Clionolithes Clarke, 1908

Wisshak, Max, 2017, Taming an ichnotaxonomical Pandora’s box: revision of dendritic and rosetted microborings (ichnofamily: Dendrinidae), European Journal of Taxonomy 390, pp. 1-99 : 23-24

Clionolithes Clarke, 1908

Olkenbachia Solle, 1938: 156 .

Ramodendrina Vogel et al., 1987: 270.

Platydendrina Vogel et al., 1987: 274.

Type ichnospecies

Clionolithes radicans Clarke, 1908 by subsequent designation in Clarke (1921) or Fenton & Fenton (1932) (see Remarks below).

Original diagnosis

n/a

Emended diagnosis

Dendritic or rosetted boring network spreading immediately beneath the surface of calcareous skeletal substrates, with tunnels radiating and branching outward from a central node that shows deepest penetration of the trace and may expand into palmate fans. Tunnels taper, cross, or anastomose, and connect to the substrate surface at their terminations or along their entire length.

Original description

[…] the generic designation Clionolithes for a group [… are] very much smaller [than Vioa prisca = Palaeosabella prisca ], much more intricate, arborescent or vagrant tubules. [ Clarke (1921), restricting the use of the ichnogenus, previously given with species descriptions only in Clarke (1908).]

Remarks

The ichnotaxonomical status of Clionolithes experienced a rough history after its original description by Clarke (1908). He did not designate a type ichnospecies or give an ichnogenus diagnosis, but merely described three ichnospecies, including C. priscus (McCoy, 1855) (original designation: Vioa prisca ) which is, however, a worm boring (ichnogenus Palaeosabella) and erratic within the suite of his other ichnospecies. Clarke (1921) recognised this misplacement and restricted his earlier definition. In the same account he suggested C. radicans as the type ichnospecies ( Clarke 1921: 88) using the partly ambiguous phrasing “It is this form of sponge that may be taken as the type of the genus”. Fenton & Fenton (1932: 43) provided a more explicit definition of Clionolithes and defined C. radicans as the type ichnospecies by subsequent designation, albeit Clarke’s statement ( Clarke 1921) possibly already fulfilled this purpose. Notwithstanding, Solle (1938) established a new set of morphologically very similar ichnospecies under the new ichnogenus name Olkenbachia . This synonymy was recognised by Teichert (1945), who confirmed the validity of Clionolithes and regarded Olkenbachia as its junior synonym. In contrast, Vogel et al. (1987) considered both, Clionolithes and Olkenbachia , as nomina dubia and instead offered the new replacement ichnogenera Nododendrina, Ramodendrina and Platydendrina. Plewes (1996) reinvestigated and illustrated Clarke’s type material and found it, contrary to Vogel’s statement, sufficiently well-preserved to merit determination of morphological traits, thus again re-validating Clionolithes and in turn considering Nododendrina, Ramodendrina and Platydendrina as junior synonyms. Recently, Furlong & McRoberts (2014) followed this view and confirmed the junior synonym status of Nododendrina and Ramodendrina. The morphologically similar ichnogenus Granarborus Plewes, 1996 and its two ichnospecies are nomina nuda, since they were not formally published. Irrespective of this repeated rejection and revalidation, a number of further authors ( Thomas 1911; Lees & Thomas 1918; Ruedemann 1925; Branson 1937; Talent 1963) added additional ichnospecies to Clionolithes .

As discussed in the context of the ichnofamily definition above, there is a considerable morphological overlap of some ichnospecies of Clionolithes with Entobia megastoma (Fischer, 1868) and E. dendritica Pleydell & Jones, 1988 , both of which are only vaguely camerate and have a dendritic branching pattern. However, both ichnospecies of Entobia are far larger in dimension. Nevertheless, since the entobians and possibly some of the ichnospecies of Clionolithes are produced by excavating sponges, they partly share the feature of a cuspate microsculpture produced by individual etching cells. This texture is smaller in dimension, thus addressed as “pseudo-chips” by Plewes (1996), and corresponds to the texture exhibited by the two micro-entobians E. nana and E. mikra , both established by Wisshak (2008). This circumstance basically leaves two ichnotaxonomical options, the first one being to consider Clionolithes a junior synonym of Entobia based on the relatively broad emended diagnosis provided by Bromley & D’Alessandro (1984: 238), which allows the inclusion of non-camerate microborings with a diagnostic cuspate microtexture. The second one is to not consider a cuspate microsculpture as an exclusive morphological feature of entobians and to retain Clionolithes as a distinct ichnogenus. It is the latter option that is advocated herein. In consequence, one could argue that the two entobians E. megastoma and E. dendritica might better be placed within Clionolithes , but this option is not supported here because it would result in a substantial and unfortunate extension of the dendrinid size range, and would only increase the morphological overlap of the two ichnogenera.

Reinvestigation of the original type material of C. lizardensis Lees & Thomas, 1918 and C. irregularis Fenton & Fenton, 1932 clearly identified these specimens as Talpina ispp. and not as dendrinids. The same applies for C. canna Price, 1916 and for C. hackberryensis ( Thomas, 1911) , the latter originally described as a species of Cliona and later placed within Clionolithes by Fenton & Fenton (1932). Their plesiotypes, however, represent a mix of Talpina isp. and C. radicans and not a distinct ichnospecies. Plewes (1996) revised Talpina , transferred C. hackberryensis to T. hackberryensis and regarded C. irregularis and C. canna as junior synonyms. Likewise, she transferred C. lizardensis to T. lizardensis . The present reinvestigation of the type material concurs with Plewes unpublished revision and both new combinations are thus hereby formally established. The mix of Talpina and Clionolithes is based on an incorrect interpretation that the former ichnogenus represents networks of peripheral galleries originating from the dendritic main chamber of the latter ichnogenus (see description and remarks on C. hackberryensis in Fenton & Fenton 1932 ). Another one of Fenton & Fenton’s (1932) ichnospecies, C. fossiger , is a burrow in the internal mould of bivalves reminiscent of the ichnospecies Arachnostega gastrochaenae Bertling, 1992, and is not a bioerosion trace fossil but a senior synonym of the latter ichnospecies. C. reptans was transferred to the ichnogenus Filuroda by Solle (1938). C. quaerens Ruedemann, 1925 is an unidentified tubular epilith. C. pricei Branson, 1937 and C. hunanensis Chow, 1957 have to be considered nomina dubia due to their holotypes currently being lost and the inadequate original illustrations. Hyde (1953) erected three new Clionolithes ichnospecies, with C. implicatus being a junior synonym of Palaeosabella prisca , C. ramosus representing an unidentified tubular boring with affinity to Talpina and C.? rectus being another tubular boring system with a characteristic trifurcation pattern that was later transferred to the new ichnogenus Trifurcus by Plewes (1996). Trifurcus, however, was not formally published and is thus a nomen nudum, just like C. bullahirsuta which would be a junior synonym of C. alcicornis anyway.