Pseudagnostus rugosusErgaliev, 1980: a key agnostoid species for intercontinental correlation of upper Furongian (Cambrian) strata

Abstract

Pseudagnostus rugosusErgaliev, 1980 is described from the FurongianCtenopyge tumidaZone at Gislövshammar, Scania, southern Sweden. This is the first record of this distinctive agnostoid in Scandinavia. The species is known previously from Malyi Karatau, Kazakhstan, and northwestern Hunan and western Zhejiang, South China, and provides a newly recognized link between middle–upper Furongian successions in Baltica, Kazakhstan and South China. The occurrences ofP. rugosusallow a correlation between theC. tumidaZone of Baltica, the lowerEolotagnostus scrobicularis–JegorovaiaZone of Kazakhstan and the lowerLotagnostus americanusZone of South China.

Intraspecific variation and taphonomic alteration in the Cambrian (Furongian) agnostoid Lotagnostus americanus: new information from China

“…This view contrasts with evidence published by many specialists, who have long noted that many agnostoids have similar morphologies and similar ranges of morphology in collections made from widely separated areas of the world (e.g. Daily & Jago 1975;Rushton 1978;Ergaliev 1980Ergaliev , 1983Lu & Lin 1980Robison 1982Robison , 1984Robison , 1994Shergold et al 1990;Peng 1992;Pratt 1992;Shergold & Laurie 1997;Peng & Robison 2000;Ahlberg 2003;Choi et al 2004;Peng et al 2004Peng et al , 2009Peng et al , 2012cPeng & Babcock 2005;Babcock et al 2007;Jago & Cooper 2007;Lazarenko et al 2008aLazarenko et al , b, 2011Terfelt & Ahlberg 2010;Terfelt et al 2011;Ahlberg & Terfelt 2012). Evidence of species that were broadly distributed in open-shelf lithofacies accords well with the interpretation that many agnostoids, at least in their juvenile stages, were nektic or pelagic.…”

The Lawsonian Stage - the Eoconodontus notchpeakensis FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage

“…We do not base the GSSP of Stage 10 on the FAD of a rare, taxonomically problematical species (e.g., Terfelt & Ahlberg 2010), but rather on a taxonomically "non-controversial" conodont which is readily identified. In addition, we did not select a species that is characteristically so highly habitat-limited (i.e., limited to primarily dysoxic facies as most agnostoids) that it precludes precise correlations onto the extensive, oxygenated platforms of the terminal Cambrian.…”

“…By comparison, the genus comes from dysoxic, mudstone-dominated, middle Upper Cambrian shelf facies in North American and British Avalon and Baltica (e.g., Landing 1996, Schovsbo 2001, Terfelt & Ahlberg 2010. Other occurrences of "L. americanus" sensu are from habitats that have been interpreted as or (in the earlier literature) show lithologic features consistent with the lowoxygen habitats of outer shelf/ramp or slope facies.…”

“…2); the lower part of this interval was subsequently recast as the "L. americanus Zone" by Terfelt et al (2008) and Terfelt & Ahlberg (2010). As noted by Ahlberg (2003), agnostoids show low diversity and are not abundant in the Swedish Furongian.…”

“…An interpretation that Terfelt & Ahlberg's (2010) "L. americanus" has a diachronous FAD is suggested by Pseudagnostus rugosus Ergaliev, 1980, which is stated to occur in the lower-middle part of their "L. americanus" Zone in Baltica, Kazakhstan, and South China. Although Terfelt & Ahlberg (2010) stated that this helped demonstrate the biostratigraphic significance of "L. americanus", they could not explain a report of P. rugosus in older strata of the Eolotagnostus decorus Zone (i.e., upper Jiangshanian Stage) in South China. This uncertainty may reflect an anomalously low range of P. rugosus or the possibility of the higher range of a Lotagnostus FAD in Asian successions.…”