Statement of Research
My current research efforts are divided between macroevolutionary paleobiology and tradional field paleontology. With regard to the former, I am primarily interested in the evolution of large-scale morphological changes within the non-tetrapod Vertebrata and the Echinodermata, and the origination of higher taxonomic groups, i.e. classes, orders, and families. In particular, I am investigating how various constraints, developmental mechanisms, mass extinctions, and large scale geologic changes have affected the course of metazoan life throughout the Phanerozoic. With regard to the latter, I am performing systematic and taxonomic studies involving both vertebrate, primarily chondrichthyan, and invertebrate faunas from South-Central, Mid-Western, Southeastern, Mid-Atlantic, and Gulf Coastal regions of the US.
The pattern of decreasing morphological diversification (or disparity) within the Metazoa and Land Plants throughout the Phanerozoic, i.e., the decreasing trend in rate of origination of higher taxa: phyla, classes, and orders, has been observed within numerous groups. For example, significant decreases in disparity have been reported in Paleozoic gastropods and Rostroconchia, stenolaemate bryozoans, higher taxonomic ranks of Carboniferous and Pennsylvanian ammonites, teeth of the Artiodactyla and Perissodactyla, crinoids and blastozoans, Silurian and Devonian vascular plants, articulate brachiopods, and Paleozoic seeds.
This pattern of decreasing disparity raises the issue of whether constraints of some sort increase. Numerous types of constraint have been postulated, for example, functional constraints, structural constraints (sometimes referred to as constructional or formal constraints), developmental constraints, genetic constraints, historical constraints (sometimes referred to as phylogenetic constraints), environmental constraints, and ecological constraints.
The current view is that constraints fall into two broad categories, internal or “developmental” and external or “ecological.” It is likely that historical and structural constraints are those that are expressed primarily in ontogeny. In this view, both historical and structural constraints fall under the category of developmental constraints. Historical constraints can originate because of past interactions between particular organisms and/or between the particular organisms and the physical environment. Thus, past adaptations, arising from ecological constraints, can have a hand in shaping present morphologies. Likewise, effects of genetic alterations, that is, changes in mutation rates, chromosomal rearrangements, and regulatory gene mutations, will be manifested mainly during ontogeny; therefore, genetic constraints fall primarily under developmental constraints.
Functional constraints, like historical constraints, can be either developmental or ecological (the same argument applies when defining functional constraints as either an external constraint, as in above, or an ecological constraint). Environmental constraints can be ecological constraints (e.g., when global cooling changes adaptive zones) or developmental (when the rise of atmospheric oxygen led to the evolution of collagen).
Thus, developmental constraints incorporate components of genetic, structural, functional, historical, and environmental constraints, whereas ecological constraints incorporate components of functional, historical, and environmental constraints.
Given that these two broad categories of constraints have been proposed to explain the phenomenon of decreasing disparity, the following two evolutionary hypotheses have gained popularity in recent years: (1) the empty ecospace hypothesis, and (2) the developmental constraint hypothesis. The first hypothesis borrows heavily from the classic model of ecospace filling. Here, early radiations begin in an unfilled ecospace. At first it is relatively easy to move long distances into new ecospace. The long jumps are associated with major morphological innovation, but as the ecospace becomes filled it becomes increasingly difficult to find novel terrain. Disparity decreases because competitive exclusion prevents further filling of densely occupied ecospace.
The second hypothesis proposes that the early metazoan morphological innovation was due to limited canalization of developmental processes. In this model it is proposed that during the Cambrian radiation there was a proliferation of cell types, and establishment of hierarchies of developmental processes and epigenetic cascades. Once these were established, only slight modifications were possible without detrimental effects upon fitness and viability. Although any model of morphological change will require changes in development, the developmental model argues that major morphological changes are due mainly to this mechanism. Thus, disparity decreases because of the effect of increasing developmental constraints upon morphological innovation.
Measuring the change of disparity over a mass extinction interval provides an ideal way in which to effectively remove ecospace limiting constraints, if indeed they are operating, and thus to distinguish the ecological constraint and developmental constraint hypotheses. The reasoning behind this approach is as follows. Given hypothesis 1, extensive morphologic innovation should occur whenever widespread ecospace becomes available, i.e. during mass extinctions. Under hypothesis 2 developmental programs severely constrain the amount of morphologic innovation possible. Each mass extinction event, therefore, provides an independent opportunity to test among hypotheses (1) and (2).
