The Non-Jawed Chordate Lineages of the World Series Part II

A typical lancelet Branchiostoma. Drawing by Giovanni Maki.

If you recall last time I have briefly talked about the kinds of animals that make up Phylum Chordata, what unites us all in this extraordinary lineage, and some of the conflicting phylogenetic work on the interrelationships among the chordate subphyla. All of this can be read here. Today in Part II of the series will be a post on the lancelets of Subphylum Cephalochordata.

Brief Introduction
The lancelets (also referred to as "amphioxus" or "amphioxi") are small, translucent and elongated fishlike chordates that are entirely marine and live in shallow sandy environments. They are often used in classrooms as "living fossils" to describe the ancestral chordates. I do find "fishlike" to be too broad of a term to describe these marine invertebrates. I would say they look (though vaguely) resemble lamprey larva or fry in overall shape. And despite what professors in college talk about, are lancelets really good model organisms?

Systematics and Evolutionary History
Cephalochordata has the smallest number species of the three subphyla with at least 34 species. They are classified in the Order Amphioxiformes which is also the only extant clade in Class Leptocardii. Within Amphioxiformes we have two families and a total of three extant genera:

• Branchiostomidae which only contains the genus Branchiostoma
• Asymmetronidae which includes the genera Epigonichthys and Asymmetron

Pikaia fossil. Photo by Jstuby.

The fossil record of lancelets is very scarce due to their small, translucent bodies. Needless to say there are at least three fossil genera, which unsurprisingly look like modern lancelets. Indeed lancelets as a whole have virtually unchanged for 530 million years. Although I should point out there is a whole cast of fossil chordates and/or stem-chordates that resemble lancelets such as the relatively famous Pikaia gracilens. These primitive chordates and lancelets probably were similar in anatomy, although it should be noted that these animals can not be placed firmly in any of the three modern subphyla (Lacalli, 2012). Despite this, this makes lancelets prized as lab animals or modeled organisms in college classrooms and labs when discussing about the earliest chordates. I can certainly understand the attraction, although I think we need to be mindful that lancelets could be slightly more derived than an animal like Pikaia. What is more, the probable behavior and some aspects of their biology in lancelets and early chordates was probably a bit different (Morris & Caron, 2012). Needless to say, lancelets still serve a purpose in understanding the evolution of chordate anatomy.

Anatomy

A closeup look at the head of a lancelet. Note the cilia.

As mention earlier the overall appearance of these chordates is somewhat not unlike that of lamprey larva. However lancelets lack a cranium case around the head region, thus they lack a distinctive head shape. The brain is very simple and lacks most of the sensory organs, although they have a photoreceptive frontal organ which is ancestral to the vertebrate eye. The pharynx and the gill slits act as filter-feeding apparatus, which the movement of water containing food particles goes through via cilia action. The cilia are dozens of tentacle-like structures near the opening or the ridges of the mouth known as the "wheel of organ". Another series of tentacle-like organs are the oral cirri which also partakes in the action.

A - Lamprey larva; B - Lancelet adult.

Being a invertebrate it has no true backbone. To protect the notochord lancelets have stiffen cells that surround the region. The notochord extends from the tip of the snout to the end of the tail. In addition to giving the animal support and structure, it also helps lancelets to burrow themselves in the sand in coastal waters. To move around lancelets swim in side-to-side action with the help of the myomeres. The tail is fishlike in appearance and can swim surprisingly well. They do not have an recognizable fins except for a dorsal fin.

But what is peculiar about the overall anatomy of lancelets is that most of the organ systems are alternated on either sides of the animal as opposed to being set in a series of successions on either side seen in vertebrates. Not surprisingly, their organ systems in particular their circulatory system and digestive system is simple in comparison to our own For example the lancelets do not have a recognizable true heart nor neural control for pumping blood; the circulatory system is more large and open and no red blood cells. There is no muscular stomach, liver and pancreas (though midgut cecum might be homologous to the last two organs; Pough et. al, 2005).

Lancelets have multiple gonads that produce large quantities of sperm and eggs (noticed the circular organs in the image above in this post.), which leads us to our final segment for the lancelets.

Life History

Typical feeding fashion. Photo by Colin Gray.

All species of lancelets have more or less the same life story. All species reproduce sexually and spawn sperm and eggs which simultaneously fertilized in the water. Once the young hatch they buried themselves in the sand where they mature. Most of their adult too is buried in the sand, with their heads sticking out as they are filtering out the food from the environment. However lancelets are forever capable of free-swimming animals and they hardly changed their physical appearance. It would probably surprise some people to know that lancelets are considered to be a food source in Asian countries, often used as animal feed for domesticated animals.

What's Next?
The next group will be the tunicates. As they are the most diverse and numerous of the groups that will be cover in this series, there might be a two-part articles concerning them. In the first post of the two articles will be in similar fashion to this article, but in the second post will briefly go over the life histories of the three classes of the tunicates.

References

• Hildebrand, M. & Goslow, G. (2001). Analysis of Vertebrate Structure. John Wiley & Sons, 24-25.
• Lacalli, T. (2012). The Middle Cambrian fossil Pikaia and the evolution of chordate swimming. EvoDevo, 3(1), 1-6.
• Li, G., Yang, X., Shu, Z., Chen, X., & Wang, Y. (2012). Consecutive spawnings of Chinese amphioxus, Branchiostoma belcheri, in captivity. PloS one, 7(12), e50838.
• Morris, S. C., & Caron, J. B. (2012). Pikaia gracilens Walcott, a stem‐group chordate from the Middle Cambrian of British Columbia. Biological Reviews, 87(2), 480-512.
• Pough, F. H., Janis, C. M., & Heiser, J. B. (2005). Vertebrate Life. Pearson/Prentice Hall, 23; 27.

