Ammonoid Locomotion

Evolutionary Patterns of Ammonoids: Phenotypic Trends, Convergence, and Parallel Evolution

“…Although hydrodynamic capabilities of these extinct animals are impossible to measure, it appears reasonable to assume that they were no enduring high-speed swimmers (Chamberlain 1980;Jacobs 1992). This interpretation is corroborated by mechanical experiments on shell models and analytical calculations of shell hydrodynamics (Chamberlain 1976(Chamberlain , 1980Saunders and Shapiro 1986;Elmi 1991Elmi , 1993Jacobs 1992;Jacobs and Chamberlain 1996;Seki et al 2000;De Blasio 2008;Naglik et al 2015), as well as by analogy with recent nautilids (the only extant cephalopod with a chambered external shell ;Ward 1988;Jacobs and Landman 1993). It has been widely demonstrated that, for shells with oxyconic shell shapes (involute and compressed), the energy consumption for swimming is the lowest and potential maximal swimming speed is the highest (decreasing drag, increasing streamlining, etc.…”

“…By contrast, the widespread adaptive interpretations of the ammonoid conch are ad hoc explanations in many cases, partially because their behavior cannot be observed (e.g., swimming speeds, habitat depths, vertical movements; compare Ritterbush et al 2014, Naglik et al 2015. This is a common problem in paleontology (Ebbighausen and Korn 2013), strongly limiting the range and number of falsifiable hypotheses.…”

“…It has been widely demonstrated that, for shells with oxyconic shell shapes (involute and compressed), the energy consumption for swimming is the lowest and potential maximal swimming speed is the highest (decreasing drag, increasing streamlining, etc. ; Schmidt 1930;Raup 1967;Chamberlain 1976Chamberlain , 1980Chamberlain and Westermann 1976;Jacobs 1992;Jacobs and Chamberlain 1996;Hassan et al 2002;Klug and Korn 2004;Klug et al 2008;Naglik et al 2015). Increased involution of the shell therefore appears to represent an adaptation toward improved hydrodynamic properties of the shell ( Fig.…”

“…5.5,5.8) morpho-functional explanations. With regard to trends of increasing involution, it may well result solely from an increase in body size, and not directly from a selection pressure on the coiling itself and its associated swimming advantage; increase in body size may itself be a swimming-related factor, because it provides the possibility for a larger volume of propulsive muscles and hydrodynamic properties change with body size as well (Naglik et al 2015). Therefore, some conclusions on improved hydrodynamics of the shell may be speculative and represent secondary adaptations (Gould and Lewontin 1979; but see Levinton 2001).…”

“…But it must be acknowledged that environmental parameters (e.g., bathymetry, temperature) are usually difficult to assess and quantify in the past and in most cases, evidence for the ammonoids' actual habitats is weak because they might have lived anywhere in the water column above where they are found (De Baets et al 2015) and their shells could easily be transported (Wani and Gupta 2015). Nevertheless, some indication of their habitat can be constrained by combining multiple lines of evidence (Ritterbush et al 2014;Naglik et al 2015), including predator-prey interactions (e.g., Keupp 2006;Kruta et al 2011;Hoffmann and Keupp 2015;Tanabe et al 2015) and stable isotopes of their shells (e.g., Lécuyer and Bucher 2006;Lukeneder et al 2010;Lukeneder 2015). Interestingly, the co-occurrence in time of different evolutionary trends leading to very disparate co-existing morphologies may reflect the existence of multiple adaptive peaks in the ammonoid phenotypic landscape and/or that the triggers of these trends are not global and not only adaptive.…”