The trouble with flippers: a report on the prevalence of digital anomalies in Cetacea

Abstract

The forelimbs of cetaceans (whales, dolphins, and porpoises) are unique among mammals as the digits exhibit hyperphalangy, and the entire limb is encased in a soft tissue flipper that functions to generate lift. The typical morphology of cetacean digits has been well documented by detailed anatomical studies. This study however furthers our understanding of cetacean forelimb anatomy by conducting a taxonomically broad survey of cetacean digital anomalies. Forelimb radiographs from museum collections provided the basis upon which we calculated the prevalence and documented the morphology of cetacean digital abnormalities. Results indicated that 11% (n = 255) of toothed whales displayed some type of aberrant ossification: the majority of these cases displayed a fusion of elements within a single digital ray, whereas cases exhibiting branched digits were rare. A small sample of baleen whale radiographs (n = 6) contained the only documented case of baleen whale polydactyly in a specimen of the gray whale (Eschrichtius). Furthermore, some Balaenoptera specimens displayed ossified elements within the interdigital spaces that lacked attachment to the adjacent digits and carpus. In addition, we speculated on the role that several genes may have played in creating cetacean digital anomalies.

Evolutionary and developmental aspects of phalangeal formula variation in pig-nose and soft-shelled turtles (Carettochelyidae and Trionychidae)

“…A number of studies have focused on the morphology, functional diversity, and evolution of chelonian autopods, but only a few extant species distributed among diverse clades have been studied (Carettochelyidae : Walther 1922;Chelidae: Fabrezi et al 2009, Sánchez-Villagra et al 2007aCheloniidae: Sánchez-Villagra et al 2007b;Chelydridae: Rieppel 1993; Emydidae: Rosenberg 1892, Sheil andPortik 2008;Geoemydidae: Fritz et al 2006, Ludwig et al 2007; Pelomedusidae: Sánchez-Villagra et al 2007a;Podocnemididae: Fabrezi et al 2009;Testudinidae: Auffenberg 1966, Bramble 1982, Crumly and Sánchez-Villagra 2004, Hitschfeld et al 2008Trionychidae: Ogushi 1911, Sheil 2003general: Baur 1892, Burke and Alberch 1985, Rabl 1910, Walker 1973, Zug 1971. By contrast, much is known about the mechanisms of limb development, including those of the skeletal elements in autopods (Cooper and Dawson 2009;Fröbisch 2008;Gilbert 2006;Richardson et al 2009;Shapiro et al 2007;Wagner and Larsson 2007), suggesting autopod evolution as an attractive system for studying the diversification of function and development in the limbs. In this context, examination of variation among taxa and within populations can be useful (Stern 2000).…”

Ichthyosaurian palaeopathology: evidence of injury and disease in fossil ‘fish lizards’

“…osteoarthritis/osteoarthrosis) (Lingham-Soliar, 2004;Rothschild, 2012). Alternatively, osteological pathologies can result from other factors causing mechanical or physiological stress (Kompanje, 1999;Rothschild & Martin, 2006;Cooper & Dawson, 2009).…”

Case Report of Flipper Anatomic Anomaly of Sotalia guianensis From Sepetiba Bay, Rio de Janeiro

“…In general, digital anomalies are poorly detected and studied because the interdigital membrane in the cetacean flipper masks underlying skeletal anomalies (Cooper and Dawson, 2009). Flipper pathologies can result from developmental or acquired circumstances.…”

“…The loss or duplication of bone elements may be caused by alterations in genes or developmental pathways in the presence of a teratogen, for instance. Whereas acquired conditions can show different features and are result of traumas, degenerative, or metabolic disease (Cooper and Dawson, 2009). There are studies on genes involved in the flipper development and the hypothesis to the evolution toward hyperphalangy, polyphalangy, and cases of polydactily (Bejder and Hall, 2002;Richardson and Oelschl€ ager, 2002;Cooper et al, 2007;Cooper and Dawson, 2009), but no reports of infranumerary digits or phalanges.…”