Something dramatic happened to a lot of very big animals between 20,000 and 10,000 years ago. During this time period, 34 major groups of large animals died-out. Among those that disappeared, were ten species that weighted more than a ton. Giant sloths, mammoths, mastodons, giant kangaroos, and moa were just a few of the fast-vanishing fauna.

It has long been clear that these large animals, also known as "megafauna", perished in a short period of time. But scientists disagree about what caused their rapid decline. One explanation was that the humans that moved into the area about 13,000 years ago hunted the large animals to extinction. Another eplanation attributes the decline of large animals to an extraterrestrial object hitting the earth about that same time.

To better understand what brought about the demise of large land animals, a team of scientists set out to reconstruct the ecosystems of the past. The team, led by Jacquelyn Gill of the University of Wisconsin, Madison, went to Appleman Lake in Indiana. There they sampled the sediments that lined the lake looking for clues about the animals and ecology that once thrived in that region.

Gill and her colleagues sought three basic artifacts: fungal spores, pollen, and charcoal. Each of these clues held different bits of information. The fungal spores, distributed in the dung of large herbivores, provided a way of estimating how many "mega" animals were present in the region (more spores meant more dung and more dung meant more animals). Pollen grains provided scientists with to reconstruct the type of vegetation that existed in the region. The third clue, charcoal, held information about the fires that raged (or didn't rage) through the region in prehistoric times. More charcoal meant more fires.

The data Gill and her team collected indicated that large animals started to disappear from the region 14,800 years ago. This finding was surprising, archeologists previously thought that humans did not arrive to the region until 13,300 years ago. Gill and her team also showed that the dominant habitat, open savanna, gradually gave way to mixed woodlands. Fires became increasingly more common, a measure of how dramatically the landscape was changing as the megafuana vanished.

Refs:

Gill, J., Williams, J., Jackson, S., Lininger, K., & Robinson, G. (2009). Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America Science, 326 (5956), 1100-1103 DOI: 10.1126/science.1179504

Johnson, C. (2009). Megafaunal Decline and Fall Science, 326 (5956), 1072-1073 DOI: 10.1126/science.1182770

Image courtesy of Barry Roal Carlsen / University of Wisconsin-Madison.

Leaf-cutting ants have the power to slice, dice, and pilfer the foliage of an entire grove of trees in a matter of days. With impressive efficiency, swarms of leaf-cutters clip and carry leafy material in vast quantities back to their subterrainean colony. There they process the clippings into compost piles, atop which the ants cultivate crops of fungi. The ants tend these fungal gardens and in return the fungi provide a constant source of food for the ant colony.

Leaf-cutter ants and their fungal crops are among the most impressive symbiotic pairings known in the animal kingdom. This ant-fungus relationship is estimated to be between 8 and 12 million years old. But leaf-cutting ants are not the only type of ants to rely on fungus as a food source. There are, in fact, over 230 species of fungus-farming ants, a group referred to as the "attine ants".

The first ants to cultivate fungal gardens lived over 50 million years ago. These ants practiced what is referred to as "lower agriculture", operating small-scale fungi gardens consisting of parasol mushrooms or coral fungi.

The symbiotic relationships in the lower agriculture systems are characterized by a looser symbiotic relationship than later evolving systems. Fungi in lower agricultural systems rely less on their ant hosts and can grow outside of the ant colony. Additionally, the ants are not as particular about the type compost they collect for their fungal garden. They don't harvest leave cuttings but instead settle for decaying material and insect feces.

The agriculture of later-evolving attine ants is more specialized though and their symbiosis with their cultivar is more intimately intertwined. These fungal species in these "higher agriculture" systems, including the fungi grown by leaf-cutting ants, must be tended by ants to ensure their survival. Additionally, the fungi pay the ants back well for their work by sprouting nutritious nodules called "gongylidia" that serve as a food source for the ants.

Refs:

Schultz, T., & Brady, S. (2008). From the Cover: Major evolutionary transitions in ant agriculture Proceedings of the National Academy of Sciences, 105 (14), 5435-5440 DOI: 10.1073/pnas.0711024105

Photos © Bandwagonman / Wikipedia.

Yesterday, I wrote about some extinct scorpionflies that scientists think may have fed on the nectar of seed ferns, conifers, and other ancient plants. Now you can get a pretty good idea of what some of these primitive pollinators looked like in this photo album of scorpionfly fossils.

A new study suggests that scorpionflies that lived during the Jurassic Period fed on the nectar-like juices of seed ferns, conifers, and other primitive plants. As the scorpionflies feasted on the sweet liquid from these plants, they may have also acted as animal pollinators—couriers of pollen grains that are vitally necessary to the reproductive cycle of their host plants. If this scenario is true, scorpionflies represent the earliest known animal pollinators.

In general, for plants to reproduce, pollen grains must be transported from the stamen of a flower to the pistil. There are numerous ways that this transfer can take place—pollen can be carried from stamen to pistil by the wind, water, or by animals.

Until now, scientists believed that primitive plants—plants that predated flowering plants—relied mainly on wind for pollination, not on insects. The understanding was that it animal pollination didn't become widespread until flowering plants evolved during the late Cretaceous period (99.6 to 65.5 million years ago).

But that reasoning has now been called into question by Dong Ren of Capital Normal University, Beijing, China and his colleagues. The scorpionfly fossil evidence they present suggests that scorpionflies may have been pollinating plants as early as 167 million years ago, long before animals started pollinating flowering plants during late Cretaceous.

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