A Silurian “Shark” Tale: Nerepisacanthus denisoni
What comes to mind when you hear or read the word “jaws”? For many, it will be the eponymous 1975 Hollywood blockbuster, starring a memorable mechanical menace in the form of a ravenous Great White Shark – along with a few notable human actors, of course. Or perhaps it invokes images of beasts of a slightly later cinematic – but much earlier geological – vintage, and you conjure up one of the slavering carnivorous dinosaurs depicted in the Jurassic Park series. Whatever your imagination runs to, aquatic or terrestrial – living or extinct, it will likely involve some sort of nasty animal with a backbone and lots of pointy teeth in those snapping jaws.
But it hasn’t always been that way. Vertebrate predators with definitive jaws and teeth did not make their evolutionary debut on this planet until sometime around 440 million years ago, at the beginning of the Silurian Period, and long after the likely origin of jawless vertebrate animals in the so-called Cambrian Explosion. These most ancient gnathostomes (from the Greek words for ‘jaw’ and ‘mouth’) belong to an extinct group of odd-ball fishes called the Acanthodii, whose earliest fossil remains consist almost entirely of tiny mineralized body scales, larger fin spines, and rare jaw bones, isolated or dispersed over rock surfaces. The rest of the internal skeleton of acanthodians was not bony - it consisted instead of cartilage, like sharks and their relatives. This feature, along with a generally streamlined body shape and the rigid fin-supporting spines, has given rise to their colloquial group name of “spiny sharks.” Although there is general agreement among palaeontologists that they predate the evolution of true sharks, the precise affinities of acanthodians have been hotly debated.
The recent discovery by an amateur fossil collector of exciting new evidence in upper Silurian rocks (about 420 million years old) in southern Ontario is now shedding much needed light on the shadowy early history of jaw-bearing vertebrates. Until now, most of what we knew about acanthodians was based on relatively rare, but far more complete, fossils from geologically younger freshwater deposits of Devonian and Carboniferous age, after the group had evolved a variety of traits that tend to obscure their deeper origins. The unique new specimen, generously donated to the Royal Ontario Museum by its discoverer, represents the only near-complete acanthodian from pre-Devonian rocks anywhere in the world, and provides the first clear ‘road map’ of how all the dispersed elements of these very early gnathostomes fit together into a compact swimming predator. It forms the basis of a new paper co-authored by Dr. Carole Burrow (Queensland Museum, Brisbane – a world authority on early fossil fishes) and me in the journal PLOS ONE [published August 5th]. The fossil is assigned to Nerepisacanthus denisoni, a species previously named from only partially articulated incomplete remains found in Silurian rocks in New Brunswick.
The new fossil, consisting of part and counterpart on opposing faces of a rock split, measures just 112 millimetres in length, from the tip of the jaws almost to the end of the tail fin - it likely represents an immature fish. Although difficult to see without close examination, the specimen retains a wealth of minute detail.
Working with the authors of the paper, talented palaeo artist Danielle Dufault has painstakingly created a beautiful 2D reconstruction of the toothy little fish against the backdrop of its tropical Silurian lagoon home.
- PLOS ONE: Oldest Near-Complete Acanthodian: The First Vertebrate from the Silurian Bertie Formation Konservat-Lagerstätte, Ontario
- ROM: Tiny Ontario Fossil Fish Takes a Big Evolutionary Bite
- Original post
Guest Post By Dave Rudkin. Last Updated: August 10th, 2014.
The 505 Million Year Old Fish Metaspriggina: New fossils reveal first hints of the evolution of jaws in primitive fish
Here, Prof. Simon Conway Morris from the University of Cambridge and myself report the description of a half a billion year-old fossil fish, Metaspriggina walcotti, that we think fills an important piece in the earliest story of the vertebrates as a whole. This research paper is published in the scientific journal Nature (June 11, 2014).
- Metaspriggina walcotti as it might have looked in its environment. Reconstruction by Marianne Collins. © Conway Morris and Caron.
