How did dinosaurs sit down?

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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.

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Restoration of Early Jurassic environment preserved at the SGDS, with the theropod Dilophosaurus wetherilli in bird-like resting pose, demonstrating the manufacture of SGDS.18.T1 resting trace.

Here’s the section of the trace fossil they used to reconstruct the animal’s posture.

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A, Overhead, slightly oblique angle photograph of SGDS.18.T1 resting trace. Note normal Eubrontes track cranial to resting traces (top center) made by track maker during first step upon getting up. Scale bar equals 10 cm. B, Schematic of SGDS.18.T1 to scale with A: first resting traces (manus, pes, and ischial callosity) in red, second (shuffling, pes only) traces in gold, final resting traces (pes and ischial callosity) in green, and tail drag marks made as track maker moved off in blue. Note long metatarsal (“heel”) impressions on pes prints. C, Direct overhead photograph and D, computerized photogrammetry with 5 mm contour lines of Eubrontes trace SGDS.18.T1. Color banding reflects topography (blue-green = lowest, purple-white = highest); a portion of the berm on which the track maker crouched is discernible. Abbreviations: ic = ischial callosity, lm = left manus, lp = left pes, rm = right manus, rp = right pes, td = tail drag marks.

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

A brief moment in the magnificent history of mankind

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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:

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Tessellated swath of optical laser scans of the main footprint trail on the upper footprint surface at FwJj14E. Color is rendered with 5-mm isopleths.

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.

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Optical laser scan images color-rendered with 5-mm isopleths for footprints at both FwJj14E and GaJi10. (A) Isolated left foot (FUI1) on the upper footprint surface at FwJj14E. (B) Photograph of FUI8 on the upper footprint surface at FwJj14E, showing good definition of the toe pads; the second toe is partially obscured by the third toe. (C) Second trail on the upper footprint surface at FwJj14E, showing two left feet. (D) Third trail on the upper footprint surface at FwJj14E, showing a right and a left foot. (E) Print R3 from GaJi10 (22), re-excavated and scanned as part of this investigation. (F) Partial print (FUT1-2) on the upper footprint surface at FwJj14E; the heel area has been removed by a later bovid print. (G) Print FLI1 on the lower footprint surface at FwJj14E, rendered with 5-mm alternating black and white isopleths. (H) Inverted image of the toe area of print FUT1-1 with alternating 5-mm black and white isopleths. Note the locations of the pads of the small toes and the presence of a well-defined ball beneath the hallucial metatarsophalangeal joint. The first, third, and fifth toes are marked D1, D3, and D5, respectively.

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.

Exposing the intimate details of the sex lives of placoderms

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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.

[Read more…]

Schinderhannes bartelsi

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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:

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Holotype of Schinderhannes bartelsi. (A) Ventral. (B) Interpretative drawing of ventral side. l, left; r, right; A1, great appendage; A2, flaplike appendage; sp, spine; fm, flap margin; te, tergite; ta, trunk appendage. (C) Partly exposed dorsal side, horizontally mirrored. (D) Interpretative drawing of dorsal side. (E) Interpretative drawing of great appendages, combining information from the dorsal and ventral sides. (F) Radiograph. (G) Reconstruction. Scale bar, 10 mm [for (A) to (G)]. (H) Mouth-part. Scale bar, 5 mm.

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.

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Cladogram; tree length, 87. Consistency index, 0.5402; retention index, 0.6552. (1) Peytoia-like mouth sclerites, terminal mouth position, lateral lobes, loss of lobopod limbs, and stalked eyes. (2) Great appendages. (3) Sclerotized tergites, head shield, loss of lateral lobes, and biramous trunk appendages. (4) Stalked eyes in front and loss of radial mouth. (5) Post-antennal head appendages biramous and antenna in first head position. (6) Free cephalic carapace, carapace bivalved, and two pairs of antennae. (7) Maxilla I and II. (8) Exopods simple oval flap. (9) Two pre-oral appendages and a multisegmented trunk endopod. (10) Post-antennal head appendages biramous and tail appendages fringed with setae. (11) Long flagellae on great appendage and exopods fringed with filaments. (12) Trunk appendages uniramous and eyes not stalked. (13) No posterior tergites. (14) Tail spines and chelicere/chelifore on first head position. (15) Proboscis. (16) Six post-antennal head 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.

