Life on Land: The evolution of five fingers and toes

Well it didn’t take long for avid readers to spot the oddity in Friday’s posted picture of the early tetrapod, Acanthostega. This strange animal did not have the ‘usual’ number of digits, instead it had eight. Having more than five fingers or toes is called polydactyly and is a rare condition.

Few examples of polydactyly occur in the animal kingdom today, the panda’s thumb though, is one classic example. The panda has five digits on its paw plus an opposable 'thumb' but this thumb is not a sixth digit like the others, but actually an unusual outgrowth of a wrist bone. Thus even the panda’s thumb is not truly an example of more than five digits.

So what about Acanthostega and his buddies? The Late Devonian was a busy time, plant life was diversifying and insect life was gaining ground on land. Tetrapods, were making their first steps on to land and living semi-aquatic lifestyles about 375 million years ago. These animals had many characteristics advantageous to aquatic life, such as streamlined bodies, webbed feet and tail fins. But they also had weight-bearing limbs with which they could lift themselves out of the water. Acanthostega had eight digits on its front and hind limbs and two other early tetrapods, Ichthyostega and Tulerpeton, also had more than five digits.

So how could these animals have had such a wide variety of limb structures when all of their descendants seem to have a variation upon the five digit structure? It is thought that pentadactyly evolved in an animal that was ancestral to all present day tetrapods (amphibians, reptiles, birds and mammals) and that this event event happened 340 million years ago in the Lower Carboniferous (about 35 million years after the first tetrapods evolved).

To be honest, we don#t understand how these animals could have been so experimental while their descendants were so conventional. And why 5 anyway? No one knows. And we have no examples to examine. There are few animals who have extra digits. The most common is the novelty polydactyl cat, but this species is the result of selective breeding of animals with a genetic anomaly.

In a general sense, we know that it easier to ‘lose’ a trait then to gain it, hence the large number of animals who have reduced digits. But the striking lack of polydactyl examples in the long history of tetrapods since the Devonian implies there may be an evolutionary constraint at work. For example, pleiotropy is the multiple effects of genes on more than one physical characteristic. Hand-Foot-Genital syndrome illustrates such a condition. This rare disorder malforms limbs and the urinary system because the same defective genes pattern both systems. So perhaps the constraint on tetrapod limb structure is part of a greater pattern.

My Research into Palaeozoic Communities

Yesterday I began writing a little bit about what I do, so if you want to catch up check out Part 1. My goal while I’m at Bristol is to compile a community-level study of tetrapod diversity and to compare it to Mike Benton’s global pattern of tetrapod diversity. I hope that my research will aid our understanding of some ‘big’ questions such as:
1) Is global diversity a reasonable measure of true biodiversity?
2) How did tetrapods diversify? Did they conquer new niches or expand into new habitats?
3) How did mass extinction events effect community structure?

But even more interestingly, this study has an application to our present situation. We are witnessing a biodiversity crisis right now and it is not clear whether it is simply a part of Earth’s natural cycle or massive impact by human presence (though to be honest I lean towards the latter). Studying past communities helps us understand more about our present situation.

The first part of my research covered the Palaeozoic, from the origin of tetrapods about 375 million years ago to about 250 million years ago. At this time there were no birds, no mammals and no dinosaurs. The landscape was dominated by large amphibians and the first reptiles. Amphibians at the time were not like frogs but more like very large salamanders, and the largest of these superficially resembled crocodiles (For example, see my post of Parotosuchus). This period of time ended with the largest mass extinction event, in Earth’s history, the Permo-Triassic event 251 million years ago, when over 90% of Earth’s species went extinct.

During the 125 million years though, a lot of changes took place. I realize this post has gotten long already so I will continue more next week starting with a look at the first tetrapods, who possessed a strange oddity that we rarely see today and one that has changed our understanding of the evolution of life on land. Can you spot this oddity in the image to the right?

