Sci-Day 15: Speciation

Happy Sci-Day, everyone! This week will be somewhat related to last week's topic, as well as topics that I will be covering related to evolutionary biology in future posts. The topic for today is speciation - basically, the formation of new, distinct species.

The reason this relates to last week's post is because in order to understand how a 'species' is formed, we have to have some idea of what a species actually is. Speciation basically involves the splitting of an original, single population of organisms into two new populations, each of which is reproductively isolated from the other. Through some process, whether that is biological or abiotic, this isolation means there is no gene flow between the two populations, leading to independent evolution in each new population. Over time, mutations build up in each lineage, and they become more and more distinct (This could be purely on a genetic level - there don't necessarily have to be any evident morphological differences).

There are two main modes of speciation, defined by the process that split the original population. The first mode, and the one that is the easiest to identify in paleontology, is called allopatric speciation. In allopatric speciation, the ranges of the two new populations do not overlap - one example would be a large mountain range rising within the range of some species, where populations of that species on one side of the range are isolated from the population on the other side due to geographical factors - the species cannot cross that new barrier and as such the population is split.

A second type of speciation that is a bit harder to examine, especially from a paleontological standpoint, is called sympatric speciation. Unlike allopatric speciation, the ranges of the two new populations are not separated geographically - the two populations at least partially overlap at some part of their range. Since observing sympatric speciation relies primarily on genetic/molecular data, it is not exactly an issue that paleontologists can investigate with long-extinct creatures. For that reason, we will focus on allopatric speciation.

There are two main subtypes of allopatric speciation - these are allopatric and peripatric. The difference is that for peripatric speciation, rather than an existing population being split by the creation of some barrier to gene flow, some portion of a population enters a new area that is geographically isolated from the rest of the population. One very good example of this mode of speciation is island colonization by various organisms. Many islands across the world are formed by volcanism, rising up over many thousands of years to finally break the surface of the ocean. This means that no terrestrial organisms exist there to start out with. Basically, through some process, plants and animals from other islands (or perhaps even the mainland) manage to colonize the new island - since said island is geographically isolated from the original population, over time there will be a divergence.

Out of the two subtypes, allopatric is the most easy to observe in paleontology. This is because we have a good understanding of the movement of tectonic plates through geological time, and thus we can understand how continents moved, mountains formed, sea levels changed, etc. There are mounds of easily observable evidence of this type of speciation throughout organisms in history.

As many of you all know, all of the continents were joined into a single landmass called Pangea during the Triassic period. This meant that any population of terrestrial organisms had relatively continuous gene flow - there were no seas to split up these populations. This is why we see very closely related organisms from Triassic rocks across continents that today are thousands of miles away from each other. An example would be Coelophysis - while Coelophysis bauri is found in the Southwest United States, there are closely related species (sometimes even classified in the same genus) in Africa - this is because at that time, there was little to no isolation.

Throughout the rest of the Mesozoic, the continents began to split up, and we can actually see the effects it had on diversity and speciation over time by looking at species from different stages. In the Late Jurassic, we find species of Allosaurus, Ceratosaurus, and Torosaurus from both the Western United States and from Portugal, because during that time those regions had only just started to split up - the populations had only recently become isolated and as such had not diverged all that much.

Another very cool pattern we see is due to the fact that there was a clear North-South divide in the way the continents split, and this is reflected in the types of Theropods we find on different continents. In the Northern continents such as Asia and North America, Tyrannosauroids dominated as the largest carnivores during the Late Cretaceous, whereas the Abelisaurs dominated the Southern continents at that time. We do not find any Abelisaurs in those Northern continents at that time, nor do we find Tyrannosaurs in the South. However, another note is that we see closely related Tyrannosaurs [and dromaeosaurs] in both Mongolia and Western North America. This is because Asia and North America had only split relatively recently, much more recently than the split that resulted in the North-South divide.

Another interesting thing is that North America was split in two during much of the mid to late Cretaceous by a shallow sea, creating two subcontinents called Laramidia [on the west side] and Appalachia [on the East side]. While we have a rich collection of fossil organisms from Laramidia, there is very little material of that age from Appalachia. Since this sea would have isolated any species that ranged across the continent prior to the rise of sea levels, it is certainly plausible, if not probable, to assume that Appalachia would have been home to organisms somewhat similar to those in Laramidia, but still somewhat distinct. However, until more remains from Appalachia of the relevant age are recovered, we will not know to what extent this is true, if it is at all.

Well, I hope this has helped you learn about the fascinating topic of where species come from! Have a wonderful weekend, everyone!

Creature Feature 17

Hello, Dinosaur Battlegrounds fans! Today's creature feature is going to be a grab bag - I'm going to cover most of the remaining species of dinosaur from Hell Creek that have not been addressed in previous Creature Features! This is because the majority of the remaining dinosaurs are known from relatively fragmentary remains (or as in the case of Struthiomimus, are so similar to creatures that have already been featured that there is very little to add), so there is not much I can really say about any of them individually. Thus, I would not want to take a whole week to write just a tiny amount about one species. Without further adieu, here are some of the last few dinosaurs from Hell Creek!

Sphaerotholus buchholtzae

 Sphaerotholus buchholtzae model, WIP. Model primarily based on Stegorceras due to extremely fragmentary nature of Sphaerotholus material.

Sphaerotholus buchholtzae was a highly derived Pachycephalosaur, initially described from a partial skull. The genus Sphaerotholus was quite long-lived, with the earliest species S. goodwini from the Late Campanian showing that this genus lasted for at least 7-8 million years (Carr and Williamson, 2002).

Some researchers believe that this taxon is actually synonymous with Prenocephale edmontonensis (Sullivan, 2003), though recent research based on new S. buchholtzae material (a complete postorbital) seems to support its status as a distinct taxon (Mallon et al., 2015).

