Do ornithologists agree birds evolved from dinosaurs?

If you like birds, dinosaurs, anatomy, evolution or paleontology, you need to go read this post... twice.  Here's why...

Over at Tetrapod Zoology, Darren Naish has a great exposition on the question above (as well as a recommendation/review of a book that any bird-nerd should have on their shelf) which I encourage you to go read at least once.  The title of Darren's post (and his book recommendation) is Gary Kaiser's The Inner Bird: Anatomy and Evolution.

I find that most people who aren't biologists or bird-nerds are unaware of the idea that birds evolved from dinosaurs. While most of my ornithologist friends accept the idea, I'm not sure how many really understand the evidence behind the claim (in their defense - it's well outside of their areas of expertise, so this is hardly a criticism).  That said, this book (and even Darren's post) could help clear up some of that evidence.

Here's a little of what Darren writes on the origin of birds...

Kaiser is convinced by the evidence for the dinosaurian origin of birds, and long sections of the book are devoted to discussing the similarities and differences seen between birds and their non-avian relatives*. The notion that birds cannot be dinosaurs is heavily promoted in the ornithological literature - most notably in Alan Feduccia's The Origin and Evolution of Birds (Feduccia 1996). Because Feduccia's book is one of the most visible of volumes on bird evolution, audiences can be forgiven for thinking that ornithologists as a whole reject the hypothesis of a dinosaurian ancestry for birds. This is absolutely not true, and those interested should take every opportunity to note that all of Feduccia (et al.'s) criticisms are invalid or erroneous (e.g., that non-avian theropods are too big to be ancestral to birds, that they occur too late in the fossil record, that their anatomy bars them from avian ancestry, and that other Mesozoic reptiles make better potential bird ancestors). It is also worth noting that many of Feduccia's proposals about the phylogeny of neornithines are idiosyncratic and that his volume does not accurately represent current thinking on avian evolutionary history. The Inner Bird helps provide part of the antidote, bringing home the point that the dinosaurian origin of birds is well supported and robust, and adopted by many ornithologists interested in palaeontology.

You can read the rest of the article here.

Feather Color Revealed in Dinosaurs

Unrelated to my previous post, news came today from the journal Nature that a group of scientists have used SEM techniques to reveal color patterns from some well preserved dinosaur feathers -- cool stuff!

Here's a figure from the paper, showing some of the melanosomes (pigment containing structures within cells).

"Melanosomes in the integumentary filaments of 

the dinosaur Sinornithosaurus (IVPP V12811). 

a, Optical photographs of part of the holotype and SEM samples (insets). 

b, Mouldic phaeomelanosomes.
c, Aligned eumelanosomes preserved as solid bodies (at arrows). 

d, Strongly aligned mouldic eumelanosomes. 

Scale bars: a, main panel, 50mmand inset, 5 mm; b–d, 2 mm." 

[Source: Nature article, via The Z-Letter Archive]

In addition to the coloration details, this paper also gets into other aspects of feather structure confirming that these structures are indeed feathers:

Our results demonstrate conclusively that the integumentary filaments of non-avian theropod dinosaurs are epidermal structures. In birds, melanin is synthesized endogenously in specialized pigment producing cells, melanocytes, that occur primarily in the dermis; the melanocytes migrate into the dermal pulp of the developing feather germ, where the melanin is packaged into melanosomes and then those melanosomes are transferred to keratinocytes for deposition into developing feathers. In various avian species melanin granules also form, and are apparently retained, in dermal melanocytes; melanin granules can form a discrete layer in the dermis, but below, and not as part of, the collagen layer. The occurrence of melanosomes embedded inside the filaments of Jehol non-avian dinosaurs thus confirms that these structures are unequivocally epidermal structures, not the degraded remains of dermal collagen fibres, as has been argued recently. Our work confirms that these filaments are probably the evolutionary precursors of true feathers, and it will be interesting to determine whether any fossil filaments might relate to other kinds of epidermal outgrowths in modern birds.

For further discussion of the paper, see...

• Dinosaurs, now available in colour | Dave Hone's Archosaur Musings
• Dinosaurs in color | The Z-letter Archive
  
• Moving Dinosaurs Into Technicolor | The Loom
• Feathered dinosaurs -- in color! | Why Evolution Is True
  

New bird-like dinosaur fossil?

Update: Links to the articles in Science are here and here.  Also see the posts here and here on Dave Hone's blog.

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Looks like there might be something tomorrow (27 Jan 2010) in the journal Science announcing a new bird-like dinosaur fossil? Details over at Dave Hone's blog in the posts:

• The wonderfully weird alvarezsaurs by Dave Hone
• A brief history of Alvarezsaur research by Jonah Choiniere

"Jonah Choiniere with a typically small alvarezsaur - Mononykys."

A Dinosaur on the Christmas Dinner Table

If you recall my post from back around Thanksgiving, the Wild Turkey -- like all birds -- is a modern day dinosaur.  What better opportunity to share this little fact with your friends and family than over the Christmas Turkey?

Below are some resources for turning the remains of your holiday feast into a biology lesson, but before we get into details I want to first answer a simple question: What exactly is a dinosaur anyway?

Dinosaur's are a group of (mostly extinct) reptiles that arose around the early Triassic period about 230 million years ago (mya).  They persisted until the mass extinction event that occurred 65mya at the end of the Cretaceous period, (also the end of the Mesozoic era and start of the Cenozoic era), when all of the dinosaur lineages save modern birds died out.

To put this talk of dinosaurs and birds into perspective, lets take a crash course in vertebrate taxonomy. Starting with the ancestor of all land vertebrates, we can follow evolution forward to the present, noting major points of divergence along the way.  We're of course skipping a lot, taking the fast track from the first vertebrate land animals to modern day birds.

