Tetrapterygidae? More like "Anchiornithidae"!

Somewhat of a spiritual sequel to my Protoavis article I do want to discuss another idea that Chatterjee had purposed in the second edition of his book The Rise of Birds: 225 Million Years of Evolution. On the chapter of the origin of birds where he reviews and discusses on the relationships among theropods, Chatterjee took note that some taxa that have usually been classified as deinonychosaurs (the group that includes the two “raptor” families Dromaeosauridae and Troodontidae) might be closer to the clade Avialae (the stem branch that leads up to our modern crowned birds). In particular a new family he has created for a particular bunch of paravian dinosaurs that are seen proof for the naturalist William Beebe's "four-winged" bird Tetrapteryx.

In the past few years large systematic analyses have shown this complex relationship of these two paravian clades. In particular there is the notion that Troodontidae and two of the subclades of Dromaeosauridae - Unenlagiinae and Microraptoria - might be closer to the ancestry of birds than they are related to Eudromaeosauria (Agnolin & Novas, 2013; Godefroit et. al, 2013 and Lefèvre et. al, 2014). Thus “Averaptora” is the clade defined as paravians closer to Passer but not to Deinonychus (Agnolin & Novas, 2013), thus consists of Troodontidae + ((Microraptoria + (Unenlagiinae + Avialae)). This makes Deinonychosauria paraphyletic.

This also has huge implications on a group of paravians that have been somewhat problematic. I am of course talking about the genera Xiaotingia, Aurornis, Anchiornis, and Eosinopteryx. These paravian genera have been placed all over the tree, with some commonly suggesting they are basal troodonts (Godefroit et. al, 2013; Brusatte et. al, 2014), archaeopterygids (Xu et. al, 2011), or basal avialans (Lefèvre et. al, 2014). Despite these different placements for these paravians there is one thing they all had in common - they always come out as a monophyletic clade. True there are some papers that have disputed this, whether that the genera are really a mixbag of basal paravians of different ancestry (Senter et. al, 2012) or a paraphyletic grade in respect to the rest of Avialae (Lefèvre et. al, 2014), but majority of the systematic work has support a monophyletic family of sorts otherwise.

Reconstruction of the conceptual Tetrapteryx by William Beebe.

This is where Chatterjee comes in. He created the family Tetrapterygidae (in honor of good ol' Tetrapteryx) where he used the character trait of a biplane bauplan (basically long feathers on the arms and legs) as a synapomorphy (Chatterjee, 2015). This meant that Xiaotingia, Aurornis, Anchiornis, and Microraptor are members of this family and as a whole are the sister taxon to Avialae (Chatterjee, 2015). However there is a problem with this as he is only using one character. Most other work uses at least 1,000 characters! This affects the overall phylogeny of Paraves. What I find peculiar is Chatterjee seems to be completely unaware that Archaeopteryx being biplane bauplan animal (Foth, 2014) and not the “monoplane bauplan” Chatterjee claimed it was (Chatterjee, 2015), and the fact he only place Microraptor in Tetrapterygidae but not other microraptorans (Sinornithosaurus was placed in Dromaeosauridae) despite Microraptora being an otherwise a widely supported monophyletic group (particularly them being “four-winged” dinosaurs; e.g Gong et. al, 2014 and Han et. al, 2014). In addition he places Eosinopteryx as a basal paravian and Deinonychosauria (to some extent) as a monophyletic group (Chatterjee, 2015), which is perhaps not the case.

