… is a cartilaginous fish (not actually a shark but a ratfish or chimera) native to the Southwest Pacific off southern Australia and New Zealand. Because of its relatively small genome, this species has been targeted as a model organism for vertebrate molecular evolution.
In a whole-genome analysis published in Nature today, Byrappa Venkatesh & colleagues report that the elephant shark has the slowest rate of evolution of any known vertebrate. Its genome has not changed substantially in hundreds of millions of years. Comparison of the elephant shark genome with those of other vertebrates also provides intriguing insights into the evolution of vertebrate skeletons and immune systems.
'Elephant Shark' Takes Record for Slowest Evolution
by Bob Homes
It’s a living fossil to beat all others. The elephant shark, Callorhinchus milii, has the slowest-evolving genome of any vertebrate.
C. milii is not actually a true shark but belongs to a group known as ratfish, which diverged from sharks about 400 million years ago. When a team led by Byrappa Venkatesh of the Institute of Molecular and Cell Biology in Singapore compared its genome with those of other vertebrates, they found it had changed less from its presumed ancestral form than any other.
C. milii outstrips the coelacanth, the fish that previously held the slow-evolution record.
Such limited change means the elephant shark’s genome is the closest yet to that of the first jawed vertebrate, which lived more than 450 million years ago and gave rise to many modern animals including humans. It makes the elephant shark an important reference point for unlocking how this long-lost ancestor evolved. As well as jaws, the earliest fish pioneered bony skeletons and a sophisticated immune system, but it is not known when or how these features appeared…
Salmon sharks, Lamna ditropis (Hubbs and Follett, 1947), are closely related to porbeagle sharks, Lamna nasus. Salmon sharks measure up to 3.7 m in length and weigh a maximum of 454 kg. They have heavy spindle-shaped bodies with short, blunt, conical snouts and large gill slits relative to their body size. Their first dorsal fin is dark in color. Their dorsal (upper) sides and flanks are dark blue to gray or black in color. Their ventral (under) sides are white with darker blotches or spots.
Salmon sharks have been observed both singly and in schools, usually feeding. This species is a very fast swimmer.
In the eastern North Pacific, female salmon sharks live up to 20 years, males to at least 27 years.
In the western North Pacific, males mature at about 1.77-1.86 m in total length and 5 years of age, and females mature at about 2.00-2.23 m when they are 8-10 years old…
Like other sharks in Lamnidae family, salmon sharks are endothermic, meaning they are able to thermoregulate, or maintain a body temperature above the temperature of the surrounding water. Most other marine life is ectothermic, which means they maintain an internal temperature that matches the surrounding water. Fast swimmers, like sharks and tuna, are more commonly endothermic…
A prehistoric shark species is the earliest animal known to migrate, over 300 million years ago. The sharks lived in rivers but swam down to the sea to breed and care for their young.
Bandringa were primitive sharks that lived about 310 million years ago. They did not look much like typical modern sharks, having long spoon-shaped snouts.
Until recently scientists thought there had been two species of Bandringa, one that lived in fresh water and one that lived in the sea. But according to Lauren Sallan of the University of Michigan in Ann Arbor, there was only one species. The sharks migrated from their freshwater habitat to a saltwater nursery to reproduce.
Sallan and her team examined Bandringa remains from three sites in the Mazon Creek deposit in Illinois, including egg casings, bones, and soft tissue from juveniles and hatchlings. One site was originally on the coast but the others were inland. They found no evidence that fossils from the different sites belonged to different species…
(read more: New Scientist)
illustration byJohn Megahan, University of Michigan
Great white sharks are longer in the tooth than we thought. Traditionally, researchers age a great white (Carcharodon carcharias) by tallying the alternating light and dark bands that form on the animal’s vertebrae as it grows, similar to rings on a tree. Using this method, experts believed the species had a life expectancy of about 30 years.
This shark’s teeth resemble those of Goblin Sharks, Frilled Sharks and Viperfish, but it’s actually a squaloid. This is remarkable because no other dogfish sharks have teeth that are so large, slender, and widely-spaced; they would appear to be more suited for grasping rather than cutting prey. This species was first discovered off Japan in 1986, described as Trigonognathus kabeyaiin 1990, and given the common name “Viper Dogfish” in 2000.
The Broadnose Sevengill Shark is the only extant member of its genus. Whereas most other sharks have 5 gill slits, sevengill sharks are recognisable because of its 7 gill slits.
Like many other fish, the shark uses counter shading as a of camouflage. Its dorsal surface is silvery grey in colour, which allows it to blend with the dark waters beneath it when viewed from above. Conversely, its ventral surface is light in colour, matching the sunlit surface when viewed from below.
An opportunistic predator, the broadnose sevengill preys on a great variety of animals. It has been found to feed on sharks, rays, chimaeras, cetaceans, pinnipeds, bony fishes, and carrion. These sharks occasionally hunt in packs to take down larger prey, using tactics such as stealth to succeed.
The spotted ratfish aka spotted chimera, Hydrolagus colliei, can be found off the coast of California to depths of about 3,000 feet. Its common name comes from the white spots that cover its body and its pointed rat-like tail. These fish are chimeras, meaning they have characteristics of bony fishes and sharks, from which they descended millions of years ago.
While exploring the debris slope of the collapsed side of the underwater volcano Kick’em Jenny near Grenada in the Caribbean, the Nautilus expedition crew had a surprising find of a large cold methane seep and rich biology around it. Here are a few of the amazing creatures we spotted there and more can be found at http://www.nautiluslive.org.
Shovelnose Chimera, swimming sea cucumber, deep sea octopus, unidentified species of Snailfish.
Chimaeras are perhaps the oldest and most enigmatic groups of fishes alive today. Their closest living relatives are sharks, but their evolutionary lineage branched off from sharks nearly 400 million years ago, and they have remained an isolated group ever since. Like sharks, chimaeras have skeletons composed of cartilage and the males have claspers for internal fertilization of females.
Unlike sharks, male chimaeras also have retractable sexual appendages on the forehead and in front of the pelvic fins and a single pair of gills. Most species also have a mildly venomous spine in front of the dorsal fin.
Chimaeras were once a very diverse and abundant group, as illustrated by their global presence in the fossil record. They survived through the age of dinosaurs mostly unchanged, but today these fishes are relatively scarce and are usually confined to deep ocean waters, where they have largely avoided the reach of explorers and remained poorly known to science.
Chimaeras are the only vertebrates to retain traces of a third pair of limbs.
New Hammerhead Shark Species Found Off South Carolina
by Douglas Main
When new species are found near populated areas, they are often small and inconspicuous, not, for example, a hammerhead shark.
But that’s exactly what a team of researchers discovered along the coast of South Carolina. The new species looks virtually identical to the scalloped hammerhead, but is genetically distinct, and contains about 10 fewer vertebrae, or segments of backbone, new research shows.
The new species, named the Carolina hammerhead (Sphyrna gilbert), gives birth to shark “pups” in estuaries near the shore off the Carolinas, according to a study published in August in the journal Zootaxa…