Evolution Brings Extinct Bird Back to Life! Except it Didn’t

A news story has been circulating a fair bit in the past couple of weeks. This story has been picked up by numerous news and science outlets. How it is being reported and explained is just plain misleading and inaccurate.

The Aldabra Rail is a subspecies of the White-throated Rail.

Here are a few titles that show how the subject is being covered.

Science Magazine – Evolution Brings Extinct Island Bird Back into Existence

Smithsonian Magazine – How Evolution Brought a Flightless Bird Back from Extinction

CBS News – An Extinct Bird Species Has Evolved Back into Existence, Study Says

From these titles, and from the bodies of the articles themselves, readers would think that the same species of bird existed at some point in the past, went extinct (as in died out completely), and then re-evolved!

That does not happen.

Here is what actually did occur.

The small atoll of Aldabra is a pretty spectacular spot. It is very remote. It is quite beautiful. It is home to a bunch of unique animals found no where else on earth. It has one of the longest fossil records on any island in the Indian Ocean.

That fossil record includes a lot of the animals that have called the atoll home over the past few million years. One of those animals was the Aldabra Rail. This rail was a small flightless bird that was probably found hunting through reed beds along the edges of water. The Aldabra Rail went extinct about 136,000 years ago at about the same time that global sea level was rising and submerging oceanic islands like Aldabra. After a few thousand years, sea level dropped and Aldabra became an exposed island once more. Not long after that fossils of a rail on Aldabra start showing up again.

There are a couple of possible explanations. One is that some remnant population of the Aldabra Rail hung on, some how, and did not die. These were flightless birds, so it is not clear how this might have happened, but perhaps a small population managed to survive on a floating raft of vegetation long enough to reach an exposed bit of land. This seems like a very long shot. It is much more likely that the Aldabra Rail simply died out completely. It went extinct.

The other possible explanation is much more likely and widely understood and accepted, and it is this: the Aldabra Rail went extinct when the atoll went under water. Then after it re-emerged, a group of birds likely from the same parent stock of the original Aldabra Rail re-colonized the atoll (quite probably from Madagascar). This new group of colonizers eventually became flightless and filled the same, or very similar, ecological niche as the original Aldabra Rail.

This is a process called iterative evolution and it is pretty rare. The definition of iterative evolution is: the evolution of similar or parallel structures in the development of the same main line.

But iterative evolution does not produce the same species twice. It may produce similar species, but to produce the same species twice would require starting with the same gene pool twice. The group of birds that first colonized Aldabra, and became the Aldabra Rail 1.0, had a unique combination of genes to work with. The group of birds that later colonized Aldabra, and became the Aldabra Rail 2.0, had a unique combination of genes to work with. Those two combinations of genes may have been similar, but they were not the same. Therefore the decedents of those two groups would not be the same.

I really think that the implications of how this story is being reported is really misleading and possible even damaging.

Misleading because they imply that a species can evolve twice. To go back to the definition of  iterative evolution, it the evolution of “similar or parallel structures…” Similar or parallel structures are not the same as identical species. Two rails that evolved at different times in the same place and that are both flightless, are not the same species.

Damaging because there is weight to the idea of extinction. Extinction is forever. It means that an entire evolutionary lineage has ended, and any potential future that that lineage may have had is gone. If the idea of extinction becomes an impermanent one, it looses its urgency and tragedy. People may well not worry about extinction as that species can just re-evolve. No harm, no foul.

Again, no species can ever occur twice. Once a species goes extinct, that is it for that evolutionary lineage. Even if some other lineage emerges that is close, it will not be the same and will not have the same evolutionary trajectory or potential.

When reporting on science, I feel strongly that the ideas behind the science should be accurately represented. I think it is especially distressing when the sources of the misrepresentations are otherwise reputable sources for science.

I hope the current Aldabra Rail has a long future filled with descendants, and I mourn the loss of the previous rail of Aldabra and the lineage it might have left behind, but never will.

Read Full Post »

Information is Important

Information is important. With information each of us as individuals, and our society as a whole, can learn about the world. With information, we can all make decisions that make sense. With information, we can all discuss ideas.

Without information none of that is possible. Without information, we are, at best, at the mercy of our current, limited knowledge, and our base instincts. Without information we are, at worst, at the mercy of the limited knowledge and instincts of someone else.

This is why the gag order, and insistence that all reports and data be pre-screened before release to the public, issued by the President to the EPA are so concerning to me, and I think should be so concerning everyone else. This is exactly the kind of action that limits access to, and spread of, information. It will only hamper all of our abilities to operate as rational, critically thinking individuals. It is the kind of action that is put in place to control what we, as citizens, know and when we know it. This is censorship and it has no place in science or a free society.

#thisisnotnormal

Read Full Post »

Dinosaur Feathers

Single feather, and a mite, preserved in Late Cretaceous amber found in Canada.

In the movie, Jurassic Park, humans are able to get dinosaur DNA from insects that were preserved in fossilized amber millions of years ago. Well, it has been very convincingly shown that any DNA that might get trapped in amber during the age of dinosaurs would degrade too badly over time to still be viable today. However, this does not mean that amber is useless in preserving amazing structures that we can find and learn from and marvel at.

