Dobunnodon mussettae, (Sigogneau-Russell, 2003)

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 : 1333

DOBUNNODON MUSSETTAE (SIGOGNEAU- RUSSELL, 2003) COMB. NOV.

BOREALESTES MUSSETTI SIGOGNEAU- RUSSELL, 2003

BOREALESTES MUSSETTAE AVERIANOV, 2004 (EMENDED GENDER)

Holotype: NHMUK PV M46495 , a right lower molar ( Fig. 5C 1–4 ).

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

Ty p e l o c a l i t y: K i r t l i n g t o n C e m e n t Q u a r r y, Oxfordshire, UK.

Referred material: From the Forest Marble Formation of Kirtlington , Oxfordshire: NHMUK PV M46224 , NHMUK PV M46239 , NHMUK PV M46001 , NHMUK PV M46066 , NHMUK PV M46836 , NHMUK PV M46319 , NHMUK PV M46809 and NHMUK PV M46835 , all lower molars. From the Forest Marble Formation of Watton Cliff , Dorset: NHMUK PV M46001 , lower molar .

Etymology: The species name was given in honour of Dr Frances Mussett for her ‘major participation in the accumulation of the Kirtlington fauna’ (Sigogneau-Russell, 2003).

Differential diagnosis: Dobunnodon mussettae resembles other docodontans in that it possesses an anterior ‘pseudotalonid basin’ on the lower molars, formed by cusps a, b, and g, has cusps b–a–c in a triangular arrangement, the lower molars are elongated anteroposteriorly, with labial row of higher cusps arranged in anteroposterior alignment with largest cusp a, and it has a lingual row of smaller cusps with distinctive anterior cusp g and larger posterior cusp c. The lower molar of Dobunnodon is unlike most docodontans, but is similar to Tashkumyrodon in being mediolaterally compressed. It resembles most docodontans, but differs from Borealestes in that the a–g crest is present on both cusp g and cusp a, and in having a strong a–d crest on cusp a ( Fig. 5c ). Cusp g is slightly more developed, and cusps c and g are placed further apart anteroposteriorly, than in Borealestes . Unlike Simpsonodon , Agilodocodon and Docodon , but like most other docodontans, Dobunnodon lacks creases and pits’ ‘ornamentation’ on the teeth. Dobunnodon has an anterior lingual cingulid that passes below cusp g to midway along the molar anteroposteriorly. The df cusp is more developed in Dobunnodon than in Borealestes and is distinct from the d cusp. Cusp e is positioned in alignment with the anteroposterior axis of the molar, whereas cusp e is lingual of the anteroposterior axis on molars of Borealestes . The upper molars are not yet known for this taxon.

Description: The holotype NHMUK PV M46495 , is a single, right, lower molar, lacking a root and broken at the base of cusp a (reconstructed for Fig. 5C ), previously described by Sigogneau-Russell (2003) and Panciroli et al. (2019).

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 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 4. Phylogeny ofDocodonta based on updatedphylogenetic analysis. Strict consensus ofsix trees of 131 steps resulting from parsimony analysis of data matrix for docodontans and outgroups as in Panciroli et al. (2019), with the addition of Borealestes cuillinensis and revision of Dobunnodon (= ‘Borealestes’ mussettae). First-to-last appearances represented by black bars (see Supporting Information). Nodes uniting taxa do not imply divergence times.

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.