Why can't we all just get along?: Morphological vs. Molecular Data

Hello everyone, staying on top of things in a timely manner is far harder then I care to admit. Still, here is a new post. These may still be somewhat infrequent until I can finish up my thesis, or a least the first draft of it. But once February hits, perhaps these will be more on track. Here's hoping.....

http://txtwriter.com/Backgrounders/Dinosaurs/dinoBG2.html

So, for those of you who have looked into phylogenies, especially those concerning modern taxonomic groups and modern genera in particular, you may have run into some problems (or you may not have, I don't actually know for sure). I will focus on a specific case, but this will not be the end.
 




Many people are aware of phylogenies, cladograms, and the concept of systematics in general. These are ways to convey the relationships between organisms and help (or possibly help) show evolution through time. These are commonly used in biology and paleontology today. These two fields don't always use the same data sets though. This is not really surprising, since biologists working with modern taxa have the ability to get far more data, while paleontologists commonly only have morphological characters from the fossils they can find. While biologists commonly have several types of data they can use to acquire phylogenies, a relatively common one is molecular data. And this makes sense, DNA should be able to be used for discussing and discovering the relationships of living things to each other.

http://www.onlpharmacy.com/blog/tag/genomic-information

Sure enough, phylogenies based on molecular data are quite common. A simple search for "molecular phylogeny" in Google Scholar gives >326,000 results. While these can deal with anything from bacteria, to plants to animals, to distinct parts of animals. These have allowed people to discover far more information about relationships of living things. The concept is simple enough, use the same basic thing to compare, say a certain nucleotide or protein, pick your set of organisms with one or more outgroups, align them, then compare them. As a note, you want to have roughly the same numbers for each individual you use. So, say you investigate the cytochrome b protein in felids, you would want the total number of proteins in each taxon to be roughly, say all around 200 total aa proteins (or whichever number you decide upon).

After aligning all of them and running them through a program like PAUP, you will get at least one cladogram. It may look something like this:

Stephens and Wiens 2003, fig. 3

The above figure is figure 3 from Stephens and Wiens (2003). It shows two molecular phylogenies, one as maximum parsimony (a) and the bottom as maximum likelihood (b). I won't be getting into the difference between the two at the moment, just realize they are two slightly different ways of analyzing the same data. The two phylogenies actually do combine three separate data sets though and combine them. They both use cytochrome b, 16S and ND4 data sets.

At first glance, it seems that these do a very good job of agreeing with the known taxonomy presented by the different genera. The only problem is that Clemmys is strongly split at the bottom of the phylogenies. This was cleaned up after this paper was published, however, with the Western pond turtle (Actinemys) and the wood turtle and bog turtle (Glyptemys) being placed in different genera.

Actinemys marmota (left) Glyptemys muhlenbergii (top), Glyptemys insculpta (bottom)

 So, in just looking at the molecular data, the family Stephens and Wiens (2003) were investigating seems to be pretty well off. But they didn't leave it to just that data. They also looked into the morphological data as well:

Figures 4 and 5 from Stephens and Wiens (2003)

Graptemys flavimaculata

These two figures above [figs 4 and 5 from Stephens and Wiens (2003)] show the authors' results on there morphological data alone. They did use soft tissue, osteological, morphometric, and statistical data as part of this set. The use of any of those sets can be debated, and has by some people. They also use two ways of attempting to scale the data so that weighting would be, presumably, the same. I won't get into those here, but be aware of them and that they are not agreed upon fully. What can be easily seen is that the two phylogenies above do not agree with each other. The relationships shown are not the same. In the phylogeny on the left, Pseudemys comes out as the most derived member, while the one on the right has Graptemys in the same position.

Trachemys scripta elegans

I would like to focus on Trachemys though. The slider turtles are the subject of my Master's thesis at the moment, and have been the topic of much debate for quite a while now. Without getting too detailed at the moment, it is apparent that many researchers have been well aware of the problems, but no one has taken it upon themselves to completely clear it up. Dale Jackson did some work on the group in the 1970's and 1980's, but their is still far too little known about them. What can be seen is that the members of Trachemys in the phylogenies above does not come out as a cohesive or monophyletic group. Not only the genus, but, many times, the supposed species (with their respective subspecies) don't group together well either. In these instances, Trachemys comes out as either paraphyletic or polyphyletic. It can even be seen in the phylogeny on the right that the Pseudemys group is well nested within Trachemys.

This is a bit disturbing to someone researching the group. What exactly is going on? One key aspect to keep in mind is that convergence due to similar lifestyles can be a big problem. If different taxa have evolved the same or similar features to do the same things, they may be seen as more closely related then they truly are. This depends on the characters and features that people use to make their phylogenies though. The hope is that, with enough characters and features being used, the true relationships will come to light. If that is the case or not is not actually known at the moment.

