Supplementary Information
S1. Description of the individual bone modelling patterns
Bone modelling patterns
Figures 3 and 4 show the individual bone modelling patterns of the facial skeleton and the
mandible of the Pan troglodytes and Gorilla gorilla specimens. These maps show a high
preservation of the bone histological features and reflect that each bone modelling map is a
mosaic of growth fields with a variable size and shape and a particular distribution indicating
intraspecific variability. In order to provide a detailed description of these patterns, we first
explain the results obtained from the facial skeleton and mandible of chimpanzees and gorillas.
Last, we have described the general modelling pattern for each age group (Figures 5 and 6).
Pan troglodytes – facial skeleton
Histological data from both age groups indicate that the facial skeleton of the
chimpanzee is typically depository, while resorption activity occurs as small fields that differ in
location among specimens. Three subadults (48-439, 39-949 and 1939-1001) and two adults
(1939-3386 and 1939-3362) show resorbing surfaces on the posterior region of the maxillary
complex close to the zygomatic apophysis. Few of these specimens also present resorption
activity on the zygomaticomaxillary suture (1939-3374, 1939-998 and 1939-3362) and on the
zygomatic arch (1939-3374).
Pan troglodytes – subadult mandible
The chimpanzee mandibles show more variability in the distribution of modelling fields
than the facial skeleton and each age group show a particular bone modelling pattern which we
describe separately. In the symphyseal region, the buccal side shows bone formation fields but
displays bone resorption activity on the inferior border of the symphysis (39-949) or in the
alveolar region (48-439). Histological data recorded from the lingual side indicate a mainly
depository surface with bone resorption fields in the sublingual fovea (1939-1002).
The mandibular corpus shows a better preservation of the bone modelling fields on the
lingual side than on the buccal side. In subadult specimens, the buccal side shows bone
forming surfaces on the anterior region of the corpus (from the canine to the mandibular
foramen), whereas on the posterior region (from the mandibular foramen to the ramus) bone
resorption fields are located on the inferior border of the corpus and close to the anterior border
of the ramus. The lingual side is predominantly depository but in four subadult specimens (48439, 1939-1001, 1939-3374 and 1939-998) there are bone resorbing fields of variable size in
the region extended from the first molar to the mandibular ramus. In that posterior region, bone
resorption is observed on the alveolar component at the level of the first/second molars (19391001, 39-949 and 1939-3374) and in the submandibular fossa at the level of the premolars
(1939-1001), at the level of the second molar (48-439) or resorbing fields in the area from the
first molar to the mandibular ramus (1939-3374 and 1939-998).
The mandibular ramus shows differences in the modelling patterns between the buccal
and lingual side. On the buccal side, all subadult specimens show bone depository fields
distributed on the inferior half of the ramus except in the specimen 1939-1002 which shows no
histological data because the mandibular bone surface is highly altered. The specimens 19391001 and 1939-3374 also show depository fields on the mandibular notch and on the condylar
neck and the specimens 1939-998 and 1939-1001 close to the anterior border of the coronoid.
Bone resorption surfaces are mainly located on the upper half of the ramus from the anterior to
the posterior border but a resorptive field extends to the inferior half close to the posterior
border (48-439), a small field is observed on the gonial region (1939-3374), and two fields are
located on the central region of the ramus and close to the inferior border (1939-1001). The
bone surface of the lingual side is altered in two specimens, 48-439 and 1939-1002, whereas in
specimen 39-949 shows no histological data on this side of the ramus. The lingual side displays
predominantly bone formation activity in all specimens. Bone resorption activity is located on the
posterior region of the ramus from the mandibular foramen to the posterior border (1939-3374,
1939-998, and 1939-1001) and extends toward the condylar neck (1939-3374, 1939-998, and
1939-1001) and the gonial region (1939-10021939-998, and 1939-1001). Resorbing surfaces
are also observed on the corpus-ramus contact area (1939-1001 and 1939-998).
Pan troglodytes – adult mandible
The symphyseal region shows a similar pattern to that observed in subadults
chimpanzees which is characterized by depository surfaces both on the buccal and on the
lingual sides. Additionally, adult specimens display on the buccal side fields of bone resorption
activity on the inferior border of the symphysis (1939-3379), whereas on the lingual side bone
resorption fields are restricted to the sublingual fovea (adults: 1939-3367, 1939-3379, 19393386).
