Borealestes serendipitus, WALDMAN & SAVAGE, 1972

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 SERENDIPITUS WALDMAN & SAVAGE, 1972

Holotype: Partial left dentary, BRSUG 20570.

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

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

Referred material: From the Kilmaluag Formation, Isle of Skye: NMS G.1992.47.121.1, partial skeleton.

Etymology: Species name from noun serendipity, defined as the faculty of making happy and unexpected discoveries by accident.

Differential diagnosis: Dental formula 4.1.?5.4/?4.1.5.5(6). Borealestes serendipitus differs from Borealestes cuillinensis , the only other species in the genus, in having distinct anterolabial and anterolingual crests between cusps A and X in the upper molars, and in that cusp Z is reduced ( Figs 5a and b , 6 ). The anterior fovea is more distinct than in B. cuillinensis . The lower molar cusps are slightly less dorsoventrally tall in B. serendipitus than in B. cuillinensis . The lappets of the dentary enclose the cartilage of the Meckel’s sulcus of B. serendipitus from the point ventral to the m3–m 4 in adult specimens, leaving a faint line running anteriorly, unlike in B. cuillinensis where it remains an open sulcus in the adult ( Fig. 7 ). The mandibular symphysis of B. serendipitus remains distinct until ventral to the p3– p4, whereas it is much less distinct in B. cuillinensis .

Description: The holotype BRSUG 20570 is a partial left dentary, removed from matrix, with nine teeth in their alveoli (one only comprising roots). It measures 11 mm in length.

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 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.