Paleontologists only have the luxury of morphological data sets. Perhaps one day we will get some DNA from a dinosaur or other long extinct species, but that is not so today. They use what they can, and come up with phylogenies and relationships based on that data alone. It has been said by some researchers, including John Wiens on numerous occasions, that combining the molecular and morphological data sets is a good idea. The idea being that they will strengthen each other, assuming that they are both working towards the same end (correct?) phylogeny. It was suggested to me that, even working with fossils and modern taxa, and even only having molecular data for the modern taxa, that combining the data sets would be recommended and should strengthen all the relationships in a phylogeny of fossil and modern taxa. Stephens and Wiens (2003) did this as well with their modern taxa, combining all their data sets with the following phylogeny:

Figure 7 from Stephens and Wiens (2003)

Malaclemys terrapin

In the figure above, which shows all taxa in their study, Trachemys first appears to fall out all together. All Trachemys species appear within a "group", all their names above or below each other, with no other nested genera present. If you look more closely though, you will see that Trachemys is still not monophyletic. In this instance, they should either be split apart into 5 (yes 5!) different genera, or have other genera combined as Trachemys. This seems somewhat crazy, since most researchers have felt that the group was either fairly well set, or that they should be combined with Pseudemys and/or Chrysemys. In fact, with this grouping, it would be Graptemys and Malaclemys that should be grouped with Trachemys to make it a monophyletic group. As a note, I DON'T believe that the idea of subgenera is a good idea and/or the answer.

They also had a second phylogeny which only took into account the taxa with complete data sets (Stephens and Wiens, 2003, fig. 8), which is to the right here-------------------------------->

These groupings seem to become far nicer and follow known taxonomic groups. It is of note, though, that only a single Trachemys species is present in this table. So, is it Trachemys alone that is causing all these problems?







I am not so sure of that. It makes more sense for it to be a problem with a number of taxa within the Deirochelyinae, although Trachemys may be the biggest trouble-maker. I believe that convergence is one of the biggest problems here. Many of these turtles live in similar environments and do similar things. Because of this, they have developed many of the same features. A key area to look at may simply be what features are being used for these phylogenies. Another key area could be that more molecular data needs to come to light on this group in general.

Regardless, I have talked with Dr. Jacques Gauthier, who has informed me that this kind of concept, where the molecular and morphological data do not agree, is a relatively common occurrence. Not just with this group, or even just turtles, but many groups. This is especially true when dealing with fossils and fossil groups.

The molecular data seen above does not agree with the morphological data. In essence, because they don't agree, they are working against each other. When combining the two different sets, the one with the most data will simply win out. This is not what we are scientists are striving for. We want the two different kinds of data to agree and give us a stronger idea of the true relationships present. Sometimes this does happen and they data sets essentially agree, but all too often that is not the case.

Ray-finned fish evolution from Hurley et al. (2007), image from Dracovenator blog

So, why can't the molecular data and morphological data agree? While I don't know the exact answer, I believe that eventually they will. We just haven't gotten enough of either. We must believe that the true relationships will eventually come to light with enough good data. So keep plugging away, and we will figure these things out. Even if the organisms themselves do not care how they fit in together; Trachemys doesn't care how it relates to the Alligator that may be trying to eat him, many people, myself included, do care.

Trachemys and alligatorid

Look to the Dracovenator blog post titled: Problems in Ray-Finned Evolution to see another case of disagreement with a different group, the ray-finned fishes.


References:

Stephens, P. R. amd J. J., Wiens. 2003. Ecological diversification and phylogeny of emydid turtles. Biological Journal of the Linnean Society 79:577-610.

Hurley, I.A., Lockridge Mueller, R, Dunn, K.A.,Schmidt, Friedman, M., Ho1, R.K., Prince, V.E., Yang, Z., Thomas, M.G. and Coates, M.I. (2007)A new timescale for ray finned fish evolution. Proc. R. Soc. B 274, 489–498 

Alamosaurus and the North American sauropod hiatus

Hello all, I know I've really dropped the ball on this one. It's been far too long. But I'm finally back from SVP in Las Vegas and have a bit of free time to try to catch up and write some things. The meetings went rather well and, as is always the case with these things, I gained tons of information and ideas, and I can't begin to actual use all of them. That leads me in to today's post though. Jeff Wilson and Mike D'Emic, two excellent sauropod paleontologists gave two very good talks on titanosaurs, Alamosaurus, and North America at the meeting, and I will discuss them briefly here, along with some of my questions and ideas.

