6 research outputs found
Appendix. Morphological characteristics of Estherites jocelynae specimens
Measurements of the type series
The Orientation Of Strophomenid Brachiopods On Soft Substrates
Strophomenid brachiopods have long been interpreted as ‘‘snowshoe’’ strategists, with their flattened concavoconvex
valves providing resistance to foundering in very soft sediments. There has been a sharp difference of opinion in
whether the shells were oriented with their convex or their concave surface in contact with the sediment. This study, along
with independent evidence from sedimentology, ichnology, and morphology, indicates that the strophomenids lived with
their shells concave down (convex up). Experiments indicate the force required to push shells into soft cohesive muds is
much greater for the convex up than for the convex down orientation. Forces also increase with shell curvature. All
measured forces greatly exceed estimates of the downward force exerted by the weight of the shell, indicating that
foundering resistance may not have been the key functional requirement. Instead, a convex up orientation would have
provided resistance to overturning in currents, in particular if the valves gaped widely. The ‘‘snowshoe’’ may not be the
relevant paradigm for the shell morphology of these forms. An alternative is that they functioned more as a tip-resistant
base, similar to those of garden umbrellas or stanchions