While the degree of disparity within a group is clear intuitively it is very difficult to measure. Various measures have been devised, but their properties and relative merits for capturing different aspects of disparity are not well understood. For these reasons, I undertook a comparative study of seven different measures. I found that no one method provides an adequate means for detecting all aspects of disparity. Thus, studies that use only one or two methods of disparity analysis may overlook certain patterns of morphological diversification. For the above reasons I concluded that a combination of measures should be used in most cases.
To distinguish empirically among the empty ecospace hypothesis and the developmental hypothesis I measured disparity in the Crinoidea, Blastozoa, and articulated Brachiopoda. For the first two groups, I used published data, but separated the character sets into “developmental characters” and ecological characters”, and measured changes in disparity over the End Ordovician, Late Devonian, and Permian (Crinoidea) Mass Extinction events. In the majority of the cases investigated, disparity rebounded to comparable levels or in some cases higher levels in both the Crinoidea and Blastozoa. The results indicate that developmental constraints are not solely responsible for the decrease in disparity throughout the geologic range of the taxa. The results indicate that the more likely scenario is that increasingly structured ecological guilds have made it much more difficult to allow large increases in disparity.
For the case study involving the articulated brachiopods, I generated my own data set from museum and field collections. I collected data from over 600 genera. A maximum of 10 ordered and unordered morphological characters, representing size, shape and various valve morphologies, were assigned to each specimen.
To empirically distinguish between the ecospace and developmental hypotheses, the change in disparity before and after the End-Ordovician, Late Devonian, End-Permian, Late Triassic, and End-Cretaceous mass extinction events was measured. For each taxon within the group, both continuous and discrete character sets were analyzed. Four different measures of disparity were used to analyze each character suite. Additionally, a separate analysis was performed on a subset of the articulated brachiopods, the rhynchonellids and terebratulids. As in the case of blastozoans and crinoids, in most cases disparity rebounded to comparable levels, with the rhynchonellids and terebratulids showing the largest increase in disparity after the end-Permian extinction, a clear example of an increase in disparity without a significant increase in taxonomic diversity. Again, the results indicate that developmental constraints may not be solely responsible for the decreasing disparity in this group.
Although mechanisms of niche replacement, entrenchment, and ecospace filling have been discussed thoroughly in the evolutionary paleontological literature (i.e., extinctions, competition, evolution of new adaptive morphologies), actual studies involving quantitative analyses have been lacking. To address this issue, morphological features of dentition in Late Cretaceous and Cenozoic marine vertebrate predators were analyzed. The analysis included species of Late Cretaceous and Cenozoic sharks, Late Cretaceous marine reptiles, and Cenozoic marine mammals. Dental characters utilized in the study were both discrete and continuous. Species included in the analysis were originally collected from Late Cretaceous and Cenozoic Formations located in the south-central, southeastern, and the mid-Atlantic US, as well as Europe and the Pacific Rim.
A morphometric “tooth space” was constructed using the eigenvectors generated from the PCA of the dental character data. The results of the analysis show that Mesozoic marine reptiles occupied a small, discrete region of the tooth morphospace, whereas Cretaceous sharks occupied a much larger, diffuse region of the morphospace. During the Paleogene a profusion of shark tooth morphologies occurred, and subsequently expansion into new areas of tooth morphospace. Yet no overlap with the morphospace previously occupied by Mesozoic marine reptiles occurred. With the evolution of marine mammals during the Cenozoic a large number of novel tooth morphologies evolved. Remarkably, many of the tooth forms converged on the Mesozoic marine reptile designs, and hence a major overlap of marine mammal tooth morphospace with the previously occupied Mesozoic marine reptile morphospace occurred. Additionally, the shift from heterodonty to homodonty occurred in several members of both the Mesozoic marine reptiles and the Cenozoic marine mammals.