Image of Alamosaurus from SV-POW blog: http://svpow.wordpress.com/2009/09/02/how-big-was-alamosaurus/

Sphaerotholus (also sometimes called Prenocephale)

First, D'Emic's talk (D'Emic, 2011) focused on much of his Ph.D. research on titanosaurs, and this led into the "27 million year sauropod hiatus' in North America toward the end of the Cretaceous. This was ended, for anyone who isn't aware, by the appearance of Alamosaurus in the Late Cretaceous. D'Emic presented a very interesting phylogeny for the Titanosauriformes. Alamosaurus came out on the end of the cladogram as one of, if not the most, dervied member of the Titanosauria. D'Emic hypothesized that the sauropod hiatus was a result of regional extinction. This regional extinction may have been the result of the infusion of other taxa (such as hadrosauroids), or could have been brought about by other factors, of which we are not certain or aware of at this time. Still, many authors have hypothesized that sauropods, namely Alamosaurus, migrated to North America from South America (where titanosaurs are relatively abundant) or from Asia, where a large number of other taxa are thought to have come from, such as anykylosaurids (Nodocephalosaurus) and pachycephalosaurids (Sphaerotholus, Prenocephale). While we aren't sure yet where they came from, we do know they were here.

The presentation by Wilson (actually presented by D'Emic at the meeting) was mainly discussing whether Alamosaurus is a valid taxon (Wilson and D'Emic, 2011). As reported by Jasinski et al. (2011) Alamosaurus was named based on a nearly complete scapula as the holotype and a nearly complete ischium as the paratype, The material was collected by Reeside in 1921 in the Naashoibito Member of the Ojo Alamo Formation in the San Juan Basin of New Mexico, and named and described by Gilmore (1922).

Fig. 12 from Jasinski et al. (2011), showing A-B, USNM10486 (holotype), left scapula and C-D, USNM 10487 (paratype), right ischium, bars scales  = 10 cm.

These specimens, and this taxon have been the topic of a lot of discussion. Part of the reason for this is the fact that they are somewhat scrappy, and this means that the taxon itself is based on less then ideal material. This also makes it quite difficult to confidently refer other material to Alamosaurus. Nevertheless, the prevailing thought has been that there is a single taxon of sauropod present in North America during the Late Cretaceous. Due to the normalized acceptance of this idea, essentially all sauropod material from North America during this time has been referred to Alamosaurus. Some have conservatively identified some material to Sauropoda indet. or to Titanosauria indet., but this is a small minority. Wilson and D'Emic (2011), however, completed a thorough revision of the type material for Alamosaurus and took this re-investigation further. As was commonly the practive in the early twentieth century, Gilmore (1922) did little to offer some kind of diagnosis for a newly named taxon. Wilson and D'Emic (2011) found that the holotype (and other type) material did contain several autapomorphies, signifying that Alamosaurus is, certainly, a valid taxon.

Herd of Alamosaurus sanjuanensis

Now this was an important step to take. Many authors had used Alamosaurus in phylogenetic analyses and comparisons without being certain of its validity. Some authors, however, have other questions regarding Alamosaurus. Jasinski et al. (2011) did not question its validity, but they did, however, question whether it was being used as a garbage (or waste-basket) taxon. A garbage taxon is when where many taxa or specimens are commonly lumped together without real distinct reasons or definitions. Their thought was that all sauropod specimens were being thrown together even though they couldn't be confidently referred to Alamosaurus. Regardless of whether it was true or not, Alamosaurus was being made the only possible sauropod in North America at this time.

Who's to say there wasn't more than one sauropod taxa in North America in the Late Cretaceous?

Wilson and D'Emic (2011) attempted to address this issue as well. Due to their re-evaluation of the type material, and the material that could then be referred to the taxon through their determined autapomorphies, they were able to come up with a far more thorough diagnosis. Several of the newly referred specimens were far more complete, and this allowed for several confident referrals.This does clear up some of the confusion and some of the problems. It does not, however, clear up all of them. While Wilson and D'Emic attempted to use this as a way of saying that Alamosaurus was, indeed, not a waste-basket taxon, I must thoughtfully disagree.

Although they were able to refer more specimens to Alamosaurus, they were not able to confidently refer all Late Cretaceous sauropod material from North America to Alamosaurus. Their is still plenty of material out their that has not, or can not, be referred. I have seen several specimens of the same element that appear to be significantly different in various aspects, including morphologically. This means that Alamosaurus is still being used, in many ways, as a waste-basket taxon.

I find it somewhat unlikely that only a single sauropod taxon occupied North America from the time of a "sauropod migration" back into North America until sauropods died at at the end of the Cretaceous or just before. It seems far more likely for there to have been more taxa and, assuming they were rare (or more rare) we have not found their remains or have just not been able to positively identify them as such. Wilson and D'Emic (2011) took a very positive first step in this, and their study is very important. I hope to see a complete paper on this in the not too distant future. One thing to remember is that even some of what they do is referral by provenance, so they do have some problems with their study. Still, this may be a good first step in, not only re-evaluating Alamosaurus, but re-evaluating numerous other taxa that face similar or other key problems.

Alamosaurus defending themselves, special thanks to artist for this great artwork

Let me know if you have any thoughts on this though. I would love to know if I am vastly in the minority on this subject, or if other people share my reservations and thoughts.