The Non-Jawed Chordate Lineages of the World Series Part I

It is is true that the majority of animals in the Phylum Chordata are jawed vertebrates of the Infraphylum clade Gnathostomata. This is where we, along with other mammals, birds and reptiles, amphibians, and jawed fishes are a part of. It is no surprise that these are often considered to be crowd favorites and among the charismatic species. There is a biases for this as we are gnathostomes like ourselves.

Polycarpa aurata. Photo by Nick Hobgood.

Of course there is more to Chordata than just jawed vertebrates. In fact Chordata has some pretty interesting non-jawed animals. For starters we have the jawless fish, hagfish and lamprey (which sounds like the name of a band if you ask me!) which are surprisingly successful in their own way. As we go further down the evolutionary tree we meet some really cool, alien-like creatures, lancelets and tunicates. These marine invertebrates come in a dazzlingly variety of colors, shapes, and astonishing behavior! It is a shame that these chordates are often in the shadows of us jawed vertebrates, and until recently there has not been much information about them.

This will be the first series presented here on the blog and it will cover the lancelets, the tunicates, the hagfish and the lampreys of the world. We will begin this series with characteristics that unite these non-jawed chordates with their jawed chordate relatives.

The Synapomorphies of Chordata

A diagram of a chordate with the synapomorphies. By Miss Buchheit.

What defines an animal as a chordate is the following that were present at some point in their development (Mallatt, 2009):

1. A segmented, muscular post-anal tail
2. An endostyle
3. A notochord
4. A dorsal hollow neural tube
5. Pharyngeal slits

In adult individuals in Craniata/Vertebrata modified Traits 2-5 into various homologous structures.

• Endostyle becomes the thyroid gland
• Notochord becomes the spine
• Dorsal hollow neural tube becomes the spinal chord
• Pharyngeal slits become the gills (which in jawed vertebrates some gill arches become the jaws) 

Regardless of the physical changes that took place, embryological work has shown that the embryos of vertebrates is very much the same in terms of anatomy with the other chordate subphyla before the changes as mentioned above.

A Brief Discussion of the Evolution and Interrelationships among Chordates

Drawing of the hemichordate Ptychodera flava. By A. Wiley.

According to the fossil record and molecular clocking, Chordata originated from a common ancestor of the Terreneuvian series of the Cambrian (~540 million years ago). We chordates as a whole are part of the Superphylum Deuterostomia which also includes marine invertebrates like the Phylums Echinodermata (e.g. sea stars and urchins) and Hemichordata (e.g. acorn worms).  The latter phylum was thought of as the fourth Subphyla of Chordata due to having a stomochord which was previously thought as a homologous structure to the notochord (Bateson, 1886) and having a similar muscular system (Hildebrand & Goslow, 2001). However recent molecular studies have shown that the stomochord is not homologous to the notochord and that hemichordates are more related to the echinodermates in the clade Ambulacraria (Satoh, 2014). Regardless chordates and ambulacrarians share a common ancestor and share the feature of the blasterspore becoming the anus in development and gill slits.

Within Chordata there are three subphyla:

• Cephalochordata - Lancelets
• Tunicata/Urochordata - Tunicates and Sea Squirts
• Craniata/Vertbrata - Cranium chordates (majority of which are vertebrates)

Both tunicates and lancelets were initially classified in the clade Acraniata. Both groups lack a true cranium and head as seen in the other chordate clade, Craniata. However it has been proven that Acraniata is paraphyletic in respect to Craniata. This lead to the debate over the placement of the tunicates. The traditional theory is that tunicates are a basal branch in Chordata and the sister group to Notochordata (the lancelets and vertebrate clade) based on apomorphies such as extension of the notochord across the body and differentiation in head and tail. Indeed one author went further and classified lancelets as members of the vertebrate Subphylum Vertebrata (Haeckel, 1894). It is commonly thought that chordates are descended from a sessile, tunicate-like ancestor (Pough et. al, 2005).

A more recent theory, however, based on the molecular data is that it is the tunicates, not the lancelets, that are related to the vertebrates in the clade Olfactores (Delsuc et. al, 2006). The evidence for this is largely based on genetic material, although both have neuromast cells. This raises all sorts of question in regarding the evolution of modern chordates and the bio-ecological nature of this common chordate ancestor. I find this to be equally possible that the divergence and relationships among the chordates is trifurcation in origin as we have both evidences supporting in Notochordata and Olfactores. At least one author suggests that the three subphyla should be best be recognized as phyla due to their distinctive anatomy and uncertainty of the sister taxon to the cranium vertebrates (Satoh, 2014) although it is redundant to do so in my opinion honestly as the synapomorphies as listed above are enough to support a single phylum.

The current consensus of the phylogeny of Vertebrata. Diagram by Joseph Keating.

