What is life?

The oldest fossil record of life on earth is photosynthesizing cyanobacteria found in stromatolites. However, photosynthesis is a complex process, and these cyanobacteria probably had precursors that are yet unknown. What were these first hypothetical life forms like?

To answer that question we must first decide on a definition of what constitutes a living thing. This definition is not as clear-cut as it might appear.

Living things grow and reproduce, but inorganic crystals do this, too. Viruses are not regarded as living, as they require a host in order to survive and reproduce, but the existence of viruses highlights the fuzzy line between life and non-life, and reflects the fact that life must have originated from a non-living, “prebiotic” stage.

The British biologist J.B.S. Haldane concluded that “The line between living and dead matter is …somewhere between a cell and an atom.”

Photo and information on research on artificial life here.

Filling an empty niche

Despite the occupation by reptiles of almost every ecological niche during the Mesozoic Era, there were no large planktivorous marine reptiles, the niche filled today by baleen whales.

Recent discoveries in museum drawers may hold the answer to this gap in Mesozoic reptile ecology. Fossils that had lain unstudied or incorrectly identified have been newly identified as suspension-feeding pachycormids, a group of giant bony fish.

These fish were previously thought to have been a short-lived group, limited to the Jurassic Period. Mesozoic marine reptiles may have been excluded from the large-bodied, suspension-feeding trophic niche by these supersized fish.

The pachycormids were extinct by the end of the Cretaceous Period, opening up the planktivorous niche to a new group--the whales.

Matt Friedman, et al., 100-Million-year dynasty of giant planktivorous bony fishes in the Mesozoic Seas. Science 327

A new spin on an ancient predator

More than 100 years after its discovery the Middle Cambrian Burgess Shale of British Columbia Canada, continues to offer up new insight into the history of life.

One of the many enigmatic soft-bodied animals of the 500 million year old Burgess Shale of British Columbia is Nectocaris (fossil shown above) long thought to be a shrimp-like arthropod (reconstruction, above, left), but a recent study shows that the animal is most likely a cephalopod, ancestral to the group includes modern squid, octopus, and the pearly Nautilus (reconstruction above, right).

This re-classification of Nectocaris extends the geologic range of the cephalopods back 30 million years and dramatically changes hypotheses of cephalopod evolutionary history.

Nectocaris does not have an external shell, as did other ancient fossil cephalopods, and this discovery scuttles previous hypotheses that cephalopods evolved the ability to float and then swim after the evolution of their chambered shell. Nectocaris shows that cephalopods shells evolved later in cephalopod evolution, possibly in response to increased predation during the Late Cambrian.

Martin Smith and Jean-Bernard Caron, Nature 2010. Photos by the authors. Reconstructions from Discover Magazine blog

Getting batty

Many modern bats use echolocation to help navigate and capture prey in flight. Most echolocating bats produce the signal in their larynx, but a few species create echolocation sounds by tongue clicks, and other bats do not echolocate at all.

Scientists used CT scans to study the articulation of the ear bones in modern bats and found that the bats that use echolocation produced from the larynx have a distinctive articulation of the stylohyal bone with the tympanic bone not seen in the bats that do not echolocate or that use tongue clicks.

In other words, the ability to produce echolocation using the larynx is recorded in the skeletal structure of bats, and this makes it possible to look for this feature in fossil bats.

The oldest known fossil bat appears to have this distinctive articulation but a conclusive answer awaits more fossil finds.