REFERENCES

D'Emic, M. 2011. Early evolution of titanosuriform sauropod dinosaurs: taxonomic revision, phylogeny, and paleobiogeography. Journal of Vertebrate Paleontology 31(Supplement): 95A. (abstract) 

Gilmore, C. W. 1922. A new sauropod from the Ojo Alamo Formation of New Mexico. Smithsonian Miscellaneous Collections 72: 1-9.


Jasinski, S. E., R. M. Sullivan, and S. G. Lucas. 2011. Taxonomic composition of the Alamo Wash local fauna from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin 53: 216-271.

Wilson, J. and M. D'Emic. 2011. The validity and paleobiogeographic history of the titanosaur sauropod Alamosaurus sanjuanensis from the latest Cretaceous of North America. Journal of Vertebrate Paleontology 31(Supplement): 215A. (abstract) 

Cretaceous Turtles of New Mexico Part 1: Here comes the meteor?

Since some of you may be aware that one of my major interests revolve around turtles, both alive and dead, its surprising that its taken me this long to post anything on this amazing group or reptiles. While there are an incredible number of things that can be posted, this will be more of a simple post based around one of my recent papers (Jasinski et al., 2011). From what is known about the San Juan Basin, specifically in New Mexico, these are the last turtles known before the K-T extinction event and the moment in time when the bolide hit the Yucatan.

Glyptodontopelta mimus from Naashoibito Member (Ojo Alamo Formation)

Ojoceratops fowleri

The study itself was on all the fossil vertebrates recovered from the Naashoibito Member of the Ojo Alamo Formation (Jasinski et al., 2011). The fossil vertebrates from this stratigraphic unit have been grouped together in what is called the Alamo Wash local fauna and were originally studied by Lehman (1981), but were in thorough need of revision. There are several key dinosaur taxa within this fauna, including the recently named Ojoraptorsaurus boerei. Other endemic taxa to this fauna include the ankylosaur Glyptodontopelta mimus and the ceratopsid Ojoceratops fowleri. It is also contains the types of Alamosaurus sanjuanensis, the youngest sauropod from North America. Alamosaurus has a number of potential problems though, and I will be touching on those in later posts.

So, the focus of this post is on those lovely creatures how keep their houses on their backs. The turtles from the two underlying formations are under study by Dr. Robert Sullivan and others and the study is currently waiting to come out in an upcoming volume on fossil turtles dedicated to Dr. Eugene Gaffney. So we will hope it comes out sooner rather than later. The turtles from the Naashoibito Member are vastly understudied and little attention has been paid to them. Much of this is because most material is very fragmentary, and there has been little there that would even qualify as a potential holotype for a turtle species.

reconstructed Basilemys, similar to Basilemys nobilis

Even so, two turtle species have been named from this unit. The first, called Basilemys nobilis, was named by Hay (1911) based on several carapace and plastron fragments. Basilemys is a member of the Nanhsiungchelyidae, and represents the only definitive terrestrial turtle from this turtle fauna. The forthcoming study by Sullivan et al. came to the conclusion that B. nobilis was a nomen dubium. While a recently recovered specimen may yet prove that a legitimate species of Basilemys is present in the Naashoibito Member, the holotype of B. nobilis will still probably be taxonomically undiagnostic.

reconstructed shell of Adocus

The second holotype, named Adocus vigoratus by Hay (1911), is based on several carapace fragments. Adocus is currently part of the family Adocidae, although at one point it was considered in the same family as Basilemys. Being an aquatic species, it probably inhabited a familiar niche throughout the late Cretaceous and into the Paleocene. Jasinski et al. (2011) felt that the type specimen of A. vigoratus was undiagnostic though, and considered it a nomen dubium, although it does represent an adocid in the fauna.

Kinosternon subrubrum, close living relative of Hoplochelys

Recent studies on Compsemys (Knauss et al., 2011) and Hoplochelys (Lyson and Joyce, 2011), have revealed many synonymies for these two previously ill-studied turtles. While the specimens of the ?pleurosternid Compsemys and the kinosternoid Hoplochelys are generally quite fragmentary in this fauna, both have been referred to specific species. The ?pleurosternid is now called Compsemys victa and all North American Compsemys are thought to represent one species. The kinosternoid Hoplochelys has now been referred to the species H. clark, as has all Cretaceous specimens of Hoplochelys. Both turtles would have represented small aquatic species. Compsemys was a small gracile turtle with a number of distinct places on the shell with small and distinct bumps and small ridges.

Neurankylus (a baenid) showing color spots found on specimen from Paleocene in San Juan Basin

Boremys (Baenidae)

The Baenidae are a group of aquatic turtles well-represented throughout the Cretaceous and Paleocene. They come in a variety of sizes, but are commonly quite robust for water turtles. Considering the overall number of turtle fossils recovered from the Naashoibito Member, baenids are some of the most common. Even with the generally large number of turtle fossils, none have been identified to a given genus yet. This is because most are very fragmentary or undiagnostic.

