NEWSLETTER 04/2014 25.04.2014

"Sharks are traditionally thought to be one of the most primitive surviving jawed vertebrates. And most textbooks in schools today say that the internal jaw structures of modern sharks should look very similar to those in primitive shark-like fishes," said Alan Pradel, a postdoctoral researcher at the Museum and the lead author of the study. "But we've found that's not the case. The modern shark condition is very specialized, very derived, and not primitive."

The new study is based on an extremely well-preserved shark fossil collected by Ohio University professors Royal Mapes and Gene Mapes in Arkansas, where an ocean basin once was home to a diverse marine ecosystem. The fossilized skull of the new species, named Ozarcus mapesae, along with similar specimens from the same location, were part of a recent donation of 540,000 fossils from Ohio University to the Museum.

The heads of all fishes -- sharks included -- are segmented into the jaws and a series of arches that support the jaw and the gills. These arches are thought to have given rise to jaws early in the tree of life.

Because shark skeletons are made of cartilage, not bone, their fossils are very fragile and are usually found in flattened fragments, making it impossible to study the shape of these internal structures. But the Ozarcus mapesae specimen was preserved in a nearly three-dimensional state, giving researchers a rare glimpse at the organization of the arches in a prehistoric animal.

"This beautiful fossil offers one of the first complete looks at all of the gill arches and associated structures in an early shark. There are other shark fossils like this in existence, but this is the oldest one in which you can see everything," said John Maisey, a curator in the Museum's Division of Paleontology and one of the authors on the study. "There's enough depth in this fossil to allow us to scan it and digitally dissect out the cartilage skeleton."

Working with scientists at the European Synchrotron, the ESRF, Pradel imaged the specimen with high-resolution x-rays to get a detailed view of each individual arch shape and organization. "We discovered that the arrangement of the arches is not like anything you'd see in a modern shark or shark-like fish," said Pradel. "Instead, the arrangement is fundamentally the same as bony fishes."

The authors say it's not unexpected that sharks -- which have existed for about 420 million years -- would undergo evolution of these structures. But the new work, especially when considered alongside other recent developments about early jawed vertebrates, has significant implications for the future of evolutionary studies of this group. "Bony fishes might have more to tell us about our first jawed ancestors than do living sharks," Maisey said.

Story Source:

The above story is based on materials provided by American Museum of Natural History. Note: Materials may be edited for content and length.

Journal Reference:

1. Alan Pradel, John G. Maisey, Paul Tafforeau, Royal H. Mapes, Jon Mallatt. A Palaeozoic shark with osteichthyan-like branchial arches. Nature, 2014; DOI:10.1038/nature13195

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Biggest great white shark ever tagged in Australia off coast of WA

The massive female, estimated to weigh about 1.6 tonnes, is the biggest ever internally tagged in Australia, and one of the largest in the world. Photo: Fisheries WA

The tagging of a huge five-metre white pointer in King George Sound has presented a potentially huge breakthrough in shark research and a triumph for local Fisheries staff.

The massive female great white, estimated to weigh about 1.6 tonnes, was the biggest ever internally tagged in Australia, and one of the largest in the world.

The shark was measured at 5.04m to the fork in its tail, suggesting an overall length of around 5.3m.

Shark Monitoring Network project manager Mark Kleeman said internally tagging a white pointer of this size was almost unprecedented. Photo: Scott Coghlan

It took three Fisheries staff two-and-a-half hours to subdue the shark, which was hooked close to Mistaken Island in around 15 metres of water on Sunday, March 30.

The same shark had been externally tagged the previous Wednesday when it approached a Fisheries vessel close to Limestone Head, and then set off receivers at Ellen Cove on the following Thursday and Friday, leading to beach closures.

The great white took a salmon bait, culminating in it being fitted with an internal tag to help monitor its movements for up to 10 years.

Shark Monitoring Network project manager Mark Kleeman said internally tagging a white pointer of that size was almost unprecedented and a cause for celebration.

"This is very exciting and potentially a world first," he said.

"It is something we have been striving for and it is great to prove we can handle an animal of that size.

"The main thing is that tracking larger animals opens up a whole new world.

"Lots of juveniles have been tagged, but to have a fully-mature female and get 10 years of data out of it is a big thing for us.

"We are excited by the potential of what this shark can give us."

