Research Projects

Since we are definitely better at starting projects than we are at finishing them, we always have a few different ones going on at once. Although we work on a wide variety of specimens from localities all over the world, most of the papers we publish relate to a few broad areas of interest that Dr. Reisz has been pursuing over the years with the help of a succession of colleagues and students:

Varanopid Revision

One of the clades of basal synapsids (see below) currently receiving an inordinate amount of attention in our lab is Varanopidae. These are small predatory animals that, unlike most other groups of "pelycosaurs," persist relatively unchanged from the Upper Carboniferous of North America to the Upper Permian of South Africa and Russia. This stasis is interesting given that other "pelycosaurs" are replaced by more derived synapsids in later times. Studies underway, involving many of the denizens of the lab, are examining the most primitive varanopids, which are very interestingly from both the beginning and end of their known duration. This suggests that not only are varanopids survivors, but that they maintain their diversity throughout their time on the planet.

Early Herbivores

Suminia is an unusual, small anomodont mammal-like fossil from the Late Permian (260 million years old) of central Russia. Preliminary preparations of the skeletons have revealed some truly striking anatomical features, unexpected for such an ancient animal. Two recently discovered skeletons display specializations of the body, especially of the hands and feet, that shed light upon its way of life.

Suminia may represent the oldest known vertebrate to exploit food resources inaccessible to larger and bulkier herbivores. The fossil record shows close relatives of this animal in South Africa, but they possess none of the striking adaptations shown by Suminia. Additional, more detailed study is underway in collaboration with former Master's student Natalia Rybczynski.

Variation in Dicynodonts

As an additional facet of the research program on herbivorous vertebrates, we are studying the mammal-like Diictodon from the Late Permian (260 my) of South Africa. Diictodon is represented by hundreds of specimens. This allows us to examine not only its anatomy, but also aspects of its life history as shown by patterns of morphological variation. Taphonomic evidence suggests a lifestyle unique to Paleozoic tetrapods. Additionally, our detailed studies using measurements from numerous specimens indicate that there may be discrete differences in body types that might indicate complex social behavior.

Ongoing work is focused on characterizing the patterns of observed variation and the associations between the different morphs. This work is in collaboration with former Master's student Corwin Sullivan.

Growth in the Prosauropod Dinosaur Massospondylus

The preserved fossilized eggs of the prosauropod Massospondylus have been given to our lab recently to be studied in a collaborative effort with Hans-Dieter Sues of the Smithsonian National Museum of History, and the Bernard Price Institute (University of Witwatersrand, South Africa). They are located in a partially preserved nest. Many of the eggs have already hatched and are therefore empty. However, at least two of the eggs retain beautifully preserved embryos that need to be studied carefully using Computer Assisted Tomography and mechanical preparation. As the oldest known well preserved vertebrate embryos, these fossils are intrinsically of great interest. Additionally, their study will contribute significantly in studies of dinosaur evolution.

The tiny skeletons are preserved exquisitely, and even impressions of the body outline seems to be preserved inside one of the eggs. However, the skulls of these tiny animals need to be exposed since these fossils are surrounded by rock even inside the eggs. Together with several other fossil remains of Massospondylus, ranging from juveniles to full adults (5m long), these tiny embryos will allow us to study the pattern of growth in this early sauropodomorph. We are particularly excited at the prospect of being able to study the mystery of how an embryo that fits inside a 6cm long egg managed to grow rapidly into an adult of much greater size. As the best known predecessor of the giant sauropod dinosaurs like Diplodocus, the study of its growth pattern from embryo to adult is also critical to our gaining a better understanding of the fascinating problem of the origin and ontogeny of the largest animals to have ever walked the earth.

A growth series of skulls of Massospondylus at the same scale showing the changes in the shape and proportion of the skull. Quantifying these types of changes helps us better distinguish between characteristics that are truly diagnostic of different species from size related features. Additionally, understanding patterns of growth can inform us to possible genetic mechanisms underlying evolutionary changes.

Parareptiles and the Origin of Turtles

The ancestry of turtles has always been something of a mystery, largely because their body shape is so greatly modified by the presence of a shell that they are difficult to compare to other reptile groups. Traditionally their closest relatives were thought to lie among a primitive group of superficially lizard-like reptiles known as captorhinids, but better candidates were discovered as the early stages of reptilian evolution became more thoroughly known. Most recent debate has focused on two groups of parareptiles (see our Bestiary), the pareiasaurs and procolophonids; our lab has published evidence in support of the procolophonid side, but others - who interpret detailed skeletal features differently - favour pareiasaurs. Over the past few years certain researchers, including Robert and Michael deBraga, have mischievously complicated the issue by finding support for a third alternative, that turtles are actually related to a more advanced group of reptiles known as diapsids. Some of our publications have dealt with other parareptiles, and Sean Modesto has done important anatomical, taxonomic and biogeographic work on the marine amniotes known as mesosaurs, which may be considered either as parareptiles or as close relatives of this group.

• Reisz, R. R. and Head, J. J. 2008. Turtle origins out to sea. Nature 456:450-451.
• Rieppel, O. and Reisz, R. R. 1999. The origin and early evolution of turtles. Annual Review of Ecology and Systematics 30: 1-22.
• Modesto, S. P. 1999. Observations on the structure of the Early Permian reptile Stereosternum tumidum Cope. Palaeontologia Africana 35: 7-19.
• deBraga, M. and Rieppel, O. 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society 120: 281-354.
• Reisz, R. R. and Laurin, M. 1991. Owenetta and the origin of turtles. Nature 349: 324-326. Rieppel, O. and deBraga, M. 1996. Turtles as diapsid reptiles. Nature 384: 453-455.

