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.