The shark was caught using 14-16mm rope attached to 3mm cable, and a hook considerably smaller than that with which Premier Colin Barnett infamously posed a few months ago.

After the shark was finally subdued, Fisheries staff had to attach three ropes around it and roll it upside down.

However, once it was upside down the shark went into a state of "tonic immobility", similar to being asleep.

That enabled Fisheries workers, aboard a 6m vessel not much bigger than the shark, to make a small incision in its stomach without lifting it out of the water and insert the tag.

The whole process took about five minutes.

Mr Kleeman said only about 340 sharks of various species, including a small number of white pointers, had been tagged in Australian waters.

While there has been so much attention on the drum line program off the west coast, Fisheries staff in Albany have been putting in long hours to quietly tag these sharks, which are around in good numbers at the moment, possibly due to the salmon schools in the area.

However, it did not make them easy to catch.

Mr Kleeman said there had only been five great whites tagged in Albany over the last 12 months and 17 along the south coast since 2009, making each successful tagging significant.

When this newly-tagged great white comes close to the network of receivers dotted along the southern WA coastline from east of Albany to Ocean Reef, Fisheries will receive instant notification of its location.

The shark remains in King George Sound. It set off receivers again earlier this week. Beaches were reopened on Tuesday.

"We will be able to see where it is travelling and how often," Mr Kleeman said.

"We will get a good picture of the movements of this particular animal.

"Over time we will be able to build the data and then we can see if there are any patterns forming, which is a great start for understanding more about them."

The satellite-linked network is part of a long-term project to help scientists better understand the movements of tagged white sharks through WA waters as well as improve safety at Western Australian beaches.

Along with the satellite-linked receivers, there are also more than 320 seabed monitors located off various parts of the WA coast which also record movements of tagged sharks.

External tags on great whites usually only last around two years, making internal tags the preferred option.

Mr Kleeman said it was believed female great whites didn't mature until 15-20 years of age, with this shark estimated at being more than 30 years of age.

"It is the first one we have caught of breeding size," he said.

"It had signs of mating scars, with bites down one side."

They also took DNA samples from the shark to enable researchers to study genetics, with the east and west coast appearing to have separate populations.

Mr Kleeman said it was interesting the shark set off the receivers near Middleton Beach at 4.41pm on Thursday and 4.42pm on Friday, possibly suggesting a pattern of behaviour.

He asked anyone who saw a great white report it to the water police immediately on 9442 8600, as sighting reports from members of the public remain a vital contribution to coastal safety.

- The Great Southern Weekender

Reef fish represent one of the largest and most diverse assemblages of vertebrates, according to Samantha Price, a postdoctoral researcher in the Department of Evolution and Ecology at UC Davis. Price is first author on a paper describing the work, published April 2 in the journal Proceedings of the Royal Society B.

The fossil record of reef fish is patchy, so Price and colleagues traced their ancestry by developing a comprehensive family tree of the major group of modern ocean fish, the acanthomorphs or "spiny-finned fish," and calculating the times when different groups migrated into or out of reef habitats.

The first wave of colonization occurred between 70 and 90 million years ago, before the end of the Cretaceous period, they found. At that time, most the world's reefs were built not by coral but by mollusks called rudists.

Rudists disappeared in the mass extinction at the end of the Cretaceous, 66 million years ago, and corals became the world's great reef builders. While the first-wave reef fish hung on to leave descendants in the present, a second wave of colonization took place as the world recovered from the extinction event.

The early wave of colonization began with lots of different-looking fish and over time there was an eventual filling of ecological niches accompanied by a decrease in colonization, Price said.

By about 50 million years ago, the fundamentals of modern coral reefs, including the ancestors of most major families, such as clownfishes and parrotfishes, were in place, Price said.

"If you were able to dive on a coral reef 50 million years ago, the fishes would seem familiar, you would recognize it as similar to a modern reef," she said.

Story Source:

The above story is based on materials provided by University of California - Davis.Note: Materials may be edited for content and length.

Journal Reference:

1. S. A. Price, L. Schmitz, C. E. Oufiero, R. I. Eytan, A. Dornburg, W. L. Smith, M. Friedman, T. J. Near, P. C. Wainwright. Two waves of colonization straddling the K-Pg boundary formed the modern reef fish fauna. Proceedings of the Royal Society B: Biological Sciences, 2014; 281 (1783): 20140321 DOI:10.1098/rspb.2014.0321

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