Like in subadult specimens, the lingual side of the mandibular corpus in adults shows a
better preservation than the buccal side, whereas the specimen 23-3-1-1 shows no histological
features. The specimens 1939-3367, 1939-3379, 1939-3386 and 1939-3362 show depository
surfaces on the alveolar component but the specimen 1939-3379 also displays a large
resorptive field at the level of the molars. The basal component shows bone formation fields
from the mental foramen to the corpus-ramus contact area (1939-3367 and 1939-3379) and
close to the inferior border of the corpus (1939-3386). The specimen 1939-3379 displays a
large resorptive field parallel to the inferior border and extending from the symphyseal region to
the corpus-ramus contact area. The lingual side of the corpus is mainly depository. Compared
to subadult specimens, adults show small resorption fields which are reduced to the alveolar
component at the level of the first premolar (1939-3367) and at the level of the second premolar
(1939-3379), in the sublingual fossa at the level of the first molar (1939-3362) and the second
molar (1939-3379), and in the submandibular fossa at the level of the first molar (23-3-1-1) and
at the level of the second molar (1939-3379).
In the ramus of adult chimpanzees, all specimens preserve bone modelling fields in the
buccal side except the specimen 23-3-1-1, which shows the bone surface totally altered.
Specimens 1939-3367, 1939-3379 and 1939-3362 are characterized by bone resorbing
surfaces, whereas in the specimen 1939-3386 the ramus is mainly depository. Resorption fields
are identified in the coronoid area (1939-3367, 1939-3362 and 1939-3379), the mandibular
notch and condylar neck area (1939-3367, 1939-3362, 1939-3379, and 1939-3386), on the
central region of the ramus (1939-3367, 1939-3362, 1939-3379, and 1939-3386), in the gonial
area and on the inferior border close to the corpus-ramus contact area (1939-3379 and 19393386). As we commented before, the specimen 1939-3386 shows predominantly depository
surfaces, which are located in the coronoid area, the mandibular notch and the neck of the
condyle, some small fields are close to the posterior border and in the gonial area, and in the
corpus-ramus contact area. The lingual side is well-preserved in all specimens and show mainly
depository surfaces. Bone resorbing fields are observed on the endocoronoid crest on the
coronoid process and close to the third molar region (1939-3386), in the mandibular notch area
(1939-3386), on the condylar neck (1939-3367, 1939-3379 and 1939-3386), close to the
posterior border (1929-3379, 1939-3386 and 1939-3362), and in the gonial region (23-3-1-1,
1939-3367, 1939-3379, 1939-3386 and 1939-3362). In the specimen 1939-3379 resorbing
fields are also observed in the gonial area extending to the corpus-ramus contact area and in
the area close to the mandibular foramen.
Gorilla gorilla – facial skeleton
The facial skeleton of the subadult and adult gorillas show a similar bone modelling
pattern characterized by depository surfaces. In both age groups, resorbing surfaces are
identified on the zygomaticomaxillary suture area (subadults: 1864-12-1-3 and 1939-937;
adults: 1951-9-27-13 and 1948-3-3-2) and in the posterior region of the maxillary complex
(subadult: 61-7-29-8, 1939-961, 1939-937 and 61-7-29-4; adult: 1951-9-27-13, 48-435 and
1948-3-3-2). Subadult specimens also displays bone resorption activity in the alveolar
component at the level of premolar/molar (61-7-29-8, 1864-12-1-3 and 1939-961), on the
temporal-zygomatic suture area, and in the anterior region of the nasomaxillary complex (185711-2-2). In adult gorillas, it is noteworthy the presence of resorbing surfaces in the area beneath
the facial foramen (1939-934 and 1949-3-3-2), an extension of the resorbing surfaces from the
zygomaticomaxillary suture and facial foramen to the alveolar component at the premolar and
molar level (1948-3-3-2), and small resorbing fields in the alveolar component of the canine
(1939-934, 1951-9-27-13 and 1948-3-3-2).
Gorilla gorilla – subadult mandible
Like in chimpanzee, the bone modelling patterns of the gorilla’s mandible show more
variability than the facial skeleton. Additionally, the modelling pattern differs between subadult
and adult specimens as we describe below. In the subadult group, the symphyseal region
displays bone depository surfaces both on the buccal and lingual sides (61-7-29-8, 1864-12-1-3,
1939-961, 1939-937 and 61-7-29-4). The specimen 1857-11-2-2 shows the mandibular region
completely altered and the only bone modelling preserved is a field of bone resorption activity
on the lingual side of the alveolar component on the specimen. The mandibular corpus is also
characterized by bone depository surfaces on the buccal and lingual sides. Bone resorbing
fields are observed in the alveolar component of the buccal side at the level of the canine and
premolar (1864-12-1-3 and 1939-961) whereas on the lingual side resorbing fields are located
at the level of the premolar/molar area (1864-12-1-3, 1939-937 and 61-7-29-4).
