Posts Tagged ‘exaptation’

The Last Tapu

23 June 2010

All images from the fantastic collections of the Alexander Turnbull Library

Got to wondering why my four-year-old post about the Huia, a fascinating and sadly extinct bird from New Zealand, was suddenly seeing a deluge of web traffic (well, by microecos standards), broken links and all.

Turns out, a single Huia feather just went to auction in Auckland and fetched NZ $8400 (about $6800 US), setting a new world record for the auction value of a single feather.

Huia feathers were important status symbols among the Maori.  The variation in the number of feathers worn in the hair of the individuals pictured above probably correlates broadly with their social standing, though it is interesting that the number of feathers in the images appears to dwindle with time.  An echo of the Huia’s decline, or a society in peril?  Perhaps a bit of both, certainly the two seem to have something of a common cause in the influx of European invaders, of the two-legged and four-legged variety.

Also noteworthy is that some of the photographs postdate the last confirmed sighting of a wild Huia in 1907.

One suspects the anonymous winner in the recent auction had status on their mind as they cast their bid.  As, I suppose, did their unnamed adversaries that  helped them drive the price up well above the expected NZ $500.  I mean the Huia’s tail feathers have a striking beauty to them, though I can’t help but find them more beautiful when the rest of the bird is attached:

When seemingly deeply vacuous contemporary status symbols like this fetch $10K, $7K for a Huia feather almost feels like an injustice.

But then, I guess that attitude misses the real injustices at work here.

Niedźwiedzki’s Gap

6 January 2010

Mudskipper (Periophthalmus) at the California Academy of Sciences

So yeah, just wanted to go on record and coin that one really.  An early contender for Top Paleo Story of 2010 is hitting the media shores like a flotilla of stem-tetrapods:

Nice (if rather breathless) promotional video from Nature

Detailed post on Nature editor Henry Gee’s blog

And the paper (Niedźwiedzki et al., 463, 43-48, 7 January 2010) here

Tetrapod tracks 20 million years before we would expect to find them.  Dude.

One interesting implication of this paper is that it may force us to rethink the environmental context of the water-to-land transition of early tetrapods.  The newly discovered trackways were left on exposed marine tidal flats, suggesting the “Tangled Bank” picture of the earliest tetrapods clambering around in vegetation-choked streams and rivers before taking to the land may not be exactly the entire story.  The role of freshwater as an avenue for sea>land and land>sea evolutionary transitions is an interesting subject in its own right, remind me to blog about it some time.

Another interesting angle is how this story contrasts with the last big “origins of tetrapod story”. The discovery of Tiktaalik has been relentlessly touted as an example of how we can make “predictions” about when (stratigraphically) and where we expect to find important fossils based on what we already know about the history of life and then go look for them.  That is true, to a point.  However there is also a very important place for unexpected discoveries in paleontology despite the fact that they don’t fit in as nicely with fairy tales about how “THE” scientific method is supposed to work.  Granted, it’s difficult to write successful grant applications along the lines of “well, I have no idea what the eff I’m going to find, but I’m sure it will transform what we think about evolutionary history.”  Still, I’ve always that old line (usually attributed to Asimov, perhaps apocryphally)–“the most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…’–was particularly true in paleontology.

What will get the most attention however, is that the new discovery pushes back the divergence of true tetrapods and elpistostegids like Tiktaalik by 20 million years or so.  So, news flash to everyone who went ga-ga over Tiktaalik as THE missing link, it isn’t.  But you already knew that.  Before you feel to sorry for Tiktaalik getting summarily kicked to the curb though, it’s good to remember Neil Shubin’s words back in 2006 when the discovery of “the fishapod” was first announced:

Mudskippers and the other walking fish are all very interesting, but are they extraordinary in an evolutionary sense? No, they are not, and the reason is instructive. Hopping, climbing, and breathing fish are just animals that have evolved to live in different kinds of aquatic and subaereal habitats. They are able to breathe air, hop, or climb because of subtle changes to their bodies; no revolutionary changes are needed…If paleontologists 300 million years from now dig up the remains of a mudskipper, they will write chapters about its role in a “great” transition only if its part of the evolutionary tree has branched into many twigs. The mudskipper will get extra special treatment if one of its evolutionary branches leads to the paleontologists’ own species. (Shubin 2006 “The ‘Great’ Transition”)

Hear that Mudskipper?  Nice try.  We’re not impressed.

