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Steno bredanensis (rough-toothed dolphin)

Mammalia - Artiodactyla - Delphinidae

Taxonomy
Delphinus bredanensis was named by Lesson (1828). It is extant.

It was synonymized subjectively with Steno rostratus by Gray (1846); it was synonymized subjectively with Steno frontatus by Trouessart (1898); it was recombined as Steno bredanensis by Miller and Kellogg (1955), Scheffer and Rice (1963), Hershkovitz (1966), Barnes (1977), Vidal (1991), Rice (1998), Mead and Brownell (2005), West et al. (2011) and Perrin et al. (2013).

Synonyms
Synonymy list
YearName and author
1828Delphinorhynchus santonicus Lesson
1828Delphinus bredanensis Lesson
1829Delphinus bredanensis Fischer p. 505
1829Delphinus planiceps Van Breda p. 236 figs. Pl. 1, 2
1841Sotalia santonicus Lesson p. 15 figs. Pl. 2, Fig. 1, 2
1841Delphinus reinwardtii Schlegel p. 27
1841Delphinus chamissonis Wiegmann p. 359
1843Delphinus compressus Gray p. 105
1846Delphinus compressus Gray p. 17
1846Steno compressus Gray p. 17
1846Steno fuscus Gray p. 44 figs. Pl. 26, Fig. 1
1850Delphinus oxyrhynchus Gray
1850Steno compressus Gray p. 128
1850Delphinus oxyrhynchus Gray p. 131
1850Steno fuscus Gray p. 131
1866Steno compressus Gray p. 213
1866Steno fuscus Gray p. 239
1868Steno compressus Gray p. 4
1868Steno fuscus Gray p. 5
1876Delphinus perspicillatus Peters p. 360
1889Steno perspicillatus True p. 25
1898Sotalia santonicus Trouessart p. 1027
1898Steno perspicillatus Trouessart p. 1029
1904Sotalia santonicus Trouessart p. 763
1904Steno perspicillatus Trouessart p. 764
1955Steno bredanensis Miller and Kellogg
1963Steno bredanensis Scheffer and Rice p. 7
1966Steno bredanensis Hershkovitz p. 16
1977Steno bredanensis Barnes p. 323 figs. Table 1
1991Steno bredanensis Vidal p. 5
1998Steno bredanensis Rice p. 102
2005Steno bredanensis Mead and Brownell p. 734
2011Steno bredanensis West et al. p. 177
2013Steno bredanensis Perrin et al. p. 571 figs. Table 1

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
subphylumVertebrata
superclassGnathostomata
Osteichthyes()
Sarcopterygii
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda()
Reptiliomorpha
Anthracosauria
Batrachosauria()
Cotylosauria()
Amniota
Synapsida()
RankNameAuthor
Therapsida()
infraorderCynodontia()
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
orderArtiodactyla()
Cetacea()
Pelagiceti
Neoceti
Odontoceti()
infraorderDelphinida
superfamilyDelphinoidea
familyDelphinidae
genusSteno
speciesbredanensis(Lesson 1828)

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

Diagnosis
ReferenceDiagnosis
K. L. West et al. 2011In the wild, Steno bredanensis can most easily be distinguished from other small delphinids by a forehead that gradually slopes into a long and slender rostrum, lacking the demarcation that separates the melon and beak (Fig. 1). Although Stenella and the Indo-Pacific bottlenose dolphin (Tursiops aduncus) have a similarly long rostrum, they have the clear demarcation that is absent in S. bredanensis. The bottlenose dolphin (T. truncatus) has a much shorter rostrum and a dorsal fin that is less erect but may still be confused with S. bredanensis (Jefferson and Leatherwood 1993; Perrin et al. 2007).
The color pattern appears to vary according to geographic location and age of the individual (Miyazaki and Perrin 1994). S. bredanensis is gray in color with a slightly darker gray cape and often has distinctive white lips (Baker 1987; Jefferson and Leatherwood 1993). The darker cape is apparent from above the eye to the dorsal fin, gradually widening, and extending down the sides of the animal (Miyazaki and Perrin 1994; Fig. 1). The sides of the animal are typically a lighter gray color, and there may be white, pink, or yellow splotches or scarring on the tip of the rostrum, along the lower jaw, and in the ventral region. The mottled appearance is more frequently seen in older individuals, whereas uniform shades of gray are common in younger animals (Miyazaki and Perrin 1994).
The skull (Fig. 2) may be confused with that of the Indo-Pacific humpback dolphin (Sousa chinensis) or Stenella but the skull of S. bredanensis is generally longer than those of Stenella (condylobasal length . 472 mm—Miyazaki and Perrin 1994). The rostrum of S. bredanensis is also long, approximately 60% of the condylobasal length, similar to the ratio between condylobasal length and rostrum in the spinner dolphin (Stenella longirostris), Pantropical spotted dolphin (Stenella attenuata), and striped dolphin (Stenella coeruleoalba—Perrin and Gilpatrick 1994; Perrin and Hohn 1994; Perrin et al. 1994). The mandibular symphysis of S. bredanensis is about one-third the length of the mandible, whereas the mandibular symphysis does not generally exceed 30% of the mandibular length in Sousa (Ross et al. 1994). The orbits of S. bredanensis also are relatively large (. 13% of condylobasal length) compared to Sousa. There are 19–26 teeth on each side in the upper jaw and 19–28 teeth in the lower jaw (Miyazaki and Perrin 1994). Tooth counts also can be used to distinguish between S. bredanensis and Sousa because S. chinensis has 30–38 teeth in each jaw and alveoli that are larger and more widely spaced (Van Waerebeek et al. 1999). The common name comes from fine, longitu- dinal ridges apparent on the surface of the teeth (Fig. 3). This character can be diagnostic when comparing teeth from S. bredanensis side by side with teeth from other delphinids.