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.

References:

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

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.

Phew, one species out of fourteen down...





References:

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

Ziphius

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...


References:

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.

Hyperoodon

This post fell behind "schedule" thanks to the status of Hyperoodon ampullatus as the best known ziphiid and apparently a fairly well known cetacean. Completely contrary to other ziphiids, H. ampullatus will actually approach boats (Reeves et al. 2002) and was hunted in substantial numbers as a result. Currently the species also seems well known in terms of population studies and I wonder if B. bairdii and other giant ziphiids could be studied similarly. I bring this up because the genera share latitude preferences in the north Pacific (Berardius), north Atlantic (Hyperoodon) and southern oceans (both genera) and do not appear to overlap with Indopacetus (much? oceanic ID is difficult) (MacLeod et al. 2006) - do they occupy the same niche? H. planifrons apparently migrates to warmer waters from the Antarctic with sighting peaks in South Africa in October (early spring) and February (mid-summer) [see here] and they apparently calve off there in spring/early summer (Reeves et al. 2002) but data for the genera seems too scant to make many inferences. Plus seasons in that other hemisphere are confusing. Great, I've already digressed...

While giant ziphiid genera may be functionally similar, none appear to be closely related and one morphological study placed Hyperoodon rather unexpectedly: within the genus Mesoplodon. Superficially Hyperoodon is much larger than mesoplodonts, has a rotund rather than laterally compressed body and has a much more prominent melon (Reeves et al. 2002) - I don't think anybody has suspected this close a relation before. Bianucci et al. 2007 used 18 osteological characters in their ziphiid phylogeny and the data (Appendix 3) shows that while 15 of those characters are shared, only one was both shared and derived - apical teeth. However, only 5 of 14 extant mesoplodonts were included and I'm pretty sure that M. perrini and M. hectori also have what can be considered apical teeth (Dalebout et al. 2002 - Fig. 3). The limited number of characters led Bianucci et al. to recommend that a morphological and molecular study could resolve the paraphyletic Mesoplodon issue but current mtDNA analyses seem best used for taxonomic purposes (species identification) than phylogenetic ones (Dalebout et al. 2007). Apparently Dalebout et al. have some unpublished data from slower evolving nuclear markers that would be better suited to phylogeny, I'll have to keep my eye open. While a decently resolved phylogeny for ziphiids is a bit beyond the horizon, I think the data in Bianucci et al. 2007 can at least be taken to indicate close relation between Hyperoodon and Mesoplodon. The Hyperoodon-like (and also Berardius-like, apparently) Indopacetus appears to be in the same subfamily as Hyperoodon (Hyperoodontinae) but data in Bianucci et al. suggests numerous fossil taxa are more closely related to Hyperoodon and it would seem any similarities are convergence.

Unlike Berardius, the anti-tropically distributed Hyperoodon species have traits that can convincingly distinguish them. Mead 2007 mentions H. planifrons* is sufficiently distinctive to warrant a different subgenus (Frasercetus) and that while only the stomach anatomy of H. ampullatus was described by Mead, he predicted that there would be differences. The book Australian Mammalogy (available here in part) reports that the stomach of H. planifrons has three major compartments with the last and largest having five sub-compartments; most ziphiids (including H. ampullatus) have a generalized anatomy with two compartments (one main, one pyloric) and derived mesoplodonts and B. bairdii stomachs have two main and two pyloric stomachs. Hopefully future publications by Mead will address (and diagram) this feature - phylogenetic and functional implications will probably not be known for some time. According to Hardy 2005 other differences in the species include an apparently denser skull and higher temporal fossa in H. planifrons and much larger, narrower and abruptly ending maxillary crests in H. ampullatus. The sample size in that study was very small (4) and none of the specimens had a determinate gender so it seems that speculating on the implications of the apparent lack of enlarged premaxillary crests in H. planifrons is a bit preliminary.

*Dalebout et al. 1998 noted that H. planifrons sequences differed more from each other than the Berardius species. It probably doesn't have multiple "Evolutionarily Significant Units" but is just diverse (since it is so populous).


Gowans and Rendell 1999 observed that H. ampullatus males have very little scarring and relatively (to other ziphiids) unmodified apical teeth, but greatly enlarged melons were present. Once in a 10 year study of the species in the Gully (off Nova Scotia) adult males showed what appeared to be ritualized head-butting in an aggressive context - as opposed to other cetaceans using this behavior in play or courtship. While the infrequence of observation seems a bit odd, morphological developments in mature males indicate that this behavior is of importance. The thesis of Hardy 2005 goes into much more detail and explained that the enlarged premaxillary crests form a "tube-like channel" which protects the actual melon organ which shrinks, shifts position and becomes more fibrous as the ziphiid matures. Development of a flattened melon from a bulbous one appears to occur before the development of the maxillary crests (at ~ 7.2 to 7.5 m and 9-11 years old) and an increasingly white patch in the largest males (>8.3 m) appears to signify that it is fully mature. While male H. ampullatus apparently reach larger sizes than females (9.8 vs. 8.7 m - Dalebout et al. 2006) an article by MacLeod cited by Hardy (I can't find or access it) notes that the median size is not significantly different and a person communication with MacLeod brought up the idea that larger size with hinder maneuverability. Sources like Reeves et al. 2002 cite female H. planifrons with a larger maximum size than males but presumably the cryptic paper by MacLeod also discounted this (only three mesoplodonts have significantly larger females) - I still would like to know if this species really is smaller than H. ampullatus (much like how the sympatric B. arnuxii is reportedly smaller than B. bairdii). I really wish I had that paper...*

*Post script: It was included in MacLeod's doctoral thesis. Although the mean values for H. ampullatus were similar for males and females (6.4 vs. 6.51), at least some males obtain larger sizes (10 m vs. 8.6 m). Mean values for H. planifrons were similar for males and females (6.425 m vs. 6.5 m) but maximum sizes were smaller (6.93 m vs. 7.45 m).


H. ampullatus in the Gully live at the southernmost consistent range for the species and are significantly smaller (0.7 m) than the next nearest population in Labrador (Whitehead et al. 1997) nearly 2000 kilometers away (Dalebout et al. 2006). The small population has been estimated to contain 163 individuals and suspicions that it was distinct (e.g. Whitehead et al. 2000) have been confirmed by mtDNA (Dalebout et al. 2001) and microsatellites with mtDNA control regions (Dalebout et al. 2006). The former study estimated that only two whales per generation will likely disperse to the Labrador population and there does not seem to be seasonal migration. Possible morphological distinctions (besides size) have been alluded to by Dalebout et al. 2006 but have yet to be described. 65,000 H. ampullatus were taken from the N. Atlantic from 1850 to the early 1970's but it does appear that the population is a fragment of a much larger one, but merely habitat preference (Dalebout et al. 2006). Dalebout et al. also note that the 87 H. ampullatus taken from the gully between 1962 and 1967 did not appear to cause a bottleneck but suggest that this population be regarded as endangered. Biopsy samples taken before and after major oil and gas development in the region show show that while health problems are not being caused, the fact that it was last carried out in 2003 and the population is so small is a potential concern (Hooker et al. 2008).

Ecologically, Hyperoodon is mainly a teuthivore that commonly preys on cephalopods over 0.5 kg and commonly over 1 kg (MacLeod et al. 2003). Stomach contents reviewed by MacLeod et al. 2003 reveal that H. ampullatus has a less diverse diet of smaller squids than H. planifrons but differences in the amount of fish consumed are unknown since fish digest more quickly than squid and are less frequently found in stranded specimens (H. planifrons) than ones caught by whalers (H. ampullatus). And for those interested, H. planifrons is yet another predator of the colossal squid Mesonychoteuthis, although the record is only a ~4 kg specimen. Hooker et al. 2002 estimate that the average Gully H. ampullatus is about 6.5 m long and weighs 5500 kg (~21' and 6 tons) and estimate that it needs to consume 110,000 kcals a day, equivalent to 300 Gonatus squid per day and 15-20 per dive. The number of prey items in the average Hyperoodon stomach was 1452 - much higher than Ziphius (454) and Mesoplodon (34) - so the small prey preferring H. ampullatus may be even busier on its dives than Hooker et al. estimate (or has a slower digestive system?). While we aren't even entirely clear on the coloration of H. planifrons, Kasamatsu and Joyce 1995 estimated that most of the Antarctic ziphiid population (~93%) was from that species; this presumably indicate that half a million individuals are present and that they equal the mass of all the other odontocetes combined (judging from Table IX). The fact that so little is written on such a major player in Antarctic ecology is a bit alarming, and hopefully by our decent knowledge of its northern cousin can help us learn basic information about it.



References:


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, 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. 2006. Nuclear and mitochondrial markers reveal distinctiveness of a small population of bottlenose whales (Hyperoodon ampullatus) in the western North Atlantic. Molecular Ecology 15, 3115–3129

Dalebout, Merel L. et al. 2002. A new species of beaked whale Mesoplodon perrini sp. n (Cetacea: Ziphiidae) discovered through phylogenetic analyses of mitochondrial DNA sequences. Marine Mammal Science 18 (3) 577-608.

