…and this is a 
Answers in Genesis has evolutionary biology on the run now. In an article from 2002, Ostrich eggs break dino-to-bird theory, they explain that development shows that evolution is all wrong, since developmental pathways in different animals are completely different, and can't possibly be the result of gradual transformations.
The first piece of evidence against evolution is the old avian digit problem. Birds couldn't have evolved from dinosaurs, because they have the wrong finger order!
The research conclusively showed that only digits two, three and four (corresponding to our index, middle and ring fingers) develop in birds. This contrasts with dinosaur hands that developed from digits one, two and three. Feduccia pointed out:‘This creates a new problem for those who insist that dinosaurs were ancestors of modern birds. How can a bird hand, for example, with digits two, three and four evolve from a dinosaur hand that has only digits one, two and three? That would be almost impossible.’
The second problem is that frogs and people develop hands in completely different ways, ways that are even more different than the order of the digits.
This is not the only example where superficially homologous structures actually develop in totally different ways. One of the most commonly argued proofs of evolution is the pentadactyl limb pattern, i.e. the five-digit limbs found in amphibians, reptiles, birds and mammals. However, they develop in a completely different manner in amphibians and the other groups. To illustrate, the human embryo develops a thickening on the limb tip called the AER (apical ectodermal ridge), then programmed cell death (apoptosis) divides the AER into five regions that then develop into digits (fingers and toes). By contrast, in frogs, the digits grow outwards from buds as cells divide (see diagram, right).
Dang. I might as well hang it up right now. There is no possible way around these intractable differences. Take me, Jesus, I have seen the ligh…oh, wait a minute. That isn't right. It looks to me like Jonathan Sarfati is just hopelessly confused on the first problem (I can't really blame him, though—it is a complicated issue that has been the subject of scientific arguments for two centuries), and is simply completely wrong on the second (and that one I do blame him for. Tsk, tsk.)
So first, let's tackle the tricky problem, digit identity in evolution. Extend your right hand out in front of you, palm down. Your thumb should be sticking out towards the left, and by convention, that's Digit I. Counting from left to right, your index finger is Digit II, middle finger is Digit III, ring finger is digit IV, and your pinky is Digit V. We have the primitive pentadactyl (five-fingered) hand, so figuring out who is who is fairly easy. The difficulties arise in species that have reduced the number of their digits—when they extend their three-fingered hand, we have to figure out which digits are missing before we assign numbers to the remaining fingers.
One way is by looking at the adult anatomy. Looking at your hand, you probably notice that your thumb is quantitatively different from the other fingers: it only has two joints, instead of three. This is common, that Digit I has fewer phalanges, or segments, than the others, and this is the kind of property that allows anatomists to figure out whether Digit I is present or not. To the right, for instance, is the hand of the raptor Deinonychus (the left hand, sorry to confuse you) with its digit numbering, from DI to DII to DIII, an assignment that was made on the basis of the anatomy. You can see that the 'thumb', DI, has fewer phalanges than the others.
You can try to do the same thing with the digits of birds, but it's harder. Avian digits are reduced and fused into that pointy thing you find at the end of a chicken wing, and it takes an expert to sort out what bones are blended together in there. Anatomists tried, though, and initially and long ago (Meckel came to this conclusion in 1825), decided the bones were numbered DI, DII, and DIII, just like the ones we see in three-fingered dinosaurs…so no dilemma, right?
Wrong. There's another way of looking at the identity of these bones, and that is by watching them develop. What some birds do is start to make five fingers—they form four or five little nubbins of cartilage, called condensations, and then shut down the development of some of them. What another old time anatomist noticed (Owen, in 1836) was that one of the condensations that got thrown away was the first one—which means that the bird digits are actually derived from Condensation II, Condensation III, and Condensation IV. The data is even stronger in this day of molecular markers: bird digits arise embryonically from the second, third, and fourth cartilaginous condensations.
Now this is a complication for evolution. We have three-fingered dinosaurs, and three-fingered birds, but it looks like they aren't the same fingers. Bird ancestors would have had to resurrect their discarded Digit IV, then eliminate Digit I, all before fusing the whole assemblage into a bony gemisch anyway. It's not parsimonious at all. (Of course, it's even less parsimonious to throw away more than a century of data supporting evolution, as Jonathan Sarfati would like us to do.)
There is another, better explanation that Wagner and Gauthier have made that clarifies everything to me, at least.
Note that anatomists initially assigned digit numbers I, II, and III to bird limbs on the basis of their form, but later had to revise that to II, III, and IV on the basis of embryology. Dinosaur digits are assigned numbers I, II, and III on the basis of their adult form (which is admittedly much less ambiguous than adult bird digits!)…but what about their embryology? If we had access to information about expression of molecular markers and early condensations in the dinosaur limb, would we have to revise their digit numbers?
