Looking for the evolutionary origins of our pretty smile
It takes both teeth and jaws to make a pretty smile, but the evolutionary origins of these parts of our anatomy have only just been discovered, thanks to a particle accelerator and a long dead fish.
All living jawed vertebrates (animals with backbones, such as humans) have teeth, but it has long been thought that the first jawed vertebrates lacked pearly gnashers, instead capturing prey with gruesome scissor-like jaw-bones. However new research, led by the University of Bristol and published today in Nature, shows that these earliest jawed vertebrates possessed teeth too indicating that teeth evolved along with, or soon after, the evolution of jaws.
Palaeontologists from Bristol, the Natural History Museum and Curtin University, Australia collaborated with physicists from Switzerland to study the jaws of a primitive jawed fish called Compagopiscis.
The international team studied fossils of Compagopiscis using high energy X-rays at the Swiss Light Source at the Paul Scherrer Institut in Switzerland, revealing the structure and development of teeth and bones. Lead author, Martin Ruecklin of the University of Bristol said: “We were able to visualise every tissue, cell and growth line within the bony jaws, allowing us to study the development of the jaws and teeth…
(images: Sculptured reconstruction of the placoderm Dunkleosteus - Credit: Esben Horn; CT-scan courtesy of Phil Anderson, University of Massachusetts Amherst; Michael Ryan and Eric Snively, Cleveland Museum of Natural History; model and images Martin Rücklin, University of Bristol)
More information:‘Development of teeth and jaws in the earliest jawed vertebrates’ by Rücklin, M., Donoghue, P. C. J., Johanson, Z., Trinajstic, K., Marone, F. and Stampanoni, M., Nature, 2012.
Oxygen increase triggered by vascular plants enabled the development of complex animals.
by Joseph Milton
Plants made the evolution of large, complex animals such as predatory fish possible, a study of ocean sediments suggests. The findings, published in this week’s Proceedings of the National Academy of Sciences1, are the first empirical evidence to support a theory that there was a dramatic rise in oxygen levels in the Devonian period, 400 million years ago, and the first to indicate that the rise and spread of higher plants probably drove the increase.
“The evolution of vascular plants completely changed history, allowing a high concentration of oxygen in the atmosphere to be sustained. Eventually, that process led to higher animals such as ourselves,” says Tais Dahl, an earth scientist at the University of Southern Denmark in Odense, who led the study.
Dahl’s team looked at the concentration of molybdenum and the ratios of its isotopes — atoms of the same element with different numbers of neutrons and different masses — in oceanic rocks for clues to the concentration of oxygen in the seas over time…
What: Dunkleosteus is one of the biggest placoderms to ever swim in the paleozoic oceans. Placoderms were some of the first jawed vertebrates, and rapidly put these jaws to use, becoming the top predators of the devonian seas. Dunkleosteus was the apex predator of its days, with nothing to fear but other Dunkleosteus (some specimens show evidence of cannibalism). It reached lengths of up to 33 feet (~10 meters) and is estimated to have weighed 8,000 lbs (~3,600 kg). Studies have shown that these giant fish could open their mouths extremely fast, creating massive suction that would draw prey into their mouths. Larger prey would then be captured and crushed by the giant ‘teeth’ of Dunkleosteus. These animals did not have true teeth, but instead what served as their teeth were sharped and exposed projections of bone.
Placoderms were an early off shoot of jawed vertebrates, and have no living descendants. Modern fish are more closely related to land animals than they are to Dunkleosteus. This giant placoderm, along with the rest of it’s clade, went extinct at the end of the Devonian. Their disappearance is primarily attribute to large anoxic (a lack of oxygen) events on the ocean floor, which dramatically disrupted the food chain - leading to one of the largest extinction events in Earth’s history.
By Devonian standards, Dunkleosteus was highly evolved. It was one of the earliest jawed fishes. Instead of actual teeth, Dunkleosteus possessed two long, bony blades that could slice through flesh and snap and crush bones and almost anything else. Dunkleosteus had the most powerful bite of any fish, well ahead of sharks, including the Great White.
There are no modern descendants. Although Placoderms only existed for 50 million years, their mark on the fossil record is quite visible. They were a pioneer in the later scenes of the Paleozoic, and were vital to the success of the vertebrates. The Placoderms died out in the late Devonian for reasons that are still not well understood…
New studies have revealed several features in both its food and biomechanics as its ecology and physiology. Placodermi first appeared in the Silurian, and the group became extinct during the transition from the Devonian to the Carboniferous, leaving no descendants. The class lasted barely 50 million years, in comparison to the 400 million year long history of sharks…
Dunkleosteus detail - The Royal Tyrrell Museum of Paleontology (by Karen Carr)
Dunkleosteus was a heavily armored fish of the late Devonian, living about 400 million years ago. Dunkleosteus wasn’t a shark—in fact, it may have fed on sharks—but a placoderm. Fossil remains give no clue to coloration, of course, but Karen chose the black-and-white coloration of the modern orca to suggest the size and power of this ancient hunter.
A photograph of the Dunkleosteus terrelli fossil skull. This ancient fish had a bite that exerted 11,000 pounds of force, the strongest bite of any fish ever. The bladed dentition focused the bite force into a small area, the fang tip, at an incredible force of 80,000 pounds per square inch.