Centrichnidae

Ichnofamily Centrichnidae Wisshak et al., 2019

Type ichnogenus: Centrichnus Bromley & Martinell, 1991 .

Original diagnosis. —Single to multiple, roughly circular depressions on the surface of hard substrates, shallower than wide, with individual grooves often arranged concentrically or excentrically (from Wisshak et al. 2019).

Emended diagnosis. —Roughly circular, elliptical, or tearshaped bioerosion structures on the surface of hard substrates, shallower than wide.

Remarks. —The original diagnosis includes only the “roughly circular depressions”, while Centrichnus eccentricus Bromley & Martinell, 1991 , the type ichnospecies of Centrichnus Bromley & Martinell, 1991 , being representative of Centrichnidae , is tier-shaped (as is Lacrimichnus Santos et al., 2003 ). Reinvestigation of C. eccentricus has furthermore shown that the complete morphology includes not only that tier-shaped byssus attachment scar but also abrasion marks of the anomiid trace maker’s shell margin and hinge area ( Neumann et al. 2015). This fact was originally accounted for by the, now deleted, “Single to multiple”, which was misleading because it would have included clusters of several attachment scars produced by several individuals. Instead, the more complex morphology of C. eccentricus is now accommodated by using the term “structures” instead of “depressions”. The reference to the concentric/eccentric grooves has been deleted to use a broader definition while retaining a clear distinction to the related ichnofamily Renichnidae ( Wisshak et al. 2019).

The family Centrichnidae includes Augoichnus Arendt, 2012 , Centrichnus Bromley & Martinell, 1991 , Patellichnus Dragastan in Dragastan et al., 1998 (see also Brustur 2020), Lacrimichnus Santos et al., 2003 , Ophthalmichnus Wisshak et al., 2014 , Solealites Uchman et al., 2018, and Tremichnus Brett, 1985 (for ichnotaxonomic history of Tremichnus see Wisshak et al. 2015b and Buatois et al. 2017), according to a primary assignment ( Wisshak et al. 2019). The ichnotaxonomic status of Thatchtelithichnus Zonneveld et al., 2015 , known from the turtle plastrons and bones (see Collareta et al. 2021), is still under debate. It was initially established as a trace fossil but later considered a bioclaustration structure ( Wisshak et al. 2019) and recently defended again as a trace fossil ( Zonneveld and Bartels 2020), in which case it should be included in the Centrichnidae .