We don't have fetal dinosaur hands to experiment on, but our growing knowledge about how limbs develop suggests that that might just be the case. This diagram illustrates the sequence of development in the hand of an alligator (a) and an ostrich (b).
What you're seeing is the pattern of early condensations in the limb. We tetrapods have a standard pattern: the very first digit to develop as an extension of the limb is Condensation IV, your ring finger, forming what is called the metapterygial axis. Next, the pinky (CV) forms as a little afterthought along one side of the metapterygial axis, and a new axis of condensation hooks over the palm, with the middle finger (CIII) forming next, then the index finger (CII), and lastly the thumb (CI). From a developmental standpoint, the easiest digits to lose are that odd little CV, and the thumb, CI. CI is the very last to form, so you can stop its formation by changing the timing of development in a process called heterochrony, and just halting the development of that axis hooking across the palm early. You can see that in the ostrich, which just stops making fingers after CII, so CI doesn't form. The hardest digit to lose is CIV, because it's kind of the lynchpin of the process—all the other digits follow after IV, so it would be difficult to suppress IV without losing all of the other digits. (Who would have thought that the ring finger was so central and important to hand development?)
The numbering of the dinosaur limb is a problem then…it suggests that they don't have a Digit IV, which looks like a complicated and unlikely thing to do. But they do have a 'thumb', or Digit I. How do we resolve this seeming contradiction?
The answer is that there are two developmental processes going on. The first is the formation of the condensations, CI through CV. This process partitions the terminal region into an appropriate number of chunks, but doesn't actually specify the identity of the digits. The second process takes each of those chunks and assigns a digit identity to them, and this process is to some degree independent of the first and uses a different set of signals. Wolpert et al. have noticed this in modern embryos:
For example, digit identity is specified at a surprisingly late stage in limb development, and identity remains labile even when the digit primordia have formed. It now appears that digit identity is specified by the interdigital mesenchyme and requires BMP signaling. There is also evidence that mechanisms other than a diffusible morphogen operate to lay down the initial pattern of cartilage, which is then modified by a signal from the polarizing region…
What Wagner and Gauthier propose is that three-fingered dinosaurs accomplished that reduction by shedding the two easiest digits to lose, CI and CV, so that if we enumerated them by the same criteria we use in modern birds, they possess Condensations II, III, and IV. What also happened, though, was that there was a frame shift in the mechanism that assigns digit identity, so CII develops as DI, CIII as DII, and CIV as DIII.
The timing of this shift can be mapped onto saurian phylogeny, and it all makes sense and is consistent. And it doesn't involve taking seriously the silly sequence of the biblical account, which has birds appearing before all of the land animals.
What about Sarfati's second line of evidence against evolution, that frogs and humans use completely different mechanisms to build their limbs?
Simple answer: it's all bullshit. It's a blatant denial of basic information you'll find in any developmental biology textbook.
We've got a pretty good handle on the outline of limb development in multiple tetrapod lineages now, and they all use the same tools. Contrary to Sarfati's implication, they all have apical ectodermal ridges (with some rare exceptions in a few highly derived, direct-developing frogs) and zones of polarizing activity, they all use the same set of molecules, including FGF-4 and FGF-8 and the same Hox genes and retinoic acid and BMPs. If there's one thing we know, it's that limb development is dazzlingly well conserved.
It is true that frogs have less apoptosis between their digits than we do, but that's because they have webbed feet. Suppress apoptosis in other vertebrates, and you get the same phenomenon, retention of membranous webs between the digits. There is a simple functional reason why they differ in this regard, and it takes advantage of a common property of limb development in all tetrapods.
I can sympathize with Sarfati having difficulty sorting out digit numbering—it's subtle and sneaky and has puzzled smarter people than either of us. But the uninformed rejection of some of the most straightforward, clearest examples of common mechanisms in development, something that you can find described in the most introductory biology textbook…that's hard to forgive.
Wagner GP, Gauthier JA (1999) 1,2,3=2,3,4: A solution to the problem of the homology of the digits in the avian hand. Proc. Natl. Acad. Sci. 96:5111-5116.
Wolpert L, Beddington R, Jessel T, Lawrence P, Meyerowitz E, Smith J (2002) Principles of Development. Oxford University Press.
Comments
Posted by: Rorschach | June 18, 2009 9:24 AM
Excellent post !
I used to love embryology in med school,but there sortof wasnt really enough time to get into it properly,too much other stuff going on.
This post has finally convinced me to go out and buy a book on it again,thanks PZ !
Posted by: ConcernedJoe | June 18, 2009 9:35 AM
GOOD ONE!!!
Posted by: Albatrossity | June 18, 2009 9:36 AM
Developmental Biology these days is simply amazing; thanks for posting that.
