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DISPLAYING POSTS TAGGED: baleen whales (2)

First fossil of Pygmy Right Whale

Author
by Kate C
Publish date
10 August 2012
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The Pygmy Right Whale (Caperea marginata) is the oddball of the whale world. The bizarre anatomy of this species has confounded researchers for years – even its common name demonstrates our historical lack of understanding. Its arched upper jaw and skim-feeding behaviour is similar to the right whales however DNA analysis shows that Pygmy Right Whales are more closely related to the rorquals (family Balaenopteridae) than the true right whales (family Balaenidae).

The puzzle of the evolutionary history of this species was not helped by the fact that it appeared completely absent from the fossil record. Palaeontologist and whale expert Erich Fitzgerald was therefore extremely pleased to identify a lone fossil specimen in the Museum Victoria as a partial periotic (the bone that surrounds the inner ear) of an ancient relative of the Pygmy Right Whale.

One theory about this group, explains Erich, is that "the bizarre features of the Pygmy Right Whale evolved rapidly within the last three to four million years. But this fossil suggests that they're much older than that." The specimen, which Erich describes as "looking like a coconut," is larger than the periotic of the living Pygmy Right Whale and dates to the late Miocene. This makes it six million years old, which will help calibrate the whale phylogenies (evolutionary trees) that are based on DNA sequences.

four views from different angles of whale earbones. Comparison of the incomplete fossil specimen (left) with a complete earbone of a juvenile Pygmy Right Whale.
Image: Erich Fitzgerald
Source: Museum Victoria / Journal of Vertebrate Paleontology

 
It is the peculiar skeleton of the Pygmy Right Whale, particularly of its ear bones, that allowed Erich to identify such an odd and incomplete fossil. "Baleen whales in general have strange skulls but in Pygmy Right Whales the ear bones are particularly strange because the back end, of the periotic, is enormous and bulbous. This fossil has no features that would ally it with any other family."

The strangeness of this whale doesn't end with its skull. First up, there is its size; at just 6.5 metres long, it's the smallest living baleen whale. Compare this with its colossal distant relatives, such as the 33 metre Blue Whale. But there's more, says Erich. "If we look beyond the head, there are some really strange things. In particular, the Pygmy Right Whale has ribs that are flattened and expanded. It almost looks like the ribs have formed a shield over the organs." This may relate to their unusual way of swimming which requires a stiffer trunk. "A young animal filmed underwater in South Africa shows that they flex their entire body not just the tail. It's thought that the ribs may be expanded to help keep the body rigid during this movement."

Until this footage, almost all knowledge of the species came from stranded individuals. Recent aerial photographs of a pod of Pygmy Right Whales off the coast near Portland showed some kind of social behaviour but exactly what it is – feeding, reproducing or something else – is still unknown.

Museum of New Zealand Te Papa Tongarewa made this video with a dissection of a stranded whale which clearly shows the unusual ribs.

 

Links:

Erich M. G. Fitzgerald. 2012. Possible neobalaenid from the Miocene of Australia implies a long evolutionary history for the pygmy right whale Caperea marginata (Cetacea, Mysticeti). Journal of Vertebrate Paleontology 32(4): 976-980. DOI:10.1080/02724634.2012.669803

The Tetrapod Zoology blog has a series of three terrific posts about Pygmy Right Whales:
Caperea is really weird
More on little Caperea
Caperea alive

Evolving the biggest mouth in history

Author
by Kate C
Publish date
17 August 2011
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Comments (1)

Imagine that your face was articulated so that your jaw could split down the middle and expand sideways until the tips were out as wide as your ears. Imagine that you could move all the bones of your face... not just the soft tissue, but the bones themselves.

Sound bizarre? Alien, even? Yet this is exactly what happens every time a Blue Whale takes a gulp of water. The filter-feeding whales, otherwise known as baleen whales or mysticetes, have feeding adaptations that are unique among mammals. Their intriguing evolutionary history is the subject of Dr Erich Fitzgerald's research, and today he's published a paper that overturns a long-held belief about how the baleen whales evolved.

Blue Whale Illustration of the biggest mouth in history at work. The Blue Whale can expand its mouth to gulp huge volumes of krill-filled water.
Image: Carl Buell
Source: Museum Victoria
 

For several years, he has worked on an extraordinary 25 million-year-old species known from fossils that were found in the 1990s near Jan Juc on Victoria's west coast. Called Janjucetus, this early baleen whale predated the evolution of baleen – the hairy structure used by modern baleen whales to filter tiny crustaceans from the sea. Instead, Janjucetus had the large eyes and ferocious teeth of a hunter.

Erich Fitzgerald with Janjucetus Dr Erich Fitzgerald holding the jaws of Janjucetus with Melbourne Museum's massive Blue Whale skeleton in the background.
Image: Jon Augier
Source: Museum Victoria
 

There are two key changes in the skull that permit the filter feeding of modern whales. The first is a lower jaw that can split down the middle. In humans, the seam (or symphysis) where the two halves of the jawbone meet at our chin is fused, thus our jaws are rigid. In contrast, baleen whales have greatly elongated jawbones that do not meet in the middle. The second change is in the width of the upper jaw; baleen whales have evolved a wide mouth, allowing them to engulf massive volumes of water.

"Previously it was thought that the origins of both features were intimately linked to filter-feeding and that's what differentiated baleen whales from toothed whales and dolphins," explains Erich. His research has just overturned this theory since Janjucetus had a wide upper jaw yet its lower jaw had a tightly connected, immobile symphysis. "So, the loose symphysis is not typical of all baleen whales, it's a later innovation. The earliest baleen whales could not expand and contract their lower jaws so were anatomically incapable of filter-feeding, yet they had these wide upper jaws."

Jaws of Janjucetus The fossilised jaws of Janjucetus, clearly showing the immobile symphysis at the tip.
Image: Jon Augier
Source: Museum Victoria
 

What Erich describes is an elegant example of an exaptation, where a feature evolved to serve a particular function but was later co-opted into a new role. Erich believes that its wide jaw helped Janjucetus to suck in large singe prey items, such as squid or fish, and didn't evolve for filter-feeding at all.

Says Erich, "Charles Darwin reflected upon this in The Origin of Species. He wondered how you could go from a whale that has big teeth like Janjucetus does and catching fish and squid one at a time, to something like a modern Blue Whale that feeds en masse. This is the kind of fossil palaeontologists dream of finding because it shows a transitional form."

"It's an exciting discovery, but actually not as surprising as you might think," concludes Erich. "Evolution by natural selection implies that we should expect to find these kinds of fossils in the rocks." The next question he looks forward to answering is how whales shifted from suction feeding to filter-feeding. "I think we're really close to finding a transitional series of fossils that illuminate this."

Erich's paper about this discovery, 'Archaeocete-like jaws in a baleen whale', is published today in Biology Letters.

Links:

Video: Erich discusses whale evolution

MV News: Ferocious fossil

Dr Erich Fitzgerald

Baleen and toothed whales

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