Egertonia sp.

Ostrowski, Summer A., 2021, Late Cretaceous Elopomorpha (Actinopterygii: Teleostei) from the Mahajanga Basin of Madagascar and impacts on paleobiogeography, Palaeontologia Electronica (a 31) 24 (3), pp. 1-15 : 4-6

Egertonia sp.

Figure 3

Material. Four tooth plates ( UA 11389, DMNH EPV. 136302, DMNH EPV.136303, and UA 11390).

Occurrence. Berivotra Study Area (Anembalemba Member and Miadana Member).

Description. Tooth plate UA 11389 ( Figure 3 A-B) is incomplete on both ends and measures 0.9 cm

long, and 0.9 cm wide; the height is domed and ranges from 0.2-0.4 cm in thickness. On cross-sectional view through the thicker portion, there are five layers of vertically stacked teeth. The teeth are flattened hemispheres and range in width from 0.25-1 mm at the crown and have a smooth or slightly punctate surface texture. There is a remnant of a bony base that exhibits symmetry, but it is incomplete with little surface texture. Tooth plate DMNH EPV.136302 ( Figure 3 C-D) measures 1.4 cm long, 0.8 cm wide, and ranges in thickness from 0.2-0.5 cm. There is no clear bony base present, the surface is smooth, and the thin end is broken and incomplete. Upon view in cross-section through the tooth plate, there are four layers of vertically stacked teeth. Individual teeth are mostly complete and flattened hemispheres range in size from 0.25-1 mm in width at the crown and have a smooth or slightly punctate texture. Tooth plate DMNH EPV.136303 ( Figure 3 E-F) measures 1.25 cm long and 0.8 cm wide, and ranges in thickness from 0.2-0.6 cm tall. The thicker end is relatively complete, but the thin end is broken. In cross-section there are four layers of vertically stacked teeth. Individual teeth are flattened hemispheres and have a uniform size distribution of 1 mm across the crown with a relatively smooth surface texture. No bony base is present. Tooth plate UA 11390 ( Figure 3 G-I) is oblong and 1.7 cm long, 0.9 cm wide, and ranges in thickness from 0.2-0.5 cm thick. The thicker end is complete, and the thin end is nearly complete, which shows vertically stacked teeth in cross-section. Individual teeth are flattened hemispheres and range from 0.25-1.0 mm in crown width and are mostly smooth in texture with relatively thick enamel. Opposite the occlusal surface, there is a poorly preserved, symmetrical, partial bony base with cortical bone texture.

Remarks. The first account of Egertonia from the Maevarano was mentioned by Gottfried and Krause (1999) and further described in the PhD thesis of Ostrowski (2012). Egertonia is an extinct genus within Phyllodontidae . Egertonia tooth plates are defined by having three characteristics: 1) vertically stacked replacement teeth; 2) regularly convex (nearly hemispherical or flattened) teeth; and 3) relatively thick enamel ( Estes, 1969). These tooth plates alone cannot be identified finer than genus level. The holotype for Egertonia isodonta (NHM 38814) exhibits all three of these characteristics and is directly comparable to the four Madagascar specimens described above.

Figures

FIGURE 3. Egertonia sp. fossils from the Maevarano Formation. A-B, occlusal and cross-section views of tooth plate (UA 11389). C-D, occlusal and cross-section views of tooth plate (DMNH EPV. 136302). E-F, occlusal and cross-section views of tooth plate (DMNH EPV.136303). G-I, occlusal, cross-section, and basal views of tooth plate (UA 11390). Scale bar equals 1 cm; small arrows used in cross-section view to highlight vertically stacked teeth.