Sunday, February 05, 2006

Missing Link To Crocodile/Avian/Mammalian Past Rediscovered At Museum of Natural History


By Elaine Meinel Supkis

Researchers noticed what looked like a crocodile ankle poking out of a very old cast stored in the Museum's back rooms. Upon opening it, the fossil, which hasn't been seen in many years, turned out to be an important missing link from right after the great Permian extinction.

From National Geographic News:
Ankle aside, Effigia had large eyes, a long tail, and a toothless beak—not unlike the ostrich dinosaurs.

Effigia also walked on two feet, unlike modern crocs.

These physical similarities suggest that Effigia and the ornithomimid dinosaurs evolved similarly during two different eras, the scientists say.

The fossil record shows that many different features have been reinvented time and again in different species. But the Effigia example is a bit surprising.
Untangling the tree of life is a challenge. When we apply genetic tools, it is always surprising and filling out the record by classifying fossils enables us to understand all the many odd things that happened in the past for evolution is all about things happening.
Modern crocodiles are but one remnant of what was once a far more diverse croc family.

"Today we think of crocodiles as looking basically the same," said Nesbitt, of the American Museum of Natural History and Columbia University's Lamont-Doherty Earth Observatory. "But in their history they took on a wide variety of different body plans."

"Some looked like reptilian armadillos or cats, and others looked like little dinosaurs," Nesbitt said.

The crocodilian family may have been at its peak during the Triassic period.

"Toward the end of the Triassic period you have this crazy diversification of these crocodile relatives, including this animal," Nesbitt said.

"It was really the heyday of the crocodile-like animals, but the only lineage to really make it out of the Triassic was the lineage that led to modern crocodiles."


Recent research now shows that birds, turtles and crocodiles all split off from the main trunk of the dinosaur family pretty quickly and each struck out upon its own path which increasingly diverged. This splitting happened when many species were cut off from each other by the tremendous disaster of the end of the Permian when not only did the planet become very hot, the oxygen supply nearly disappeared again, it being an artifact of plants releasing oxygen when processing CO2. Each species the survived, and very few individuals survived this disaster, lived in small, restricted, protected areas. This allowed them to change rapidly without being interfered with.

Prior to the disaster, proto-mammalian Theraspids hunted proto-dinosarus. It looked like the earth would be inherited by the mammals who could keep their young warm. The bulk of all our fossil fuels comes from this balmy, wet, fertile period. For 100 million years, thick forests of fern-type plants covered the landscape. This mass of greenery and the milling insects and animals thrived happily. From Berkeley University:
In addition to having the ideal conditions for the beginnings ofcoal, several major biological, geological, and climatic events occurred during this time. One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. The amniote egg allowed the ancestors of birds, mammals, and reptiles to reproduce on land by preventing the desiccation of the embryo inside. There was also a trend towards mild temperatures during theCarboniferous, as evidenced by the decrease in lycopods and large insects and an increase in the number of tree ferns.
All this got buried suddenly and totally, under rock, no less. This doesn't happen inevitably. The only way to build up rock to seal in great masses of organic matter that couldn't rot easily is by suddenly turning the climate inside/out.

So hot winds, blowing sand, rains falling on bare rocks high up, causing mud flows to pour into deep valleys that were deep graves of former tremendous forests, compressing it all over the eons to turn it all into rock called "coal" or a liquid called "oil".

Here is more on the debate about warming vs asteroid impact: From GSA:
Rapid end-Permian extinctions probably intensified conditions that were already developing on Earth including: 1) extreme warmth, 2) deep-sea stratification and anoxia facilitated by warm, saline bottom water, 3) limitation of nutrient availability, and 4) reduction in atmospheric oxygen levels. All of these factors could have delayed Early Triassic biotic recovery. Decay of unburied biomass would release considerable carbon dioxide to the atmosphere. Destruction of most photosynthetic organisms (land plants and phytoplankton) would sustain warmth by sharply reducing Earth’s capability for CO2 drawdown. Water lost during forest destruction would facilitate desertification that would foster erosion resulting in depletion of soil nutrients and release of CO2. Additional greenhouse gas probably entered Earth’s atmosphere from the Siberian Traps eruptions, gas hydrate release, and ocean overturn. Absence of active, low-latitude Late Permian orogenic belts had already reduced long-term silicate weathering and CO2 drawdown.
Like any terrible disaster, multiple forces coiciding with each other amplify each other's effects and thanks to this being a fairly complex system, once out of whack, everything falls rapidly apart since the entire ecosystem is built one part interacting with all neighboring parts which is why we are seeing so many extinctions today, for example.

It so happens, when all animals struggled to survive the great Permian extinction, when things got better over several million desperate years, the niche occupied by the dinosaurs happened to be bigger and more fertile than the one mammalians occupied and when the two lineages met each other again as oxygen levels rose, mammals were much tinier than before and little dinosaurs were much bigger than the poor mammals. So dominating the former dominators was easy and mammals spent the following 100 million years, dodging the thundering footsteps of the dinosaurs.

Until, again, the ecology collapsed, the climate changed and the dinosaurs lost their grip on the planet and became helpess fossils.
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