Redescription, paleogeography, and experimental paleoecology of the Silurian phyllocaridGonatocaris

Abstract

AbstractGonatocaris decora(Clarke, 1901) is an unusual, highly ornamented Silurian phyllocarid from the Pittsford Shale Member of the Vernon Formation, Salina Group of New York, that has been allied withEmmelezoein the past due to the possession of an ‘optic tubercle.’ The systematic positions ofGonatocarisandEmmelezoehave been difficult to assess due to the lack of complete remains, attributions based on spurious characters, and missing and unfigured specimens. Relatively recent collections ofGonatocaris decora, along with a relocation of the original type material ofEmmelezoe, have allowed a reexamination of all relevant genera and a more robust systematic placement forG. decora. Characters of generic importance forGonatocarisinclude a greatly elongated abdomen; an acute angle of the ventral carapace margin separating distinct anteroventral and posteroventral margins from each other; and distinctive, multiscale horizontal ridge-like ornament of the carapace valves. Growth was found to be isometric. Experimental work done using a model of the scale-like ornament and multiple grain sizes of substrate indicates that cuticle ornament may have served to increase friction between the animal and a fine sand substrate, although resistance to predation is the currently favored hypothesis. BecauseGonatocarisspecies are currently known only from the eastern margin of Laurentia and northern South China, it is likely that this genus was nektonic. Accumulations of similarly sized carapaces and other disarticulated sclerites in shallow-water settings may indicate spawning events following molting en masse.