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Taxonomy
Mesoplodon hotaula was named by Deraniyagala (1963) [Columbo Museum]. It is extant. Its type specimen is CM 3W, a skeleton. Its type locality is Ratmalana, which is in a Holocene marine horizon in Sri Lanka.
It was synonymized subjectively with Mesoplodon ginkgodens by Rice (1998) and Mead and Brownell (2005).
It was synonymized subjectively with Mesoplodon ginkgodens by Rice (1998) and Mead and Brownell (2005).
Synonymy list
| Year | Name and author |
|---|---|
| 1963 | Mesoplodon hotaula Deraniyagala p. 13 figs. Plate I, Figs. 1-4 |
| 2014 | Mesoplodon hotaula Dalebout et al. p. 1081 |
| 2016 | Mesoplodon hotaula Lambert and Louwye |
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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.
Mesoplodon hotaula Deraniyagala 1963
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| M. L. Dalebout et al. 2014 | Molecular Characters
M. hotaula can be differentiated from M. ginkgodens and all other species of Mesopl- odon beaked whales based on molecular genetic characters (Fig. 2, Tables S1–S3). Mitochondrial DNA—In phylogenetic analyses of combined CR and CYB sequences (Fig. 2), M. hotaula specimens cluster together in a strongly supported clade (BS 100%, BPP 1.00) that is reciprocally monophyletic to the clade formed by the M. ginkgodens specimens. The number of apparently fixed nucleotide substitutions (diagnostic characters) that distinguish M. hotaula from M. ginkgodens (Table S1), together with the overall degree of genetic differentiation (% net divergence, Table S2), is similar to what is observed between other recognized Mesoplodon species: CR, n = 18 (dA, 3.6% 0.91%), CYB, n = 26 (dA, 8.2% 1.79%), COXI, n = 49 (dA, 5.5% 0.76%). Branch lengths in phylogenetic reconstructions using these sequences reflect this trend. Nuclear DNA—Autosomal introns: a nucleotide substitution at position 2199 (ACT) distinguishes M. ginkgodens from M. hotaula and all other Mesoplodon species sampled. Y-chromosome DBY7: nucleotide substitutions at positions 156 and 191 distinguish M. ginkgodens and M. hotaula from one another, and from all other Mesopl- odon species sampled (Table S3). Morphological Characters The following characters of the teeth and skull are, when combined, diagnostic for M. hotaula (Fig. 3–6). (1) Single pair of very large, triangular, laterally compressed mandibular teeth. (2) Alveoli of the teeth fully posterior to the mandibular symphysis. (3) Teeth with vertical growth form, taller than they are wide, asymmetric; posterior margin convex, anterior margin almost planar. (4) Short mandibular symphysis (distal portions of mandibles appear “stubby”). (5) Greatest transverse span of combined premaxillary bones in adults ≥60 mm (Table S4, measurement 32) and “flattened” in cross section. Character 1 is shared with M. ginkgodens, M. bowdoini, M. carlhubbsi, M. densirostris, and M. stejnegeri. Character 2 is shared with M. ginkgodens, M. densirostris, M. peruvi- anus, and M. stejnegeri. Characters 3, 4, and 5 distinguish M. hotaula from M. ginkgodens. Tooth form in adult males is particularly distinct. In contrast, the teeth of M. ginkgo- dens are generally wider than they are tall, both the posterior and anterior margins are convex, and they are nearly symmetrical (Fig. 5). In M. ginkgodens, the distal por- tion of the mandibles appears long and gracile (Fig. 4), and the greatest transverse span of the combined premaxillary bones at the midpoint of the length of the beak is greater than 40 mm but less than 60 mm (diagnostic feature 5, Moore and Gilmore 1965; also TKY, unpublished data). Further, the premaxillary bones in M. ginkgodens are angled upwards (ca. 30o–45o) rather than flattened (ca. 10o–15o) as in M. hotaula (Fig. 6). Adult male M. ginkgodens also appear to be larger in size (total length, 472– 496 cm) than adult male M. hotaula (total length, 386–432 cm; Table 1). Additional images of M. hotaula and M. ginkgodens, together with details of skull and mandibular measurements, can be found in the online supplemental material (Fig. S1–S6). External Appearance To date, we only have information on external appearance for two specimens; the holotype (3WZS), an adult female from Sri Lanka, and an adult male (MM-0001) from the Seychelles. The holotype, which was freshly dead when examined, was described as having a relatively compressed body, a strong lateral ridge, a slender head with an elongate beak, and eyes located about half a beak length behind the angle of the gape. It was blue gray ventrally and the tail had a median lobe with a small caudal notch. There was a single, unerupted pair of teeth in the mandible, located slightly behind the symphysis (Deraniyagala 1963a, b, 1965). The Seychelles specimen (Fig. 7), also freshly dead, was similar in overall appear- ance, though the tail lacked a median notch. It was examined in the early morning, shortly after its discovery, by W. and L. Thompson. The specimen was blue-black dorsally, grading to a slightly lighter shade ventrally. There were a small number of white cookie-cutter shark (Isistius spp.) scars on its ventral surface, predominantly at the posterior end. There were also two large, fresh shark bites; one out of the ventral peduncle and one out of the head-neck area, behind the blowhole. The blue-black color of the body continued on the head, forming a dark cap that extended along the anterior surface of the rostrum and to the posterior end of the mouth line. Coloration around the eye was a lighter mottled gray, becoming lighter ventrally. The tip of the lower jaw was gray but the lower jaw itself was predominantly white. This white color pat- tern extended on the lower jaw to behind the tooth and continued above the mouthline to the rostrum. The upper lips were whitish, grading to gray and blue-black on the rostrum. The gray mottling of the cheek and eye area formed a distinct wedge of color against the white of the ventral chin and throat region, cutting across the posterior ends of the throat grooves (see also Fig. S5). Note that the tips of the teeth of both this and the Palmyra adult male (USNM593426) were broken (see also Fig. S3). This sug- gests that male:male combat using the teeth as weapons does occur in this species, although the Seychelles specimen did not have any of the white linear tooth rake scars that appear to result from such behavior (Mead et al. 1982, Heyning 1984). In contrast, the two New Zealand adult male M. ginkgodens were brownish-gray dorsally (though blue-black coloration has been described from Japanese animals; Nishiwaki and Kamiya 1958, Nishiwaki et al. 1972), grading to lighter tones ven- trally (Fig. 7, see also Fig. S6). There was a darker patch around the eye that extended further in front and a bit below the eye. The beak was white-tipped, both upper and lower jaws. This white coloration reappeared on the upper lip behind the tooth. Where M. hotaula appears to have a gray tip to the lower jaw and a white chin and throat region (Fig. 7, arrows), M. ginkgodens appears to have a white tip to the lower jaw and a gray-brown chin and throat region (Fig. 8, arrows). However it is difficult to tell from such a small number of animals whether these are fixed color pattern dif- ferences or individual variation. These suggested differences need to be confirmed from additional fresh strandings or sightings of living whales at sea. |