Here’s a great opportunity for Minnesota fossil freaks: Minnesota Atheists is organizing a fossil hunting trip to Lilydale park on Saturday, 20 June. Sign up and go collect 440-480 million year old marine fossils. Maybe I’ll have to rummage around and find my old rock hammer.
It’s yet another transitional fossil, everyone! Oooh and aaah over it, and laugh when the creationists scramble to pave it over with excuses.
What we have is a 23 million year old mammal from the Canadian arctic that would have looked rather like a seal in life…with a prominent exception. No flippers, instead having very large feet that were probably webbed. This is a walking seal.
What it tells us is that marine pinnipeds almost certainly had an origin in the arctic, derived from terrestrial and semi-aquatic forms — these were more otter-like animals.
You’ll want to learn more about this beautiful creature. There is a website all about Puijila (in English, French, and Inuktitut) where you can find all kinds of images…and you can also find out how to pronounce “Puijila“, something we’re all going to have to practice. Who knew paleontology was going to lead us all into learning a few words of Inuktitut?
Rybczynski N, Dawson MR, Tedford RH (2009) A semi-aquatic Arctic mammalian carnivore from the
Miocene epoch and origin of Pinnipedia. Nature 458:1021-1024.
A fish is a fish, right? They’re just a blur of aquatic beasties that most people distinguish by flavor, rather than morphology or descent. But fish are incredibly diverse, far more diverse than terrestrial vertebrates, and there are significant divisions within the group. Most people know of one big distinction, between the Chondrichthyes (fish with cartilaginous skeletons, like sharks and rays) and the Osteichthyes (fish with bony skeletons), but there’s another particularly interesting split within the Osteichthyes: the distinction between Sarcopterygians (the word means “fleshy fins”, and we call them lobe-finned fishes colloquially) and the Actinopterygians, the ray-finned fishes. The lobe-finned fishes most distinctive feature is the muscular and bony central core of their fins — extant forms are the coelacanth and lungfish. It is this lineage that led to us terrestrial tetrapods, but other than that successful invasion of the land, the sarcops were something of an aquatic failure, with only a few genera surviving. The ray-finned fishes, on the other hand, are a major success story, with more than 28,000 species today. To put that in context, there are only about 5,500 species of mammals.
The Sarcopterygii and the Actinopterygii must have begun diverging a long time ago, and a couple of questions of interest are a) when did the last common ancestor of both groups live, and b) what did it look like? We don’t have a good and specific answer yet, because Osteichthyes origins are lost far, far back in time, over 400 million years ago, but every new discovery edges us a little closer. What we now have is a well-preserved fossil of a fish that has been determined to be an early sarcopterygian, and it tells us that a) the last common ancestor had to have lived over 419 million years ago, the age of this fossil, and the divergence probably occurred deep in the Silurian, and b) this animal has a mosaic of primitive Osteichthyan features, which tells us that that last common ancestor may well have shared some of these elements. It is another transitional fossil that reveals much about the gradual separation of two great vertebrate groups.
And here it is:
That may be a bit disappointing at first — it looks like Silurian road-kill — but really, that’s a remarkable good and useful specimen. The animal was covered with thick bony scales, and the skull was built of thick bony plates, and so while it was squashed flat by pitiless geology, the pieces are all there, and it can be reassembled into a much more fishy state. This drawing may be more satisfying:
Now it looks like a kind of armored, spiky salmon with a thick muscular body (and yes, I too wonder about flavor, and would like to taste a slab of that). It’s definitely not a salmon, though — the bony structure is a curious set of compromises where some features are distinctly sarcopterygian, some look like they belong on a primitive actinopterygian, and others are unique or show affinities to characters of ancient extinct fishes, like rhipidistians. This is very cool. What we see here are relics of an ancient common osteichthyan ancestor, which are being honed into the specific characteristics of the Sarcopterygii. The analysis of the totality of the animal’s features, though, place it more in the lobe-finned than the ray-finned clade. That places it on a branch of the line leading to us…a very, very old branch, making this your many-times-great grand uncle, or cousin only a few million times removed. Now my curiosity about a taste-test is making me feel mildly cannibalistic.
When you look at that diagram, what should jump out at you is all the diversity in the Devonian, the so-called Age of Fishes, and the paucity of representative fossils from the Silurian…which is exactly where all the interesting branch points in the fish family tree are located. Once again, paleontology is a predictive science, and this tells us where to look for the next batch of exciting and informative fossils.
Zhu M, Zhao W, Jia L, Lu J, Qiao T, Qu Q (2009) The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature 458:469-474.
I’m not going to say much about this since Ed Yong has an excellent write-up, but a new feathered dinosaur has been discovered, called Tianyulong. As you can see in this image of the fossil, it was bristling with a fuzz of thin fibers — proto-feathers.
There are a couple of noteworthy features in this creature. One is apparent: feathers just didn’t bloom suddenly in evolution, but appeared in steps. This animal has ‘feathers’ that don’t branch like those of modern birds, but instead form more of a furry coat than a set of flat blades.
The other cool thing is that this is an ornithischian dinosaur; most of the other dinosaurs that have been discovered to have feathers were saurischian. What that means might be made more clear by this diagram:
It implies that just maybe the last common ancestor of the saurischia and ornithischia were also covered with proto-feathers, which means that feathers may be a primitive state in this lineage.
Zheng X-T, You H-L, Xu X, Dong Z-M (2009) An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458:333-336.
