The only complete articulated early Miocene chameleon skull (Rusinga Island, Kenya) suggests an African origin for Madagascar’s endemic chameleons

We here present the first detailed study of the specimen KNM-RU 18340 from Rusinga Island (Kenya), the only known complete early Miocene chameleon skull, using micro-CT. This specimen represents one of the oldest chameleon fossils ever recovered. For the first time, the skull bone internal surfaces, their sutures, and elements contained inside the rocky matrix are observed. Our morphological comparisons and phylogenetic analyses place this specimen confidently in the genus Calumma and a new species, Calumma benovskyi sp. nov., is erected for it. Since all species of this genus are endemic to Madagascar, this fossil uniquely demonstrates the existence of Calumma on continental Africa in the past. Our results challenge the long-held view that chameleons originated on Madagascar and dispersed over water to Africa, and provide a strong evidence of an African origin for some Malagasy lineages. The Oligocene–early Miocene dispersal to Madagascar, using oceanic currents that favoured eastward dispersal at that time, is a highly supported scenario matching the suggested dispersal of lemurs to this island. This is consistent with a previously suggested hypothesis based on molecular data.

tooth (counted from posterior) , where it merges gradually with the bone. An essentially straight supradental shelf supports a single row of 15 teeth. Tricuspidity starts from the 9th tooth (counted from anterior). On the dorsal surface, the posterior portion of the posteroventral process of the maxilla bears a concave and deep articulation area for the jugal.
The internal wall of this articulation is higher than the external one in this posterior region.
Nasals. The nasals are paired, and both are preserved. They are flat and elongated elements, but small relative to the overall size of the skull (Supplementary Fig. 2a-d). The right and left nasals have no mutual medial contact as they are separated by a strut of bone formed by the contact of the premaxilla with the anteromedian process of the frontal. The anterior portion of the nasal bears the facet for the maxilla anterodorsally, and it is overlapped by the frontal in the posterior region. Thus, only mid-portion of the nasal is exposed externally. This region partly forms the lateral margin of the prefrontal fenestra. Virtually isolated right jugal in g lateral; and h medial views.
Jugal. The jugals are preserved on both sides, but the right one is in better condition. This element is crescent-shaped and can be divided into two processes: a suborbital process and a postorbital process ( Supplementary Fig. 2g-h). They form the posteroventral and posterior margins of the orbit. The jugal exhibits facets for the maxilla, postorbitofrontal and ectopterygoid. The postorbital process is slightly wider than the suborbital process, although it gradually tapers dorsally. This process bears a sculpture along its external mid-region. It consists of several protuberances arranged in a single line and more strongly developed in the dorsal region. These protuberances more-or-less decrease in size ventrally. The internal surface of the postorbital process bears a large facet for the postorbitofrontal, which becomes narrower ventrally and slightly disappears. The suborbital process of the jugal is longer than the postorbital one, protruding anteriorly into a very narrow process. Its external surface is largely covered by the maxilla, such that only the dorsalmost portion of the suborbital process is exposed at its lateral aspect. At the internal aspect, the jugal possesses a well developed medial ridge of the type 3 (sensu Čerňanský et al. 21 ). Since the ventral portion of the jugal is wedged in the maxilla, an articulation surface with the latter is present on this side as well.
Dorsally to it, the articulation with the ectopterygoid is present. It approximately mirrors the course of the medial ridge.
Frontals. The frontals are fused to a single element. It is large, forming the dominant element of the skull roof. It is excluded from the orbit by the contact of the prefrontal and postorbitofrontal. The frontals are elongated and relatively broad, widening posteriorly to form the wedge-shaped posterolateral corners ( Supplementary Fig. 3). At the level of these triangular posterolateral processes, the bone is pierced in its central region by a small, anteroposteriorly elongated foramen. Anteriorly to this region, the element only slightly narrows. However, the anterior-most portion of the bone is markedly extended into a thin but distinct anteromedian process. The central region is somewhat depressed, whereas the lateral margins of the frontal are slightly inclined dorsally. A well-developed ornamentation is formed by protuberances. They are moderately spaced and rather regularly distributed, covering the otherwise smooth external surface. Toward the posterior margin of the bone, the protuberances become gradually bigger and anteroposteriorly elongated. In the anterior half of the bone, they are less distinct.
The internal surface of the fused frontals bears two distinct frontal cranial crests, being strongly developed especially at the posterior half of the bone. Here, they are sharp, running posterolaterally toward the lateral end of the posterolateral processes. Medially and posteromedially to this region, a large wedge-shaped facet for the parietal tab is located at both sides. These facets are associated with the posteriorly slightly expanded central portion of the frontal. This portion overlaps the anterior region of the parietal. In the anterior region, the crests converge close to each other, running almost parallel anteriorly. In this region, they are, however, less defined. A very shallow groove (or longitudinal depression) can be found between them. The bony portions lateral to these crests are flat. In the anterior region, two ovoid and moderate sized facets for the nasals are located. They are separated by a strong central ridge, which extends the anteromedian process of the frontal.
Parietal. The parietal is an anteroposteriorly elongated element, that is constricted in its midlength. This gives the entire parietal an hourglass shape, but with the anterior portion being wider than the posterior one ( Supplementary Fig. 4). The main sculpture of the dorsal surface of the parietal is formed by protuberances arranged in three lines -the central one and two laterally located ones (although only the right branch is completely preserved). At the level of

