Snagged from the web:
"..Several characters that typify a theropod: hollow, thin-walled bones are diagnostic of theropod dinosaurs."
Well, since Archeopteryx (the earliest known reptilian-like bird) had SOLID bones... seems they're on the wrong evolutionary branch.
"...Archeopteryx is connecting link between reptiles & birds. 53. Reptilian characters of archeopteryx are- teeth in jaw, thecodant dentition, [my note: described as AQUATIC IN NATURE, almost as if its ancestor came from a marine environment] long tail [like most archosaurs], solid bones [my note: typical of bird groups who are grounded and/or swimmers]."
Objective Zoology By S. K. Sharma
Solid bones? Then its not a theropod dinosaur.
CONVERGENT EVOLUTION EXPLAINS THIS:
"...The bones of ceratosaurians, like those of all known theropods, are hollow. Known specimens of ceratosaurians show that the group began to exhibit "bird-like" features (more appropriately, birds show ceratosaurian-like ones) early on. The bones of ceratosaurians, like those of all known theropods, are HOLLOW. [...] Birds have taken this step even further, having large air-filled spaces in their bones. Ceratosaurians also had strongly curved S-shaped necks like birds do; this is a trait inherited from a distant archosaurian ancestor."
(Source)
ARCHEOPTERYX HAD... SOLID BONES... Theropod dinosaurs have hollow bones.
Will the real ancestor of Archeopteryx, please, stand , up?
Feels like we're all being made to play a sorry rendition of the game show "To Tell The Truth".
Archeopteryx had SOLID BONES:
"Compsognathus is believed by many scientists to be an early elative of Archaeopteryx, often considered to be the first bird. Supporting this belief is the fact that the bone structure of Compsognathus is quite similar to that of Archaeopteryx, and the two dinosaurs were about the same size. They also lived at the same time in history, which would have made it difficult for Compsognathus to be an ancestor. It is still possible, though, that Compsognathus lived earlier than Archaeopteryx. On the other side of the argument, Compsognathus had hollow bones, like modern birds, but Archaeopteryx had solid bones."
Source: dinosaur-world (Dot) com
And other sources claim that Archeopteryx has hollow bones.
Seems that some want force the facts and Archie into the theropod dinosaur clan.
HOLLOW BONES are one of the main arguments for "similarity" between birds and dinosaurs, so they use "hollow bones" to say birds "evolved from" dinosaurs, and attempt to deny the stronger link to reptiles and...even mammals.
--> "...The bird's bones are thin and hollow, unlike the reptile's solid ones." <--
Which proves??
Nothing.
The following birds do not have hollow bones... so that makes birds closer relatives to reptiles and even mammals?
"...Cornell researchers first reported in 2005 on the ability of these birds to rub specialized wing feathers together to produce a high hum. Now they report in the June 13 edition of the Royal Society journal Biology Letters that these are the first flying birds known to have solid wing-bones. This is what allows these birds to produce their courtship sounds."
(Source)
Manakin
Adaptations for Flight
"...The pneumatization of bird bones led to the belief that birds had skeletons that weighed proportionately less than those of mammals. Careful studies by H. D. Prange and his colleagues have shown this not to be the case. More demands are placed on a bird's skeleton than on that of a terrestrial mammal. The bird must be able to support itself either entirely by its forelimbs or entirely by its hindlimbs. It also requires a deep, solid breastbone (sternum) to which the wing muscles can be anchored. Thus, while some bones are much lighter than their mammalian counterparts, others, especially the leg bones, are heavier. Evolution has created in the avian skeleton a model of parsimony, lightening where possible, adding weight and strength where required. The results can be quite spectacular: the skeleton of a frigatebird with a seven-foot wingspan weighs less than the feathers covering it! Not all birds have the same degree of skeletal pneumatization. To decrease their buoyancy and make diving easier, some diving birds, such as loons and auklets, have relatively solid bones. Those birds are generally less skillful fliers than ones with lighter skeletons."
(Source)
"...Grebes are ancient, highly specialized diving birds with no obvious close relatives, living or fossil. The earliest fossil is possibly Neogaeornis wetzeli, a diving bird that dates back to the Late Cretaceous Epoch (about 80 million years ago) of Chile..."
(Source)
[And, from what I can find on the web of those scientists who examined the fossils, concluded they were similar to the modern species [with solid bones], making no comment (that I could find) in regard to a transition between hollow bone in the fossil to solid in the modern bird.]