Dalebout, Merel L. et al. 2001. Genetic diversity and population structure among northern bottlenose whales, Hyperoodon ampullatus, in the western North Atlantic Ocean. Can. J. Zool. 79: 478–484

Dalebout, Merel L. et al. 1998. Molecular genetic identification of southern hemisphere beaked whales (Cetacea: Ziphiidae). Molecular ecology 7, 687-694.

Dixon, Joan M. et al. 1994. New information on the Southern Bottlenose Whale, Hyperoodon planifrons (Cetacea: Ziphiidae) from a recent stranding in Victoria, Australia. Australian Mammalogy 17: 85-95. Available

Hardy, Mathew D. 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

Gowans, Shannon et al. 2000. Population size and residency patterns of northern bottlenose
whales (Hyperoodon ampullatus) using the Gully, Nova Scotia. J. Cetacean Res. Manage. 2(3): 201–210

Gowans, Shannon and Rendell, Luke. 1999. Head-butting in northern bottlenose whales (Hyperoodon ampullatus): A possible function for big heads? Marine Mammal Science 15 (4) 1342-1350

Hooker, Sascha K. et al. 2008. Changes in persistent contaminant concentration and CYP1A1 protein expression in biopsy samples from northern bottlenose whales, Hyperoodon ampullatus, following the onset of nearby oil and gas development. Environmental Pollution 152 205-216

Hooker, Sascha K. et al. 2002. Ecosystem consideration in conservation planning: energy demand of foraging bottlenose whales (Hyperoodon ampullatus) in a marine protected area. Biological Conservation 104, 51–58

Kasamatsu, F. and Joyce, G. G. (1995). Current status of odontocetes in the Antarctic. Antarctic Science, 7: 365-379.

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, C. D. et al. 2003. Review of data on diets of beaked whales: evidence of niche separation and geographic segregation. J. Mar. Biol. Ass. U.K. , 83, 651-665

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

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

Whitehead, Hal. 1997. Population analysis of northern bottlenose whales in the Gully, Nova Scotia. Marine Mammal Science. 13 (2) 173-185

Berardius

As is the case of all beaked and bottlenose whales, exactly where Berardius fits into Ziphiidae is currently not clear. Morphological analysis of Cetacea by Geisler and Sanders 2003 placed Berardius and Mesoplodon into a clade - nobody else seems to have gotten this result and it is worth noting that Hyperoodon and Indopacetus were not included. Lambert et al. 2005 studied the morphology of extinct and extant ziphiids and placed Berardius in a basal position and possibly in a clade with Tasmacetus on the basis of one apomorphy (nasals wider than frontals on the vertex). Bianucci et al. 2007 defined the subfamily Berardiinae as an outgroup to other ziphiids mostly on the basis of symplesiomorphies such as a low vertex, a narrow and thin premaxillary crest and a supraoccipital lower than frontals; the only apomorphy shared by all the taxa* was a nodular protuberance formed by either the interparietals or frontals on the vertex. Dalebout et al. 2004 noted previous morphological and molecular studies that placed Berardius as the basal-most species and used it to root their tree but molecular studies of Cetacea by May-Collado and Agnarsson 2006 did not place it basally and noted that positions in the family are unresolved.

*Other members of the subfamily include the middle Miocene Archaeziphius from Belgium (Lambert and Louwye 2006), Microberardius from South Africa (Bianucci et al. 2007), an indeterminate species (Berardiinae indet. - Bianucci et al. 2007) from the same locale and a possible member of Berardius from Japan. Archaeziphius was only estimated at 3.5-4 m and Microberardius seemed similarly sized.

The osteological characters and genetic analyses don't really convey how much of a derived oddball Berardius is. Male ziphiids of other species have on pair of enlarged teeth (even many-toothed Tasmacetus and M. grayi) but Berardius* has both an apical and sub-apical pair on the mandible (Bianucci et al. 2007). The fossil genera did not have mandibles so we can't tell if they had the extra teeth - and I'll admit that I'm not quite sure what the smaller posterior pair do. Enlarged teeth in ziphiids are used in intraspecific combat and create parallel scars (except in M. ginkgodens?) which the cetacean delays pigmenting so they can accumulate and give a signal of "quality" so unnecessary aggressive behavior between unevenly matched males can be avoided (MacLeod 2003). If attaining scars as a status symbol seems odd, it should be pointed out that a Homo sapiens fad at Heidelberg University involved fencing duels for the sole purpose of getting scars. Back in the day when Berardius was still quite mysterious, Pike 1953 noted scars on both males and females of the species - but for some reason thought that neither had erupted teeth and the most parsimonious explanation was that the long parallel scars were caused by squid beaks (not squid hooks?). That aside, it is now established that both genders of both species have "battle teeth" (to use Connor et al. 1998's terminology) when mature. MacLeod et al. 2003 suggest that the teeth may be important in social interactions for females and could indicate dominance, but it remains to be studies how much scarring exactly occurs in females relative to males. MacLeod et al. also speculate that females may retain teeth due to "ontological constraint" - but Risso's dolphin and sperm whales were also being mentioned in the paragraph and the statement was probably directed more towards them since other ziphiids showed no signs of such a restraint.