Titanoboa!

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Just wait — this one will be featured in some cheesy Sci-Fi channel creature feature in a few months. Paleontologists have dug up a fossil boa that lived 58-60 million years ago. They haven’t found a complete skeleton, but there’s enough to get an estimate of the size. Look at these vertebrae!

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a, Type specimen (UF/IGM 1) in anterior view compared to scale with a precloacal vertebra from approximately 65% along the precloacal column of a 3.4 m Boa constrictor. Type specimen (UF/IGM 1) shown in posterior view (b), left lateral view (c) and dorsal view (d). Seven articulated precloacal vertebrae (UF/IGM 3) in dorsal view (e). Articulated precloacal vertebra and rib (UF/IGM 4) in anterior view (f). Precloacal vertebra (paratype specimen UF/IGM 2) in anterior view (g) and ventral view (h). Precloacal vertebra (UF/IGM 5) in anterior view (i) and posterior view (j). All specimens are to scale.

Just to put it in perspective, the small pale blob between a and b in the photo above is an equivalent vertebra from an extant boa, which was 3.4 meters long. The extinct beast is estimated to have been about 13 meters long, weighing over 1100 kg (for us Americans, that’s 42 feet and 2500 pounds). This is a very big snake, the largest ever found.

The authors used the size of this snake to estimate the temperature of this region of South America 60 million years ago. Snakes are poikilotherms, depending on external sources of heat to maintain a given level of metabolic activity, and so available temperature means are limiting factors on how large they can grow. By comparing this animal’s size to that of modern tropical snakes, and extrapolating from a measured curve of size to mean annual temperature, they were able to calculate that the average ambient temperature was 30-34°C (American cluestick: about 90°F); less than that, and this snake would have died.

From other data, they know that the atmospheric CO2 concentration at this time was about 2000 parts per million, and that the forests it lived in were thick, wet, and rainy. They also estimate that slightly later, about 56 million years ago, mean tropical temperatures would have soared to 38-40°C (102°F), and would have killed off many species.

So there you go…this is one place I think I’d avoid if I had a time machine. It was a thick-aired, muggy, sweltering oven, with giant snakes crawling about. They were likely to have eaten large crocodilians, so I suspect a time-traveling human would be nothing but a quick hors d’ouevre. They’re still interesting, though, especially as an example of evolution and climate science meeting in a mutually revealing fashion.

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Head JJ, Block JI, Hastings AK, Bourque JR, Cadena EA, Herrera FA, Polly D, Jaramillo CA (2009) Giant boid snake from the Palaeocene neotropics
reveals hotter past equatorial temperatures. Nature 457(7230):715-718.

Maiacetus

My teaching schedule this semester is a major time-suck; I’m teaching genetics and all of its associated labs (you really don’t want to know how much prep time goes into setting up fly labs), I’m doing some major revision of the content this year, and I’ve got this asymmetric schedule that packs everything into the first half of each week. So I simply have to protest when those evil (Stein was right!) scientists announce a major discovery on a Tuesday, which just happens to be the very worst day of the week for me. They’ve gone and found another important whale transitional fossil, Maiacetus, and I’m just going to have to tell you to go read a bunch of other fine blogs that already have it covered.

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Skeletons of the Eocene archaeocete whales Dorudon atrox and Maiacetus inuus in swimming pose.

(A, B)- Dorudon atrox (5.0 m; 36.5 Ma) based on UM 101222 and 101215 [11] in lateral and dorsal views, respectively. (C, D)- Maiacetus inuus (2.6 m; 47.5 Ma) based on male specimen GSP-UM 3551 in lateral and dorsal views, respectively.

It’s beautiful. It’s clearly adapted for aquatic life, but it has another revealing feature: this specimen was pregnant at death, and the fetus is oriented for a head-first birth, which is not good for birth at sea (the head would pop out, baby would take its first breath, and drown before the tail emerged), so this animal would have had to give birth on land.

