Friday, September 12, 2014

Four-winged flyers

An interesting video, which unfortunately is biased to the dino to bird theory.
Especially note from 48:00 to 49:00.
Note that at 48:17 they point to exactly the spot where we find Scansoriopteryx.

And particularly see 27:00 to 28:00.
At 27:37 notice the lineage that Larry Martin proposes that links archosaurs to basal paraves.
In what I am suggesting, that line is a branch of PTEROSAURS.

Also see here for the extra section that was not televised, of flight with splayed legs.
"The lift climbs steadily and more predictably than anything they've seen so far".

Microraptor had four wings, one on each of its forelegs and hind legs. The long feathers on the legs of Microraptor were true flight feathers as seen in modern birds, with asymmetrical vanes on the arm, leg, and tail feathers. As in modern bird wings, Microraptor had both primary (anchored to the hand) and secondary (anchored to the arm) flight feathers. This standard wing pattern was mirrored on the hind legs, with flight feathers anchored to the upper foot bones as well as the upper and lower leg. It has been proposed that the animal glided and probably lived mainly in trees, because the hind wings anchored to the feet of Microraptor would have hindered their ability to run on the ground.[9] It had long pennaceous feathers on arms and hands (10–20 centimetres long or 3.9–7.9 in), with legs and feet 11–15 cm long (4.3–5.9 in). Toward the tail end, Microraptor was covered in shorter downy (plumulaceous) feathers, 2–6 cm long (0.79–2.36 in). Though not apparent in most fossils under natural light, due to obstruction from decayed soft tissue, the feather bases extended close to or in contact with the bones, as in modern birds, providing strong anchor points.[10]
When describing specimens originally referred to the distinct species Cryptovolans pauli, paleontologist Stephen Czerkas argued that Microraptor may have been able to fly better than Archaeopteryx, noting the fused sternum and asymmetrical feathers of Microraptor, as well as features of the shoulder girdle that indicate flying ability closer to modern birds than to Archaeopteryx. Czerkas cited the fact that this possibly volant animal is also very clearly a dromaeosaurid, to suggest that the Dromaeosauridae might actually be a basal bird group, and that later, larger, species such as Deinonychus were secondarily flightless. The work of Xu and colleagues also suggested that basal dromaeosaurs were probably small, arboreal, and could at least glide, though later discoveries of even more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view.[9][11]
Whether or not Microraptor could achieve powered flight or only passive gliding has been controversial. While most researchers have agreed that Microraptor had most of the anatomical characteristics expected in a flying animal, some studies have suggested that the shoulder joint was too primitive to have allowed flapping. The ancestral anatomy of theropod dinosaurs has the shoulder socket facing downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Some studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the vertebral column until relatively advanced avialans like the enantiornithes appeared.[12] However, other scientists have argued that the shoulder girdle in some paravian theropods, including Microraptor, is curved in such a way that the shoulder joint could only have been positioned high on the back, allowing for a nearly vertical upstroke of the wing. This possibly advanced shoulder anatomy, combined with the presence of a propatagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an alula or "bastard wing" may indicate that Microraptor was capable of true, powered flight.[13] 
Chatterjee also used computer algorithms that test animal flight capacity to test whether or not Microraptor was capable of true, powered flight, in addition to passive gliding. The resulting data showed that Microraptor did have the requirements to sustain level powered flight, so it is theoretically possible that the animal flew on occasion in addition to gliding.[5]

One distinctive feature of Scansoriopteryx is its elongated third finger, which is the longest on the hand, nearly twice as long as the second finger (in most theropod dinosaurs, the second finger is the longest). This is unlike the configuration seen in most other theropods, where the second finger is longest. The long wing feathers, or remiges, appear to attach to this long digit instead of the middle digit as in birds and other maniraptorans. Shorter feathers are preserved attached to the second finger.[6]
Scansoriopteryx had a non-perforated hip socket, which is more open in most, but not all, other dinosaurs. It also had a pubis (hip bone) which pointed forward, a primitive trait among theropods, and unlike some maniraptorans more closely related to birds, where the pubis points downward or backward.[6] The legs were short, and preserve small pebbly scales along the upper foot (metatarsus), as well as possible impressions of long feathers in the same area, possibly similar to the "hind wings" of Microraptor and other basal paravians.[6]
A monophyletic Scansoriopterygidae was recovered by Godefroit et al. (2013); the authors found scansoriopterygids to be basalmost members of Paraves and the sister group to the clade containing Avialae and Deinonychosauria.[8]

One final point to add here is that the discovery of the wonderful 4-winged Microraptor gui seemed to come as complete shock to everyone. In hindsight of course it really should not have done so since Archaeopteryx clearly has long flight feathers on the legs.

Part of the program description
The two markedly different reconstructions play into a long-running scientific controversy over the origin of flight in birds. For years the debate has been a standoff between two camps—those who believe dinosaurs were the ancestors of birds, and those who do not.
Believers in the dinosaur-bird connection have generally assumed that flight must have begun from the ground up, with fast-running dinosaurs that eventually got airborne as feathered arms evolved into wings, and running leaps evolved into powered flight.
Skeptics of the bird-dinosaur link say it would have been physically impossible for running dinosaurs to overcome gravity and get off the ground. It made more sense for flight to evolve from the trees down, with small, arboreal reptiles that glided from the treetops on their way to becoming full-fledged fliers. And that seemed to rule out dinosaurs, which presumably couldn't climb trees.
As seen in this program, the American Museum's Mark Norell is one of the proponents of the "birds-are-dinosaurs" hypothesis, which is the predominant view among most paleontologists, while Larry Martin of the University of Kansas speaks out for the minority view that birds descended from non-dinosaur tree dwellers.
Tantalizingly, Microraptor is the unexpected missing link that has reignited the debate and, with the help of NOVA's model and wind tunnel tests, just might settle the issue–or at the very least deepen our understanding of the long-ago era when the ancestors of birds first took to the air.


It seems that there may be three possibilities.
Ground up (dinosaurs)
Trees down (not dinosaurs)
A mishmash, with ground based dinosaurs developing feathers (for some other purpose than flight), then climbing trees, then using their feathers for the new purpose of gliding and eventually powered flight.
The problem with the mishmash, is that there is ZERO evidence for that.

To be even more precise, there is ZERO evidence for ground based dinosaurs climbing trees.

There is evidence of arboreal feathered creatures using their feathers for the purpose of gliding and powered flight. But there is no evidence that those arboreal feathered creatures had any connection to ground-based dinosaurs developing feathers (for some other purpose than flight) and then climbing trees.

Also, the mere presence of arboreal feathered creatures using their feathers for the purpose of gliding and powered flight, is no evidence of how they came to be.

1 comment:

  1. For comparison: