Bivalve borings in Lower JurassicLithiotisfauna from northeastern Italy and its palaeoecological interpretation

Abstract

Random shell sections of the Pliensbachian (Early Jurassic) larger bivalve Opisoma from columns within the Main Post Office building of Ferrara, northern Italy, have been discovered to bear neat clavate-shape boreholes. These boreholes belong to the ichnogenus Gastrochaenolites Leymerie and represent bivalve borings. Opisoma is a subordinate component of the Lithiotis fauna characterised by aberrant shells thriving in tropical lagoonal settings which were widespread throughout the Tethyan and Panthalassa coasts. Although the Lithiotis fauna is well known in the palaeontological literature, no bivalves boring have been so far been formally described. The uniqueness of the morphology, size and substrate of these borings merits the designation of the new species Gastrochaenolites messisbugi ichnosp. nov. which thereby represents the first ichnospecies described from this fauna. The morphology of the boreholes and the included bivalves allows the boring activity to be ascribed to a mytilid bivalve. Palaeoecological and taphonomic analyses allowed the presence of the boreholes to be correlated to the Opisoma mode of life (epifaunal, free-living form) as well as to generally low sedimentation rates and seasonal mesotrophic conditions during an overall oligotrophic regime

Distinguishing core and flank facies based on shell fabrics in Lower Jurassic lithiotid shell beds

“…This suggests that (1) sedimentation rates were high enough to hamper encrusting epifauna and bioeroding endofauna and (2) parautochthonous to allochthonous lithiotid shells, which could have been exposed for longer, to show increased encrustation and bio-erosion. The only detailed study on the occurrence of bioerosion in a member of the lithiotid fauna suggested seasonal or temporal mesotrophic conditions within an overall oligotrophic regime as a factors for this rare occurrence in Pliensbachian larger bivalves (Bassi et al, 2017).…”

Palaeoecology of Chondrodonta (Bivalvia) from the lower Aptian (Cretaceous) Apulia Carbonate Platform (Gargano Promontory, southern Italy)

“…The Mesozoic cementers predominantly inhabited shallow water environments, where some gregarious forms (e.g., lithiotids, rudists, oysters) originated highly dense aggregates (bivalve mounds, reefs, pavements, carpets), influencing the sedimentation rates and carbonate platform dynamics (e.g., Fürsich et al, 1994;Gili et al, 1995;Riding, 2002;Fraser et al, 2004;Skelton and Gili, 2012;Harper, 2012;Posenato and Masetti, 2012;Bassi et al, 2017). Despite the high abundance, widespread geographic diffusion and long-time ranging distribution, little is known about the functional morphology of the shell, taphonomy and geometries of the Chondrodonta accumulations.…”

Drilling predation on Early Jurassic bivalves and behavioral patterns of the presumed gastropod predator—evidence from Pliensbachian soft-bottom deposits of northern Germany

“…Drill holes in fossil shells and other hard substrates from the Lower Jurassic may have had different origins and served different purposes. For example, domichnia were previously reported from the Lower Jurassic, made by bivalves on epifaunal bivalves ( Gastrochaenolites ; Bassi et al 2017) and by acrothoracid barnacles on hard substrates ( Rogerella ) from the Amaltheenton Formation (Keupp and Schweigert 2021). The drill-hole characteristics in the studied specimens—the shape of the drill holes ( Oichnus paraboloides ), the presence of boreholes on shells of infaunal taxa, and the concentration of holes on certain sites (site selectivity)—do not support their interpretation as domichnia.…”