But like I said, you’ll have to read Carl Zimmer, Ed Yong, Brian Switek, or Greg Laden this time around for all the details. Or read the paper yourself! It’s freely accessible.

Seattle! Get off your butts!

Lucy’s skeleton is on tour, and is currently on display at the Pacific Science Center — a lovely and interesting place even when the most famous australopithecine in the world isn’t holding court. Here’s the surprising news: Pacific northwesterners are not flocking to the museum. The science center is losing big buckets of money on the exhibit, and other museums around the country are hesitating about booking it — it may close after its Seattle run, and I won’t get to see it!

I can’t believe this. You have a once-in-a-lifetime opportunity to see a wonderful relic of our ancient history, and you’re staying home?

You still have time. It closes on 8 March. Go!

Ancient spiders

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Spiders are amazingly sophisticated animals, and probably the premiere complex adaptation of modern spiders is the ability to spin silk. They have multiple internal glands that can produce multiple kinds of silk — webs contain different kinds, from structural strands to adhesive strands, and other kinds are used for spinning egg cases and for wrapping prey — and they are sprayed out through small spigots mounted on swiveling spinnerets, which are modified opisthosomal (abdominal) limbs. Obviously, these detailed features did not spontaneously appear all at once, but had to have evolved progressively. A couple of fossils have recently been described that reveal a) silk spinning is ancient, from at least the Permian, but that b) these early spiders did not have the full array of modern adaptations.

Here is a pair of fossils: Permarachne novokshonovi, from the Permian in Russia, and a more recent specimen, and Palaeothele montceauensis, from the Carboniferous in France. Both are eight-legged arthropods, and if you saw one scuttling about now you wouldn’t hesitate to call them spiders. There are some differences, though: Permarachne in particular shows a little less tagmosis, or fusion and specialization of segments, than we usually see in spiders, and it also has that prominent flagellum (which is completely different from a bacterial flagellum!), a long segmented ‘tail’ covered with sensory hairs that was probably a sense organ; it has no sign of a web-spinning function.

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Paleozoic Araneae and Uraraneida. (A-C) Permarachne novokshonovi, Permian of Russia, PIN 4909/12. (A) Holotype part in rock matrix. (B) Explanatory drawing of A. (C) Close-up of flagellum showing whorls of setae. ch, chelicera; cx, coxa; fe, femur; mt, metatarsus; pa, patella; pl, ventral
plate; st, sternum; ta, tarsus; ti, tibia. (D) Palaeothele montceauensis, Carboniferous of France, In 62050a, X-ray CT scan showing appendages buried in the rock matrix; note, anal tubercle (arrowed)
is not a flagellum. (Scale bars: B, 1 mm; C and D, 0.1 mm.)

What about the production of silk and webs in these old spiders? Here’s another specimen, Attercopus fimbriunguis, a 376 million year old fossil. It’s a little less dramatic because these are fragments of cuticle that have been carefully extracted by dissolving the rocky matrix with acid; it means, unfortunately, that it is more fragmented, but the advantage is that now we can zoom in microscopically and see far more detail in the structure. What we can now see in pieces of the ventral plates of the opisthosoma are small spigots, and in a few cases, there are even strands of spider silk still extended from these pores. In F, there’s also a nice shot of a chelicera (fang) from the spider — it’s wicked sharp, but the small holes seem to be preservation artifacts, and there’s no sign that venom secretion, another important spider adaptation, has evolved yet.