Plastomenus, similar to a turtle found in Naashoibito Member

The Trionychidae are a group of aquatic turtles today commonly called soft-shell turtles. These turtles have been around since the Cretaceous and continue today around the world. Surface texture makes shell fragments easy to identify to the species, and one or more new species may yet be named from the trionychid material already collected from the Naashoibito Member. The only turtle skull material from this member is also from a trionychid, identified by Jasinski et al. (2011) as the right parietal of a large trionychid called Plastomenus.

A modern trionychid, Apalone spinifera, the spiny softshell turtle

Various other fragments of turtles have been recovered as well, but these are too fragmentary to assign to any specific family of turtles. I realize that this was a relatively small post, but I wanted to put this out there for the future. This is a small look at the last turtles known from the Cretaceous in this region of the world. While the age of this member has been debated for years, the two generalized camps range from either an early Maastrichtian age (~68 Mya) or later Maastrichtian (~66 Mya). I am currently working on a study into how the turtle fauna of the San Juan Basin across the K-T Boundary, which is leading to some interesting conclusions. I won't go into to much detail, but if you are going to SVP this year in Las Vegas, hopefully you will seek me out and ask me about them.

REFERENCES CITED

Hay, O. P. 1911. Descriptions of eight new species of fossil turtles from the west of the one hundredth meridian. Proceedings of the United States National Museum 38:307-325.

Jasinski, S. E., R. M. Sullivan and S. G. Lucas. 2011. Taxonomic composition of the Alamo Wash local fauna from the upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin 53:216-271.

Knauss, G. E., W. G. Joyce, T. R. Lyson, D. Pearson. 2011. A new kinosternoid from the Late Cretaceous Hell Creek Formation of North Dakota and Montana and the origin of Dermatemys mawii lineage. Paläontologische Zeitschrift 85:125-142.

Lehman, T. M. 1981. The Alamo Wash local fauna: A new look at the old Ojo Alamo fauna; pp. 189-221 in Lucas, S. G. (ed.), Advances in San Juan Basin paleontology. University of New Mexico Press, Albuquerque. 

Lyson, T. R., and W. G. Joyce. 2011. Cranial anatomy and phylogenetic placement of the enigmatic turtle Compsemys victa Leidy, 1856. Journal of Paleontology 85:789-801.

Sullivan, R. M., S. E. Jasinski, and S. G. Lucas. in press. Re-assessment of Late Campanian (Kirtlandian) turtles from the Upper Cretaceous Fruitland and Kirtland formations, San Juan Basin, New Mexico; in Brinkman, D., J. Gardner, and P. A. Holroyd. (eds.). Morphology and evolution of turtles. Springer Press, Dordrecht.

Stegoceras novomexicanum, a tiny southern dome-headed pachycephalosaur

Illustration of Pachycephalosaurus wyomingensis

Stegoceras novomexicanum is a new (ish) pachycephalosaur from the late Cretaceous of northwest New Mexico (Jasinski and Sullivan, 2011). I was lucky enough to name and describe this taxon recently with Bob Sullivan, a paleontologist who has spent a lot of time working on this enigmatic group of ornithischian dinosaurs. Pachycephalosaurids are essentially characterized by a dome on top of their skulls of thickened bone. They do have other synapomorphies that make them a monophyletic group, but the thickened skull rook is the most recognizable characteristic. Pachycephalosaurs are only known from the Late Cretaceous, and are best known from North America and Asia. Recently, Watabe et al. (2011) reported on what may be the earliest definite pachycephalosaur known, Amtocephale gobiensis from the Cenomanian-late Santonian of the Gobi Desert in Mongolia. I was lucky enough to help out with that study a bit, although I was not an author on the paper. Although Amtocephale appears to currently be the oldest known pachycephalosaurid known, it is not the most basal.

There are many problems surrounding pachycephalosaurs. These include questions about taxonomy, paleobiology, systematics, origin, and many other things. While these are all great topics for discussion, we will not be getting into them at the moment, although perhaps at a later time we will.

Skull of Pachycephalosaurus wyomingensis with lower jaws

In North America, pachycephaolsaurs are most well known from Canada and the northern United States. South of Wyoming there is almost nothing known of the pachycephalosaurs that roamed the land n the late Cretaceous. Longrich et al. (2010) recently reported on one such southern pachycephalosaur from Texas. Texacephale langstoni is based on a highly weathered frontoparietal dome The specimen itself is not highly diagnostic in general. In my newly published paper (Jasinski and Sullivan, 2011), we discuss its validity and make a case for why the holotype and referred specimens are not actually diagnostic and do not have any autapomorphies. We conclude that Texacephale langstoni is, therefore, a nomen dubuim. The specimens themselves, however, are still quite important. They mark some of the southern-most pachycephalosaur specimens known from North America and I hope that further material is found. Lehman (2010) actually reported on other pacycephalosaurid specimens from Texas that same year, although he felt that the material wasn't complete enough and only identified it to an indeterminate pachycepalosaurid. Hopefully more specimens are found that provide actual diagnostic features and it can be shown that it really is a valid taxon. I hope that it is, or will be, but only time will tell.

