Monday, July 28, 2008

Even More Pacific Mesoplodonts

This should have been posted a long time ago, but unfortunately my internet access was fried by lightning.

There is fairly convincing evidence that a triad of Atlantic mesoplodonts distribute according to temperature (and latitude) preferences; three species of Pacific mesoplodonts may mirror them, but further research is needed on those poorly-known species. Mesoplodon densirostris exists in both oceans and appears to avoid competition with other mesoplodonts by specializing in a shallow water niche, but it does not appear to inhabit the northernmost parts of the oceans (due to small size?) and it is not clear if other species "fill in". Things in the Pacific quickly get complicated thanks to a possible sister species/subspecies of M. ginkgodens, Pitman's Mesoplodon sp. B sightings* and two recently described species.

*These cetaceans, mistakenly referred to M. grayi by previous authors, had extremely long and narrow beaks with strait mouthlines, a dark gray rostrum contrasting with a white lower jaw, and a pale patch behind the eye and similar coloration in both the mother and calf (Pitman and Morgan 2001). The last feature was previously known only from Indopacetus, a species Pitman is familiar with. This is the only mention of M. sp. "B" that I am aware of.

Bandolero Beaked Whale or Pygmy/Lesser/Peruvian Beaked Whale
Mesoplodon peruvianus

Reyes, Mead and Van Waerebeek, 1991

Much like the tropical bottlenose/Indopacetus situation, it wasn't until quite recently that sightings (and one 1955 stranding) of "Mesoplodon sp. A" were found to be synonymous with M. peruvianus. The 65 "Mesoplodon sp. A" sightings are highly concentrated off central Mexico and range from the tropical waters of the Gulf of California to central Peru corresponding strongly with M. peruvianus strandings (Pitman and Lynn 2001), except for a northern Chile and New Zealand specimen (MacLeod et al. 2006). The latter record is probably a stray since M. sp. A. appears to be parapatric with M. densirostris, which replaces it to the south and west (Pitman and Lynn 2001).

It could be possible that M. peruvianus and M. densirostris occupy the same niche, with the former able to out-compete the latter in very warm waters thanks to its small body size. M. sp. A was originally estimated at 5-5.5 m, but this was from a considerable distance (rarely under 3.5 km); subsequent sightings estimated animals with chevrons (mature males) at 3.52 m average and 3.79 m maximum (some were still developing at 3.68 m) and unpatterned animals over 3 m (mature females) at 3.74 m average and 4.07 m maximum (Pitman and Lynn 2001). The median length of 15 M. peruvianus specimens (including a 1.59 m animal) was 3.385 m but there were modes of 3.3-3.4, 3.6-3.7 and 3.7-3.8 (MacLeod 2005 - App. I). M. densirostris has modes of 3.9-4.0 and 4.3-4.4 m (4.15 m avg.) (MacLeod 2005 - App. I) and even though it is smaller than the previously discussed Pacific mesoplodonts, there seems to be a considerable size difference. However, MacLeod 2005 suggests that the smallest beaked whales (including M. perrini, M. bowdoini and M. hectori) may have their own distinctive guild of very small prey consumers, but this needs further investigation.

Unfortunately, the original description of this species is not available online (to me anyways) so I'll have to piece together what I can. M. peruvianus has rather diminutive teeth (Dalebout et al. 2002) which are not laterally flattened like other mesoplodonts but are oval in cross-section and Ziphius-like (and M. mirus-like) (Dalebout et al. 2003) and are placed behind the mandibular symphysis. A male M. peruvianus carcass that washed up in Peru in 1955 (classified then as M. bowdoini) showed that scarring was very heavy behind the dorsal fin and may indicate that the male ziphiids are aiming for their opponent's genitals with their battle teeth (M. carlhubbsi may do this as well) (Pitman and Lynn 2001). Judging from photographs in Pitman and Lynn 2001, it looks like the teeth are elevated enough to cause parallel scarring, and they're apparently as elevated as those of M. carlhubbsi. At least one molecular analysis seemed to indicate that M. peruvianus was a sister species to the parapatric M. perrini (Dalebout et al. 2002) and later mtDNA control region and cytochrome b put them reasonably close together (Dalebout et al. 2007).

Adult males have a distinct three-part coloration with orangish brown on the anterior end followed by a white chevron starting a bit behind the blowhole and then blackish brown (Pitman and Lynn 2001), Fig. 2 in that publication shows the coloration very clearly. I really appreciate it that Pitman et al. gave this species an informal name ("Bandolero beaked whale") that's informative about the coloration and pretty witty at the same time, as opposed to somebody's last name. Unfortunately, other common names have gotten pretty ingrained and the only instances of this name's usage are from Darren Naish, but I'll go edit Wikipedia later.

Like the tropical bottlenose/Indopacetus, an adult male M. peruvianus clearly demonstrating the bandolero coloration (or any coloration) has yet to wash up, but it seems very likely that Mesoplodon sp. A and M. peruvianus are one in the same.

I couldn't find a place to put this in the article, but it is worth mentioning that M. sp. A is still considered a cryptid by some. Bille 1995 does not directly cite Pitman et al. 1987 (well, I couldn't either) and described mysterious beaked whales seen off Mexico as 16 feet long (~4.9 m) with a flattened head, wide low-based dorsal fin and white "racing stripes" (scars?) on black adult males, which were larger than females. Some of these traits may be due to observational difficulties or the third-hand nature of this description and others are non-distinctive. Reading it initially, I wasn't even sure it was M. peruvianus. I seem to recall somebody actually arguing that M. sp. A was not M. peruvianus at some point, but I completely forgot where.