[pedantic mode]
But I think you meant "linchpin" rather than "lynchpin" in the paragraph after the ostrich/alligator figure.
[/ped]
Posted by: Albatrossity | June 18, 2009 9:39 AM
Developmental Biology these days is simply amazing; thanks for posting that.
[pedantic mode]
But I think you meant "linchpin" rather than "lynchpin" in the paragraph after the ostrich/alligator figure.
[/ped]
Posted by: Mobius | June 18, 2009 9:42 AM
Interesting. This fits right in with an article at The Loom
http://blogs.discovermagazine.com/loom/2009/06/17/of-birds-and-thumbs/
on a new dinosaur species, Limusaurus, and what it says about the fused fingers in a bird's wing.
Limusaurus has a tiny remnant of CI which is evidence that the digits the dinosaurs (or at least theropods) lost were CI and CV.
Posted by: Joel | June 18, 2009 9:46 AM
Oooooh, that's nifty. I think I may have just learnt something here...
Posted by: wunderkammer | June 18, 2009 9:47 AM
Did you run out of Comic Sans today? Pity, that.
Otherwise, good post.
Posted by: Richard Harris
|
June 18, 2009 9:51 AM
PZ, Take me, Jesus, ...
Does your trophy wife know about this? ;-)
Posted by: GregV | June 18, 2009 9:56 AM
Great write-up. Of course, the simple reply is that no matter what problems they dredge up with evolution, that does NOT make the biblical account true. That's a core logical fallacy right there, and it's the whole premise of these misguided attempts to deny or overlook real evidence.
Posted by: speedwell | June 18, 2009 10:01 AM
Fascinating, thank you!
Posted by: Neil Gostling | June 18, 2009 10:01 AM
See Nature this week with regard to dinosaur and bird digits......
A Jurassic ceratosaur from China helps clarify avian digital homologies p940
The bird hand is thought to derive from the second, third and fourth digits of an ancestral five-digit hand. However, the three-fingered hand of theropod dinosaurs, which are the closest extinct relatives of birds, are thought to derive from the first, second and third digits. The discovery of a small, primitive herbivorous theropod from the Jurassic period of China with a stub of the first digit alongside more developed second, third and fourth digits, sheds light on this problem.
Xing Xu, James M. Clark, Jinyou Mo, Jonah Choiniere, Catherine A. Forster, Gregory M. Erickson, David W. E. Hone, Corwin Sullivan, David A. Eberth, Sterling Nesbitt, Qi Zhao, Rene Hernandez, Cheng-kai Jia, Feng-lu Han & Yu Guo
doi:10.1038/nature08124
Posted by: Neil Gostling | June 18, 2009 10:04 AM
See Nature this week with regard to dinosaur and bird digits......
from Nature.com:
A Jurassic ceratosaur from China helps clarify avian digital homologies p940
The bird hand is thought to derive from the second, third and fourth digits of an ancestral five-digit hand. However, the three-fingered hand of theropod dinosaurs, which are the closest extinct relatives of birds, are thought to derive from the first, second and third digits. The discovery of a small, primitive herbivorous theropod from the Jurassic period of China with a stub of the first digit alongside more developed second, third and fourth digits, sheds light on this problem.
Xing Xu, James M. Clark, Jinyou Mo, Jonah Choiniere, Catherine A. Forster, Gregory M. Erickson, David W. E. Hone, Corwin Sullivan, David A. Eberth, Sterling Nesbitt, Qi Zhao, Rene Hernandez, Cheng-kai Jia, Feng-lu Han & Yu Guo
doi:10.1038/nature08124
Posted by: adam | June 18, 2009 10:08 AM
Who would have thought that the ring finger was so central and important to hand development?
Further proof that marriage is a divine GOD given gift, and that the Bible is true.
Posted by: frog | June 18, 2009 10:09 AM
Very nice review.
Posted by: S-E Zaccheus | June 18, 2009 10:14 AM
PZ, IANAB but the picture used to illustrate the the "importance" of the ringfinger seem to point at the index finger(?).
Posted by: S-E Zaccheus | June 18, 2009 10:18 AM
Ha, nevermind.
Posted by: Thomas R. Holtz, Jr. | June 18, 2009 10:20 AM
Excellent post. I agree that I find the Wagner & Gauthier arguments very compelling.
Limusaurus does indeed add evidence for a possible scenario of theropod manual evolution, but like all such models it runs into the difficulties of interpreting homology in an evo-devo world.
