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From XKCD:

Contents of XKCD comic 1211

XKCD comic 1211 claims that the anatomy of sparrows and T. Rex are more similar than those of T. rex and stegosaurus. While it looks like neither T. rex nor sparrows would be any good at boxing (unless they used the Mike Tyson approach), I'm still skeptical.

Explain XKCD has an article on this comic, linking to a Science article published that week, which says within the full text [emphasis added by me]:

One of the most transformative ideas to affect understanding of living birds has been the recognition of their perch within the tree of life on branches crowded with their extinct dinosaurian cousins. This insight came first from comparisons of bones, the most commonly preserved part of a fossil vertebrate. Fossilized soft tissues are only preserved in a few exceptional places (Lagerstätten). The Chinese deposits provide one such unique snapshot, where over a thousand specimens with fine details of soft tissues such as feathers, hair, and skin are preserved in ash-rich lake deposits ranging from the Late Jurassic (∼150 million years ago) to the Early Cretaceous (∼120 million years ago). Fossils from these deposits have revealed that dinosaurs that were inferred from bone characteristics to be closely related to living birds also share more features of feather structure.

So the Science article states that they're more anatomically similar, and it states that using that knowledge has made a prediction that has been confirmed. But it doesn't provide any citations in that paragraph.

Is T. Rex more anatomically similar to sparrows than stegosaurus?

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    The comic strip talks about "related" not "similar". Similarity is somewhat subjective, while "related" as in proximity in time, and common ancient ancestor is not. – SIMEL May 22 '13 at 9:04
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    @IlyaMelamed it mentions "physical similarity" underneath the red rectangle surrounding the T. rex and the sparrow. – Andrew Grimm May 22 '13 at 9:34
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    Physical similarity is only 1 of 3 aspects. – SIMEL May 22 '13 at 10:34
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    And it says "physical similarity" not anatomical similarity. Because it just shows an crude skeletal view, I'm assuming by "physical similarity", he means a first-impression judgement, not anything more. – user5582 May 22 '13 at 15:24
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The T.Rex is more closely related to birds than to Stegosaurus.

The comic shows it in 3 different aspects:

Time:

From the T.Rex Wiki page, it lived during:

Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 67 to 65.5 million years ago.

While the Stegosaurus lived:

They lived during the Late Jurassic period (Kimmeridgian to early Tithonian), some 155 to 150 million years ago in what is now western North America.

Which means that the time period between the T.Rex and the Stego (83 million years) is longer than the time period between the T.Rex's existence and the sparrow (65.5 million years)

Phylogenetic Distance:

The Wiki article for Origin of Birds says:

most researchers now support the view that birds are a group of theropod dinosaurs that evolved during the Mesozoic Era.

Also from this article at Discovery:

"The evolution of the many characteristics of birds –- things like feathers, flight, and wishbones -– has traditionally been a difficult problem for biologists," Mark Norell, chair of the division of paleontology at the American Museum of Natural History and one of the paper's co-authors, added.

"By analyzing fossil evidence from skeletons, eggs, and soft tissue of bird-like dinosaurs and primitive birds, we've learned that birds are living theropod dinosaurs, a group of carnivorous animals that include Velociraptor," Norell continued. "This new work advances our knowledge by providing a powerful example of how developmental changes played a major role in the origin and evolution of birds."

There is also this chart from dino-web (The T.Rex is part of the coelurosauria):

birds are dino too

The T.Rex is a part of the coelurosaurian theropod dinosaurs, while the Stegosaurus isn't, which supports the claim that birds and the T.Rex are on a common phylogenetic branch, later than the T.Rex and Stegosaurus.

Bone Structure:

There is the article linked to by explain XKCD which says that (as the question quotes).

There is also this article on Discovery which states:

Modern birds retain the physical characteristics of baby dinosaurs, according to a new Nature study that found birds are even more closely related to dinos than previously thought.

Depending on the non-avian dinosaur and bird compared, that might be hard to believe. A toothy, angry reconstruction of Tyrannosaurus rex, for example, on first glance looks little like a common garden blue jay. Also, look at the bone structure yourself.