Pied-billed Grebe, Podilymbus podiceps
"...The pied-billed grebe is a small, brown, duck-like diving bird with a stocky body, thin neck, and relatively large head. The undertail coverts are white and the tail feathers are short and brown, making the grebe appear stubby and tail-less. The legs and lobed toes, which are situated far back on the body, are gray. The bill is thick and stout, enabling the grebe to crack open hard shells of mollusks and crustaceans. As denizens of aquatic habitats, pied-billed grebes spend nearly all their time on water. Leaping forward during headfirst dives, the grebe has been nicknamed “hell diver.” If threatened, a grebe may quickly dive or sink slowly into the water, emerging with only its head visible. Pied-billed grebes are well adapted for swimming underwater. Grebes are able to waterproof their feathers by preening them with secretions from the oil gland located at the base of the tail. Their eyes possess cone-dense retinas, an adaptation for locating prey underwater. Relatively solid bones and the ability to compress their feathers, releasing trapped air to reduce buoyancy, enables grebes to remain underwater longer. Their short, narrow wings aid in maneuverability when swimming and the location of the legs far back on the body facilitates underwater propulsion. Although the location of their legs makes them strong swimmers, it also renders grebes awkward on land."
(Source)
"...Unlike most birds that have hollow bones, common loons have solid bones which reduce their buoyancy. When they compress their feathers, and force the air from their lungs, loons are able to move through the water with only their heads showing above the surface. Dense bones, however, do not keep loons from moving quickly through the air. As they fly, their wings beat 250 times per minute, propelling them to speeds greater than 80 miles per hour."
(Source)
Wikipedia says: ---> "...Birds have many bones that are hollow (pneumatized) with criss-crossing struts or trusses for structural strength. The number of hollow bones varies among species, though large gliding and soaring birds tend to have the most. Respiratory air sacs often form air pockets within the semi-hollow bones of the bird's skeleton.[1] Notably, the bones of diving birds are often less hollow than those of non-diving species. Loons[2] and puffins, are without pneumatized bones entirely.[3] Somewhat surprisingly, flightless birds such as ostriches and emus demonstrate osseous pneumaticity, possessing pneumatized femurs[4] and, in the case of the emu, pneumatized cervical vertebrae.[5]" (Wikipedia): "Polarornis was in all likelihood aquatic and fed on fish and large invertebrates, probably being an ecological equivalent of loons, grebes, or the Cretaceous Hesperornithes of the Northern Hemisphere. One analysis of the structure of the femur (TTU P 9265) showed that the bones were dense, rather than hollow and lightweight as in flying birds, suggesting that Polarornis was a flightless or near-flightless diving bird similar to hesperornithines and penguins.[8]" <---
The dino-bird hypothesis crowd may argue that this species of bird "evolved" genes to grow solid bone through "convergent evolution" to attempt denying that birds already have a strong genetic link to reptiles and mammals, and that birds are a group that evolved independently from dinosaurs. See attached pic:
Manakin
(Source)
So, I have just provided many links demonstrating "true birds" have both solid and hollow bones. Hollow bone proves nothing. However, there is one dinosaur with "solid bones" like the most early reptilian protobirds -- before Archeopteryx, may have had.
The only dinosaur who was AQUATIC... had SOLID bones.
"...--> On land, spinosaurus probably shuffled on all fours — a lousy walker, but a great swimmer. Plus its bones are solid, not hollow like most dinosaurs'. That suggests that, as in whales and penguins, the bones of spinosaurus acted as ballast. And its feet are wide, like a wading bird's. <--
The _ONLY KNOWN_ Aquatic Dinosaur. So they say.
Aquatic or semi-aquatic dinosaurs. I'm willing to look at those for a bird ancestor, but the candidates are very few. Also, I don't think this beast laid eggs and "out popped" an Archeopteryx. Plus, birds were already around on the timeline 65 million years before this aquatic or semi-aquatic "Spinosaurus".
"The ONLY KNOWN dinosaur adapted to life in water, Spinosaurus swam the rivers of North Africa a hundred million years ago. (Art: Davide Bonadonna, and Oct. edition of National Geographic magazine)" the fossils were identified as those of Spinosaurus aegyptiacus.
(Source)
(September 11, 2014)
Crocodile Meets Godzilla — A Swimming Dino Bigger Than T. Rex"...There once was a place on Earth so overrun with giant, meat-eating predators that even a Tyrannosaurus rex would have been nervous. One predator there was even bigger than T. rex, and scientists now say it's apparently the only aquatic dinosaur ever found. [...] He collected the bones and, along with Chicago paleontologist Paul Sereno, determined that it was indeed a swimmer.
Ibrahim describes the place in North Africa where this spinosaurus lived 97 million years ago as a "river of giants."
