Smithsonian.com

A cast of a (real) baby Triceratops skull. From Flickr user Cryptonaut.

When I took a college course about dinosaurs a few years ago, I took the opportunity to confirm what a family member told me when I was very young. Someone had given me a small lump of irregularly-shaped rock and said it was a dinosaur bone. It certainly looked like some kind of fossil, and in 2003 I brought it to my professor to see if he knew what it was.

If my professor was sure of anything, it was that my specimen was not a fossil. It looked like a bone, sure, but it was just a small rock that had formed in a way that looked bone-like. It did not have the honeycomb-like internal structure that is a tell-tale sign of fossilized bone. Such mistakes are easily made, though, and it seems that a similar fossil-like rock has been making a bit of news lately.

This past weekend, DL-Online posted a story about a “baby dinosaur” skull discovered by Minnesota rockhound Mitchell Voss. Held the right way there is something dinosaur-like about the image on the rock, but this resemblance appears to be due to irregular swirls on the rock. This is similar to the famous (and now lost forever) Old Man of the Mountain from New Hampshire. While the side of the mountain appeared to present a human-like face, the “Old Man” was just a series of cliff ledges that, viewed from the right angle, looked like a human face. The same phenomena is at work with this “baby dinosaur”, and I have no doubt that an examination of the internal makeup of Voss’ find will reveal it to be a rock.

The wonderful exhibit “Dinosaurs: Ancient Fossils, New Discoveries” will soon be coming to the Denver Museum of Nature & Science, and to promote it the museum has commissioned a special TV ad that can only be described as “Apatosaurus on Ice.”

Unfortunately, though, some people might think this is a bit of false advertising. There are no ice-skating dinosaurs in the exhibit, but the commercial is very impressive all the same! If you want to know more about how it was made, see this article from VFX World.

The skeleton of Limusaurus (the head is to the right). From the Nature paper.

As I have written about many times here on Dinosaur Tracking, paleontologists presently have an overwhelming amount of evidence that birds are living dinosaurs. That doesn’t mean that everything about the dinosaur-to-bird transition is well-understood, though. For years scientists have been faced with a puzzle involving the hands of living birds and bird-like dinosaurs. The dinosaurs most closely related to birds appeared to have a thumb and two fingers (digits I-II-III) while studies of the embryonic development of birds showed that they have fingers II-III-IV. This difference would have to be accounted for, and a bizarre new theropod dinosaur described by an international team of scientists in yesterday’s edition of Nature provides a crucial clue to this fossil puzzle.

The new dinosaur, named Limusaurus inextricabilis, is so strange that I almost don’t know where to start describing it. It lived about 156 million to 161 million years ago in what is now western China, and it was one of the dinosaurs that became mired in the famous “Dinosaur Death Trap” featured by National Geographic. Yet while scientists were able to identify it as a ceratosaur, one of the early groups of theropod dinosaurs, it was like no other ceratosaur they had ever seen. Instead of packing a mouthful of sharp teeth, like Ceratosaurus, Limusaurus did not have a tooth in its entire mouth! A pile of stones was found in its stomach region that probably ground up food inside its gut, and it is likely that this theropod dinosaur was actually a herbivore.

What is making headlines, though, is that Limusaurus had at least one feature that is very important to understanding how avian dinosaurs (i.e. birds) evolved.  Since we know that theropod dinosaurs evolved from five-fingered ancestors, it has long been assumed that, to end up with digits I, II and III, they lost two fingers: their pinky and ring fingers (or digits IV-V). In this way the fingers were reduced and lost, probably due to changes during embryological development, from the outermost finger moving in. What Limusaurus shows, though, is that after some dinosaurs lost their pinky they began to lose their thumb.

This is not what would have been expected, but it is clear that Limusaurus has a greatly reduced thumb and an enlarged second digit. In this way the second finger functionally became like a thumb, but what if Limusaurus was just an oddball? We can’t know if it was directly ancestral to any other dinosaurs, but the paleontologists then looked at the hands and fingers of other dinosaurs more closely related to birds (the coelurosaurus) and found their answer not in the finger bones, but in the wrist bones. The finger bones of these later dinosaurs alone might make it hard to tell if they were really I-II-III or II-III-IV, but the wrist bones provided a clearer picture. The wrist bones of dinosaurs more closely related to birds did not change as much as the fingers. They retained signs that the modified finger bones they were attached to were really II-III-IV, and this finally makes sense of both the fossil and embryological evidence.

Now keep in mind that Limusaurus is probably not directly ancestral to the dinosaurs that gave rise to birds. It is not a “missing link” (and the phrase “missing link” itself is more confusing than helpful when thinking about evolution).  What the skeleton of Limusaurus suggests, though, is that there was a significant shift in hand shape going on among ceratosaurs during the Jurassic, and Limusaurus provides a window into how this change occurred. If the hypothesis of the authors is correct, and there is much reason to think it is, then we should expect to find other theropod dinosaurs with similar hand anatomy that link some ceratosaurs to tetanuran dinosaurs, the group to which coelurosaurs (and hence birds) belong.

There is much more to discuss about Limusaurus than any one blogger can cover, though, so have a look at what some other science bloggers have to say about this new find:

Archosaur Musings

Chinleana

The Loom

When Pigs Fly Returns

Parents of young dino fans know it has to happen eventually. When birthday time rolls around, their future paleontologist wants a cake in the shape of, or at least adorned with, dinosaurs. There’s plenty of ways to do this. For those short on time there’s always the option of running to the supermarket and placing a few plastic dinosaurs on top, but what if you want to make something a little more elaborate? Lucky for you, the website Howdini.com has a step-by-step video showing you how to make a pretty neat-looking dinosaur cake:

How to make a dinosaur birthday cake

I’m no wiz in the kitchen (I almost have all the scorch marks cleaned up after my last attempt at cooking), but this doesn’t look too difficult. Maybe I’ll make it for an end-of-summer dinosaur party, but knowing my luck with baking, I might want to try a practice run first.

Every day, President Barack Obama takes on tough political questions, but what does he think about space dinosaurs? That is what Steven, an 11-year-old from St. Louis, Missouri, would most like to know. In a new book containing children’s letters to the president, Kids’ Letters to President Obama, Steven considers whether dinosaurs could survive beyond our upper atmosphere;

Are space dinosaurs real? I think not, because for one, it’s really unlikely for a dinosaur to be alive and not have to breathe oxygen, but my uncle believes in them.

I’m sure NASA will get right on searching for space dinosaurs if they haven’t found some already.