*Heuvelmans claims that B. arnuxii has "teeth which no mammalogist would have believed in had they been described by a layman, for they are embedded in cartilaginous sacs, and it seems that they can be erected at will". Heuvelmans does not make clear whom he is citing and Mead 2007 notes that morphology and osteology in B. bairdii and B. arnuxii are similar enough to possible be considered conspecific.

The social system of Berardius bairdii is described as "alien" to those more familiar with large terrestrial mammals (Connor et al. 1998). Connor et al. summarized a paper by Kasuya and Brownell using data from Japanese whalers (which I can't access) which suggest that adult males are much more common, mature 4 years earlier and live up to 30 years longer. To them, this indicates that the male plays a large role in parental care and/or for the young of a close female relative. The former scenario makes evolution sense because you always know that a sister and her offspring are related to you, but you can never be sure about "your own" kid. What doesn't make sense is how exactly female mortality fits into this scenario - unless they're the ones doing most of the fighting. It seems that all female ziphiids are larger than males judging by record sizes (Reeves et al. 2002) despite the aggressive intraspecific behavior of males and the fact that the males have a coloration pattern whereas females are nondescript. Kinda reminds me of frigatebirds. Berardius still retains larger females, but these ones have tusks and a similarly nondescript coloration (as far as I can tell) - the significance of which is totally beyond me. Reeves et al. 2002 noted that B. bairdii remains have been found in Orcas (Orcinus orca) and scars from Orcas have been found on B. bairdii as well. Could the enlarged teeth on female B. bairdii be used as a defense mechanism against orcas? More data would be nice, but again, it'll probably come from "scientific" whaling...


That's right, a species of ziphiid was and is still being hunted. B. bairdii is the largest ziphiid at 10 m average (MacLeod 2005)* and is apparently more approachable by boat than other species (Barlowe et al. 2006)** which is not a good trait for a cetacean occurring off the coast of Japan. It is likely that the species is below historical levels (Barlowe et al. 2006) and the Japanese killed 4000 between 1948 and 1986 with a peak of 300 per year in 1952 (Reeves et al. 2002). The IUCN considers this species as "Lower risk conservation dependent" (and not data deficient!) but suggests that more surveys are needed to make sure the Japanese quota of 62 animals per annum isn't depleting any local populations. Barlowe et al. 2006 note that in some "hot spots" the density of B. bairdii off Japan can reach 40-68 animals per 1000 Kilometers² - but in other areas surveyed in the Pacific it ranged from 0.1 to 1.2. It still appears that overall abundance is somewhere in the thousands and being a species with a multi-tonne average weight***, Berardius has a significant biomass and is likely important ecologically.

* Lengths of 22 individuals indicated an average of 10.5 m (~34') for females and 9.6 m (~31'). MacLeod did not have sufficient evidence to give an average for B. arnuxii and from the 7 individuals measured the longest was 9.3 m (~30') as compared to the longest B. bairdii which measured 11 m (36'). Morisaka and Connor 2007 cite something I cannot locate which gives a length of 8.61 (~28') for the average B. arnuxii and this seems proportionally correct. Wikipedia claims that sightings of B. arnuxii included 12 m animals, but it is Wikipedia. Such lengths are probably unusual even for B. bairdii.

** Reeves et al. 2002 and Minamikawa et al. 2007 say that they are shy and difficult to approach. The latter study approached 35 of 63 pods sighted and were able to approach 3 pods within 30 m and 10 within 100 m. Maybe the species is more approachable relative to other ziphiids since it is so much more conspicuous.

***Minamikawa et al. 2007 and others apparently estimate the weight of these ziphiids by assuming 1 m of body length equals 1 tonne. They're going to need to be re-estimated.



