Paleoecology of a large Early Cambrian bioturbator

Abstract

The Lower Cambrian Poleta Formation in the White‐Inyo Mountains of eastern California contains well‐preserved and laterally extensive exposures of the large looping and meandering trace fossil Taphrhelminthopsis nelsoni n.isp. Such traces are typical features on upper bed surfaces of Lower Cambrian shallow marine sandstones and occur with Ediacaran fossils at other localities. Morphologic, sedimentologic and goniogram analyses suggest that the inferred tracemaker was a large soft‐bodied echinozoan‐ or mollusc‐grade animal with a volume greater than 14 cm 3 that actively grazed or ingested sediment at the sediment‐water interface. Although portions of these traces appear to reflect relatively ‘complex’ behavior, looping patterns are not periodic as expected for a systematic foraging strategy. T. nelsoni traces are patchy in distribution and commonly associated with suspect‐microbial features, suggesting that tracemakers may have been targeting microbial‐based or related concentrations of food resources. Such behavioral patterns are typical of shallow late Neoproterozoic‐early Cambrian settings, and like suspect‐microbial structures are later restricted to deep marine or stressed settings.

When Life Got Smart: The Evolution of Behavioral Complexity Through the Ediacaran and Early Cambrian of NW Canada

“…The continued presence of microbial grazers of the Helminthopsis ichnoguild, and rare Ediacaran-aspect discs implies that microbial mats still existed in patches, while the presence of deposit feeders and filter-feeders imply the increasing presence of a firmground/mixground (Buatois and Mángano, 2011a;Mángano et al, 2012). Larger Cambrian grazing burrows, such as Psammichnites, probably also targeted these microbial patches for food resources (Hagadorn et al, 2000;Buatois and Mángano, 2011a). The tighter meandering patterns exhibited in these larger burrows is consistent with the presence of a patchy resource environment.…”

Behavioral biology of trace fossils

“…For example, a trilobite that produces a resting trace (Rusophycus) and then transitions into a directed locomotion trace (Cruziana) has engaged in three distinct behaviors. Hagadorn et al (2000) illustrated examples of the Cambrian form Taphrhelminthopsis that have both meandering and looping movement phases. Alternating walking (Stiaria) and jumping (Tonganoxichus) by Permian apterygote insects was documented by Minter and Braddy (2006), with the jumping possibly a response to predator threat.…”

“…Some of these methods and models can be applied to the analysis of ancient paths, but there are limitations, in particular for surface movement paths. The first of these is that most are only short samples of the extended path; it is relatively rare to be able to map a large path (see Hagadorn et al 2000). A more important limitation is the lack of absolute temporal data.…”

“…The inferred steps are thus equal length, rather than equal time divisions of the path. This was the approach used by Kitchell (1979), Hofmann (1990), and Hagadorn et al (2000). The choice of discretization interval can directly affect the values of descriptive metrics (Benhamou 2004).…”

Efficient search of multiple types of targets

“…Consider, for example, animal foraging. Though homogeneous habitats can be found in distinct situations, different extents of heterogeneity and fragmentation in the spatial distribution of resources are reportedly much more frequent [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. In particular, whereas some kinds of patchy distributions display typical scales [12][13][14][15][16][17][18][19][20], other aggregate forms [21][22][23][24][25][26][27] suggest a hierarchical structure consistent with a scale-free fractal pattern.…”