Quadrate and palate region
The palatal region is preserved, although somewhat damaged ( Supplementary Fig. 7). There is no dentition present on the palate.

Quadrate.
A more-or-less complete quadrate is available on the right side ( Supplementary   Fig. 6e-h), whereas only the dorsal portion of the left quadrate is preserved ( Supplementary   Fig. 6i, j). In lateral view, the quadrate is dorsoventrally elongated and quite narrow. It gradually widens dorsally. The dorsal portion forms a cephalic condyle, which is divided into two parts. The lateral protuberance is lower, whereas the medial protuberance is higher and medially inclined. The concave area between the two protuberances forms the contact with the squamosal and the supratemporal. The ventral portion of the quadrate gradually tapers (both in lateral and medial views). The straight tympanic crest runs laterally along the entire central region of the quadrate. The quadrate is wide in posterior aspect and this side possesses a centrally located shallow depression. The mandibular condyle is mediolaterally wide and appears to be rather concave (best seen in posterior and anterior views).

Vomer:
The vomers lie in the anteromedian portion of the palate (Supplementary Fig. 7). process, mainly exposed in the ventral region. Posterior to its contact with the ectopterygoid, the pterygoid forms a large, but thin, ossified pterygoid wing. It is posteroventrally expanded, being heart-shaped in lateral view. Its anteromediodorsal region possesses an articulation with the basipterygoid processs. There is no contact with the quadrate.

Braincase
The stapes is preserved only on the right side ( Supplementary Fig. 8), but the braincase is almost completely preserved ( Supplementary Fig. 9). Stapes. Only the right stapes is preserved (Supplementary Fig. 8). It is a small, laterally elongated, straight and needle like element. Its medial portion is located in the oval window of the braincase (fenestra ovalis, Supplementary Fig. 9a) and forms the foot-plate. It is a rounded and knob-like structure. From the foot-plate, the bone becomes thinner laterally, but is again slightly thicker in its mid-portion, until the lateral termination tapers into a point. There is no stapedial foramen.
Supraoccipital. The unpaired supraoccipital forms the dorsal portion of the braincase, the dorsal part of the inner ear capsule, and the dorsal margin of the foramen magnum ( Supplementary Fig. 9a-c, e, f). It has a high ascending process with which the ventral crest of the parietal articulates. In dorsal view, the ascending process is broadest and more robust in Otooccipital. The otooccipitals are the units formed by co-ossification of the opisthotics and exoccipitals (Supplementary Fig. 9f). The fusion area is marked by the vagus foramen ( Supplementary Fig. 9b). Immediately next to it is a small foramen for the hypoglosal nerve ( Supplementary Fig. 9h) Fig. 9D, F). The overall shape is roughly rhomboidal in ventral view. Its posterior portion forms the ventral 1/3 of the occipital condyle. The occipital condyle itself, when including the two otooccipital parts, is heart shaped and its maximum width equals its maximum height. In dorsal view, the condyle has anteriorly concave margin. The basal tubercles of basioccipital are ventrolaterally oriented and short.
Sphenoid. Anterior to the basioccipital, the sphenoid is present and the suture between these two bones is still well-visible ( Supplementary Fig. 9D). The suture is not straight, but resembles the letter M. The sphenoid is a midline unpaired element, forming the anteroventral portion of the osseous braincase and the connection between the palate and the braincase. The contacts with pterygoids consist in the large, robust anterolaterally oriented basipterygoid processes. Anteriorly, the mid-portion of the sphenoid protrudes into a short, but distinct parasphenoid process. In ventral view, the central region of the sphenoid bears a deep and rounded fossa. Laterally, close to the root portion of basipterygoid process, the bone is pierced by the posterior opening of the Vidian canal ( Supplementary Fig. 9e, g). Anteriorly, this canal opens lateral to the base of the parasphenoid process. The anterior foramen for the abducens nerve is located directly above the anterior opening of the Vidian canal. A pair of the internal carotid foramina are located centrally, dorsal to the base of parasphenoid process. A sharp crista sellaris is found dorsal to these foramina and runs between the well-developed alar processes. Medially to the alar process, the dorsal surface is pierced by the posterior foramen for the abducens nerve.