Based on dental morphology, this study indicates that following the extinction of the Mesozoic marine reptiles during the Late Cretaceous, Cenozoic sharks failed to occupy the vacated niches, yet Cenozoic marine mammal dentition converged on the previous Mesozoic marine reptile tooth designs. Thus, Cenozoic marine mammals likely occupied the vacated Mesozoic marine reptile dietary niches.
Current and Future Macroevolutionary Research
While past research efforts have documented changes in disparity, niche replacement, and ecospace expansion of major marine taxonomic groups over epoch-level geologic intervals, some aspects, such as the phylogenetic relationships among species, were ignored. My current research efforts are concentrated on high resolution stratigraphical sampling, throughout the Phanerozoic and particularly before and after mass extinction events, coupled with a detailed phylogeny of the group under analysis. Using a phylogeny enables the identification of sister groups and provide the direct line of descent of each group undergoing analysis. Sister taxa from different environmental settings (determined by analysis of high-resolution facies sampling) can be used in order to gauge the effects of biotic and abiotic variables upon morphological innovation. Chondrichthyans and echinoids are currently being utilized in the high-resolution studies.
Another interesting area of my research focuses on groups that have undergone diversity “bottlenecks” during one or more mass extinction events. During a diversity bottleneck most of the disparity within the group is lost, leaving in some cases a single genus as the progenitor of all subsequent diversity and disparity. Thus, the amount of disparity generated and pattern of morphospace occupation from a single progenitor can be determined more than once for the group in question. (In cases where clades have undergone diversity bottlenecks during a mass extinction, each rediversification can essentially be treated as an origination of the group.)
The echinoids are an ideal group in which to analyze the pattern of disparity before and after mass-extinction-caused diversity bottlenecks. The echinoids experienced such a bottleneck (perhaps one of the most severe of the Metazoa) during the end-Permian extinction. Only a single genus, Miocidaris, is known to have survived the event. This single genus gave rise to the rich post-Paleozoic diversity of the echinoids. Today the echinoids comprise one of the most ubiquitous and diverse members within marine communities. Additionally, the echinoids are quite amenable to disparity analysis, with many discrete and continuous homologous morphological features.
Perhaps the most promising direction in disparity research, yet one of the most daunting, is the creation of a “universal” metazoan character set. The development of the universal character set would enable comparisons of disparity among groups in different phyla. Such a character set would be based upon functional morphology and also homology, in the form of developmental pathways, homeobox genes, and their resultant structures.
Here, form and differences in form, regardless of systematic relationships or origins are considered significant. Using homologous characters only, the tentacles of an ammonite, the tube-feet of an echinoid, and the legs of an arthropod would all be different structures, each arising from non-related groups . However, using a universal character set, the structures - legs - would all be considered comparable, both functionally, and in some respects developmentally, since the Hox gene distal-less is involved in each case.
The universal character set would allow for the measurement of disparity among the entire sampled fauna of a particular time period. For example, instead of separate values of disparity among brachiopods, arthropods, mollusks, echinoderms, and vertebrates, one single value could be calculated. This would enable thorough comparisons of disparity across time periods. A total measure of disparity for the entire fauna present in a facies would represent a measure of an ecosystem’s disparity. Furthermore, it would be possible to estimate the pattern of disparity change of the Metazoa (at least among the fossilized representation of the Metazoa) throughout the Phanerozoic.
Cambrian Poriferan Faunas - The Cambrian fossil Brooksella was first described by Walcott from cherty “star cobbles” that occur abundantly in the Conasauga Formation of the Coosa River Valley of Alabama and adjacent areas of Georgia. Walcott assigned three species to Brooksella: B. alternata, the type species of Brooksella; B. confusa, and B. cambria, to the cnidarian order Scyphomedusae. Subsequent interpretations of Brooksella indicated uncertainty about the origin of the fossil. Some fossils referred to Brooksella from the Coosa Valley and elsewhere have been interpreted as trace fossils, or as features of inorganic origin.
