Exoskeletal abnormalities in paradoxidid trilobites from the Cambrian of Spain, and a new type of bite trace

Abstract

Exoskeletal abnormalities in middle Cambrian paradoxidid trilobites from Purujosa (Eastern Iberian Chain, NE Spain) are herein analyzed for the first time. Two distinct types are reported. The first is represented by triangular or asymmetrical V-to W-shaped breaks on margins of isolated sclerites (cranidia, free cheeks and hypostomes). The second group is represented by shortened thoracic pleural spines in complete or nearly complete individuals. Possible causes of these injuries are discussed, but in some cases a single cause/effect explanation is not apparent. A new ichnotaxon, Mandibulichnus serratus nov. ichnogen., nov. ichnosp., is erected to refer to serrated breakage of the margins of isolated trilobite sclerites produced by active predation or scavenging.•

Abnormal xiphosurids, with possible application to Cambrian trilobites

“…Their exoskeletons were ideal protection against predators and recorded injuries from failed predation (Babcock, 2003;Zamora et al, 2011). As such, the record of potentially predatory injuries to Cambrian trilobites is extensively documented (see examples in Rudkin, 1979;Babcock, 1993Babcock, , 2007Pratt, 1998;Nedin, 1999;Fatka et al, 2008;Pates et al, 2017;Vinn, 2017;Bicknell and Paterson, 2018, table 1).…”

Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event

“…Oichnus, Trypanites, and Mandibulichnus are known from Cambrian strata (17)(18)(19)(20), the former being already present in Ediacaran strata (21). Two microbioerosion ichnogenera (Granulohyalichnus and Tubulohyalichnus) have their first occurrence in the Archean (22,23).…”

Quantitative Analysis of Repaired and Unrepaired Damage to Trilobites From the Cambrian (Stage 4, Drumian) Iberian Chains, Ne Spain

“…These two sites are geographically closer to each other than to Purujosa, where there is evidence for repaired injuries in the Drumian (see Figs. 1, 2; Table 1) and from other levels of the Purujosa 3 section (Table 1; Zamora et al 2011). This suggests a geographic rather than temporal cause for the difference in predation, although the absolute distances between these sites in the Cambrian would have been different than at present as the Iberian Chains have been subjected to substantial tectonic activity.…”

“…Trilobite abnormalities and repair have been attributed to predation, problematic molting, genetic malfunction, parasites, and accidental damage. The predation or scavenging trace fossil taxon Bicrescomanducator serratus (Zamora et al 2011) describes unrepaired damage on trilobite sclerites that consists of asymmetric V-or W-shaped serrated breakage of variable length, with a first-order path that is straight, or sometimes slightly arcuate (Zamora et al 2011;Buatois et al 2017). This trace can be seen on trilobite exoskeletons and fragments from the Cambrian Series 3 (Drumian) Purujosa 3 section of the Murero Formation, NE Spain (Zamora et al 2011, fig. 2), Cambrian Drumian (Marjuman) section of the Rabbitkettle Formation, SW Canada (Pratt 1998, figs.…”

“…This trace can be seen on trilobite exoskeletons and fragments from the Cambrian Series 3 (Drumian) Purujosa 3 section of the Murero Formation, NE Spain (Zamora et al 2011, fig. 2), Cambrian Drumian (Marjuman) section of the Rabbitkettle Formation, SW Canada (Pratt 1998, figs. 8-10), and the Ordovician Valongo Formation in Portugal (Sá and Gutiérrez-Marco 2015, fig. 12), and is attributed to Anomalocaris in the Cambrian and orthoceratids in the Ordovician (Zamora et al 2011;Sá and Gutiérrez-Marco 2015). Sá and Guitiérrez-Marco 2016; Buatois et al 2017), here we treat the differences between these bioerosion traces at the species level, and so use Bicrescomanducator serratus.…”