As you can tell, Chatterjee needed to add more characters and more taxon which he was in lacking of. If he would have done otherwise, he might have come to more similar results with other, more comprehensive systematic work (such the concept of Averaptora versus Deinonychosauria). Not to mention that just because Eosinopteryx lacks the feathering does not mean it is not related to these other “four-winged” dinosaurs. Based on modern families of birds and mammals, there can be quite an extraordinary variance among the family’s taxa (I am thinking of Phasantidae and Anatidae especially!) so it would not be surprising if one of these "four-winged" dinosaurs lacks any feathering on their legs. That is why some paleontologists might consider Chatterjee’s work as cringe worthy for he seems to not have an open mind or a pragmatist concerning the subject and the characters he uses is not sufficient. Lastly, why name a family of animals where there is no such genus as Tetrapteryx to begin with? You need the type genus as the basis for the family name. This automatically makes this family invalid according to the Article 29.1 of the ICZN! It should be "Anchiornithidae" instead!

Does this make "Anchiornithidae" invalid? Not necessarily, but perhaps only of Xiaotingia, Aurornis, Anchiornis, and Eosinopteryx. Microraptoria as a whole may be included as well, but some earlier work suggest otherwise for the time being. It would be interesting to see what other workers have to say about this, as well as testing out the placement of these stem-birds among Paraves. I would not be surprise if the family turns out to be a basal Avialae family (perhaps a sister taxon to Archaeopteryx perhaps? a junior synonym of Archaeopterygidae? or if "Anchiornithidae" is another family in Archaeopterygiformes?). But as mention earlier the evolution of flight and feathers is a complicated story (Godefroit et. al, 2013), and is possible that "Anchiornithidae" are paraphyletic in respect to the rest of Avialae. But these are just mere speculations and only time will tell. We need a more comprehensive data and multiple characters and not the old fashion using a single trait that Chatterjee had used.

Further Reading
The awesome Matthew Martyniuk on his blog DinoGoss recently discussed this as well. He more or less said the same thing as I said, although he made an interesting comment I was not aware of. His post can be read here.

References

• Agnolin, F., & Novas, F. E. (2013). Avian Ancestors: A Review of the Phylogenetic Relationships of the Theropods Unenlagiidae, Microraptoria, Anchiornis and Scansoriopterygidae. Springer Science & Business Media. 
• Brusatte, S. L., Lloyd, G. T., Wang, S. C., & Norell, M. A. (2014). Gradual assembly of avian body plan culminated in rapid rates of evolution across the dinosaur-bird transition. Current Biology, 24(20), 2386-2392. 
• Chatterjee, S. (2015). The Rise of Birds: 225 million Years of Evolution. Johns Hopkins University Press, 45-48. 
• Foth, C., Tischlinger, H., & Rauhut, O. W. (2014). New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature, 511(7507), 79-82. 
• Han, G., Chiappe, L. M., Ji, S. A., Habib, M., Turner, A. H., Chinsamy, A., ... & Han, L. (2014). A new raptorial dinosaur with exceptionally long feathering provides insights into dromaeosaurid flight performance. Nature communications, 5. 
• Godefroit, P., Demuynck, H., Dyke, G., Hu, D., Escuillié, F., & Claeys, P. (2013). Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature communications, 4, 1394. 
• Godefroit, P., Cau, A., Dong-Yu, H., Escuillié, F., Wenhao, W., & Dyke, G. (2013). A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature, 498(7454), 359-362. 
• Gong, E. P., Martin, L. D., Burnham, D. A., Falk, A. R., & Hou, L. H. (2012). A new species of Microraptor from the Jehol Biota of northeastern China. Palaeoworld, 21(2), 81-91. 
• Lefèvre, U., Hu, D., Escuillié, F., Dyke, G., & Godefroit, P. (2014). A new long‐tailed basal bird from the Lower Cretaceous of north‐eastern China. Biological Journal of the Linnean Society, 113(3), 790-804. 
• Senter, P., Kirkland, J. I., DeBlieux, D. D., Madsen, S., & Toth, N. (2012). New dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the evolution of the dromaeosaurid tail. PloS one, 7(5), e36790. 
• Xu, X., You, H., Du, K., & Han, F. (2011). An Archaeopteryx-like theropod from China and the origin of Avialae. Nature, 475(7357), 465-470.