"Leptorhynchos" elegans

[Model for this taxon has not been made yet, as I need a copy of the Anzu model to make it]

The reason the scientific name is in quotation marks in this case is because the remains from Hell Creek are assigned to this species but most likely represent a unique taxon (whether this is a new genus or just a new species of Leptorhynchos is uncertain), and thus this name is being used until a new name is proposed and accepted. Leptorhynchos elegans was a species of Caenagnathid Oviraptorosaur (belonging to the same family as Anzu), known from the Late Campanian of Western North America. Distinct characters for this genus include small size, a short, robust mandible, and an upturned tip of the beak (Longrich et al., 2013). In the future I will try to communicate with these authors and perhaps others so that I can figure out the best way to go about making a model of the similar taxon from Hell Creek.

Avisaurus archibaldi

 Avisaurus archibaldi model, WIP. In-game version will be feathered.

Avisaurus archibaldi was one of several avian theropods from the Hell Creek formation, and unfortunately both A. archibaldi and its sister taxon A. gloriae are known only from the tarsometatarsus (a single bone in the foot) (Varrichio et al., 1995). Avisaurus was a genus of enantiornithine - the most abundant group of avian dinosaurs in the Mesozoic. They were extremely similar to modern birds, though most retained teeth and clawed fingers on their wings. The tarsometatarsus of A. archibaldi measures 73.9mm, which is the longest known in any enantiornithine (Varrichio et al., 1995). It was one of the largest volant [flying] dinosaurs from the Late Cretaceous, with an estimated mass of 5kg (Longrich et al., 2011).

Cimolopteryx maxima

[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]

C. maxima was a species of Charadiiforme bird, known from several late Maastrichtian formations. It was a rather small bird, approximately the size of a small gull (Hope, 2002). It is known almost exclusively from isolated coracoids, though their anatomy is distinct enough for several species to be identified (currently four species are recognized). C. maxima was an estimated 2kg in weight (Longrich et al., 2011).

Brodavis

[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]

B. baileyi was a species of freshwater hesperornithiform bird, known only from the holotype - a single left metatarsal. The genus Brodavis belongs to its own family, Brodavidae. Interestingly, while the marine members of the Hesperornithoform order appear to have lost volant abilities by the end of the Cretaceous, the minimal amount of pachyostosis in Brodavis suggests that it may have had at least a limited ability to fly (Martin, 2012). One of the unnamed Hesperornithiforms from Hell Creek was also attributed to a second species in this genus, Brodavis americanus.

Potamornis skutchi

[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]

Potamornis was another hesperornithiform, described from remains collected from the Lance Formation - remains from Hell Creek have been attributed to this taxon. While it was almost certainly a member of the Hesperornithes clade, its precise relationships within the group are not certain. Though, it does share the unique pterygoid articulation with the family Hesperornithidae (and poorly defined [or even absent] division of the head), the hinge-like temporal articulation, exceptionally small orbital process, and prominent attachment site for the deep layers of the protractor pterygoidei et quadrati muscle as well as several other details set it apart. These unique characters, combined with its smaller size (roughly 1.5-2kg), seem to suggest a feeding specialization differing from that of Hesperornithidae (Elzanowski et al., 2001). 

Unnamed taxa:

There are three ornithurine taxa that currently lack formal names, though they are informally referred to as "Ornithurine B", "Ornithurine C", and "Ornithurine D". Each of the three are known only from partial coracoids, and as such there is not enough material to publish a sufficient description for a new taxon. Size estimates based on a graph in Longrich et al. (2011) estimates masses of around 500-600g for "Ornithurine B", 700-800g for "Ornithurine D", and around 2.9-3kg for "Ornithurine C". Since the data was presented as a bar graph rather than a table of mass estimates, these numbers are my estimates based on what I can see, so I could certainly be wrong. I would encourage anyone to look at the original literature and make your own informed decision.

I hope this Creature Feature has filled your brains with more knowledge about some of the more mysterious taxa from Hell Creek! There are one [possibly two] more dinosaur taxa for me to cover, but after that I will be doing more of these grab-bag Creature Features due to many of the other vertebrate fauna being rather fragmentary.

Acknowledgements:

Carr, T. E.; Williamson, T. D. 2002. A new genus of highly derived pachycephalosaurian from western North America. Journal of Vertebrate Paleontology 22 (4): 779-801. 

Sullivan, Robert M. 2003. Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae). Journal of Vertebrate Paleontology 23 (1): 181-207.
Mallon, Jordan C.; Evans, David C.; Tokaryk, Tim T.; Currie, Margaret L. First pachycephalosaurid (Dinosauria: Ornithischia) from the Frenchman Formation (upper Maastrichtian of Saskatchewan, Canada. Cretaceous Research 56: 426-431.
Longrich, N. R.; Barnes, K.; Clark, S.; Millar, L. 2013. Correction to Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a Revision of the Caenagnathinae. Bulletin of the Peabody Museum of Natural History 54 (2): 263.
Varrichio, David J., Chiappe, Luis M. 1995. A New Enantiornithine Bird From the Upper Cretaceous Two medicine Formation of Montana. Journal of Vertebrate Paleontology 15 (1): 201 - 204.
Longrich, Nicholas R.; Tokaryk, Tim; Field, Daniel J. 2011. Mass Extinction of Birds at the Cretaceous–paleogene (k-pg) Boundary. Proceedings of the National Academy of Sciences of the United States of America 108 (37): 15253-15257.

Hope, S. 2002. The Mesozoic radiation of Neornithes. 339-388 In: Chiappe, L.M. and Witmer, L. (eds.), Mesozoic Birds: Above the Heads of Dinosaurs.

Martin, Larry D.; Kurochkin, Evgeny N.; Tokaryk, Tim. 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld 21 (1): 59-63.

Elzanowski, Andrzej; Paul, Gregory S.; Stidham, Thomas A. 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology 20(4): 712-719

Sci-Day 14: What is a Species?

Happy Sci-Day, everyone! I hope you have all enjoyed this blog so far, at least as much as I have enjoyed writing it! As I've said before, the biggest goal of this blog is to educate people more about the science behind dinosaur battlegrounds, and biology in general (including paleontology in this context). This week, I will be covering one of the most hotly debated topics in modern science - when we talk about a "species", or refer to an organism as a "species", what exactly do we mean? How do we distinguish different species - where do we draw the line from say a subspecies, locality, or individual variation and a full-fledged species?