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Attercopus fimbriunguis, Devonian of New York (localities: G, Gilboa; SM, South Mountain), macerated from matrix with HF and slide-mounted. (A) First-described “spinneret,” G 334.1b.34; darkness of cuticle reflects number of layers, so this fragment is folded over
twice. (B) Palpal femur, SM 1.11.12; arrow indicates patch of distinctive spinules. (C) Piece of cuticle from corner of opisthosomal ventral plate showing setae, spigots, and possible silk strand, SM 1.11.4.
(D) Close-up of E showing possible silk strand emerging from spigot shaft, SM 1.11.4. (E) Flagellar structure with 12 segments (including possible distalmost) from original Gilboa locality; segments show distal
collars and setae, G 334.1a.4. (F) Close-up of cheliceral fang showing a number of holes (arrowed), the most distal of which had been interpreted as a venom-gland
opening, G 329.22.9. (Scale bars: 0.5 mm, except F, 0.25 mm.)

One of the critical observations here is very simple: no spinnerets. These spiders did not have the modified limbs with sets of spigots that we see nowadays, but instead, had a series of spigots arrayed across the bottom of the abdomen. They almost certainly were not able to make webs: what they could have done was produce sheets of silk, of the kind that could be used to make egg cases or wrap around prey. These are another example of a transitional fossil, forms that have only some of the capabilities of a later organism.

(via Cheshire, who promises to have his own post on this paper soon.)

Selden PA, Shear WA, Sutton MD (2008) Fossil evidence for the origin of spider spinnerets, and a proposed arachnid order. Proc Nat Acad Sci USA 105(52):20781-20785.

Odontochelys, a transitional turtle

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Now this is an interesting beast. It’s a 220 million year old fossil from China of an animal that is distinctly turtle-like. Here’s a look at its dorsal side:

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a, Skeleton in dorsal view. b, Skull in dorsal view. c, Skull in ventral view. d, Body in dorsal view. Teeth on the upper jaw and palatal elements were scratched out during excavation. Abbreviations: ar, articular; as, astragalus; ca, calcaneum; d, dentary; dep, dorsal process of epiplastron; dsc, dorsal process of scapula; ep, epiplastron; fe, femur; fi, fibula; gpep, gular projection of epiplastron; hu, humerus; hyo, hyoplastron; hyp, hypoplastron; il, ilium; ipt, interpterygoid vacuity; j, jugal; ldv, last dorsal vertebra; m, maxilla; n, nasal; na, naris; op, opisthotic; p, parietal; phyis, posterolateral process of hypoischium; pm, premaxilla; po, postorbital; prf, prefrontal; q, quadrate; sq, squamosal; st, supratemporal; sv1, 1st sacral vertebra; ti, tibia; ul, ulna; vot, vomerine teeth; I, V, 1st and 5th metatarsals.

Notice in the skull: it’s got teeth, not just a beak like modern turtles. The back is also odd, for a turtle. The ribs are flattened and broadened, but…no shell! It’s a turtle without a shell!

[Read more…]

Epidexipteryx

The Mesozoic was inhabited by some strange-looking critters, and here’s another example: a Jurassic dinosaur called Epidexipteryx, which has spiky teeth, big claws, fluffy feathers all over its body, and four long decorative feathers coming off a stumpy tail. It resembles a particularly ugly bird with a nasty bite, but it couldn’t fly — none of the feathers covering its forelimbs are pennaceous, but are more like an insulating fur. Or, alternatively, its feathers were all about display, a possibility suggested by the odd long feathers of the tail. Here are the bones; as you can see, the integument is remarkably well preserved, with a scruffy ruff of short, non-shafted feathers over the body and limbs, and a surprising spray of just four very long feathers coming off the tail.

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a, Main slab; b, c, skull in main slab (b) and counterslab (c); d, four elongate ribbon-like tail feathers; b’, c’, line drawings of b and c, respectively. Abbreviations: l1, l2 and l7, 1st, 2nd and 7th left teeth of upper jaw; l1′, r1′ and r5′, 1st left, 1st right and 5th right teeth of lower jaw; l2 and r2, 2nd left and right teeth of upper jaw.

And here’s what it would have looked like in life (only the colors are imaginary). It would have been about the size of a pigeon — I think a pack of these scurrying about New York’s Times Square would be both scenic and would quickly clean up the pigeon problem there.

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For all the details, read the write-up on Tetrapod Zoology.

Zhang F, Zhou Z, Xu X, Wang X, Sullivan C (2008) A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455:1105-1108.