Architecture of the integument in lower teleostomes: Functional morphology and evolutionary implications

Abstract

A bony ganoid squamation is the plesiomorphic type in actinopterygians. During evolution, it was replaced by weak and more flexible elasmoid scales. We provide a comparative description of the integument of "ganoid" fishes and "nonganoid" fishes that considers all dermal components of mechanical significance (stratum compactum, morphology of ganoid scales, and their regional differences) in order to develop a functional understanding of the ganoid integument as a whole. Data were obtained for the extant "ganoid" fishes (Polypteridae and Lepisosteidae) and for closely related "lower" actinopterygians (Acipenser ruthenus, Amia calva) and "lower" sarcopterygians (Latimeria chalumnae, Neoceratodus forsteri). Body curvatures during steady undulatory locomotion, sharp turns, prey-strikes, and fast starts in "ganoid" fishes were measured from videotapes. Extreme body curvatures as measured in anesthetized specimens are never reached during steady swimming, but are sometimes closely approached in certain situations (sharp turns, prey-strike). During extreme body curvatures we measured high values of lateral strain on the convex and on the concave side of the body. Scale overlap changes considerably (66-127% in Lepisosteus, 42-140% in Polypterus). The ganoid squamation forms a protective coat, but at the same time it permits extreme body curvatures. This is reflected in characteristic morphological features of the ganoid scales, such as an anterior process, concave anterior margin, and peg-and-socket articulation. These characters are most pronounced in the anterior body region, where maximum changes in scale overlap are required. The anterior processes and anterior concave margin, together with the attached stratum compactum, guide movements in a horizontal plane during bending. Displacements of scales relative to each other are possible for scales of different scale rows, but are impeded in scales of the same scale row due to the peg-and-socket articulation. Furthermore, ganoid scale rows, fibers of collagen layers of the stratum compactum, and the lateral myoseptal structures follow the same oblique orientation, which is needed to achieve extreme body curvatures. There is no evidence that body curvatures are limited by the ganoid squamation in Polypterus or Lepisosteus to any larger extent than by a type of integument devoid of ganoid scales in teleostomes of similar body shape. Our results essentially contradict former functional interpretations: 1) Ganoid scales do not especially limit body curvature during steady undulatory locomotion; 2) They do not act as torsion-resisting devices, but may be able to damp torsion together with the stratum compactum and internal body pressure.

Insights into an Early Jurassic dinosaur habitat: ichnofacies and enigmatic structures from the Portland Formation, Hoover Quarry, Massachusetts, U.S.A.

“…Hartford Basin fish include semionotids and diplurid coelacanths (Olsen et al 1992;McCune 1996). Semionotids have heavy ganoid scales, but they are generally rhomboid in shape (Gemballa and Bartsch 2002;McCune 2004). Diplurid scales are ovate to elliptical, may possess radiating ridges, and are covered in finer striae that terminate in a centrally located, occasionally raised focus (Schaeffer 1952).…”

Scale development in fish: a review, with description of sonic hedgehog (shh) expression in the zebrafish (Danio rerio).

“…Alizarin red staining of juvenile zebrafish has revealed that scale appearance is neither related to size nor to age alone, but to a combination of both (Sire et al, 1997a). and their organisation suggests that they can exert traction forces upon the skin (Gemballa and Bartsch, 2002;Gemballa and Vogel, 2002). The vertical collagen bundles that form in the primary dermal stroma long before scale initiation could be related to the anchoring of the myoseptal tendons, and could thus participate in skin patterning.…”

The Relationship Between Cephalic Scales and Bones in Lizards: A Preliminary Microtomographic Survey on Three Lacertid Species

“…Such changes are supposed to influence the biomechanical distribution of biting forces, characterizing the different figures recorded for small and large species (Herrel et al, 2004). Mechanical properties of the integument vary in different regions and can be modulated by the internal pressure exerted by the underlying structures (e.g., Wainwright et al, 1978;Hebrank, 1980;Gemballa and Bartsch, 2002;Rivera et al, 2005). To our knowledge, there is no data on the mechanical properties of frontoparietal scales in lizards, but larger fronto-parietal scales could serve as protective shell for the underlying fronto-parietal suture.…”

“…To our knowledge, there is no data on the mechanical properties of frontoparietal scales in lizards, but larger fronto-parietal scales could serve as protective shell for the underlying fronto-parietal suture. Gemballa and Bartsch (2002) suggested that ganoid scales in fishes may be able to damp torsion together with the stratum compactum and internal body pressure. Considering the significance of the fronto-parietal region in the mechanics of the Lacertids and Podarcis (and, in general, of squamates), fronto-parietal scales may play a role in damping the strain generated during biting or other activities in this region.…”