A recent report that appeared in the journal Science is an excellent example of what I mean. Researchers examined a number of fossilized feathers that were preserved in amber during the Late Cretaceous. These feathers likely came from dinosaurs! And they are beautiful, having been spectacularly preserved in the amber that surrounds them. At this point, no one is exactly sure if these some of these feathers came from early members of what would become the bird lineage, or if they came from non-avian dinosaurs, but either way, the feathers are stunning. In fact, the feathers are in such high quality condition that even tiny features can be observed. Impressively, many of these tiny features on the dinosaur feathers look exactly like the tiny features one would see on the feathers of a modern bird. One example of this is the way that the barbs of some of the feathers twist like a corkscrew. This is a feature also found in modern water birds and may suggest that the dinosaur that those feathers came from lived in close association with water as well. The researchers can even take a stab at figuring out what color some the feathers were; colors that range from white to brown to black. This backs up a lot of other research that has suggested that dinosaur feathers probably had a wide range of colors and patterns, some of them quite bright and dramatic!

A feather found in Late Cretaceous Canadian amber. The dark masses all along the filaments are regions of pigment concentration. This feather was probably medium to dark brown.

Another exciting outcome of all these fossils is that they represent a range of stages in feather evolution. Some of the fossils are little more than very thin filaments, sometimes referred to as protofeathers (or dino fuzz). These protofeathers are probably some of the earlier stages in the evolution of the structures that would eventually become the tail feather of a Peacock or the crest feather of a Royal Flycatcher. These filaments have been found preserved in the rock surrounding other non-avian dinosaur fossils, but they have never been seen in such detail as they can be in the amber. Others of these fossil feathers show much more elaborate feathers that have many of the same complex features of modern feathers.

Follow this link: http://io9.com/5840854/dinosaur-feathers-discovered-in-canadian-amber to see more photos of feathers fossilized in amber. And next time you see a member of the only living lineage of dinosaurs (a.k.a. a bird), take a moment to think about the feathers that cover its body and to realize that millions of years ago, there were animals sporting feathers that look just about the same. Pretty amazing!

A cluster of 16 feathers preserved in Canadian Late Cretaceous amber.

Read Full Post »

Powered Flight in Vertebrates

Powered flight, the ability to propel oneself through the air against the force of gravity, requires a great deal. From specialized bones to specialized skin, and everything in between, the demands of flight penetrate all aspects of an animals’ life. And yet, despite how mechanically difficult powered flight is to achieve, it has evolved three different times in vertebrate evolution, once in birds, once in bats, and once in the now extinct pterosaurs. One of the things that make the three different evolutions of flight especially interesting is that the three different groups accomplished the feat is such different ways.

A pterosaur wing has a large upper arm bone, two smaller forearm bones, a few wrist bones, and then four fingers. The first three are small fingers that have small claws at their tips and are free to move and grasp objects. The fourth finger is extremely long, extending all the way to the tip of the wing. The bones of this fourth finger are longer and thicker than the bones of the other fingers, and this is because this fourth finger supports the entire wing membrane. The wing membrane attaches all along the rear surface of the fourth finger, the rear surface of the arm, and then to the side of the trunk of the animal and even to the leading edge of the hind legs. That means that, when a pterosaur is in flight, the whole weight of the animal is being supported on once finger of each hand! Some pterosaurs got to an estimated 550 lbs (although most were about 25 lbs) with a 10 or 11 meter wingspan, so those are some strong fourth fingers!

A bat wing is the same upper arm bones of the pterosaur, but the hand is very different. Instead of supporting al the body weight of the animal on just one finger, all five of the fingers of a bat are elongated (the thumb is the only finger that is small and clawed and free to grasp). In between each of these fingers, and extending from the pinky finger to the body are membranes that the bat can stretch or fold as needed by moving the bones in its fingers, hands, and arm. Since all the fingers are sharing the load, each one is proportionately much finer and thinner than the fourth finger of a pterosaur. Additionally, bats have thin muscles that cover the surfaces of the membranes just beneath the skin. By tensing or relaxing these muscles, the bat has very fine control over the sharp and tension of the wing membranes, and this turns out to be very important in bat flight. It is not known if pterosaurs had similar muscles on the membranes of their wings, but it seems likely that they did.

A bird wing also has the same basic upper arm bones seen in the other groups, but instead of elongating bones and making them delicate and distinct, birds go the opposite direction. Most of the bones in the hand and fingers of a bird are fused together. This makes a structure that is short, thick, and strong. Out of this support structure extends feathers. Not a membrane made of skin like a pterosaur or a bat, but a completely different evolutionary innovation. Feathers, and flight feathers in particular, are strong and thin and light. Flexible enough to bend a bit to change shape, but rigid enough to support the weight of the bird and the forces of air-speed, drag, lift and gravity that all flying organisms have to contend with. In modern birds, muscles in the skin at the base of the feathers allow for independent control of each feather. This allows birds to have amazing control over the shape of their wing.

Flight is a fascinating example of how a complex structure or function can arise by natural selection. In these three cases, natural selection favored three very different, and ultimately successful, experiments in how to get an animal airborne. All three were very different solutions, which is worth remembering. Most of the problems out there, even really hard ones, probably have many different solutions, you just have to tinker and figure them out.

Read Full Post »