Lotagnostus Whitehouse, 1936

Taylor, John F., Loch, James D. & Repetski, John E., 2024, Taxonomy and stratigraphic distribution of Lotagnostus (Agnostida: Agnostidae) and associated trilobites and conodonts in the Upper Cambrian (Furongian) of Laurentia, Zootaxa 5422 (1), pp. 1-66 : 34-35

Lotagnostus Whitehouse, 1936

Type species. Agnostus trisectus Salter, 1864a , by original designation from the White-Leaved Oak Shale , Malvern, England .

Other species. Lotagnostus americanus ( Billings, 1860) ; L. trisectus ( Salter, 1864b) ; L. ponepunctus ( Matthew, 1901) ; L. germanus ( Matthew, 1901) ; L. asiaticus Troedsson, 1937 ; L. hedini ( Troedsson, 1937) ; L. peladensis ( Rusconi, 1951a) ; L. verrucosus Rusconi, 1951a ; L. obscurus Palmer, 1955 ; L. atenuatus ( Rusconi, 1955a) ; L. punctatus Lu, 1964 ; L. ergodes ( Shergold, 1971) ; L. irretitus ( Shergold, 1975) ; L. spectabilis Xiang & Zhang, 1985 ; L. shergoldi Tortello in Esteban & Tortello, 2007; L. salteri Westrop & Landing, 2016 ; L. matthewi Westrop & Landing, 2016 ; L. nolani n. sp.; L. clarki n. sp.; L. rushtoni n. sp.; L. morrisoni n. sp.

Discussion. For most species of Lotaganostus only a few specimens have been illustrated from a single bed or thin stratigraphic interval. The resultant lack of information on morphologic variation from such stratigraphically constrained collections has allowed for strongly divergent opinions regarding the range of intraspecific variation within Lotagnostus species, and the number of valid species within the genus. Some ( Peng & Babcock, 2005; Peng et al., 2015) contend that many species described in earlier studies constitute a single, widespread, highly variable species for which Lotagnostus americanus ( Billings, 1860) is the senior subjective synonym. Others ( Rushton, 2009; Landing et al., 2011; Westrop et al., 2011; Westrop & Landing, 2016) have challenged the extensive synonymy resulting from that broad species concept, in part because of the inadequacy of type material for many species. The abundant material from collection 5/22/08B allows for an assessment of the contrasting hypotheses on the variation of Lotagnostus .

In a re-evaluation of the species diversity and biostratigraphic distribution of Lotoganostus in North America, Westrop et al. (2011) recommended restriction of the type species, L. trisectus , to its type area in Avalonian Britain, arguing that the loss of critical morphologic information resulting from compaction in shale rendered comparison with less deformed material recovered elsewhere highly problematic. Having discovered in the present study the importance of features such as the steepness and variation in slope of the pleural fields and genae for discrimination of Lotagnostus species, we endorse that recommendation. Although the compacted condition of the holotype of L. punctatus from China could be offered as justification for similar geographic restriction of that species, the availability of non-compacted specimens preserved in limestone from the same area and formation allows for effective comparison and eliminates the need for such limitation.

The problem of small sample sizes also lies at the heart of conflicting interpretations regarding the material assigned to Lotagnostus asiaticus (Troeddson, 1937) offered in previous studies. In response to criticism by Landing et al. (2010) regarding lack of evidence of intraspecific variation within individual collections, Peng et al. (2015) cited co-occurrence of weakly and strongly scrobiculate morphs within the collections from which that species was described, as well as from a single bed of the Siyanshan Formation in China sampled by Lu & Lin (1980). However, Westrop & Landing (2016) noted that co-occurrence alone does not confirm that the two morphs are conspecific and, given the absence of evidence of intergradation, argued that they represent separate, sympatric species. The absence of transitional forms between the strongly scrobiculate and largely effaced Lotagnostus specimens in our large collections from the Windfall Formation strongly supports the latter interpretation. Consequently, we follow Westrop & Landing (2016) in considering L. asiaticus a valid, weakly scrobiculate species, and exclude the strongly scrobiculate specimens of the type suite. Those sclerites represent a different species, like L. punctatus , which might ultimately prove to be the appropriate assignment for coarsely scrobiculate material previously assigned to L. trisectus from Australia ( Bao & Jago, 2000), Kazakhstan ( Ergaliev, 1983), Siberia ( Pegel, 2000), and Sweden ( Westergard, 1922) as well.