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Tuesday, February 14, 2006

Paleontology for the Masses

Before Christmas I had the wonderful opportunity to attend the Prehistoric Journey Symposium at the Denver Museum of Nature and Science. The symposium was open to the public, although museum members were given reduced admission, and featured seven paleontologists who each lectured for 40 minutes on a subject of current research in which they're active. In this post I'll review two of the seven lectures.

The lectures were attended by approximately 150 people, many of whom are associated with the museum either as employees or through its paleontology certification program (which now has over 100 graduates). The museum first held this symposium in 1995 when it features such heavyweights as Stephen Jay Gould and Lynn Margulis.

It was interesting to note in the opening remarks by one of the curators that since the Prehistoric Journey opened in 1995 the number of named dinosaur genera has doubled and that the museum now has over 110,000 specimens. Paleontology is alive and well it would seem.

I had never attended lectures by professional paleontologists before and was surprised both by their humor and the clarity with which they presented their material. Although I shouldn't have been, I was a bit surprised by the extensive use, of statistics within each specialty and, as you might be able to tell from this blog, a few good numbers always warm my heart.

More seriously, however, I think what I was most struck with was the ingenuity with which these scientists apply the scientific method in order to carry out their research and how extensive is their reliance on life today ("the present is the key to the past" in the words of Charles Lyell) in reconstructing the ecology, environment, and biology of these long dead creatures.

As an illustration of that point Dr. Ryosuke Motani of the University of California-Davis in his talk "When Reptiles become Fish-Shaped: A Story of Ichthyosaurs" did a great job of inferring some of the characteristics of these marine reptiles, mostly known from just two locations in England and Germany, from the characteristics of modern marine mammals and fish as well as from simple physics and the science of optics.

Ichthyosaurs (205-150 million years ago), evolved in early Triassic and when they first appear their body shape indicate that they used an eel-like swimming motion (anguilliform) which is characteristic of vertebrates living in shallow waters on the continental shelf, for example Catsharks. However, as they evolved into the Jurassic they took on their more characteristic dolphin-like shape. That shape is more characteristic of animals who cruise the open ocean. Motani then used the ratio of caudal fin height to length which puts a limit on the amount of force that an animal is able to create, and was able to estimate that the Ichthyosaurs of the Jurassic were probably not able to swim as fast as dolphins but rather more like that the speed of tuna.

He was also able to estimate an f-number (focal ratio which measures the amount of light, and therefore the relative brightness of an optical system) of the Ichthyosaur eye by estimating the focal length and the aperture diameter using the fossil skulls of Ichthyosaurs as well as analogs in modern animals. The result is Montain’s conclusion that over time Ichthyosaurs evolved better eyesight akin to owls and rats (with an f/0.8 to f/1.1) who are nocturnal feeders. It was interesting that he plotted the ratio of eye size to body size in a variety of animals and showed that Ichthyosaurs across the board were higher than most other animals.

Finally, Montani pieced together clues that include the fact that Ichthyosaurs possessed a type of bone that allows for compressibility, vision, squid eating diet preserved in fossils, even their body size to estimate that Ophthalmosaurus (Jurassic Ichthyosaurs) were fairly deep divers (although not as deep as dolphins) that could descend more than 600 meters and stay submerged for 20 minutes, a task that would take advantage of their keen eyesight to allow them to see to depths of at least 1,000 meters.

Is it Getting Hotter?
There were several other themes to the day which although not explicitly called for in the program, made an impression as they were touched on again and again. The most prevalent of these was climate change. Dr. Linda Ivany of Syracuse University in her talk titled “Marine Ecosystems and Climate Change: The Beginning of the Icehouse World in Antarctica”.

Ivany described her and her colleagues’ research in exploring the relationship over time between predators and prey (for example clams) in Antarctica and how those changes were affected by climate change. To do so she traveled to Antarctica to collect fossils on Seymour Island in what is known at the La Meseta formation, one of the few places that has no permanent ice cover and is littered with Eocene fossils.

She concluded that the same type of low predation environment in the seas around Antarctica which includes mainly starfish, slow moving anti-freeze fish, anemones, and worms, has persisted for the last 36 million years. To come to this conclusion, however, she couldn’t look directly at prey fossils since they are more rare and often don’t fossilize at all. Instead she collected around 1,000 fossil clams from a variety of stratigraphic horizons and locations on the island and measured shell characteristics such as thickness in order to infer the types of predators that were present.

Interestingly, she found that between two levels 15 of the fossil clam species that disappear are more heavily defended than the 16 remaining species. When plotted against data from the deep sea drilling project this matches nicely with the global cooling trend that intensified during that time. So it would appear that shell crushing predators did die out as a result of a cooler ocean.

She also looked shell chemistry in order to measure water temperature using the ratio of oxygen isotopes. This too showed temperature differences over time that supported the data from the predator/prey analysis. Her data even illustrate the warming trend of 41-42 million years ago.

One of the things I found fascinating was that she reported that two species of clams showed vastly different temperatures for the ocean during the same period. A couple of her graduate students dug into it and realized that, like tree rings, the growth bands from which they were taking measurements may not be laid down uniformly during each year. In other words, one species grew only in the winter when the water was cooler while the other grew the entire year.

Finally, she also found evidence on Seymour Island of glacial expansion in the early Oligocene (34 million years ago) at a time that corresponds with global cooling.

Although the oceans have warmed considerably since then there are still no shell crushers in Antarctica. The reason she hypothesizes is that the circular currents around Antarctica serve to isolate it and therefore don’t allow crabs, starfish and other animals to colonize the continent.

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