An important thing to note about a species is that it is fundamentally distinct from other terms that are used in classification, such as family, genus, order, class, etc. The key difference is that the latter terms are arbitrary - a genus is not a defined unit. If you are comparing two genera, for example, and one has more species than another, this does not tell you that the one with more species has evolved or diversified more quickly - there is no strict definition as to what constitutes a genus or any other term besides species - as long as the higher ranks are monophyletic (see Sci-Day #1 for more details on what monophyletic means), it doesn't matter where they are placed on a cladogram or phylogeny. A species, however, is a meaningful and distinct unit - it is a unique population of organisms that is not arbitrary. One of the biggest problems in biology, however, is figuring out how to identify species. This can also be referred to as "the species problem."

This question has no clear or 'right' answer, because the issue is so complex. One scientist named Edward Wiley stated in 1978 that "a species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate" [quote retrieved from Evolutionary Biology lecture]. This essentially means that a species is in some way distinct from other organisms, and its population evolves on its own trajectory - ie, the population may be influenced by changes in environment or other organisms that it interacts with (like in coevolution), but the species does not evolve the exact same changes as the other or evolves in its own unique way. This definition of a species is called the "Evolutionary Species Concept".

There are many different species concepts, all of which have benefits and drawbacks in their application. The most relevant one in paleontology is called the Phenetic [or Morphological] Species Concept. This concept identifies species based on morphological characters such as length of certain bones or other structures, or any observable morphological character. To distinguish species, one can create a chart in "phenotype space", as shown in this image:

First, the character states are graphed in a chart like the one above, and one looks for distinct clusters. In the example above, there appear to be three distinct clusters, which would represent 3 different species.

However, there are several drawbacks to this concept. One issue is choosing characters to analyze. How do we choose what characters to plot? Which characters are important to distinguish species, and which ones are simply representations of variation between localities or individuals? Another drawback is that some species may actually look very similar, but are actually different species (known due to a lack of gene flow between them) - these are called cryptic species. Unfortunately, it is the only species concept that we can use when examining fossil taxa - this could mean that specimens which we all lump into a single species may actually represent several different species - differences between them might have been limited to soft tissue or genetics, which would mean if this were the case we might never even know it. This issue with applying species concepts to modern taxa is also displayed by the fact that the species status of several dinosaurs (including Dracorex, Stygimoloch, Nanotyrannus, and Torosaurus latus) is disputed as being due to ontogenetic variation. If we had fully intact specimens like we have of modern animals, we would be able to tell whether or not these are species in their own right or are just juvenile/adult forms of other species.

Another concept that I will briefly address is one of the most commonly used ones in biology of extant organisms - the Biological Species Concept. the Biological Species Concept says that "species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups" [Quote retrieved from Evolutionary Biology lecture]. Observations that led to the formulation of this concept include variation within populations, sexual dimorphisms, life cycle (some organisms display extreme morphological changes in development), geographic variation, and cryptic species [as described above]. While this is beneficial due to addressing some of the limitations of the Phenetic Species Concept, it too has its drawbacks.

Drawbacks of the BSC are mostly related to the issue of 'reproductive isolation'. How can we determine the species boundaries of animals if we have no data on their reproductive habits or capabilities? Another issue is that occasionally, two species might interbreed and hybridize, which would mean they are the same species if one takes the BSC at face value. However, if this is only occasional and the populations seem to represent distinct species in all practical purposes, should we really lump them together? Additionally, many times the offspring of these hybridizations are nonviable or infertile - meaning that they are an evolutionary dead end. What do we do in these cases? This is a conundrum that the BSC has trouble answering.

I have only talked about two commonly used Species Concepts, but there are many more, each with their own pros and cons. I do not have time to talk about all of them in detail, but if you are interested you can find plenty of information about them on the good ol' internet! I hope that this post has educated you a bit more on a very hotly debated topic that we may never truly have an answer for!

A special thanks to my professors in Evolutionary Biology, as their lectures are very helpful for providing good quotes and other useful information!

Creature Feature 16

Greetings, fans! It's hard to believe that we've already done 15 Creature Features!

This week we'll be looking at the recently discovered Oviraptorosaurian Anzu wyliei!

Anzu wyliei model, WIP. Feathers will be added.

Anzu wyliei is easily distinguishable amidst the dinosaurs of Hell Creek by it's toothless beak, large crest, long arms with relatively straight claws (as opposed to the more curved claws found in dromaeosaurs), and rather short tail. It was the largest known Oviraptorosaur from North America , at approximately 3-3.5 meters in length, 1.5 meters tall at the hips, and weighing in at an estimated 200-300kg (Lamanna et al., 2014).

Cladistic analyses place Anzu wyliei in the family Caenagnathidae, as sister to Caenagnathus collinsi (Lamanna et al., 2014). It is possible that in the future this species will be reassigned to Caenagnathus (the revised name would be Caenagnathus wyliei), though since both genera remain monophyletic in current phylogenies such revision is not necessary [at least in my opinion]. The relationships revealed by the phylogeny demonstrated that North American Oviraptorosaurs were more closely related to each other than they were to their Asian relatives (Jemison, 2014).

The diet of A. wyliei is still not certain - it may have been an omnivore or an herbivore, though its beak is less robust than those in the Asian family Oviraptoridae (Lamanna et al., 2014). Other differences from the Asian Oviraptoridae include thinner legs and a different mandibular structure (Fawcett, 2014). Additionally, it lived in a much less arid environment - the remains were found in mudstone attributed to a floodplain environment (typical of Hell Creek) (Jemison, 2014). In the original description, the authors hypothesize that it was likely able to consume a wide variety of foods, ranging from vegetation to small animals, and even eggs (Lamanna et al., 2014).