Click to view a larger image at http://universe-review.ca/I10-72-Acanthostega.jpg

A little bit about my job…

I’m a palaeontologist at the University of Bristol, currently in the (yikes!) third year of my PhD. But what exactly DO I DO?!?!? Well I don’t fit into the stereotypes of Jurassic Park and Ross from Friends. I don’t spend most of my days in the hot Mongolian desert carefully brushing sand away to reveal amazing and perfectly intact dinosaur skeletons. Sometimes I wish I did though, because to be honest I spend most of my time in the office, counting.

Yes, counting, This is what I do, count animals form different parts of Earths’ past and from all over the world. But to what end? I’m a ‘Macroevolutionist’ so I like to think about the ‘Big picture’, which sounds grand but to be honest can be a bit tedious because big picture stuff often means gathering lots of data, compiling it, and producing graphs. To add a little excitement to my day sometimes I add colour to my graphs and occasionally throw in a pie chart just to be a little crazy.

Seriously though, my supervisor, Mike Benton, has spent a lot of his career counting and has come up with some pretty intriguing insights about biodiversity and Earth’s past. One of his biggest contributions has been the this graph, which is a count of the all of the tetrapods (amphibians, reptiles, mammals and birds) that we have found in the fossil record, from their origin, almost 400 million years ago to the present. As you can see the diversity of tetrapods has risen almost exponentially since their origin to the present day, punctuated occasionally by a mass extinction event, such as the Permo-Triassic event 250 million years ago, when over 90% of Earth’s species went extinct.

But the trouble with this graph is that counting the number of fossils we have from different times is Earth’s history reveals a similar pattern, so it is difficult to say whether Mike’s graph is a true reflection of diversity or simply an artifact of the rock record. This is where my research comes in. I am studying the diversity within communities through time, a study that is independent of these artifacts so I will see if community diversity is similar to global diversity and what the implications are. If you’re still with me and haven’t fallen asleep, tomorrow I will discuss some of early research, including (just for you Will:), Romer’s Gap.

Shark vs. Dinosaur

A recent find in Utah reveals a large prehistoric lake around 200 million years with an amazing fossil cache including an enormous, carnivorous dinosaur and several species of sharks. Anatomical features of the dinosaur suggest it specialized in eating fish, including sharks and huge bony fish, meals which palaeontologist James Kirkland describes as “like biting through chain mail [since] fish in the past were more armored than they are today."

The dinosaur, a relative of the crested dino Dilophosaurus, was about 20 feet long and so would have been a formidable adversary for its ferocious prey. The dinosaur’s slender, serrated teeth are quite unusual and only found in dinosaurs like Spinosaurus and Suchimimus.

Dilophosaurus was well adapted to being a fisherman. Its nasal openings retracted back from the end of its snout so that it could, like today's crocodiles and alligators, still breath when its mouth was underwater.

There are clear tracks and claw scrapes showing the dinosaur wading into the lake to catch its prey. "We have counted over 3,000 individual claw marks and toe scrapes that show incredibly detailed preservation," reveals palaeontologist Andrew Milner. "We can see details of cuticle on the tips of claws, skin impressions, scale scratch lines and where claw cuticle was overlapped by the fleshy toe pads at the end of the toes."

Feathered Dinosaurs

A reader sent me this cartoon. Pollen has been found in high concentration with some Neanderthal bodies suggesting they buried their dead with flowers. But what about before flowering plants evolved?

Scooped (or rather Bitten) again!

Once again, Brian Switek of Laelaps and Mike Ryan of Palaeoblog have beaten me to the punch on reporting on a recent publication that suggests the first tetrapods were able to bite their prey (rather then suck their food up).

Reference: Markey, M.J. and Marshall, C. R. 2007. Terrestrial-style feeding in a very early aquatic tetrapod is supported by evidence from experimental analysis of suture morphology Proceedings of the National Academy of Science. Early Edition on April 16 2007.

What were T. rex’s tiny little arms for anyway?

American palaeontologist Henry Osborn first described T. rex but initially expressed doubts that the diminutive arms he found belonged to this enormous animal. After investigating further and finding it to be true, he considered their purpose and advanced the first theory in 1906: that they were used as ‘graspers’ or stabilizers during copulation.