- Front part of a specimen of Metaspriggina walcotti (ROM 62933) from the Marble Canyon Burgess Shale locality in Kootenay National Park (BC) – head, showing a pair of eyes, to the left with pairs of pharyngeal bars to the top. Photo by: Jean-Bernard Caron.
- Kate Allen, Toronto Star – Incredible’ fossil find pinpoints a never-before-seen moment in the rise of our ancestors
- Emily Chung, CBC News – Ancient Rockies fish fossils reveal origin of jaws
- Carrie Tait, The Globe and Mail – Feature key to evolution found in fossil in Canadian Rockies
- Carl Zimmer, New York Times – A Long-Ago Ancestor: A Little Fish, With Incipient Jaws
- Tia Ghose, Live Science – Tiny Fish May Be Ancestor of Nearly All Living Vertebrates
- Abridged from original post found HERE.
Guest post by Jean-Bernard Caron. Last update: July 15th, 2014.
1.5 million years ago, the Toxodon, a rhinoceros sized beast, roamed South America, where, according to fossil records, was one of the most abundant large mammals on the continent. Though not related to the rhinoceros, there’s evidence that the Toxodon may have also had a horn.
Interesting Charles Darwin, during his Voyage of the Beagle, was one of several Western scientists to take an interest in the beast from which he would ponder why and how these giant animals were different than those in Europe.
Written by @kironcmukherjee. Last update: March 28th, 2014.
My buds David Evans & Kentaro Chiba gave me a peek at some of their research a few weeks back on dinosaur dating. Like trees, rings inside of dinosaur bones can tell you how old the animal was at death. I was invited to take a look at a hadrosaur shin bone they’re studying and observe the rings.
— Kentaro Chiba (@kchibs)January 22, 2014
In order to gain this data, Kentaro cut a slice along the width of the fossil to later observe under a microscope, photograph, and then study. The image Kentaro took is gorgeous not only in its beauty but also in its quality.
David and Kentaro gave me a peek at the image explaining the rings and details. They’re still in the process of analyzing their data, but once ready, they’ll debut their work for the world to see. At that point I might make a print and hang it above my desk!
Written by @kironcmukherjee. Last update: March 21st, 2014.
The Helmet Of A Titan: Ankylosaur Skull
Recently I hung out with my pals, Brian Iwama & Kevin Seymour from Palaeontology, who were hard at work reinstalling our Ankylosaurus skull back into its case. Occasionally our palaeontology staff will remove specimens from display to take quality photographs to keep their files up to date and for use by colleagues outside of the Museum.
Hanging out with this behemoth was a fascinating experience. The skull is ridiculously heavy as it still houses much of the rock bed it was buried in, within its skull. Ankylosaurus was covered in dermal scutes (essentially armour like bones), which not only added to its heft, but also made it the tank of its time. The scutes are incredibly rough. If you’re not carefully you could easily scratch your skin against the surface.
What I found most amazing was the teeth. Ankylosaurus was a huge beast, whose armour and strong, clubbed tail provided it with weapons to wield against predators. But Ankylosaurus was also a peaceful giant that seemingly preferred to eat alone. What is startling is just how small and few teeth they had. Think of a child’s molar, an Ankylosaurus’ teeth were smaller. Further these teeth wore down fast from the tough low lying vegetation it ate. Many Ankylosaurus had few to little teeth left at the end of their life. But this specimen has a nearly full compliment!
It was great getting an opportunity to hang out with Brian and Kevin while they reinstalled the Ankylosaurus skull into the Dinosaur Gallery!
Written by @kironcmukherjee. Last update: February 10, 2014.
Genuine Albertosaurus tooth. One of the most famous Canadian dinosaurs (just check out the name!) Albertosaurus was a smaller cousin of the Tyrannosaurus rex, similar to the Gorgosaurus. Check out the fine serrated edge along the tooth, similar to a steak knife. The detail is remarkable!