Lastly there is also the issue of the placement of the hagfishes and the lampreys. Despite being similar creatures of habit, both of these jawless fishes share mixed characteristics with each other as (both are jawless fishes with gill pouches) and vertebrates (hagfish have a similar nervous system to vertebrates but the lamprey has a true vertebrate; Hildebrand & Goslow, 2001). As a result there are two theories with equal amount of evidences of physiological data and molecular work. There is Cyclostomata a clade containing our hagfish and lamprey (mostly by the molecular work), and there is Craniata where essentially lampreys are more related to the gnathostomes (mostly the morphological work; Pough et. al, 2005). This is why Craniata and Vertebrata have been used interchangeably in the literature. It is still debated to this day, although as of now the evidence seems to suggest that Cyclostomata is more likely than a lamprey-gnathostome clade as the larval development of both hagfish and lampreys are extremely similar and their "adenohypophysis arises ectodermally" (Oisi et. al, 2013). In other words, this is one of the few morphological evidences that supports the otherwise molecular supported Cyclostomata.

What is Next?
In the next part of the series I will be discussing about the lancelets. As there is only one class of these animals, it will be a short post discussing the bio-ecology of these animals. From there we will work our way to the tunicates and finally the cyclostomes. 

References

• Bateson W. (1886). The ancestry of the Chordata. Q. J. Microsc. Sci. 26, 535–571.
• Delsuc, F., Brinkmann, H., Chourrout, D., & Philippe, H. (2006). Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature, 439(7079), 965-968.
• Haeckel E. (1894). Systematische Phylogenie. Berlin, Germany: Verlag von Georg Reimer.
• Hildebrand, M. & Goslow, G. (2001). Analysis of Vertebrate Structure. John Wiley & Sons, 24-27; 309.
• Mallatt, J. (2009). Evolution and phylogeny of chordates. In Encyclopedia of Neuroscience (pp. 1201-1208). Springer Berlin Heidelberg.
• Pough, F. H., Janis, C. M., & Heiser, J. B. (2005). Vertebrate Life. Pearson/Prentice Hall, 19-23.
• Oisi, Y., Ota, K. G., Kuraku, S., Fujimoto, S., & Kuratani, S. (2013). Craniofacial development of hagfishes and the evolution of vertebrates. Nature, 493(7431), 175-180.
• Satoh, N., Rokhsar, D., & Nishikawa, T. (2014). Chordate evolution and the three-phylum system. Proceedings of the Royal Society B: Biological Sciences, 281(1794), 20141729.

Reptilia? Sauropsida? Diapsida? Sauria?

Komodo Dragon and Hoatzin. Photo by Thore Noernberg. 

During my sophomore year in college I was fortunate enough to have two professors that had their preference for their “ideal” taxonomy and their reasonings behind it. My vertebrate professor loved cladistics. She explained to the class in a lecture once that cladistics is ideal as life is one, big evolutionary saga where lineages (even species) are potentially one and the same. It is all about the last common ancestor. My anatomy professor prefer the traditional Linnaean system, where organisms were classified based on shared morphological traits and there is ranking involved. To her, cladistics can be "rather clunky” and potentially confusing but my vertebrate professor found ranking of organisms is rather silly. They did both agree that it was important to categorize organisms based on relationships - the monophyletic clade the ideal group which biologists love. While most of my peers find taxonomy and systematics to be trivial and a nightmare to study, I find them to be quite enjoyable and also important in understanding not just how organism lineages came to be but also how nature had selected certain behaviors and anatomical features that are best fit for reproduction for a species. I strongly agree we need to categorize organisms into monophyletic clades and I can understand why both of my professors have chosen their prefer taxonomy system. Of course then you have people like Colin Tudge (2000) and Robert Bakker (1986) that tries to combine the best of cladistics and Linnaean taxonomy (known as “Neo-Linnaean”), but that is a whole other animal and one that can be very flawed. More so - in my opinion - than both cladistics and the Linnaean system! Indeed the chose of the taxonomic system that scientists use can affect the way we see the relationship of species. A classic group that beautifully illustrates the point are the reptiles and the birds.

Taxonomic Segregation

Despite the overwhelmingly amount of evidence and the obvious that birds are reptiles, majority of major herpetological and ornithological organizations (as well as some books, particularly field guides) still place reptiles and birds into two separate clades Class Reptilia and Class Aves respectfully. I have yet to see a field guide to birds and reptiles of North America being placed in the same clade together. Even more so there are still people that cannot quite see how birds are reptiles, even though feathers and reptile scales are homologous structures made of keratin, same type of blood, and most important of all molecular and morphological work has shown a close relationship between birds and crocodilians. The problem stems from the fact that in the Linnaean system, a class cannot be in a class. Classes can be sister taxa but that is it and nothing else. It is a paradox for it is not the fact that the world’s ornithologists and herpetologists do not acknowledge this relationship. On the contrary, these majority of these scientists do support the recognition of birds being “glorified reptiles” it is just they prefer the less clunky route. If they are so focused on updating evolutionary relationships (and they do. Taxonomy changes amongst scientists is a vicious, political game. But here is not to discuss that.), then they would lump. General biologists and paleontologists do a good job in placing birds and reptiles in the same clade that could regard as a class. If one were to simply follow the cladistic approach you are truly not only finally acknowledging the evolutionary relationship on paper at these meetings, but you are also helping eliminate “how birds are reptiles” from the public and educate them to understand the closeness. This will end taxonomic segregation.

Divide Reptilia! Wait, No!