MacLeod et al. 2003 commented that while a lot of B. bairdii specimens have been taken, information on stomach contents was rather limited. Previous studies cited by them suggested that B. bairdii migrated north in spring to feed on deep water fish and squid were primarily consumed while migrating south in fall. Ohizumi et al. 2003 studies diet more in depth and determined that B. bairdii was not dependent on vertical migration in deep water fish (i.e. upwards at night and vice versa) since the mass of consumed prey peaked during the day (but stomachs were empty in some). Data logging by Minamikawa et al. 2007 indicated that there were both dives that followed the bottom topography in very deep water (>1000 m) and others that did not appear to reach the bottom. Ohizumi et al. 2003 recorded mesopelagic squid in the stomach contents but Minamikawa et al. could not find indication of a feeding event (a zigzag pattern) and further acoustic study needs to be done. While most sources state that squid are the preferred prey of ziphiids, Ohizumi et al. 2003 suggest that desmeral fish (particularly hake and rat-tail) are important in their diet and may possibly be the reason for their migration.

Tying in with the previously mentioned notion that Berardius is an oddball, Mead 2007 first described the apomorphy of a derived stomach anatomy in B. bairdii. The main chamber of the stomach has a valvular closure which divides it into another compartment. After a complex of connecting chambers is a pyloric stomach of similar size to the main stomach which communicates freely with a much smaller pyloric stomach chamber. Mead noted that functional anatomy of multiple stomachs even in familiar ungulates (cows, sheep) is not yet conclusive, so how exactly this relates to diet cannot yet be known. Interestingly, he predicts that the stomach anatomy of B. arnuxii will be very similar...

So what exactly should the status of Berardius species be? Judging by distribution data (in MacLeod et al. 2006) it seems that B. bairdii and B. arnuxii are separated by 60-70 degrees of latitude so they can be considered species by the biological species concept. Bianucci et al. 2007 note that a bone interpreted as the interparietal is in a plesiomorphic (?) position in B. arnuxii, but apparently not always. Aside from the reported size difference between species (maybe - this isn't really a character anyways) some very early authorities reported a difference in body length relative to head length, but this has been discounted as variation since Slipp and Wilke 1953. Mead 2007 simply states that the osteology and morphology between species is extremely similar and externally it is stated that the species are indistinguishable (Reeves et al. 2002). Molecular analysis by Dalebout et al. 1998 revealed that the interspecific variation in Berardius spp. is somewhat less than variation within Hyperoodon planifrons - and presumably variation between H. planifrons and H. ampullatus (the other antitropical giant whales) is a whole lot greater (Mead mentions that they are in different subgenera). Regardless of what species placement may be in the future, for conservation purposes they should most certainly be treated as separate entities. I couldn't help but be a little curious that the IUCN gave the species the same conservation status - is B. arnuxii really not data deficient?


Anyways, more ziphiids coming at some point. I'm not sure which ones.

References:

Barlowe, Jay et al. 2006. Abundance and densities of beaked and bottlenose whales (family Ziphiidae). J. Cetacean Res. Manage. 7(3):263–270

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.

Connor, Richard C. et al. 1998. Social evolution in toothed whales. TREE vol. 13, no. 6.

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

Dalebout, Merel L. et al. 1998. Molecular genetic identification of southern hemisphere beaked whales (Cetacea: Ziphiidae). Molecular ecology 7, 687-694.

Geisler, Jonathan H. and Sanders, Albert E. 2003. Morphological Evidence for the Phylogeny of Cetacea. Journal of Mammalian Evolution, Vol. 10, Nos. 1/2,

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

Lambert, Oliver and Louwye, Stephen. 2006. Archaeoziphius microglenoideus, a new primitive beaked whale (Mammalia, Cetacea, Odontoceti) from the middle Miocene of Belgium. Journal of Vertebrate Paleontology 26(1):182–191

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. 2003. Intraspecific scarring in odontocete cetaceans: an indicator of
male `quality' in aggressive social interactions? J. Zool., Lond., (244) 71-77

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

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

Minamikawa, Shingo et al. 2007. Diving behaviour of a Baird’s beaked whale, Berardius bairdii,
in the slope water region of the western North Pacific: first dive records using a data logger. Fish. Oceanogr. 16:6, 573–577,

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. Vol. 20, No. 4, pp. 1439-1458.

Ohizumi, Hiroshi et al. 2003. Feeding habits of Baird’s beaked whale Berardius bairdii, in the western North Pacific and Sea of Okhotsk off Japan. Fisheries Science 69: 11-20

Pike, Gordon S. 1953. Two records of Berardius bairdi from the coast of British Columbia. Journal of Mammalogy. Vol. 34, No. 1, pp. 98-104.

