Functional aspects of Placoid Scales: A review and update

Raschi, William; Tabit, Christopher R.

doi:10.1071/mf9920123

Cited by 131 publications

(161 citation statements)

References 12 publications

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“…The presence of keeled scales in P. kornhuberi (preserved along the hypaxial margin of the tail, above the ventral 'belly' scale row) suggests that within the clade Pythonomorpha, as reconstructed by Lee & Caldwell (2000), single-keeled scales may be the plesiomorphic condition. Still, the possibility that such a feature might arise convergently within mosasauroids finds strong support from the presence of multiple parallel keels that are structurally similar to the longitudinal ridges on the crown surface of the dermal denticles in pelagic sharks (see Raschi & Tabit 1992). We therefore see no reason to reject the idea that the constraints imposed by the hydrodynamic requirements of life in the water might have influenced the evolution of multiple-keeled body scales in advanced mosasauroids, such as Plotosaurus.…”

Section: Squamation and Aquatic Adaptations In Mosasaursmentioning

confidence: 85%

“…On the contrary, small-sized, multiple-keeled and possibly osteoderm-reinforced scales might have served multiple functions, not only by means of protection from rivals, predators and ectoparasites, but also as an efficient cover to reduce frictional drag when swimming. By comparison to modern sharks (Raschi & Tabit 1992), a longitudinal ridge and valley topography might have reduced microturbulent burst activities within the boundary layer of the water thereby impeding an energetically expensive separation by this layer from the skin of the mosasaur (see Walker & Liem 1994 for drag reduction in extant animals). Moreover, because keeled scales reduce shininess (Klauber 1997), these rugosities may have provided a dull and nonreflective appearance, thus facilitating concealment during predation.…”

Section: Squamation and Aquatic Adaptations In Mosasaursmentioning

confidence: 99%

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Skin of the Cretaceous mosasaur Plotosaurus : implications for aquatic adaptations in giant marine reptiles

Alwmark

Fiorillo

2009

Biol. Lett.

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The physical nature of water and the environment it presents to an organism have long been recognized as important constraints on aquatic adaptation and evolution. Little is known about the dermal cover of mosasauroids (a group of secondarily aquatic reptiles that occupied a wide array of predatory niches in the Cretaceous marine ecosystems 92-65 Myr ago), a lack of information that has hindered inferences about the nature and level of their aquatic adaptations. A newly discovered Plotosaurus skeleton with integument preserved in three dimensions represents not only the first documented squamation in a mosasaurine mosasaur but also the first record of skin in an advanced member of the Mosasauroidea. The dermal cover comprises keeled and possibly osteoderm-reinforced scales that presumably contributed to an anterior-posterior channelling of the water flow and a reduction of microturbulent burst activities along the surface of the skin. Thus, hydrodynamic requirements of life in the water might have influenced the evolution of multiplekeeled body scales in advanced mosasauroids.

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Section: Squamation and Aquatic Adaptations In Mosasaursmentioning

confidence: 85%

Section: Squamation and Aquatic Adaptations In Mosasaursmentioning

confidence: 99%

Skin of the Cretaceous mosasaur Plotosaurus : implications for aquatic adaptations in giant marine reptiles

Alwmark

Fiorillo

2009

Biol. Lett.

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“…1 & 2). Crowns can possess ridges of varying length, height, orientation, and spacing and may or may not terminate in an equal number of peaks (Tway 1979, Reif 1985a, Raschi & Musick 1986, Raschi & Tabit 1992 (Fig. 2).…”

mentioning

confidence: 99%

“…Crowns can possess ridges of varying length, height, orientation, and spacing and may or may not terminate in an equal number of peaks (Tway 1979, Reif 1985a, Raschi & Musick 1986, Raschi & Tabit 1992 (Fig. 2).Individual sharks possess multiple types of denticles arranged systematically along their bodies (Reif 1985a, Raschi & Tabit 1992, Bargar & Thorson 1995, Salini et al 2007, and denticle morphotypes can be shared across taxa (Reif 1982, Muñoz-Chápuli 1985a, Tanaka et al 2002, Gilligan & Otway 2011. Denticle morphology can also vary with sex (Crooks et al 2013) and ontogeny (Reif 1985a).…”