But this was only the start of a debate that still rages. In 1970 British palaeontologist Barney Newman suggested that the small arms braced the beast's body as it stood up.
Another, contrasting theory suggested that the small limbs are vestigials (degenerated organs that have lost their use).

To add to the confusion it seems that the muscular of the T. rex was very well defined and though the arms were disproportional to the animal's body, they were still very strong. So some people consider that the most useful function of the limbs was to be used as meat hooks while the animal fed. This theory is supported by the beautifully sharp claws on T. rex’s two fingers.

In contrast, Greg Erickson has recently commented on a biomechanical analyses of a new specimen. The aim of this study was to try and understand the physical capacities of T. rex's diminutive structures. Erickson has concluded that the elbow could not be extended beyond 90° and though the arms were very strong (they could lift about 180 kg or 400lbs) they had a very limited side-to-side and up-and-down motion.

It is also known that T. rex's arms were often broken (and mended) during its life, suggesting that the arms were poorly suited for their function that these animals could go without using their arms for extended periods of time.

I read an interesting theory a while back that suggested the arms were most useful in juveniles, as a counterbalance to the young dinsaurs fast quickly. The suggestion was made that the arms were proportionally longer in childhood compared to adulthood. However, as far as I know this theory did not gain popularity.

The truth is that no one knows the answer. Scientific inquiry into this issue has been going on for a century and it doesn’t seem likely that the mystery will be solved soon. If you have any other ideas, please let me know!

Launch of Dinobase

Well it is has FINALLY happened. After a lot of hard work on the part of many people in Bristol, DinoBase was officially launched today. DinoBase is a new interactive resource for dinosaur fans of all ages.

As Mike Benton notes, ‘We all know that people have a natural curiosity for dinosaurs, so we hope that the information on DinoBase will satisfy people's enthusiasm.'

You can search the database for your favourite dinosaur, find out its species, when and where it lived, what it ate, how big it was and how to pronounce its tongue-twisting Latin name. Also try browsing the colourful picture galleries to see what dinosaurs looked like in their prehistoric world.

Did you know, for example, that the Albertaceratops nesmoi, which means ‘Alberta horn-faced’, was only discovered this year in Canada? It is a centrosaurine ceratopsian dinosaur with a pair of long horns on the brow and a blade-like nasal horn. It lived about 75 million years ago, was 6 metres long and weighed 2 tons.

DinoBase also has an online forum, where you can ask questions about dinosaurs, which experts at Bristol University will answer. The database will continue to grow in the future as new discoveries are made and more features are added. There will be a news section that will report the most recent happenings in dinosaur research, and a ‘New Dinosaur’ alert system that will let visitors know about new discoveries.

I would like to thank a lot of people for their hard work, but most especially for the people on our team who have made the final push in last week, including Paul Ferry, Manabu Sakamoto and Tom Fletcher.

Check out DinoBase at http://dinobase.gly.bris.ac.uk/

Ancient proteins link T. rex to chickens

Well I’m sure everybody has seen this sensationalist headline in the last week, instead of tackling the controversy myself, I’ve decided to list a few posts by bloggers who have already posted on the topic:

PZ Meyers of Pharyngula posts Stone soup; or, extracting protein fragments from T. rex bones

Brian Switek of Laelaps in his post, And the T. rex goes… cock-a-doodle-do?

Mike Ryan of Palaeoblog posts T. rex Protein Sequenced

And the original article:
Analyses of soft tissue from Tyrannosaurus rex suggest the presence of protein. 2007. Science 316: 277 - 280

Winner: Fossil Caption Contest

Thanks to everyone who sent in their entry. The submitted captions include:

Sometimes, fishing is about patience. Sometimes, fishing is about lots of patience.
Or…
Given sufficient time, an improperly hooked baitfish will eventually win its freedom, though it may tear its flesh from its bones in the process.
-TheBrummell

Sepia-tone ink on micrite matrix of a Diplomystus dentatus fossil. Snap.
-Neil

Almost got it, just a little bit longer...
-tradwolley

"It was (stretches arms sideways) this old!"
Or ...
"New proof that Neolithic humans possessed sandwiches, vacuum flasks and funny little collapsible chairs."
-John Hopkin

Guess we found Nemo after all....
-KAi

Great captions! I had a hard time deciding so enlisted the help of one of my colleagues. And the winner is:

TheBrummell for “Sometimes, fishing is about patience. Sometimes, fishing is about lots of patience.”

