Posts Tagged ‘origins of flight’

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

That Which Absorbs Everything Within Itself

9 September 2007

17th century Tibetan thangka

Mahakala has never been known to harm one being, even in the slightest manner, because he is constantly benefiting beings through the continuous play of the enlightened mind.Khenpo Karthar Rinpoche

Snap. Or, if you’ll pardon the expression (which is unlikely) ‘sniz-ap’. When Pigs Fly Returns has a nice work up of the newly published eentsy dromeosaurid Mahakala omnogovae, complete with an original, appropriately plumy reconstruction.

The new dinosaur, creatively named after the eponymous dharmapala figured above, takes her debutante turn in last weeks Science. Woah! birds! dinosaurs! Cope’s ‘rule!’ Rahonavis! Microraptor! Size diversity in mammalian carnivora! Size diversity in felids! Size diversity in Varanus!

My mind, and readership, reels then attenuates. I still have unpacking to do!

Blasé Feathered Tyro

29 January 2007

 

Photo: J & S S INTERNATIONAL, INC., DBA Kokoro Dinosaurs Copyright 2006

Microecos is nothing if not loose with the English language. Even so “feathered dinosaurs are relatively blasé” seems an especially exapt case of modifier mis-use.

For those awaiting the follow-up phugoid post: if you think I’m stalling… well, you’re right. But as we’re soon to see, stalling well is a very important skill.

Kokoro persists while Dinamation goes extinct. Selection or stochasm?

Glight of the Cryptophugoid I

24 January 2007


A piece of Lanchester’s phugoid theory (above left), a schematic representation of phugoid oscillation (above center), and a forward-staggered balsa biplane glider (above right). A reconstruction of Microraptor from the American Museum of Natural History’s Liaoning Diorama (below).

PNAS has recently published Chatterjee and Templin’s biplane reconstruction of the famous tetrapteryx Microraptor. As mentioned briefly in the two-headed choristodere post, Microraptor was part of the Archaeoraptor‘ fossil chimera along with the early avialan Yanornis. By a quirk of nomenclature it’s possible that the name Archaeoraptor has priority although the name is universally eschewed and many regard it as invalid.

In spite of the nude and dubious circumstances, ‘Archaeoraptor‘ is a rather appropriate signifier for the dinosaur half of the forgery, which appears to be a basal Deinonychosaurian (i.e. an early ‘raptor’). Of course, Microraptor certainly fits the diminutive dinosaur equally well and it appears that this is the name that will stick. Another synonym ‘Cryptovolans‘, forms half the inspiration for the incredibly weak pun in the title. As if that weren’t enough, the bird half of ‘Archaeoraptor‘ was briefly known as Archaeovolans before being sucked into synonymy with the bilingual chimera Yanornis.

At any rate, the true Microraptor is far more stunning than any Chinese farmer or ‘agenda-driven evilutionist‘ could have dreamed.

Figure from Xu et al. (2003)

A few things make microraptor particularly noteworthy. First of all, it’s not a bird, but a non-avian theropod. Feathered dinosaurs are relatively blasé at this point, but this is a dinosaur with wings (or something rather like them). And not just wings, but four wings one for each limb.

The next question becomes “what the hell was Microraptor doing with four wings?” Well, dragonfly-style tandem flight seems unlikely, it appears that Microraptor wasn’t really well constructed for powered flight (although it may have equally adept in the air as its distant cousin Archaeopteryx). In the paper from which I ganked the above figure, Xu et al. imagine Microraptor as a flying-squirrel-style glider using it’s fore and hindwings to create a large gliding plane around much of its body. The new PNAS paper has Microraptor as a split-level glider, holding the hindwings below the forewings to create two distinct gliding planes.

Chatterjee and Templin’s biplane idea has been kicking around for a while, but the new paper shows the results of some aerodynamic performance modelling for different configurations of the hindwing. While they can’t rule out the single-plane model, the calculations suggest that in this configuration Microraptor would have difficulty controlling the speed of its descent requiring a soft landing pad (either flexible branches or soft ground cover). In contrast the biplane model appears much more stable and the authors indicate that this was the more likely configuration.

While the thought of dinosaurs perfecting biplane gliding several hundred million years before the Wright brothers is certainly appealing, this isn’t what interests me the most about the new paper. What’s far more interesting is the suggestion that Microraptor may have used its biplane to achieve phugoid flight. But for more on that you’ll have to wait for the follow up post.

Picasso and Braque by Mark Tansey (1992)

Postscript: As usual I’ve been scooped by Matt at HMNH. Living the Scientific Life also has a very nice summary which appears in I & The Bird #41.

Just Checking In…

18 December 2006

If you’ve been chatting with vertebrate paleontologists at cocktail parties in the last week or so, chances are good that the two unlikely critters pictured below were mentioned:


Miocene mammal jaw fragment from New Zealand(!), Worthy et al. 2006 (left) and reconstruction of Volaticotherium antiquum a MESOZOIC gliding mammal from Mongolia by Chaung Zhao and Lida Xing, Meng et al. 2006 (right).