Follow My Nose It Always…uh I think I’m having a hot flash

23 July 2009

toucan_sam2 Very cool paper out in Science today demonstrating that the Toco Toucan (Ramphastos toco) uses its bill for thermoregulation.

The story seems to be getting some good traction with the popular press, unsprisingly given the winning combination of outside the box thinking, novel application of hi-tech toy tool (an infrared camera) and charismatic megafauna.

Check out LiveScience for an awesome video (or if you are lucky enough to have access to Science you can watch the video–commercial free–in the supplementary info for the new paper).

Picture 1

Adapted from Figure 1 - Tattersall et al. 2009

Note that the new study does not explicitly rule out sexual selection or foraging strategies as important factors in the evolution of the Toucan bill.  Multifunction is ubiquitous in nature (something paleontologists who argue that X structure evolved for Y reason would be well-served to remember).  Nevertheless the Tatterall et al. paper poses an interesting question as to whether thermoregulation has been an overlooked factor in the evolution of other bird groups. The Hornbills of tropical Asia and Africa–often claimed as ecological analogues of Neotropical Toucans–would be a logical candidate for similar study.

Oh yeah, here’s some hive mind Wikipedia brilliance on Toucan Sam:

Biologically speaking, Toucan Sam appears to be a Keel-billed Toucan parrot. Keel-billed Toucan Parrots are well-known for their colorful beaks and propensity for fruit in their diets, two features which are very consistent with the character.

Really Wikipedia?  Toucans are parrots?  RU SURE? And anyway I thought he was a Mountain Toucan you know, biologically speaking.  He is blue after all.

And before anyone calls me out for complaining about a Wikipedia entry without fixing it, I mean, come on, it’s really too awesome to amend isn’t it?

Tattersall, GJ, DV Andrade and A Abe Science 24 July 2009 Vol. 325. no. 5939, pp. 468 – 470 DOI: 10.1126/science.1175553

Something my body needs anyway…I like that.

16 September 2008
As you’ll note from the logo over there, this marks the first issue of “blogger half-assedly opining about peer-reviewed publications when, really no one asked in the first place anyway.”  I’ll use this logo whenever I…well you get the picture.  Feel free to borrow the logo for your own half, or even whole-assed efforts.

Invert-workers are always carping1 about vertocentrism, and of course they have a point: tardigrades are like a gajillion times radder than tyrannosaurs and it’s a shame that Discovery Channel programming doesn’t reflect this fact.  I guess they’re busy vetting questions for Cash Cab or whatever.  But it occurs to me: it’s actually unfair to resent vertebrates as a whole for this injustice because, let’s face it, aside from lamnids no one gives a swimming crap about fish.

I know, I know, cladistically speaking, tetrapods like Sue and me are just aberrant terrestrial fish. Aside from our freakish lineage however, the silent majority of “values” vertebrates (i.e fish) might as well be ostracods for all the press attention they get.  I mean, ostracodes. Whatever.  (Actually ostracods/es have a pretty good PR person these days).

A few cases in point2: Funisia, an ediacaran with all the charisma of a sodden mop head, got major press attention thanks to some good old fashion sexing up by the media.  Likewise, Martialis heureka, the recently discovered basal ant, is already generating major buzz3 well before the peer-reviewed paper announcing the discovery has even hit the presses.  And don’t get me started about Aptostichus stephencolberti.

Meanwhile, the discovery of a new and extraordinarily bizarre fossil fish, Hsianwenia wui, announced in last week’s issue of PNAS (Chang et al. 2008), sank with less of a splash than a 49 kg Chinese diver making a perfect entry4.  And that’s unfortunate, because if the public has an inordinate fondness for things with hydroxylapatite endoskeletons, well Hsianwenia is about as bony as they come.

Hsianwenia (which I’m pronouncing “shee-An-Wen-ya” until someone corrects me) was discovered in Pliocene lake sediments from the Qaidam basin on the north side of the Tibetan plateau.  Hsianwenia belongs to the largest family of freshwater fishes the Cyprinidae which also includes minnows, carp and goldfish among many others.  The uplift of the Tibetan plateau over the past several million years has created multiple small, isolated lakes and waterways.  This in turn has driven the evolutionary radiation of an endemic suite of Cyprinids.  These 100 or so species in 15 genera are grouped together the subfamily Schizothoracinae, known to the more poetically-minded as “snow trout” or “snow carp” (Qi et al. 2006).

