Gunnellichnus bartelsi Zonneveld, 2025

Diagnosis: Shallow, linear to gently curved furrows in bone with approximately consistent width and frequent to intermittent hemispherical pits in the groove bottom resulting in variable depth and an undulatory basal surface; width to depth ratio typically exceeds 10:1 but is less than 50:1; offset pitting may result in a twin-furrow appearance.

Description: The holotype of Gunnellichnus bartelsi occurs on the carapace bone of UM 10134, a large Baptemys wyomingensis individual (Figures 3 and 4). In total, eight specimens of G. bartelsi of various lengths were identified on this individual. All specimens occur on either the external surface of costal bones (Figure 3) or the internal exposed surface of peripheral carapace bone (Figure 4(A)). The traces are remarkably consistent in width, ranging from 5.03mm to 6.86mm (5.72mm average). The traces may meander gently (Figure 4(A)), but more commonly form long (2–8 cm) linear trends (Figures 3(A–D) and 5(A–D)). The margins of the trace are gently undulose. Terminae are rounded. The depth of the traces is also remarkably consistent, ranging from 0.10 to 0.18mm, with the exception of the hemispherical pits that are characteristic of this ichnospecies. The pits themselves range from 1.32 to 2.4 mm in width and 0.31 to 0.94 in depth, occurring intermittently along the length of the trace. Spacing of the pits ranges from 2.2 to 4.3 mm. In some cases (Figure 5(A–D)) the pits occur closer, separated by less than 0.2mm giving the trace a distinctive bilobed, track-like appearance.