Due to the number of alternate interpretations of Brooksella, Loren Babcock and I conducted a restudy of Brooksella from the Conasauga Formation. It was immediately evident that the “star cobbles” represented body fossils of simple ellipsoidal construction. Brooksella specimens show wide morphologic variation, including a variable number of radially disposed lobes divided by deep radial grooves, and often a central opening on one side. The lobes typically terminate in small openings. The “star cobbles” do not regularly have lobes numbering in multiples of four, nor do they show tentacles or gonads, as expected if they had a cnidarian affinity. Seilacher and Goldring interpreted Brooksella from Alabama as a trace fossil on the basis of inferred radial tunnels and teichichnoid backfill structures. Using CT analysis it was evident that radial internal cavities occupy the lobes, but we were unable to find backfill in any specimen, and therefore we rejected the trace fossil interpretation.
Careful morphological analysis of the "star cobbles" indicated that Brooksella was closely allied with the Porifera. This interpretation was confirmed when numerous newly collected specimens were shown to have siliceous spicules preserved surficially and internally and a distinctive spongy appearance. The three-dimensional nature of most “star cobbles” suggested rapid fossil diagenesis of siliceous (probably hexactinellid) sponges. Additionally, the “star cobbles” show great variability in external shape, and morphologic patterns are gradational, which suggested that a single species name (B. alternata) should be used to embrace all forms described from the Coosa Valley.
As a follow-up to the Brooksella study, we are currently studying several other soft-bodied fossils, including another species of sponge, which we believe has been mistakenly misidentified as Eiffelia globosa typically found in the Canadian Burgess Shale.
Eocene Sepiid Faunas - I am currently working with the Department of Paleontology at the North Carolina Museum of Natural Sciences, conducting field research and performing systematic studies, on Paleogene sepiids. We revised the sepiid genus Belosaepia by creating a new, separate genus Anomalosaepia, and described four new species of Anomalosaepia found within the Castle Hayne Formation in southeastern North Carolina. Additionally, we described two new coleoid phragmacone steinkerns from the same locality.
We have recently described two exceptionally well preserved sepiid phragmacones from the Moodys Branch Formation, located in south-central Mississippi. Additionally, we are performing fieldwork in South Carolina, Georgia, and Alabama, collecting bulk samples from Eocene exposures. We are processing the samples in order to determine if there are new occurrences of previously described species, and to look for new, undescribed species.
We have recently begun description and analysis of several Eocene rhyncholites from the Castle Hayne Limestone. While known to collectors from the Carolinas, these intriguing fossils have eluded systematic scientific description.
Recently I have been involved in a research group that is isolating, analyzing, and characterizing ancient biomolecules found within the sheaths or cuttlebones of belosaepiids. A variety of techniques have been employed, including; Fourier Transform Infrared (FTIR) spectra, Immunohistochemistry (IHC) using anti-chitin antibodies, ultrastructural analysis using Transmission Electron Microscopy (TEM) and elemental mapping of non de-mineralized portions of the sepiid test. All evidence points to the preservation of original organics consistent with chitin from the Late Eocene sepiids.
Oligocene Sepiid Faunas - Recently, we described two new genera, Oligorostra and Oligosella, and two new species Oligorostra alabami and Oligosella longi, of coleoids from the Oligocene Chickasawhay Limestone of Alabama. Oligorostra alabami is assigned to the Spirulida with uncertain family affinities. Oligosella longi is so unlike other coleoids, that at this juncture, no order or family affinities are assigned. These specimens are the first Oligocene coleoids described from North America.
Eocene Crinoid Faunas - In conjunction with the North Carolina Museum of Natural Science, I have identified six comatulid crinoids; Palaeantedon caroliniana, Microcrinus conoideus, Hertha plana, Himerometra bassleri, Amphorometra parva, Glenotremites carentonensis, and described one new species Placometra n. sp., from the Martin Marietta Quarry near Castle Hayne, New Hanover County, North Carolina. Identification of Hertha plana, Amphorometra parva and Glenotremites carentonensis, though possibly reworked from sediments below the Eocene Castle Hayne Limestone from North Carolina, extends the paleobiogeographic range of European species to southeastern North America. Additionally, extension of the paleobiogeographic ranges of these three species has implications for timing Tethyan influence upon distribution of comatulid taxa.
