Introduction
In this paper are described two bats from Lower Miocene sites in Kenya colony. Incomplete skull of a batis found at Koru in 1931, and subsequently several specimens were obtained from Songhor and Rusinga Island. Detailled accounts of the sites are given by Kent (1944), Le Gros Clark & Leake (1951) and Shackleton )1951).The bats appear to belong to families still living in Africa : Emballonuridae and Megadermidae. Each is represented by a single specimen, from Koru ans Rusinga respectively.
Order Chiroptera
Family
Emballonuridae
Genus
Saccolaimus (Lesson, 1842)
Name
Sacolaimus incognita sp. nov.
Diagnosis
A species of Saccolaimus of fairly large size, a little larger than S. nudiventris (P2-M2 inclusive 8.2mm); differing from S. nudiventris in the less divergent frontal crests, the larger size of P2, and the position of the zygomatic root opposite M2.
Holotype
The left half of a rostrum lacking much of the bone, but showing the interior of the orbit and part of the crowns of P4 and M2. Brit. Mus. Geol. Dept., M.14222. From the Lower Miocene of « Maize Grib », Koru, Kenya colony.
Skull
The part of the skull that is preserved is silghtly larger than S. nudiventris and smaller than S. peli. It agrees fairly closely in proportions with S. nudiventris. In the description that follows it is compared with these two species, and also with S. perforatus, S. mauritanius, Coleura afra and Emballonura atrata: all these recent species are from Africa, except the last, which is a Madagascar form.
The frontal crest makes s smaller angle with the middle line than in recent pecies of Saccolaimus, and the degree of fivergence of the crest must have been about the same as in Emballonura. There is a concavity in the roof of the skull between the orbits, about as deep as in S. nudiventris or Coleura. Behind the concavity the profile rises steeply, but the skull is broken off at the level where the frontal crests unite to form the sagittal crest. The postorbital process is broken off, but its base shows that it was stongly constructed, as in other Emballonuridae.
The nasal has broken away anteriorly, but the natural cat of its inner surfece shows a moderate dorsal inflation of the region medial tot the nasoturbinal attachment. The premaxilla is not preserved, but a facet where it articulated with the maxilla at the side of the external nares is present. The supra-orbital crest is about as strongly developped as in Coleura afra, S. nudiventris and S. perforatus. It appears to have been notched for the lachrymal formaen, as in Saccolaimus and Coleura, whereas in Emballonura the foramen opens on the face. Immediatly below the lachrymal foramen and in front of the crest which marks the edge of the orbit, is the infraorbital foramen, which is situated above P4. In this part of the skull, S. incognita closely resembles the recent species of Saccolaimus : in Emballonura artata the infraorbital foramen is placed farther forward, above the diastema between P2 and P4.
Much of the palate has broken away, but two foramina are visible, one opposite the posterior part of M1, the other opposite the anterior part of M2. In the recent species, one or two foramina may occur on each side, but their exact position is probably subject to individual variation. In the fossil, as in recent species of Saccolaimus, the palate and opposite the posterior end of M2; in Coleura and Emballonura it extends further back, in association with the larger size of M3. The zygomatic root arises opposite M2 in S. incognita; in recent species it is situated farther back, in Saccolaimus, opposite the posterior part of M2 and part of M3, and in Coleura and Emballonura mainly opposite M3.
Inside the orbit may be seen the orbito-nasal foramen (posterior opening of the palatine canal) and the posterior opening of the infraorbital canal. These are situated as in S. nudiventris, the former at the level of the posterior end of M2, and the latter over he posterior end of M1. In the other species of Saccolaimus, as well as in Coleura, the infraorbital canal opens nearer to the anterior and of the orbit, whereas in Emballonura the opening of the palatine canal is situated more posteriorly. A small foramen is situated above the teeth in the floor of the orbit, proably for the alveolar nerve; similar formanina occur in the recent species.
| S. incognita | S. nudiventris | S. peli | |
| Posterior edge of C – posterior edge of M2 | 8.2 mm | 7.3 mm | 8.7 mm |
| Upper border of orbit – mid-line dorsally | 4.7 | 3.6 | 5.6 |
| Postero-buccal apex of M2 – mid-line of palate | 6.7 | 3.6 | 5.6 |
| M2 length | 2.7 | 2.6 | 2.8 |
| M2 posterio width | 3.0 | 3.0 | 3.2 |
| P4 length | 2.1 | 1.9 | 2.1 |
| P1 posterio width | 2.0 | 2.0 | 2.5 |
Teeth
Noting is known of the incisors. The canine is represented only by its broken alveolus. P2 is placed immediately behind the canine. It has a single, oval root, apparently relatively larger than in recent species. The crown is not preserved. The next premolar, P4, is placed immediately behind P2, without any intervening diastema. It is triangular on outline, relatively narrower than in Coleura or Saccolaimus peli, but ressembling Emballonura atrata and the other species of Saccolaimus. The buccal part of the crown is broken away; the part that is preserved shows a postero-lingual basin, the rim of which rises anteriorly to form a lingual cusp (protocone). M1 is missing. From the space left it appears to have been slightly longer than M2. M2 has lost the buccal edge of the crown and part of the posterior-lingual portion, but what remains shows that the pattern of this tooth was of the normal chiropteran type. Both the paracone and the metacone are V-shapped, the metacone being slightly the higher cusp. There is a narrow anterior cingulum, almost obsolete in front of the posterior edge. The narrow posterior cingulum, almost obsolete in front of the paracone, bit widening lingually to form the protocone, which is about half the height of the paracone. The outline of the tooth is quadrate, with a shallow bay in the posterior edge. The narrow posterior cingulum widens out lingually to form a talon, which is dammaged in the specimen, but which probably carried y hyppocone in the form of an antero-posterior ridge, connected with the protocone. M2 thus agrees very closely with that of the existing Emballonuridae. M3 is represented by fragments of root, but, to judge by the limited space available, it was much rduced, and thus resemble Saccolaimus rather than the other genera.
Relationships
The close resemblance in many details to recent Emballonuridae leaves no doubt as to the family to which the specimen should be referred. Altought the postorbital process has broken off, it was evidently well-developped in the manner characteristics of the Emballonuridae.
The recent members of the family found in Africa are referred to the genera Coleura and Saccolaimus, and a third genus, Emballonura, occurs in Madagascar. Both Saccolaimus and Emballonura have wide distribution in the Indo-australian region, but Coleura is confined to Africa. The remaining genera are from tropical America.
The fossil is referred to the genus Saccolaimus for the following reasons :
- it is excluded from Emballonura and Coleura by the small size of M3 and the characters associated with this, e.g. the termination of the palate opoosite the posterior and of M2, and the more forward position of the root of the zygoma;
- it is further excluded from Emballonura by the position of the lachrymal foramen, which opens at the edge of the orbit instead of on the face.
S. incognita differs from recent species of Saccolaimus in the smaller divergence of the frontal crests, he larger size of P2, and the more anterior position of the zygomatic root. It resembles S. nudiventris rather than the other species in the position of the opening of the infraorbital canal into the orbit.
Ref. : Fossils Mammals of Africa : Insectivora and Chiroptera from the Miocene rocks of Kenya colony, PM Butler & AT Hopwod, British Museum (Natural History), London, 1957