Friday, June 13, 2008

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

2 comments:

KeaponLaffin said...

I'll freely admit I didn't understand or research most of the details. But can this a possible example of a 'vertical'(N-S rather than E-W) ring-species?
I'm proly a moron, but like yer blog so far.

Cameron McCormick said...

The northern and southern bottlenose species (Hyperoodon) are much more closely related to each other than the tropical Indopacetus - plus it doesn't seem that any ranges overlap. I'm guessing that at some time in the past Hyperoodon lived throughout the Atlantic and got isolated at the poles when the climate warmed. If Indopacetus lives (or lived) in the Atlantic, then I'm guessing that somebody had to be occupying a different niche until fairly recently.

Oh and thanks, and I think you not understanding something says more about me as a writer than you as a reader...