Congratulations! And now your prize: You can post on Fish Feet for a day.

Book Review: How To Keep Dinosaurs by Robert Mash

This book is not new, but I only discovered recently. If you haven’t read it and enjoy palaeo-humor I suggest you pick it up! It is picturesque, surreal and an equally amusing read for geeks and children:)

Synopsis: Hollywood and the popular press would have us believe that all dinosaurs are gigantic, hostile and untameable. In fact, there are many species that make charming and even useful companions. From Compsognathus (mild-mannered and affectionate - once it has learnt to recognise its owner) to Deinonychus (will not eat dog food - dogs are another matter) this book advises you which dinosaur is right for you and your home, from the city apartment dweller looking for a lap pet, to the country estate owner looking to tighten up on security. How To Keep Dinosaurs is packed with the sort of information keen dinosaur keepers crave - from feeding and housing to curing common ailments, breeding and showing your animal. It will even tell you where you can purchase your new pet. The author, a zoologist with extensive experience of dinosaurs, has provided a timely and much-needed source book for all those who keep dinosaurs and for the huge numbers who are contemplating getting one. It is as essential to every dinosaur keeper as a stout shovel and a tranquilizer rifle.

Fossil Hunting in Britain

Last week was quite busy at uni, we hosted a conference for palaeontology students on Friday and on Saturday we went fossil hunting at Aust Cliff and Manor Farm in Southwest England. There were great finds (I will post pictures soon), ranging from microscopic teeth and scales to dorsal fish spines and bones of Pachystropheus, a crocodile like animal that wandered the cliffs about 200 million years ago.

We also made an episode of Fossil Field Guides, created by Paul Williams. Fossil Field Guides are podcast guides to the best field locations in Britain. I will post a link to the Aust Cliff podcast when production is complete, in the meantime, check out Paul’s other Fossil Field Guides.

Reminder: Fossil Caption Contest

A reminder that Monday I started a humerous Fossil Caption Contest. There will be a prize for whoever comes up with the best caption!

Contest closes Sunday.

Fish Finds Land-Legs

Evolution doesn’t happen all it once, it takes a few tries :)

Arrogant scientist to represent all of humanity

American paleontologist Edward Drinker Cope, died on 12 Apr 1897.

Cope is best remembered for his rivalry with O.C. Marsh, called the Great Bone Wars; he also led many great expeditions into the American West and was prolific in the naming of dinosaur species.

When a new species of dinosaur (or any other organism for that matter) is discovered, scientists choose a holotype specimen, this is an example of the new species that will forever define it. Usually it is the first example found, for example, the holotype for T. rex was collected by Barnum Brown in 1902 and is housed at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. It is important to remember that a holotype is usually the first example of a new species and it is not necessarily the best or typical example (although ideally it should be). Sometimes when a new species is found and the holotype named, there are only very poor or fragmentary examples available. But it is the practice that even if a better specimen is subsequently found, the holotype is not superseded.

But back to our story now, which began back in 1735 with Swedish botanist named Carolus Linnaeus. Linnaeus was fascinated by the diversity of life around him and became obsessed with categorizing it. This is very difficult to do since there are millions of species in the world but Linnaeus went about it in a very systematic way. He devised a hierarchical system for categorizing plants, animals and minerals. Interestingly, he named, described and classified human beings as a part of this system. He named humans Homo sapiens, Latin for man and wise. The concept of a holotype had not been invented yet but the humble Linneaus did consider himself to be the best example of Homo sapiens.