The first amphibian-like terrestrial tetrapods appeared over 350mya (Late Devonian into the Carboniferous period), with the Synapsids (whose descendants became the modern mammals) splitting off 25+ million years later.  Another 25 million years or so later, ancestral turtles and other Testudines appeared, then the sphenodonts (the tuatara) and the squamates (lizards and snakes), then crocodilians, then dinosaurs and birds.

These relationships can be summarized as follows (here I've included proper group names as well as extant representatives):

•  Amniotes - Descendants of the first egg-laying terrestrial vertebrates (~ 340mya) split around ~325mya
• Synapsids - Mammalian ancestors
• ...
• Mammals ~ 200 mya
• Primates ~ 55+ mya
• Human-Chimp Split ~ 5-10 mya
• Saurapsids - Modern Reptilians
• Anapsids - Turtles
• Diapsids - Other modern reptiles (including birds), split ~ 300mya
• Lepidosauria -Tuatara, Lizards and Snakes
• Sphenodonts - Tuatara
• Squamates - Lizards, Snakes
• Archosauria - Crocodilians, Dinosaurs (including birds)
• Crocodilia
• Dinosauria - Two dinosaur groups diverged ~250 mya
• Ornithischia - "bird-hipped", beaked - but not birds!
• Saurischia - "lizard-hipped", toothed ancestors of birds.
• Sauropodomorpha - big herbivores like Diplodicus.
• Theropoda - bipedal carnivores like T. rex, Velociraptor and...
• Aves - modern birds, originating ~ 150mya

Whew!  So to sum up, birds have been around since their divergence from the other dinosaurs during the Cretaceous period (145-65mya), and are the only surviving Dinosaurs of the big Cretaceous extinction 65mya. Their closest living relatives are the Crocodilians (together with dinosaurs and other relatives, these are the Archosaurs), then the lizards and snakes (which all together form the Diapsid reptilians), then turtles (all together, the Saurapsids). After all the reptilians, the next closest relatives are the mammals (all together, these are all of the living Amniotes), then amphibians, fishes, etc.

So how do you bring all this information to the dinner table?  Well the easiest way to see the relationship between dinosaurs and birds is from the differences and similarities in their skeletal structure.

Source: The Origin and Early Evolution of Birds | Geology Rocks

Other ideas can be found here, and for a nice reference you can bring with you to the Christmas dinner table...

Source: Image from here, modified by Tom Holtz here.

Resources:

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1. Prothero, S. 2007. Evolution: What the Fossils Say and Why It Matters. Columbia Univ. Press.
2. The Dinosauria, from the University of California Museum of Paleontology website.
3. Wikipedia (links above).
4. Wedel, Matt. Your Holiday Dinosaur, University of California Museum of Paleontology website.
5. Holtz, Tom. Your Thanksgiving/Christmas Therapod from Dave Hone's Archosaur Musings.

Dinosaurs, Birds and Interdisciplinary Science

I just came across a 2008 NOVA program on bringing to life the biomechanics of an interesting type of dinosaur from over 110+ million years ago, known as microraptor. In short, this program documents the story of how a group of scientists used fossil information and a little bit of modern biology to construct a model of microraptor, and then teamed up with others to explore how it might have used its unique four-winged body.

You can watch the program from the NOVA page "The Four-Winged Dinosaur," and/or watch the preview for the program here.

Click to enlarge fossil image.

Why mention this little PBS show? Simply to point out a nice little glimpse of how science works in practice. The story line in this case is a pretty good example of how (what some would call "interdisciplinary") science works, and highlights the importance of having a working relationship between experts in different scientific disciplines.

For scientists, a recognition of this way of doing science can shape what we read, what conferences we go to, and the sorts of discussions we have with other scientists outside our area of expertise. More generally, this style of science typifies the notion that science is a community endeavor, which has implications for the way science is taught to future scientists and to the general public.

Another reason for sharing the program is to illustrate the pace at which science often progresses - it's an incremental process and often a lot slower than people think! Progress does occasionally happen larger steps, and these can sometimes be driven by (1) new empirical data or methods of data collection that result in new questions (how did this dinosaur use 4 wings!?) and (2) new ways of thinking about these questions and the tools those new ways of thinking bring to bear on trying to answer those questions.

Julia Clarke points out the role the microraptor work has played in this process towards the end of the program: "Microraptor has thrown our understanding into a new and productive chaos. It doesn't solve the problem, it doesn't give us an answer, but it gives us another way of thinking about the data, and I think eventually, we are going to get to some answers."

So where do those new tools and new ideas come from? Some sort of scientific genius or amazing luck? Well, sure, probably sometimes - but for your average scientist, the best place to start looking for those new insights can often come from "down the hall" - if done right, it can be very fruitful for some researchers to venture out of their own area of expertise, and to team up with experts in other fields on relevant problems. In the case of microraptor, questions about flight brought together expertise from paleontology, comparative vertebrate anatomy, ornithology, aerodynamics, and other disciplines and together these scientists have incrementally advanced our understanding of the origin of flight in birds and reptiles.

In wrapping up this post, I should mention the idea of "interdisciplinary science," the value of which is well illustrated by the very interdisciplinary team of researchers in this program. Scientists, technology experts and in this case artists coming together to try and answer a basic scientific question that demanded more than any one area of expertise to try and answer.

In practice, however, there are often significant challenges present in bringing together such a diverse group of "experts". These challenges include things like the problem of field-specific and/or conflicting terminology, and a great many other challenges that can hinder the development of a productive meeting of minds on a given project.

I'll keep myself from running off on this tangent, but if you're interested a little digging on the web should turn up some of those challenges to doing "interdisciplinary science" plus ways to avoid and deal with them (feel free to comment below if you find anything worth sharing!)