First specimens of Ancylotherium pentelicum (Mammalia, Chalicotheriidae) from the new excavations at the Late Miocene locality of Pikermi (Attica, Greece)

1. First specimens of Ancylotherium pentelicum (Mammalia, Chalicotheriidae)
from the new excavations at the Late Miocene locality of Pikermi (Attica, Greece).
Giaourtsakis I.1, Sklavounou S.2, Filis P.2, Roussiakis S.2, Theodorou G.2
1 Ludwig-Maximilians-Universität München, Department of Earth and Environmental Sciences,
Section of Paleontology and Geobiology, Richard-Wagner-Str. 10, 80333 München, Germany
2 National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment,
Department of Historical Geology and Palaeontology, Panepistimiopolis, 15784, Athens, Greece
Introduction
The classic reconstruction of Ancylotherium pentelicum from Pikermi by Abel (1920: fig. 12)
The schizotheriine chalicothere Ancylotherium pentelicum (Gaudry & Lartet, 1856) is one
of the most characteristic but rare elements of the Late Miocene mammalian faunas of
the Eastern Mediterranean and adjacent regions. The classic locality of Pikermi, the type
locality of the species, has been extensively explored and studied since the mid-19th
century, revealing a rich and diverse vertebrate fauna of Turolian age. Since 2008, a new
series of stratigraphically and taphonomically controlled excavations has begun at
Pikermi by the National and Kapodistrian University of Athens, under the direction of
Prof. G. Theodorou and under the auspices of the Rafina-Pikermi Municipality, which
have yielded new and prolific fossiliferous sites (Theodorou et al. 2010; Filis et al. 2019).

2. Material
PV1/1963: An incomplete right radius of a subadult individual (Fig. 1). The proximal
epiphysis is partly preserved; most of its posterior half, including the ulnar facets, is
broken. In proximal view, the articular fovea of the radius is divided into two
asymmetrical concavities; the medial concavity is better preserved, most of the lateral
one is missing. There is no prominent radial tuberosity, but a slightly coarse surface for
the attachment of the biceps tendon. The shaft is long and appears quite slender with
respect to the broadened proximal epiphysis. The distal epiphysis is not preserved.
• Radius in dorsal view (1).
• Astragalus in dorsal (2) and distal view (3).
• Phalanx in dorsal (4) and plantar view (5).
PV1/2813: A moderatelly well-preserved left astragalus (Fig. 2, 3). The bone is notably
shortened and broad, with a very short neck. The trochlea is deep and the trochlear
lips asymmetrical, the medial one being more robust. The plantar aspect of the bone is
dominated by a large ectal calcaneal facet, which is notably widened and deeply
concave. It features a small vertical flattened extension on its mediodistal corner. The
sustentacular calcaneal facet is small, flattened, and mostly damaged. The presence or
not of a third, distal calcaneal facet, can not be confirmed, due to surface loss on the
bone. The distal aspect features a large and rather flattened sub-trapezoidal articular
facet for the navicular. A facet for the cuboid seems not to have been present.
PV1/2101: A well preserved proximal (first) phalanx of the pes (Fig. 4, 5). The proximal
aspect features a single articular facet, which articulates with the head of the
corresponding metapodium. The outline of this articular concavity is wide-oval with a
small notch on the middle of its plantar border. The distal aspect features a trochlear-
shaped articular surface for the subsequent phalanx. The size of the specimen (L=84.5
mm) suggests a pedal phalanx (compare also Saraç et al. 2002: Tab. 11).
1
3
2
4 5
10
cm
5 cm

3. Material
PV1/1973: A well-preserved left Mt-3 (Fig. 1, 2). In proximal view, the articular facet
for the ectocuneiform is flattened. The lateral aspect of this facet is incompletely
preserved, so that the presence of a small articular facet for the cuboid cannot be
verified. The presence or not of this small cuboid facet is a variable feature in A.
pentelicum (Giaourtsakis & Koufos 2009). On the medial aspect, the ectocuneiforme
facet tapers gently towards a single low and wide articular stripe for the Mt-2. In
lateral view, a large, but incompletely preserved, articular concavity corresponds to
the articular surface for the Mt-4.
• Mt-3 in proximal (1) and dorsal view (2).
• Mt-4 in proximal (3) and dorsal view (4).
PV1/2000: A complete left Mt-4 that was found in close taphonomical proximity with
the previous one. The proximal aspect (Fig. 3) is dominated by the subcircular articular
surface for the cuboid, which is slightly depressed towards its medioplantar corner.
The lateral and plantar borders of this facet are surrounded by coarse rugosities that
correspond to ligamentous attachments. In medial view, a single, large and notably
bulbous articular facet is present (Fig. 3, 4 indicated by arrows), which articulated with
the corresponding articular concavity on the Mt-3. This feature may have enhanced
the interlocking between these two metatarsals by reducing the abductive and
adductive movements, providing also additional stability to the tarsometatarsal joint.
Morphological and metrical evaluation and comparisons follow previously published
works (Roussiakis & Theodorou 2001; Giaourtsakis & Koufos 2009; Kampouridis et al.
2021 and references therein). The material is currently housed in the local “Exhibition
of Paleontological Treasures of Pikermi” at the Rafina-Pikermi Municipality.
Methods
1
2
3
4
5 cm