Another mystery is the function of the large crest on the head. While all oviraptorosaurs have a crest, the crest of Anzu is exceptionally large. The crest was made of extremely thin bone, and as such would not have been able to handle stress without risk of severe damage. Given the similarities in shape to the crest of the modern Cassowary, some believe it may have served a similar purpose, serving as a display to attract mates.

Another interesting note is that some remains show evidence of injuries. These include a healed broken rib and an avulsion fracture on one of the toes (possibly proximal phalanx IV). Currently, it is unknown whether these injuries were the result of intraspecific combat or are due to interactions with predators (though those are not the only two possible causes, of course) (Lamanna et al., 2014).

I hope you have learned a bit more about the rather interesting Anzu wyliei! Since it was only described 2 years ago, there has not been enough time for lots of research to be published, so that is why my sources are rather repetitive. Hopefully, as time goes by more people will be working on this amazing creature!

Acknowledgements:
Lamanna, M. C.; Sues, H. D.; Schachner, E. R.; Lyson, T. R. 2014. A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the Latest Cretaceous of Western North America. PLoS ONE 9 (3): e92022.
Jemison, Micaela. 2014. One Scary Chicken - New Species of Large, Feathered Dinosaur Discovered. insider.si.edu. Retrieved April 19, 2016.
Fawcett, Kirstin. March 19, 2014. Scientists Discover a Large and Feathered Dinosaur that Once Roamed North America. Smithsonianmag.com. Retrieved April 19, 2016.

Sci-Day 13: Sexual Selection

Hello, everyone! This week, I'm going to talk about a specific mechanism of evolution that can shape species in many different ways - sexual selection. One thing to keep in mind while reading this is that it is incredibly difficult, if not impossible to tell the sex of a fossil organism in the vast majority of cases, so even if there are two distinct morphs of a species it is not necessarily possible to tell whether it is due to sexual dimorphism, geographical variation, or some other factor. However, there are some features in many groups of fossil organisms that seem to have played some role in mating behaviors and displays, and sexual selection may have helped to shape their development.

One of the key requirements for sexual selection is anisogamy - this means that one sex produces small gametes, and the other sex produces large gametes. Biologically, this is how we can assign male or female - it is not the presence of a certain chromosome (not all creatures share the same sex chromosome system, and some species have temperature-dependent sex determination), but rather the size of the gametes they produce that defines their sex. Males produce the smaller gametes, and females produce the larger gametes. Since these two gametes are very distinct, selection can favor different traits in males and females.

One of the very important things about the size difference is that the larger gametes (eggs) are MUCH more expensive to produce than smaller gametes (sperm), and as such they are a limiting resource. For this reason, females are often much "choosier" than males - they stand to lose far more fitness than males by making bad mate choices (a male can easily produce more sperm if he makes a bad choice, it costs far more for the female to make more eggs).


As you may have noticed as you've read this, sexual selection is a logical equivalent to natural selection. Heritable traits in males that increase mating success should increase in frequency, whereas heritable traits that decrease mating success should decrease. These traits may be elegant displays, horns or spikes to fight off other males, or simply a high sperm count.

There are two subtypes of sexual selection. These two types are called intrasexual selection and intersexual selection:

Intrasexual selection is the result of interactions between individuals of the same sex. One of the most easily observed examples are those that happen before copulation. In these scenarios, there is competition between individuals of the same sex for mating opportunities (often males). Examples of traits that may be favored by this type of sexual selection are visual displays, traits that make the animal look larger, horns/tusks [or other features] used for physical confrontation, and features that help to establish dominance such as coloration or vocalizations.

Intersexual selection is the result of interactions between individuals of the opposite sex. In these scenarios, one sex preferentially mates with individuals of some specific phenotype, and consequentially those individuals displaying said phenotype produce more offspring. Examples of features that may be favored by intersexual selection include vivid color patterns/ornamentation, vocalizations, and display behaviors.

As I stated above, it is unfortunately very difficult to distinguish sexes of fossil animals, and as such we can not always determine whether or not there was sexual selection occurring. For example, it was originally hypothesized that the crests on species such as Dilophosaurus were used to attract mates, but due to the fact that there is no evidence of sexual dimorphism in the species (and even if there was, it would be very difficult to be sure), it is considered more likely that they were used for species recognition.

However, there are some species that show evidence of specialized features that may have been at least partially shaped by sexual selection. One such example are the frills and horns of Triceratops. There is considerable evidence that Triceratops engaged in non-fatal intraspecific combat (Petersen et al., 2013; Reid, 1997; Horner and Goodwin, 2009; Horner and Lamm, 2011; Farlow and Dodson, 1975), though we do not know if this was based on competition for mates - if one were to identify all individuals showing cranial pathologies linked to such combat as the same sex, that might reinforce the idea that sexual selection played a role, but the behavior could also be unrelated to mating and simply be a way of settling territorial disputes. Triceratops frills apparently began to develop at a young age (before the onset of sexual maturity), and were likely also used for display and species recognition (Goodwin et al., 2006). Whether the display was simply shape or if there were vivid colors is unknown, though if the idea of sexual selection playing a role in the evolution of frills and horns is correct, there may have been distinct colors patterning that area to help attract mates.

Additionally, as I talked about in my Creature Feature about Pachycephalosaurus, there is similar evidence for headbutting behavior in that species. Like with Triceratops, it is not known whether or not this behavior was based on competition for mates, or if it was simply a way of settling territorial disputes (or both), but the idea is the same.

To sum it up, sexual selection is a very important driver in the development of many features as observed in modern taxa, and I personally believe it is safe to assume that it played some role in the evolution of prehistoric creatures as well. However, the difficulty of sexing fossil animals and the lack of preservation of soft tissues such as non-bony crests/flaps or vivid colors means that even if it did play a role, it would be very difficult if not impossible to say so with any great degree of certainty. Dinosaur Battlegrounds could help to investigate the possibility of sexual selection playing a role in the evolution of certain animals by running simulations with different AI behaviors specifically regarding mating preferences/behaviors in one [or both] sexes, and see whether or not the results match existing data. This is yet another example of how Dinosaur Battlegrounds' nature as a full paleoecosystem restoration can help us answer questions that we cannot uncover from the rocks.

