Cratonavis zhui: A Dinosaur-like Bird?

A Mixed Evolutionary Bag

Cratonavis has some features which are considered more dinosaurian and less like modern birds as well as some features which purportedly bridge the gap between dinosaurs and birds and even between Archaeopteryx (dated at 150 MY) and modern birds. Some of the most noticeable differences between Cratonavis and Archaeopteryx are the shorter tail in Cratonavis, four digits on the foot (compared to three on Archaeopteryx) and the scapula and coracoid fused into a scapulocoracoid on Cratonavis but unfused in Archaeopteryx. This latter trait is a bit perplexing as the fused scapulocoracoid is considered a more primitive trait than what is found on the allegedly 30 MY older Archaeopteryx.

In addition to having a more “primitive” feature than its alleged ancestor, Cratonavis also has some perplexing anatomical features, some of which it shares with “direct ancestors,” confuciusornithids, and others which differ from even that “immediate ancestor clade.” For example, both groups have the fused scapulocoracoid and a pygostyle, which is a fused set of caudal vertebrae at the end of the tail. But Cratonavis has a toothed jaw, whereas the supposedly slightly older Confuciusornithidae (dated between 131 and 120 MY) have no teeth. And the digit count between the two clades also differs, with the Confuciusornithidae having only three digits on each foot (most modern birds have four toes, though a few [mostly flightless ones] have three or even two toes [e.g., ostriches]).

Cratonavis’ closest “sister clade” is Chongmingia, which also shares more “primitive” traits and contrasts more “modern” features with Cratonavis. Chongmingia has a much smaller scapula (shoulder blade) but a longer femur (upper leg bone) and humerus (upper arm bone). Perhaps most striking is the obvious presence of feathers for Chongmingia and no discernable ones for Cratonavis. And although feathers are mentioned in the paper, there do not appear to be any definitive feather impressions found with the creature. However, it is possible that poor preservation of the matrix surrounding Cratonavis is to blame. While it is difficult to be sure, there may be some indication of at least the impression of feathers below the wing bones (on the right side) and the pygostyle—indicating possible wing and tail feathers, respectively.

So, Cratonavis contains a combination of features which the authors of the paper suggest:

exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton, revealing the key role of evolutionary mosaicism in early bird diversification.1

As one of the earliest-branching pygostylians, jinguofortisids (~8 million years of duration for the known members) preserve a suite of unique morphologies that is further complicated by Cratonavis. Cratonavis has a heavily built skull that is morphologically more like that of non-avialan theropods than most contemporaneous avialans....2

The combination of a non-avialan dinosaurian skull and avialan post-cranial skeleton documented in Cratonavis adds to the tally of examples where avialan evolution has been shaped deeply by mosaicism.3

And as coauthor Dr. Zhonghe Zhou stated in a press interview, “The aberrant morphologies of the scapula and metatarsals preserved in Cratonavis zhui highlight the breadth of skeletal plasticity in early birds.”4

In other words, the phylogenies of Jurassic and Cretaceous birds (or non-birds) are built based on characteristics which jump back and forth between more primitive and advanced features among supposed ancestors and descendants and can even fluctuate dramatically among “sister clades” as discussed above. There is no clear-cut anatomical progression from dinosaur to bird, only “plasticity.” For the derived phylogeny list from the Cratonavis paper, see Fig. 1 below.5

Fig. 1

Does Cratonavis Really Have a Dinosaurian Head?

If you look over the image of the fossil find, you’ll notice that the entire skull does not look complete—the lower jaw is missing, but researchers mention that they found structures of the lower jaw, so it appears that the lower jaw was compressed underneath the upper jaw. See also the artist’s impression here. While the journal paper is less sensational than the popular science writeups (with one site claiming that Cratonavis’ “skull is almost the same as that of dinosaurs like Tyrannosaurus rex”6) they nevertheless claim that “Cratonavis has a heavily built skull that is morphologically more like that of non-avialan theropods than most contemporaneous avialans....”7

But how accurate is this comparison? If the evolutionary dino-bird paradigm is stripped away, does the actual fossil denote a bird with the “dinosaurian head” overexaggerated or a dinosaur with the “birdlike body” qualities overexaggerated? The authors had the skull digitally reconstructed (Fig. 2 a and b) and also had an interpretative skull reconstruction (Fig. 2 e), which looks quite different from the digital reconstruction. See Fig. 2 below.