Applying classical Owenian concepts of homology are becoming somewhat difficult as the mechanisms by which anatomical structures are actually constructed become better understood (as PZ highlights here!) Most significantly, there are multiple phases of development at which homology can be assessed: initial condensation of cartilage, is a separate event from and subject to separate control than later identity assignment by (for example) Hox genes (Vargas et al. 2008, for instance). For instance, given our new understanding of the generation of vertebrae in snakes (Gomez et al. 2008) as produced by a increased rate of somitogenesis, can we directly assess the homology between any given dorsal of a snake and a dorsal of a non-ophidian squamate (aka, a lizard) with 22 dorsals? Would we regard the first 22 dorsals of the snake as homologues to D1-22? Or the first 1/22 as collectively homologous to D1? Or would regard some snake dorsals as neomorphs intercalated among "true" homologues? Or would someone even try to argue that snakes lack homologues to varanids dorsals?
In the case of Limusaurus and theropod hands more generally, Vargas et al. (2008) have very recently shown experimental evidence from chickens, alligators, and mice supporting a frameshift model. In this interpretation, the anterior digit of birds (and presumably other tetanurine theropod dinosaurs) is indeed homologous to condensation II of five-fingered tetrapods, but receives an identity of digit I during late phase HoxD expression (more specifically, from the lack of expression of HoxD-10-12 in the anterior part of the limb bud).
In light of these and related studies cited by the authors, the hand of tetanurines might sensibly be considered to have the formula X-2-3-4-X (that is: no thumb, a pointer finger with two bones, a middle finger with three bones, a ring finger with four bones, and no pinky) only with regards to the condensation homology of the limb. In contrast, using the late phase HoxD identity of the manus, it would indeed have the traditional formula 2-3-4-X-X. Both senses would seem to be valid within their particular context of their different developmental stages.
This is not to say that the Xu et al. (2009) scenario is incorrect or unsupportable: on the contrary, they do highlight anatomical features of these and tetanurine theropod elements that might indicate a closer affinity of the tetanurine "thumb" with digit II of five-fingered(and four-fingered) forms. However, we have reached a point where one must explicitly state that you are are using a condensation reference point for assessing homology, which is independent of late phase identity assignment.
Gomez, C., E.M. Özbudak, J. Wunderlich, D. Baumann, J. Lewis & O. Pourquié. 2008. Control of segment number in vertebrate embryos. Nature 454: 335-339
Vargas, A.O., T. Kohlsdorf, J.F. Fallon, J. VandenBrooks & G.P. Wagner. 2008. The Evolution of HoxD-11 Expression in the Bird Wing: Insights from Alligator mississippiensis. PLoS ONE 3(10): e3325 doi:10.1371/journal.pone.0003325
Posted by: azqaz | June 18, 2009 10:22 AM
IANAB also, but... I believe all of those images are of the right limbs of the creatures, so that small, slightly offset digit on the right is the "pinky", not the thumb.
Posted by: who is your creator | June 18, 2009 10:25 AM
This is a perfect example of the sad state of science now, in which anyone can make up anything and then claim it's 'proof' that it actually occured.
Here is the truth:
Discovery raises new doubts about dinosaur-bird links
June 9th, 2009
"The conclusions add to other evolving evidence that may finally force many paleontologists to reconsider their long-held belief that modern birds are the direct descendants of ancient, meat-eating dinosaurs, OSU researchers say.
"It's really kind of amazing that after centuries of studying birds and flight we still didn't understand a basic aspect of bird biology," said John Ruben, an OSU professor of zoology. "This discovery probably means that birds evolved on a parallel path alongside dinosaurs, starting that process before most dinosaur species even existed."
These studies were just published in The Journal of Morphology, and were funded by the National Science Foundation ...
The implication, the researchers said, is that birds almost certainly did not descend from theropod dinosaurs, such as tyrannosaurus or allosaurus. The findings add to a growing body of evidence in the past two decades that challenge some of the most widely-held beliefs about animal evolution.
"For one thing, birds are found earlier in the fossil record than the dinosaurs they are supposed to have descended from," Ruben said. "That's a pretty serious problem, and there are other inconsistencies with the bird-from-dinosaur theories.
"But one of the primary reasons many scientists kept pointing to birds as having descended from dinosaurs was similarities in their lungs," Ruben said. "However, theropod dinosaurs had a moving femur and therefore could not have had a lung that worked like that in birds. Their abdominal air sac, if they had one, would have collapsed. That undercuts a critical piece of supporting evidence for the dinosaur-bird link.
"A velociraptor did not just sprout feathers at some point and fly off into the sunset," Ruben said.
The newest findings, the researchers said, are more consistent with birds having evolved separately from dinosaurs and developing their own unique characteristics, including feathers, wings and a unique lung and locomotion system."
http://www.physorg.com/news163760732.html
See other equally sad attempts that PBS (#1) PZ (#2), Dawkins and Eugenie Scott (#3) invented to explain how the eye evolved:
http://www.whoisyourcreator.com/how_does_evolution_occur.html
"Professing themselves to be wise, they became fools ... who exchanged the truth of God for the lie, and worshiped and served the creature rather than the Creator ..."
