Canadian fossil important new find

Tiktaalik roseae

Paleontologists have discovered fossils of a species that provides the missing evolutionary link between fish and the first animals that walked out of water onto land about 375 million years ago. The newly found species, Tiktaalik roseae, has a skull, a neck, ribs and parts of the limbs that are similar to four-legged animals known as tetrapods, as well as fish-like features such as a primitive jaw, fins and scales.

A model of a newly discovered species, Tiktaalik roseae, that fills in the evolutionary gap between fish and land animals, depicted in what scientists believe to be the animal's environment about 375 million years ago. (Model by Tyler Keillor, Photo by Beth Rooney)

These fossils, found on Ellesmere Island in Arctic Canada, are the most compelling examples yet of an animal that was at the cusp of the fish-tetrapod transition. The new find is described in two related research articles highlighted on the cover of the April 6, 2006, issue of Nature.

The full article is here.

Meet Dr. Will

Hi everybody. Mom apologizes for the long absence. We have a really special treat for you today. We would like to introduce you to Dr. Will Straight. He is a vertebrate paleontologist at Yale University. He has offered to answer some of our questions about dinosaurs and he sent us some really cool pictures. Here is his introduction:

You folks in Canada have some of the best dinosaur fossils in the world. I have been lucky to work with the Royal Tyrrell Museum on tyrannosaurs and hadrosaurs from Alberta for about ten years. Right now I am working at Yale University in New Haven studying the way dinosaurs healed if they broke a bone. I have attached a few pictures I have taken of fossils--there is an Allosaur skull, a jaw and teeth from a Tyrannosaurus rex that paleontologists named Stan, and an Albertosaurus tooth I found in Alberta.

We asked Dr. Will some questions and he sent us some awesome answers. Here we go!

Let's start with your questions. Your first one--Do dinosaur bones heal like our bones?--is tricky. You see, we don't know. That's why I'm working on this problem. I can say that the way they get injured--being broken from a fall or a fight, or getting an infection, or getting a disease like cancer--seems to be about the same. Their bones form large rough bony crusts to cover injured spots, just like ours; these bony crusts are called calluses, and they last a few years while the injury finishes healing. I have attached a picture of a hadrosaur (probably Edmontosaurus) specimen with a callus on it; this bone is a spine (called a process) that sticks up from a vertebra (part of the spinal column) that was a few vertebra behind the hips. This process got broken in the middle, near the white arrow. There are lots of different ways of making these calluses when a bone gets injured; and at least some of our data shows that dinosaur bone healing (and its growth) *are* different than in people. We want to know how different the dinosaur bone repair is, and why.

Then we wanted to know what the skulll was in the background of the picture of Stan the T-Rex's jaw. Can you see it? It reminded us of a cynodont.

You are off to a good start with your guess that the skull in Stan's picture is a cynodont. The skull in the picture is a model of a skull from a pelycosaur called Dimetrodon. Pelycosaurs and cynodonts were, however, closely related--the pelycosaurus are Permian ancestors of the therapsids and thus also ancestors of the cynodonts, the group that eventually produced modern mammals and us. Dimetrodon and the cynodonts share some of the same structures in their skulls, so it isn't surprising they look similar.

Then Mom had a question. She thought that Dr. Will's work with paleo climate looked really interesting...

Now Mom's comment. One kind of geochemistry I do involves the oxygen in water. Look at the second picture I sent--this diagram will help here. Water falls as rain; the rain fills rivers and ponds; the dinosaurs (or other animals) drink; their drinking water enters their bloodstream; and the bone and teeth are made of a mineral called apatite that gets its oxygen from the bloodstream. This many-step exchange may not take very long, a few hours or days, but the local climate (how hot and wet it is) can change the oxygen chemistry in the water even more rapidly, and always in the same way. So, whenever the dinosaur makes new bone or makes a little tooth enamel, it's taking a chemical "snapshot" of the environment. If we can string these snapshots together, we can detect change in the climate over time. The way dinosaur teeth grow allows us to do just that--their teeth grow in cone-shaped layers, one layer per day, like an upside-down stack of paper cups. Big carnivores like Albertosaurus (a type of small tyrannosaur) have a year or more of those daily layers, so I can get a whole year of the climate story. This research means I have to grind up parts of the dinosaur tooth, so museums are reluctant to give me a Tyrannosaurus rex tooth for research, but I could get three years of a climate record there.

Thanks Dr. Will we can't wait to ask you some more questions. Maybe you could help us answer our friend Raffi's questions? Chat soon,
The dinokids!