Perrin's Beaked Whale
Mesoplodon perrini
Dalebout, Mead, Baker, Baker and van Helden 2002

This species became the newest member of the beaked whale family when it was discovered to be distinct from M. hectori , now recognized as a Southern hemisphere species (Dalebout et al. 2002). This species is known from five strandings in California (MacLeod et al. 2006) although figure 2n in that publication has a black dot indicating a sighting, which may be a typo. It is not known how much more (if any?) the range is. Since this species is parapatric with M. peruvianus it may occupy a similar niche, albeit one more specialized for somewhat warmer temperatures. The limited data on length gives males a maximum size of 3.9 m (n=3) and females 4.43 m (n=1) (MacLeod 2005 - Appendix I) possibly allowing it to out-compete M. peruvianus at slighter colder temperatures. It does not seem to be obviously parapatric with M. densirostris judging by distribution maps in MacLeod et al. 2006, but seasonality may need to be taken into account.

Mesoplodon perrini is superficially very similar to M. hectori, and field guides (e.g. Reeves et al. 2002) illustrating the latter species actually take the coloration pattern from the former. After Dalebout et al. 2002 showed with mtDNA that the California specimens were not M. hectori, they thoroughly documented the many morphological differences between these two superficially similar species. M. perrini differs by having slightly posterior (1-2 cm) rather than apical teeth, a synvertex that narrows upwards (upper skull triangular in frontal view) as opposed to one that is flatter (box-like in frontal view), much narrower premaxillaries and many many others. It doesn't seem like there's any unique information on this species that isn't published in Dalebout et al. 2002.

So why does the Pacific ocean have a greater mesoplodont diversity than the Atlantic? Perhaps it is related size to the former body of water or the (apparently) unique nature of its eastern shores. Or maybe the Atlantic has sub-populations of a known species (M. densirostris?) that occupy an analogous niche - or maybe dwarf and/or pygmy sperm whales (Kogia spp.) do. Dalebout et al. 2002 point out that we only learned about M. peruvianus and M. perrini through chance strandings and fishing bycatch, so I suppose that there's the chance that analogous mesoplodonts have yet to be discovered. The problem is, of course, that the only "leads" that I know about for new mesoplodonts (besides M. mirus) occur in the Pacific (the M. ginkgodens-like species and M. sp. B).

Things get more difficult from here on out.


Bille, Matthew A. Rumors of existence. Hancock House Publishers, 1995.

Dalebout, Merel L. et al. 2007. A divergent mtDNA lineage among Mesoplodon beaked whales: Molecular evidence for a new species in the Tropical Pacific? Marine Mammal Science 23 (4): 954–966

Dalebout, Merel L. et al. 2003. Appearance, distribution, and genetic distinctiveness of Longman's beaked whale, Indopacetus pacificus. Marine Mammal Science 19 (3) 421-461

Dalebout, Merel L. et al. 2002. A New Species of Beaked Whale Mesoplodon perrini sp. n. (Cetacean: Ziphiidae) discovered through phylogenetic analyses of mitochondrial DNA sequences. Marine Mammal Science. 18 (3), pp. 577-608

MacLeod, Colin D. et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

Pitman, Robert L. and Lynn, Morgan S. 2001. Biological observation of an unidentified mesoplodont whale in the Eastern tropical Pacific and probable identity of Mesoplodon peruvianus. Marine Mammal Science. 17(3), pp. 648-657

Reeves, Randall R. et al. 2002. National Audubon Society Guide to Marine Mammals, Alfred A. Knopf, New York.

Tuesday, July 22, 2008

Indo-Pacific Mesoplodonts

Not to be confused for the Tropical Bottlenose whale, Indopacetus pacificus, previously classified as Mesoplodon pacificus.

This post won't cover every species in the Indian and Pacific oceans, mesoplodonts living in the higher latitudes of the southern hemisphere's oceans will be covered in a future posts. There is an article, either in press or unpublished ("known key areas for beaked whales around the world" by MacLeod et al.?) that apparently brought up the possibility of mesoplodonts having distributions affected by latitude, like the North Atlantic mesoplodonts discussed in the previous post. There appeared to have been prey preference and trophic level difference between the North Atlantic species but these may be due to small sample sizes; temperature preference and subsequent temporal/geographic distribution seems to be the most parsimonious explanation. The purpose of morphological differences (sexual size dimorphism, body size, stomach morphology, etc.) and potential physiological mechanisms for such temperature preferences aren't too clear at the moment.

Stejneger's Beaked Whale
M. stejnegeri
True, 1885

This is a sub-polar to cold-temperate species that lives on both sides of the Pacific from 57 to 35 degrees N (MacLeod et al. 2006). The numbers of specimens that have been measured (n=99) is second only to Hyperoodon ampullatus and Ziphius and is is similar to M. bidens (n=95) (MacLeod 2005), the most northerly Atlantic species. There is no obvious or great sexual dimorphism, females have a median length of 4.88 m and a mode of 4.8-4.9 compared to 4.76 and 4.6-4.7 and 5.0-5.1 in males - males max out at 5.77 m compared to the 5.44 m record for females (MacLeod 2005 - Appendix I). Body size in M. stejnegeri may be slightly larger than M. carlhubbsi which in turn may be slightly larger than M. ginkgodens, but size may not be the only factor in determining distribution. Wide-ranging M. densirostris does not appear to overlap this species (or M. bidens in the Atlantic) and M. stejnegeri shares a generalized stomach anatomy (unlike M. bidens) with it to the exception of M. carlhubbsi (Mead 2007). Stomach anatomy in M. ginkgodens is not known and the function of additional stomachs is not obvious.