Romans 1:22,25
Posted by: Billy C | June 18, 2009 10:33 AM
"This is a perfect example of the sad state of science now, in which anyone can make up anything and then claim it's 'proof' that it actually occured."
Matt. 7:3
'nuff said.
Posted by: The_Mess | June 18, 2009 10:34 AM
..Except Ruben et al's claims in the press are completely bullshit given what we already know about pneumatisation of dinosaur vertebrae and other bones. Which is strongly indicative of dinosaurs possessing a respiratory system more kin to birds, than to crocodiles. Which is all nicely covered by Darren Naish of Tetrapod Zoology, and over at the Sauropod Vertebrae Picture of the Week blog.
Then again, creationists are deluded fuckwits with an almost astounding inability to critically think, let alone tie together multiple lines of evidence properly. So your insipid stupidity is entirely unexpected.
*adds whoisyourcreator to killfile*
Posted by: raven | June 18, 2009 10:40 AM
PZ's discussion is clear. The dinosaur-bird finger problem disappears because, in fact, the 3 fingers of dinosaurs are homologious to the 3 fingers of birds.
How widely accepted is this in paleontology , evolutionary biology, and developmental biology?
It convinces me, but I'm not a specialist and always regarded the digit conundrum as a tempest in a tea pot.
The new fossil evidence seems to be strong independent support for it.
Incidentally, birds start out with fingers and then toss them into a tiny bone at the end of their wings because birds don't need fingers with their wings. This would not be consistent or predicted by either creationism or the ID version. Goddidit, predicts a sky fairy would wave a magic wand and fingers would never even appear to disappear.
Posted by: James Sweet | June 18, 2009 10:42 AM
This is a repost, right? I totally remember having read this before...
In any case, it's assume. I am definitely not a biologist of any sort, so to have explained an idea this subtle so that I can (mostly) understand it is quite a feat. Keep it up!
Posted by: The_Mess | June 18, 2009 10:45 AM
Oh yeah, Ruben also fails epically by not bothering to even research current models of positions of abdominal air-sacs in therapods. As the leg-movements issues Ruben et al says don't apply, as all air-sacs are in the chest in therapods...
As birds evolved though, the pubis migrates backwards, along with the air-sacs, which the "fixation" of the femur probably also follows, side-stepping the issues Ruben et al claim. Pretty simple bit of evolutionary thinking, and completely, utterly irritating that the science-news sites didn't bother fact-checking before posting, as at least the claims Ruben made on ScienceDaily are entirely erroneous.
Posted by: Kelseigh | June 18, 2009 10:47 AM
"Looking at your hand, you probably notice that your thumb is quantitatively different from the other fingers: it only has two joints, instead of three."
Actually, the thumb does have three joints. The first is under the fleshy part of the hand, so it's not as obvious as the finger joints. It's what allows you to move your thumb across the plane of the hand, a lovely evolutionary advantage.
Yeah, I'm being a pedantic artist. I'll stop now.
Posted by: Raiko | June 18, 2009 10:49 AM
It seems to completely fly over their heads that they themselves rest their arguments on the obvious homology between our fingers and those of birds and dinosaurs. Their other argument rests upon the fact that amphibians and mammals have the same number of digits we have, which is also something they accept in their argument.
'Scuse me, but what are the odds?!
Posted by: littlejohn | June 18, 2009 10:50 AM
Don't these fuckwits read? The whole digit problem was just dealt with in "How to Build a Dinosaur," by Jack Horner. Since the way they frame the problem is similar to the way Horner describes it, I'm guessing the scanned his book, saw the "problem," but didn't bother to read the solution.
However, I have to admit that's how I read the Bible. I usually just scan for transparent bullshit and ignore the other three or four sentences.
Posted by: joe_schmoe | June 18, 2009 10:51 AM
Excellent article PZ! Now I understand digits in dinosaurs. But how do you explain the four digits of the Simpsons?
Posted by: raven | June 18, 2009 10:54 AM
Wherearemymeds is a perfect example of the sad state of US xianity. It has become the domain of ignorant vicious liars who engage in bigotry, hate, terroism, and murder. Normal people are disgusted and leaving the religion at 1-2 million people/year.
Incidentally, Ruben's paper barely made ripples in the scientific community and has sunk without a trace. There are many problems with the conclusions he drew from the data he has. But where-are-our-terrorists wouldn't know that because she is a stupid, crazy religious fanatic, not a thinking human being.
Posted by: Raiko | June 18, 2009 10:57 AM
HAHA!
And JUST now Nature published an article to possibly solve the three-digit-riddle between birds and dinosaurs.
http://news.bbc.co.uk/2/hi/science/nature/8105513.stm
Posted by: Zipplenom | June 18, 2009 10:58 AM
Excellent article PZ! Now I understand digits in dinosaurs. But how do you explain the four digits of the Simpsons?