While FishBase reports that the flesh of living schizothoracines is “much relished”, eating Hsianwenia would have been a chore.  That’s because unlike its relished relatives, Hsianwenia is characterized by a peculiar thickening of the skeleton.    This “pachyostosis” is so extreme that the authors state that the bones appear to leave little room for muscle.

Hsianwenia wui from Chang et al. (2008).

While no known living fish possess a similar super-skeleton, another extinct fish, Aphanius crassicaudus—from Miocene sediments on the northern margins of the Mediterranean—apparently independently evolved extremely thick bones.  Multiple specimens from both species demonstrate that the pachyostosis is not evidence of disease or disorder, but was a natural feature in each fish.  More over, this condition was amplified through the course of ontogeny with fish becoming progressively stouter as they aged.

What factors could have selected for this unusual evolutionary quirk not once but twice?  The sediments containing the two fish species—though separated by space and time—share some provocative mineralogical clues: gypsum and calcium carbonate.  Both of these minerals are calcium salts and their presence as inorganic precipitates suggests that the bodies of water these fish lived in had extraordinarily high concentrations of dissolved calcium and other minerals.

The authors of the recent paper suggest that the hypertrophied skeleton of Hsianwenia (and Aphanius) was a novel solution for ridding the body of excess calcium5.  By thickening their bones, these fish were able to sequester calcium before it built up to toxic levels within its tissues.  Chang et al. also speculate that the saline waters were toxic to other vertebrate species given the absence of other vertebrate fossils.  So, these strange fishes may have had no need to escape from predators and could afford to reduce muscle space and add bulky bone.  Pollen and, yes, ostracods/es provide circumstantial support for generally arid and saline conditions in and around the lake while the fish were thriving.

Hsianwenia’s solution to it’s hard-water environment worked pretty well for 200,000 years or so, allowing it to thrive in waters where no other fish could.  Of course, Mother Nature’s a vindictive bitch, and all evolutionary solutions are by definition, temporary.  A thick evaporite deposit capping the fish-bearing layers speaks to our tale’s tragic end: the aridification of the Qaidam basin continued, the lake dried up, the freaky thick-boned fish died, the end.

So there you have it: tectonics, climate, aqueous geochemistry, evolution, morphological novelty and million-year-old fossil fish bones scattered across the high desert.  A fish story worth telling.

And you thought fish were boring.

REFERENCES

Chang, M. et al. 2008.  “Extraordinarily thick-boned fish linked to the aridification of the Qaidam Basin (northern Tibetan Plateau).” PNAS 105: 13246-13251.

Porter, S. M. 2007.  “Seawater Chemistry and Early Carbonate Biomineralization.” Science 316: 1302.

Qi, D. et al. 2006. “Mitochondrial cytochrome-b sequence variation and phylogenetics of the highly specialized schizothoracine fishes (Teleosti: Cyprinidae) in the Qianghai-Tibet Plateau.” Biochemical Genetics 440: 270-285.

1 As we’ll soon see, this is a hilarious pun.
2 There is one, sort of.  Be patient.
3 I suppose I’m mixing hymenopteran metaphors here.
4 Credit where it’s due: a German science blogger has already written about Hsianwenia here (in German).
5 One hypothesis to explain the “explosive” evolution of organisms with hard parts in the Cambrian holds that changes in seawater chemistry (perhaps linked to tectonic activity) drove organisms to begin precipitating minerals to prevent toxic buildup inside their cells.  Subsequently these structures were exapted into shells and carapaces and bones and teeth ultimately triggering an adaptive arms race.  While this hypothesis is speculative and controversial recent research does support the importance of seawater chemistry in setting the patterns of biomineralization among various lineages (Porter 2007).

Enigmatic Triassic Hellasaur Thursday — The mostest unkindestest cut

8 August 2008

Venom–toxic fluid injected to subdue prey or deter potential predators–is widespread in the animal kingdom, from jellyfish to scorpions to platypodes. A case could even be made that stinging nettle is an example of a venomous plant, since it injects its toxin into victims. However, most toxic plants, as well as toxic animals and fungi that rely on passive delivery of toxins (e.g. newts) are considered poisonous but not venomous.