In 2002, Williamson and Carr reported on a juvenile pachycephalosaur from the Fossil Forest Member of the Fruitland Formation and a part of the Hunter Wash local fauna. Following this, Sullivan and Lucas (2006) reported that the specimen represented a juvenile Stegoceras validum based on, among other things, a squamosal shelf at the posterior of the frontoparietal dome. This would have been a vast geographic expansion of the taxon southward.

Figure of the skull and frontoparietal dome of a pachycephalosaur, Stegoceras validum

Stygimoloch spinifer

In the summer of 2008, I went out to the San Juan Basin of New Mexico with Dr. Bob Sullivan for field work. I had never done field work in Mesozoic strata before, so it was all new to me at that time. Oh the things I had to learn, so anything I found that I thought was interesting of weird or whatever the case may be, I showed to Bob in the hopes that I had struck "gold". While exploring a new area, I came across a weird piece of bone with no idea of what it was. When I showed Bob, he immediately knew it was a partial frontoparietal dome. I went back and found a few more fragments, but nothing substantial. The following summer we were at a relatively close site about a mile away, and I found a small bone sticking out of the side of a small hill. While Bob and I couldn't tell what it was, I made sure to get it out quickly before we left for the day. In the field it was identified as part of a croc skull, but we later saw it was a pachycephalosaur squamosal.


We were eventually able to identify both as from the same type of animal as the juvenile pachycephalosaur reported on by both Williamson and Carr (2002) and Sullivan and Lucas (2006). The paper was originally going to report on further Stegoceras validum specimens based on the earlier reports. But something didn't seem quite right. Thanks to the one specimen I had found the first summer (2008), we could tell that it was from an animal nearly full-grown and essentially the same age range as the type of Stegoceras validum. The specimens were all smaller and more gracile though. There were several other differences that I could find. I talked to Bob and told him that I felt it was a taxon distinct from Stegoceras validum. After discussing it for awhile, Bob agreed.

Stegoceras

Stegoceras novomexicanum is distinguished from Stegoceras validum based on possessing the following features: posteromedial extensionof the parietal reduced and sub-rectangular; squamosal sutural surface contacts of the posteromedial extension of the parietal roughlyparallel; supratemporal fenestrae more medial and enlarged; gracile and small adult size. While the small adult size can possibly be a contentious one and not the lone feature to distinguish two taxa, it can, nonetheless, be an added characteristic. The other features though, were confirmed by both Bob and myself through the direct inspection and comparison of many, and perhaps all, of the Stegoceras specimens known from Canada and northern United States.

Size comparison between Stegoceras validum and Stegoceras novomexicanum

Stegoceras novomexicanum is a smaller version of Stegoceras validum, and contains a more pronounced squamosal shelf, giving the back of its skull a somewhat more flattened appearance. Other than Texacephale langstoni (considered a nomen dubium), Stegoceras novomexicanum is the southernmost named member of the Pachycephalosauridae in North America. This small, taxon provides further evidence to the distinct nature of the animals from this time (late Campanian) from New Mexico and furthers the difference between the animals from the North (Canada, Montana, Dakotas, Wyoming, etc.) and those further south (New Mexico, Texas, etc). Here's hoping that more information is found on Stegoceras novomexicanum and other pachycephalosaurs in the not-too-distant future and that people realize that this will help to show more about this strange group of dinosaurs than previously known.

For another view of Stegoceras novomexicanum and a look at Amtocephale gobiensis, take a look at Jamie Headden's blog (The Bite Stuff - New domes-New Interpretations)

Literature Cited

Jasinski, S.E. and Sullivan, R.M., 2011, Re-evaluation of pachycephalosaurids from the Fruitland-Kirtland transition (Kirtlandian, late Campanian), San Juan Basin, New Mexico, with a description of a new species of
Stegoceras and a reassessment of Texacephale langstoni. New Mexico Museum of Natural History and Science, Bulletin 53, p. 202-215.

Lehman, T.M., 2010, Pachycephalosauridae from the San Carlos and Aguja formations (Upper Cretaceous) of West Texas, and observations of the frontoparietal dome: Journal of Vertebrate Paleontology, v. 30, p. 786-798.

Longrich, N.R., Sankey, J. and Tanke, D., 2010, Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA: Cretaceous Research, v. 31, p. 274-284.

Sullivan, R.M. and Lucas, S.G., 2006b, The pachycephalosaurid dinosaur Stegoceras validum from the Upper Cretaceous Fruitland Formation, San Juan Basin, New Mexico: New Mexico Museum of Natural History and Science, Bulletin 35, p. 329-330.

Williamson, T.E. and Carr, T.D., 2002a, A juvenile pachycephalosaur (Dinosauria: Pachycephalosauridae) from the Fruitland Formation, New Mexico: New Mexico Geology, v. 24, p. 67-68.