Mandible
Dentary. The dentary is elongate, forming the dominant component of the mandible (in lateral view, it is four times longer than the postdentary portion of the mandible; Supplementary Fig. 10). The dentary is slightly convex laterally at its dorsal aspect and mediolaterally compressed. In lateral view, the height of the dentary gradually increases posteriorly. The straight subdental shelf bears 13 teeth. Ventrally to it, the dental groove is present, being shallow rather than deep. The ventral portion of the dentary in medial view bears a deep Meckel's groove for Meckel's cartilage. It is roofed by a well developed straight supra-alveolar ridge and floored by a slightly thickened ventral margin of the dentary.
Meckel's groove gradually narrows anteriorly and turns ventrally at the level of the 6th tooth (counted from anterior). The alveolar foramen is located at the level of the penultimate tooth.
The symphysis is well developed, but narrow. The posterior region of the dentary forms two In lateral view, however, only a short portion of the angular is exposed.

Surangular.
Only the right surangular is more-or-less completely preserved. The surangular is a short, but massive element forming the posterodorsal portion of the mandible. It is roughly rectangular in cross-section. At the posterior end, the bone is slightly elevated dorsally and forms the anterior border of the glenoid fossa.

Hyoid
Ceratohyal. The long, rod-like element visible on the left side is interpreted here as a ceratohyal ( Supplementary Fig. 11). The element is straight in anterior and posterior aspect, and very slightly narrows ventrally. In lateral view, it is however slightly bent, convex anteriorly.

Postrcanial
Atlas. The atlas of chamaeleonids is composed of three parts that are united: the two halves of the atlantal neural arch and the ventrally located first intercentrum ( Supplementary Fig. 12).
However, the intercentrum is not preserved here. The neural arch consists of paired pedicles and paired laminae. The laminae are straight in anterior view, forming a triangular structure.
In lateral view, they are anteriorly inclined, wide, but short relative to the height of the neural  spine is slightly extended and projects more anteriorly, whereas the posterior 2/3 of the dorsal margin is less rounded. In dorsal view, the neural spine has robust appearance, being slightly constricted in its mid-region. The prezygapophyseal articular facets are rather small. They are elliptical, slightly prolonged anteroposteriorly and inclined ventrolaterally (around 30° from the horizontal plane). The postzygapophyses are laterally expanded and slightly inclined posteriorly. They possess oval articular surfaces. The neural canal is medium-sized, almost pentagonal in shape. Its height is approximately 22% of the entire vertebra. The synapophyses are absent. The odontoid process, which is formed by an atlantal pleurocentrum, is incompletely fused in this specimen.The process is anteriorly directed and protrudes visibly. It fits into the atlantal ring anteriorly. The condyle is large, almost rounded. The anteriorly located ventral margin of the centrum is concave in its lateral aspect. In anterior direction, it gradually declines ventrally. In ventral view, the lateral margins of the body are slightly concave. A pair of small foramina is located in mid-region of the centrum. The intercentrum is large. It is triangular and is fused tothe centrum with traces of this fusion still visible. The intercentrum is oriented ventrally.
Third cervical vertebra. The vertebra is high relative to its length ( Supplementary Fig. 13).
The neural spine is smaller and exhibits a different morphology in comparison to that of the axis. The neural spine starts to rise gradually dorsally, being narrower and posteriorly inclined. It is tall and roughly rhomboidal in shape. In dorsal view, the neural spine is thin -its thickness is largest at its mid-region. However, its dorsal margin is damaged. The