I hope you enjoyed this week's Sci-Day! I'd like to thank my Evolutionary Biology professors for providing great lecture materials that I could use to help organize this post.

Acknowledgements:
Peterson, J. E.; Dischler, C.; Longrich, N. R. 2013. Distributions of Cranial Pathologies Provide Evidence for Head-Butting in Dome-Headed Dinosaurs (Pachycephalosauridae). PLoS ONE 8 (7): e86820.
Reid, R. E. H. 1997. Histology of bones and teeth. In: Currie, P. J. and Padian, K, editors. Encyclopedia of Dinosaurs. Academic Press, San Diego, CA. 329-339.
Horner, J. R.; Goodwin, M. B. 2009. Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus. PLoS ONE 4 (10): e7626.
Horner, J. R.; Lamm, E. 2011. Ontogeny of the parietal frill of Triceratops: a preliminary histological analysis. Comptes Rendus Palevol 10: 439-452.
Farlow, J. O.; Dodson, P. 1975. The behavioral significance of frill and horn morphology in ceratopsian dinosaurs. Evolution 29: 353-361.
Goodwin, M. B.; Clemens, W. A.; Horner, J. R.; Padian, K. 2006. The smallest known Triceratops skull: new observations on ceratopsid cranial anatomy and ontogeny. Journal of Vertebrate Paleontology 26 (1): 103.

Creature Feature 15

This is the 15th week of Creature Features - it's hard to believe it's been so long already! At this point we've already looked at most of the well-described species from Hell Creek, so some of the future Creature Features may not be able to go as in-depth due to lack of information on some of the other organisms found in Hell Creek that are known from very fragmentary material. However, I will do my best to give whatever info I can! We still have a few decently-described species to cover, so those will be done first.

Anyways, this week's Creature Feature will be looking at the family Azhdarchidae as a whole.

Azhdarchid model, based mostly on Quetzalcoatlus, WIP. Pycnofibers will be added.

The reason that this creature feature will be looking at the family as a whole is because while the remains found from Hell Creek are thought to be those of Quetzalcoatlus, they are not diagnostic at the generic level and as such we can only be sure that the Hell Creek pterosaur was an Azhdarchid (Henderson and Peterson, 2006).

Azhdarchids were a group of pterosaurs that included some of the largest animals ever to roam the skies. They were among the pterosaurs that lasted until the very end of the Cretaceous - originally it was thought that most pterosaur families had already gone extinct towards the end of the Cretaceous, but more recent evaluations suggest a significant diversity of pterosaur fauna (Agnolin and Varricchio, 2012).

There are several distinctive features in Azhdarchid pterosaurs, including large heads with eyes placed just behind a large nasal foramen (likely to reduce the weight of the skull), extremely long and toothless jaws, a long neck, and stiltlike limbs (Averianov, 2013). As has been stated, some of the more recent members grew to truly immense sizes - up to 13m wingspans, yet weighed only an estimated 70-85kg (Witton, 2007). Unfortunately, many Azhdarchids are only known from very fragmentary remains, making it very difficult to completely reconstruct their anatomy, and many localities are like Hell Creek in that the remains are not diagnostic at the generic level (Averianov, 2013). However, the most complete collection of bones preserved with a minimal amount of flattening belong to Quetzalcoatlus, though only the cranial material of this collection has been described (Kellner and Langston, 1996). The shape of the jaw also suggests the presence of a throat sac (Kellner and Langston, 1996; Averianov, 2010).

The biology and behavior of Azhdarchids was a subject of much controversy for a long time due to the fragmentary nature of most remains, as well as the lack of suitable modern analogs and relative scarcity of materials (Averianov, 2013). Originally, it was suggested that Azhdarchids were skimmers (Nesov, 1984; Kellner and Langston, 1996), but more recent analyses seem to show that this is unlikely. Recent research shows that Azhdarchids did not possess the necessary adaptations for a skimming lifestyle, and may have fed like modern storks or ground hornbills - foraging for small animals or carrion in a variety of environments (Witton and Naish, 2008). However, Averianov (2013) hypothesizes that Azhdarchids would fly slowly over the surface of large water bodies (such as rivers and lakes, and possibly sea coasts), scanning for fish or small shoals of fish. When it saw potential prey, they would open the mouth, which would expand their throat sac due to their spiral jaw joint. They would use this as a scoop net, capturing the prey and throwing their head back quickly and swallowing their prey.

Well, I hope this has taught you a little bit more about this most fascinating group of pterosaurs!

Acknowledgements:

Henderson, M.D. and Peterson, J.E. 2006. An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana. Journal of Vertebrate Paleontology 26(1): 192–195.

Agnolin, Federico L. and Varricchio, David. 2012. Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird (PDF). Geodiversitas 34 (4): 883-894.

Averianov, A. O. 2013. Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47 (2): 203-209.

Witton, M.P. 2007. Titans of the Skies: Azhdarchid Pterosaurs. Geol. Today 23 (1): 33-38.

Kellner, Alexander W. A.; Langston, W. 1996. Cranial Remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous Sediments of Big Bend National Park, Texas. Journal of Vertebrate Paleontology, 16(2), 222–231.

Averianov, A. O. 2010. The Osteology of Azhdarcho lancicollis Nessov, 1984 (Pterosauria, Azhdarchidae) from the Late Cretaceous of Uzbekistan. Proc. Zool. Inst. Russ. Acad. Sci., 314 (3): 264-317.

Nesov, L. A. 1984. Upper Cretaceous pterosaurs and birds from Central Asia. Paleontologicheskii Zhurnal 1984 (1): 47-57.

Witton M. P.; Naish, D. 2008 A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271.

