Abstract
Abstract. Articulated holaspid specimens of Placoparia Hawle and Corda, 1847 and Eoharpes Raymond, 1905 entombed inside cephalopod conchs and under the remains of large illaenid, asaphid, cyclopygid and dalmanitid trilobites from the Middle Ordovician Šárka Formation of the Prague Basin (Czech Republic) are described and discussed. Two such samples were also found in the overlying Dobrotivá Formation of Middle/Late Ordovician age. Four articulated juvenile exoskeletons of Placoparia preserved under a cephalon of the cyclopygid trilobite Degamella Marek, 1961 represent the first record of shelter strategy of non-holaspid trilobites. The sheltered preservation of trilobites could be explained by a hiding behaviour associated with the danger of predation, storm disturbances, seeking for food or high vulnerability after moulting. It is obvious that Placoparia and Eoharpes deliberately entered the restricted space under skeletal parts of large trilobites or inside cephalopod conchs. These exceptional finds provide a new insight in the life strategy of some Ordovician benthic trilobites and are classified as cases of “frozen” behaviour.
Highlights
We describe 16 examples with articulated specimens of two trilobite genera, namely the harpetid Eoharpes Raymond, 1905 and the pliomerid Placoparia Hawle and Corda, 1847, entombed under pygidial and cephalic shields of much larger asaphid and illaenid trilobites, as well as several specimens of both taxa preserved inside cephalopod shells
Fourteen samples from the Middle Ordovician Šárka Formation and two specimens from the overlying Dobrotivá Formation contain one to six trilobite exoskeletons preserved in the protected space inside of empty cephalopod conchs or under thorax, cephalic and pygidial shields of much larger disarticulated trilobites
Analyses of the level of articulation of trilobite exoskeletons in combination with their orientation, disposition, and placement makes it possible to conclude that the hidden trilobites deliberately entered shells of dead cephalopods for food, refuge, ecdysis, reproduction or lodging
Summary
Hiding (cryptic) behaviour of trilobites has been documented from Cambrian to Carboniferous fossil associations (e.g. Brett, 1977; Chlupác, 1996; Peder and Feist, 1998; Suzuki and Bergström, 1999; Davis et al, 2001; Chatterton et al, 2003; Chatterton and Fortey, 2008; Valent et al, 2008; Flick and Flick, 2009; Radwanski et al, 2009; Rakocinski, 2009; Fatka and Budil, 2014; Hsieh and Plotnick, 2020). Comparable behaviour was described in Cambrian agnostids (Chatterton et al, 2003; Fatka et al, 2009; Fatka and Szabad, 2011; Fatka and Kozák, 2014). This specific type of defensive strategy is supposed to be triggered by an increasing predation pressure connected with hunting activities of lobopods, diverse arthropods, cephalopods and gnathostome fishes Brachiopod and molluscan conchs and valves as well as trilobite exoskeletons show evidence of healed bite marks and peeling from the Cambrian onward, but with an increased frequency in the Devonian (Brett and Walker, 2002; cf. Bambach, 1999; Klug et al, 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