Then in 1897, an equally humble scientist, Edward Drinker Cope died. In his will, Cope had a final request: that his remains be used as the holotype specimen for Homo sapiens. However, Cope’s dream did not materialize. His brain was saved and preserved in a jar for future study at the Anthropometric Society. But unfortunately, when his skeleton was stripped and cleaned, taxonomists found evidence of incipient syphilis in Cope's bones, a discovery that led his suceedors to deem his remains “unsuitable” to be the type specimen for humanity. His bones were discreetly filed away and perhaps even conveniently ‘lost’ for almost 100 years.

Then in 1991, while working on a story, National Geographic photographer Louie Psihoyos discovered Cope's bones stored at the Museum of Archaeology and Anthropology at the University of Pennsylvania. Psihoyos borrowed the bones to use in his story and while out in the Western United States, he showed the bones to palaeontologist Robert Bakker who was a great admirer of Cope. Bakker began a mission to fulfill Cope’s last request: that his remains be used designated the type specimen of Homo sapiens. Bakker published his description in the Journal of the Wyoming Geological Society.

Unfortunately, Bakker and Psihoyo's efforts were not successful and Cope's remains are unlikely to receive official status for a variety of reasons: the standards for type specimens are very strict and complex and not only do Cope’s bones bear marks of syphilis, they have also suffered damage from their travels: his skull has been dropped, broken and even repaired.

To make the situation more complicated, in 1959, another palaeontologist wrote a paper declaring Carolus Linneaus the holotype of Homo sapiens, especially as his body is well-preserved in the Cathedral in Uppsala, Sweden. Well since nobody can agree, the job still remains open and there is no official holotype for humanity, but is it likely that when (if) a holotype is chosen it will be an arrogant scientist that represents humanity?

Palaeobarbius malibui

I have no idea if this letter, that was supposedly sent to the Smithsonian Institute, is real but regardless it is hilarious.

Paleoanthropology Division
Smithsonian Institute
207 Pennsylvania Avenue
Washington, DC 20078

Dear Sir:

Thank you for your latest submission, labeled "93211-D, layer seven, next to the clothesline post...Hominid skull." We have given this specimen a careful and detailed examination, and regret to inform you that we disagree with your theory that it represents conclusive proof of the presence of Early Man in Charleston County two million years ago. Rather, it appears that what you have found is the head of a Barbie doll, of the variety that one of our staff, who has small children, believes to be "Malibu Barbie." It is evident that you have given a great deal of thought to the analysis of this specimen, and you may be quite certain that those of us who are familiar with your prior work in the field were loathe to come to contradiction with your findings. However, we do feel that there are a number of physical attributes of the specimen which might have tipped you off to its modern origin:

1. The material is molded plastic. Ancient hominid remains are typically fossilized bone.

2. The cranial capacity of the specimen is approximately 9 cubic centimeters, well below the threshold of even the earliest identified proto-homonids.

3. The dentition pattern evident on the skull is more consistent with the common domesticated dog than it is with the ravenous man-eating Pliocene Clams you speculate roamed the wetlands during that time.

This latter finding is certainly one of the most intriguing hypotheses you have submitted in your history with this institution, but the evidence seems to weigh rather heavily against it. Without going into too much detail, let us say that: A. The specimen looks like the head of a Barbie doll that a dog has chewed on. B. Clams don't have teeth. It is with feelings tinged with melancholy that we must deny your request to have the specimen carbon-dated. This is partially due to the heavy load our lab must bear in its normal operation, and partly due to carbon-dating's notorious inaccuracy in fossils of recent geologic record. To the best of our knowledge, no Barbie dolls were produced prior to 1956 AD, and carbon-dating is likely to produce wildly inaccurate results. Sadly, we must also deny your request that we approach the National Science Foundation Phylogeny Department with the concept of assigning your specimen the scientific name Australopithecus spiff-arino. Speaking personally, I, for one, fought tenaciously for the acceptance of your proposed taxonomy, but was ultimately voted down because the species name you selected was hyphenated, and didn't really sound like it might be Latin. However, we gladly accept your generous donation of this fascinating specimen to the museum. While it is undoubtedly not a Hominid fossil, it is, nonetheless, yet another riveting example of the great body of work you seem to accumulate here so effortlessly. You should know that our Director has reserved a special shelf in his own office for the display of the specimens you have previously submitted to the Institution, and the entire staff speculates daily on what you will happen upon next in your digs at the site you have discovered in your Newport back yard. We eagerly anticipate your trip to our nation's capital that you proposed in your last letter, and several of us are pressing the Director to pay for it. We are particularly interested in hearing you expand on your theories surrounding the trans-positating fillifitation of ferrous ions in a structural matrix that makes the excellent juvenile Tyrannosaurus rex femur you recently discovered take on the deceptive appearance of a rusty 9 mm Sears Craftsman automotive crescent wrench.

