tholden wrote:"Tensegrity(TM)" doesn't appear to have helped this guy very much
So by not letting them suffocate on the beach, but observe their structure and tissues and general behaviour, whales allow us a good insight into effects of the structural principles applied by different organisms in even different environments. By building up pressure from the inside to the outside both whales and dinosaurs are able to cope with the pressure distributed on the outside to the inside.
And as a extra bonus we even can see that dinosaurs and whales also have started to use pneumaticity in the connective tissues.
At least that was what I wrote in the thread I linked. I think you get my point. Take an organism out of it's natural environment/habitat and often the organism will die. The bigger the change the quicker the death.
balsys wrote:The size of the Petrosaurs given here is another issue. Tensegrity can explain the structural issues, but not the flight one.
Maybe I was a little to quick.
http://www.depts.ttu.edu/communications ... theory.php
Pterosaurs were not dinosaurs, nor were they birds. “Pterosaurs could fly like birds, and they flew above the heads of dinosaurs. Some were small, like a modern sparrow, and some were large, like an F-16 plane. These animals are very enigmatic because they are extinct and we have no modern animals with which to compare. Pterosaurs seem to be half bat, half bird, but actually they are reptiles,” Chatterjee explains.
“For 1,000 years we envied birds because they could fly, and no doubt, watching birds fly, we invented the plane,” Chatterjee says, pointing out that NASA officials will build future aircraft based on this natural model of flight for the first time. Complex and difficult, NASA’s designers and engineers will be attuned to the researchers’ observations that pterosaurs and birds did not have fixed wings, like today’s aircraft. Instead, the creatures had flexible wings that could fold into the body as well as expand into limbs required for flight. They evolved into being able to twist their wingtips to take advantage of the forces of thrust and drag, in the same way that humans turn their hands as they swim.
Although pterosaurs have been found all over the world, scientists knew hardly anything about their brains, even though they knew about their anatomy. Pterosaur fossils generally are found in two-dimensional form, as a paper-thin sheet, because the inside of the bones are entirely hollow (necessary for flight) and become crushed under layers of time. With new finds of pterosaur fossils in China and Brazil of wholly preserved three-dimensional skulls and skeletons with intact wings, paleontologists were able to reconstruct the paper-thin wings in cross-sections. “Like any soft part of a body, such as blood and muscles, skin is fragile, delicate and normally is not preserved in fossils,” Chatterjee notes. “Pterosaurs’ wings are made of leathery skin, like bats, but the creatures are closer to birds than bats from an evolutionary point of view. Like birds, pterosaurs are born with hollow and very delicate bones, however the skin on their wings is reinforced by a kind of rod, called actinofibrils,” Chatterjee says. “The rods in the wings indicate that pterosaurs could tuck in their wings and fold out their wings, in the same fashion that an umbrella opens and closes. Such reinforcingrods are lacking in the bat wings; this is probably why bats never became large.”
Through their complex calculations, Chatterjee and Templin studied the aerodynamics, postures and brains of pterosaurs to determine whether they could hover, flap, glide or soar on their wings, as well as answer how the animals walked on land. Studying the 10 species of pterosaurs, from the smallest to the largest, the researchers examined footprints, wing designs, brains, the inner ear, stereoscoping vision, the orientation of the head, as well as environmental air patterns, or thermals, among many other factors, in determining how animals gained the ability to fly. “Throughout time many animals tried to conquer the air. The animal has to defy gravity with the use of a wing that gives the animal lift and thrust. The emergence of flight among birds and pterosaurs happened independently and separately as the different species evolved in their designs to be able to fly,” Chatterjee observes. “In science, we call this convergence. In other words, in nature only a few solutions are available for a creature to achieve a goal, for example, going through water. Just one or two designs have been invented by fish to maneuver through water. That streamlined body design of fish has been copied by marine reptiles, such as plesiosaurs, and marine mammals, such as dolphins and whales.”
http://news.softpedia.com/news/Dinosaur ... 5021.shtml
Dinosaur Inspires Modern Air Drone
The pterodactyl hasn't lost its touch – a plane is to be constructed in its memory
All of the bird's "components," including blood vessels, nerves, the cranial plate and its skeletal system, are to be thoroughly mimicked by the scientists, so as to create the closest replica possible.