I couldn't help but wonder why the deep water preferring mesoplodonts in the Atlantic have strait to sinusoidal mouthlines while the possibly analogous mesoplodonts in the Pacific all have stepped or arched mouthlines. M. stejnegeri can only open its mouth a few centimeters (Loughlin and Perez 1985) which limits prey size substantially, is this a side-effect of exaggerated sexual dimorphism between males or females or does ecology play a role? Is it possible that there was both an inter- and intra-specific "arms race" for male sexual dimorphism in these species?

The high number of strandings in a fairly small area (and without much hunting) would seem to indicate that this species is fairly common, but MacLeod et al. 2006 only appear to have two sightings on their distribution map. It was not possible to confirm the species status of north Pacific mesoplodonts until fairly recently (Loughlin and Perez 1985) although Mesoplodont spp. sightings in northern waters were assumed to represent this species (Loughlin et al. 1982). Whalers have stated that they are either found alone or in groups of two to three but possible M. stejnegeri sightings in the Bering Sea showed groups of 5-15 animals (Loughlin et al. 1982).

On the trivial side, it is speculated that mesoplodonts may dissipate heat by dilating their blood vessels and turn from gray/black to brown (Loughlin et al. 1982). This species also apparently darkens with age (Reeves et al. 2002) and this could provide an alternate explanation for observed color. Even more curiously, a paper that I can't access documents the milk of this species, which lacks lactose in its milk and is blue-green thanks to bilverdin. An abstract from Milk Science does not mention this pigment in M. ginkgodens.

Hubbs' Beaked Whale
M. carlhubbsi
Moore, 1963

This species has at least 26 stranding records (MacLeod et al. 2005 - Appendix I) ranging from 35 to 42 degrees off the coast of Japan and from 33 to 54 degrees north on the North American coast (MacLeod et al. 2006). There seems to be a considerable amount of overlap with M. stejnegeri (except off Alaska and northern Russia) and very little with M. densirostris (up to 37 degrees N in the East Pacific) so the possibility that M. carlhubbsi has a niche similar to the latter species should be addressed. There do not appear to be any confirmed sightings (MacLeod et al 2006 - Fig. 2f) and the presence of this species in the central Pacific (and the possibility of two separate populations) also needs to be addressed.

This species is similar in size to M. stejnegeri (and larger than M. densirostris) with a median male size of 4.72 m, a female median size of 4.85 m and maximum sizes of 5.3 and 5.32 m, respectively (MacLeod 2005 - Appendix I). The jawline of M. carlhubbsi is also rather similar to M. stejnegeri in appearance due to an arched mandible with very prominent teeth appearing to constrain the gape of the animal. The melon is moderately bulbous, unlike M. stejnegeri, and males have a white "beanie" on top of it (Reeves et al. 2002). Unlike M. stejnegeri and M. densirostris, M. carlhubbsi has a derived stomach anatomy similar to M. europaeus i.e. with an additional blind main and pyloric stomach but it differed by having trabeculae in the blind accessory main stomach (Mead 2007). Interestingly, Mead predicted that M. bowdoini would have a very similar stomach setup since the two species are "extremely similar". I'll discuss this in a following post.

Interestingly, Carl Hubbs thought that M. carlhubbsi was rather tasty and recommended that it should be roasted or fried for tenderness - but other people have complained of diarrhea after eating mesoplodonts (Loughlin and Perez 1985). Okay....

Ginkgo-toothed Beaked Whale
M. ginkgodens
Nishiwaki and Kamiya, 1958

It was recently discovered through cytochrome b and mtDNA control sequences that mesoplodonts from Kiribati and Palmyra (in the central Pacific) are a deeply divergent sister group to M. ginkgodens from California, New Zealand, Japan and Taiwan (Dalebout et al. 2007). There does not seem to be any information on the distribution of M. ginkgodens in the central Pacific (it does not appear to have any confirmed sightings) (MacLeod et al. 2006) and exactly what is going on here in terms of eco-geography is rather unclear. There will be future investigations on this subject before too long (Robert Pitman pers. comm.).

MacLeod et al. 2006 report 23 strandings of this species with most (15) from Japan and others from China, Taiwan, Malaysia, Guam, Sri Lanka, SE Australia, California, Mexico and the Galapagos - genetic data from Dalebout et al. 2007 also included a couple specimens from New Zealand. There have been unconfirmed sightings in the Arabian sea (MacLeod et al. 2006) although since the only other ziphiids in the area are M. densirostris, Ziphius and Indopacetus it would seem likely that this species occupies the niche of a deep-diving small prey consumer in that area and other across the Indo-Pacific. Only 16 accurate measurements appear to have been taken, male median size (n=4) was 4.86 m compared to 4.45 m (n=9, median = 4.8-4.9 m) for females; maximum male size was 5.1 m compared to 4.9 m (MacLeod 2005 - App. I) and it does not appear that there is any sexual size dimorphism.