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

Slipp, T. W. and Wilke, Ford. 1953. The Beaked Whale Berardius on the Washington Coast. Journal of Mammalogy, Vol. 34, No. 1, pp. 105-113

Indopacetus

The Mystery of the Tropical Bottlenose Whale

As you can see, this isn't going to be much of a mystery, but determining the identity of what probably was the largest animal with an unknown external appearance is certainly not an everyday occurrence. At times the situation resembled - dare I say it? - cryptozoology, well, aside from the fact that nobody doubted the existence of the animal, evidence was presented in the peer review by experienced observers and it wasn't a monster (or "prehistoric survivor") so naturally nobody calling them self a "cryptozoologist" payed much attention. But I guess there is a sort of spiritual similarity.

Our story begins with Morzer Bruyns in 1971, who brought attention to sightings of what appeared to be bottlenose whales in tropical waters. One the basis of two large skulls, occasionally assigned to the rather un-Hyperoodon-like genus Mesoplodon (well, externally at least), Bruyns speculated that the whales were Indopacetus pacificus (Pitman et al. 1999). Photographs of bottlenose whales taken near the equator were actually used to portray H. planifrons in a couple sources despite that genus having an antitropical distribution (Pitman et al. 1999) so it was quite understandable how that hypothesis did not catch on. Pitman et al. 1999 documented 45 sightings of good quality from experienced observers (the authors has 12 of them) and while some do outright identify the whales as H. planifrons, others classified it as Hyperoodon sp., Hyperoodon-like or as an unidentified beaked whale. Why the uncertainty? While also a large (~7 m max?) and robust beaked whale with a similar coloration, the tropical bottlenose whale occurred about 20-30 degrees farther north than H. planifrons, had a less stubby beak, a smaller and less bulbous melon and possesses the largest dorsal fin (relatively and absolutely) amongst ziphiids (Pitman et al. 1999). While nothing more was known about Indopacetus, Pitman et al. 1999 reconsidered the hypothesis and seemed to prefer it.


And suddenly, certainly without any warning, Indopacetus went from being the most poorly known ziphiids (which is saying something) to one of the better known ones - as an article by Pitman claims.

The range of H. ampullatus is in green, the range of H. planifrons is blue (after Reeves et al. 2002). "Tropical bottlenose whale" sightings are closed squares and Indopacetus strandings are open ones (Perrin et al. 1999, Dalebout et al. 2003, Watson et al. 2008). Potential range in yellow is speculative. I unfortunately can't access this recent article on distribution in the Western Indian. Perrin et al. mention a possible sighting in the Gulf of Mexico, which would greatly expand the range of the species. If anybody has Jefferson et al. 1993's Marine Mammals of the World, how certain is it that the sighting was not of H. ampullatus? Perrin joked that if it is a subspecies it should be named Indopacetus pacificus atlanticus.

Indopacetus Revealed!

Indopacetus showed up alive in July 2002 in Kagoshima, Japan. The specimen never made it into a journal and was apparently covered in a conference I can't access (Watson et al. 2008). Fortunately, a web page giving preliminary morphological and genetic data for this specimen reveals that it indeed was Indopacetus. The authors were not convinced it was the tropical beaked whale and thought yet another species was out there. The pictures provided didn't show much morphology reminiscent of Hyperoodon, the melon wasn't bulbous and the beak was long - for some reason the ADW page keeps on comparing Indopacetus to Berardius and this may be why. This actually isn't too much of a problem since larger observed tropical bottlenose whales were described as being "nondescript brown or gray-brown" and the melon is variable and varies from moderately bulbous to near-perpendicular (i.e. Hyperoodon-like) (Pitman et al. 1999).

It turns out that this was not the third known specimen of Indopacetus, but the seventh. This specimen was described as Dalebout et al. 2003 were in press with an article that gave an unprecedented amount of information on the species. Specimens four and five were juvenile males from Natal, South Africa (from 1976 and 1992) which were initially identified as H. planifrons until Dalebout et al. demonstrated their affinity with Indopacetus with genetic tests. Both specimens were similar to but distinct from H. planifrons and had such features as: a slimmer build, black coloration dorsally fading to white ventrally posterior from the blowhole, a "flipper stripe" (a delphinid-like character also in Tasmacetus), a patch of white pigment in the "ear" region, a mostly black upper jaw, white lower jaw and a lightly colored melon. This matches the photographs of calf tropical bottlenose whales taken and was used by Dalebout et al. to cement the identity of Indopacetus. Judging by photographs, it seems that adult males (i.e. the ones with linear scars) have many of the same coloration patterns as the juvenile - but Reeves et al. 2002 noted that the coloration was apparently variable and dominated by grayish-brown tones, apparently in adults. A 5.73 m male washed up in the Philippines and was discussed at yet another conference I can't access (Watson et al. 2008) and can theoretically answer any questions we have about adult coloration (if it was an adult).