The new morphing technology the Pterodrone will be equipped with should allow it to change its wing configuration according to the tasks it performs. When in the air, the wings will be spread, whereas on the ground they will retract, just like in a normal, living bird. This feature will allow the drone to see in currently "blind spots," such as areas beneath overpasses or under ledges.
As power saving measures, it will also be able to sail at sea, remaining under radar detection capabilities.
It was once thought that pterosaurs were not well adapted for active flight and relied largely on gliding and on the wind to stay in the air. However, based on analyses of pterosaur skeletal features (including work done by Berkeley's own Kevin Padian), it is now thought that all but the largest pterosaurs could sustain powered flight. Pterosaurs had hollow bones, large brains with well-developed optic lobes, and several crests on their bones to which flight muscles attached. All of this is consistent with powered flapping flight.
The basal Pterosauria (including Rhamphorhynchus, pictured at the top of this page) first appeared in the Late Triassic and all went extinct at the end of the Jurassic. The more derived pterosaurs (including Pteranodon, below) that were the descendants of this group appear first in Late Jurassic rocks, and the last of them died out at the end of the Cretaceous.
Pteranodon. Photo by Dave Smith, © 2005 UCMP
The genus Pteranodon includes several species of large pterosaurs from the Cretaceous period in North America. As you can tell from this photo, it had a large crested head, a huge wingspan (some 20-25 feet; the UCMP specimen is about 22 feet), and a comparatively small body. This is deceiving; it looks like the head and wing bones were too bulky, and the hindlimbs appear small and weak. Not so; the bones of Pteranodon are actually completely hollow (about 1 millimeter thick!), and were quite light.
The whole animal probably weighed about 25 pounds, only slightly heavier than the largest flying birds. The hindlimbs are actually perfectly sized for the body; Pteranodon would have been capable of bipedal terrestrial movement (but was no rapid runner, unlike its ancestors, some of whom seem to have been fast bipedal runners). The wing bones look thick because a large bone diameter is more vital for resisting the bending stresses involved in flight (as opposed to large bone thickness, which is important for resisting compressive forces, such as those imposed by the weight of a large body), so actually the wings of Pteranodon were more than adequate for flight.
Pteranodon was almost certainly a soaring animal; it used rising warm air to maintain altitude; a common strategy among large winged animals (among birds, albatrosses and vultures are adept at soaring). Its scooplike beak was used for snapping up fish as it soared over the oceans that it nested by. A good modern analog for Pteranodon would be the pelican.
Pterosaurs were highly modified from their reptilian ancestors for the demands of flight.
Pterosaur wings were formed by membranes of skin and other tissues, strengthened by various types of closely spaced fibers.
The membranes attached to the extremely long fourth finger Finger of each arm Arm and extending along the sides of the body. A novel bone called the pteroid
connected to the wrist and helped to support a membrane between the wrist and shoulder. The pteroid might have been able to swing forward to extend this membrane, although this is very controversial. In later pterosaurs, the backbone over the shoulders fused into a structure known as a notarium, which served to stiffen the torso during flight, and provide a stable support for the scapula
Pterosaur's hip sockets were oriented facing slightly upwards, and the head of the femur was only moderately inward facing, suggesting that pterosaurs had a semi-erect stance. It would have been possible to lift the thigh into a horizontal position during flight.
There has been considerable argument among paleontologists about whether the wings attached to the hindlimbs as well. Fossils of the rhamphorhynchoid Sordes, the anurognathid Jeholopterus, and a pterodactyloid from the Santana formation demonstrate that the wing membrane did attach to the hindlimbs, at least in some species. However, modern bat Bats and flying squirrel Flying squirrels show considerable variation in the extent of their wing membranes and it is possible that, like these groups, different species of pterosaur had different wing designs. Many if not all pterosaurs also had webbed feet, and although these have been considered to be evidence of swimming, webbed feet are also seen in some gliding animals such as colugo , and may have had an aerodynamic function.
