Bustylus folieae, Bast & Sigé & Smith, 2012

Bast, Eric De, Sigé, Bernard & Smith, Thierry, 2012, Diversity of the adapisoriculid mammals from the early Palaeocene of Hainin, Belgium, Acta Palaeontologica Polonica 57 (1), pp. 35-52 : 42-45

Bustylus folieae sp. nov.

Fig. 5 , Table 3.

Etymology: In honour of Dr. Annelise Folie, for her contribution to the knowledge of the herpetofauna of Hainin.

Type material: Holotype: IRSNB M1996 (Y1−01), left M1 . Paratypes: IRSNB M1997 ( R1−40 ), left M2 ; IRSNB M1976 (N2−04), left M3 ; IRSNB M1998 (N2−06b), left mandible fragment with p3–m2 and alveoli of p2 ; IRSNB M1999 (P2−14), left p3 ; IRSNB M2000 ( R1−31 ), left p4 ; IRSNB M2001 (N2−08), right dp4 ; IRSNB M2002 (P2−04), left m1 ; IRSNB M2003 (N1−01), left m2 ; IRSNB M2004 ( R1−10 ), right m3 .

Type locality: Hainin , Hainaut province, Belgium .

Type horizon: Early Palaeocene, Hainin Formation, Mons Basin.

Referred material.—IRSNB M1995 (Z2−01), left dP4, Q2−38, left M3; O1−08, right p4; N2−07, right m1; O2−01, right m1; Q2−09, left m3; R1−34, left m3; Q1−18, left m3; P1−09, lingual part of right M1; R1−77, lingual part of right M2; P2−08, labial part of right p4; R1−91, trigonid of left dp4; Q2−22, trigonid of right m1; R1−20, talonid of left m1; N1−10, trigonid of left m3. Diagnosis.—Size intermediate between B. marandati and B. cernaysi (20% smaller than B. cernaysi and 15% larger than B. marandati ). Upper molars differ from those of B. cernaysi in their less developed stylar cusps and a narrower lingual region, and from B. marandati and B. cernaysi in the presence of a transversely wider M1. Lower molars differ from those of B. marandati and B. cernaysi in the presence of a much larger precingulid and a deeper and wider hypoflexid. p4 morphology similar to that of B. cernaysi , and differs from that of B. marandati in the presence of a larger paraconid and a lower and more individualised metaconid.

Measurements.—See Table 3.

Description.—The dP4 ( Fig. 5G ) is morphologically similar to M1, but is slightly longer anteroposteriorly and much less developed transversely, especially in the stylar shelf region. The paracone and metacone are less sharp than on M1. The parastylar lobe points more anteriorly, and the metastylar lobe is directed more labially. The ectoflexus is somewhat deeper, and the stylar cusps are almost invisible. Some of these differences may be explained by the high level of wear that the tooth exhibits.

The M1 ( Fig. 5H ) shows a moderate degree of transverse development. The stylar shelf is wide and exhibits four marked cusps: the parastyle, stylocone, mesostyle and D cusp. The metastyle is a very faint bulge at the labial end of the postmetacrista. The ectoflexus seems relatively shallow owing to wear on the labial edges of the parastylar and metastylar lobes, but was probably relatively deep. It forms two relatively symmetrical lobes. The metastylar lobe is slightly smaller than the parastylar lobe and points more posteriorly. The preparacrista and postmetacrista are long, the latter being more oblique to the labiolingual axis of the tooth. The paracone and metacone are well separated down to their bases, linked by a rectilinear centrocrista, similar in size and aligned anteroposteriorly. The paracingulum is relatively

http://dx.doi.org/10.4202/app.2010.0115

wide, whereas the metacingulum is very narrow, short and terminates at the posterolingual base of the metacone. The lingual part of the tooth displays a greater degree of transverse development than the labial part, and is slightly shifted anteriorly. The protofossa is deep and well delimited. The paraconule and metaconule are well developed, whereas the internal crests are not well marked, and rather short. The protocone is slightly procline and similar in height to both the paracone and metacone.

The M2 ( Fig. 5I ) is similar to M1, but is characterised by a slightly greater degree of transverse development and a wider protofossa. The stylar cusps are less visible than on M1 and the metacingulum extends more labially.

The M3 ( Fig. 5J ) presents a well−developed parastylar lobe, whereas its metastylar lobe is reduced. The metacone is relatively small, and the protofossa is shorter anteroposteriorly than on M1 and M2. The conules are well developed and present no internal crests.

Specimen IRSNB M1998 ( Fig. 5K ) is a fragmentary left dentary bearing the posterior part of the alveolus for p1, the alveoli for p2, and p3 to m2. The alveoli for p2–p4 are biradiculate, with those for p2 and p3 being similar in length and somewhat shorter than p4. A short diastema is present in front of p3. The dentary is relatively high (1.5 times the height of the crown of p4) and carries two dental foramina below the anterior roots of p2 and m1.

The p3 ( Fig. 5A ) resembles p4, but is shorter and lower and displays a somewhat simpler morphology. The trigonid is narrower, the paraconid smaller, and the metaconid much more reduced and posterior in position. The talonid is smaller and exhibits a single cusp in the position of the hypoconid.