What's really curious about this species is that while males have erupted tusks (or "battle teeth") like any other ziphiid, they have been reported to lack (Reeves et al. 2002) or almost lack linear scarring (MacLeod 1998). The sample size was limited for MacLeod 1998 (n=16) and it has been suggested that observations of live animals may yield a different and more complex color pattern (Reeves et al. 2002) and will presumably clear up this matter. It would be interesting for a mesoplodont to have (possibly quite recently) abandoned a near-ubiquitous behavior and there could be a reason why it retained the anatomy anyways. Well, that is assuming the loss wasn't very recent or an artifact of the limit data. The following paragraph may contain speculation:

It has been suggested that large sharks are the only natural predators of ziphiids (Loughlin and Perez 1985) but mesoplodonts have an average length similar to Carcharodon carcharias and may be unfeasibly large prey. Sleeper sharks (and Hexanchus?) will attack ~4 meter elephant seals (Mirounga) but echolocation and similar size may prevent predation in deep waters. The only evidence of shark attacks that I know of are scars from cookiecutter sharks (Isistius). Scars from either Orcinus or Pseudorca have been observed on a live mesoplodont and there is one record of Orcinus consuming a Ziphius individual that it may have killed (Tyack et al. 2006). Ziphiids do not appear to make sounds above 200 m and it appears that this is done to avoid encounters with Orcinus (Tyack et al. 2006). Since it appears that at least one mesoplodont escaped from Orcinus or Pseudorca alive, how did it manage that? The maximum reported swimming speed of M. stejnegeri is 6 knots (~11 km/h) (Loughlin and Perez 1985) is not fast enough for a "flight" response (15-20 km/h) (Ford and Reeves 2008) unless the ziphiid took a crash dive. Male Right whales (Eubalaena) use encrustations on their heads in intraspecific confrontations but females posses them to a lesser degree as well and it is possible that both genders use this as a weapon against Orcinus (Ford and Reeves 2008). Is it possible for the ossified rostrums of male and female ziphiids to be analogous to this? The fighting style would have to be different from normal male encounters, and possible more risky, but it could provide explanations for why "battle" characteristics are retained in individuals who do not appear to otherwise have a use for these resource-consuming features. An alternative explanation is that females have ossified rostrums because of some sort of ontogenetic "requirement" and that M. ginkgodens does engage in "battle", although possibly less commonly than other species for unknown reasons.

I think I'll cut off this post here for the time being. While the mesoplodonts discussed so far roughly mirror those in the Atlantic, there is a major departure: two more species discovered in the past two decades!


Dalebout, Merel L. et al. 2007. A divergent mtDNA lineage among Mesoplodon beaked whales: Molecular evidence for a new species in the Tropical Pacific? Marine Mammal Science 23 (4): 954–966

Ford, John K. B. and Reeves, Randall R. 2008. Fight or flight: antipredator strategies of baleen whales. Mammal Rev. 38 (1) pp.50–86.

Loughlin, Thomas R. and Perez, Michael A. 1985. Mesoplodon stejnegeri. Mammalian Species No. 250, pp. 1-6.

MacLeod, Colin D. et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

MacLeod, Colin D. 2005. Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Doctoral Thesis. Available

MacLeod, Colin D. 1998. Intraspecific scarring in odontocete cetaceans: an indicator of
male `quality' in aggressive social interactions? J. Zool., Lond. 244, 71-77

Mead, James G. 2007. Stomach Anatomy and Use in Defining Systemic Relationships of the Cetacean Family Ziphiidae (Beaked Whales). The Anatomical Record. 290: 581–595

Tyack, Peter L. et al. 2006. Extreme diving of beaked whales. The Journal of Experimental Biology 209, 4238-4253

Reeves, Randall R. et al. 2002. National Audubon Society Guide to Marine Mammals, Alfred A. Knopf, New York.

Tuesday, July 15, 2008

Mesoplodonts of the North Atlantic

The North Atlantic is a relatively well-studied area that is home to six species* of ziphiids, two (or three?) of which are endemic. It was previously discussed that ziphiids preferring large prey items (Ziphius and Hyperoodon) prefer different temperatures and as a result avoid direct competition through temporal and geographic separation. A widespread small prey consumer, (Mesoplodon densirostris) appears to prefer relatively shallow water and occupies a niche separate from potential competitors.

* Mesoplodon grayi once stranded in the Netherlands but this is around 80-90 degrees latitude higher than its normal range (MacLeod et al. 2006). I had previously mentioned a vague reference to an Indopacetus sighting in the Gulf of Mexico which MacLeod et al. 2006 did not mention (was it a misidentification?).

We're still left with three mesoplodonts which all appear to be small prey consumers with deep water preferences. How do they avoid direct competition?

Left: Sowerby's Beaked Whale (Mesoplodon bidens)
Middle: True's Beaked Whale (M. mirus)
Right: Gervais' Beaked Whale (M. europaeus)
From MacLeod et al. 2006

There does seem to be rough geographic separation between the mesoplodonts, although the amount of overlap (i.e. all species have been recorded from the UK) still needs explanation. MacLeod 2005 draws similarities between the H. ampullatus/Ziphius antagonistic pairing and the distributions of M. bidens and M. europaeus since there seem to be similar temperature preferences and seasonal migrations which further decrease any competition. Everything would be pretty neat and tidy if it wasn't for M. mirus occuring in between the species and apparently out-competing them only in a rather narrow band of water. It appears that we're going to need more information to figure out what sort of eco-geographic (and temporal?) separation is occuring or if there is some habitat segregation (MacLeod 2005).