Fig. 2

A Matter of Definition

It is important to understand that there are a lot of terms and definitions used by the authors of Cratonavis’ paper that need attention. First, we need to understand that the word theropod has been changed because of the influence of evolutionary ideas. Its first definition, created in 1881 by Othniel Charles Marsh, grouped all known dinosaurs from the Triassic and the carnivorous dinosaurs from the Jurassic and Cretaceous. But in 1986, Jacques Gauthier gave a new definition for theropods via cladistics (an evolutionary method that infers ancestry) as a group of birds and all saurischians (dinosaurs).8 That is, before 1986, theropod meant a group of dinosaurs. After 1986, this term means a group that includes both birds and dinosaurs. Secondly, because of evolutionary ideas, dinosaurs comprise avian dinosaurs (which they call birds) and non-avian dinosaurs (all the extinct dinosaurs other than birds). So, when they say non-avian theropod, they mean everything from T. rex to oviraptorids, dromaeosaurids, and troodontids. That is, it is a mixed bag of so many different traits and animals that the term non-avian theropods does not really say much about any specific feature.

The Akinetic Skull

Despite the claim that scientists neutrally approach the data, this is never the case.

Kinesis is related to bone movements in the skull. These movements are important for the mobility of the jaws that “increases the versatility and precision of biting, grasping, holding and swallowing of food items, as well as preening of the plumage.”9 Other authors agree, concluding that it “is present in most living birds, occurring in a variety of forms strongly associated with specialized feeding mechanisms.”10 That is, kinesis is related to many functions necessary for animal life. But because evolutionists believe that “The closest nonavian dinosaurian relatives of Aves are thought to have akinetic skulls with an unreduced palatal complex,”11 they mostly relate this feature in the skull to ancestry, evolution, and the relationship between birds and dinosaurs.

Despite the claim that scientists neutrally approach the data, this is never the case. There is no neutrality. We all have a worldview, a way of seeing and interpreting the universe around us. We all have assumptions, concepts, and ideas that influence our interpretations and conclusions. We can see that applied in scientific papers very often. For example, the principal point of the paper is that Cratonavis zhui “exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton....”12 This “unique combination” leads them to interpret those features as “revealing the key role of evolutionary mosaicism in early bird diversification.”13

Summing Up: Oversimplification of Character Traits Leads to “Dino-Bird” Determination

So, with the above “neutral approach” comment in mind, it is important to discern certain points.

