Kermackodon multicuspis, Butler & Hooker, 2005

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 : 195-199

Kermackodon multicuspis sp. nov.

Figs. 6A–C , 7A , 8A , 9 .

Holotype: BMNH M46822 , a left upper molar (M2) from the Old Cement Works Quarry, Kirtlington, bed 3p(iii)).

Referred specimens: (a) BMNH M46684, a left lower last premolar (p4), from the Old Cement Works Quarry, Kirtlington. (b) BMNH M46640, an incomplete right upper premolar, not the last (P3 or P4); from the Old Cement Works Quarry, Kirtlington, bed 3w(i).

Derivation of name: From Latin multus, many and cuspis, sharp point.

Distribution.—Late Bathonian of England.

Diagnosis.—As for the genus.

Description of upper molar ( Figs. 6A , 7A ).—BMNH M46822 is heart−shaped in crown view, almost as wide as long (2.85 × 2.6 mm), buccally and lingually convex, mesially transverse with a slight embayment, and pointed distally. The distal point is probably artificially sharpened by breakage of the distal end of the lingual margin. There are buccal and lingual rows of cusps on either side of a longitudinal valley. The cusp rows are somewhat curved, especially the lingual row, and they converge towards the distal end. The cusps are pointed, with enamel ridges on their slopes, and those of each row are joined by a longitudinal crest.

There are five buccal cusps, of which the most distal (B5) is the highest as preserved, B4 is somewhat lower but worn or damaged at the tip, and B3–B1 are smaller elevations on the mesial crest of B4. B5 is pyramidal, with a mesial ridge to B4 and a strong mesiolingual ridge running obliquely into the valley. Buccally to B4–B1 the margin of the crown is swollen to form a smoothly rounded shelf at cingulum level without enamel ornamentation.

There are seven lingual cusps, forming a series that follows the curvature of the lingual margin. They diminish in size mesially from a maximum at L6. L6 is less high than B5. L7 is smaller than L6 and placed nearer to the midline, on the distal prominence of the outline and partly blocking the central valley. At its mesial end the lingual row is continuous with a transverse marginal ridge, which joins the end of the buccal row. Each lingual cusp bears, in addition to the longitudinal connecting ridge, a ridge on its buccal (valley) side, best developed on L6. A mesiobuccal ridge on L5 descends obliquely down the buccal surface of L4 and L3, where it gives rise to a series of three small cusps. Both sides of the mesial part of the central valley are ornamented by numerous enamel cuspules, irregularly arranged. On the lingual margin below L3–L5 is a series of three small cingulum cusps, of which the first and third are connected by ridges to L3 and L4 respectively. Below L6 and L7 the lingual margin is broken. This may have happened in life as the exposed enamel is smoothed.

A striking feature of the central valley is the longitudinal wear groove, which runs horizontally along most of the length of the tooth, but does not cross the margins. It begins mesially in a shallowly basined area distal to the transverse ridge, and ends at the mesial side of L7. The groove is narrow and clearly marked, as if produced by the tip of a sharp cusp. On the lingual side of the valley there is wear on the buccal ridges of L5 and L6, and on the supplementary cusps below L3 and L4. No wear could be detected on the lingual side of the lingual cusps. On the buccal side of the valley, there is some wear on the mesiolingual crest of B5, and small facets near the tips of B4, B3 and B2, inclined lingually. The tips of the highest cusps, L6, L5, B5, and B4, have been removed, perhaps by abrasion. The buccal surface of the buccal cusps, and the buccal shelf, appear to be unworn. If the occlusal relation between the second molars was that typical of multituberculates, the opposing m2 must have had a high lingual cusp row, but the buccal row was probably poorly developed.

The roots have been broken off close to the crown, and the pulp cavity is fully exposed. A bay in the mesial margin of the root base indicates that the mesial root was grooved and perhaps divided.