Protoavis and Brief Insight in the Herbivory in Theropoda

Everyone who is interested in the evolution of birds should at least be aware of the controversial Protoavis texensis. For those who have not the slightest of idea, this taxon was found in 1987 and described in 1991 by Sankar Chatterjee after finding them in a quarry in Texas, which date back to the Late Triassic period. After studying the remains of the animal, Chatterjee claims that he discovered the world's oldest known bird - a creature older than Archaeopteryx lithographica by 75 million years! It would have been a remarkable and revolutionary discovery IF not for the extremely fragmentary nature of the bones. This post will discuss briefly on Protoavis and its controversial history and a possible connection with the evolution of herbivory in theropods.

What in the World is Protoavis?
Chatterjee promotes it as the oldest known bird. Not only just that, but he also argues that Protoavis is the sister taxon to Pygostylia (the clade that contains our crowned birds and stem-bird avialans with a short, stubby tail) as it shows anatomical features more akin to Pygostylia than to earlier stem-bird maniraptorans (e.g, Chatterjee, 1997). This would mean that not only would be more older than Archaeopteryx but more derived as well. Not just that, but it would also mean that all of our major coelurosaurian lineages (especially those of Maniraptora and Paraves) have already been established at this time some 225 million years ago!

It was not surprising that there is a lot of criticism. The critics who have examine the material have stated that there is nothing uniquely avian about this animal - there seems to elements similar to more primitive theropods such as coelophysoids (after Chiappe & Witmer, 2003). Not to mention, Chatterjee seemed to have destroyed the matrix where it comes from (resulting in some of the bones to break as well), and thus losing context. This resulted in the on-going debate whether Protoavis texensis is a bird, an indeterminate theropod or even a chimera of different species that happen to mix up (after Chiappe & Witmer, 2003).

Where are the Bloody Photos???

As far as I am aware of, this is the only photo there is of Protoavis texensis. Photo by Chatterjee.

Before we get to the next topic, I wanna address something. One of the things I have found most interesting the most is, for a fossil that is claimed to be very extraordinary, there is hardly any photos. The only photo I am aware of is a somewhat decent quality photo that is found on the Wikipedia page for Protoavis. It is too hard to make out any sort of positive judgement if the bones do belong to a single species and, if so, are they truly avian? I am surprised that Chatterjee has failed to produced additional photographs, especially on individual bones.

The next closet thing to see the bones for people (or at least for me) are the drawings Chatterjee provided in his book The Rise of Birds: 225 Million Years of Evolution. There are two editions and I have read both. The drawings are, however, more or less the same. The drawings are pretty detailed and look pretty avian. But the problem is that the drawings are based on his interpretations. Other scientists had given a look and offer contradicting interpretations as the kind of animal Protoavis is. Another thing worth mentioning is it is frown upon to conduct any sort of phylogenetic studying based on photos and drawings of poor-quality fossils as you miss some important detail.

Not exactly from the book, but this is the sort of thing that occurs a lot. Note the comparison and contrasts with the photo above. Reconstruction by Chatterjee.

The best thing is for someone take more photos of the fossil or do a digital 3D scan/modeling and post it online. It would still not be using the actual fossil, but it is better than using a picture and studying in the realm of 2D format. With that said, let us move on.

Herbivory in Theropoda
Until in the last score Theropoda was seen as a clade of mostly flesh-eating dinosaurs. This includes some of the most iconic dinosaur genera of all time such as Tyrannosaurus, Velociraptor, Allosaurus, and so forth. Yet there has been a stacking amount of evidence is showing that theropods had evolved herbivorous or omnivorous diets independently from time and time again. Indeed living theropods the birds have done a fantastic job in exploiting different diets.

