This learn node features a tiny dinosaur with big canine teeth that the Natural History Museum reports shows for the first time how one of the earliest dinosaurs grew into an adult. The webpage explains:

The turkey-sized reptile called Heterodontosaurus lived around 190 million years ago in the Early Jurassic period and had an unusual combination of molar-like and canine teeth.

Reptiles usually have small same-sized teeth along the length of their mouth but Heterodontosaurus had 2 fang-like canines at the front.

The image posted here is from a video narrated by Dr. Richard Butler, a dinosaur expert at the museum and featured on the page linked above.

For nodes of related learning: An excellent overview article about Anatomy and Physiology of the Reptile Mouth is provided at PetEducation.com. For time frames for the dinosaurs, the big picture can be seen in the Chart of Geological Ages at Connexions.

Early Cambrian arthropod chain gangs this learn node describes are fossilized in chain formation that reveals community behavior. The chain gang 525-million-year-old fossils were found in southern China’s Chengjiang Lagerstatte fossil field. A Science News report of the discovery says that the discovery site is “a treasure trove of fossils often compared to Canada’s Burgess Shale.” The above image from Science News (credit Derek Siviter) shows the that newly discovered species of Early Cambrian arthropod formed sturdy chains of about 20 individuals. In the report:

Nigel Hughes, a paleobiologist from the University of California, Riverside comments that these types of finds provide snapshot scenes of “normal” life.

“Of the millions of fossils, the chances of getting an occurrence where we can determine collective behavior is quite rare,” says coauthor Derek Siveter of the University of Oxford in England. He and his colleagues found 22 complete or partial chains, but only one solitary specimen.

A Brief History of Life on Earth provided at Connexions sets the time frame for these fossils

The map illustrating this learn node, from the University of California Museum of Paleontology, shows the Cambrian Period 500 million years ago and explains: “The location of the Burgess fauna is indicated by a star on the continent of Laurentia (western North America). Notice that Canada is located just south of the equator!” A Smithsonian web exhibit called Strange Creatures: A Burgess Shale Fossil Sampler begins: “more than half a billion years old, the fossils of the Burgess Shale preserves an intriguing glimpse of early life on Earth.” Britain’s Open University includes the Burgess Shale in a Science and Nature course on the Cambrian explosion.

The Burgess Shale became well known to the public through the late Stephen Jay Gould’s 1990 best selling book Wonderful Life: The Burgess Shale and the Nature of History. The fossils in the Burgess Shale have evoked awe and controversy over the century since they were first discovered. Called “Showdown on the Burgess Shale,” two lectures in The Unofficial Stephen Jay Gold Archive provide a framework for learning some of the basic ideas and issues for the evolution of life. The first lecture is “The Challenge” by Simon Conway Morris which is followed by Gould’s “The Reply.” In the latter, Gould writes:

The Burgess Shale, in the Canadian Rockies, contains the world’s most important fossil fauna—a detailed and exquisite record (with rarely preserved soft parts included) of marine life about 520 million years ago, just following the Cambrian explosion and therefore permitting us to census the results of this seminal episode in the history of animal life on earth.

More learn nodes at: learnodes.com