Eleutherodon oxfordensis K.A. Kermack, D.M. Kermack, Lees, and Mills, 1998

Butler, Percy M. & Hooker, Jerry J., 2005, New teeth of allotherian mammals from the English Bathonian, including the earliest multituberculates, Acta Palaeontologica Polonica 50 (2), pp. 185-207 : 186-189

publication ID	https://doi.org/ 10.5281/zenodo.13618797
persistent identifier	https://treatment.plazi.org/id/03E187B9-FFD3-0266-FCBF-28D3FCB9F8DE
treatment provided by	Felipe
scientific name	Eleutherodon oxfordensis K.A. Kermack, D.M. Kermack, Lees, and Mills, 1998
status

Treatment

Figs. 1A–C View Fig , 2 View Fig .

pars Eleutherodon oxfordensis sp. nov.; Kermack et al. 1998: 586–595,

figs. 1–14, 15A, 16, 18, 22, 23 [non figs. 15B, 17 = Millsodon superstes sp. nov.; non figs. 19–21 = Hahnotherium antiquum sp. nov.].

Holotype: BMNH M46460 ; right upper molar from the Old Cement Works Quarry , Kirtlington, Oxfordshire, England, bed 3p.

Paratypes (excluding those referred herein to other taxa): BMNH M46185 , BMNH M46459 , BMNH M46585 (bed 3w(iii)), BMNH M46681 , BDUC J 771 View Materials (bed 3w(i)), BMNH M46814 (bed 3u), EF FM K/56, BMNH M46461 , BMNH M46649 (bed 3w(i)) .

Distribution.—Late Bathonian of England.

New material.—From Kirtlington: BMNH M46654, incomplete left lower molar; BMNH M46821, right upper molar (bed 3p(iii)); BMNH M46832, right upper molar; BMNH M46851, left lower molar, rolled (bed 3w(i)). From Watton Cliff: BMNH M34986, left upper molar; BMNH M44985, right upper molar, worn and rolled.

Comment.—The following specimens, described by Kermack et al. (1998) as Eleutherodon oxfordensis have been re−identified in this paper: BMNH M46183, left lower molar of Millsodon gen. nov.; BMNH M46763 and BMNH M46796 are multituberculate molars ( Hahnotherium gen. nov.).

Description

Upper molars ( Figs. 1A, B View Fig , 2A–D View Fig ): These show the characteristic Eleutherodon pattern, as described by Kermack et al. (1998). The largest cusp (A of Kermack et al. 1998, B1 of Butler 2000, the terminology used herein) is at the narrow end of the tooth, presumed to be distal by analogy with Haramiyavia and Thomasia . Mesial to this there are three longitudinal rows of numerous minor cusps. The buccal row is at the top of a ridge that forms the buccal wall of the main longitudinal groove. The central row, which forms the lingual side of the groove, connects cusp B1 to a moderately high cusp Bx on the mesial border. The lingual row follows the lingual margin, from cusp B1 to an enlarged cusp BB (B of Kermack et al. 1998), at the mesiolingual corner of the crown. The groove between the central and lingual rows is much shallower than the main groove. Both grooves are richly ornamented by minor transverse ridges or flutings.

The four additional specimens illustrate the variability of the upper molars, evident from the eight examples figured by Kermack et al. (1998). BMNH M46821 ( Figs. 1B View Fig , 2B View Fig ) is a large tooth (3.0 × 2.2 mm), resembling BMNH M 46585 in size, but longer and narrower, and with the large distal cusp B1 projecting for a greater distance beyond the end of the buccal cusp row. It is moderately worn. BMNH M46832 ( Figs. 1A View Fig , 2A View Fig ) is of intermediate size (2.45 × 1.8 mm), longer and proportionately narrower than the holotype . It is also moderately worn. The two specimens from Watton have lost the minor cusps on the ridges and the basin fluting by rolling. BMNH M34986 (2.3 × 1.8 mm) is a little longer and narrower than the holotype . BMNH M44985 (2.7 × 1.9 mm) is a poorly preserved tooth in which much of the lingual cusp row, including cusp BB, has been removed .

The twelve specimens now known range in length from 2.1 to 3.0 mm (mean 2.46); the width/length ratio in eleven specimens ranges from 0.67 to 0.93. How much of this variation is due to position in the dentition is unknown. Seven teeth, ranging in length 2.4–2.9 mm and in width 1.6–2.3 mm might represent one molar, and four shorter and proportionately broader teeth (including the holotype), with length 2.1–2.25 mm and width 1.6–1.95 mm, might represent another molar. In any case, there is no indication that the difference in occlusal relations between M1 and M2 that characterises the multituberculates exists in Eleutherodon .