This class, according to the cladistic approach, would be the most speciose and successful of all the terrestrial vertebrates, colonizing every single corner on the planet. It would have about 20,808 species worldwide, from the Tuatara to passerines. But what should the name of this class be? You would think that the name for the class would be Reptilia, given the argument that name of ancestral lineages has priority over daughter lineages (a classic example would be when the then Order Pinnipedia was found out to be nested in the Order Carnivora. Pinnipeds are now seen as members of the Order Carnivora). But there is a problem. Some cladistic scientists have argued that the general concept of Class Reptilia is extremely invalid for it is pretty much a synonym of Amniota (Tudge, 2000); stem-mammals (“synapsids”) were originally classified as members of Class Reptilia, but majority of work today suggests they have diverge before true reptiles, adding more fuel to the invalidity of Reptilia. Lastly the most common argument is Class Reptilia did not intended on including the clades Class Aves and Class Mammalia. This left two options. One option by the Neo-Linnaeanists was to make Lepidosauria, Testudinata and Archosauria as classes, which Baker (1986) advocated very much so in his book The Dinosaur Heresies. Other scientists and myself disagree with this. It is redundant and would create confusion in regards to the many fossil reptiles that do not fall within any of these three groups. The second option was of course giving a new name. The name cladistic taxonomists use is Sauropsida.

Class Sauropsida? Or How About Class Diapsida?

This diagram is Reptilia vs. Sauropsida. Diagram by Petter Bøckman

Sauropsida does seem to be a good name. It is define to include the last common ancestor of reptiles, including birds which they most closely related to crocodilians. So not only it is good, but it is also valid as well. However I do have to detest. I never truly see Sauropsida as something as class worthy. Rather I see it as more of a stem-branching that contains stem and crowned animals just as how most scientists view Synapsida. Synapsids contain both stem-mammals and crowned-mammals. I can make an argument that Sauropsida is a stem-branching as it contain both stem-reptiles and crowned-reptiles. Indeed this thought probably never occur as for a while there was a possibility that turtles might be the last, surviving anapsids on the planet. It has become very clear that turtles are definitely diapsids and the definition of a crowned-group is it must contain extant members. Therefore, the anapsids of Parareptilia are not crowned-reptiles as well as the earliest sauropsids and even the early eureptiles in my opinion. Not to mention that all my professors prefer Reptilia over Sauropsida as they feel you can simply redefine the definition and its membership - see Modesto & Anderson (2004) as well for more reading. An old name are better to keep than make a new one, as new names can be redundant to make. Of course this would not eliminate the whole Amniota issue and I would still think Reptilia as a stem-branching group. So if not Reptilia or Sauropsida, then what would be a prefer name for a class of reptiles and birds in a field guide concerning them? Diapsida? Possible, since molecular data has shown all reptiles and birds are descended from a diapsid ancestor (Crawford et. al, 2015). However there are diapsids that fall outside a lineage consisting the lepidosaurs, turtles and archosaurs. They would be stem-reptiles still. So scratch that one off the list. All might seem to be lost. There is, however, one I have found and I actually prefer.

Class Sauria?

Sauria was originally intended as a suborder containing the lizards in Order Squamata. Of course, the name has fallen out of use and is almost obsolete. However I have seen the name a couple of times in some papers, with at least one paper using Sauria as a clade containing the lepidosaurs, turtles and archosaurs and their stem representatives (Crawford et. al, 2014). Sauria would be/is the ideal name for a class. Sauria can be defined as a crown-based grouping for it contains extant members which are our modern day reptiles and birds. The interrelationships among reptiles and birds is still the same, is not at risk of being the same thing as Amniota and it can be use for the designation of class (we would still have the problem of making classes for stem-reptiles, but we have to look at the context for our modern species. Not to mention I feel as if we are coming to a point where “crowned” can equal to a Linnaean ranking, such as crowned-mammals being in the clade Class Mammalia). Lastly we can collectively call reptiles and birds as “saurians”. In short the name of a single clade containing reptiles and birds is ideally Class Sauria. I don’t have high hopes for this catching on, but I do hope someone would also come to the same conclusion as I have. I would love it in the near future to see book stores selling field guides of saurians of North America. Such a thought might cause herpetology to fully divide into batrachology (the science and study of amphibians) and a new field that might merge with ornithology. Perhaps “saurology” and the birth of major saurological organizations and parties?

Birds being a Single Clade Order

Self explanatory; crocs and Tuatara make up 0.02%! Based on the Reptile Database and TiF.

Despite not being the main focus of the article, there is something that also needs to be address as well. How many orders would there be in Sauria? The number of reptile orders is not the issue, it is the number of bird orders. Should Sauria have a total number of at least 50 orders? In my mind that is a bit excessive. Not to mention birds as a group are just as diverse as the squamates, yet I find nobody arguing or suggesting splitting the squamates up into several different orders. One could make an argument that birds are actually a pretty much a homogenized group with feathers, a beaked head and bipedal. Of course bird species do vary in these attributes, but so do various insect orders such as beetles. And for a single order to contain 10,000 species would not be an issue. After all, squamates approach at least 9,000 species. What would the name of the order be? Since birds are descended from theropods and defined as such, it would be Order Saurischia. Under this argument, crocodilians might have a similar predicament as they are descended from rauisuchians (Nesbitt, 2011) so therefore the clade is Order Rauisuchia, not Order Crocodylia. This does not mean we have to call them “saurischians and rauisuchians” from now. We can still call them "birds and crocodylians” as they used much more in everyday usage in regards to modern species. But that is only a suggestion of mine. Still, we need future scientists to finally end the coffin to Reptilia and Aves and bring out Sauria.