4. Results and Discussion
● Ancylotherium pentelicum is a characteristic but notably rare element of the Late Miocene
mammalian faunas of the Sub-Paratethyan (Balkano-Iranian) bioprovince. The fact that in
the new stratigraphically and taphonomically controlled excavations at Pikermi only a few
specimens have been thus far identified, among several thousands prospected, confirms its
rarity. Of particular interest are the two metatarsals, which increase the known hypodigm of
the species (Roussiakis & Theodorou 2001; Kampouridis et al. 2021 and references therein).
● Apart from some minor variable morphological features, the known metapodial elements
of A. pentelicum from various localities exhibit a significant size variation. For instance, the
recorded differences of the maximal length may reach up to 35% within a single element
(Kampouridis et al. 2021). This notable degree of variation has been often interpreted as
indicative for the existence of a significant sexual dimorphism in the species (Kampouridis et
al. 2021), and has been previously reported for other chalicotheriids, as well (Coombs 1975).
The most complete posterior limb assigned to the species is an in-situ subadult pes from the
locality of Kiro Kuchuk (Spassov et al. 2018: Pl. 6, fig. 5). The Mt-4 of this specimen currently
represents the minimum value of the maximal length, whereas the Mt-2 the respective
second largest; the Mt-3 is close to the median of its known range. The comparative
assessment of this specimen thus indicates that the known limits of the intra-specific
variability, as well as the anticipated overlapping between male and female specimens may
require additional material in order to be fully comprehended.
● Another possibility, is that the observed metrical variation may have been also affected by
differential spatiotemporal evolutionary patterns among locally adapted populations of the
species throughout its dispersal in the Eastern Mediterranean and adjacent regions. Such
notable size variation of potentially subspecific value is known to exist among extant
perissodactyl mega-herbivores such as the hook-lipped rhinoceros Diceros bicornis (Groves
1967; Guérin 1980).
Univariate plot of the maximal length (L max) of the
Mt-2, Mt-3, and Mt-4 of Ancylotherium pentelicum
from various localities. Red circles represent the
associated Mt-2,3,4 from Kiro Kuchuk (Spassov et al.
2018). Green circles the presumably associated Mt-
2,3,4 from Pikermi (Gaudry 1862-67). Yellow circles
the presumably associated Mt-3,4 from Pikermi PV1.
Mt-2 Mt-3 Mt-4

5. Acknowledgments
The new fieldwork campaigns at Pikermi
have been supported by the Municipality of
Rafina-Pikermi, several private sponsors, and
the NKUA-Special Account Research Grant
project no. 70/3/12977. Additional financial
support for comparative studies has been
provided to I. Giaourtsakis by the European
Commission’s Research Infrastructure Action
(EU-SYNTHESYS: GB-TAF-574, FR-TAF-1226,
AU-TAF 5710). For facilitating access to
specimens under their care we are indebted
to P. Tassy (MNHN, Paris), J. Hooker (BMNH,
London), and U. Göhlich (NHMW, Vienna).
Conclusions
● Ancylotherium pentelicum is one of the most characteristic but rare elements of the Late Miocene mammalian faunas of the
Eastern Mediterranean and adjacent regions (Sub-Paratethyan bioprovince).
● The known metapodial specimens of A. pentelicum from various localities show a notable range of metrical variation.
● This variation may be indicative of sexual dimorphism, as has been previously discussed and also documented in other
chalicotheriids. Additional material is required to evaluate the limits of intra-specific variability and the potential overlapping.
● In addition, this variation may have been further affected by differential spatiotemporal evolutionary patterns among locally
adapted populations in the Eastern Mediterranean and adjacent regions, within the anticipated boundaries of a single species.
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