Yours in Science,

Harvey Rowe
Curator, Antiquities

Fossil Caption Contest

This is a great picture, I have no idea how it was done, but it is very funny.

A prize for whoever comes up with the best caption!

Contest closes on Friday.

High Stakes Custody Battle for Fossil Dinosaur Continues

Custody battles for fossils can bring big money these days so it comes as no surprise that it was announced today that a 2 ½ year custody battle for the ownership of Tinker, a juvenile Tyrannosaurus rex will continue. A federal court of appeal ruled that a the lease formed between fossil hunters, who dug up the 65 million-year-old fossil and the County of Harding County, South Dakota was valid. This reverses a ruling made last year that deemed the lease void because it didn't follow a state law that requires leases exceeding 120 days and $500 USD to go before a public hearing.

Tinker is currently interned in Pennsylvania. An offer of $8.5 million USD has been made for the extraordinary fossil skeleton. In 1992, South Dakota saw another a custody battle for a dinosaur skeleton: Sue, a beautifully preserved, 13m (42ft) long T. rex specimen was at the center. Claims to Sue were made by a local rancher, a team of fossil hunters, a Sioux Indian tribe and the United States Government. It ended seven years later by awarding the dinosaur to the rancher on whose land the find was made. He then auctioned her off at Sotheby's, the winning bid went to Chicago's Field Museum with corporate sponsorship from McDonald’s and Walt Disney to the tune of $8.4 million. To date, it has been the most expensive fossil ever sold, I wonder if Tinker will break the record?

Creationist Museum Signs

Earlier today I wrote post about how Tyrannosaurus rex ate coconuts and how all dinosaurs used to be herbivores, at least according to a new Creationist museum in Kentucky, USA. In response, a reader sent me some hilarious signs that would be well suited to the museum:

Environmental message
“Another flood will make fossil fuels a renewable energy source”

Cafeteria menu
“Fish Sticks are organic and are not your relatives”

“Today’s special: Buy a spaghetti monster and get a free drink”

Museum Shop
“The Danny Dinosaur Adventure Ride is closed today. Please visit the Adam and Eve organic fruit and pet store”

T. rex ate coconuts

A new museum in Petersburg, Kentucky greets visitors with a 20ft tall tumbling waterfall and at its base, mannequins of frolicking children play amongst dinosaurs. The Creation Museum, which cost $25 million to build, is home to many unusual sites: a diorama of ancient people overshadowed by a towering T. rex, Adam and Eve swimming in a river with giant reptiles, and even a scale model of Noah's Ark. It seems Noah solved the problem of fitting dinosaurs into his vessel by only taking baby dinosaurs. Indeed, the ark has a detailed display of many animals happily boarding the boat: dinosaurs cavort with giraffes, penguins, hippos, and bears.

Museum guides tell visitors that before Adam and Eve were expelled from paradise all of the dinosaurs were peaceful plant-eaters. In Genesis 1:30 God gives ‘green herb’ to every creature to eat and so there were no predators. When a curious museum visitor asks, why exactly T. rex had six-inch long serrated teeth, the guides go on to explain that T. rex used his big teeth to open coconuts. Apparently it was only after Adam and Eve sinned and were cast out of paradise that the dinosaurs started to eat flesh.

My opinion: I think the people who built this museum are smoking a bit too much ‘green herb’.