Look at their bone structures:

A sparrow:

dead sparrow

A T.Rex:

dead trex

A Stegosaurus:

dead stego

The bone structures of the sparrow and T.Rex are a lot more similar to one another than to the bone structure of the Stegosaurus. They are both bipedal, upright, have small "hands" and more.

Here is a list of similarities between birds and dinosaurs (from dino-web):

The British palaeontologist Thomas Huxley presented a theory in 1868, which claimed that birds are descended from dinosaurs. His theory stated these reasons for it:

Only dinosaurs had the same sort of ankle joint as birds

Only dinosaurs had the same sort of ilium as birds

Some dinosaurs had the same sort of rear foot as birds with a rear-pointing fourth toe (phalanx)

Advanced dinosaurs had the same sort of build as birds with a short torso, stable hips, long and very flexible neck and long rear limbs

Only dinosaurs and pterosaurs had hollow bones or the air sacks which are connected to a bird-like lung. Pterosaurs are in every other aspect a lot less bird-like than advanced dinosaurs

Some dinosaurs had the same sort of hip as birds (ornithischian dinosaurs).

Also from same source:

The theory of the common ancestor

Because birdlike dinosaurs had only very small collar bones and birds have very large ones, the theory that birds are descended from dinosaurs was rejected. It was belived that, Dinosaurs had the same ancestors as birds, until the following was proven scientifically: there are genes which are suppressed but exist nevertheless. They can be reactivated in situations when they are needed. Chickens, for example, have a suppressed gene which would allow them to develop teeth if they needed them. Scientists transplanted this gene into another part of the chicken's body where it could be reactivated and the chickens developed teeth. Dinosaurs probably had a suppressed gene which allowed them to develop larger collar bones. This is what deinonychus did, which had a collar bone very similar to that of archäopteryx. Deinonychus also had a hand very like that of archaeopteryx. It is therefore very likely that birds are descended from dinosaurs.

The only "major difference" between the sparrow and the T.Rex is their size, but this is not a good measure for relation, one of many examples is the Elephant and Hyrax which are closely related to each other much more than the elephant and giraffe, rhino or hippo, or the hyrax and guinea pigs and rabbits. source1, source2.


Here is a picture of a dino-bird being awesome:

It'll kill you, and eat your body. Fear me, I'm the awesomely frightening dino-bird!

source: Discovery

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    "Here is a picture of a dino-bird being awesome" made me laugh xD. Is there any other ways 'relatedness' is measured, than the ones you brought up? – Wertilq May 22 '13 at 11:21
  • @Wertilq, I confirmed only the 3 ways that XKCD mentions. Usualy in Biology (to the best of my knowledge) relation is denoted by common ancestors and physical and genetic similarities (2 of the 3 criteria). Time doesn't mean relation, people and sparrows live at the same time, yet biologically sparrows are more closely related to T.Rex or even the Stago than to humans. (They are all awesome dinosaurs, while we are (sadly) just plain old boring mammals), I put it there only because it appears in the comic. – SIMEL May 22 '13 at 11:30
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    I wasn't convinced by "bipedal, upright, have small "hands"", but I was by the tree listing what anatomical changes exist between different parts of the tree was the kind of thing I was hoping for. – Andrew Grimm May 22 '13 at 11:53
  • @Wertilq The most reliable way (and the one effectively trumping all others in case of conflicting conclusions) is by sequence comparison of the genomes. Since that’s not really feasible (there is no preserved genetic information for T. rex), phenotypic characteristics like the above are used. For more information I can recommend The Greatest Show On Earth by Dawkins which details several different measures of relatedness. Phylogenetic trees like the one in this answer used to be created by aggregating such phylogenetic information. Now they are mostly created via sequence comparison. – Konrad Rudolph May 22 '13 at 13:21
  • The pose of reconstructed dinosaur skeletons is up to whoever is setting them up at that point in time and is often based on the accepted understanding of the day but may be due to some new theory of the person doing it. These opinions have not remained constant over time. So a photo of a dinosaur skeleton in any specific pose should not on its own really count as evidence. – hippietrail May 25 '13 at 8:27

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