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paleoanthropology, genetics and evolution

dinosaurs

  • Hiding above the dinosaurs

    Sun, 2012-12-02 13:00 -- John Hawks

    The early bin at PNAS has a cool, short paper by Yongjie Wang and colleagues, which matches a ginkgo tree with its insect mimic [1]. The cool part is that both of them lived during the Jurassic. I'm quoting a passage from the discussion that adds some more context to the fossils in this case:

    This association joins a previously published instance of leaf mimesis from the same deposit by another group of insects, the Neuroptera, whereby two species of saucrosmyline lacewings were mimetic, although only their forewings resembled particular cycadophyte leaves (9). The association of J. ginkgofolia and the Ginkgoitesleaves of Y. capituliformis considerably extend this phenomenon. More importantly, it adds a more finely tuned example of leaf mimesis wherein the entire insect body participates in the de- ception. This mimicry would necessitate a quantum increase in the coordination and integration of somatic development to achieve replication of a leaf model in size, shape, surface texture, and probably behavioral control of motion, sufficient to either deceive a potential predator or prey item. This similarity only could occur during an interval wherein the multilobed ginkgoa- lean leaf (the model) was present in sufficient numbers to con- tinue the deception. In any event, Y. capituliformis became extinct during the Jurassic–Cretaceous boundary (19), as possibly did its mimic, J. ginkgofolia, significantly before the initial appearance of angiosperms during the mid Early Cretaceous. The interpretations of these two different examples of leaf mimesis can provide unusual insight (2, 16) into a preangiospermous world of elevated counterdefensive plant–insect associations such as leaf mimesis.

    The artist's reconstruction of the mimic insect upon a prehistoric ginkgo branch is one of the coolest pieces of paleoart I've seen. I hope they don't mind me spreading this, it's a wonderful image:

    Hangingfly mimic of Jurassic ginkgo, artist's reconstruction, from Wang et al. 2012

    Figure 3G from Wang et al. 2012. Original caption: "(G) Artist’s reconstruction of J. ginkgofolia mimetic on Ginkgoites leaves of Y. capituliformis."

    Breathtaking. As the text above indicates, this isn't the only known mimic from the same formation, but it is truly interesting to see this kind of association long before the intricate insect-plant mutualistic relationships that accompanied the rise of the angiosperm plants.

    References

    1. Wang Y, Labandeira CC, Shih C, Ding Q, Wang C, Zhao Y, Ren D. Jurassic mimicry between a hangingfly and a ginkgo from China. Proc Natl Acad Sci U S A. 2012.
    Tags: 
    insects
    non-primate
    dinosaurs
    Mesozoic

  • Drilling past the feathers

    Thu, 2012-10-25 15:08 -- John Hawks

    An article by Veronique Greenwood covers the discovery of feathers on a North American dinosaur: "Paleontologists Uncover the First Feathered Dinosaur Fossils in the Americas". Dinosaurs are remote from hominins, but there is one aspect of the story to which I wanted to draw attention:

    The finds had implications beyond the obvious. Ornithomimids were first unearthed more than 100 years ago, but paleontologists only learned about the existence of dino feathers 15 or so years ago. And the fact that no one had ever looked for feathered dinosaurs in river sandstone before got the researchers thinking: "What about fossils that were collected 10, 20, 30, 50, 100 years ago?" Therrien says. "If paleontologists had known it was possible to preserve impressions of soft tissue in sandstone, well, maybe these other specimens were covered with feathers, and they were just destroyed during preparation."

    Our methods of recovery and preparation of fossils may, in some cases, be destroying evidence of soft tissue or non-bony structures. The preservation of such structures is idiosyncratic and rare, and so not readily predicted in any particular fossil context.

    Archaeology has gone through similar revolutions in the past. Archaeologists used to discard sediment after it was sifted; later they began to employ flotation of the material in water, which in some cases allowed organic remains to be separated and identified. Calculus was once scraped off teeth to make them easier to study; now we know that the calculus can preserve phytoliths and starch grains that provide strong evidence of diet.

    It's not obvious how fossil preparation and recovery might be altered, but clearly with the Malapa site, excavation and preparation team is planning with extreme care for exactly this kind of reason. If paleontologists are finding dinosaur feathers in sandstone, any context with articulated hominin bones needs to be considered with extreme care.

    Tags: 
    Malapa
    Malapa Soft Tissue Project
    preservation
    dinosaurs

  • Pod pimping

    Sat, 2010-12-25 07:30 -- John Hawks

    Sauropod Vertebra Picture of the Week author Matt Wedel has two recent posts about the artistic reconstruction of sauropods. The one about head anatomy is especially perceptive.

    I think these are dynamite, because they show that you can avoid “shrink-wrapped dinosaur syndrome” (SWDS) and still make an anatomically detailed, realistic-looking life restoration. SWDS is what I call the common convention in paleo-art of simply draping the skeleton–and especially the skull–in Spandex and calling that a life restoration. I think it’s a popular technique because you can show off the skeleton inside the animal and thereby demonstrate that you’ve done your homework (especially to an audience that already knows the skeletons*). It gives artists an easy way to add detail to their critters; if you actually slab on realistic soft tissues and lose most of those skeletal and cranial landmarks, you have to come up with something else to make your animals look detailed and visually interesting. And by now it’s been going strong for several decades, so people expect it.

    Yes, hominin reconstructions are also subject to shrink-wrapped syndrome. I'm less critical of that than the "thousand-mile stare" pose that many reconstructions are given. There's more emotion in the Lincoln Memorial.

    Wedel's earlier post, "Pimp my pod" discusses the idea of "too big for camouflage".

    Tags: 
    art in science
    art
    dinosaurs

  • The failures of dinosaur splitters

    Mon, 2010-09-27 10:57 -- John Hawks

    A-HA! We all lecture in our classes about the perils of naming too many species, but now the facts have been statistically proven! Well, at least for dinosaurs:

    Top dinosaur hunters are worst at naming

    The more fossil species you describe, the less likely the names are to stick.

    ...

    "I would have expected that more prolific, experienced authors might be better at recognizing genuinely new species, yet they were less successful than authors who name only a few dinosaurs," says [paleontologist Michael] Benton. "It is hard, and maybe impossible, to construct a case that experience in naming dinosaurs makes one better at the job."

    OK, dinosaurs are a much bigger sample than hominins. But our rate of discard is actually much higher -- we must still be using only 10 or 20 percent of the names that have been proposed, and probably half the ones we're using now will bite the dust. By contrast, more than half the dinosaur names are still accepted.

    It's the failure of the "prolific" taxonomists that deserves to be cited again and again. Oh, they got it right 41% of the time, and a lot of the sunken names date to before 1950, but the phenomenon has not abated with names of the last 50 years. Prolific namers seem to have a lower threshold for erecting a new taxon, and they get it wrong more than half the time.

    Tags: 
    metascience
    dinosaurs
    taxonomy
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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

Denisova

From a finger bone of an ancient human came the record of a completely unexpected population. My lab is working on the science of the Denisova genome.

Acceleration

The advent of agriculture caused natural selection to speed up greatly in humans. We're uncovering some of the ways that populations have rapidly changed during the last 10,000 years.

Malapa

Just outside Johannesburg, the Malapa site is producing some of the most exciting finds in human evolution. This site is the headquarters of the Malapa Soft Tissue Project.