True's (Wonderful) Beaked Whale
Mesoplodon mirus

Despite living in the North Atlantic, this species seems to be rather poorly known. For one thing, the first three confirmed sightings in the Northeastern Atlantic were recorded from 2001-2003 (two sightings may have occurred in 1997 and '99) and apparently the only earlier sighting(s) were from North Carolina (Weir et al. 2004). This ziphiid can be distinguished by other local species due to its apical teeth and resulting closely set parallel scars, a rounded melon that slopes steeply into a short rostrum, a head that is not dorsally or laterally compressed and an appearance overall similar to a big Tursiops ("bottlenose dolphin") (Weir et al. 2004). At least one decomposed specimen appeared to show both a blind accessory main stomach and a blind pyloric stomach in a condition similar to M. europaeus (Mead 2007). Animals in the sightings were estimated at 3.9, 4.5 (n=2), and 4.8 meters long (Weir et al. 2004) and stranding data (n=34) gave males a median length of 4.56 m and females a 4.87 m median length (4.8-4.9 mode) - however males were recorded with a somewhat larger maximum size (5.33 m vs. 5.26 m) (MacLeod et al. 2005 - Appendix I). Although the sample size is limited, M. mirus appears to be larger than the more southernly M. europaeus and slightly smaller (or similarly sized?) than the more northernly M. bidens - possibly echoing the larger size attained by H. ampullatus in comparison to Ziphius.

It was first realized in 1959 that M. bidens also occurred in the southern hemisphere (MacLeod 2005) and some have suspected that this antitropical population may represent a separate species (MacLeod et al. 2006). Molecular evidence suggests that the populations of M. mirus form a monophyletic clade with a deep divergence that suggests either separate species or subspecies (Dalebout et al. 2007). Apparently Dalebout et al. have some unpublished data on the subject so this may be a subject we'll hear about again.

Gervais' Beaked Whale
Mesoplodon europaeus

This species is roughly similar in appearance to M. mirus but it can be distinguished by proportionally smaller pectoral flippers, teeth located 1/3 the length of the mouth from the apex, rostral flattening and a less dolphin-like profile (Norman and Mead 2001). It has been suggested that the tooth placement suggests that this species is rather basal for a mesoplodonts (somewhat more derived than M. mirus) (Norman and Mead 2001) but I'm wary about a one character phylogeny. What's really weird is that one study placed this species in a clade with Hyperoodon to the exclusion of other mesoplodonts (Bianucci et al. 2007) but only 4 of 14 extant mesoplodonts were included and it looks like we're going to have to wait for a hybrid morphological/genetic analysis to sort out ziphiid phylogeny. It probably would tell us a great deal about why the mesoplodonts have the distributions that they do.

M. europaeus is also unusual since it is the only ziphiid where sexually dimorphic size seems to be consistent (and considerable) in both maximum and median sizes (MacLeod 2005 - Appendix I). Males have a median length of 4.09 m compared to 4.32 m for females (mode = 4.5-4.6 m) and males reach a maximum length of 4.57 m compared with 4.85 m in females (MacLeod 2005 - Appendix I). MacLeod brings up the possibility that strandings may have some bias towards size and of course the implications of such sexual dimorphism are not known. This species does appear to be larger than more northernly mesoplodonts and is roughly the same size as M. densirostris.

I should point out that this species is also not endemic to the North Atlantic either and while its southern hemisphere distribution is not clear, if the water temperature preferences are consistent it should range south to Uruguay and Angola.

While Norman and Mead 2001 have photographs of a stranded whale being held in captivity, up until recently this species has never been positively identified at sea (Reeves et al. 2002) and judging by the distribution maps in MacLeod et al. 2006 both populations now have a single definite sighting.

I believe this is another specimen that also happened to wash onshore in Florida.

Sowerby's Beaked Whale
Mesoplodon bidens

This species can be distinguished by other north Atlantic mesoplodonts by tooth projection in the middle of an arch-less mandible coupled with a concave forehead (Carlstrom et al. 1997). M. bidens only appears to have around a dozen sightings to its name (MacLeod et al. 2006) so these features are probably not very distinctive for an open-ocean animal that avoids ships (many sightings were probably categorized as "Mesoplodon spp."). The presence of an "ossicular dental support" is an autapomorphy for this species and not only does it let us know what forces are being put on the teeth, it could provide evidence as to how the incredible stepped jaw of M. densirostris evolved. M. bidens does appear to occupy areas where M. densirostris is absent (i.e. very high latitudes) (MacLeod 2005) but it doesn't seem obvious why one mesoplodont species would begin to develop more extreme sexual dimorphism.

Sowerby's beaked whale does not seem to have sexual size dimorphism, males and female medial lengths are 4.5 and 4.49 m respectively and the modes are 4.7-4.8 for males and 4.8-4.9 for females (MacLeod 2005 - Appendix 1). There was a reported 5.5 m maximum for males, but it appears that the max is likely 4.95 m, in comparison to 5.1 m for females (MacLeod 2005 - Appendix 1). This species does appear to reach larger sizes than the warmer water-inhabiting M. europaeus but there isn't any obvious size difference in comparison to M. mirus which inhabits somewhat lower latitudes. It is possible that the sample size was insufficient to see the pattern (or it was biased somehow) but is there a chance than something other than proportionate bodily surface area plays a role in distribution? M. mirus and M. europaeus both have a derived stomach anatomy with secondary blind main and pyloric stomachs but M. bidens has a second main stomach in a direct series (in addition to a blind pyloric stomach) (Mead 2007). Analysis of stomach contents showed that this species seems to be heavily reliant on benthopelagic fish, but M. mirus also appeared to be heavily reliant on fish (MacLeod 2005). It could very well be possible that this was due to some localized abundance of prey items since sample size is limited of course. Analysis of a nitrogen isotope in order to determine trophic level also curiously predicted that this species preyed on much larger items than stomach content shows, also this could also possibly be related to a fish-heavy diet (MacLeod 2005). For now it seems safe to assume that mesoplodonts are generalists, but if there are some prey preferences this would make the whole situation even more complicated...