Comparison.—The Kermackodon molar is in the length range of upper molars of Eleutherodon and much larger than the molars of the Late Jurassic and Early Cretaceous multituberculates classified by Kielan−Jaworowska and Hurum (2001) in the paraphyletic suborder “Plagiaulacida”. It differs from Eleutherodon and resembles multituberculates in the horizontal, rather than basined longitudinal wear groove, and in the absence of the third (lingual) row of cusps (unless the lingual cingulum cusps represent this). The approximately triangular shape of the tooth, wide mesially with an embayment and pointed distally, approaches M2 of some paulchoffatiids, e.g., genus A ( Hahn and Hahn 1998a: figs. 19, 20) and genus D sp. 1 ( Hahn and Hahn 1998a: fig. 23). In these the lingual row is curved so that the last lingual cusp is near the distal buccal cusp, closing the central valley ( Fig. 7B ). The number of lingual cusps in paulchoffatiids (3 to 6, most frequently 4 or 5) is smaller than in Kermackodon (7). In the buccal row the two large cusps, B4 and B5, correspond to B1 and B2 of paulchoffatiids. Mesially three small cusps develop from the crest of B4, but in paulchoffatiids a cusp B0 may develop from the marginal crest. The mesiobuccal rounded ledge may represent the anterobuccal ridge, which varies in Paulchoffatiidae and is absent in genus A; however, the absence of a wear facet and of wrinkling makes this identification uncertain.

Kermackodon differs from Paulchoffatiidae in the form of the molar cusps. These are pointed, with well developed radial ridges, and they are connected by longitudinal crests; in paulchoffatiids and in nearly all later multituberculates they are blunt and separated by transverse grooves. Possibly the difference is due to greater thickness of enamel which results in swelling of the cusps. Pointed cusps resembling those of Kermackodon occur in M1 of Proalbionbaatar ( Hahn and Hahn 1998b) , the only albionbaatarid upper molar known. In this all the cusps are ornamented with radial enamel ridges, and the lingual cusps, 6 or 7 in number, are joined by a longitudinal crest. The narrowness of the wear groove on the Kermackodon M2 indicates that the lingual cusps of m2 were also pointed.

In M2 of other “Plagiaulacida” the number of lingual cusps is reduced to 3 (the tooth identified as Parendotherium or Eobaatar by Hahn and Hahn (1992) is exceptional in having 4). The lingual row is straight and the distal end of the tooth is broadened so that the outline becomes trapezoidal rather than triangular. The central valley is open distally, the distal lingual cusp being more widely separated from the distal buccal cusp. Development of a cusp (B0) at the mesial end of the buccal row varies. It is best developed in Eobaatar , where it differentiates from the marginal ridge. The anterobuccal ridge is most frequently a cingulum−like structure ( Fig. 7C ), whose wear continues that of the central valley of M1, due to the buccal cusps of m1, as in Bolodon (see Kielan−Jaworowska and Ensom 1992: pl. 3). It is more strongly developed in Glirodon , where it forms two cusps ( Kielan−Jaworowska and Hurum 2001: pl. 1). It seems to be absent in Ctenacodon , but: the type of C.laticeps figured by Kielan−Jaworowska et al. (1987) shows a wear facet on the buccal surface of B1. Lingual cingular cusps are developed only in the pinheirodontid Iberodon ( Hahn and Hahn 1999) .

M2 of Kermackodon shows some resemblance to Paulchoffatiidae among multituberculates, but differs particularly in the more numerous cusps, which are pointed, with sharp ridges. We classify Kermackodon in a new family Kermackodontidae . A relationship with Albionbaataridae is possible, but M2 of that family is unknown. The multituberculate−like premolars described below, because of their large size and aberrant character, are provisionally included in the Kermackodontidae and referred to Kermackodon multicuspis . Description of referred lower premolar ( Figs. 6B , 8A ).—