At left is the as-yet undescribed mammal of “unknown relationships” from New Zealand. That’s right, apparently that purportedly mammal free avitopian sliver of Gondwana had some furry stowaways that eked out a modest survival at least into the Miocene. More on this if I ever get around to posting on the Huia (decimated bird number four for those still counting). Especially intriguing is that the bones appear to belong not to a placental or marsupial or even a monotreme, but to an extinct group of archaic mammals with roots deep in the Mesozoic.

At right is the remarkable Volaticotherium antiquum1, “ancient airborne mammal”, a Mesozoic mammal which apparently employed a patagial membrane to glide between trees much like the familiar flying squirrels (Pteromyini), as well as more esoteric mammalian gliders like the colugo and the sugar glider. This pushes the record of gliding mammals back by about 70 million years and provides yet one more blow to the misconception of Mesozoic mammals as uniformly unremarkable shrewoids. Worth noting is the volaticotheres insectivorous dentition, more on that too later. Maybe.

I always saw GW as more of the Bullwinkle type…

Once upon a time, microecos was going to keep abreast of the publication of notable vertebrate fossils complete with vaguely insightful quasi-scientific analysis. Alas, the pace of discovery in 2006 proved well beyond my means. Fortunately a number of other weblogs already fill that gap (without the vagueness etc. of course).

Michael Ryan’s Palaeoblog is one-stop shopping for the late-breaking paleonews, illuminated with vintage comics covers. Palaeoblog has posts on both the new New Zealander, and the Mesozoic glider.

HMNH also has a post on the glider, and a very interesting discussion of the New Zealand fossils with respect to “ghost lineages”, a concept with close ties to the more popularly parlayed “living fossils” of the last post (remember, the bit from last September with the naked lady? Oh yeah it’s down there).

Darren Naish also writes a bit about both on his highly anticipated recent post about mid-continetal seals. If you make a paypal pledge maybe he can be convinced to stop taunting us like that.

All three blogs are mandatory reading for those not wishing to make ignorant asses of themselves at their next social drinking engagement with paleontologists, although you probably will anyway.

1 – Note the old-school Latinate name, bucking the recent trend of borrowing from languages local to the discovery site.

Terminal Velocity – Ant Style

4 April 2006

If you are a paleontologist lucky enough to have run into me at a cocktail party recently, you have probably been subjected to a diatribe concerning arthropod life history patterns, dispersal strategies, cladogenesis and the origins of insect flight. Sorry again about that.

Now, via Rollicking Boils, comes this NYT article about "gliding ants."

Those with an afternoon to kill should probably spend it watching the videos.

Having not yet read the Nature paper, here are my poorly-informed, unqualified opinions:

  • "…this is fucking awesome." I concur. (Note: this quote comes from the person who sent me the link, the rest are from the NYT article)
  • "…may reveal the origins of insect flight." Not so sure. As Yanoviak states clearly in the gliding ants FAQ ants are a highly derived group of insects and workers are secondarily wingless. Reproductive adults (queens and drones) are born with wings which they employ to full effect during their nuptial flight. Thus these ants are a poor analog for the earliest insect fliers and it's hard to imagine a scenario which would lead to these ants developing powered flight.
  • "There are very few similarities between insect gliders and other gliders." Well, beyond the superficial dissimilarity (i.e. no gliding membrane1), gliding ants seem to me quite similar to gliding vertebrates in that they:a) Are arboreal as a rule. Though note that not all arboreal ants (nor vertebrates for that matter) are gliders. (Anyone know if this is also the case for the flying silverfish mentioned in the article?)b) Use gliding as a means for predator-evasion and locomotion but not for prey-capture or reproductive dispersal.c) Have independently evolved gliding habits multiple times within different lineages. Much as several unrelated arboreal mammals (flying squirrels, sugar gliders, colugo etc.) have.
  • "The scientists' hunch that the ants' movements, not their body shapes, chiefly dictated their gliding paths was confirmed when they started chopping off appendages to see if the insects could still soar." I love this kind of old-school field biology, no electrophoresis trays, no centrifuges, not even any randomly distributed plots, just some guys chopping the legs off of ants, dropping them from trees and videotaping it.Nevertheless, take a close look at the head of Daceton:


    Beautiful photograph courtesy of April Nobile and the Cal Academy of SciencesBroad and flat, with rear projecting lobes (and even little spoilers on the thorax?)…I think there is a good chance that these ants DO exhibit morphological adaptations related to this behavior beyond just the acrobatic techniques emphasized in the NYT article. In fact this looks like an awesome functional morphology/biomechanics project for anyone with access to a very tiny wind-tunnel

    The NYT article and this one from Cal hint at a different model of insect evolution than the "mayfly skipping across the pond with modified gills" story that was once in vogue. It is interesting to note that the explosion of flying insects seems to correspond with the advent of forests in the Carboniferous.

    Will we eventually see a full-blown "tree down" vs. "ground (or pond) up" debate like the one which is at the core of current research into the origins of bird flight?

    More on my notions about the origins of insect flight in an upcoming post.

    1 – Given that ants are several orders of magnitude smaller and lighter than vertebrate gliders it is fairly unsuprising that ants would not develop gliding membranes. First, they are unneccesary for an organism with such a large surface area:mass. Second, gliding membranes on such a light organism would probably be a liability (imagine ants being whisked away involuntarily with every small gust).

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