Smithsonian.com

A Tyrannosaurus greets visitors at an IGA supermarket. From reader Cameron.

Today’s Dinosaur Sighting comes to us from reader Cameron, who snapped this photo of a Tyrannosaurus popping out of an IGA grocery store wall in Drumheller, Alberta, Canada. The dinosaur may look mean, but I’m sure he’s just enthusiastic about helping shoppers take bags to their cars. Too bad he’s got such tiny arms….

Have you seen a dinosaur in an unusual place? Snap a photo and send it to dinosaursightings@gmail.com and you may see it here!

Dinosaur Odyssey by Scott Sampson

Given the number of books that are published about dinosaurs, there is bound to be some overlap among them. Most titles fall into a handful of categories: the “menagerie” approach, where a collection of various dinosaurs is prefaced by a few short summaries of paleontology; the “life in the field” perspective, in which the scientific content is tied to the author’s experiences, and the “Age of Reptiles” summaries, which focus on which dinosaurs lived when.

But paleontologist Scott Sampson’s new book, Dinosaur Odyssey, cannot be pigeonholed into these categories. Relatively late in the book, Sampson recounts how paleontologist Jack Horner, harried by reporters asking whether a meteor had wiped out the dinosaurs, replied that he didn’t give a whit how dinosaurs died, he wanted to know how dinosaurs lived. Sampson uses this as his guiding principle throughout Dinosaur Odyssey, and gives readers a rare peek at what dinosaurs might have been like as living, breathing creatures.
Sampson starts things off not by diving into a discussion of bleeding-edge research, but by gradually setting the scene. Using dinosaurs as examples, Sampson discusses evolution, ecology, geology, biogeography and other concepts that provide essential background for the latter half of the book. In different hands, this material could easily be the stuff of dry, textbook-type recitation, but Sampson’s use of dinosaurs as examples and his injection of personal anecdotes into the storyline keep the text flowing nicely.

The second half of the book builds upon these topics by looking at looking at how dinosaurs interacted with one another and their world. Did the origin of flowering plants influence dinosaur evolution? Were the fancy horns on dinosaurs such as Triceratops for fighting or for display? Were dinosaurs really “warm-blooded”? How could so many different kinds of large predatory dinosaurs have lived at the same time? In answering these and other questions, Sampson refers to specific localities and studies, allowing the reader to get a better understanding of what particular places were like during the age of dinosaurs. Dinosaurs might seem almost like mythical creatures now, but Sampson shows that they were real animals that were affected by phenomena that are still shaping our world. His “dinosaur odyssey” offers a new way of linking the past to the present.

Part of the Dalton Wells bonebed exacavation. From the Palaeo paper.

It is often assumed that dinosaur paleontologists are interested only in getting the fossils they discover out of the ground as quickly as possible. This is not true. Paleontologists generally take great care to document and catalogue every fossil removed from a dig site, because the position and surroundings of those fossils may say something about where the animal lived and how it died. This can be especially important when multiple skeletons are found together. Were the animals part of a herd? Did they die at the same time? Were their bones washed to the same place by a river? Did scavengers pick at the bones?

Paleontologists studying the Dalton Wells bone beds near Moab, Utah, have grappled with such questions for a long time. Dated to the Early Cretaceous, about 127-98 million years ago, the site contains the remains of at least 67 individual dinosaurs of eight different genera. Bones from sauropods, ankylosaurus, Iguanodon-like herbivores and the predatory Utahraptor are all mixed together, and many of them appear to have been trampled. What happened?

In a new study published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, researchers led by Brooks Britt of Brigham Young University try to envision how the massive bone bed was formed.  As scientists excavated the bone bed, they found not a collection of articulated skeletons, but a heap of bits and pieces jumbled together. This suggested that the dinosaurs did not die all at once in an event that covered up the bones en masse, but that the bodies probably accumulated over a relatively short span of time, maybe as the result of a drought, and were subjected to the elements. The bones show little sign of scavenging by predatory dinosaurs, but they were extensively damaged from being scattered by water, trampled by other dinosaurs and eaten by insects. Eventually, the dinosaur graveyard was covered with sediment and preserved for tens of millions of years.