It seems amazing how little we know about animals that live in the North Atlantic but incredibly this appears to be one of the best studied area for mesoplodonts. Things get murkier and more complicated from here, and hopefully the picture that is beginning to form here will be useful trying to make sense of everything.


Bianucci, Giovanni et al. 2007. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. Geodiversitas 29 (4) : 561-618.

Carlstrom, Julia et al. 1997. Record of a new northern range of Sowerby’s beaked whale
(Mesoplodon bidens). Polar Biol 17: 459±461

Dalebout, Merel L. 2007. A divergent mtDNA lineage among Mesoplodon beaked whales: Molecular evidence for a new species in the Tropical Pacific? Marine Mammal Science 23 (4): 954–966

MacLeod, Colin D. et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

MacLeod, Colin D. 2005. Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Doctoral Thesis. Available

MacLeod, Colin D. and Herman, Jerry S. 2004. Development of tusks and associated structures in Mesoplodon bidens (Cetaceae, Mammalia). Mammalia 68 (2-3) pp. 175-184.

Mead, James G. 2007. Stomach Anatomy and Use in Defining Systemic Relationships of the Cetacean Family Ziphiidae (Beaked Whales). The Anatomical Record. 290: 581–595

Norman, Stephanie A. and Mead, James G. 2001. Mesoplodon europaeus. Mammalian Species. No. 688, pp. 1-5.

Weir, Caroline R. et al. 2004. Three sightings of Mesoplodon species in the Bay of Biscay: first confirmed True’s beaked whales (M. mirus) for the north-east Atlantic? J. Mar. Biol. Ass. U.K. 84, 1095-1099

Wednesday, July 9, 2008

Mesoplodon densirostris

The ziphiid genera covered so far in this series have either had one or two species making it remarkable that Mesoplodon has at least 14 (the most for any cetacean genus). In an attempt to understand why there are so many mesoplodonts, I'll be looking at broad geographic locales (e.g. the North Atlantic) to try and determine any niche differences or exclusion that may be occurring. This species doesn't exactly fit in that framework since it inhabits tropical to warm temperate waters (and sometimes cold temperate) in the Atlantic, Indian and Pacific oceans with a range apparently second only to Ziphius in size (MacLeod et al. 2006). However, distribution maps from MacLeod et al. 2006 also show that there does not appear to be much overlap with M. stejnegeri in the North Pacific and M. layardii, M. hectori, M. grayi and M. bowdoini in the southern hemisphere so it could be possible for one or two to be occupying the same niche as M. densirostris.

So what niche exactly does M. densirostris occupy? We know that this species has a generalized ziphiid stomach whereas other North Atlantic mesoplodonts (M. mirus, M. europaeus, M. bidens) have derived ones (Mead 2007) but currently we can't predict what sort of implications this may have. MacLeod's thesis classifies M. densirostris as a small prey consumer (as all mesoplodonts appear to be) but notes that in the North Atlantic it prefers shallower waters (<700>1000 m). The dwarf sperm whale (Kogia simus) is another possible competitor that seems to prefer even shallower waters (MacLeod 2005). A matter for future investigation should be if M. densirostris has a preference for relatively shallower waters in other areas with greater mesoplodont diversity and if there is some sort of physiological preference.

I can't find a citation for this, but I'd venture to say that M. densirostris is the best known of the mesoplodonts. It is at least the only species for which there are readily available videos, and surprisingly clear ones at that:

Additional videos of M. densirostris swimming underwater can be found here. As you can see from the videos (and not some notoriously low-fi drawing by yours truly) males have some outrageously arching mandibles, apparently more so than any other mesoplodont.

In addition to having an extreme range and appearance amongst the mesoplodonts, the dense-beaked whale holds the record for the densest (MacLeod 2001) and most mineralized bone (Zylberberg 2004) described thus far. The rostrum of a dolphin (Delphinus delphis) has a density of 0.79 grams per cubic centimeter whereas the mesorostral ossification has a density of 2.6 - it should be noted that the (morphologically similar) M. carlhubbsi has a density of 2.4. There is a shockingly large number of papers on this ossification from a materials science perspective (more of my dad's thing) and I couldn't help but note the conclusion of Currey et al. 2001: "we have no idea of the adaptive reason, if any, for the production of such a brittle material".

This is of course where the ubiquitous Colin MacLeod comes in to explain the hyperossification in the larger context of the animal. The only ziphiids lacking extreme ossification are members of Hyperoodon, which as we know are specialized headbutters, and scars on male mesoplodonts indicate that there are jousts with the males facing each other and "flipped" (MacLeod 2001). Previous authors assumed that the rostrum would be subjected to direct ramming but did not take soft tissues and other apparent adaptations (e.g. buildup of bone around the tusks and anterior of the mandible) - MacLeod reasons that the rostrum will be mostly subjected to forces of compression and longitudinal grains will prevent any major (transverse) breaks. Adult females also have this ossification but as you can see they also develop an extreme "stepped" mouthline with no protruding tusks so this is probably an ontogenetic quirk as opposed to the hyperossification being used for ballast, sound transmission or no reason at all.

