNH 43300, mature
male, skull only, Mindoro Island, Philipines; FMNH 43301, young
male, skull only; UMMZ 84106 (holotype of Anoa mindorensis
Steere), mature male, skeleton only, from Catuiran River, Mindoro
Island, Philippines.
Bubalus (Bubalus) bubalis.—FMNH 92912, immature male, skull
and skeleton, from Khuzistan, Iran; FMNH ?31711, 2 young female
specimens, skulls only, differing in stage of wear, exact provenance
unknown; UMMZ 157862, mature female, skull and skeleton, from
Tanjay, Negros Oriental, Philippines.
October 2006 1051CROFT ET AL.—DIMINUTIVE BUBALUS FROM CEBU ISLAND
... Among these are the 'dwarf' buffaloes, namely the tamaraw of Mindoro Island (Bubalus mindorensis), the mountain and lowland anoas of Sulawesi and Butung islands (B. quarlesi and B. depressicornis), and the extinct Bubalus cebuensis of Cebu (Croft et al. 2006) among other fossil species. Genomic age estimates (Tanaka et al. 1996;Bibi 2013;Hassanin et al. 2013) suggest that the divergence date of the water buffalo (Bubalus bubalis) and the lowland anoa was probably between 2 and 1 Ma, implying an early Pleistocene age for the first colonization of these islands by the mainland buffalo. ...
... The fossil record of the Southeast Asian archipelago is primarily Pleistocene in age. Fossil sites are known from the islands of Java, Sumatra, Flores, Borneo, Sulawesi, and several of the Philippine islands, among others (e.g., Croft et al. 2006;Louys and Meijaard 2010). The fossil record of these islands tells a story of insular evolution of mainland mammal lineages, with waves of dispersal into the islands associated with the major and cyclical sea level drops characteristic of the Pleistocene (discussed above). ...
... quarlesi and B. depressicornis) of Sulawesi and Buton (Groves 1969). Records of fossil buffalo from the modern SE Asian archipelago include Bubalus cebuensis of Cebu (Croft et al. 2006), and the oldest records may be of Bubalus palaeokerabau at 1.2 Ma at Ci Saat in Java ). This latter date matches the early Pleistocene age estimates for the dispersal of Bubalus from the mainland onto the islands (Tanaka et al. 1996;Bibi 2013;Hassanin et al. 2013). ...
... cebuensis Croft et al., 2006;B. grovesi Rozzi, 2017; for extant taxa, see Croft et al. (2006) and Groves and Grubb (2011). ...
Chapter
Extant wild bovids of Greece include only the Balkan Chamois and the Wild Goat of Creta, though past bovid biodiversity was tremendously higher, accounting up to ten contemporaneous species and representing a wide array of ecomorphological types. Despite the known stratigraphic discontinuity of the Greek fossil record, the review of the Greek fossil bovids from a total of 80 fossil localities revealed the presence of at least fifty two (52) genera and eighty three (83) valid species of Bovidae [among which 17 species of Bovinae, and 66 of Antilopinae] distributed from early middle Miocene (Orleanian) till latest Pleistocene. Fifty eight (58) of these species were named from type localities in Greece, and twenty three (23) represent genotypes, mostly from Pikermi, Samos, and Axios Valley classical fossil sites. The peak in bovid taxonomic diversity is noted during the Turolian. Gazella s.l. stands as the taxon with the widest temporal distribution from late Vallesian to late Villafranchian (ca. 7 Ma). Most of the Greek bovids through time seem to represent the westernmost populations of taxa with a Central-West Asian distribution, though taxa with a more restricted South European/European distribution are also present especially during late Pliocene and Early Pleistocene.
... Relative shortening and/or thickening of metapodials is recorded in several fossil and extant insular ruminants, such as dwarf buffaloes (Bubalus cebuensis, B. mindorensis, B. depressicornis, B. quarlesi ;Croft, Heaney, Flynn, & Bautista, 2006;Rozzi, 2017;, the Formosan serow (Capricornis swinhoei; , all species of Myotragus (Bover, 2004;Bover et al., 2010), the smallest Hoplitomeryx (H. matthei and H. devosi sensu Van der Geer, 2014b; see Mazza et al., 2016;Van der Geer, 2014b), the Ryukyu deer (Cervus astylodon; Van der Geer, 2014a; Van der Geer et al., 2011), the Kassos deer (Candiacervus cerigensis; Van der Geer, 2014a; Van der Geer et al., 2011), the Karpathos deer (C. ...