Cretaceous Crinoid Faunas - While Cenozoic comatulids have been well described, Cenozoic fossil stalked crinoids are poorly known. Based on a large, new collection of disarticulated columnals and cups, a new gracile bourgueticrinid, Democrinus simmsi species nov., was described from the Eocene Castle Hayne Formation exposed at the Martin Marietta Quarry, New Hanover County, North Carolina. This is the first nominal bourgueticrinid from the Paleogene of North America, despite their moderate diversity locally in the Paleogene of Eurasia.
Currently, my lab is analyzing nearly 450 feet of the 1500 foot Kure Beach, NC core (USGS sponsored coring project). This section of core represents the entire Late Cretaceous Peedee Formation exposed at the coring site. To date, we have retrieved several comatulid centrodorsal elements and bourgueticrinid calyxes. These represent the first known occurrences of Cretaceous crinoids along the coastal plain of the Carolinas, and may represent new species.
Silurian Crinoid Faunas - My lab is also focusing on lower to middle Silurian crinoids found within active carbonate quarries of west-central and southwestern Ohio. This research has resulted in the discovery of a moderately diverse crinoid fauna, including new taxa. The last comprehensive study of the mid-Silurian crinoid fauna of the Silurian carbonates in west-central and southwestern Ohio was included in the 1900 study by Stewart Weller, “The Paleontology of the Niagaran Limestone in the Chicago Area.” Since then, a limited number of individual studies have identified additional faunas found within the Silurian bedrock, particularly the Brassfield Formation and the Cedarville “Dolomites”.
Current research in these bedrock deposits of Shelby, Miami, Mercer, and Dark Counties, has uncovered a greater diversity of Silurian crinoids than originally documented – many of which have not been described nor identified. Unidentified genera and species found within rock formations can be important factors in understanding past and present environmental conditions, morphological variations and evolutionary traits.
Determination of these organisms' identification will most certainly help fill in the gaps that remain in the historical existence of these marine organisms as well as the possibility in revealing new, unfounded species. A complete reexamination of this fauna will result in a detailed description, and if required, genus and or species classification of these newly discovered crinoids.
Mississippian Crinoid Faunas - I am currently performing systematic studies on the crinoid fauna from the Mississippian Burlington Limestone of southern Missouri and that of the Lower Mississippian Edwardsville Formation of central Indiana. Recently, a very diverse echinoderm site was uncovered southwest of Springfield, Missouri. Although several species of crinoids have previously been described from other Burlington exposures, this site contains several new species of crinoids, as well as a new species of echinoid. The Lower Mississippian Edwardsville Formation in Monroe County, Indiana has perhaps one of the most diverse and varied crinoid faunas of that age anywhere in North America. Although, some elements of the fauna have been extensively studied, these tend to be represented by calyxes weathered out and found along the reservoir where the formation is well exposed. The new material is found within the siltstones which form the exposure. Here the crinoids are finely preserved and are represented by a number of new species. Both sites will undoubtedly expand our view of the evolutionary history and paleoecology of the Pelmatozoa during the Mississippian period
Mississippian Blastoid Faunas - Tricoelocrinus is an uncommon blastoid found in mid-continent Mississippian (Meramecian) age formations. Members of the genus grow to relatively large sizes and have one of the most dramatically varied ontogenies recorded in the blastoid record. Early workers assigned species based on the size and shape of the theca. Some species may actually be artificial constructs, based on ontogenetic stages. Furthermore, the genus Tricoelocrinus appears to be derived from the blastoid genus Metablastus, through the process of heterochrony.
In order to determine species relationships among members of the genus Tricoelocrinus, my lab is currently investigating the ontogenetic relationship between Tricoelocrinus and Metablastus. The ontogeny of these groups has been little studied, and never quantified using modern morphometric methods.
Images of specimens used in the study are digitized and analyzed using the morphometric technique Procrustes Method. Procrustes Method is a least squares method that attempts to resolve objects of similar shape regardless of size by translating, scaling, and rotating the objects to achieve the best fit. The generalized Procrustes Method of superimposition generates an ‘average’ shape from all the input shapes and then offers residuals between the ‘average’ shape and the original input shapes. This method is well suited for analyzing the growth trajectories among blastoid species.
The definition of the parameters of this ontogeny may allow the synonymy of Metablastus and Tricoelocrinus species. Furthermore, the analysis has also provided additional evidence suggesting that Tricoelocrinus was derived from the blastoid genus Metablastus, through heterochronic process of peramorphosis.
