Early Molluscan Evolution: Evidence From the Trace Fossil Record

Abstract

For many organisms, chemoreception is critical for activities such as foraging, the detection of potential mates, and the avoidance of possible predators. The spatial pattern of odors, the odor landscape, is a function of the distribution of the odor sources and of fluid dynamics. Microscopic organisms, and probably most infaunal organisms, are in a physical realm where the detection of distant odor sources is controlled by diffusion and movement that takes place in response to chemical gradients. For larger organisms, chemical detection of distant sources is largely controlled by turbulence and thus by spatially and temporally complex odor plumes.An individual-based, spatially explicit movement model allows the examination of the importance of contact and distant chemoreception for foraging movements in spatially heterogeneous and patchy environments. Gain curves allow the importance of sensory range in settings of differing degrees of patchiness to be compared. As patchiness increases, distant chemoreception becomes increasingly important for efficient foraging.Movement patterns within patches are different from those between patches. The spatial distribution of resources, therefore, should be a major control of trace geometry.During the Ediacaran-Cambrian interval, the spatial complexity and patchiness of the marine odor landscape may have increased due to disruption of Neoproterozoicstyle microbially bound substrates and the packaging of biomass into spatially discrete carcasses and fecal pellets. At the same time, larger and non-infaunal mobile bilaterians would have entered a fluid regime dominated by turbulence. These changes may be partially responsible for the evolution of external bilateral sensory organs.

The Tommotian phase of the Early Cambrian Agronomic Revolution in the carbonate mud environment of central Siberia

“…Seilacher and Hagadorn () included the Early Cambrian Psammichnites in their proposed line of descendance of naked molluscs starting from the Ediacaran Kimberella (leaving also probable radular scratch marks), the Late Cambrian (Furongian) Climactichnites ‐ Musculopodus animal with radular scratches, and the mainly Carboniferous ‘ Aulichnites ‐ Olivellites ’ and Dictyodora (Mángano et al . ).…”

“…While feeding at the clay-lime interface with loop-forming behaviour, it did not strengthen the channel walls that were later filled with sediment from the clay layer. Seilacher and Hagadorn (2010) included the Early Cambrian Psammichnites in their proposed line of descendance of naked molluscs starting from the Ediacaran Kimberella (leaving also probable radular scratch marks), the Late Cambrian (Furongian) Climactichnites-Musculopodus animal with radular scratches, and the mainly Carboniferous 'Aulichnites-Olivellites' and Dictyodora (M angano et al 2002). There is a possibility that halkieriid molluscs were involved in production of the Siberian traces (Seilacher-Drexler & Seilacher 1999).…”

Possible evolution of mobile animals in association with microbial mats

“…Many of these interactions record animal grazing on biomats as a food resource. Examples of this include radular rasping at the top of fossil mats 6,[14][15][16] or systematic probing and mining at the base of fossil biomats 17,18 . By the dawn of the Cambrian period, back-filled undermat grazing burrows are comparably common.…”

Behaviors mapped by new geographies: Ichnonetwork analysis of the Val Dolce Formation (lower Permian; Italy-Austria)

“…9). Psammichnites is interpreted as the trace of an infaunal deposit feeder (probably a mollusc) with a snorkel-like device Seilacher, 2007;Seilacher and Hagadorn, 2010;Alonso-Muruaga et al, 2013). Psammichnites is a common component of the Psilonichnus and Cruziana ichnofacies, being reported from intertidal flats MacEachern et al, 2012).…”