1. The first and main conclusion drawn by the authors in the paper regards evolution. As secular scientists, evolution is the idea that permeates their way of seeing and interpreting the universe around them. The data is treated based on evolutionary assumptions, which leads them to conclude that evolution is true. That is, they assume evolution to prove evolution. That is known as circular reasoning, a type of logical fallacy. It sounds and seems logical, but it is not. In the end, they are not proving anything—they are assuming evolution and coming up with conclusions that fit their evolutionary worldview.
2. The paper did not mention any reference of the akinetic skull and its relationship with feeding means. They only address ancestry and evolution. That alone shows their evolutionary bias.
3. The transition of an akinetic skull to a kinetic skull is interpreted as a result of the loss of some bones. However, this idea is countered by other possibilities. “The disappearance of two more structures is attributed by Hofer to the development of the avian type of kinesis, the ectopterygoid and the epipterygoid.” This hypothesis could be true, but there seems to be an alternative explanation.14 Either way, if the loss of the bones was the cause of this “evolutionary transition,” that still does not show any evolution happening as there is no increase of information but a loss.
4. An akinetic skull is not a feature that is unique to dinosaurs. The authors of the Cratonavis zhui paper claim that their “study reinforces the latest hypothesis that a true kinetic cranium is absent over a large part of Cretaceous avialan history.”15 In related work, they suggest that other extinct birds, such as enantiornithines, also presented an akinetic skull. While their findings remain open to other interpretation, it is still reasonable to conceive that this characteristic (if it truly exists in most Cretaceous birds as the authors claim) is related to a function required for different extinct birds’ lives and has nothing to do with evolution. Indeed, there are some modern birds that exhibit what is called a pseudoprokinetic skull.16
5. The fossil record presents challenges—some of the skulls are not found in their entirety, some are crushed, and some are just not found at all. Hu et al. say, “Although the fossil record of stem birds and their closest relatives has grown enormously over the past 3 decades, detailed information concerning palatal morphology in these taxa is extremely rare due to their delicate nature and the crushed, 2D preservation of most specimens. With only few exceptions, the palate is partially preserved in 2D.... Consequently, despite great interest, the origin of the modern avian palate and cranial kinesis from the akinetic nonavian theropod condition remains poorly understood.”17 The structure of the palate, based on evolutionary thought, seems to be related to kinetic movement.18 But the preservation of the palate encounters many challenges. Which brings the authors to admit that they cannot understand much about it. Despite this lack of knowledge, they make many claims of the significance of an akinetic skull to the supposed relationship between dinosaurs and birds.
6. Those challenges presented by the fossil record also lead to possible errors in identifying some skull elements or even interpreting them differently. Wellnhofer presents some of those examples related to the skull bones of Archaeopteryx.
   1. Quadrate interpretations:
      1. a possible sphenoid fragment
      2. bearing a single head, which is a dinosaur feature
      3. bearing a double head, which is a bird feature
   2. Palatine interpretations:
      1. as triradiate, which is a bird feature
      2. as tetraradiate, which is a dinosaur feature.19
   So, when dealing with skull bones, much caution needs to be taken. There are many possibilities of mistakes and that needs to be taken into consideration before making claims and interpretations.
7. Most of the features of the supposed “non-avian theropods” compared to Cratonavis zhui belong to troodontids, oviraptorids, and dromaeosaurids, which have also been considered birds by some secular scientists. Feduccia, in his book published in 2020, suggests and gives evidence that supports the placement of troodontids, dromaeosaurs, and oviraptorosaurs as part of the Aves group.20 That is, when the authors compare Cratonavis zhui to those three groups, he is comparing bird with bird, not bird with dinosaur.
8. Many characteristics Cratonavis zhui presents are the same as other birds, including Archaeopteryx, which, despite some scientists’ attempts to prove the contrary, continues to be considered a bird.

Conclusion

Judging a creature from one fossil specimen is rather difficult, however the Cratonavis specimen shows many features of a bird.

Now we tackle the big question of whether Cratonavis zhui is a bird or a dinosaur (and not some dino-bird mosaic as the evolutionists spin it). Judging a creature from one fossil specimen is rather difficult, however the Cratonavis specimen shows many features of a bird. Keep in mind that there were no clear-cut feathers or definitive feather impressions found on this fossil (but see previous comment on this). There was no keel on the fossil, and a keel is a rather important diagnostic characteristic for flying birds because their flight muscles attach there. But that doesn’t rule out a flightless bird. There are even a few other fossil birds which lack a keel but have other flight muscle attachment sites and could fly (like Archaeopteryx). Also, a keel is a very interesting animal part that can be easily lost in a watery environment. Once the muscles and tendons degrade, it easily becomes disarticulated. Cratonavis has other features too, like a pygostyle, semilunate metacarpals, etc., that are very birdlike. Also, the paper mentions that they found some other features that could have helped the flight system, like an elongated scapula and first metatarsal.

As noted above in the akinetic skull section, this type of skull is commonly thought to be diagnostic of non-avians, but even that assumption has been called into question by evolutionary ornithologists since other birds possess this feature. Much more needs to be known about the habitat and diet of Cratonavis before that question can be answered. The authors of the paper want this to be a mosaic form, although they admit that its morphology is puzzling (like its possessing a toothed jaw, whereas its “slightly older ancestors,” the Confuciusornithidae, have no teeth). The authors even comment on the “plasticity” of fossil bird morphology. It has a supposed mix of primitive and advanced traits which runs counter to the smooth, linear progression from Archaeopteryx to albatross, which is what is always stressed in the dino-to-bird evolutionary story.