BMNH M46684 is a mesiodistally elongated tooth, much longer than wide (3.5 × 1.5 mm), and similar in size to p4 of Plagiaulax becklesii . It is narrower mesially than distally. The crown is dominated by a longitudinal crest (“blade”), which is triangular in profile, with the highest point slightly mesial to the middle. In crown view the blade is seen to be somewhat oblique to the long axis of the tooth, being more lingual distally. At the distal end the edge of the blade is continuous with a series of cuspules which extends onto the buccal side for about one−quarter of the length of the crown. In buccal view the maximum height of the blade measures 2.2 mm from the base of the enamel. There are three small elevations (serrations) near the highest part of the blade; the second is the highest, the first is on the anterior slope, and the third is closely behind the second. From the first two serrations arise low ridges that run halfway down the buccal surface with an obliquely forward inclination. They resemble the “Kannelierungen” ( Hahn 1969) that are associated with the serrations on lower premolars of other multituberculates. A ridge from the third serration has a different character: it is vertical, longer, reaching cingulum level, and it takes the form of a slight angulation of the tooth surface; more distally the buccal surface is shallowly concave. The distal slope of the edge of the blade has been blunted by wear, but halfway down there is an indication of a fourth serration. That this is not an artefact due to wear is shown by the presence of a short ridge on the lingual surface. A series of six small cusps forms an arc from the end of the blade, at cingulum level, along the distal margin and the distal end of the buccal margin. The series is continued as a ridge, weakly differentiated into three cuspules, that runs up the buccal surface in the direction of the fourth serration. Mesial to the series of cusps, the buccal cingulum is represented by a horizontal convexity that meets the vertical ridge from the third serration. On the lingual surface a ridge arises from the second serration and runs obliquely forward, closely parallel to the mesial edge of the blade. There are two slight swellings at cingulum level above the root bifurcation, and from these faint vertical ridges arise. Near the distal end a short vertical ridge runs from the fourth denticulation. The enamel reaches a somewhat lower level above the anterior root than above the posterior root. There is no groove in the anterior surface, such as exists in paulchoffatiids for reception of the more anterior tooth. The roots are slightly distally curved towards the tips and slightly flattened buccolingually; the posterior root is the larger.

The only evidence of wear is on the edge of the posterior part of the blade, between denticulations 3 and 4. It is inclined distally at an angle of 60 degrees to the long axis of the tooth.

Comparison.—The longitudinal serrated blade with oblique ridges, and the distobuccal series of small cusps, are characters of multituberculate lower premolars. Because of its elongated form and comparatively large size BMNH M46684 is identified as a last premolar (p4). The triangular profile of the blade, however, differs from that of other multituberculates, in which the top of the blade is arched or horizontal; exceptional is the reduced p4 of taeniolabidoids such as Catopsalis . BMNH M46684 is larger than p4 of paulchoffatiids ( Fig. 8B ), and longer in proportion to width and height. It is narrower mesially, and the mesial end is not truncate as in paulchoffatiids and plagiaulacids. With only four serrations, M46684 agrees with paulchoffatiids, but the serrations are unequally spaced, and oblique ridges are confined to the mesial part of the tooth. A trace of a triangular profile survives in paulchoffatiids, in which the height of the blade declines from a maximum at serration 2. However, the blade remains high at its mesial and distal ends, whereas in BMNH M46684 it falls to cingulum level. Thus at the mesial end there is in paulchoffatiids a concavity below the blade for reception of p3, but this does not exist in BMNH M46684, in which the premolars would not form an integrated unit as they do in paulchoffatiids. Distally the blade is continuous with the buccal cusp row in BMNH M46684, but in paulchoffatiids it ends well above the buccal cusps, and is linked to them by a vertical ridge. The buccal cusp row in paulchoffatiids extends farther forward along the tooth, to the level of serration 2, but there is a resemblance to BMNH M 46684 in that the series curves upward at its mesial end. Kielan−Jaworowska and Ensom (1994: pl. 2: 6, 7) described a p4 from the Purbeck Limestone, which they suggested might belong to Albionbaatar . It has a short, arcuate buccal row, which rises distally to join the end of the blade.

Owing to its almost unworn condition, BMNH M46684 provides little evidence bearing on function. In paulchoffatiids the top of the blade wears against the lingual cusp row of P 5 in a longitudinal grinding action, but the Bathonian tooth clearly did not function in this way. Wear on the distal edge of the blade is steeply inclined, in contrast to the horizontal wear of the M 2 holotype. In the Paleocene neoplagiaulacid Xanclomys ( Rigby 1980) , in which p4 is triangular in profile, it is tilted so that the distal slope of the edge is horizontal. Though curvature of the roots suggests that BMNH M46684 may have been tilted forward to some extent, this would not be enough to correct the inclination of the wear surface. Perhaps the wear was not due to contact with an opposing tooth but with food, as in the orthal slicingcrushing action of Ptilodus ( Krause 1982) .

