The taxonomy and stratigraphical significance of the Anglo–Welsh Cryptolithinae (Trinucleidae, Trilobita)

Abstract

ABSTRACT. The taxonomic status of the stratigraphically-important Caradoc genera Salterolithus Bancroft, 1929, Broeggerolithus Lamont, 1935 and Smeathenia Dean, 1960 and the species therein is critically reviewed. The radial alignment patterns of the fringe pits within the E arcs are used to distinguish Salterolithus from Broeggerolithus; fringe morphology and pit counts are used to distinguish species within these genera.`Broeggerolithus' harnagensis is reassigned to Salterolithus and S. praecursor, S. caractaci paucus and Smeathenia smeathenensis are all regarded as junior synonyms of Salterolithus harnagensis. This revision of the Anglo-Welsh Cryptolithinae reveals the evolution of morphologically very variable populations and environmentally constrained morphotypes and species. Eight species and subspecies of Salterolithus and Broeggerolithus are retained and redescribed and their stratigraphical distribution in the Caradoc of Britain, Ireland, Belgium and Scandinavia is clari®ed.

The Upper Ordovician trinucleid trilobiteBancroftolithusfrom the Precordillera of Argentina

“…The number of pits per arc refers to half fringe counts (variability currently ranges in ±2 pits). Different authors have documented that this practice does not induce much error despite fringe asymmetries (e.g., Whittington, 1968;Hughes, 1970;Bowdler-Hicks et al, 2002). Pits are counted in In and II; irregularities in distribution prevented objective Pothe, 1995, originally assigned to the former genus, is considered by us to be a subjective synonym of the type species of Hunickenolithus (H. pozoensis).…”

Extraordinary Ordovician trilobite Fantasticolithus gen. nov. from Peru and its bearing on the trinucleimorph hypothesis

“…Many trinucleid genera have a limited palaeogeographical distribution, and a high degree of endemicity is typical: Chinese trinucleids (Zhou & Zhen 2008) are mostly different from Bohemian and Moroccan (Havlíček & Vaněk 1966) and Scoto‐Appalachian (Bowdler‐Hicks et al . 2002) faunas. Ordovician microcontinents and terranes were characterized by another suite of endemics, such as in Avalonia (Owen & Ingham (1988) and references therein; see also Kennedy & Stammers 2018), the Central Andean Basin of Gondwana (Hughes & Wright 1970; Přibyl & Vaněk 1980; Waisfeld & Vaccari 2003) and the Precordillera – Cuyania Terrane, Argentina (Baldis & Pöthe de Baldis 1995; Waisfeld & Vaccari 2003).…”

“…However, it is probably not true of such genera as Protolloydolithus or Declivolithus Přibyl & Vaněk, 1967, which had extensive and apparently flattened fringes, and some others with steeply inclined fringes, such as Salterolithus Bancroft, 1929 (Bowdler‐Hicks et al . 2002, pl. 1 fig.…”

Inorganic geochemistry of the type Caradoc series (Sandbian to middle Katian, Upper Ordovician), Onny valley, Shropshire, UK

“…All the shelly fossils used to subdivide the type Caradoc are, however, environmentally controlled facies fossils that appear wherever the palaeoenvironment suited them, and thus biostratigraphic correlations based on them are useless (Hurst, 1979 a ). For example, it is not very encouraging to find that Heterothis alternata (J. de C. Sowerby), the brachiopod dominating the Alternata Limestone Formation, also occurs sporadically in lenses throughout the overlying strata, from basal Cheneyan to topmost Streffordian stages (Harper, 1978); nor that modern taxonomic studies have shown that the important cryptolithinid trilobites, widely used for Caradocian zonation, consist of very variable populations with environmentally constrained morphotypes and species (Owen & Ingham, 1988; Bowdler-Hicks, Ingham & Owen, 2002).…”