Cretaceous Echinoid Faunas - I have recently re-described the echinoid fauna from the Coon Creek Formation, McNairy County, Tennessee. This study forms part of a larger work re-describing (and outlining future directions of study that are needed) the very diverse, Late Cretaceous Coon Creek fauna. While this study addresses the coarse taxonomic nature of the echinoids present, much work needs to be performed in order to identify, and describe many of the unknown species found at this site.
While the Late Cretaceous echinoids of the North Carolina coastal plain are better known and more thoroughly researched than their Tennessee counterparts, published reports on them have been sparse. Most descriptions dealt with irregular echinoids, including Hardouinia from the Peedee Formation. In most guides dealing with North Carolina fossils figures of the Late Cretaceous irregular echinoid Hardouinia mortonis are common. While local collectors have reported occurrences of Late Cretaceous regular echinoids, to date we have found no mention of Cretaceous regular echinoids from North Carolina in the literature.
Recent fieldwork by my lab brought to light two phymosomatoid echinoids, described as Phymotaxis tournoueri and phymsomatoid ident.from the Rocky Point Member of the Peedee Formation. These new specimens give a more complete list of the Cretaceous echinoid fauna of southeastern North Carolina.
In conjunction with the Mississippi Museum of Natural Science, we recently described a new Late Cretaceous cassiduloid echinoid, Hardouinia saucierae sp. nov.
This new species is found in northeast Mississippi within the Tombigbee Sand and in eastern Alabama within the Blufftown Formation. Our field investigations in Mississippi, Arkansas, and Texas have also uncovered several other undescribed Late Cretaceous, which we will be describing shortly.
Eocene Cassiduloid Faunas - As part of a larger project, my lab analyzed the morphological relationship between Late Eocene cassiduloids Echinolampas appendiculata, Rhyncholampas carolinensis and Eurhodia rugosa, all from the middle Eocene Castle Hayne Limestone in southeastern North Carolina. We also investigated the heterochronic relationship between R. carolinensis and E. rugosa. Specimens that were analyzed quantitatively using a truss consisting of 18 distinct morphological measurements. Principle component analysis (PCA) of these data indicated that the three groups are morphologically distinct. The analysis also showed that the groups shared parallel growth trajectories. Together with the PCA analysis, bivariate analyses showed a strong heterochronic relationship between R. carolinensis and E. rugosa. Additionally, statistical analysis of the data indicated Echinolampas appendiculata exhibited the most morphological variability among the three groups. Extinct and extant members of the three genera were found to inhabit fairly distinct water depths and substrates, thus the groups may have divided up their environment according to water depth. In light the morphological results and phylogenetic data we speculated that Rhyncholampas carolinensis and Eurhodia rugosa initially diverged from a Rhyncholampid ancestor. Competition between the highly variable E. appendiculata and a morphologically similar Rhyncholampid species may have provided the selective pressure for the evolution of the relatively deep-water cassiduloid Eurhodia. This work has paved the way for synonymizing the group Eurhodia within Rhyncholampas.
Currently I am describing a new species of Protoscutella, a clypeasteroid echinoid from the Middle Eocene Santee Limestone of southeastern South Carolina. Unlike other members of the genus, the newly discovered species is distinctly triangular in outline, with its periproct on the test margin. To date, this peculiar clypeasteroid has only been found in the Jamestown Quarry, in Orangeburg County, SC. At this locality, the new species is always found in the basal portion of the Santee Limestone, where it is outnumbered 50:1 by its conspecific relative, Protoscutella mississippiensis.
Eocene Clypeasteroid Faunas - The Late Eocene clypeasteroid echinoid Periarchus lyelli Conrad, 1834, is found in the Southeastern and South-Central United States, from Texas through North Carolina. Its wide geographical range, high abundance, and narrow stratigraphic zonation make this “sand dollar” an ideal index or marker fossil. Although the distribution and gross morphology of P. lyelli are well known, much controversy exists as to whether P. lyelli represents one species, consists of two sub-species, or two distinct species.