Of course the understanding of the dietary change in theropods is still not 100%. It has the potential, however, to play a major role in the evolution of birds, in regards to the the avian beak (Zanno & Makovicky, 2010). Bird beaks are covered in a special keratin call rhamphotheca that covers the outing. Herbivory might have had evolved early on in the evolution of crowned birds (Zhou & Zhang, 2002). Below is a list of known herbivorous stem-bird theropods:

1. Elaphrosaurs
2. Chilesaurus diegosuarezi
3. Ornithomimosaurs
4. Therizinosaurs
5. Oviraptorosaurs
6. Jeholornis prima

How does this got to do with Protoavis? Well, there are actually some things that Protoavis and  Lineages 1-6 had in common: they have small box-shaped heads with long necks for probable foraging. The premaxilla of lacked any teeth and there seems to be lack of tooth replacement (Zanno & Makovicky, 2010). Given that the rhamphotheca beak had evolved twice in elaphrosaurs (Lineage 1) and coelurosaurs (Lineages 3-6) (Xu et. al, 2009), whose says it did not occur in earlier lineages in the Triassic? In addition the Triassic was a time where vertebrates were continuing to experiment and evolve herbivory (Reisz, 2000) perhaps theropods had experimented eating plants early in their evolution at this time. Perhaps Protoavis was a herbivorous theropod that might have mosaic features linking coelophysoids and more derived neotheropods. Again, this is assuming the remains do not suggest a chimera.

In some of the therizinosaurs and ornithomimosaurs elongated forelimbs were used for grasping and hooking on to branches (Lautenschlager, 2014). This could be a more reasonable reason for the wing-like forelimbs in Protoavis. Protoavis also has a manus that is similar to a modern bird, especially in the reduction of the digits. However this can be seen in elaphrosaurs and Chilesaurus (Novas et. al, 2015) and their arms were too short for them to able to thrust off and fly. This suggests that this did not coevolve with flight (just as how feathers are seen nowadays). Why the forelimbs and fingers are reduced is not clear, but it is possible they have lost their function as they became more cursorial.

Probably a more ideal and less controversial statement? Please note that I might have accidentally made the neck too long or the forelimbs too short. Might update this in the near future. Art by yours truly.

Looking back at the photo with this in mind, it is quite possible that Protoavis is a pretty revolutionary dinosaur. But for a different reason. Instead of the flying, Triassic "bird" that Chatterjee had envision, Protoavis might have been a terrestrial herbivore that used its forelimbs for - not for flying - but for hooking and grasping branches to reach for leaves. Long legs meant it had to be a fast sprinter to escape the jaws and teeth of predatory stem-crocodilians, other dinosaurs, stem-mammals and crowned mammals. But this requires a fresh look at the material with an open, clear mind before hand in order to understand the validity of Protoavis texensis, the biology and its phylogenetic placement. To quote Sherlock Holmes in A Scandal in Bohemia:

"It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts."

Further Reading
Jaime A. Headden did a fantastic job discussing the evolution of herbivorous theropods in his blog "Gilong", which can be read here.

References

• Chatterjee, S. (1997). The Rise of Birds: 225 Million Years of Evolution. Johns Hopkins University Press.
• Chiappe, Luis M., & Witmer, Lawrence M. (Eds.)(2003). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, California, 7-9.
• Lautenschlager, S. (2014). Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution. Proceedings of the Royal Society B: Biological Sciences, 281(1785), 20140497.
• Novas, F. E. et, al. (2015). An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature.
• Reisz, R. R., & Sues, H. D. (2000). Herbivory in late Paleozoic and Triassic terrestrial vertebrates. Evolution of Herbivory in Terrestrial Vertebrates. Cambridge University Press, New York, 9-41.
• Xu, X., et, al. (2009). A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459(7249), 940-944.
• Zhou, Z., & Zhang, F. (2002). A long-tailed, seed-eating bird from the Early Cretaceous of China. Nature, 418(6896), 405-409.
• Zanno, L. E., & Makovicky, P. J. (2010). Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution. Proceedings of the National Academy of Sciences, 201011924.