Snakes are one of the most familiar groups of venomous animal although a majority of snakes lack venom. Most people are also aware of the venomous beaded lizards (or, “gila monsters”) in the genus Heloderma. Far less well known is that varanid monitor lizards and bearded dragon, Pogona, popular in the pet trade, also possess a mild venom. We’re talking real venom here, not the bacterial brew that produces the much discussed septic bite of some varanid lizards. In fact, the discovery that venom occurs in reptiles aside from snakes and Heloderma was made only a few years ago and has forced us to rethink the evolutionary origins of venom among squamates (Fry et al. 2006).

So, what does any of this have to do with enigmatic Triassic hellasaurs? Read the rest of this entry »

Enigmatic Triassic Hellasaur Thursday…who’s counting anway? — The Duck-billed Ichthyopus

8 May 2008

When George Shaw received the first platypus skin to make it to England in 1789, he took a pair of scissors to it to look for stitches, or so the story goes. It is impossible not to entertain some doubts as to the genuine nature of the animal,” wrote Shaw. Surgeon, and racist, Henry Knox argued that the Asian itinerary by which the specimen had traveled was, “sufficient to rouse the suspicions of the scientific naturalist, aware of the monstrous impostures which the artful Chinese had so frequently practiced on European adventurers.” Of course, the reality of this chimerical creature has long since been recognized, and, as of this week, we have the unique genome to prove it.

More recently the Archaeoraptor” scandal raised echoes of Knox’s Sinophobia, and this weeks’ hellasaur is certainly enough to raise eyebrows. Hupehsuchus nanchangensis, has that “designed by committee” look, with the limbs of a basal ichthyosaur, the dorsal armor of a placodont and the bill of a…well, duck. But the fossils indeed check-out: this is no “monstrous imposture”, just one freaky-ass (or if you rather, enigmatic-ass) hellasaur.

Hupehsuchus drawing by Zach Miller

Hupehsuchus nanchangensis by Zach Miller

And the more you look, the weirder it gets…more tomorrow!

Enigmatic Triassic Hellasaur Thursday: Part the, um fourth?, Kyrgyz Kameleon

17 April 2008

If you’re hoping to make it into the fossil record, being a small, arboreal insectivore is probably not the best way to go. Forest soils are veritable compost heaps: acidic and crawling with critters and fungi that would happily mill your remains to humus given half a chance. And your scrawny, flexible skeleton is highly unlikely to endure the vicissitudes of long distance transport to some more suitable sedimentary environment.

Of course if you’re reading this blog chances are good that you’ve already been born so it may be too late to fix this. But don’t worry–there is a back up plan: find a lake, and fall in. Hey, it worked for Longisquama and Sharovipteryx, though a case could be made that they would have saved everyone a lot of trouble if they had just rotted on the forest floor like a respectable forest dweller.

Landsat

The Triassic Madygen Formation of Kyrgyzstan is among the most important sources of Triassic insect fossils in the world (Fraser 2006). In fact, I’d almost rather write about the titanoptera, an “enigmatic” insect group which included the 30-cm wing-spanned Gigatitan vulgaris that may have looked something like the result of an unholy love-affair between a coackroach and a mantis…on crack. But this is “Hellasaur” Thursday so I’d better stay focused.

Left: LANDSAT image of Madygen Formation outcrops – de.wikipedia

In fact, it was the search for insect fossils that led to the discovery of two the Triassic’s more problematic hellasaurs. The first, Sharovipteryx mirabilis, is bad enough, what with its bizarre hind-limb “delta wing” and its purported link to pterosaur evolution despite its patagium-backward construction. We’ll leave Sharovipteryx be for now because our topic at hand is going to require the full bottle of Excedrin.

Longisquama insignis type specimen.

Behold, Longisquama insignis, “remarkably long-scaled” as the rather prosaic scientific name would have it. “Remarkable” is certainly *one* way to describe Longisquama. Whether the protarded 10 to 15 cm long structures which appear to project from its back are scales is (as Zach noted in the comment to a previous post) up for debate.

