The Paradoxides puzzle resolved: the appearance of the oldest paradoxidines and its bearing on the Cambrian Series 3 lower boundary

The Burlingiidae (Trilobita): revised generic composition, stratigraphy, and the first species from the early Middle Cambrian of West Gondwana

“…Jbel Wawrmast Formation, Brèche à Micmacca Member; M. notabilis Zone, Agdzian Stage (Cambrian Stage 4-Stage 5 boundary interval) (see Geyer et al 1995 andVincent 2014 for details).…”

“…The lower part of the Jbel Wawrmast Formation at Bou Tiouit is characterized by five shoaling-up sequences (Heldmaier 1998;Geyer & Vincent 2014). It is interesting that the quarries for the commercially exploited giant trilobites Cambropallas telesto and Acadoparadoxides briareus (see Geyer et al 1995) are located in the extraordinarily thick, lowest energy depositional settings of these shoaling-up sequences.…”

“…This zone is part of the West Gondwana Agdzian stage and Celtiberian series (Fig. 1) and has been shown to be lower, but not lowest part of the "Middle Cambrian" in a traditional Acadobaltic definition based on the occurrence of the genus Paradoxides in broad sense (Geyer & Landing 2004;Geyer & Vincent 2014). It should also be emphasized that the level with S. vincenti suggests a fairly good correlation with the FAD of O. granulata, which is a prime candidate for defining the base of a global Series 2 -3 and Stage 4-5 boundary (e.g.…”

Buenellus chilhoweensisn. sp. from the Murray Shale (lower Cambrian Chilhowee Group) of Tennessee, the oldest known trilobite from the Iapetan margin of Laurentia

“…Sequence stratigraphic data might also prove useful in this endeavor. For example, attempts have been (and continue to be) made to correlate the late Dyeran "Hawke Bay Regression" around Laurentia and further afield (e.g., Palmer and James, 1979;Palmer, 1981;Landing et al, 2002Landing et al, , 2006Bordonaro, 2003;Landing, 2012;Geyer and Vincent, 2015;Webster and Landing, 2016). Sequence stratigraphic interpretations and sometimes sea level curves are being developed for Montezuman and lower Dyeran strata of both the Iapetan (Whisonant, 1974;Mack, 1980;James et al, 1989;Barnaby and Read, 1990;Lavoie et al, 2003;Landing, 2007Landing, , 2012Tull et al, 2010;see above) and Cordilleran margins (Hollingsworth 2005(Hollingsworth , 2007(Hollingsworth , 2011Dilliard et al, 2007Dilliard et al, , 2010English and Babcock, 2010;Webster and Bohach, 2014).…”

Paradoxidid trilobites from a mid-Cambrian (Series 3, stage 5) limestone concretion from Jämtland, central Sweden

“…Various workers have attempted to group the numerous species into genera or subgenera, as listed by Dean & Rushton (1997), but those attempts have not met with general acceptance. Difficulties have been highlighted by Geyer & Landing (2000), Fletcher et al (2005) and Geyer & Vincent (2014); these include the incomplete knowledge of the exoskeleton of several species, a general lack of knowledge of the ontogeny in most species, and the difficulty of distinguishing convincing apomorphic features that could enable the characterisation of natural clades. We agree with the observation by Geyer (1993) that a paradoxidid species cannot well be characterised without knowledge of, at the least, the whole cranidium and the associated pygidium, and in the present paper we also draw attention to features of the thorax.…”