Sci-Day 12: The K-T Extinction Event

Happy Sci-Day, everyone! This week, I will be writing about one of the most tragic events in Earth's history. This event spelled the doom of many creatures, with non-avian dinosaurs among the casualties. Reading about this catastrophic time in history always makes me feel a bit sad - as a herpetology enthusiast, the Mesozoic represents a golden age for reptiles. In the Mesozoic, you could go to any ecosystem and almost universally the largest animal present would be a reptile. In the sky, you had pterosaurs - in the sea, there were the plesiosaurs and mosasaurs, and of course there were dinosaurs on the land. All of these groups were completely extinguished by this event - I would give almost anything to be able to travel back and study such creatures in the same way that I can study extant taxa.

The K-T extinction event marks the end of the Cretaceous period and the close of the Mesozoic Era. It also marks the beginning of the Paleocene period and Cenozoic Era, the latter of which continues today. While older estimates date this event at 65 million years ago, more recent estimates have revised this to around 66 million years (Renne et al., 2013).

One of the most common hypotheses for the cause of the K-T extinction is that it was triggered by a large comet or asteroid impact. Such an impact would have caused devastation on a global scale - the effect would be like nuclear winter on steroids. With all the debris and dust from the collision blocking out much of the sun's light and warmth, plants and phytoplankton would find it all but impossible to undergo photosynthesis (Alvarez et al., 1980), leading to widespread plant death and subsequent food chain collapse. In the 1990s, this hypothesis was further supported by the discovery of a 180-km wide impact crater (dubbed the Chicxulub crater) in the Yucatan peninsula (Hildebrand et al., 1991). Additionally, there is a thin layer of sediment marking the KT event (known as the 'KT boundary) present in all sedimentary rocks of the relevant age. This sediment shows high concentrations of iridium - this metal is rare in the Earth's crust, but is common in asteroids. This fact could mean that the KT boundary layer represents deposit of debris from the impact (Schulte et al., 2010). Furthermore, the fact that there is the fact that the extinctions seem to have happened around the same time as the impact, which is interpreted by some as strong situational evidence for this hypothesis.

While this hypothesis is generally accepted as the event that caused the demise of the non-avian dinosaurs [as well as many other groups of organisms], it is still a somewhat controversial issue. Some have actually argued that the extinction of non-avian dinosaurs was more gradual than some might claim, and both sides of the debate have support from the fossil record. A study of 29 fossil sites in Europe revealed that dinosaurs had significant diversity up until the KT event, with over 100 species present across the sampled sites (Riera et al., 2010) - this appears to support the hypothesis of a sudden extinction. Additionally, further research suggested that global non-Avian dinosaur diversity was significantly higher, with somewhere between 678 and 1078 species existing up until the event (Le Loeuff, 2012). However, there is evidence of a gradual decrease in non-avian dinosaur species richness at some fossil sites - a study of fossil-bearing rocks along the Red Deer River in Alberta shows that the number of species declined from roughly 45 to around 12 over the course of 10 million years (Ryan et al., 2001). If this is indeed true and is not due to differing preservation potentials of the sediment with age, it seems to support the gradual extinction hypothesis of non-avian dinosaurs. One possibility is that dinosaurs were gradually on the decline in some parts of the world, while they continued to thrive in other regions. However, without more data/evidence, we will not know for sure.

Dinosaurs were not the only group affected by the KT event. Many groups of squamates such as monstersaurs and polyglyphanodonts were nearly wiped out by the event, taking 10 million years to recover (Longrich et al., 2012). Additionally, both mosasaurs and plesiosaurs died out (Chattergee and Small, 1989). Mosasaurs and plesiosaurs were the apex marine predators of their time, growing to truly immense proportions. It is truly a pity that they are no longer with us.

The K-T extinction also spelled the end for the last pterosaurs. By the end of the Cretaceous, the only family definitely present was the Azhdarchidae; while there is some evidence of other families, the remains are far too fragmentary to assign them to any specific groups (Barrett et al., 2008). Evidence seems to suggest that pterosaurs were on the decline at the time, while modern families of birds were simultaneously increasing in diversity. While it was originally thought that this increase was indicative of birds 'replacing' pterosaurs due to interspecific competition or by filling niches left empty by the disappearance of pterosaur species (Robertson et al., 2004), the correlation between pterosaur diversity decline and bird diversity increase is simply not conclusive to the competition hypothesis (Butler et al., 2009). Additionally, there were small pterosaurs during the Late Cretaceous (Prondvai et al., 2014), further disputing the idea of direct competition.

I hope that this has given you a bit of a better understanding of the K-T extinction! While many groups of taxa were devastated in addition to the non-avian dinosaurs, it would take far too much time and space for me to go into any great depth on all of them. If you are interested in learning more, I encourage you to find resources online such as Google Scholar to read more about this subject!

Acknowledgements:
Renne, Paul R.; Deino, Alan L.; Hilgen, Frederik J.; Kuiper, Klaudia F.; Mark, Darren F.; Mitchell, William S.; Morgan, Leah E.; Mundil, Roland; Smit, Jan. 7 February, 2013. Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary. Science 339 (6120): 684-687.
Alvarez, Luis. W.; Alvarez, Walter; Asaro, Frank; Michel, Helen V. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208 (4448): 1095-1108.
Schulte, Peter. March 5, 2010. The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary. Science (American Association for the Advancement of Science) 327 (5970): 1214-1218.
Riera, V.; Marmi, J.; Oms, O.; Gomez, B. March 2010. Orientated plant fragments revealing tidal palaeocurrents in the Fumanya mudflat (Maastrichtian, southern Pyrenees): Insights in palaeogeographic reconstructions. Palaeogeography, Palaeoclimatology, Palaeoecology 288 (1-4): 82-92.
Le Loeuff, J. 2012. Paleobiogeography and biodiversity of Late Maastrichtian dinosaurs: how many dinosaur species went extinct at the Cretaceous-Tertiary boundary? Bulletin de la Société Géologique de France 183 (6): 547-559.
Ryan, M. J.; Russell, A. P.; Eberth, D. A.; Currie, P. J.. 2001. The taphonomy of a Centrosaurus (Ornithischia: Ceratopsidae) bone bed from the Dinosaur Park Formation (Upper Campanian), Alberta, Canada, with comments on cranial ontogeny. PALAIOS 16 (5): 482-506.
Longrich, Nicholas R.; Bhullar, Bhart-Anjan S.; Gauthier, Jacques A. 2012. Mass extinction of lizards and snakes at the Cretaceous-Paleogene boundary. Proceedings of the National Academy of Sciences of the United States of America 109 (52): 21396-21401.
Chatterjee, S.; Small, B. J. 1989. New plesiosaurs from the Upper Cretaceous of Antarctica. Geological Society, London, Special Publications 47 (1): 197-215.
Barrett, P. M.; Butler, R. J.; Edwards, N. P.; Milner, A. R. 2008. Pterosaur distribution in time and space: an atlas. Zitteliana 28: 61-107.
Robertson, D. S.; McKenna, M. C.; Toon, O. B.; Lillegraven, J. A. 2004. Survival in the first hours of the Cenozoic. GSA Bulletin 116 (5-6): 760-768.
Butler, Richard J.; Barrett, Paul M.; Nowbath, Stephen; Upchurch, Paul. 2009. Estimating the effects of sampling biases on pterosaur diversity patterns: implications for hypotheses of bird/pterosaur competitive replacement. Paleobiology 35 (3): 432-446.
Prondvai, E.; Bodor, E. R.; Ősi, A. 2014. Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity. Paleobiology 40: 288-321.