Article
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Aim Mammals on islands often undergo remarkable evolutionary changes. The acquisition of ‘low gear’ locomotion, namely short and robust limb elements, has been typically associated with the island syndrome in large mammals and, especially, ruminants. Here we provide an investigative framework to examine biotic and abiotic selective factors hypothesized to influence evolution of this peculiar type of gait. Location Islands worldwide. Taxon Bovidae. Methods We calculated response variables associated with ‘low gear’ locomotion in 21 extinct and extant insular bovids. We assembled data on the physiography of 11 islands and on life history and ecological traits of the focal taxa. We estimated 10 predictors (island area and four topographic indices, body mass, body size divergence, number of predators and competitors, large mammal richness) and used multiple regressions, regression trees, and random forests to assess their contextual importance. Results The acquisition of ‘low gear’ locomotion generally happens on islands with a small number of competitors. However, the roughness of the island terrain appears to be also important, without being a main driver. Finally, although the most extreme cases of ‘low gear’ locomotion occurred on islands with no mammalian predators, our models show a non‐significant relationship with this factor. Main conclusions The evolution of ‘low gear’ locomotion in insular ruminants does not simply result from phyletic dwarfing and predatory release. Variation in morphological responses within Bovidae to ecological and topographic traits suggests, instead, a complex interplay of biotic and abiotic factors. Current understanding on the main drivers of species evolutionary pathways and biogeographic patterns are disproportionally based on few taxa, mainly vertebrates, and in some extreme cases (like this one) even on few species. Here we show how adding more data, even within the same taxonomic group, can challenge historically accepted macroevolutionary and macroecological concepts.
... Bovids are unusual components of endemic insular faunas and are only recorded in some Mediterranean and South East Asian islands (Palombo et al., 2006a, b; Croft et al., 2006 and references therein). Some of the most interesting and enigmatic bovids, belonging to the Myotragus lineage, have been found in the Plio-Pleistocene deposits of the Eastern Balearic Islands (also known as Gymnesic Islands) (see inter alios Alcover, 1976; Pons-Moyà et al., 1979; Alcover et al., 1981;Moyà Solà and PonsMoyà , 1982;Moyà Solà et al., 1985; Bover, 2004; Ko¨hlerKo¨hler andMoyà Solà , 2004; Palombo et al., 2006a and references therein). ...
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The endemic bovid Myotragus, from the Plio-Pleistocene deposits of Majorca, underwent a significant reduction in relative brain size, especially affecting the vision and locomotor centres. These important modifications allow the hypothesis that, under altered conditions in predator free insular environments, functional demands on neural performance are reduced, allowing a reduction in brain structures and associated sense organs. This is suggested, for example, by the small orbits and reduced visual brain structures of Myotragus balearicus Bate, 1909. These changes, which parallel those shown by domesticated animals, have been interpreted as an adaptive response to insular environmental conditions, in particular to a lack of interspecific competitors and predators. Results obtained from analysis of the smallest Cretan deer (Candiacervus ropalophorus de Vos, 1984, and Candiacervus spp. II) are not as outstanding as it is in Myotragus, and apparently run counter to the fact that dwarfed insular artiodactyls living in environments without any predation pressure would be characterised by a proportional decrease in brain volume as a rule. Brain/body mass proportion of the smallest Candiacervus species provides evidence that this endemic deer underwent only minor changes in the relative size of brain after its geographic isolation. On the other hand, orbit and foramen magnum size are proportionally reduced. Accordingly, different evolutionary process likely affected brain and sense organs changes of these endemic artiodactyls. Other factors, nature of available niches, inter-specific competition, maybe island size and time from isolation, would have played a role in the possible differential evolution of insular ruminants in addition to the change in adaptive strategy for a more efficient energy use under the free-predators environmental conditions of the insular ecosystem.
