A new type of entombment of Peronopsis (Agnostida) in a hyolithid conch

Abstract

An enrolled exoskeleton of the holaspid specimen of a tiny agnostid Peronopsis integra (BEY-RICH, 1845) entombed inside a conch of the hyolithid ?Buchavalites sp. is described from the middle Cambrian (Drumian) Jince Formation of the Příbram-Jince Basin (Czech Republic). The agnostid is associated with an ichnofossil of the feeding trace classified as Arachnostega-type behaviour. The enrolled attitude of the agnostid exoskeleton suggests that the specimen is a carcass rather than moult. Either the storm disturbance and/or well-protected source of food hypotheses could explain the entombed agnostid. This additional example supports a benthic mode of life in the agnostid P. integra. The studied association of feeding tunnels of an unknown Arachnostega-strategist and Peronopsis preserved inside a hyolithid conch is a case of "frozen" behaviour.

The bivalved arthropod Tuzoia from the Balang Formation (Cambrian Stage 4) of Guizhou, China, and new observations on comparative species

“…; Wang et al . ; Conway Morris & Peel ; Mángano ; Fatka & Kozák ). Sinuous traces, for example, are common on skeletal animals (echinoderms, brachiopods, hyoliths, trilobites, etc.…”

Seven 365-Million-Year-Old Trilobites Moulting within a Nautiloid Conch

“…However, there are few advances in the study of the individual and social behaviours and survival strategy of trilobites, perhaps due to the scarcity of fossils that can reflect such processes. The cryptic behaviour of trilobites is an intriguing form of behaviour, which arose in the Cambrian 3 , mainly among tiny trilobites, such as Pagetia and Skreiaspis , and also agnostids that hid within the tubes of hyoliths and priapulids, or the exoskeletons of large polymerid trilobites 3 4 5 6 7 . Since the Ordovician, increasing numbers of predators, as well as the explosion of other competitive organisms that occupied similar ecological niches to trilobites, resulted in increased survival pressure on trilobites.…”

Coprolites in the Ravens Throat River Lagerstätte of Northwestern Canada: Implications for the Middle Cambrian Food Web

“…The outstretched agnostoids are taken to demonstrate that this is the normal feeding attitude, as implied by Fortey and Owens (1999) and suggested by individuals entombed in hyolith conchs, in priapulid tubes, and under paradoxidid trilobites (Chatterton et al 2003;Fatka et al 2009;Fatka and Szabad 2011;Fatka and Kozák 2014). This is in contrast to the notion based on phosphatized specimens pf Agnostus pisiformis in the Alum Shale of Sweden which have been taken to indicate they were planktic filter-feeders that kept their shields slightly agape (Eriksson and Horn 2017).…”