As observed in the symphyseal region and in the mandibular corpus, the mandibular
ramus is predominately depository. On the buccal side of this region, we have observed two
patterns, one displays bone resorption fields on the condylar neck and bone formation fields in
the coronoid area (61-7-29-8, 1864-12-1-3) and another contrary pattern with bone formation
fields on the condylar neck but bone resorbing surfaces in the coronoid area (1939-937 and
1857-11-2-2). The specimen 61-7-29-4 shows a small resorbing field in the mandibular notch
area, whereas the specimen 1939-961 displays a resorbing surface close to the gonial area.
The lingual side is depository with bone resorption activity on the condylar neck (61-7-29-8,
1864-12-1-3, 1939-961, 1939-937 and 61-7-29-4), in the mandibular notch area (1864-12-1-3,
1939-937, 61-7-29-4 and 1857-11-2-2), in the gonial area (1864-12-1-3, 1864-12-1-3, 1939-961,
1939-937, 61-7-29-4 and 1857-11-2-2), close to the mandibular foramen (1864-12-1-3, 186412-1-3, and 1857-11-2-2), and in the corpus-ramus contact area (61-7-29-4, 1864-12-1-3 and
61-7-29-4). The specimen 1857-11-2-2 also shows a resorption field in the endocoronoid area
close to the anterior border of the ramus.
Gorilla gorilla – adult mandible
In the symphyseal region, the buccal side is mainly depository but two specimens show
bone resorption activity. The specimens 1939-934 and 1948-3-3-2 display a small resorbing
field in the alveolar component at the level of the canine, whereas in the specimen 1948-3-3-2
this activity is also observed in the inferior region of the basal component of the symphyseal
region. On the lingual side, three specimens preserve bone modelling fields (1939-922, 1939934 and 1948-3-3-2). In this group, the specimens 1939-922 and 1948-3-3-2 show bone
resorption fields in the alveolar component and in the upper area of the basal component of the
lingual side, whereas the inferior area of the basal component shows bone formation fields. The
specimen 1939-934 shows depository surfaces in the alveolar component and in the upper area
of the basal component and no resorbing fields are identified on this side of the symphyseal
region. On the mandibular corpus, the lingual surface shows a better preservation of the
histological features than the buccal surface. In general, adult gorillas display fields of bone
deposition throughout the buccal side of the corpus with resorbing surfaces in the alveolar
component at the level of the canine and second molar region (1951-9-27-13 and 1948-3-3-2).
The specimen 1948-3-3-2 also shows bone resorption activity in the region between the mental
foramen and the inferior border at the level of the canine and premolar region, and on the
corpus-ramus contact area. The lingual side is predominantly depository with resorbing surfaces
in the alveolar component (1939-922 and 1951-9-27-13), which extends to the sublingual
fossae at the level of the molar region (1939-934 and 1948-3-3-2). Small resorbing fields are
also observed in the submandibular fossa (1939-922 and 1948-3-3-2) and on the corpus-ramus
contact area (1948-3-3-2). The buccal side of the mandibular ramus mainly shows depository
surfaces. Fields of bone resorption are observed in the coronoid area (1939-934, 48-435 and
1949-3-3-2) and parallel to the anterior border of the ramus in the specimen 1949-3-3-2. This
modelling activity is also located on the mandibular notch, close to the posterior border, in the
gonial area and on the corpus-ramus contact area (1939-934 and 1949-3-3-2). The specimen
1939-934 shows small resorbing fields in the condylar neck area. The lingual side of the ramus
shows a high variability in the distribution of the modelling fields among specimens. The
resorbing surfaces are observed in the area between the anterior border and the endocoronoid
crest (1939-934, 1951-9-27-13, 48-435 and 1948-3-3-2) but bone deposition activity is also
observed on the tip of the coronoid (1939-922, 1951-9-27-13 and 1948-3-3-2) and on the base
of this area (1949-3-3-2). The area posterior to the endocoronoid crest is depository in 1951-927-13 and 1948-3-3-2 specimens, whereas in 48-435 this area shows mainly resorption fields.
The mandibular notch shows both deposition and resorption fields (1939-934, 1951-9-27-13,
48-435 and 1948-3-3-2), whereas the anterior area of the condylar neck displays predominantly
resorbing surfaces (1939-934, 1951-9-27-13 and 1948-3-3-2). The posterior region of the ramus
and the gonial area are mainly resorptive (1951-9-27-13 and 1948-3-3-2) whereas in the
specimen 1939-922 these areas display bone formation surfaces. The area extending from the
mandibular foramen to the corpus-ramus contact area shows depository surfaces (1939-922,
1939-934, 1951-9-27-13 and 1948-3-3-2) but fields of resorption activity are also observed in
the specimen 1948-3-3-2.