In The Simpsons, God has 5 fingers, so at the very least we know the weren't made in his image.
Posted by: Tommy Traddles | June 18, 2009 10:59 AM
Humans More Closely Related to Orangutans, Not Chimps
Molecular studies challenged
"Schwartz and Grehan contend in the Journal of Biogeography that the clear physical similarities between humans and orangutans have long been overshadowed by molecular analyses that link humans to chimpanzees, but that those molecular comparisons are often flawed: There is no theory holding that molecular similarity necessarily implies an evolutionary relationship; molecular studies often exclude orangutans and focus on a limited selection of primates without an adequate "outgroup" for comparison; and molecular data that contradict the idea that genetic similarity denotes relation are often dismissed.
"They criticize molecular data where criticism is due," said Malte Ebach, a researcher at Arizona State University's International Institute for Species Exploration who also was not involved in the project but is familiar with it.
"Palaeoanthropology is based solely on morphology, and there is no scientific justification to favor DNA over morphological data. Yet the human-chimp relationship, generated by molecular data, has been accepted without any scrutiny. Grehan and Schwartz are not just suggesting an orangutan–human relationship—they're reaffirming an established scientific practice of questioning data."
Contact: Morgan Kelly
mekelly@pitt.edu
412-624-4356
University of Pittsburgh
Posted by: raven | June 18, 2009 11:05 AM
There seems to be two problems at least with Ruben's idea.
1. The bird thigh, lung air sack system is a derived characteristic. You can't use a derived character to negate primitive ancestor-descendant relationships (phylogeny).
2. He also bases his conclusion on an enigmatic fossil called Longisquama from the Triassic, very old. This reptile has structures that some consider feathers, some do not. There is only 1 speciment and the taxonomy isn't clear. Some claim it is an archosaur, which if Longisquama is an ancestor of birds would make birds derived from...dinosaurs.
Both of Ruben's pieces of evidence are slim reeds of questionable relevance to base a sweeping hypothesis on. No one is buying it.
Posted by: DaveH | June 18, 2009 11:09 AM
Kelseigh#25. That's the first carpo-metacarpal joint, which all the other fingers have as well, so if you count that as three joints for the thumb, the other digits all have 4 joints! ;)[/anatomy pedant]
Nice to see whois accepting the truth (her word), though:
"This discovery... means that birds evolved...."
Even if Ruben were correct (he isn't, see Tetrapod Zoology blog)there would not be a word in the paper supporting any interference by a "creator".
Posted by: SteveM
|
June 18, 2009 11:21 AM
Kelseigh @25:
Read the rest of PZ's description, "Looking at your hand, you probably notice that your thumb is quantitatively different from the other fingers: it only has two joints, instead of three. This is common, that Digit I has fewer phalanges, or segments, than the others,...", Yes the Thumb has a segment "hidden" in the palm, but so do all the other fingers. Count the segments of each finger back to the wrist,the thumb has 3, all the others have 4.
James Sweet @23: "This is a repost, right? "
in the upper right corner of the posting there is a cute little image with the word "Repost" in it.
Posted by: SteveM
|
June 18, 2009 11:27 AM
And JUST now Nature published an article to possibly solve the three-digit-riddle between birds and dinosaurs.
ORLY? Like, maybe that was what motivated PZ to repost this article?
Posted by: oneunderthesun | June 18, 2009 11:55 AM
A little evolutionary science on a Thursday morning does a mind good. Keep it up PZ. I happened to be in West Central area over the weekend and was hoping to see you to shake your hand. Maybe next time.
Posted by: John Scanlon, FCD | June 18, 2009 11:56 AM
Tom Holtz asks
Most of these questions are obviated to some extent by observing that dorsal vertebral number varies within species geographically, between sexes and among siblings, as well as ranging from just below 100 to over 400 in different modern snakes (i.e. generally there can't be a one-to-one homology of segments, but only of things like regions, transitions or continua). They're still interesting questions to think about.
To evolve from typical lizard numbers to the lowest ones in snakes might have occurred by a random walk (accumulation of small tweaks) or, perhaps, by doubling it and redoubling in a couple of big hopeful-monster-type whacks. The fossil record for the transition's still spotty (getting better all the time!), but among 'dolichosaurs' there are some with about 26 presacrals, Dolichosaurus which apparently had about 50, and then pachyophiids (and various modern snakes) with about 100. In cylindrical-bodied aquatic ectotherms with highly reduced limbs, big changes in body length might be reasonably viable (snakes also have short tails, so you can think of it as sliding the dorsal-caudal transition along a relatively fixed total segment number).