Roots are preserved in BMNH M46821 and BMNH M46832 ( Fig. 2 View Fig ), which can be compared with those of BMNH M46771, BMNH M46814, and EF FM K/56, figured by Kermack et al. (1998). In all these the basal portion of the root forms an undivided root−trunk, with a height greater than that of the crown. The more apical portion is divided into a number of root elements, which remain connected to various levels, but appear as ribs on a longitudinal flange. In BMNH M46832 four elements can be distinguished: a distal root (I) below the large cusp B1, a mid−buccal ( II) and a mesial buccal ( III) root supporting the buccal cusp row, and a mesial lingual root ( IV), below cusp BB. Root I is the first to separate; II and III remain joined for most of their length, and III and IV are united to the tip. Corresponding root elements can be recognised in the other specimens. In BMNH M46821 the distal root (I), the largest, diverges from the rest and there is an additional root (Ia) on its mesial side. There is another additional root (IIa) on the lingual side between Ia and IV. In the remaining specimens root I is vertical and the additional roots are absent. In EF FM K/56 the roots are united for the whole of their length, and root IV appears to be absent. The root pattern of Eleutherodon molars differs widely from that of multituberculates, which normally have two equal and separate roots, except in some Late Cretaceous forms. It also differs from the tooth described by Freeman (1976), which has a single root at one end and a pair of divergent roots at the other; this is interpreted in the present paper as possibly an upper molar of Hahnotherium new genus.

Lower molars.— BMNH M46851 and BMNH M46654 are incompletely preserved, but so far as they can be compared they agree with the β type tooth BMNH M46649 ( Kermack et al. 1998: fig. 18). BMNH M46851 ( Figs. 1C View Fig , 2F View Fig ), a left tooth, has lost all enamel except in the basin, where the fluting is preserved, showing that the tooth was lightly worn. It is oval in outline, more convex buccally than lingually, and with a mesial prominence towards the buccal side; it measures 2.2 × 1.55 mm. The highest cusp, b2 (α of Kermack et al. 1998), on the mesial prominence, is preserved only in dentine. It is followed distally by the buccal ridge, on which there appear to have been six cusps, to judge from the broken margin of the enamel. One of these, midway along the tooth, appears to have been elevated, as in BMNH M46649. The mesial lingual cusp, a1 (β of Kermack et al. 1998), which also lacks enamel, is smaller than the mesial buccal cusp, and slightly more distal. About six more lingual cusps are represented by minor elevations of the dentine. The lingual and buccal cusp rows are continuous round the distal end of the basin.

BMNH M46654 ( Fig. 2G View Fig ) is a left tooth that has lost the mesial half of the lingual cusp row, together with enamel on the mesial surface of cusp b2. The flutings in the basin have been completely removed by wear and the marginal cusps are represented by areas of exposed dentine. Wear seems to have been particularly heavy on the mesial half of the buccal cusp row, which declines from cusp b2 to a minimum height near the middle of its length. There is evidence of seven buccal cusps. The series is continuous round the distal end of the tooth with the lingual series, of which only the last cusps are represented. The central groove is basined, reaching its greatest depth about halfway along the tooth, and it does not cut through the distal cusp row. The tooth as preserved measures 2.25 × 1.4 mm.

BMNH M46461, described by Kermack et al. (1998: figs. 15A, 16), differs from the other β type teeth in that the cusps are more numerous, and those of the buccal row are more equal in size. The difference is probably due to position in the dentition.

“ Haramiyida ” family indeterminate

Genus Millsodon nov.

Type species: Millsodon superstes sp. nov.

Derivation of name: In memory of the late Professor J. R. E. Mills, whose orthodontic expertise has much aided the functional interpretation of Mesozoic mammalian teeth.Also Greek, οδους, οδοντος, tooth. Masculine.

Diagnosis.—Lower molariforms (provisionally identified as m1 and m3) differ from Thomasia and Staffia in the larger mesiolingual cusp (a1), of which the height is greater than half the length of the tooth. Mesiobuccal cusp absent on m1, rudimentary on m3. Resembles Staffia and differs from Thomasia in that cusp a1 is blunt and curved distally. Differs from Staffia in the absence of deep synclines between the cusps.

Referred upper molar has an enlarged distobuccal cusp, an inclined basin on its mesial side, and a third (lingual) cusp row.