References

• Bakker, R. T. (1986). The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction. William Morrow, 165 p.
• Crawford, N. G., et. al. (2015). A phylogenomic analysis of turtles. Molecular phylogenetics and evolution, 83, 250-257.
• Modesto, S. P., & Anderson, J. S. (2004). The phylogenetic definition of Reptilia. Systematic biology, 53(5), 815-821.
• Nesbitt, S. J. (2011). The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History, 1-292.
• Tudge, C. (2000). The Variety of Life. Oxford: Oxford University Press, 407-410. 

Common, Boring Species can be Cool Too!

For my ornithology class we had a midterm paper that was a species account. We could choose any species we wanted and we would also have to present to the class. Of course most of us in the class have chosen charismatic, exotic or endangered species. Only one of my friends has chosen a common, everyday bird we see the Eastern Bluebird (Sialia sialis). Once we were done with the assignment and the presentations, my professor had made an interesting comment.

Male Eastern Bluebird (Sialia sialis). Photo by William H. Majoros 

His comment was that he does not understand why in the years he has been teaching, none of the students he has taught usually never a "common" or "boring" species like a House Sparrow (Passer domesticus), a European Starling (Sturnus vulgaris) and/or the American Robin (Turdus migratorius). While he understood the attraction of exotic/rare/endangered/charismatic species in all vertebrate sciences, my professor made a interesting point in that more common and everyday species are just as complex and exciting to research with. He went further saying how meticulous European Starlings are when it comes to foraging in a flock where each individual has their own space. Or how House Sparrows peck baby bluebirds to death by putting a hole in their skull, or the different dialects of American Robins.

I never really have thought about this before but once he mentioned it I have been thinking about this ever since. Indeed science is a never ending space of knowledge. Sometimes we might be surprised in what we find in common species that was never seen before. For example domesticated cattle or even deer would consume bird nests containing young (Furness, 1988 and Nack & Ribic, 2005) or the complex coevolution between humans and dogs (Schleidt, 2003). In fact domesticated (or at least those we keep as pets) animals in general are just as fascinating as their wild relatives (if not, more!); sometimes majority of the information of the biology, evolution, development and the behavior of our vertebrates comes from mostly common animals (such as lab rodents, chickens, Zebra Finches, catfish). They can even warn us about the state of the planet; if a common everyday species like the Red-winged Blackbird is all of sudden declining in the overall population, that is something to be concern about (Blackwell & Dolbeer, 2001). That is why students and friends in my school often choose to work on more common species for not only the connivence but also the potential data we can obtain!

In essence it goes to show that every species - no matter what they are - are important for not only preserving biodiversity but also for research as well!

References

• Blackwell, B. F., & Dolbeer, R. A. (2001). Decline of the red-winged blackbird population in Ohio correlated to changes in agriculture (1965-1996). The Journal of wildlife management, 661-667.
• Furness, R. W. 1988. Predation on ground-nesting seabirds by island populations of red deer Cervus elaphus and sheep Ovis. Journal of Zoology 216, 565-573.
• Nack, J. L. & Ribic, C. A. 2005. Apparent predation by cattle at grassland bird nests. The Wilson Bulletin 117, 56-62.
• Schleidt, W. M., & Shalter, M. D. (2003). Co-evolution of humans and canids. Evol. Cogn, 9, 57-72. 

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.

South America: Motherland of all things Dinosaurs

Just a quick post. This is something I have always find interesting. South America or the Neotropical Zone has the highest species diversity of birds with 3,000 species (⅓ of the world’s birds); 31 families are endemic in this region of the world (in Brett-Surman et. al, 2012). To make this even more interesting and appropriate, the earliest known stem-bird dinosaurs (in Brett-Surman et. al, 2012) have also been discovered in South America as well. We can even go back further to the stem-bird dinosauriformes and stem-bird dinosauromorphs that have been located here (in Brett-Surman et. al, 2012). What does this all mean? Dinosauromorpha originated in South America and the motherland still has her denizens. Also an excuse to remake Hitcock’s The Birds in South America.

I will admit I was mindblown when I saw this in my ornithology class.

Reference

• Brett-Surman, M. K., Holtz, T. R., & Farlow, J. O. (Eds.). (2012). The Complete Dinosaur. Indiana University Press.

The Evolution of Ophidiophobia

Eve, the Serpent and Death. Painting by Hans Baldung.

2015 has been an incredible year for snake evolution research with the discovery of the oldest known fossil of the stem-snake line Portugalophis lignites (Caldwell et. al, 2015) and a remarkable paper that details the of the origins of snakes from Yale has found that the ancestor of snakes was a nocturnal snake-like lizard that still retain their hindlegs (Hsiang, et. al, 2015). This stem-snake first appeared around 128 million years ago around the same time that stem-therian mammals were starting to appear as well (Hsiang, et. al, 2015).

Remarkable news indeed, but today I won’t be talking about the evolution or the systematic history of snakes. In fact, I am going to be talking a bit about a different kind of evolution, one that focuses on perhaps the most common and reported phobia that humans have - Ophidiophobia, which a third of the total population of humans have (Isbell, 2009). The causes varies among individuals but it is interesting how some individuals have this phobia, even though they might have not see one in the flesh (Isbell, 2009).