Sigogneau−Russell (1989) compared the haramiyid tooth “ Thomasia II ” with p4 of multituberculates ( Fig. 3E ). It is longer than wide, and narrower mesially than distally as in BMNH M46684. There is a lingual row of three cusps connected by a ridge, which would correspond to the blade, but the cusps are larger and more individualised than the serrations of multituberculates, and the highest cusp is mesial rather than central in position. A buccal row of lower, smaller cusps occupies the distal two−thirds of the tooth, merging mesially into the slope of the largest lingual cusp. In comparison the buccal cusps of BMNH M46684 are smaller and restricted to near the distal end, but they are more extended in paulchoffatiids, which might be more primitive in this respect. Thomasia resembles BMNH M46684 and differs from paulchoffatiids in that the lingual and buccal rows are continuous at the distal end of the tooth; the connection forms the “U−ridge” of haramiyids.

Description of referred upper premolar ( Fig. 9 ).—BMNH M46640 is an incomplete tooth, interpreted as from the right side. The mesial end, with most of the anterior root, is missing. As preserved, the tooth measures 2.3 mm in length and 1.2 mm in width; assuming that the roots were equal the original length is estimated at about 2.6 mm. It is thus much longer than upper premolars of paulchoffatiids and other early multituberculates: e.g. length of P5 of Kuehneodon simpsoni is 1.7 mm ( Hahn 1969) and that of P4 of Psalodon potens is 2.2 mm ( Simpson 1929). In crown view the lingual margin is straight, the distal end is rounded and more prominent towards the lingual side, and the buccal margin has a shallow bay, above the bifurcation of the roots. Anterior to the bay the tooth is slightly wider than towards the distal end. These features can be seen again for example in P4 of Kielanodon hopsoni , Bolodon elongatus , and Psalodon potens . There are three lingual and two buccal cusps, but one or two additional cusps were probably present on the missing mesial portion. The cusps are conical, subequal in height, and with radial ridges on their slopes as in other multituberculates. The two distal lingual cusps and the distal buccal cusp form an equilateral triangle, and the mesial buccal and lingual cusps stand close together and are connate at the base. There is a buccal cingulum on the anterior part of the tooth, with three low elevations. The lingual ledge that occurs on posterior premolars of paulchoffatiids is absent, and there is no evidence of shearing wear on the lingual surface of the tooth. The posterior root is approximately circular in section at mid−length, where it has broken. There are two small accessory roots (now broken off) between the main roots; the buccal one is midway between the main roots, and the lingual one is joined by a flange to the distal root.

Comparison.—Paulchoffatiid upper premolars are differentiated into an anterior group, of mesiodistally short teeth, usually with two buccal and two lingual cusps, and a posterior group of longer, more complex teeth that are involved in shearing against the lower premolars. P1–P3 are in the first group, except in Kielanodon , where P3 is elongated like P4. P4 is in the posterior group with P5, except in Meketichoffatia and one species of Kuehneodon ( K. dryas ), where P4 is short like P3 ( Hahn 1977). In teeth of the posterior group there is a middle row of four cusps, and usually a lingual row of reduced cusps that may be represented only by a shelf, in most cases worn off against p4. BMNH M46640 does not fall clearly into either group. Its elongated form suggests comparison with the posterior group, but it has no lingual ledge, and there is no evidence of shear (though this might be due to lack of wear). P3 of Kielanodon hopsoni (Hahn 1987) is an elongated tooth with four lingual cusps and two buccal cusps; possibly BMNH M46640 had a fourth lingual cusp at the anterior end that has not been preserved. In P3 of Pseudobolodon krebsi there is a triangle of two lingual cusps and a buccal cusp on the posterior part of the crown, and a pair of cusps anteriorly ( Hahn and Hahn 1994), as in BMNH M46640, but the tooth is short. A possible dP4 of Kuehneodon figured by Hahn (1969: fig. 66) resembles BMNH M 46640 in being elongated, wider mesially, and having a triangular arrangement of cusps on the distal half, but there is an additional distobuccal cusp. However, the large size of BMNH M46640 and its robust roots make it unlikely to be a deciduous tooth. If it is a P4 the absence of the lingual ledge might be plesiomorphic.