The p4 ( Fig. 5B ) is pre− to semi−molariform. The trigonid is much longer and higher than the talonid, but has the same width. The paraconid is of moderate size and situated at the anterolingual base of the protocone. There is no precingulid. The protoconid is the biggest cusp of the trigonid, while the slightly reduced metaconid protrudes lingually and is posteriorly shifted compared to the protoconid. The postmetacristid is well developed. The talonid has two cusps corresponding to the entoconid and hypoconid, respectively. There is no trace of a crista obliqua.

The dp4 ( Fig. 5C ) is much narrower than m1, but has about the same length. The paraconid is large and located anteriorly, while the talonid is wider than the trigonid and separated from the latter by a lateral constriction.

The m1 ( Fig. 5D ) is relatively robust, with little height and width difference between the trigonid and talonid, although the trigonid is slightly narrower than the talonid and relatively long. The trigonid cusps have very sharp apices, but also strong bases. The precingulid is well developed. The paraconid, the smallest cusp of the trigonid, is projecting anterolingually, and is shifted labially compared to the metaconid. The metaconid, slightly protruding lingually, has about the same height as the protoconid. The latter is located slightly anterior to the metaconid, making the posterior wall of the trigonid, which itself is almost vertical, slightly oblique to the anteroposterior axis of the tooth. The postmetacristid is relatively well developed. The hypoconid is the largest cusp of the talonid, and the three talonid cusps are equidistant. The talonid basin is deep. The crista obliqua reaches the posterior wall of the trigonid lingual to the protocristid notch, and extends high on the trigonid wall towards the tip of the metaconid. The hypoflexid is narrow and deep.

The m2 ( Fig. 5E ) is morphologically very similar to m1, although the trigonid is markedly shorter and wider, the paraconid is located in a more lingual position, and the metaconid is protruding more lingually.

The m3 ( Fig. 5F ) is similar to m2, with the talonid being longer and narrower, and the hypoconulid being larger and shifted anteriorly. Discussion.— Bustylus folieae is placed in the family Adapisoriculidae and the genus Bustylus for the same reasons as B. marandati .

The dP4 (IRSNB 1995) was interpreted as an M1 of B. marandati by Crochet and Sigé (1983). However, its relatively larger size, as well as other features, such as the small size of the stylar shelf and the anterior development of the parastylar lobe, do not correspond to the morphology of other M1s assigned to this species. Based on this relatively different morphology (as compared to other M1s), the high level of wear, the relatively thin enamel, and the absence of root insertions, we prefer to interpret this tooth as a dP4, rather than a worn M1, with its size matching B. folieae better than B. marandati . The upper molars are similar to those of

DE BAST ET AL.—ADAPISORICULID MAMMALS FROM PALAEOCENE OF BELGIUM 45

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B. marandati , but slightly bigger, with M1 being wider transversely, and the stylar cusps being slightly more individualised and the internal crests less developed, or even absent, on M3. By contrast, B. cernaysi has much better developed stylar cusps and is also larger. The M1 (IRSNB M1273) referred to Bustylus sp. ( Smith 1997) differs from B. folieae in showing a smaller degree of transverse development and in the presence of more individualised stylar cusps. The p4 differs from that of B. marandati in the presence of a slightly larger hypoconid, a longer talonid, a less marked postmetacristid and a larger and more individualised metaconid. The morphology of this tooth seems to be close to that of B. cernaysi , but the only p4 reported for the latter is partially broken. The lower molars are similar to those of B. marandati , but slightly larger, with a much larger precingulid and a deeper and wider hypoflexid. The width of m1 much more resembles that of m2 than is the case in B. marandati , and the talonid of m3 is relatively longer. B. cernaysi has a more labially protruding hypoconid and sharper cusps. The m1 (IRSNB M1274) of Bustylus sp. from Dormaal ( Smith 1997) is very similar, but has a smaller precingulid and is slightly smaller overall. B. folieae is the best known species as regards the lower molars, and a tentative of reconstruction of the jugal teeth is proposed in Fig. 6.

Stratigraphic and geographic range.—Known only from the early Palaeocene of the Mons Basin, Belgium.

Figures

Fig. 5. SEM pictures of the adapisoriculid Bustylus folieae sp. nov. from the early Palaeocene of Hainin (Belgium). A. Left p3, IRSNB M1999 (P2−14), in labial (A1), occlusal (A2), and lingual (A3) views. B. Left p4, IRSNB M2000(R1−31), in labial (B1), occlusal (B2), and lingual (B3) views. C. Right dp4, IRSNB M2001 (N2−08), in labial (C1), occlusal (C2), and lingual (C3) views. D. Left m1, IRSNB M2002 (P2−04), in labial (D1), occlusal (D2), and lingual (D3) views. E. Left m2, IRSNB M2003 (N1−01), in labial (E1), occlusal (E2), and lingual (E3) views. F. Right m3, IRSNB M2004 (R1−10), in labial (F1), occlusal (F2), and lingual (F3) views. G. Left dP4, IRSNB M1995 (Z2−01), in labial (G1) and occlusal (G2) views. H. Holotype: left M1, IRSNB M1996 (Y1−01), in labial (H1) and occlusal (H2) views. I. Left M2, IRSNB M1997 (R1−40), in labial (I1) and occlusal (I2) views. J. Left M3, IRSNB M1976 (N2−04), in labial (J1) and occlusal (J2) views. K. Left jaw fragment with p3−m2 and alveoli of p1−p2, IRSNB M1998 (N2−06b), in labial (K1), occlusal (K2), and lingual (K3) views.