Indeed our instinctive fear of snakes can probably be traced to our primate ancestors beginning around 65 million years ago (Isbell, 2009). Indeed primates are a major food source for some of the larger species of serpents. This natural fear of snakes in our human nature accounts for the various cultural depictions of these animals - the most infamous is the serpent tricks Eve to eat the forbidden fruit in the Garden of Eden story and untold stories of giant underwater serpents across the globe. The anthropologist David E. Jones had argued that same evolutionary fear of snakes might explain the independent creations of dragons across the globe (Jones, 2002). This orgy of primal fear and human creativity have produced some of the most astonishing works of fantasy.

Now with these two papers out, perhaps our primal fear of snakes goes further in time. Ophidiophobia might have been an ancestral fear in therian mammals. Like these ancestral snakes, the earliest therian mammals were also nocturnal animals. They would have been a nice meal for these stem-snakes, which the root of ophidiophobia appeared as a survival mechanism for mammals. But as mammals begin to diversify and evolved into the various groups we see today ophidiophobia was certainly lost in different groups. We primates were not one of those mammals that have lost our fear and this is how ophidiophobia came to the world.

References

• Hsiang, Y. Allison et. al (2015). The origin of snakes: revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record. BMC Evolutionary Biology, 15
• Caldwell, M. W., Nydam, R. L., Palci, A., & Apesteguía, S. (2015). The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature communications, 6.
• Isbell, L. A. (2009). The Fruit, The Tree, and the Serpent. Harvard University Press.
• Jones, D. E. (2002). An Instinct for Dragons. Psychology Press.

“Why don't horses have horns?” (You'd be Surprised!)

A Virgin with a Unicorn by Domenichino.

Growing up around horses and having a father that knows a lot about them, you tend to ask every question concerning about their behavior and their biology. My dad can answer any question that is horse-related, but there was one question my dad could not answered me.

“Why don't horses have horns?” I asked him one time. The only response I got from him was a man in deep thought, trying to remember if he ever had read something that could answer my question. But he failed to do so.

During their evolutionary history, horses were a very successful family of ungulates. They have managed to colonize a good portion of the world save for Oceania, the oceans and Antarctica. Yet none of the dozens or so species - living or dead - had developed cranial appendages or hornlike organs on their heads. One would have thought that at least some species might have experimented with it. Some would say horses favor speed over horns in their evolution. While horses and their relatives do rely on their speed and herd strength for their survival, so do a majority of pecorans, the lineage of ungulates were cranial headgear has diversified. So why didn’t they? Why didn't nature selected horses to become real-life unicorns? If you think about it the biological concept of a unicorn - without the magical elements - is a very plausible animal. After all cranial appendages are bifunctional organs that are used for combat and sexual-visual organs of display (Bubenik, 1990; Emlen, 2008).

It was not until a few years ago that I solve the mystery and what I find is surprising. But here is are three points to consider.

It's Very Costly
The cranial appendages are very costly in nature to have. In order for a successful condition of horns or antlers, a multitude of factors come into play: the right resources, the environment being suitable and the health of the animal (Emlen, 2008). If something disastrous were to happen to the animal (such as injury or malnourishment) then there would be a negative affect on the condition of the headgear. Indeed a textbook example would be the White-tailed Deer (Odocoileus virginianus) during hunting season. Hunters have reported seeing individuals with abnormal antler growth or injury, caused by starvation, poor genetics, and injury from other bucks (Rue III, 2000). That is why male pecorans often don’t do as much activity when compared to females. They mostly relax and try to bulk up. That is why osteophagia is common among pecorans (but not in equines), as they are obtaining important calcium for their cranial development (Hudson et. al, 2013; Cáceres et. al, 2013). There even seems to be a correlation with size, with larger pecorans practicing osteophagia more (Hudson et. al, 2013). This leads to the second point.

Hunters are all too familiar with the negative affects of poor health can cause in the develepoment of antlers in deer. Photo by Soos Osborn.

Sexual Selection and Fitness of Males
Sexual selection is a major driving force in the evolution of ungulates. The horn and antler diversity among members of Pecora is no exception to this. A classic example can be seen in Africa’s incredibly diverse antelope fauna. Females selected those males who are able to maintain fitness, maintain their dominance, and fulfill the energy requirement which the cranial appendages demand (Bubenik, 1990; Emlen, 2008). This resulted sexual dimorphism among males and females, often males being bulkier and larger than the females (Bubenik, 1990). Basically the ultimate payoff for such a costly organ is the right to breed and passing on your genes. Similar can be said for rhinos - the evolutionary relative of the horse -, as their horn-shape and bulk often varies among males and females (Bubenik, 1990). It should be noted that some females also have horns as a way to defend themselves and their calves from predators and harassment from males (Geist, 1998).

Sexual selection was the driving force for the impressive variety of horns among bovids. Drawing by Encyclopedia Brittanica.

None of this ever occur in the evolution of horses. For the case of the horse, physical stamina is what matters for them. In contrary to the popular notion of the stallion being the leader of the herd, all species of equines live in matriarchal societies lead by a matriarch. The stallion is best described as the bodyguard and protector of the herd, and his “award” is the right to breed with all the females in the matriarch’s herd. This leads to the third and final point, one I thought that was very interesting.

Biters and Headbutters

While they lack horns, they make up with their teeth. Unknown source.