Creature Feature 14

Hello, fans! I hope you have all had a great weekend! This week's Creature Feature will look at Ornithomimus velox.

Ornithomimus velox model - feather texture still work-in-progress.

Ornithomimus velox was a medium-sized theropod dinosaur, somewhat resembling a modern ratite. It was likely rather swift given its large, muscular hindlimbs, and had a small, keratinized beak. While the specimens attributed to O.velox are rather fragmentary and thus hard to evaluate, its sister species O. edmontonicus is known from several extremely well-preserved specimens which allows some degree of inference on the overall biology of O. velox given their close relation.

There have been several specimens of a second species in this genus (O. edmontonicus) found with carbonized traces of feathers, and a description in 2012 concluded that this species retained plumaceous feathers throughout its life, though it only had pennaceous ('wing') feathers at maturity - suggesting that such features may have played a role in mating displays (Zelenitsky et al., 2012). However, others have disagreed on the presence of pennaceous feathers, based on the fact that the feathers like those on the wings of modern cassowaries would leave similar traces (Foth et al., 2014).

Another new feathered specimen of Ornithomimus was described in 2015. This specimen had very similar feather structure and distribution as that found in modern ostriches. Furthermore, the specimen included preserved skin from the hindlimbs, which showed scaleless skin from the mid-thigh to the feet, and a large flap of skin connecting the upper thigh to the torso. Modern birds also share this flap of skin, though in Ornithomimus it was positioned higher from the knee (Van Deer Reest et al., 2016).

The true diet of Ornithomimus and other Ornithomimosaurs is still a subject of debate. This is partially due to their endentulous jaws, which prevent the possibility of inferring diet from tooth structure (you can't analyze a feature if the feature isn't there!). Some authors have suggested that dinosaurs such as Ornithomimus were suspension feeders, using their beak to strain out food from sediments in aqueous environments, somewhat like modern anseriform birds (Norell et al., 2001). However, further analysis of the structure of the beak in Gallimimus suggests a structure more in line with that found in herbivorous chelonians and hadrosaurs, which may suggest a diet consisting of high-fiber plants (Barrett, 2005). On the other hand, there are differences in preserved beaks of Ornithomimus and Struthiomimus when compared to Gallimimus, which does suggest some degree of ecological and dietary divergence from that of Gallimimus (Kobayashi and Lü, 2003). Overall, there is still a large degree of uncertainty as to the actual diet of Ornithomimosaurs in general, though an exclusively carnivorous diet is considered unlikely (Barrett, 2005).

Well, I hope this has given you a bit more information on the rather enigmatic yet very cool theropod known as Ornithomimus!

Acknowledgements:
Zelenitsky, D. K; Therrien, F.; Erickson, G. M.; Debuhr, C. L.; Kobayashi, Y.; Eberth, D. A.; Hadfield, F. 2012. Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. Science 338 (6106): 510-514.
Foth, Christian; Tischlinger, Helmut; Rauhut, Oliver W. M. 2014. New Specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature 511 (7507): 79-82.
Van Der Reest, Aaron J.; Wolfe, Alexander P.; Currie, Philip J. 2016. A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation, Alberta, Canada. Cretaceous Research 58: 108.
Norell, M. A.; Makovicky, P. J.; Currie, P. J. 2001. The beaks of ostrich dinosaurs. Nature 412: 873-874.
Barrett, P. M. 2005. The Diet Of Ostrich Dinosaurs (Theropoda: Ornithomimosauria). Palaeontology 48 (2): 347-358.

Kobayashi, Y.; Lü, Jun-Chang. 2003. A new ornithomimid dinosaur with gregareous habits from the Late Cretaceous of China. Acta Palaeontologica Polonica 48: 235-259.

Sci-Day 11: The Scientific Core of Dinosaur Battlegrounds

Happy Sci-Day, fans! I'm sorry for missing two weeks of Sci-Day posts, but my schedule was unable to fit them in unless I tried to rush it, and I will not sacrifice the quality of what I write for the sake of a deadline. This post is based on the presentation I made at the KU Herpetology division last Friday, and in this I have attempted to explain how and why Dinosaur Battlegrounds utilizes science and could be a valuable tool to anyone wishing to better understand the prehistoric world. I hope you all enjoy, and I hope it will give you a deeper insight into what makes our vision so special.

