Animal Families With The Most Diversity Also Have Widest Range Of Size

Somewhere out there in the ocean, SpongeBob SquarePants has a teeny-tiny cousin and a humongous uncle.

That's just what one would expect from a new analysis of body sizes across all orders of animal life that was conducted by researchers at the National Evolutionary Synthesis Center (NESCent), in Durham, N.C. and the University of North Carolina, Chapel Hill.

Researchers Craig McClain and Alison Boyer created a giant database on body sizes across all orders of animal life and found that phyla -- families of animals grouped together by a similar body plan -- with the greatest diversity of species were also those with the largest range of body sizes.

The sponges, Poriferans, were found to have some of the greatest diversity of both body size and species, ranging from microscopic to the size of an automobile. Molluscs (snails, squid, clams, chitons), and Arthropods (crabs, insects, lobsters, copepods) also showed great diversity. So did our family, the Chordates, which ranges from a half-inch fish in the swamps of Borneo to the truly leviathan 100-ton Blue Whale, with all the fishes, birds and mammals in between.

On the one hand, it may seem obvious that diversity in size and diversity in species go together, acknowledges marine biologist McClain, assistant director of science at NESCent. But it also says something a little more subtle about how new species arise and adapt to all the available niches in the environment.

“This really comes down to understanding the diversity of life on Earth,” McClain said.

The group's findings appear online in Proceedings of the Royal Society B. The research was conducted in part at the Monterrey Bay Aquarium Research Institute, funded by the David and Lucile Packard Foundation, and the Smithsonian National Museum of Natural History. NESCent is a National Science Foundation collaboration of Duke, UNC and N.C. State that is housed in buildings Duke leases.

The Blue Whale, incidentally, is the largest animal ever, but the Chordate group doesn't boast the smallest. That distinction belongs to animals with names like mud dragons, brush heads, jaw worms, stomach hair worms and water bears that are so small they live between individual grains of sediment in the ocean. But this smallest group's range doesn't reach up to the largest body size.

This is a pattern that repeated itself several times in the data, McClain said. There are apparently physical limits to the range of sizes that can work for some body plans. In worms, for example, it is impossible to slither along if the girth and weight become too large. (The largest worm, Riftia pachyptila, from deep-sea vents, doesn't move.)

Within the range of sizes that works for a given body plan, evolution creates new species and new sizes, McClain said. What this sweeping analysis hasn't solved is the riddle about how different body sizes emerge. One theory says that body sizes arise through random natural variation. A second says that size diversity is driven by the availability of unused niches in the environment.

The finding also points to areas where more species might be waiting to be discovered. For example, the little-studied priapulid worms (aka “penis worms”) have only 16 species on the books, but with a very large range in size. McClain's guess is that there may be more undiscovered species within that range of sizes. “There are groups that definitely don't have a lot of people studying them,” he said.

Knowing something about a body plan's size constraints also might allow for a ballpark estimate of its number of species, McClain said.

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World’s Largest Snake Discovered in Fossilized Rainforest

Sixty million years before Jennifer Lopez starred in the film “Anaconda,” the world’s biggest snake slithered around northern South America. Excavations in Colombia co-organized by Carlos Jaramillo, staff scientist at the Smithsonian Tropical Research Institute in Panama and Jonathan Bloch, curator of vertebrate paleontology at the University of Florida’s Florida Museum of Natural History, unearthed fossil remains of a new snake species named Titanoboa cerrejonensis.

Surrounded by huge trucks extracting coal from Cerrejon, one of the world’s largest open-pit mines, researchers discovered fossilized bones of super-sized snakes and their prey, crocodiles and turtles, in the Cerrejon Formation, along with fossilized plant material from the oldest known rainforest in the Americas, which flourished at the site 58-60 million years ago.

Jason Head, the lead author of the new species description in the journal Nature, is a research associate at the Smithsonian’s National Museum of Natural History and assistant professor of ecology and evolutionary biology at the University of Toronto Mississauga. Head, with David Polly, associate professor of geosciences at Indiana University, used the ratio between vertebral size and the length of existing snakes to estimate that this boa-like snake must have reached 13 meters (42 feet) in length and weighed more than a ton. Titanoboa, as it is now called, is the largest snake ever known, and was the largest non-marine vertebrate from the epoch immediately following the extinction of dinosaurs 65 million years ago. “The discovery of Titanoboa challenges our understanding of past climates and environments, as well as the biological limitations on the evolution of giant snakes.” said Head “This shows how much more information about the history of Earth there is to glean from a resource like the reptile fossil record.”

Titanoboa’s size indicates that it lived in an environment where the average yearly temperature was 30-34 degrees Celsius. This estimate coincides with paleoclimatic models predicting greenhouse conditions. “This temperature estimate is much hotter than modern temperatures in tropical rainforests anywhere in the world. The fossil floras that the Smithsonian has been collecting in Cerrejon for many years indicate that the area was a tropical rainforest. That means that tropical rainforests could exist at temperatures 3-4 degrees Celsius hotter than modern tropical rainforests experience,” said Jaramillo.

Support for this research comes from the National Science Foundation, Fondo para Investigaciones del Banco de la Republica de Colombia, Smithsonian Tropical Research Institute Paleobiology Fund, the Florida Museum of Natural History, a Geological Society of America Graduate Student Research Grant and a National Sciences and Engineering Research Council of Canada Discovery Grant and the Cerrejon Coal Mine.

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