Juvenile Indopacetus (~3.6 m). H. planifrons juveniles look similar but have a more robust body, lack a flipper stripe and have a more robust melon. The portrayal of an adult male Indopacetus (7m?) by Reeves et al. 2002 (based off of Pitman et al. 1999) is similar, but with a medium-brown coloration that occurs lower on the flanks and dark coloration around the large dorsal fin. Adult females, or at least the senile one pictured here, are fairly nondescript. The white circular marks are from cookiecutter sharks (linear scars also occur on adult males).

So now that we know what Indopacetus looks like and where it lives, what exactly is it? While suggested to be either Mesoplodon or Hyperoodon in the past, morphological studies by Lambert 2005 and Bianucci et al. 2007 put them in a clade with the other genera. Bianucci et al. also put Indopacetus close to 5 newly described fossil genera - oh, and their tree places Hyperoodon in a paraphyletic Mesoplodon. Autapomorphies of Indopacetus include a distinctive vertex with larger nasal than frontal and premaxillaries, a deep groove above the orbit, an antorbital tubercle and a width/depth ratio of the rostrum ranging higher than other ziphiids (Dalebout et al. 2003). Aside from concave curves from the cranium to the tip of the rostrum possibly there to strengthen it (Dalebout et al. 2003) - not much has been mentioned on the functional significance (and thus evolutionary significance) of these features.

While Perrin was certainly right about this bottlenose whale being well known compared to others in a morphological sense, ecologically nothing is known. MacLeod et al. 2003 proposed that since Ziphius and Hyperoodon preyed on relatively large fish and cephalopods (0.5-1 kg+) and never coexisted geographically and/or temporally they formed a niche. Indopacetus coexists with Ziphius for a great portion of its range (all of it?) and it would be interesting to find out how a Hyperoodon-like animal avoids competition with one that apparently feeds like Hyperoodon.

Actually, it would be interesting to find out more basic information like how common or rare Indopacetus is and how humans are affecting them. Watson et al. 2008 noted that specimens 9 and 10 from Taiwan in 2005 beached along with numerous other odontocetes after local Naval sonar testing. Pods of this species appear to get fairly large and I certainly hope that the beached specimens were not just a fragment from a larger group. Finally knowing what a species looks like and having complete specimens just seems to be the beginning in understanding them and who knows how much effort will get Indopacetus listed as something other than "data deficient".


With 2 out of 21 species down there are still many ziphiids to come.


-Cameron

References:

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

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, C. D. et al. 2003. Review of data on diets of beaked whales: evidence of niche separation and geographic segregation. J. Mar. Biol. Ass. U.K. , 83, 651-665

Pitman, Robert L. et al. 1999. Sightings and possible identity of a bottlenose whale in the tropical Indo-Pacific: Indopacetus pacificus? Marine Mammal Science, 15(2):531-549

Pitman, Robert L. 2002. Alive and whale: a missing cetacean resurfaces in the Tropics - Findings. Natural History. Available

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

Watson, Alastair et al. 2008. Distinctive osteology of distal flipper bones of tropical bottlenose whales, Indopacetus pacificus, from Taiwan: Mother and calf, calf with polydactyly. Marine Mammal Science 24 (2): 398-410

Tasmacetus

The introductory post mentioned how the family Ziphiidae was the most poorly known amongst cetaceans, and this monotypic genus is certainly no exception. While 42 strandings have been documented, depictions of the coloration were erroneous (and quite variable) prior to Reeves et al. 2002 - although the textual description still seemed outdated. Pitman et al. 2006 were the first to describe the coloration and established four definitive sightings*. The lightly colored melon and long dark beak are distinctive features, but particularly noteworthy are a dorsal "cape" on a light background, a "flipper stripe" and no apparent difference in the coloration of males and females. These coloration characteristics are typical of delphinids and Pitman et al. note that the presence of teeth in both jaws may be of some significance. The authors also point out that there is a superficial similarity to the more northernly Indopacetus which is something of a tropical Hyperoodon planifrons doppelgänger....

*Five prior sightings did not mention the coloration and are therefore suspect. Videotape of one indicated an "unidentified but distinctively patterned species of Mesoplodon". The authors later state that the coloration of several mesoplodonts is unknown.