Mesoplodon densirostris, courtesy of Markus Buehler. Also available on his Flickr page.

Phew, one species out of fourteen down...


Currey, John D. et al. 2001. Mechanical Properties of Nacre and Highly Mineralized Bone. Proceedings: Biological Sciences, Vol. 268, No. 1462, pp. 107-111

MacLeod, Colin D. et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

MacLeod, Colin D. 2005. Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Doctoral Thesis. Available

MacLeod, Colin D. and Zuur, Alain F. 2005. Habitat utilization by Blainville’s beaked whales off Great Abaco, northern Bahamas, in relation to seabed topography. Marine Biology, 147: 1–11

MacLeod, Colin D. 2001. Possible functions of the ultradense bone in the rostrum of Blainville’s beaked whale (Mesoplodon densirostris). Can. J. Zool. Vol. 80, pp. 178-184.

Mead, James G. 2007. Stomach Anatomy and Use in Defining Systemic Relationships of the Cetacean Family Ziphiidae (Beaked Whales). The Anatomical Record. 290: 581–595

Morisaka, T. and Connor, R. C. 2007. Predation by killer whales (Orcinus orca) and the evolution of whistle loss and narrow-band high frequency clicks in odontocetes. Journal of Evolutionary Biology 20 (4), 1439-1458

Zylberberg, Loise. 2004. New data on bone matrix and its proteins. C. R. Palevol 3 591–604

Monday, July 7, 2008


Ziphius was first described as an extinct genus* by Cuvier from a "petrified" partial skull and it took several decades to establish that it was extant (Heuvelmans 1968). While the holotypic skull (and a paratype) were from the Mediterranean, the first complete specimen was found in New Zealand (Heuvelmans 1968) at a near-antipodal point; it is now known that Ziphius has a range from the tropics to polar waters and is the most widely distributed ziphiid (MacLeod et al. 2006) as well as the most frequently stranded (Hardy 2005). It has been observed that Z. cavirostris varies considerably across its range and while some have expressed uncertainty as to whether Ziphius is monotypic or not (Hardy 2005) recent mtDNA analysis over most of the species' range supported that it is a single species (Dalebout et al. 2005).

* The genus originally included several extinct species until Huxley whittled it down to Z. cavirostris - he was uncertain if it actually was fossilized or not (Huxley 1864). It has been suggested that this name is somehow related to the swordfish Xiphias (in the family Xiphiidae) (Hardy 2005) but I'm not clear on how. As you can see, this is the type genus for Ziphiidae, but it wasn't the first one described.

It has been proposed that Ziphius shares a subfamily "Ziphininae" (sic?) with Berardius and Tasmacetus, but molecular evidence does not support such a clade (
May-Collado and Agnarsson 2006, Dalebout et al. 2004, Dalebout et al. 1998). Fossil evidence also suggests that Ziphius is alone in Ziphiinae, but the subfamily seems to have been more diverse in the past. Members of the subfamily are defined by a transverse premaxillary crest directed anterolaterally and reduced contact between the nasal and the premaxillary crest (Bianucci et al. 2007) and it has also been defined as including the common ancestor of Ziphius and Ziphirostrum and all of its descendants (Lambert 2005). Fuller and Godfrey 2007 suggest that Messapicetus is the most basal species and outside of Ziphius/Ziphirostrum but oddly their Fig. 5 puts Messapicetus + Ziphius in the tribe (i.e. sub-sub-family) Ziphiini. Nitpicking aside, it is worth pointing out that Messapicetus has a very elongated rostrum with multiple pairs of teeth (Fuller and Godfrey 2007) quite unlike the modern Ziphius. Members of Ziphiinae did not appear to loose alveoli until the Choneziphius + Ziphius clade (Fuller et al. 2007) and despite having reduced maxillary alveoli reduced and unlikely to support teeth, Ziphirostrum still showed tooth wear and may have supported maxillary teeth mostly by gum (Lambert 2005). Ziphius has replaced alveoli with an alveolar trough but specimens with vestigial teeth in the gums of both jaws have been documented (Gomerčić et al. 2006) - apparently this is not unusual for ziphiids but further documentation is in an article ("Rows of small teeth in ziphioid whales") that is not accessible (it was cited in Fordyce et al. 2002). The presence of functional teeth would seem to suggest that extinct species had a much different niche from the extant one (less teuthophagous?) but a structure called a prenarial basin could hint at some behavioral similarities.

Hardy's thesis, previously discussed in the Hyperoodon post, also discussed the implications of the prenarial basin as a sexually dimorphic trait. Extinct members of Ziphiinae reported not to have this feature (Izikoziphius, Messapicetus) could thus be female specimens. Anyways, Hardy 2005 describes that as a male Ziphius ages, the melon changes shape and differentiates into high and low density regions - the latter of which is functional, occupies the prenarial basin and appears to be homologous with the spermaceti organ of the sperm whale (Physeter). While the development of maxillary crests in Hyperoodon ampullatus appeared to be protection from head-butting, the prenarial basin appears to protect the melon from head-on "jousts" in Ziphius (Hardy 2005). Mesoplodonts do not appear to need such a protective basin thanks to the teeth being raised and located more posteriorly (Hardy 2005) but how some mesoplodonts with more apical teeth (plus Indopacetus and Tasmacetus) and no obvious protection avoid melon damage is a good question. It should also be pointed out that in species that joust, larger male size is probably a hindrance (thanks to a larger turning radius) and the median lengths for male and female Ziphius are pretty much identical (5.5 and 5.47 m) (MacLeod 2005 - Appendix 1). If the prenarial basin was used for protection from head-butting, we would anticipate a considerably larger size in some male Ziphius - as is the case for H. ampullatus (MacLeod 2005).