As has been said before, Dinosaur Battlegrounds will simulate a dynamic, living environment. There will be day/night cycle, natural disasters such as flash floods, and aging flora and fauna. These effects simulate the natural processes that occur in any living system, and with enough trials and running time this allows one to observe trends in populations of different species while still accounting for stochastic processes that could otherwise undermine the validity of the data. This, however, relies on our ability to accurately reconstruct the flora and fauna of the paleoecosystem as accurately as possible. To do this, we must carefully examine all of the current scientific evidence. It also means that when there are two or more conflicting but equally plausible hypotheses for a certain aspect of the ecosystem or the biota residing within it, we must represent both in the game and allow the player to decide which they want to go by. This also provides a possible way for testing the validity of these hypotheses in an actual living environment, which may give new insights into the issue that had not been accounted for previously.

However, Dinosaur Battlegrounds involves other fields in addition to paleontology. We must actively consult with herpetologists, ichthyologists, ornithologists, and other scientists who study living taxa due to the fact that we are attempting to restore not only the living tissues of the animals, but also their behavior. One of the best way to infer possible behaviors or to infer the overall anatomy of fragmentary specimens is to look at their closest extant relatives, and make inferences using comparative anatomy. There are many other types of information that are not fossilized, such as diet (though this can be somewhat inferred from dentition), ecological niche, etc. Perhaps most importantly, there are many species of animal from the Hell Creek formation that are known only from extremely fragmentary remains - far too fragmentary to restore the rest of the anatomy by itself. In such cases, it is very useful to look at inferred relations to extant taxa, and to use those to attempt a restoration. One example of this is Palaeosaniwa - the missing parts were restored based on its closest modern relatives (Heloderma, according to Balsai, 2001), and in-game, its behavior will largely use knowledge of Heloderma and other related Platynotans.

In fact, almost all of the Polyglyphanodonts from Hell Creek are based on very small fragments of the dentary, making it impossible to make a full restoration based exclusively on fossil remains. In such cases, we use what I call "placeholder models" - these are models meant to represent the actual creatures, since they obviously played a role in the ecosystem, but are based mostly on modern taxa in terms of appearance. This allows us to still have the species present even though we cannot have a fully fossil-based restoration. They are called "placeholders" because as soon as there is sufficient remains of such species to make a fossil-based reconstruction, new models will be made and will subsequently replace the originals. We also use similar models to represent types of creatures that we can reasonably infer to have been present, but are not known from any body fossils. These are things such as various invertebrates (both terrestrial and aquatic) - these can be inferred based on the dentition of many Hell Creek animals supporting a diet comprised of such creatures, and various things such as molecular evolution data from those taxa supporting an evolutionary history implying their presence in certain regions at certain times.

Another example of where science fits in has been mentioned in a previous Sci-Day post, so I will not go into too much detail. We are basing the dynamics of our feeding system on the inferred metabolic rates and relative energy content per unit mass of different types of food. This further ensures the accuracy of our simulation, and also requires involvement of scientists studying living taxa since it is not possible to directly measure metabolic rates from fossils.

Perhaps one of the most important reasons why Dinosaur Battlegrounds is so amazing and important is the ideas for potential research. One idea was mentioned in the Dinosaur Metabolism Sci-Day post, and I have actually been discussing the possibility of doing that project with a professor here at my university. A related project relates to getting FEE values to use for non-dinosaur taxa, such as the reptiles, amphibians, and fish that lived in Hell Creek. These could be estimated based on data from their closest living relatives (ie for Amia fragosa and Melvius thomasi the FEE values would be based on modern Amiid fish). This gives scientists the opportunity to gather data on these species that could also be useful to studies that are not directly related to Dinosaur Battlegrounds, further increasing our positive impact on the scientific community.

Additionally, as has been mentioned many times before, Dinosaur Battlegrounds is not just a game - it can act as a simulation software that could be used to test hypotheses about many different aspects of a paleoecosystem. In many ways, it functions like any other model or simulation - if, for example, a hypothesized species distribution is unstable, the population might die off entirely, or simply settle into a completely different distribution that allows for a stable population. This is due to the integration of naturally occurring stochastic processes that are very hard to fully account for in current models/software used for this purpose. Such aspects of a paleoecosystem are extremely difficult to examine, as things such as fecundity and average population size in a given region cannot be measured in the same way as with extant flora and fauna.

Lastly, there are also many secondary benefits that contribute to the massive impact Dinosaur Battlegrounds will have:

1. As a video game, Dinosaur Battlegrounds also provides a fun experience for non-scientists, while also teaching them about the prehistoric earth. In this way, it helps getting accurate information out to the public, and feeds an interest in paleontology and other life sciences.
2.  By allowing the player to choose between conflicting theories when applicable, it can help develop a capacity for analyzing evidence for contrasting ideas, which is an important skill for any scientist and for a healthy and happy populace.
3. Perhaps most crucially, in order to ensure accuracy, we plan to use a portion of the profits we make to fund further research in Paleontology and other sciences in order to ensure that Dinosaur Battlegrounds continues to be the most accurate experience possible.
4. Dinosaur Battlegrounds requires science to be applied in a new way. It requires us to figure out how to manifest various traits of the actual animals into the gameplay itself. For example, T. Rex had a visual overlap of 55°, whereas most herbivores had much smaller overlap (if any). While we understand the effects from an "outside" perspective, we have to actually put ourselves in the animals' shoes and figure out how to represent such differences. This can lead to a deeper understanding of their biology because of this.

In closing, Dinosaur Battlegrounds is far more than just a game. Calling Dinosaur Battlegrounds a video game does not do justice to what we are truly doing with this project. Dinosaur Battlegrounds is a system - it is an integration of gaming and scientific simulation. It is a tool that makes science accessible to non-professionals in a fun and understandable way, and a tool for all of us to gain new insights into the way ancient, long-extinct animals lived and died. Thus, we will not just be having fun walking in the clawed feet of a Tyrannosaurus or swimming through the rivers as a Champsosaurus - we will be learning more than ever before about the prehistoric Earth... We will be learning more about the ancient Dinosaur Battlegrounds.

References:
Balsai, Michael Joseph. 2001. The phylogenetic position of Palaeosaniwa and the early evolution of the Platynotan (Varanoid) anguimorphs (January 1, 2001). Dissertations available from ProQuest. Paper AAI3031637. http://repository.upenn.edu/dissertations/AAI3031637