This all begs the question of where exactly Tasmacetus fits into ziphiid phylogeny. Lambert 2005 places it as a basal taxa, possibly in a clade with Berardius while Bianucci et al. 2007 notes that a mix of archaic characters and derived characters puts it in an unresolved position. Since the most prominent archaic trait is the teeth in both jaws it is worth pointing out that Ninoziphius (a relative of Berardius and/or Tasmacetus? - Bianucci et al. 2007), Messapicetus and Ziphirostrum (members of Ziphiinae e.g. relatives of extant Ziphius - Bianucci et al. 2007) all appear to have teeth in the upper and lower jaws (Lambert 2005) and the extant Mesoplodon grayi has teeth in the upper jaw only (Reeves et al. 2002) suggesting multiple tooth loss events or reversals (or both?) in ziphiids. It should be noted that male Tasmacetus still have a pair of enlarged anterior teeth in addition to 72-96 others (Mead and Payne 1975). Geisler and Sanders 2003 place Tasmacetus as the sister group to other ziphiids which share nine synapomorphies (2 deal with teeth) and it is noteworthy that the molecular phylogeny of May-Collado and Agnarsson 2005 is in agreement with this. Mead 2007 notes that Tasmacetus has a non-derived stomach anatomy - but so do Hyperoodon, Ziphius and some mesoplodonts.

The range of Tasmacetus. Numbers indicate strandings - two were from Juan Fernandez Islands and six were from Tristan da Cunha. Dots indicate sightings, the dot from Tristan da Cunha indicates two sightings. So far it is known from about 33 to 50 degrees South. After fig. 1 of Pitman et al. 2006

Tasmacetus lives in an area with notoriously bad weather and small amounts of landmass so it is not clear if it (along with the pygmy right whale, hourglass dolphin and mesoplodonts) are rare or rarely encountered. MacLeod et al. 2003 theorize (on the basis of one example and the teeth) that Tasmacetus is a specialist on bottom-dwelling fish but Pitman et al. 2006 mention another example which had a stomach entirely filled with cephalopods. The specimens were from Argentina and Tristan de Cunha, respectively. We are going to need a lot more data to make any conclusions on the physiology of this genus, but at least we know how to identify it at sea!

The following is modified from Pitman et al. 2006:

Length: The largest accurately recorded specimen was a 6.6 m (21'8") female. Their Table 1 has 7 m (23') and 7.35 m (24') "bulls" - but these are unconfirmed. It is comparable in size to Ziphius and larger than mesoplodonts (judging from Reeve et al. 2002).

Head: The dark beak lengthens with age and is proportionally similar to Indopacetus and some mesoplodonts; it is longer than those of Hyperoodon or Ziphius. The pale melon is prominent (unlike in mesoplodonts) to a degree that resembles Indopacetus or Ziphius. It does not seem to become more prominent with age in males. Aerial observations reported a "blow" whereas those on ships did not (it may just be inconspicuous).

Body: According to Reeves et al. 2002 it is cigar-shaped and thus Mesoplodon-like. The pale shoulder "patch" is considered a diagnostic feature (in addition to the long dark beak and pale melon). Aerial observations should find the black "cape" from the blowhole to mid-dorsal fin and pale gray afterwards (in contrast to the pale melon) diagnostic. The dorsal fin is smaller than Hyperoodon and Indopacetus and falcate - but similar to Ziphius and some mesoplodonts.

School Size: The four observations gave schools of 3-6, higher than the usual 1-3 for mesoplodonts and Ziphius. According to Reeve et al. 2002, school size for Indopacetus is 15-20 average (and up to 100).

An adult male Tasmacetus - the coloration is described as blue-gray/brown in adults and olive brown in younger specimens. Aerial observations show a distinctly light melon, dark ("black") cape and light gray behind the dorsal fin.

Pitman et al. 2006 is available online for free, by the way and I couldn't help but notice that every website out there on the genus was in need of an update.


Coming up next, more ziphiids of course.



References:


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.

Geisler, Jonathan H. and Sanders, Albert E. 2003. Morphological Evidence for the Phylogeny of Cetacea. Journal of Mammalian Evolution, Vol. 10, Nos. 1/2

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, C. D. et al. 2003. Review of data on diets of beaked whales: evidence of niche separation and geographic segregation. J. Mar. Biol. Ass. U.K. , 83, 651-665

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

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

Mead, James G. and Payne, Roger S. 1975. A specimen of the Tasman Beaked Whale, Tasmacetus shepherdi, from Argentina. Journal of Mammalogy, Vol. 56, No. 1, pp. 213-218

Pitman, Robert L. et al. 2006. Shepherd's Beaked Whale (Tasmacetus shepherdi): Information on appearance and biology based on strandings and at-sea observations. Marine Mammal Science 22 (3) 744-755

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