I've mentioned before that Ziphius has a huge range and while it presumably overlaps with just about every other ziphiid, it does appear to segregate with H. ampullatus (MacLeod 2005). Ziphius does not occur above 60 degrees N in the Atlantic and H. ampullatus does not occur below 40 degrees N and in the area where they are sympatric it appears that there is spatio-temporal segregation (MacLeod 2005). Both species consume large prey items (relative to mesoplodonts) and it seems probable that they occupy the same niche - Ziphius also overlaps with Berardius and Indopacetus and presumably these large prey consumers occupy different niches, perhaps related to their large group sizes (MacLeod 2005). MacLeod also made mention of body size and water temperature potentially influencing niche separation (e.g. smaller occupies warmer water) but distribution maps in MacLeod et al. 2006 have sightings of off the coast of Antarctica - overlap with H. planifrons and the accuracy of these sightings probably needs to be addressed.

Even though a lot of work has been done on Ziphius recently, it is still regarded as a poorly known species (Moulins et al. 2007). For instance, while Ziphius is well known to be widespread and strands very frequently, little is known about local populations and their abundance (which could be quite considerable) (Dalebout et al. 2005). Dalebout et al. 2005 estimated that there are 456-916,000 breeding adults worldwide (Hawai'i alone has over 12,000) and there is a population in the Mediterranean which appears to be small in population and unique. Genetically it appears that geographical location shapes genetic diversity much more in Ziphius than in the Sperm whale (occupying a roughly similar niche) and it appears that the social structure is not matrifocal such as in that species (it is not known what the social structure is) (Dalebout et al. 2005). While there don't appear to be multiple species in Ziphius, a lot more analysis needs to be done and it seems likely that more Evolutionary Significant Units (like the Mediterranean population) will become apparent.

While apparently numerous, Ziphius still does have a number of threats. They have been hunted in Japan and a few other countries and it is one of the species affected by sonar testing (Reeves et al. 2002, Dalebout et al. 2005). Reeves stated that the relatively common occurrence of the species could mask how vulnerable it is, and the status (and existence!) of small regional populations needs investigating. Well, a lot of stuff needs investigating but fortunately we know a lot more now than we did even a few years ago.

Next, ugh, mesoplodonts. This could get ugly...


Bianucci, Giovanni et al. 2007. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. Geodiversitas 29 (4) : 561-618.

Dalebout, M. L. et al. 2004. A Comprehensive and Validated Molecular Taxonomy of Beaked Whales, Family Ziphiidae. Journal of Heredity 95 (6): 459–473

Dalebout, M. L. et al. 1998. Molecular genetic identification of southern hemisphere beaked whales. Molecular Ecology 7, 687-694

Fordyce, R. Ewan et al. 2002. Australodelphis mirus, a bizarre new toothless ziphiid-like fossil
dolphin (Cetacea: Delphinidae) from the Pliocene of Vestfold Hills, East Antarctica. Antarctic Science 14 (I) , 37-54

Fuller, Anna J. and Godfrey, Stephen J. 2007. A Late Miocene Ziphiid. Journal of Vertebrate Paleontology 27 (2), 535–540

Gomerčić, Hrvoje et al. 2006. Biological aspects of Cuvier’s beaked whale (Ziphius cavirostris)
recorded in the Croatian part of the Adriatic Sea. Eur J Wildl Res 52, 182–187

Hardy, Mathew T. 2005. Extent, Development and Function of Sexual Dimorphisms in the Skulls of the Bottlenose Whales (Hyperoodon spp.) and Cuvier’s Beaked Whale (Ziphius cavirostris). Available

Heuvelmans, Bernard. 1968. In the Wake of the Sea Serpents. Hill and Wang, New York

Huxley, Thomas H. 1864. On the Cetacean Fossils termed "Ziphius" by Cuvier, with a Notice of a New Species (Belemnoziphius compressus) from the Red Crag. Quarterly Journal of the Geological Society 20, 388-396

Lambert, Olivier. 2005. Systematics and phylogeny of the fossil beaked whales Ziphirostrum du Bus, 1868 and Choneziphius Duvernoy, 1851 (Mammalia, Cetacea, Odontoceti), from the Neogene of Antwerp (North of Belgium). Geodiversitas 27 (3) : 443-497.

MacLeod, Colin D. et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

MacLeod, Colin D. 2005. Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Doctoral Thesis. Available

May-Collado, Laura and Agnarsson, Ingi. 2006. Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344–354

Moulins, Aurélie et al. 2007. Aspects of the distribution of Cuvier’s beaked whale (Ziphius cavirostris) in relation to topographic features in the Pelagos Sanctuary (north-western Mediterranean Sea). J. Mar. Biol. Ass. U.K. 87, 177–186

Reeves, Randall R. et al. 2002. National Audubon Society Guide to Marine Mammals, Alfred A. Knopf, New York.