Bird skull evolution

Earlier I attempted a color tracing of the skull of the common chicken (Gallus gallus), and I got some flak for it, but, unfortunately, no corrective illustrations.

Figure 1. Chicken skull from around 1905.

Figure 1. Chicken skull from around 1906. Note this illustration has only a smidgen of a maxilla above the anterior jugal. Sadly only a few bones and openings are identified here.

So I went to and also found several online illustrations of bird skulls (Fig. 1; anatomical studies are quite rare and typically very old) to try to figure out where I went wrong.

Here (Fig. 2) are the results. The skulls of Archaeopteryx (courtesy of Greg Paul), an Early Cretaceous enathiornithine  (Sanz et al. 1997), Struthio (the ostrich), Anser (the goose) and Gallus (the chicken) are compared (Fig. 1, click to enlarge).

Figure 2. Bird skulls compared. Here are Archaeopteryx, Struthio (ostrich), Gallus (chicken) , Anser (goose) and an unnamed Early Cretaceous enantiornithine nestling as large as Archaeopteryx (Sanz et al. 1997). Archaeopteryx by Greg Paul used with permission. Click to enlarge.

Figure 2. Bird skulls compared. Here are Archaeopteryx, Struthio (ostrich), Gallus (chicken) , Anser (goose) and an unnamed Early Cretaceous enantiornithine nestling as large as Archaeopteryx (Sanz et al. 1997). Archaeopteryx by Greg Paul used with permission. Click to enlarge.

The similarities and variations among the bird skulls are interesting. I have avoided birds for too long (probably the reason for earlier errors). Let’s discuss them in brief.

You’ll notice first off that the skulls of Archaeopteryx, Struthio and the LP specimen are quite similar overall. By comparison, the more derived Anser and Gallus skulls are less similar.

Figure 3. The Struthio toothless rostrum has regularly spaced pockets where teeth once appeared in its ancestry.

Figure 3. The Struthio toothless rostrum in palatal view has regularly spaced pockets where teeth once appeared in its ancestry. Now these provide nutrients to the ever-growing beak. Click to enlarge.

Tooth disappearance
Archaeopteryx and the LP specimen both had teeth, but extant birds do not. The last clues left by the teeth can still be seen in the primitive bird, Struthio (Fig. 3), which has living tissues, lips and gums and a beak in place of teeth. Those are not tooth roots, but nutrient foramina.

Upper temporal fenestrae disappearance
Archaeopteryx and the LP specimen have an upper temporal fenestrae bordered laterally by the postorbital and squamosal. In extant birds, the situation is not so clear. The postorbital is reduced to a vestige and the squamosal is incorporated into the brain case. That leaves the quadrate (jaw joint bone) less connected to the skull.

Lacrimal reduction
Archaeopteryx and the LP specimen have a lacrimal (stem-like bone between the antorbital fenestra and orbit) but it becomes a vestige in extant birds, still connected to the prefrontal above it.

Premaxilla/maxilla variation
Archaeopteryx and the LP specimen have a typical premaxilla tipping the snout. The maxilla extends halfway beneath the naris. In Struthio and Gallus the premaxilla extends further posteriorly, crowding out the maxilla. In Anser the premaxilla extends further posteriorly, and the maxilla is distinctly robust, both traits strengthening the rostrum.

Ectopterygoid disappearance
In most tetrapods and most dinos the ectoptergoid (a palate bone) arises from the lateral flange of the pterygoid and contacts the cheek bones, typically the maxilla, sometimes the maxilla and jugal. In Archaeopteryx it contacts only the jugal, and then just barely. In a late Cretaceous flightless bird, Hesperornithis, the ectopterygoid is a vestige not in contact with the cheek. Ultimately the ectopterygoid is not present in the extant Struthio, Gallus or Anser. So evidently the ectopterygoid doesn’t fuse to the pterygoid and become part of it. Rather the ectopterygoid becomes a vestige and disappears.

Loss of maxilla ascending process
Archaeopteryx and the LP specimen have a typical maxilla with an ascending process arising to meet the nasal and lacrimal. But note it is much more gracile in the LP specimen. In extant birds the ascending process is not visible in lateral view, either replaced or covered by the descending process of the nasal.

Shorter quadrate
Archaeopteryx has a tall quadrate. The others have a short quadrate, The others also have a larger cranium, housing a larger brain. That also lowers the ventral squamosal.