Evolutionary History of Pelycosaurs

The pelycosaurs (see our Bestiary) are a group of early "mammal-like reptiles" that, as the informal name implies, probably include the ultimate ancestors of mammals. Robert has published extensively on individual pelycosaur species, and had the opportunity to review the anatomy and classification of the group as a whole by contributing the pelycosaur volume of the Encyclopedia of Paleoherpetology, a major reference work covering the entire spectrum of fossil reptiles and amphibians. Related projects carried out in this lab include a description of the enigmatic Tetraceratops, a horned animal that seems to link pelycosaurs to their more advanced descendants, and (most recently) a phylogeny of the varanopseids, a particular group of carnivorous pelycosaurs.

• Berman, D.S, Reisz, R. R., Bolt, J. R. and Scott, D. 1995. The cranial anatomy and relationships of the synapsid Varanosaurus (Eupelycosauria: Ophiacodontidae) from the Early Permian of Texas and Oklahoma. Annals of the Carnegie Museum 58: 99-138.
• Dilkes, D. W. and Reisz, R. R. 1996. First record of a basal synapsid (mammal-like reptile) in Gondwana. Proceedings of the Royal Society of London (Series B) 263: 1165-1170.
• Laurin, M. and Reisz, R. R. 1990. Tetraceratops is the oldest known therapsid. Nature 345: 249-250.
• Laurin, M. and Reisz, R. R. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16: 95-102.
• Reisz, R. R. 1972. Pelycosaurian reptiles from the Middle Pennsylvanian of North America. Bulletin of the Museum of Comparative Zoology 144: 27-62.
• Reisz, R. R. 1986. Pelycosauria. Encyclopedia of Paleoherpetology 17A: 1-102.
• Reisz, R. R. and Heaton, M.J. 1980. The origin of mammal-like reptiles. Nature 288: 193.
• Reisz, R. R., Dilkes, D. W., and D. S Berman. 1998. Anatomy and relationships of Elliotsmithia longiceps Broom, a small synapsid (Eupelycosauria: Varanopseidae) from the late Permian of South Africa. Journal of Vertebrate Paleontology 18: 602-611.

Fauna of the Richards Spur Locality

Among the richest individual tetrapod fossil sites in the entire Palaeozoic is a Permian locality near Richards Spur, Oklahoma, which has yielded tens of thousands of bones belonging to over 30 species of small, terrestrial amphibians and reptiles. The bones occur within deep fissures that formed in a much older limestone deposit, and it is possible that at least some of these fissures represent caves in which the animals lived. Even after decades of study, the task of documenting the fauna is not complete - the list of species present at the site has recently been growing at an average rate of one animal every few months! For this reason, much of our work on Richards Spur material has been purely descriptive, but Robert and Corwin have also argued that the highly unusual fauna represents an otherwise almost unknown ecological community that inhabited upland regions early in the Permian Period.

• Dilkes, D.W. and Reisz, R.R. 1986. The axial skeleton of the Early Permian reptile Eocaptorhinus laticeps (Williston). Canadian Journal of Earth Sciences 23: 1288-1296.
• Heaton, M.J. and Reisz, R.R. 1980. A skeletal reconstruction of the Early Permian captorhinid Eocaptorhinus laticeps (Williston). Journal of Paleontology 54: 136-143.
• Laurin, M. and Reisz, R.R. 1989. Taxonomic position and phylogenetic relationships of Colobomycter pholeter, a small reptile from the Lower Permian of Oklahoma. Canadian Journal of Earth Sciences 26: 544-550.
• Reisz, R.R. 1980. A protorothyridid captorhinomorph reptile from the Lower Permian of Oklahoma. Life Sciences Contributions, Royal Ontario Museum 121: 1-16.
• Reisz, R.R., Wilson, H., and Scott, D. 1997. Varanopseid synapsid skeletal elements from Richards Spur, a Lower Permian fissure fill near Fort Sill, Oklahoma. Oklahoma Geology Notes 57: 160-170.
• Sullivan, C. and Reisz, R.R. 1999. First record of Seymouria (Vertebrata: Seymouriamorpha) from Early Permian fissure fills at Richards Spur, Oklahoma. Canadian Journal of Earth Sciences 36: 1257-1266.

Tetrapod phylogeny

With the increasing use of computers to implement new cladistic methods for analysing the relationships between different taxonomic groups, it has become possible to shed fresh light on the evolutionary history of vertebrates. Michel Laurin and Dr. Reisz have used these techniques to examine the interrelationships of early tetrapods, reaching the unexpected conclusion that both amniotes (i.e. reptiles, mammals, and birds) and modern amphibians are closely related to a group of diminutive Palaeozoic amphibians called lepospondyls. As a footnote to this work, Corwin and Dr. Reisz are presently investigating the effect of small body size on the analysis - we suspect that some groups may cluster together simply because their small size has led to the independent appearance of similar features in each case. Meanwhile, Jason Anderson has been investigating lepospondyl interrelationships and the effect that incomplete data has on the results of our analyses, and is currently studying various dissorophoid temnospondyls to expand his lepospondyl matrix into a full-blown test of lissamphibian monophyly.

• Laurin, M. and Reisz, R.R. 1995. A re-evaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113: 165-223.
• Laurin, M. and Reisz, R.R. 1997. A new perspective on tetrapod phylogeny. In Sumida, S.S. and Martin, K.L.M. (eds.) Amniote origins: completing the transition to land. Academic Press, San Diego. pp. 9-59.
• Laurin, M. and Reisz, R.R. 1999. A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of Earth Sciences 36: 1239-1255.
• Reisz, R.R. 1997. The origin and early evolutionary history of amniotes. Trends in Ecology and Evolution 2: 218-222.