mentioning

confidence: 99%

“…Only in a few cases can isolated denticles be identified beyond the family level (Reif 1985a, Mello et al 2013, Ferrón et al 2014. Conversely, denticle morphology appears to be more closely linked to the ecological guild of the shark species to which it belongs as well as to the specific function it plays on the shark's body (Reif 1978, 1985b, Raschi & Musick 1986, Raschi & Tabit 1992.Five major functional groups of dermal denticles have thus far been established: (1) drag reduction, (2) abrasion strength, (3) defense, (4) luminescence and (5) generalized functions (Reif 1982, 1985b, Raschi & Tabit 1992. In general terms, fast, pelagic sharks are covered almost entirely by thin, highly ridged drag reduction denticles, while demersal sharks possess thick, smooth abrasion strength denticles that provide protection from the substrate (Reif 1985a, Raschi & Tabit 1992.…”

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Dermal denticles as a tool to reconstruct shark communities

Dillon¹,

Norris²,

O’Dea³

2017

Mar. Ecol. Prog. Ser.

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The last 50 yr of fisheries catch statistics and ecological surveys have reported significant decreases in shark populations, which have largely been attributed to human activities. However, sharks are challenging to census, and this decline likely pre-dated even the longest fishery-dependent time series. Here we present the first use of dermal denticles preserved in reef sediments as a novel tool to reconstruct shark communities. We first built a dermal denticle reference collection and conducted a morphometric analysis of denticle characters to relate denticle form to taxonomy, shark ecology, and denticle function. Denticle morphology was highly variable across the body of an individual shark and between taxa, preventing species-or genus-level identification of isolated denticles. However, we found that denticle morphology was strongly correlated with shark ecology, and morphometric analysis corroborated existing functional classifications. In a proof of concept, we extracted 330 denticles from modern and fossil reef sediments in Bocas del Toro, Panama and found them to be morphologically diverse and sufficiently well-preserved to allow classification. We observed a high degree of correspondence between the denticles found in the sediments and the sharks documented in the region. We therefore propose that (1) denticle assemblages in the recent fossil record can help establish quantitative pre-human shark baselines and (2) time-averaged denticle assemblages on modern reefs can supplement traditional surveys, which may prove especially valuable in areas where rigorous surveys of sharks are difficult to perform.KEY WORDS: Dermal denticle · Functional morphology · Shark · Paleoecology · Baseline 566: 117-134, 2017 diurnal and seasonal movement patterns prevent sharks from being meaningfully censused in many regions (Sale & Douglas 1981, MacNeil et al. 2008, Ward-Paige et al. 2010a, McCauley, et al. 2012a. Time series or replicated surveys have also shown conflicting trends for the same area depending on the survey method used and its associated biases (Burgess et al. 2005, Ward-Paige, et al. 2010a, Nadon et al. 2012, leading to misrepresentations of the status of shark populations and their unfished baseline conditions (Heupel et al. 2009, Rizzari et al. 2014. Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerTo address this problem, we explored whether dermal denticles, the small, tooth-like scales covering the skin of nearly all elasmobranchs ( Fig. 1), can be used as a tool to reconstruct shark communities on coral reefs. Denticles are several orders of magnitude more abundant than teeth on a living shark and are continually shed (Reif 1985a, Compagno et al. 2005. Like teeth, denticles preserve well and have a long fossil record (Janvier 1996, Sansom et al. 2012, po tentially providing a unique opportunity to retrospectively 'survey' modern and pre-exploitation shark assemblages. In this paper, we (1) review denticle morphology, taxonomy, and function; (...

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