If I made any errors this time,
don’t be shy about providing illustrated corrections. I’ve only studied comparative birds skulls for one day so far. I’m sure there’s more to learn.

The animated Longisquama post had about twice as many hits as on a typical day. Thank you for your interest.

Sanz et al. 1997. A Nestling Bird from the Lower Cretaceous of Spain: Implications for Avian Skull and Neck Evolution. Science 276:1543-1546.



11 thoughts on “Bird skull evolution

  1. Laughable again. I can assure you no ornithologist would agree with your interpretations of modern bird skulls. It’s really a great example of one of the major issues with your tetrapod ideas in general- you’re not an expert in most clades. No one is. I know theropods. You give me a theropod skull, even a crappy photo of one, and I can guess pretty well what the actual bones are. You give me a younginiform or a temnospondyl, and I don’t know. But you act and code as if you know, then present your results as knowledge that the establishment is too lazy/embarrassed to admit. I’d provide you with references, but when I did that in the past, you just used that information to replace your very wrong interpretations with your newly less wrong interpretations. You didn’t indicate in your posts that your ubiquitous DGS technique was wrong in that case and thus very likely to be wrong in other cases where experts weigh in, instead letting the situation seem like you had the better interpretation all along. So why should I enable your ability to trick viewers into thinking you have better insight? For ectopterygoid homology in Aves, check an author whose surname begins with an E. For supposed alveolar remains in Struthio, Jaime pretty niftily disproved that in a recent comment.

  2. So. At least you understand that it’s my lack of knowledge, not my DGS technique, that is getting the best of me here. Sorry to hear you’re not going to help. In that case, I’m fated to continue passing on bad information. I think you misinterpret my intentions, btw.

    • How can you provide me with such a perfect example of your dishonesty in this very post? Sometime after I commented, you changed your figure 2 here to have more reduced maxillae, as you previously had the maxilla making up most of the ventral beak margin. It’s a good change, but you just replaced it without ANY notice. There’s nothing in the figure caption saying the original had errors, no indication the post was even edited. Someone reading this post would think you had that better interpretation the whole time. You left the old version on the web host though-, so we have proof this time. Changing dated blog posts without notice is not like changing or The Theropod Database. It’s as if you kept an editable pdf of your published article and continued to rewrite it and change illustrations before sending copies to colleagues. Dishonest and misleading. If your intention is to provide an accurate record of your work, this is not the way to do it.

      • Let’s face it, Mickey, you are a hater. You are happy to point out errors (for which I am grateful). Unhappy to the point of name calling when errors are corrected. I am replacing bad data with better data and you call me dishonest for doing so. That’s more than a little twisted. My intention has always been to provide accurate work. That means removing inaccurate work. You have no idea how many errors I correct every week, mostly as I add taxa and find better data. That number over the last four years is no doubt in the tens of thousands of data points. I thank you for the heads up on the pmx-mx errors. They improve my output. Some day I hope to get a “good job” from you when and if I ever do something right in your eyes. After 1200 posts and 700+ taxa, though, my hopes are fading.

      • “Some day I hope to get a “good job” from you when and if I ever do something right in your eyes.”

        Here’s how you do it- note in your posts and figure captions whenever you change or edit them. Why don’t you do that?

      • Yep, Miss Mortimer is right. The post looks very edited after her corrections. But Mr. Peters didn´t warned about this. He is trying to look like if he have reason always! Miss Mortimer is not a hater. We don´t too, We only watch this blog history …and is very unreliable. ¿ How many more reconstructions of Longisquama?
        How many mistakes?

      • No corrections were provided by M. Mortimer. Tens of thousands of corrections have been made by yours truly to prior mistakes as better data flows in (if you count all the bone drawings and tree scores) and the number keeps growing. In Science we call these corrections, and they are very much a part of the process of Science, as you know already. The correct way to help a fellow paleontologist is to note a problem and provide a reference or solution. Not to do as M. Mortimer did, with derision.

  3. Foramina for blood vessels are homologous to alveoli now? I don’t think so. I think foramina for blood vessels are homologous to foramina for blood vessels.

  4. I usually mark the changes and date them. But this time the change was made on the same date after referencing G. Paul’s illustration of a loon in Dinosaurs of the Air. You still have not said if I have provided a correct interpretation. As far as I know, the current interpretation is still, as you put it, “laughable.” So I’m in limbo. And your comments alert readers that what they are seeing is “laughable.” That is important for my readers and me to know.

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