Panama Canal expansion rewrites the story of the world’s most ecologically diverse bats

Most bats patrol the night sky looking for insects. New World leaf-nosed bats take a different approach. Among the more than 200 species of leaf-nosed bats are those that hunt insects; drink nectar; eat fruit; snack on pollen; suck blood; and feed on frogs, birds, lizards and even other bats. They are among the most ecologically diverse mammals in the world and, until recently, were thought to have originated in South America.

“The theory that people have been putting forward is that they arrived very early in South America, where their only competition was insect-eating bats. So they developed a whole series of different feeding strategies,” said Gary Morgan, curator of vertebrate paleontology in New Mexico. Natural History Museum.

A new discovery suggests the story may be more complicated. In an article published by the Journal of Mammal Evolution, Morgan and colleagues describe the oldest known leaf-nosed bat fossils, discovered along the banks of the Panama Canal. They are also the oldest bat fossils in Central America, preserved 20 million years ago when Panama and the rest of North America were separated from the south by a sea route of at least 120 miles wide.

Based on these and other fossils, Morgan thinks previous studies may have chosen the wrong continent as the birthplace of leaf-nosed bats.

“We think they might be from the north.”

A once-in-a-century opportunity leads to several new discoveries

In 2007, hundreds of engineers, excavators and geologists gathered in Panama to undertake the daunting task of widening and deepening the country’s historic canal. Paleontologists weren’t far behind. After work crews used dynamite to blow up sections of the riverbank, researchers moved in and recovered fossil fragments from the rubble. The bones contained clues to one of the largest mass migrations of animals in Earth’s history, and the canal’s expansion marked the first time anyone had gotten such a close look.

About 5 million years ago, shifting tectonic plates built a land bridge between North and South America. After more than 100 million years of separation, animals in the northern hemisphere could freely move south and vice versa.

“Animals like sloths and armadillos came north, while horses, tapirs, bears and elephants went south,” said Bruce MacFadden, co-author of the study and curator of vertebrate paleontology at the Florida Museum of Natural History. The event is called the Great American Biotic Exchange and helped shape the current distribution of countless plants and animals across the American continents.

If the Panama Canal had not been built, it is likely that this event would still remain a mystery to scientists.

“It showed that the Panama Canal Basin, then part of North America, was teeming with the type of mammals you would have found in Nebraska or Florida rather than in South America,” Jonathan said Bloch, curator of vertebrate paleontology at Florida. Museum.

Rare fossils provide clues to the origin of leaf-nosed bats

Nearly all of the animals found in fossil beds of the same age near the canal zone represent the southernmost range of species from higher latitudes. There were bear dogs; miniature horses, rhinoceroses; camels; the first relatives of modern hippos; ungulates with paired antlers protruding from the head and snout; and at least one species of chalicothere, a bizarre chimeric animal that looked like a sloth crossed with a horse grafted to a giraffe.

The first South American mammal discovered in the older beds belonged to a species of primate, which is believed to have rafted across the seaway.

The leaf-nosed bat is the second South American mammal found at the site. This may suggest that the animals were more successful in crossing the ocean barrier than previously thought. The sea lane separating North and South America was five times wider than the modern Strait of Pas de Calais between England and France and 15 times wider than the Strait of Gibraltar which separates Europe of Africa.

However, other animals seem to have had little trouble making the journey. The list of non-mammalian animals that traveled south to north includes a boa constrictor, a crocodile, and frogs. There is little doubt about the origin of these organisms, but the fossil record of leaf-nosed bats is more ambiguous.

Today, leaf-nosed bats are distributed from South America to Arizona. Although they have been around for 20 million years or more, they left behind surprisingly few fossils. Three extinct species from this family similar in age to the Panama specimen have been found in Colombia, and fossils of much younger vampire bats have been excavated from several sinkholes in Florida. Beyond that, paleontologists don’t have much to do.

Zooming out makes things even blurrier. Fossils from two closely related families that were discovered in Florida predate the fossils of South American leaf-nosed bats and their relatives by 10 million years.

Further fossil discoveries will be needed to determine where leaf-nosed bats came from and why they developed such varied and refined appetites. Fortunately, there is no shortage of canal fossils. Although the expansion project only lasted nine years, paleontologists collected enough material to keep them busy for the foreseeable future.

“Time was of the essence, so we collected fossils much faster than we could have done scientifically,” Bloch said. “There are probably fossils from the project that will be described in 50 years.”

Nicholas Czaplewski of the Oklahoma Museum of Natural History, Aldo Rincon of Universidad del Norte and Aaron Wood of Iowa State University also co-authored the study.