CHILODONTIDAE WENZ, 1938

Hickman, Carole S., 2018, A new Calliovarica species (Seguenzioidea: Chilodontidae) from the Eocene of Oregon, USA: Persistence of a relict Mesozoic gastropod group in a unique forearc tectonic setting, PaleoBios 35, pp. 1-10 : 2

CHILODONTIDAE WENZ, 1938

Transfer of Chilodontidae and CalliotropidaeHickman and McLean, 1990 from Trochoidea to Seguenzioidea, current status of the relationship between the two family groups, and revised treatment of chilodontid genera are reviewed by Herbert (2012). The classification of Calliotropidae is reviewed by Hickman (2016). There has been strong support for recognizing a third family group EucyclidaeKoken, 1897 for extinct Mesozoic genera ( Hickman and McLean 1990, Kiel and Bandel 2001). However, Bandel (2010) has further proposed five ad- ditional family-group names for extinct genera as well as two new family-group names based on living genera. Bandel’s new names and reallocation of living genera based on shell morphology are controversial where they are inconsistent with anatomical and radular data, and where molecular data are not available for testing putative relationships among genera.

A more conservative alternative proposal is that Calliotropidae is synonymous with Eucyclidae ( Kaim 2004) . This proposal is consistent with new well-preserved Jurassic material from Argentina and an argument for resolving a single long-ranging genus Calliotropis Seguenza, 1903 into two temporal subgenera, Calliotropis s.s. for Cenozoic species and Riselloidea Cossmann, 1909 , for Mesozoic species ( Ferrari et al. 2014).

Comparable nomenclatural proposals to treat chilodontid genus-group taxa with robust shells and apertural elaborations as long ranging remain controversial. Recognition of living species of the Cretaceous genus Agathodonta Cossmann, 1918 ( McLean 1984, Hickman and McLean 1990) has been rejected on the basis of detailed comparison of the type species with putative living members of the genus ( Herbert 2012).

However there is clear documentation that core Tethy- an carbonate platform, hard-substrate chilodontids did not “wait” for the Cenozoic to expand over great distances into reefal facies of the Pacific. Sohl (1987) noted the presence of the Jurassic genus Chilodonta Étallon, 1859 in Cretaceous carbonate facies on the now sunken guyots of the Mid-Pacific Mountains and hypothesized these as stepping stones for migration of “corallian facies” taxa during the Cretaceous ( Hamilton 1956, Ladd et al. 1974).

Strict maintenance of separate taxonomic names on either side of the Cretaceous-Tertiary boundary reinforces an unsupported conflation of the boundary between eras with a terminal mass-extinction event affecting all gastropods. In both Calliotropidae and Chilodontidae there is abundant evidence that prominent Cenozoic taxa originated deep in the Mesozoic, especially in the extra-tropical margins of the Tethyan realm. This was recognized perspicaciously by Sohl (1987, p. 1107) in his presidential address to the Paleontological Society when he noted: “... although (the) players may have new identities, their teams have remained the same.”

It is appropriate to note here that the name Chilodontidae is preoccupied, and the case for emended spelling to resolve homonymy ( ICZN Case 3555) is still listed as open. Accordingly, the name is retained here in accordance with ICZN Article 82.1 for maintenance of prevailing usage.