Alamosaurus Quarry

Alamosaurus Quarry in Big Bend National Park

Dinosaurs, Dogs and then some
By Dr. Anthony Fiorillo, Curator of Paleontology, Dallas Museum of Natural History
(Reprinted from the Dallas Museum of Natural History newsletter, Naturally Speaking)

Carrying capacity: the number of individuals that the environment can support.

We live on an acre of land south of Dallas and recently inherited two dogs from my in-laws, bringing to three the number of dogs in our house. I have always loved dogs. Even at someone else’s house I could entertain myself with their dog for great lengths of time. When I was younger and working at a fast-food restaurant, I was never quite sure if it was my understanding of dogs or the ever present smell of hamburgers on me (despite numerous showers) that attracted dogs to me. Regardless, I have almost always had good relationships with dogs.

However, never have I had more than one dog at a one time. Having three has proven to be a challenge. Our black lab Harlo has a habit of barking at squirrels, and when Polly and Emma showed up at the house, they didn’t quite understand squirrels. But with the big black dog barking up trees, they figured they better do something too, no matter how many times we told the dogs to shush. So now rather than the neighbors hearing one bark, they are serenaded by a trio.

And one thing I’ve noticed with three dogs is that dogs don’t seem to have a real grasp on spatial relationships. For example, if I make a move for the door, that is a signal that the dogs might be going outside. I know that no two objects can occupy the same space at the same time, let alone three objects, but it seems that these dogs need a basic lesson in physics. When I’m not getting run over by their maneuvering for the door, it reminds me sometimes of the antics of the Three Stooges. Once outside, it’s a 50-50 chance that the dogs will stay together or run off in three different directions, only to return when they like it. And of course, then I’m faced with the immediate question of which direction do I go (though I am often tempted to just head back in the house and forget about them)? I’m sure that the neighbors are quite familiar with the names of our dogs (and perhaps one or two other words not appropriate to print).

I really do think if I could evolve a third hand for petting, they would all be much happier because they wouldn’t have to bump heads so often. With only two hands and only two eyes for watching three dogs, I'’ not quite sure of the carrying capacity for dogs for our acre.

But with respect to how many animals can fit into one environment, I spent a lot of time on the road this past summer going from one paleontological excavation to another. As a result of all this travel time, I found myself wondering about the dig that I have going in Big Bend National Park (with the University of Texas at Dallas). At this excavation site, we are excavating the remains of at least two individuals of a sauropod dinosaur called Alamosaurus. Sauropods are the largest animals to ever walk the earth and had long necks and long tails. To many people, the image of a sauropod is their definition of a dinosaur. I have spent a fair amount of time thinking about sauropods over the last few years (after reading this article, some may debate whether I’ve spent too much time), and have wondered about a variety of things related to their ecology.

Alamosaurus is poorly known because its remains are reasonably uncommon, which begs the question, “How many of these animals were there?” By this I mean, on that day in the Cretaceous, some 65 million years ago when this fossil site formed, how many of these sauropods were around? Being Texas, we’ll only concern ourselves with those that might have been in Texas.

The state of Texas is approximately 700,000 square kilometers. Because of their monstrous size, sauropods are often compared to modern elephants, though it would have taken many elephants to equal one sauropod. But for the sake of argument, let’s use population data for elephants and apply it to Alamosaurus. We are of course assuming that environments in the present approximate those in the Cretaceous, and that the metabolic need of an Alamosaurus and an appropriate number of elephants is the same. In Uganda, the elephant herds are such that the density of elephants range from 2.8 to 3.5 elephants per square kilometer. The mass of an elephant is between 3 and 5 tons. The estimated mass for sauropods varies from 6 to 90 tones, depending on which sauropod is being measured. A reasonable estimate for mass for an Alamosaurus is 35 tons.

Now if we take large elephants, 7 elephants would equal one Alamosaurus. And if we use the high end of the density of elephants (3.5/square kilometer), then we estimate that the density for Alamosaurus is one per two square kilometers and that the maximum number of individuals of Alamosaurus in the state of Texas 65 million years ago was 350,000. However, we have assumed that all of Texas at that time was land but in fact part of it were covered by seas. We also assumed that Alamosaurus was capable of living everywhere on the land, and that would seem unlikely given the presence of rivers, swamps, and mountains. So the figure of 350,000 is at best a maximum number and that the carrying capacity for the Cretaceous environment in Texas was probably much less.

I really don’t know how many individuals of Alamosaurus were in Texas during the Cretaceous. The issues surrounding carrying capacity in modern environments are complex, let alone trying to figure them out for a past environment. All I do know is that on a good day, the carrying capacity for dogs in our yard is three, but on those other days I think zero may be a better approximation.