Contribution of Morphometrics to the Systematics of the Ordovician GenusNeseuretus(Calymenidae, Trilobita) from the Armorican Massif, France

Abstract

The genus Neseuretus Hicks, 1873 is the most abundant trilobite of the Ordovician siltite succession of the Andouillé and Traveusot Formations in the French Armorican massif. The systematics of some species of Neseuretus is still unclear. Armorican and Iberian domains formed part of a distinctive paleobiogeographical province in the Ordovician and, while five Neseuretus species were defined in Iberia that follow each other through time, from the Middle to the Upper Ordovician, only one Neseuretus species, N. tristani, has been identified in the Armorican massif so far. The discovery of new fossil deposits in the Ménez-Belair syncline has led to the identification and re-description of three Neseuretus taxa: Neseuretus avus Hamman, 1977 from the early-middle Darriwilian, Neseuretus tristani (Brongniart in Desmarest, 1817) from the late–middle Darriwilian to late Darriwilian and Neseuretus tardus (Hammann, 1983) from the Darriwilian–Sandbian boundary and early Sandbian. Morphological characters of the cephalon and pygidium were determined that can definitively distinguish the three identified taxa. These results stem from both traditional and geometric (outline and landmark-based) morphometric analyses. The three taxa follow each other through time and constitute a morphological sequence that contributes to improving the stratigraphy of the Middle and Upper Ordovician.

Variation on cranidial shape ofParabolinella argentinensisKobayashi (Trilobita, Olenidae) from the Tremadocian of northwestern Argentina: taxonomic implications

“…In addition, those methods can distinguish between different sources of variation (e.g., Lawing and Polly, 2010). Thus, both classical and geometric morphometry proved to be a useful method to differentiate taxa (e.g., Hughes, 1994; Adrain and Westrop, 2006; Webster, 2009; Hopkins and Webster, 2009; Gendry et al, 2013; Pandey and Parcha, 2013). The use of geometric morphometry in systematic studies has increased in the past 10 years.…”

“…Geometric morphometry proved to be a useful method to distinguish interspecific disparity from intraspecific variation, leading to more robust species delimitation, diversity estimates, biostratigraphic correlation, and to detect evolutionary patterns in a phylogenetic context (e.g., Hughes, 1994; Hughes and Chapman, 2001; Crônier et al, 2005; Adrain and Westrop, 2006; Webster, 2007, 2009; Hopkins and Webster, 2009; Webster, 2011; Abe and Lieberman, 2012; Gendry et al, 2013). Landmark-based methods allow taxonomists to obtain additional characters of the shape of a particular structure that can help delimit taxa (e.g., Mutanen and Pretorius, 2007).…”

New Middle and Late Ordovician cornute stylophorans (Echinodermata) from Morocco and other peri-Gondwanan areas

“…Babin et al 1976;Chauvel & Nion 1977;Henry 1980;Vannier 1986a, b). This fauna was dated from the middle Darriwilian (Dw2, Didymograptus artus graptolite Zone; see Henry 1980;Gendry et al 2013) The four other cornute localities all occur stratigraphically in the upper part of the Traveusot Formation. Three of them (le Domaine, la Saudrais and Traveusot) form a geographic cluster, about 1.5 km W of the côte 85 locality and about 3 km E of Guichen (Fig.…”

Geometric morphometric assessment of Guanshan trilobites (Yunnan Province, China) reveals a limited diversity of palaeolenid taxa

“…Geometric morphometric analyses are powerful tools for assessing morphology (MacLeod, 2001(MacLeod, , 2002Webster and Sheets, 2010;Crônier et al, 2015;Webster, 2015;Pates et al, 2017;Monti, 2018;Bicknell, 2019;Bicknell and Pates, 2019;Bicknell et al, 2018Bicknell et al, , 2019b and can be more informative than traditional morphometrics (Zelditch et al, 2004;Aytekin et al, 2007). Landmark-based morphometrics have been effectively used to differentiate inter-and intra-specific variation in trilobites (e.g., Hopkins and Webster, 2009;Webster, 2011;Abe and Lieberman, 2012;Gendry et al, 2013;Esteve et al, 2017;Bicknell et al, 2019a) and semi-landmarks of cranidial shape allow taxonomically useful shapes to be thoroughly assessed. Here we use landmark and semi-landmark geometric morphometrics to explore cranidial shape in Megapalaeolenus deprati, Palaeolenus "lantenoisi," and P. douvillei and combine these results with the qualitative observation in thorax to suggest that only two taxa are valid.…”