The Russian ecologist Valerius Geist - known for his work on North American ungulates - had written what I considered to be the best source on cervid deer of the world Deer of the World: Their Evolution, Behaviour, and Ecology. In this book, he has made lots of interesting hypotheses on why large mammals exhibit certain characteristics. This include why pecorans had evolved cranial appendages but not equines. Geist had found an interesting relationship between teeth and headgears. Mammals that have powerful bite forces tend not evolve cranial organs on top of their head. In these mammals, extreme canine teeth (e.g baboons) and tusks (e.g. walruses, elephants) had evolved as combat organs instead. Cranial headgear mammals, like pecorans, on the other hand generally do not have powerful bite forces, especially with the reduction in upper teeth in horned ungulates (Geist, 1998). Instead they using their head instead as a weapon (Geist, 1998).

When looking at the mandibles of equines and comparing them to, say, a bovid skull, equine jawbones are more robust. Indeed stallions, knowing from personal experiences with working with horses, are among the most dangerous animals to work with. You would be lucky if they kick you instead of biting you, because when they bite, they bite. Hard. They can cause a lot damage, including breaking your skin and even crushing bone. As mention earlier in this post, the stallion needs to use every energy in his body to protect his harem of mares and their young and use any means necessary in combat. Often times there is a lot of biting involved. With all of this said, we can finally answer my childhood question and the reason is this - natural and selective pressures favored equines to be bitters still, and that any cranial headgear would be costly or redundant.

Equines fight dirty - lots of kicking and biting involved. Photo by Fred Holley.

To sum up what we have, while horses lack the headgear their distant pecoran cousins have, stallions need the energy saved to protect the matriarch's herd from rogue males and predators. The amount of energy required for this is costly, if not more so than to have horns or antlers (Riechert, 1988). It would have been too much to have these organs for what stallions do. That is why they mostly kick, chase and bite at their predators and rival males instead. Similar can be said for other ungulates such as tapirs, camelids, swine, peccaries, chevrotains, musk deer and hippos. Like equines, they too rely on their teeth and powerful jaws to combat. These three points have finally answered my childhood question that my father could not have answered. Or does it? As Geist points out, there was one family of ungulates that had both used headgear and teeth for combat. 

Rhino-like "Horses"

Life restoration of Megacerops coloradensis. Artwork by Dmitry Bogdanov.

The fossil perissodactyl family Brontotheriidae were the among the first terrestrial mammals to have become truly massive during the Eocene. Indeed their large size is what made them such icons to the public, but what is more is in some of the species there appears to be conspicuous frontonasal horns (Bales, 1996; Mihlbachler, 2008). Unlike the horn of a rhino which is made of keratin the horns of brontotheres were made of solid bone. Of course this was common in the larger and more later species but all brontotheres have powerful jaw bones and large teeth. This has hypothesize that brontotheres were unique in that they were among the few mammals (if not, only) to have evolved both horns and teeth as combat weapons (Geist, 1998). But what makes them even more interesting is not so much of their overall size or the weapons they have - rather it is their evolutionarily relationship with today's equines.

Skull of Megacerops coloradensis. Note the jaw shape, the teeth and horn. Photo by Alan S.

Brontothere systematics is relatively well documented as at least 41 different species have been described (Froehlich, 1999; Mihlbachler, 2008 and Holbrook & Lapergola, 2011). An incredibly diverse family, the earliest brontotheres were small and vaguely pony-like. These early forms lacked horns, although as some brontotheres got larger some species evolved horns (Bale, 1996). While the larger species have a vague resemblance to rhinos these two families were not closely related at all. In fact the placement of brontotheres among the perissodactyls was not fully understood. It was commonly assumed that brontotheres were a basal lineage of perissodactyls that was only distantly related to the other families. Recent discoveries and new systematic work might have found where exactly brontotheres fit on the tree of life. According to these recent work, brontotheres might have been descendants from the same ancestral that also evolved into horses. In other words, Brontotheriidae and Equidae are sister taxa (Holbrook & Lapergola, 2011) and both are descended an ancestor that used teeth and biting for combat. In essence brontotheres were "horses" that had evolved to become bulkier. Larger mammals tend to conserve more energy than smaller mammals (Lundstedt & Burke, 1985), the brontotheres could have afford using the energy required for the growth and development of their horns as with modern horned or antlered ungulates. While brontotheres were evolving, the evolution of the horse and other equines favored physical stamina as their weapon.

With that being said, it depends on how you answer it and the reasoning behind your answer. The family Equidae never evolved horns or antlers as nature did not select them to be such creatures. Yet the family Brontotheriidae certainly did evolved horns. and given the closeness of these two families, one could make an argument that "horses" did - at some point in their evolution - evolved horns. Just that these "horses" looked more like rhinos and less like the mythical unicorns. Yet this might be the closet thing we will ever get in nature selecting "horses" becoming unicorns.