"Big predatory dinosaurs, giant fish, crocodile-like predators. In fact, the place was really pretty predator-heavy, so I call it the most dangerous place in the history of our planet," Sereno says. It was swampy, with many rivers. Now it's a desert, where Ibrahim looks for dinosaur bones. But he didn't find spinosaurus's bones, exactly. They found him.--> On land, spinosaurus probably shuffled on all fours — a lousy walker, but a great swimmer. Plus its bones are solid, not hollow like most dinosaurs'. That suggests that, as in whales and penguins, the bones of spinosaurus acted as ballast. And its feet are wide, like a wading bird's. <--
--> Now, it was well-known that big swimming reptiles existed in prehistoric times. But dinosaurs are a very different order of animal than reptiles, and nobody had an inkling that dinosaurs could swim until this one turned up. <--
--> Until recently, paleontologists figured the creature must have lived on land and snagged fish out of rivers — like a giant heron with teeth. Being a bit coldblooded has its charms, scientists say. A mammal the size of a T. rex, for example, would have to eat constantly to feed its supercharged metabolism — and would probably starve. "But we were wrong," Holtz says. "It just goes to show, you know, that evolution is pretty tricky and it does all sorts of weird and wonderful things. <--
(Source)
- Scientists unveil first semi-aquatic dinosaur, (Source)
- Scientists announce first known semi-aquatic dinosaur (Source)
- Largest predatory dinosaur ever was 'half-duck, half-crocodile' (Source)
REPTILES also had hollow bones.
Conclusion: Development of both solid and hollow bones can occur in many of groups within diapsids.
"...pterosaurs are not closely related to either birds or bats, and thus provide a classic example of convergent evolution....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"...
(Source)
Will they argue reptiles developed hollow bones through "Convergent Evolution"... speculative bologna. However, the physical ability for flight -- perhaps THAT is convergent evolution -- separately and independently.
Reptiles, Birds and Dinosaurs obviously share genes that enable development of both solid and hollow bones. As seen with the little songbird growing a solid bone on its arm.
To this day, as shown, birds have solid as well as hollow bones, as did the dinosaurs... and reptiles too.
An absence of a keel on some forms? Well, there's a lot of modern birds that don't have a keel, either.
A common argument in defense of the "Dinosaur to Bird" hypothesis may go something like this:
"...All the early bird fossils are of birds not yet fully adapted to long or powerful flight. Their skeletons are still reptilian in many respects, their keel bones in their body are not very long and could not have supported thick broad wing flapping muscles..."
I'm really not certain how the existence of a "keel bone" necessarily ties dinosaurs to modern birds. This "Keel" bone is mentioned as being absent in this group:
Ratite (Merriam Webster Dictionary) "a bird with a flat breastbone; especially : any of various mostly flightless birds (as an ostrich, rhea, emu, moa, or kiwi) with small or rudimentary wings and no keel..."
"...Ratites are flightless birds that lack the keel (high ridge) on the breastbone to which the flight muscles of flying birds are attached. Instead, the entire breastbone looks rather like a turtle's shell. It has also been described as a raft, which gives this group of flightless birds its name, Ratitae (Ratis means raft in Latin). Ratites have heavy, solid bones, while flying birds have lightweight, hollow ones. Several ratites, such as ostriches, rheas, emus, and cassowaries, are the largest living birds."
(Source)
Just some additional documentation which is supported by recent genetic evidence (2014) with birds radically diversifying at the close of the Cretaceous.
Excerpt from : Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions [2 volumes]Andrew Hund, ABC-CLIO, Oct 14, 2014 - Nature - 848 pages
Birds did not "evolve along with" dinosaurs in a co-existence sense of living as tetrapods in the "open terrain" on dry land -- because as you might now agree ------- birds, primarily confined themselves to aquatic or semi-aquatic environments, like the lagoons which Archeopteryx fossils are described being discovered in.
"...T. rex was one of the largest terrestrial carnivores of all time."
Tyrannosaurus ventured near ponds if he was thirsty and then left (because all the birds were smart enough to disappear) so he left and resumed his activities on dry land.
Terrestrial, land-roaming T-Rex ... as an ancestor of creatures who's aquatic origins are so profound, that they are written into their anatomy - - so, I have a real problem with reconciling bird origins with dry, terrestrial beasts.
"...animals like Velociraptor- and Deinonychus-sized dromaeosaurids were obviously predominantly terrestrial."
They've already told me, which creatures were definitely NOT the ancestors of birds. If you find a "true dinosaur" from the Triassic (that predates Archeopteryx) or any other early birds found in the Jurassic, that was aquatic or semi-aquatic... well, I will contemplate on the creature for a long time, study all that is known about the creature, and I might give it the benefit of the doubt as a potential ancestor. Otherwise, not at all.
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