Coelophysis biomechanics and the early part of a '"career"

In sticking with a theme of some of my papers that have come out recently, I would like to briefly talk about Coelophysis biomechanics. Coelophysis, in case some of you aren't aware, is, at least in my knowledge, a fairly well known early theropod dinosaur from the Late Triassic of New Mexico (and Arizona). With that said, I started my college career looking to follow in the footsteps of my father and uncle and become a chemist. I learned, after a little over two years (yes, it probably shouldn't have taken me quite that long) that I didn't really want to spend the rest of my life being a chemist. I bounced around for a semester or two before I took a gen ed course regarding dinosaurs and mass extinctions. As almost all young boys do, I was fascinated with dinosaurs and extinct animals. I never thought of pursuing a career till I took that course and talked things over with the instructor, a paleobotanist (Peter Wilf). He managed to convince me to pursue paleontology (geology mainly). Luckily, a vertebrate paleontologist had started there not long before (Russel Graham), and he was very accommodating with me on whatever I wanted to work on. So, for my senior thesis I conducted a project on the biomechanics of Coelophysis.

Coelophysis bauri

Coelophysis is so "famous" because of the sheer number of fossils of this animal that have been found. Almost all (if not all) of them are from a single locality, Ghost Ranch in northern New Mexico. Hundreds of individuals have been recovered, but many more are still there. The quarry has been closed, at least for the time being, but there is always hope that it may be re-opened. I suppose that looking at more of Coelophysis is not that interesting to many people, but a huge accumulation of individuals could help with paleobiologic studies and community structure, or perhaps tell us innumerable other things of this interesting little meat eater.

For my study though, I was looking for complete, or nearly complete, lower jaws. I treated the jaws as a lever, and the amount of bone at any one point in that lever can allow someone to see how strong the jaw is. The more bone present, the stronger the jaw. Of course, length and position also play a factor. I won't go into the methods too much, for that you can look at the paper itself (Jasinski, 2011).

Varanus komodoensis (Komodo dragon)

Dromaeosaurus skull

What was found though, was that the mandible of Coelophysis was most similar to Varanus komodoensis (Komodo Dragon) and dromaeosaurids. This suggests that Coelophysis may have hunted in ways similar to both the Komodo dragon and dromaeosaurids.

This is interesting by itself, but I was also able to look at the skull of a juvenile. While it may bot be especially surprising, the juvenile showed a strength profile incredibly similar to the adult Coelophysis. This suggests that juvenile Coelophysis were hunting in ways similar to the adults. This doesn't mean that they would be taking the exact same prey, but both parents and adults would have been hunting things (and these things would have been larger than insects).

The thought is then, if juveniles had to hunt on their own and take their own prey, that Coelophysis was probably not a precoccial animal and was mainly solitary. Others have thought this, but this is another method of showing it. Other techniques and studies are needed to confirm or deny this idea.  Coelophysis may be more deadly then previously expected though.

Coelophysis bauri skull and lower jaws

Take a look at the Beasts Evolved blog page as well to get another brief look at this paper and bit of different information on it and the paleobiology of Coelophysis.

So, that was my senior thesis, and, with a few add-ons, was recently published in the New Mexico Mexico Museum of Natural History and Science Bulletin. If you would like a copy, feel free to email me (sej139@yahoo.com). Otherwise, I am still early in my potential paleo career, so there should be plenty more to write about as I go.

Reference
Jasinski, Steven E. 2011. Biomechanical modeling of Coelophysis bauri: Possible feeding methods and behavior of a Late Triassic theropod. New Mexico Museum of Natural History and Science Bulletin 53: 195-201.

Ojoraptorsaurus and Epichirostenotes - 2 new caenagnathid dinosaurs

Greetings and welcome to my new found blog everyone. First, thanks for stumbling upon this page, and second, hopefully thanks for reading and commenting on this post. I want to start off with a post on two new caenagnathid dinosaurs that I and two co-authors have named [1]. A quick note on the group these two dinosaurs below two, in case you are not familiar with them, and then a few things about them in general. This post will be fairly long, but stick with it because it will be the first look at two brand new dinosaurs. The paper will be out very, very soon, but here is a sneak preview.
  
The Caenagnathidae are a group of somewhat rare and enigmatic theropod dinosaurs within the larger group known as oviraptorosaurs. They are currently known from Asia and North America, although other members of the Oviraptorosauria (not members of the Caenagnathidae) have been found elsewhere, including one recently published that is considered an oviraptorosaur or oviraptorosaur-like from Europe (read about it at http://scienceblogs.com/tetrapodzoology/2011/05/tiny_cretaceous_theropod.php). The caenagnathids are some of the least studied members, which is partly from a lack of material in general and nearly complete specimens. I am not going to get too in depth right now on all of this and the background to caenangthids because part of it was covered quite well by Jaime Headden on his blog The Bite Stuff (http://qilong.wordpress.com/2011/01/28/splitting-chirostenotes/).

An overview of  members of the Oviraptorosauria, with the two newly-named dinosaurs being new members of.