... Bovidae is a highly diverse clade of large mammals ( Bibi, 2013;Bibi et al., 2009;Hern andez Fern andez & Vrba, 2005) and encompasses several insular species that inhabited or are still living on islands located in different regions and characterized by different environmental features and palaeogeographic histories. The most intriguing and "ecologically na€ ıve" species (sensu Lomolino, 2016) include miniaturized buffaloes from Sulawesi and the Philippines ( Burton, Hedges, & Mustari, 2005;Croft, Heaney, Flynn, & Bautista, 2006;Custodio, Lepiten, & Heaney, 1996;Rozzi, 2017), the boselaphin Duboisia santeng from the Pleistocene of Java ( Rozzi, Winkler, De Vos, Schulz, & Palombo, 2013) and dwarfed extinct Caprini from the Mediterranean islands (K€ ohler & Moy a-Sol a, 2009; Palombo, Rozzi, & Bover, 2013;, 2014). Delving into space-time patterns of body size variation in insular mammals of intermediate ancestral size, such as insular bovids, may be crucial to confirm whether the island rule pattern is "graded" (sensu Lomolino et al., 2012 = "the degree of body size change decreases as we move from considering species of extreme, ancestral size, which change most dramatically, to those of intermediate ancestral size, which change more subtly or not at all") and to verify its overall stability. ...
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Aim: I provide the first comprehensive study on body size evolution of extinct and living insular bovids, exploring the causal biotic and abiotic selective factors for observed patterns. Location: Islands worldwide. Methods: I assembled data on the geographic characteristics of 13 focal islands (area, isolation, latitude, net primary productivity) and on the ecological and morphological characteristics of 32 insular bovid taxa (number of predators and competitors, richness of large mammals, body mass of mainland relatives). I used linear regressions and machine learning methods (regression trees and random forest analyses) to examine the hypothesized contextual importance of these factors in explaining variation in the body size of island bovids. I also calculated evolutionary rates of body size divergence of focal taxa in order to assess whether this phenomenon is influenced by time in isolation. Results: The results of regression, regression tree and random forest analyses were in agreement with predictions based on a hypothesis of ecological release (more pronounced body size divergence on islands with the fewest competitors and predators). Only limited support for a resource limitation hypothesis (more pronounced body size divergence for the larger taxa on smaller islands) was found. Main conclusions: The majority of insular bovids, as large mammals, do follow the main prediction of the island rule, exhibiting body size reduction, and predator diversity is the main factor influencing body size evolution of these taxa. Results obtained highlighted the crucial role of time in isolation, with body size reduction becoming more pronounced for bovids with longer residence times on the islands.
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Phylogenetic relationships within the tribe Bovini are reconstructed on the basis of morphological and genetic parameters. In the genus Bubalus, the Asiatic buffalo and anoa are closely related to each other. The generic rank of yaks (Poephagus) is substantiated. This genus originated from the same lineage as the genus Bison rather than from the genus Bos, as was thought previously.
Article
The islands of Bocas del Toro, Panama, were sequentially separated from the adjacent mainland by rising sea levels during the past 10,000 years. Three-toed sloths (Bradypus) from five islands are smaller than their mainland counterparts, and the insular populations themselves vary in mean body size. We first examine relationships between body size and physical characteristics of the islands, testing hypotheses regarding optimal body size, evolutionary equilibria, and the presence of dispersal in this system. To do so, we conduct linear regressions of body size onto island area, distance from the mainland, and island age. Second, we retroactively calculate two measures of the evolutionary rate of change in body size (haldanes and darwins) and the standardized linear selection differential, or selection intensity (i). We also test the observed morphological changes against models of evolution by genetic drift. The results indicate that mean body size decreases linearly with island age, explaining up to 97% of the variation among population means. Neither island area nor distance from the mainland is significant in multiple regressions that include island age. Thus, we find no evidence for differential optimal body size among islands, or for dispersal in the system. In contrast, the dependence of body size on island age suggests uniform directional selection for small body size in the insular populations. Although genetic drift cannot be discounted as the cause for this evolution in body size, the probability is small given the consistent direction of evolution (repeated dwarfism). The insular sloths show a sustained rate of evolution similar to those measured ih haldanes over tens of generations, appearing to unite micro- and macroevolutionary time scales. Furthermore, the magnitude and rate of this example of rapid differentiation fall within predictions of theoretical models from population genetics. However, the linearity of the relationship between body size and island age is not predicted, suggesting that either more factors are involved than those considered here, or that theoretical advances are necessary to explain constant evolutionary rates over long time spans in new selective environments.