Primitive Eggs

The Great 2013 Catch-upIn Evolutionists Scramble ‘Fossil-Egg Evidence’ (19 April 2013) Brian Thomas challenges the conclusions of a recent Nature paper, “Preservation of ovarian follicles reveals early evolution of avian reproductive behaviour” (not open access, but a Nature News article is).

Bird fossils do not generally ruffle paleontologist’s feathers, but some amazing specimens from China’s Jehol province—preserving eggs inside fossil bird bodies—might do just that. Researchers suggested that the bird egg features lend themselves to an evolutionary progression from crocodile-like reptile to chicken-like bird eggs. But if God made birds and reptiles according to separate kinds as clearly stated in Genesis, then they were and are unrelated. Which history does this recent evidence best match?

You can tell what he thinks the answer is right away, of course. Thomas explains the situation as he sees it:

A team of mostly Chinese authors described the three extinct birds in the journal Nature.One of the birds had a long tail, and the team identified the other two as short-tailed birds called Enantiornithines. All three well-preserved fossils showed flattened remains of eggs situated just in front of the pelvis, like modern birds and reptiles.

The bird with the “long tail” (we’ll get back to that later) was of the genus Jeholornis, and is labelled “STM2-51.” The Enantiornithes are STM29-8 and STM10-45. Brian adds:

Their Nature report placed these three birds onto an evolutionary tree diagram. The crocodile on the diagram represented the birds’ supposed modern reptile relations and the chicken represented the birds’ supposed modern bird relative.

The “tree diagram” (a cladogram) can be seen here. You’ll note that, to Thomas, not only is the crocodile only a “supposed” relative, the chicken is too. Strange as it may sound this is consistent with the conclusions you would have to draw from the creationist pseudoscience of baraminology: “bird” is too large a group to be a single kind, so it has to be broken up into numerous unrelated subgroups. Where the dividing lines between these groups lie I couldn’t tell you.

Next, we have a misunderstanding about the meaning of the word “primitive”:

The crocodile shown on the left of the diagram held dozens of small eggs. The Nature study authors placed their long-tailed [Jeholornis] bird next to it and described it as “primitive.” But if the long-tailed bird was more “primitive” than the short-tailed birds shown, then why were all three fossils found together in the same Chinese rocks? The primitive bird fossil should occur in rocks far below their supposed descendants.

The paper does not directly tell us the age of the specimens, but the supplementary information (pdf) says that the Jeholornis is from the Yixian Formation – which is 125-121 million years old, according to Wikipedia – while the Enantiornithes are from the Jiufotang Formation (120.3 +/- 0.7 million years old). The fossils were therefore not “found together in the same Chinese rocks,” the “primitive” Jeholornis was found in older rocks, and Thomas is wrong.

But that’s not the point. The word “primitive” has a subtly different meaning in this context: “resembling evolutionary ancestors of living things and in particular resembling them in the nature of their anatomy and behaviour,” according to that link (emphasis original). Being more “primitive” doesn’t actually require being older at all.

The other issue here is that the paper never calls Jeholornis “more” primitive than the other fossil birds studied, though it does say:

Differences in follicular morphology between Jeholornis and the enantiornithines are interpreted as forming an evolutionary gradient from the reproductive condition in paravian dinosaurs towards neornithine birds.

Thomas continues:

The “primitive” bird had fewer eggs than the crocodile, but more than the Enantiornithines. The evolutionary diagram silhouetted a chicken on the far right as holding the fewest eggs. The viewer is supposed to get the impression that as reptiles evolved into birds, they produced fewer eggs.

But why select egg number as the key trait to define evolutionary relationships? Possibly because the study authors would have a difficult time depicting transitions in beaks or feathers, since reptiles don’t even have feathers, and the dinosaurs that had beak-like mouth shapes were not the ones that allegedly evolved into birds. Clearly, the scientists hand-selected eggs to illustrate evolution, ignoring most of the anatomical data.

Yeah, no. You’ll note first that Thomas is still denying that any dinosaurs had feathers, refusing to take the easy out. Where he gets the idea that “the dinosaurs that had beak-like mouth shapes were not the ones that allegedly evolved into birds” (emphasis original), or even that they’re only using “egg number” to “define evolutionary relationships” here, I don’t know. (This is the first time that they’ve had eggs to work with, but they already knew the relationship: the eggs are being used to work out egg-related aspects.)

Thomas thinks that the Nature paper cherry-picks the egg trait over “five more relevant bird traits noted in the very same report” that “clearly show the specimens to have been complete and created birds, thus outside of evolutionary flights of fancy.” These are (quoted, with commentary in brackets):

  1. The “Jehol birds” preserve fossilized seeds in their crops. Unlike crocodiles and lizards, a bird’s crop and gizzard help digest food. [The birds mentioned by the paper to have said seeds in their crops are not the ones being studied, but who’s counting? Also, some dinosaurs may also have had a crop.]
  2. The internal eggs, called follicles, “are consistent with two-dimensional preservation of a spherical structure.” Bird eggs are nearly spherical, while reptile eggs are oblong. [Thomas may be confusing the follicles in the ovary (which are spherical) with the egg that is eventually laid (which need not be).]
  3. The fossil bird’s follicles were on the left side, consistent with the way in which, as the Nature authors described, “birds are unique [in that] only the left ovary and oviduct are functional in the adult.” Crocodiles and dinosaurs used both left and right oviducts. [This, at least, is an actual distinction between these fossils and known non-avian dinosaurs, though we don’t have a huge amount of data there.]
  4. Egg sizes in the fossil birds were large in proportion to the body, as in modern birds, but not in reptiles. [The paper says that this has also been observed in non-avian theropod dinosaurs.]
  5. One of the three bird fossils shows preserved feathers, clearly a bird and not a crocodile or reptile trait. [Again with the feather denialism.]

Thomas’ list is looking a little shaky. What’s more, his is itself cherry picked, excluding a number of features that can be used to tie these fossils closer to their dinosaurian anscestors. These include:

  1. You remember that “long tail” on the Jeholornis, right? There’s another adjective here that Thomas repeatedly fails to include: the tail is bony. Theoropods had bony tails, as did some primitive birds such as Archaeopteryx. Modern birds do not, but Jeholornis’ tail was longer than that of Archaeopteryx.
  2. Similarly, Jeholornis had a small number of teeth – modern birds have none.
  3. The fist toe of a Jeholornis was only partially reversed.
  4. The paper says that, in the Jeholornis fossil, the “size of the follicles is very consistent, suggesting a more crocodilian style of reproduction, in which a large number of follicles reach maturity near simultaneously so that follicular hierarchy is minimal.”
  5. As for the Enantiornithe STM10-45, the paper notes that the evidence suggests that “reproductive maturity was achieved before skeletal maturity, as in paravian dinosaurs and crocodilians.”

While these fossils are definitely birds, there is not the deep rift between birds and non-birds that Thomas claims. There is room for evolutionary progression, and it has been observed.


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