Is it mere coincidence that a ratio close to 4.0 features prominently in the Gomez et al. paper on somitogenesis rates? Unfortunately they don't discuss whether that's an arbitrary real number or an approximate power of 2. It'll be interesting to find out, with more evo-devo AND more fossils.
Posted by: Uncephalized | June 18, 2009 12:24 PM
Is this a repost? I remember reading the exact same explanation a while back. Good post though.
Posted by: Pierce R. Butler | June 18, 2009 12:37 PM
Hold your pointer above the "Repost" image at the right of the top of this item, and (with most up-to-date browsers) a little pop-up label will reveal it dates from the ancient era of September 7, 2004.
Some paleoarchaeologist just this morning shoveled away tons of sediment to reveal it; carbon dating of a pixel sample is not yet complete.
Posted by: Jadehawk, OM
|
June 18, 2009 12:40 PM
aaahhh... nothing like some interesting learnin' for breakfast.
I'll save the other article for after work. at least something to look forward to :-)
Posted by: devbiologist | June 18, 2009 12:41 PM
PZ, I love your blog. Usually I just enjoy reading your posts and your regular commentators, but this is such a lovely explication that I wanted to commend you for it. Actually it makes me miss graduate school. Thank you very much!
Posted by: whitebird | June 18, 2009 12:49 PM
Raven @ 33: Could Ruben's hypothesis be based on the "guess what, chicken butt, guess why chicken thigh" argument?
Posted by: Stu
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June 18, 2009 1:06 PM
devbiologist: You obviously haven't visited the archives, whence this came. There's so much more loveliness to peruse.
Posted by: David Marjanović, OM | June 18, 2009 1:06 PM
See my comment 23 on the next thread. I'm not sure if I've read Vargas et al. (2008), though.
There are three serious problems here, Ms Haberle.
1) Ruben confuses "ancestor" and "sister-group". That's like confusing "mother" and "sister": your mother has to exist before you, your sister does not.
2) Like Feduccia, Ruben does not work on dinosaurs, is not interested in dinosaurs, and does not follow the dinosaur literature. No wonder, then, that he hasn't noticed things like the troodontid skeleton from the Morrison Formation (at least as old as Archaeopteryx; currently under description, but presented at the Society of Vertebrate Paleontology congress of 2005 [ref below]) or the specificially dromaeosaurine teeth from Guimarota in Portugal, older than Archaeopteryx, which show that Dromaeosauridae as a whole must be older still.
3) The cretinists, such as you for example, lie by omission: neither Ruben nor Feduccia nor anyone else in this discussion denies evolution – they only believe that birds are not dinosaurs. That's all.
Be ashamed, Ms Haberle. You are giving false testimony unto your neighbors.
Scott Hartman, David Lovelace & William Wahl (2005): Phylogenetic assessment of a maniraptoran from the Morrison Formation, Journal of Vertebrate Paleontology, supplement to issue 25(3), 67A and 68A.
Apart from comment 24, isn't that what gastralia are for? Many Early Cretaceous birds retained gastralia.
Besides, the femora of running ostriches move through a 60° arc…
And what about the pneumatic hiatus in Haplocanthosaurus? Oh, that's a sauropod, and Ruben doesn't know sauropods. I see.
So Ruben even missed the discovery of quill knobs in Velociraptor, showing that this (nonetheless flightless… perhaps secondarily so) animal had long, strong wing feathers? Wasn't that published in Nature or something?
It was blogged about here, anyway…
Links added.
No; dinosaurs, crocodiles, and many extinct groups together are archosaurs. That said, the only "evidence" that Longisquama is an archosaur consists of desperate attempts to see an antorbital fenestra in its badly damaged snout. It's probably not there, and the rest of the skeleton hints at a very basal diapsid. Probably the birds are more closely related to the snakes and the ichthyosaurs than to this beast.
Posted by: James Sweet | June 18, 2009 1:36 PM
Heh, I feel dumb for missing the repost icon. Believe it or not, I was actually looking for one... I think it's that light grayish-green color he uses in the logo... doesn't catch the eye or something. heh.
Oh well, me = dum.
Posted by: Kate | June 18, 2009 2:36 PM
After having read this post, I feel about 15% smarter, since I, amazingly, understood every word of it.
It seems to me that the argument that because a frog does not develop EXACTLY like a human being evolution is false is a very, very, very, very stupid argument. If humans and frogs share a common ancestor (Which is quite likely, based on the similarities in cell structure of all eukaryotic organisms.), it would be WAAAAAAAAAAAAAAAAAAAAAAAAAY the heck back there in the mists of "Long, long ago", and as anyone who has even the remotest clue about evolution knows, a divergence of species along an evolutionary track can produce stunningly different morphologies and developmental paths after sufficient generations. All it takes is time, and there has been more than enough of that to allow for such differences.