Needless to say, there is a lot of confusion surrounding this group of dinosaurs, and much work that can be done. Having said this, several years ago, Dr. Robert M. Sullivan of the State Museum of Pennsylvania led a very small field party to the San Juan Basin in the northwestern New Mexico. One of his field assistants, Arjan Boere, came across a peculiar bone. After field prep, extraction, further prep and study, it was discovered that it was an incomplete pubis from a caenagnathid.

The specimen (SMP VP-1458) came from the Naashoibito Member of the Ojo Alamo Formation, which recently went through a thorough study and revision [2] and was confirmed to be early Maastrichtian in age, or roughly 68-72 Mya. The layer is not very especially fossiliferous, and often the fossils recovered from this layer are quite fragmentary or broken. Recently several new taxa have come from the layer, including the ceratopsid Ojoceratops [3]. Nevertheless, with the K-T boundary layer missing from this region, the Naashoibito Member holds the keys to the last remaining taxa present before the very end of the Cretaceous.

The pubis was determined to be distinct from all other caenagnathid pubes and was given the name Ojoraptorsaurus boerei [1]. Its genus was named for the strata in came from, and species for its original discoverer. It includes the autapomorphies: "1) a “spoonshaped” depression on the anterior dorsal surface of the pubic boot; 2) enclosed pubic fossa recessed at least one cm from the acetabular rim, positioned on the medial surface of the pubic shaft; 3) the distal portion of the pubic shaft above the pubic boot is slightly convex anteriorly; and 4) the iliac peduncle articular surface of the pubes is sub-trapezoidal in shape." While some people will feel that naming a dinosaur based on the pubis is not a good idea, there are reasons for it that I and my co-authors felt warranted this. Caenagnathids are commonly known from very fragmentary material anyway. This includes a number named only on lower jaws, and the most complete specimen (CM 78001) is currently under study and has not yet been named. The pubis itself seems like a very diagnostic element in terms of caenagnathids. Through all the trips to look at the other caenagnathid specimens, and many other oviraptorosaur specimens, SMP VP-1458 was still distinct and showed the four mentioned autapomorphies. Therefore, along with its distinct geographic provenance and interesting temporal position, it deserved to be named. This way, if others think we are completely full of crap, they can write something and tell us how and why we are. Still, science and the knowledge of this group of dinosaurs will move forward because of it.

Part of the pubes of SMP VP-1458, the holotype of Ojoraptorsaurus boerei [1]

Ojoraptorsaurus boerei would be quite similar in many aspects to other caenagnathids, including the most well-known member of the group, Chirostenotes. Since we are working off only post-crania, we must extrapolate that the rest of the animal would have been similar to other members, although we can always let our minds wander and come up with something looking completely different and amazing, which is still a possibility until more of the animal is recovered.

Illustration of Chirostenotes, close relative of both Ojoraptorsaurus and Epichirostenotes, and very similar to what both taxa would have looked like.

While doing this research, the authors came across differences between a specimen (TMP 79.20.1) of Chirostenotes that is confidently referred to the genus based on similarities with the holotype (CMN 2367), which is an incomplete set of right and lefts hands. Another specimen that was referred to Chirostenotes though (ROM 43250) was found to have some key differences with TMP 79.20.1, and therefore with Chirostenotes. My co-authors and I, therefore, decided that the differences warranted the erection of a new taxon, Epichirostenotes curriei [1]. The major differences seen firsthand dealt with the ischium, but several more were extracted from the description by Sues [4]. The entire specimen, and the new taxon that goes with it, needs more thorough study and revision. But that discussion, and the potential research surrounding it, is something that will be discussed a bit later.

Illustration of Chirostenotes, close relative of both Ojoraptorsaurus and Epichirostenotes, and very similar to what both taxa would have looked like.

 

 

NOTE: I am looking for someone to potentially illustrate both these new dinosaur taxa, so if anyone would be interested or know of someone else who may be, please let me know.



REFERENCES
[1]Sullivan, R.M., Jasinski, S.E. and Van Tomme, M., 2011, A new caenagnathid Ojoraptorsaurus boerei, n, gen., n. sp. (Dinosauria, Oviraptorosauria), from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico: New Mexico Museum of Natural History and Science, Bulletin 53: 418-428.

[2] Jasinski, Steven E., Robert M. Sullivan, and Spencer G. Lucas. 2011. Taxonomic composition of the Alamo Wash local fauna from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin 53: 216-271.

  

[3]Sullivan, R.M. and Lucas, S.G., 2010, Ojoceratops fowleri gen. nov., sp. nov., a chasmosaurine (Ceratopsidae, Dinosauria) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico; in Ryan, M.J., Chinnery-Allgeier, J. and Eberth, D.A. eds., New perspectives on horned dinosaurs: Bloomington, Indiana University Press, p. 169-180.

[4] Sues, H.-D., 1997, On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from western North America: Journal of Vertebrate Paleontology, v. 17, p. 698-716.