Given the damage to the bones, it’s surprising that there is a bone bed to study at all. Anyone who has spent a lot of time on the African savanna can tell you that the skeletons of even large animals, such as elephants, can be reduced to splinters within a relatively short time if they are not covered up. Scavengers, insects and the trampling feet of herbviores can soon turn a full skeleton into bone shards. This fact makes every fossil important, and at places like the Dalton Wells bone bed, even heavily damaged bones can provide us with a window into the distant past.

A cast of the skull of Allosaurus, photographed at the Utah Museum of Natural History.

I have always felt a bit sorry for Allosaurus. It was one of the top predators in what would become North America during the Jurassic, but the fearsome tyrannosaurs of the late Cretaceous are much more popular. In fact, the popularity of Tyrannosaurus and its kin has created the impression that the allosaurs dwindled and died out before the end of the Age of Dinosaurs, that they just could not compete with bigger, meaner predators. But a new study published in the journal Naturwissenschaften by paleontologists Roger Benson, Matt Carrano and Stephen Brusatte shows that close relatives of Allosaurus were going strong until the very end.

Over the past several decades, numerous enigmatic theropod dinosaurs have been discovered from Cretaceous rocks outside North America. A number of these, such as the recently described Aerosteon , closely resembled Allosaurus. And Aerosteon was not alone. The authors of the new study have placed it together with the theropods  Australovenator, Chilantaisaurus, Fukuiraptor, Megaraptor, Neovenator and Orkoraptor in a group called the Neovenatoridae.

If these names sound a bit unfamiliar, it’s because most relatively new dinosaurs are quite new—discovered within the last decade or so—and many of them have been hard to categorize. Megaraptor is a good example: at first, researchers thought that it was an enormous “raptor”-type dinosaur, though later studies suggested that its large claws were a sign that it was related to Spinosaurus. Now we know that it was more like Allosaurus in form and was part of a “hidden” radiation of this type of dinosaur throughout the world during the Cretaceous.

As a group, the Neovenatorid dinosaurs were smaller and more fleet of foot than their well-known relatives the carcharodontosaurids. Both groups are closely related to Allosaurus, being parts of the larger group the Allosauroidea, but they represent different sorts of adaptations. They probably played a very different role as predators in the ecosystems in which they lived.

A section of the trackway showing a ornithischian dinosaur (green tracks) walking uphill. From the PLoS One paper.

About 199 million years ago, on a small patch of land that is now preserved in the present-day African nation of Lesotho, there was an inclined slope next to a riverbed. Within hours, days, or even weeks of each other, several different dinosaurs climbed up and down the slope, leaving their footprints behind. Their tracks can still be seen there today, and as reported by paleontologists Jeffrey Wilson, Claudia Marsicano, and Roger Smith in the journal PLoS One, these tracks give us some clues as to how those dinosaurs moved.

Dinosaur footprints are effectively bits of fossilized behavior, and the Lesotho tracksite provides a rare look at how dinosaurs walked when moving up or down inclines. The site preserves the tracks of several ornithischian dinosaurs, which may have been similar to Lesothosaurus, and a single theropod dinosaur, which the researchers compare to Dracovenator. They handled the slippy slope in different ways.

The theropod dinosaur tracks show that it was walking parallel to the riverbank on the top of the slope before veering downwards to descend to the water. When it did so it stayed on two feet but it moved more slowly, as indicated by the shorter length between footprints in the portion where it was going downhill. This dinosaur also appears to have gripped into the ground with its foot claws, steadying itself as it moved downhill.

The ornithischians did something different. One of the ornithischian dinosaurs started on the riverbank and moved up the slope, and as it moved it changed the way it walked. On the riverbed it walked on all fours, holding its limbs out to the side and placing its entire foot on the ground. This was a slow-and-steady posture. As it began to move up the slope, however, the dinosaur moved its limbs closer to the midline of the body and stood on its tiptoes. Only when it reached the top of the slope did the dinosaur then stand up on two legs, keeping the same tip-toed posture.

What these tracks show is that the way dinosaurs handled walking on inclined surfaces was constrained by the type of bodies they had. The ornithischians changed their posture to cope with different obstacles and walked on all fours if they had to. The theropod, by constrast, could not do the same. It probably had arms that were too short to assist it in coming down the hill and thus relied on gripping the ground with its feet to stabilize itself.

At a time when we regularly see dinosaurs walking around on television and in movies this might seem kind of humdrum, but I think this description is still impressive. It provides us with a fleeting glimpse into the lives on animals that have been dead for hundreds of millions of years.