Pterosaur bones were hollow and air filled, like the bones of birds. Unlike typical reptiles, pterosaurs had a keeled breastbone that was developed for the attachment of flight muscle Muscles and a brain that was more developed than comparable dinosaur Dinosaurs of similar sizes.
There has been considerable debate in the past about whether pterosaurs moved about on the ground as quadruped Quadrupeds or as biped Bipeds. A large number of pterosaur trackways are now known, with a distinctive four-toed hind foot and three-toed front foot; these are the unmistakable prints of pterosaurs walking on all fours. However, it might be too much to conclude that all pterosaurs were quadrupedal, all the time.
It has been suggested that smaller pterosaurs
with longer hindlimbs such as Dimorphodon Dimorphodon
might have walked or even run bipedally
, in addition to flying, not unlike modern road runner Geococcyxs. Other small pterosaurs such as Rhamphorhynchus may have scurried around on all fours
. Larger pterosaur
s with proportionately smaller hindlimbs and massive forebodies
are generally thought to have moved about on all fours while on the ground.
A pterosaur egg has been found in the quarries of Liaoning, the same place that yielded the famous 'feathered' dinosaurs. The egg was squashed flat with no signs of cracking, so evidently the eggs had leathery shells. The wing membranes were unusally well developed for a hatchling in an egg, suggesting pterosaurs were ready to fly soon after birth, though whether a parent took care of them is unknown.
Very young animals have been found in the Solnhofen limestone beds, where they presumably flew to the middle of a lagoon, fell in and drowned.
A study of pterosaur brains using X-rays has revealed extraordinary information about their habits.
Studying fossil pterosaur skulls is extremely difficult because they are so delicate, but Lawrence Witmer at Ohio University in Athens and his colleagues used X-ray CT scans to build up 3D images of the brains of two species. One striking finding was that the animals had massive flocculi. The flocculus is a brain region that integrates signals from joints, muscles, skin and the balance organs.
The pterosaurs' flocculi occupied 7.5 % of the animals' total brain mass, more than in any other vertebrate. Birds have unusually large flocculi compared with other animals, but these only occupy between 1 and 2 % of total brain mass. "It is just ridiculously large in pterosaurs," says Witmer.
The flocculus sends out neural signals that produce small, automatic movements in the eye muscles. These keep the image on an animal's retina steady. Pterosaurs probably had such a large flocculus because of their large wing size. This extra area meant that there was a great deal more sensory information to process.
nick c wrote:Most explanations that I have seen are piecemeal, that is they might account for one aspect of the size problem but don't explain all, where as, variable felt effect of gravity does explain the entire issue.
-higher O2 levels- this could explain larger insects, but does little to explain large land animals and flying animals
When there were larger insects there were no large animals and flying animals. And again those oxygen levels were sufficient to get the insect to a somewhat larger size. Insectsize is primarily depentend on the abillity to diffuse oxygen into the tissues and the structural/physiological make-up of insects prohibits larger. Remember the trachea?
-higher CO2 levels- this could explain larger flora, again, incomplete
Flora has not reached to higher hights then now. So no need for explanations. But maybe you have data about fossil flora and current flora that I don't know. Please do share.
-tensegrity-there is tensegrity in today's fauna, why are they not gigantic too?
What fauna are you reffering to, exactly? Mammals have attained huge sizes in my opinion. Or did you mean something else?
and of course there is another debate as to what extent this architectural concept can be applied to biology.
Could you elaborate on that? I'm not sure what you mean.
-denser atmosphere-there are numerous objections to this (in addition to what Steve Smith wrote earlier on this thread)
how dense can an atmosphere get before lungs become unusable? Is there any other evidence that the Earth's atmosphere had radical differences in density in past times?
What do you mean by density differences in past times? Where is the need for a dense athmosphere?