(I think you could substitute any two eukryotic organisms for "human" and "frog" and I think it would still be a valid refutation of that argument... If it isn't, please, for the love of the Cephalopope, correct me. It's the only way I'll learn!)
Posted by: Brian | June 18, 2009 3:45 PM
Albatrossity@3:
Both spellings are considered correct, actually. (Though I would agree that linchpin-with-an-i is "more" correct.)
Posted by: Alexander | June 18, 2009 3:54 PM
Great article! PZ, respect!
Posted by: Flaffer | June 18, 2009 4:00 PM
Science is a really beautifu thing, because it tracks so elegantly with the "furniture of the world", as it were.
Posted by: Bridget McKinney | June 18, 2009 5:29 PM
Great post, PZ!
Biology is an area that I'm not super well-read about, so I'm always happy when people write stuff that is interesting and informative without being information overload for me. This post definitely falls into that category.
Thanks!
Posted by: Alan Kellogg | June 18, 2009 6:06 PM
Now digit identity is not established until fairly late in development, and on occasion the wrong identity is established for digit position. This being so, it is possible for someone to be all thumbs.
Posted by: Don Rowe | June 18, 2009 7:30 PM
My kind of post! Thanks for that PZ.
Creationists, fundies and idiots need a good bollocking from time to time, but I much prefer the informative, ammunition supplying posts. :)
Posted by: Funkjunkie | June 18, 2009 8:39 PM
PZ, your posts have been getting better and better recently. Thanks for addressing this stuff!!!!
My current research is on the roles of BMPs in frog limb development. When I first saw that statement saying that frog limb development is different to that of other animals I was like wtf? It's not. Have any of these people actually looked at pictures of frog limbs developing?
The confusion probably stems from the fact that many people have stated that the AER doesn't exist in frogs. Nevertheless, there is still a tissue that expresses the same genes and does the same job.
You rock PZ, keep up the good work.
Posted by: efrique | June 18, 2009 9:27 PM
Thanks.
I enjoy most of your posts, but I think your science-related posts are almost always your best, and read them eagerly.
I realize they're often a lot more work than a more typical post, but they're also very informative and entertaining; I appreciate the effort they require.
Posted by: Raiko | June 19, 2009 12:52 AM
SteveM, when I first read the post (rather hastily, I admit), I did not see that fossil mentioned anywhere. Rather than speculating on PZ's motivation, which isn't mine to know, I thought I could point the commenters to the article on that dinosaur fossil that way. Now with PZ's newer posts, his motivation is clear, of course. But as always, I do enjoy such nice and constructive comments, thank you. (9_9)
Posted by: Robster, FCD | June 19, 2009 12:53 AM
Brilliant. Thanks for the lesson. I'm already thinking about how to put this into my evo lecture.
Posted by: v6dino | June 19, 2009 4:11 AM
Excellent stuff PZ, your science posts really make me wish I'd studied biology back in college instead of pushing bits and bytes.
So in a nutshell, ancestors to the dinosaurs (like the alligator in the diagram) had five digits. Through bilateral digit reduction, CI and CV are lost. At the same time, the frame shift occurs and transposes the lost thumb CI back to CII to create a new thumb from the forefinger. This creates DI, DII and DIII.
I hope this isn't a stupid question... If birds are descended from dinosaurs that underwent all this, then they should show signs of a thumb in the three bones that fused together. Is this evident in modern birds? Or could they have come from another line of dinosaurs that didn't undergo the frame shift?
All this makes definite sense compared to old-beardy-in-the-sky bleatings touted as the alternative. Evolution is like a lazy programmer - always reuse code no matter how clunky, then patch it up to fit new circumstances and shove the damn thing out the window :)
Posted by: ductus_deferens
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June 19, 2009 6:14 AM
SteveM@35
as far as i know the so called first metacarpal bone is actually the first phalanx of the thumb.
check this fig.: http://upload.wikimedia.org/wikipedia/commons/e/e4/Gray234.png
it shows that the first metacarpal bone has growth plate at the proximal end (as the case of all phalanges) as opposed to the other metacarpal bones.
Posted by: ductus_deferens
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June 19, 2009 6:21 AM
that means, that the first metacarpal is missing and thumb has 3 phalanges, not 2
Posted by: DebinOz | June 19, 2009 7:21 AM
Stuff all this scientific stuff: Just be like my creotard FIL (who has a PhD in history!!!!!), who truly believes that 'god created the world complete with fossils to test our faith'.
Posted by: jim | June 20, 2009 10:32 PM
that explains everything to me!
Posted by: David Marjanović, OM | June 23, 2009 10:16 AM
Wrong.
Too bad. Must have something to do with opposability.
Compare more animals…
So he believes God is a liar? He believes God is the Great Deceiver?
Ask him.