Several new and spectacular cephalopod fossils from 95 million years ago have been found in Lebanon. “Spectacular” is not hyperbole — these specimens have wonderfully well-preserved soft parts, mineralized in fine-grained calcium phosphate, and you can see…well, take a look.
If you ever wanted to peer deeply into the decayed and shriveled eyes of Otzi, the 5,000 year old iceman, now you can. High resolution images of Otzi are available on the web, and you can pan and zoom all over his body. You can also find 3D images, and special closeups of his tattoos.
That question has an answer: they crouched like birds. A 198 million year old fossil trackway from Utah has preserved a print of a theropod dinosaur taking a break, resting with hands curled inward and knuckle down, and legs bent. Except for the forelimbs, of course, it’s very birdlike.
Here’s the section of the trace fossil they used to reconstruct the animal’s posture.
Milner ARC, Harris JD, Lockley MG, Kirkland JI, Matthews NA (2009) Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace. PLoS ONE 4(3): e4591. doi:10.1371/journal.pone.0004591
Isn’t that beautiful? It’s an ancient footprint in some lumpy rocks in Kenya…but it is 1½ million years old. It comes from the Koobi Fora formation, familiar to anyone who follows human evolution, and is probably from Homo ergaster. There aren’t a lot of them; one series of three hominin trails containing 2-7 prints, and a stratigraphically separate section with one trail of 2 prints and an isolated single print. But there they are, a preserved record of a trivial event — a few of our remote relatives taking a walk across a mudflat by a river — rendered awesome by their rarity and the magnitude of the time separating us.
Here’s one of the trails:
It’s an interesting bridge across time. There they were, a couple of pre-humans out for a stroll, perhaps on their way to find something for lunch, or strolling off to urinate, probably nothing dramatic, and these few footprints were left in drying mud to be found over a million years later, when they would be scanned with a laser, digitized, and analyzed with sophisticated software, and then uploaded to a digital network where everyone in the world can take a look at them. Something so ephemeral can be translated across incomprehensible ages…I don’t know about you, but I’m wondering about the possible future fate of the debris of my life that has ended up in landfills, or the other small smudges across the landscape that I’ve left behind me.
And what have we learned? The analysis has looked at the shape of the foot, the angle of the big toe, the distribution of weight as the hominins walked across the substrate, all the anatomical and physiological details that can be possibly extracted from a few footprints.
The answer is that these beings walked just like us. The tracks are noticeably different from the even older footprints of australopithecines found at Laetoli, from 3.5 million years ago. The foot shape and the stride of Homo ergaster was statistically indistinguishable from those of modern humans, even though we know from the bones associated with these species that they were cranially distinct from us. This is not a surprise; it’s been known for a long time that we evolved these bipedal forms long ago, and that the cerebral innovations we regard as so characteristic of humanity are a relative late-comer in our history.
Remember, though, these are 1½ million years old, 250 times older than the age of the earth, according to creationists. That’s a lot of wonder and history and evidence to throw away, but they do it anyway.
Bennet MR, Harris JWK, Richmond BG, Braun DR, Mbua E, Kiura P, Olago D, Kibunjia M, Omuombo C, Behrensmeyer AK, Huddart D, Gonzalez S (2009) Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya. Science 323(5918):1197-1201.
The media is getting another science story wrong. I keep seeing this discovery of an array of fossil placoderms as revealing the origins of sex, and that’s not right. Sex is much, much older, and arose in single-celled organisms. Come on, plants reproduce sexually. A fish is so far removed from the time of origin of sexual reproduction that it can’t tell us much about its origins.
Let’s get it right. These fossils tells us about the origin of fu…uh, errm, mating in vertebrates.
What we have are a set of placoderm fossils from the Devonian (380 million years ago) of Western Australia (The Aussies are going to be insufferable, now that they can claim to be living in the birthplace of shagging) that show two interesting features: some contain small bits of placoderm armor that show no signs of digestion, and so are not likely to be relics of ancient cannibal feasts, but are the remains of viviparous broods — they were preggers. The other suggestive observation is that the pelvic girdle has structures resembling the claspers of modern sharks, an intromittent organ or penis used for internal fertilization.
Fans of the great Cambrian predator, Anomalocaris, will be pleased to hear that a cousin lived at least until the Devonian, over 100 million years later. That makes this a fairly successful clade of great-appendage arthropods — a group characterized by a pair of very large and often spiky manipulatory/feeding arms located in front of the mouth. Here’s the new fellow, Schinderhannes bartelsi:
There are some significant differences between familiar old Anomalocaris and Schinderhannes. Anomalocaris was a monster that grew to about a meter long; this little guy is about a tenth of that, around 4 inches. He also has those interesting “wings” behind his head, which presumably aided in swimming.
Another significant feature of this animal is that it has characters that place it in the Euarthropoda, which makes great appendages paraphyletic and primitively present in euarthropods. Those great appendages have long been a curiousity, and we’ve wondered whether they are a unique innovation that was completely lost in modern arthropods, or whether they evolved into one of the other more familiar cephalic appendages; the authors suggest that this linkage with the euarthropod family tree implies that chelicera (what you may recognize as the big paired ‘fangs’ of spiders) are modified great appendages.
Kühl G, Briggs DEG, Rust J (2009) A Great-Appendage Arthropod with a Radial Mouth from the Lower Devonian Hunsrück Slate, Germany. Science 323(5915):771-773.