References

• Bales, G. S. (1996). Heterochrony in brontothere horn evolution: allometric interpretations and the effect of life history scaling. Paleobiology, 481-495.
• Bubenik, A. B. (1990). Epigenetical, morphological, physiological, and behavioral aspects of evolution of horns, pronghorns, and antlers. Horns, Pronghorns, and Antlers (pp. 3-113). Springer New York.
• Cáceres, I., Esteban-Nadal, M., Bennàsar, M., Monfort, M. D. M., Pesquero, M. D., & Fernández-Jalvo, Y. (2013). Osteophagia and dental wear in herbivores: actualistic data and archaeological evidence. Journal of Archaeological Science, 40(8), 3105-3116.
• Emlen, D. J. (2008). The evolution of animal weapons. Annual Review of Ecology, Evolution, and Systematics, 387-413.
• Froehlich, D. J. (1999). Phylogenetic systematics of basal perissodactyls. Journal of Vertebrate Paleontology, 19(1), 140-159.
• Geist, V. (1998). Deer of the World: Their Evolution, Behaviour, and Ecology. Stackpole Books, 5-8.
• Holbrook, L. T., & Lapergola, J. (2011). A new genus of perissodactyl (Mammalia) from the Bridgerian of Wyoming, with comments on basal perissodactyl phylogeny. Journal of Vertebrate Paleontology, 31(4), 895-901.
• Hutson, J. M., Burke, C. C., & Haynes, G. (2013). Osteophagia and bone modifications by giraffe and other large ungulates. Journal of Archaeological Science, 40(12), 4139-4149.
• Lindstedt, S. L., & Boyce, M. S. (1985). Seasonality, fasting endurance, and body size in mammals. American Naturalist, 873-878.
• Mihlbachler, M. C. (2008). Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History, 1-475.
• Riechert, S. E. (1988). The energetic costs of fighting. American Zoologist, 28(3), 877-884.
• Rue III, L. L. (2000). Way of the Whitetail. Voyageur Press, 88-93.

What Happen to Learning about Anatomy?

Something a bit different today and this is what I have noticed at my zoology classes. I don’t know if it is something due to with the classes being more or less introductory courses, or it is the professor that sets up the class, but I am surprised with the lack of material that concerns on anatomy. I mean, sure in the vertebrate zoology class and in the ornithology course the professors had talked to some detailed about major, unique features in vertebrates. Yes I know there is so much to know in a semester worth of class. And yes, sometimes the professor is more comfortable in the ecology and evolution of the groups they are experts on as opposed to the anatomy.

The reason I bring this up is in my spring semester when I was a sophomore, I took a comparative anatomy class. Before hand I knew this would probably be the hardest zoology class I will ever take, as I am only aware of the basics of the vertebrate anatomy. Sure enough it was a hard class, but it was still interesting and I have learned things I had not before. Not to mention it also shows just how unique lobe-finned fish and mammals are (the theme for the class was mostly the evolution of crowned mammals, with lobe-finned fish being the starting point). What made it hard was the lack of a good, up-to-date vertebrate anatomy textbook. The one we had was a dated 5th edition of Analysis of the Vertebrate Structure by Milton Hildebrand and George Goslow. The book was fine, although it was heavily Linnaean in its taxonomy, lack of good pictures and the professor noted some “errors” in the book she found. Not to mention that, instead of the chapters being center on the various chordate or vertebrate groups, the chapters are instead based on the various body systems. Which is maybe fine for some people but it became very disorienting for me.

Despite the flaws, it is still a decent book. Though be warn of scaly, cold-blood dinosaurs. Photo by Wiley Press.

As a result whenever I had to study for the class exams, I would find myself going to the library and reading the anatomy chapters in the ichthyology, herpetology and mammalogy textbooks instead of the textbook for the anatomy class. I guess in a way it actually helped me be a better researcher and taking notes in a field I was not aware of. But what is the point in having a textbook that does not do the job that you need it? So I began to search for a better vertebrate anatomy textbook. But as I search for such a textbook, I discovered that there was no books that are better than the textbook for my anatomy class in the library. None online either. I guess most of the anatomy that is covered in the various vertebrate or chordate groups can be find in those specific textbooks I have used instead. Perhaps one day there will be a book suited to more of my liking. Here are my three suggestions for the ideal anatomy book (if you happen to find such book, or a good vertebrate/chordate anatomy textbooks, feel free to comment them below!):

1. Have the book be up-to-date and use cladistics. Life is no longer just categories or rankings, but one huge whole of the same coin.
2. Chapters on clades or groups (for example, chapter one will be on lancelets, tunicates, lampreys and hagfish, chapter two on cartilaginous fishes, and so forth), and not on the body systems. Quicker and faster to look up and obtain the information needed.
3. Very good and highly detailed drawings and photographs. Anatomy can be pretty complex or overwhelming to learn for a beginner.

Of course there will still be the issue of the lack of depth in anatomy in class. Indeed even some of the newer textbooks for the various vertebrate sciences seem to be cutting down the information about anatomy and not as in-depth as it was in the older textbooks that I have read in the library. We should not briefly glance over anatomy. We should still study it extensively as it still has implication in the evolution, the ecology and the conversation even to help species. But we also must make it in a more coherent manner, one that will not scare away students who are not familiar with anatomy. For this to be successful there must be cooperation between the education industry, the professors and the students for this to happen.

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.

Greetings

Hello, this is my first blog as well as first post. My name is Christopher Rigobello and I am currently a B.S. Zoology Major student in SUNY Oswego. The blog will have interesting topics on animals, some breaking news, thoughts, reviews and some cool personal artwork.

As the blog name suggests, this blog is dedicated to animals of the phylum Chordata which is the group that contains the most remarkable animals to have evolved. These would include lancelets, tunicates and of course, us vertebrates. Chordata is defined as a monophyletic group that contains all animals that have a notochord at some point in their development.

Short post, but hopefully I will be posting more really cool stuff in the future! See you later my fellow fish!

Chordates are an incredibly diverse group that includes animals such as Humans (Homo sapiens) and Giant Pyrosomes (Pyrosoma spinosum). Image by TrickieDickie99