Shell sculpture as a defensive adaptation in ammonoids

Paleobiology ◽  
1981 ◽  
Vol 7 (1) ◽  
pp. 96-100 ◽  
Author(s):  
Peter Ward
Keyword(s):  
Late Mesozoic ◽  
Hydrodynamic Efficiency ◽  
Defensive Function ◽  
Mesozoic Marine Revolution ◽  
Shell Sculpture

Quantification of Paleozoic, Triassic, Jurassic, and Cretaceous ammonoid shell ornamentation shows that commonality and roughness of ornamentation increased throughout the geologic range of the ammonoids. The two major hypotheses concerning the function of ammonoid shell ornamentation are that 1) ornament served a protective (defensive) function against shell breakage by predators, and 2) it increased hydrodynamic efficiency of the shell during swimming. The heavily ribbed and spined ammonoid shells of the late Mesozoic have ornamentation too coarse to have served any hydrodynamic purpose. The increasing proportion of such shells during the Jurassic and Cretaceous may have been in response to increased numbers of late Mesozoic shell crushing predators and “better armed” ammonoid prey. This trend parallels adaptive trends of other invertebrate groups during the “Mesozoic marine revolution” as defined by Vermeij (1977).

Is predation intensity reduced with increasing depth? Evidence from the west Atlantic stalked crinoidEndoxocrinus parrae(Gervais) and implications for the Mesozoic marine revolution

Paleobiology ◽  
1996 ◽  
Vol 22 (3) ◽  
pp. 339-351 ◽  
Author(s):  
Tatsuo Oji
Keyword(s):  
Shallow Water ◽  
The Other ◽  
The West ◽  
Bathymetric Range ◽  
Late Mesozoic ◽  
Predation Intensity ◽  
Stalked Crinoids ◽  
The Caribbean ◽  
Mesozoic Marine Revolution ◽  
Sublethal Predation

The number of regenerated arms was counted on specimens of two distinct phenotypes of the stalked crinoidEndoxocrinus parrae(Gervais) from a wide bathymetric range in the Caribbean (178-723 m). In one phenotype, the sample was divided into two groups, one from shallower (< 500 m) depths, the other from deeper (≥ 500 m); in the other phenotype the group divided at 550 m. In both phenotypes, the frequency of regenerated arms is significantly higher in specimens from shallower water than in those from deeper water. If the regenerated arms inEndoxocrinus parraewere the result of sublethal predation, as previously suggested, then predation intensity is higher in shallow water than deep water. These results are consistent with the idea of the late Mesozoic marine revolution—that there has been stronger predation on various invertebrates in shallow-water environments since the late Mesozoic. The stalked crinoids may have been unable to cope with increased predation in shelf environments, and they migrated to offshore environments.

Hydrodynamic properties of cephalopod shell ornament

Paleobiology ◽  
1976 ◽  
Vol 2 (4) ◽  
pp. 316-331 ◽  
Author(s):  
John A. Chamberlain ◽  
Gerd E. G. Westermann
Keyword(s):  
Boundary Layer ◽  
Maximum Efficiency ◽  
Hydrodynamic Effect ◽  
Swimming Ability ◽  
Sculptured Surfaces ◽  
Hydrodynamic Properties ◽  
Hydrodynamic Efficiency ◽  
Layer Flow ◽  
Visualization Experiments ◽  
Shell Sculpture

We investigated the hydrodynamic properties of cephalopod shell sculpture in two ways: 1) flow visualization experiments with sculptured shells; and 2) application of drag coefficient data for simple geometric bodies to cephalopod shells. Results of this work suggest:1) the hydrodynamic effect of shell sculpture depends primarily on the size of the sculptural elements relative to the size of the shell and on the positions of sculpture elements on the shell and relative to each other.2) sculpture is detrimental to swimming (reduces hydrodynamic efficiency) if it exceeds the height of the lower part of the shell's boundary layer.3) sculpture is advantageous to swimming (increases efficiency) if it remains immersed in the boundary layer and induces premature conversion to turbulent boundary layer flow. To be hydrodynamically optimal, small shells (diam ≈ 10 cm) must have rough (sculptured) surfaces, whereas large shells (diam ≈ 100 cm) require smooth surfaces. Thus, in order to maintain maximum efficiency throughout life, the ontogeny of small individuals, or species, should be characterized by progressive roughening of the shell, while large forms should become increasingly smooth. Such allometries are observed among many ammonoids.4) sculpture always has an effect on the flow around a cephalopod shell. In some species this effect was probably negligible, while in others, those with compressed shells especially, it was probably of major importance. In these species, sculpture appears to have functioned primarily to increase swimming ability.

Individual Differences in the Flexibility of Peripersonal Space

2017 ◽  
Vol 64 (1) ◽  
pp. 49-55 ◽  
Author(s):  
Samuel B. Hunley ◽  
Arwen M. Marker ◽  
Stella F. Lourenco
Keyword(s):  
Individual Differences ◽  
Peripersonal Space ◽  
The Body ◽  
Laser Pointer ◽  
Baseline Measure ◽  
Bisection Task ◽  
Defensive Function ◽  
Representational Space ◽  
Laser Condition ◽  
Line Bisection Task

Abstract. The current study investigated individual differences in the flexibility of peripersonal space (i.e., representational space near the body), specifically in relation to trait claustrophobic fear (i.e., fear of suffocating or being physically restricted). Participants completed a line bisection task with either a laser pointer (Laser condition), allowing for a baseline measure of the size of one’s peripersonal space, or a stick (Stick condition), which produces expansion of one’s peripersonal space. Our results revealed that individuals high in claustrophobic fear had larger peripersonal spaces than those lower in claustrophobic fear, replicating previous research. We also found that, whereas individuals low in claustrophobic fear demonstrated the expected expansion of peripersonal space in the Stick condition, individuals high in claustrophobic fear showed less expansion, suggesting decreased flexibility. We discuss these findings in relation to the defensive function of peripersonal space and reduced attentional flexibility associated with trait anxieties.

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