Borealestes cuillinensis, Panciroli & Benson & Fernandez & Butler & Fraser & Luo & Walsh, 2021

Panciroli, Elsa, Benson, Roger B. J., Fernandez, Vincent, Butler, Richard J., Fraser, Nicholas C., Luo, Zhe-Xi & Walsh, Stig, 2021, New species of mammaliaform and the cranium of Borealestes (Mammaliformes: Docodonta) from the Middle Jurassic of the British Isles, Zoological Journal of the Linnean Society 192 (4), pp. 1323-1362 : 1331

BOREALESTES CUILLINENSIS SP. NOV.

Zoobank registration: LSID urn:lsid:zoobank.org:act:E2EDCA4C-B0F7-46F1-AB7A-118C3575BE69 .

Holotype: NMS G.2020.4.1.1, a partial skull and postcranial remains ( Fig. 3 ).

Stratigraphic provenance: Kilmaluag Formation, Late Bathonian, Middle Jurassic (Retrocostatum Zone: Barron et al., 2012).

Type locality: Cladach a’ Ghlinne, Strathaird Peninsula, Isle of Skye, Scotland UK ( Fig. 1 ).

Referred material: From the Kilmaluag Formation, Isle of Skye: Partial left dentary BRSUG 20571; NMS G.2018.27.1, fragment of right dentary in matrix. From the Forest Marble Formation of Kirtlington, Oxfordshire: NHMUK PV M46394 , NHMUK PV M46448 , NHMUK PV M46580 and NHMUK PV M46871 , all upper molars. NHMUK PV M46316 , NHMUK PV M46396 and, possibly, NHMUK PV M46607 (uncertain), all upper molars.

Etymology: Species named for the Cuillinensis, a mountain range on the Isle of Skye, Scotland, which overlooks the holotype locality; the skyline of the mountain range resembles the cusps and ridges of the teeth.

Differential diagnosis: Borealestes cuillinensis resembles Borealestes serendipitus in most features of the upper molars, but differs in having a more rounded cusp A, so that there is no anterior crest and no anterolabial crest on cusp A ( Figs 5a and b , 6 ). Borealestes cuillinensis has a shorter anterolingual crest on cusp X than B. serendipitus , with a cuspule on the crest. Cusp Z is reduced compared to B. serendipitus . The anterior fovea is less distinct than in B. serendipitus . In the lower dentition, B. cuillinensis is almost indistinguishable from that of B. serendipitus , except for having slightly more pointed molar cusps. The lappets of the dentary do not enclose the cartilage of the Meckel’s sulcus of B. cuillinensis , unlike in B. serendipitus , and the mandibular symphysis is less distinct in B. cuillinensis than in B. serendipitus ( Fig. 7 ).

Description: The holotype NMS G.2020.4.1.1 is a partial skeleton that, following preparation for high-resolution CT scanning, is contained within a series of small blocks of blue-grey micritic limestone between ~2 and 5 cm length. The dentaries and some skull elements are partially visible on the surface, and within the rocks are the skull, vertebrae, scapulacoracoid, humerus, radii, ribs and pes and manus elements. We infer that NMS G.2020.4.1.1 is an adult individual, as the last (ultimate) lower molar is positioned directly in front the coronoid process, as in adult specimens of Docodon victor ( Schultz et al., 2017) .

Figures

Figure 1. The stratigraphy of the Great Estuarine Group, and location of type locality of Borealestes serendipitus NMS G.1992.141.1 and Borealestes cuillinensis, NMS G.2020.4.1.1, Cladach a’Ghlinne near Elgol.

Figure 3. Borealestes cuillinensis cranial elements (NMS G.2020.4.1.1 parts AA and BB) visualization from µCT data. A, digital rendering of surface of NMS G.2020.4.1.1; B, digital rendering of NMS G.2020.4.1.1 with matrix semitransparent, showing cranial skeletal elements within the block. Scale bar equals 10 mm.

Figure 5. Diagnostic dental features of Borealestes species, and Dobunnodon. A1–4, Borealestes serendipitus: A1, NMS G.1992.47.121.1 left M3 (mirrored) in occlusal view alongside diagrammatic illustration; A2, holotype BRSUG 20570 right m2 (mirrored) in occlusal view, cusps only, alongside diagrammatic illustration; A3, BRSUG 20570 right m2 (mirrored) crests only; A4, BRSUG 20570 right m2 (mirrored) in lingual view alongside diagrammatic illustration. B1–4, Borealestes cuillinensis: B1, NMS G.2020.4.1.1 right M3 in occlusal view alongside diagrammatic illustration; B2, NHMUK PV M46871 left upper molar in occlusal view (mirrored) with cusps marked; B3, NMS G.2020.4.1.1 m2 in occlusal view; B4 NMS G.2020.4.1.1 m2 in lingual view with cusps alongside diagrammatic illustration. C1–4, Dobunnodon mussettae: C1, holotype NHMUK PV M46495 lower right molar in occlusal view with crests and diagrammatic illustration below; C2, holotype NHMUK PV M46495 mirrored for comparison and diagrammatic illustration below; C3, holotype NHMUK PV M46495 lingual view with crests and diagrammatic illustration below; C4, holotype NHMUK PV M46495 mirrored for comparison. A and C adapted from Panciroli et al. (2019). Darker grey areas indicate broken surfaces. Scale bars equal 1 mm.

Figure 6. Dentition of Borealestes serendipitus and Borealestes cuillinensis for comparison. A, C, Borealestes serendipitus upper dentition of NMS G.1992.47.121.1 and lower dentition of NMS G.1992.47.121.3 (C mirrored for comparison). B, D, Borealestes cuillinensis NMS G.2020.4.1.1. Scale bars equal 1 mm.

Figure 7. Diagnostic mandibular features of Borealestes species. A1, A2, dentaries belong to Borealestes serendipitus, showing diagnostic features of Meckel’s sulcus and mandibular symphysis. Bottom dentary (B), belongs to Borealestes cuillinensis. Shows diagnostic features of Meckel’s sulcus and mandibular symphysis. Scale bar equals 1 mm, scale same throughout.