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DISPLAYING POSTS TAGGED: palaentology (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

Southern carnivorous dinosaur diversity

Author
by Kate C
Publish date
17 May 2012
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MV palaeontologist Tom Rich, along with colleagues Roger Benson, Patricia Vickers-Rich, and Mike Hall, today published a review of all the theropod dinosaurs known from early Cretaceous period deposits in southern Australia. In doing so, they present the first complete snapshot of local theropod diversity around 120-105 million years ago.

Theropods are a group of mostly carnivorous dinosaurs that walked on two legs and had three-toed feet. Included among the theropods are the infamous T.rex, the small and agile Deinonychus, the feathered Archaeopteryx and modern birds. Tom and his colleagues have been pulling theropod fossils out of Victoria's coastline deposits since the 1970s and in this review, they considered 37 bones and over 90 individual teeth. They conclude that the local Cretaceous theropod fauna comprised nine major groups (or taxa), including allosauroids, tyrannosauroids, spinosauroids and the recently-discovered ceratosaur.

fossils of therapod forelimbs Some of the fossils reviewed in this examination of southern therapod diversity. These are large theropod manual phalanges, or bones from the 'hands' of these dinosaurs.
Source: Benson et al.
 

evolutionary tree of therapod dinosaurs A summary cladogram (evolutionary tree) of the therapod dinosaurs, showing the relationships between the major groups within the suborder Therapoda.
Source: Benson et al.
 

Like the unique fauna of Australia living today, our prehistoric fauna was distinctive too, with some groups dominating the fossil record and others seemingly absent. In the past, palaeontologists have considered several explanations why the types of dinosaurs that lived in Australia were so different to the types found in other continents, even our nearby Gondwanan neighbours. Did certain groups evolve in other continents after Gondwana had split up, so those groups never dispersed to Australia? Or were there patterns of regional extinctions reflecting the differences in climate between the continents as they drifted apart?

As more fossils are uncovered and studied, the picture gets a little clearer. It now appears that many high-level dinosaur taxa, such as the tyrannosauroids and allosauroids, emereged earlier than previously estimated and were distributed all over the world during the Jurassic. This suggests they've been missing from Australian records simply because our dinosaur fauna is poorly known. The Australian fossil record is patchy – whether it's because the fossils have not been preserved or simply not discovered or properly interpreted yet – and often only one or two bones represent an entire group of animals.

However the isolation of Gondwana and Australia from the rest of the world, and the unique conditions here, did help shape a unique assemblage at the species level. During the early Cretaceous, Australia was still attached to Antarctica and was much closer to the South Pole than it is now. Earth's climate was much warmer, the poles were free of icecaps and Victoria and Antarctica were covered in lush, ferny temperate forests. Long periods of winter darkness and extended summer daylight influenced the evolution of endemic dinosaurs whereas in other parts of the world, their distant relatives were contending with quite different environments.

Australia's position near the South Pole 120 million years ago Approximate position of Australia 120 million years ago during the Cretaceous era.
Image: Ron Blakey. Altered by Cally Bennet and Fons VandenBerg
Source: Colorado Plateau Geosystems
 

The possibility remains that some dinosaurs, such as the long-necked quadrupedal sauropods, which were present in Queensland but have not been found in Victoria, could not survive in cool, dark Cretaceous southern Australia and and so they did not enter this area.

Links:

Benson RBJ, Rich TH, Vickers-Rich P, Hall M (2012) Theropod Fauna from Southern Australia Indicates High Polar Diversity and Climate-Driven Dinosaur Provinciality. PLoS ONE 7(5): e37122.doi: 10.1371/journal.pone.0037122

Monash University: The killer dinosaurs of south-eastern Australia

600 Million Years: Victoria evolves

Dinosaur Walk

MV News: Victorian tyrannosauroid found

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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