Some argue that the strange frond-like structures are the foliage of some unknown plant. They do look vaguely vegetative, although other plant matter on the slab appears to show a very different style of preservation and Fraser notes that they have “a peculiar venation pattern that is inconsistent with any known Triassic foliage types. The structures certainly appear to be physically associated with the skeleton itself, and most who have examined the fossil seem to accept that they belong to the skeleton, though the ‘consensus’ ends abruptly there.

One camp holds that they are feathers (which are, of course, modified scales) (Jones et al. 2000)! If this were true it might seriously upset the notion that birds are derived theropod dinosaurs. However, this view is a decided minority and a vast array of other skeletal evidence as well as the preservation of far more convincing feathers on some theropod fossils weigh heavily in favor of the birds-as-dinosaurs hypothesis. That is, unless maniraptoran theropod “dinosaurs” are secondarily flightless birds that merely look like dinosaurs….

Oregon State University

Anyway, if the nature of these structures remains contentious, then establishing their function has basically been an interpretive free-for-all. A number of authors have tried to turn them into a parachuting or gliding apparatus of some sort. However, unless they supported a membrane, or were filled with helium, it’s hard to imagine how this would have worked. That said, a recent phylogenetic analysis suggests Longisquama may have been closely related to Coelurosauravus a Permian diapsid with a slightly more (though perhaps not altogether) convincing gliding membrane projecting from its sides.

Left: Longisquama as plumulus glider – Oregon State University.

Display –either to attract mates or perhaps to scare off potential predators or intraspecific rivals—is another popular explanation and probably a more convincing one. Elongate plumes in birds are exclusively a sexual selection affair; in fact their value as a sexual symbol may be directly linked to their hindrance to locomotion.

Scissor-tailed FlycatcherTyrannus forficatus

Another, admittedly fanciful, scenario is that the resemblance to a plant frond is not-coincidental. Could the scales of Longisquama be some extreme cryptic adaptation? Perhaps they hid the animal from predators or provided cover allowing Longisquama to ambush its supposed insect prey? Structural mimicry of plants is rampant among arthropods and in addition to more familiar cryptic coloration patterns, a number of land vertebrates use posturing as well as modified skin surfaces to blend into their surroundings

While sexual advertising and cryptic camouflage would appear to be at odds with one another there are animals well-equipped for both. Notably, for our purposes, chameleons, who are at once exceptionally cryptic and at the same time often sport elaborate sexual signaling structures like horns and crests. While chameleons probably don’t adjust their colors to match their background as popularly believed, color switching does allow them to temporarily display their mood to another individual then switch back to their more cryptic “normal” coloration when the mood has passed.

Oregon State University

To continue our cautious, chameleon-like walk out on a very thin limb, it’s interesting to note that Longisquama’s skull, as figured by Senter (2004) (shown left), bears a remarkable superficial similarity to that of a chameleon [Note that other, very bird-like reconstructions of the skull out there are probably inaccurate, especially with regards to the supposed antorbital fenestra which is likely a preservational artifact]. The skull of Longisquama’s cousin Coelurosauravus is perhaps even more chameleon like. I’m not prepared to make an argument for functional convergence here, but to me the resemblance is quite striking.


Longisquama by Matt Celeskey

Longisquama is certainly not closely related to chameleons, but its probable close relatives the enigmatic hellasaurs known as drepanosaurs, have been inferred to have had a chameleon-esque lifestyle. One wonders if this interpretation might be extended to Longisquama. Was it lurking in the Triassic treetops, flashing chromatophoric signals across its crazy dorsal scales and snagging titanopterans with a ballistic tongue?

Left: Longisquama by Matt Celeskey

Or, have I just been out in the sun to long?

refs-

Fraser, Nicholas 2006. Dawn of the Dinosaurs Indiana University Press

Jones, Terry D. et al. 2000. “Non-avian Feathers in a Late Triassic Archosaur.” Science 23 June 2000:
Vol. 288. no. 5474, pp. 2202 – 2205 DOI: 10.1126/science.288.5474.2202

Senter, Phil 2004. “Phylogeny of Drepanosauridae (Reptilia: Diapsida).” Journal of Systematic Palaeontology 2: 257-268 DOI: 10.1017/S1477201904001427