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 : 1336

MORPHOLOGY OF BOREALESTES SERENDIPITUS AND BOREALESTES CUILLINENSIS

NMS G.1992.47.121.1 comprises a partial skeleton of Borealestes serendipitus on a block of blue-grey limestone. The block measures approximately 183 mm in length, 105 mm in width and between 148 and 340 mm in thickness. The surface of NMS G.1992.47.121.1 is undulating, with several hairline cracks visible in the prepared upper surface, also visible in synchrotron CT data. Skeletal elements are scattered on the surface of the block, including the palate and elements of the skull ( Figs 2 , 8 ). Synchrotron CT data revealed vertebrae, ribs, radius, partial humerus, ilium, femur and manus and pes elements within the block (unpubl. data EP). The surface bones sit on ‘platforms’ of rock, the result of acid and mechanical preparation, whereby the surrounding rock was removed. At least seven such platforms no longer contain fossil material, and likely indicate the original positions of bones that have been removed or detached during handling, such as the petrosal NMS G.1992.47.121.2 ( Panciroli et al., 2018a) and the dentary NMS G.1992.47.121.3 ( Panciroli et al., 2019).

NMS G.2020.4.1.1 comprises a partial skeleton of Borealestes cuillinensis contained within a series of small blocks of blue-grey limestone between ~2 and 5 cm long ( Fig. 3 ). The skull is present between two of these blocks, which were broken apart across a natural crack in the limestone. The left dentary is visible on the surface, along with the right squamosal and part of the occipital condyles. The rest of the skull is contained within the rock and visible through X-ray µCT ( Figs. 3 , 9 ).

Figures

Figure 2. Borealestes serendipitus cranial elements (NMS G.1992.47.121.1). Visualization from synchrotron µCT data. A, NMS G.1992.47.121.1, showing location of cranial elements; B, digital rendering of surface of NMS G.1992.47.121.1; C, digital rendering of surface of NMS G.1992.47.121.1 with matrix semitransparent, showing skeletal elements within the block. Scale bar equals 10 mm.

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 8. Skull reconstruction of Borealestes serendipitus in lateral (top) dorsal (middle) and ventral (bottom) views. Green shaded areas represented in specimen NMS G.1992.47.121.1 and associated material. Dotted lines indicate unrepresented areas where boundaries unknown. 1 premaxilla; 2 anterior nasal foramina; 3 maxilla; 4 infraorbital foramen; 5 posterior nasal foramen; 6 lacrimal; 7 nasal; 8 lacrimal foramen; 9 zygomatic process of lacrimal; 10 jugal (not known); 11 infraorbital foramen; 12 frontal; 13 parietal; 14 interparietal suture; 15 sagittal crest; 16 squamosal; 17 dorsal flange of squamosal; 18 postparietal; 19 occipital condyles; 20 midline ridge of postparietal; 21 postparietal foramina; 22 septomaxilla; 23 anterior projection of nasal; 24 internarial bar; 25 anterior premaxillary foramen; 26 incisive foramen; 27 palatal posterior salient of premaxilla; 28 greater palatine foramen; 29 palatal process (not known); 30 glenoid fossa; 31 external auditory meatus; 32 fenestra vestibuli; 33 pars cochlearis; 34 orbital area (not known); 35 basicranium (not known); 36 pterygoid and basicranium (not known); 37 primary palate (not known); 38 I3 foramen; 39 posterior projection of premaxilla into incisive foramen; 40 coronoid process; 41 nuchal crest; 42 angular process of dentary; 43 masseteric foramen; 44 dentary; 45 mental foramen; 46 anterior premaxillary foramen. Scale bar equals 5 mm.

Figure 9. Skull reconstruction of Borealestes cuillinensis in lateral (top) dorsal (middle) and ventral (bottom) views. Blue shaded areas represented in specimen NMS G.2020.4.1.1. Dotted lines indicate unrepresented areas where boundaries unknown. 1 premaxilla; 2 anterior nasal foramina; 3 maxilla; 4 infraorbital foramen; 5 posterior nasal foramen (not known); 6 lacrimal; 7 nasal; 8 lacrimal foramen; 9 zygomatic process of lacrimal; 10 jugal (not known); 11 infraorbital foramen (not known); 12 frontal (not known); 13 parietal (not known); 14 interparietal suture; 15 sagittal crest (not known); 16 squamosal; 17 dorsal flange of squamosal; 18 postparietal (not known); 19 occipital condyles; 20 midline ridge of postparietal; 21 postparietal foramina; 22 septomaxilla; 23 anterior projection of nasal; 24 internarial bar; 25 anterior premaxillary foramen (not known); 26 incisive foramen; 27 palatal posterior salient of premaxilla (not known); 28 greater palatine foramen; 29 palatal process (not known); 30 glenoid fossa; 31 external auditory meatus; 32 fenestra vestibuli; 33 pars cochlearis; 34 orbital area (not known); 35 basicranium known); 36 pterygoid and basicranium (not known); 37 primary palate (not known); 38 I3 foramen (not known); 39 posterior projection of premaxilla into incisive foramen (not known); 40 coronoid process; 41 nuchal crest (not known); 42 angular process of dentary; 43 masseteric foramen; 44 dentary; 45 mental foramen; 46 anterior premaxillary foramen. Scale bar equals 5 mm.