Figures

Fig. 6. Scanning electron micrographs of epoxy resin casts. A–C. Kermackodon multicuspis gen. et sp. nov. A. BMNH M46822, right M2 (holotype) in occlusal (A1), oblique lingual (A2), and oblique buccal (A3) views. B. BMNH M46684, right p4 (referred) in distal (B1), lingual (B2), buccal (B3), and occlusal (B4) views. C. BMNH M46640, right upper premolar (referred) in lingual (C1) and occlusal (C2) views. D. Allotheria incertae sedis, BMNH M46234, left I2, lingual view. E, F. Hahnotherium antiquum gen. et sp. nov. E. BMNH M46717, left M2 (holotype) in occlusal (E1) and mesio−lingual (E2) views. F. BMNH M46773, right m2 (referred) in mesio−occlusal (F1), occlusal (F2), and mesio−lingual (F3) views. Mesial end upwards in A1, B4, C2, E1, F2, crown upwards in A2, A3, B1, B2, B3, C1, D, E2, F3.

Fig. 7. A. Kermackodon multicuspis gen. et sp. nov., BMNH M46822, left M2 (holotype) in occlusal (A1), mesial (A2), distal (A3), buccal (A4), and lingual (A5) views. B. Paulchoffatiid M2 (re−drawn and simplified after Hahn 1969: fig 80). C. Bolodon osborni M2 (re−drawn from Kielan− Jaworowska and Ensom 1992: pl. 3: 8)). Mesial end upwards in A1, B, C, crown upwards in the rest. Scale bars 1 mm.

Fig. 8. A. BMNH M46884, left p4, referred to Kermackodon multicuspis gen. et sp. nov. in occlusal (A1), buccal (A2), lingual (A3), mesial (A4), and distal (A5) views. B. Paulchoffatiid p4 (redrawn and simplified after Hahn 1969: fig. 29) in occlusal (B1), buccal (B2), mesial (B3), and distal (B4) views. Lingual side upwards in A1, B1, crown upwards in the rest.

Fig. 9. BMNH M46640, right P3/4, referred to Kermackodon multicuspis gen. et sp. nov. A. Occlusal view, mesial to right. B. Basal view, mesial to left. C. Lingual view. D. Buccal view, crown upwards in C and D.

Fig. 3. “Haramiyidan” teeth. A, B. Millsodon superstes gen. et sp. nov. A. BMNH M46645, right m1 (holotype), in occlusal (A1), buccal (A2), and distal (A3) views. B. BMNH M46183, left m3 (paratype) in occlusal (B1), buccal (B2), and distal (B3) views. Mesial end upwards in occlusal and buccal views, crown upwards in distal view. C, D. Staffia aenigmatica. C1, C2, C3, right m1; D1, D2, D3, m3; redrawn after Heinrich (2002: fig. 5), corresponding views. The m3 is interpreted as a left tooth. E, F. Thomasia, redrawn after Sigogneau−Russell (1989: figs. 18, 7). E1, E2, right “Thomasia II” (?= m1); F1, F2, left (right reversed) small “Thomasia I” (?= m3). Mesial end upwards in occlusal and buccal views, crown upwards in distal views. G. BDUC J 3, right upper molar referred to Millsodon superstes, occlusal (G1), lingual (G2), and mesial (G3) views. In G1 and G2 the wear facets, indicated by vertical hatching, are probably due to the mesial cusp of the lower molar. G1, mesial end upwards; G2, G3, crown upwards. H. Postulated occlusal relations of upper and lower molars (shown as left in H2) of M. superstes, based on BDUC J 3 and BMNH M46645. H1, occlusal view, buccal side upwards; H2, lingual view; mesial end to right in both. Scale bars 1 mm.