Within the Eocene Castle Hayne Limestone of North Carolina and the Santee Limestone of South Carolina, P. lyelli has a sub-circular test, slightly domed petaliferous area, and nearly flat oral surface. This is not the case in the coastal plain region of Alabama and Mississippi. Here, within the unconsolidated sands and marls of the Moodys Branch Formation, P. lyelli has a distinctive sharply conical petaliferous area, and a very thin outer margin. To describe the difference between the two morphologies Ravenel (1844) erected a separate sub-species, Periarchus lyelli pileusinensis. Sedimentary geologists familiar with the Cenozoic geology of the Gulf Coastal Plain have long used P. lyelli and P. lyelli pileusinensis as index fossils, treating each as separate species.
In order to determine if there is a valid morphological basis for taxonomically dividing P. lyelli, modern morphometric techniques are currently being used to analyze test shape. We have performed an Elliptical Fourier analysis followed by PCA on the lateral cross-sections of 72 specimens obtained from the Castle Hayne Limestone, Santee Limestone, and Moodys Branch Formation. The resulting analysis has yielded three clusters, with specimens from the Moodys Branch Formation forming a distinct cluster, while specimens from the Castle Hayne and Santee Limestone cluster closer together than those from the Moodys Branch Formation.
This preliminary study illustrates that P. lyelli found within the unconsolidated sands and marls of the Moodys Branch Formation are morphologically distinct from specimens found within the carbonates of the Castle Hayne Limestone and Santee Limestone and confirms that P. lyelli pileusinensis warrants sub-species, or possibly species status. In order to thoroughly test this hypothesis, we are currently analyzing hundreds of specimens from various formations throughout North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, and Texas.
We are currently involved in new species descriptions and systematic revision of the genera Protoscutella. The succession of species of Protoscutella is of great importance, as the members of the genus are important index fossils of the middle Eocene faunal zones of the Carolinas. While several species and “sub-species” are well known, our preliminary investigation indicates that several of the taxa represent morphological variants.
Miocene Echinoid Faunas – The genus Abertella is restricted to the Miocene, and ranges along the east coast of the Americas from Argentina to Maryland. The genus ranges to the close of the Miocene, apparently being displaced by northward migrating mellitid sand dollars (Smith 1984). We have recently named a new species, Abertella dengerli. With the addition of Abertella dengerli the genus Abertella Durham (1953) now contains eight species. Abertella dengleri is now the second species of Abertella described from North America.
Pliocene Echinoid Faunas – Recently several new species of echinoids have been uncovered from the Pliocene Goose Creek Limestone exposures in northeastern South Carolina. The striking aspect of the recovered echinoids, is that they are extremely large. This includes both new and previously described species. This characteristic is most pronounced in the species that is currently being described, Plagiobrissus sp. nov. The largest of the specimens collected measures nearly 18 cm long. This may be the largest fossil echinoid ever described or reported. In addition to Plagiobrissus, there are three other undescribed species, including a new species of the regular urchin Lytechinus. In addition to describing this new fauna, we are currently investigating the paleoenviroment for clues as to why members of the fauna have reached such large sizes.
We are also revising the terebratulid brachiopod Plicatoria wilmingtonensis. Originally described by Arthur Cooper, all major variants or hypotypes, were grouped together as P. wilmingtonensis. Careful systematic analysis has shown that are at least four distinct species within the taxon (to be submitted).
Currently my lab is investigating the sharp rise in generic diversity that occurred during the End-Devonian Period. We are documenting species, genera, and family richness, measuring the morphological diversity of tooth types, and determining the paleoenvironmental conditions that existed during the time of deposition. While we are compiling data world-wide, our field research is centered within the Illinois and Appalachian Basins. Here, little serious work has been conducted. We are currently describing four, paleontologically important, well preserved, Upper Devonian macro- and micro-vertebrate fauna containing sites; two from central Kentucky, one from central Ohio, and a particularly rich site located in southeastern Iowa. Late Devonian chondrichthyan faunas located in Kentucky, Iowa, and Ohio are typically found within bone-beds, lithological units that are noted by the high abundance of vertebrate material; bones/bone fragments, teeth, dermal elements, and other phosphatic vertebrate remains. Bone-beds tend to occur at the interface between two lithological units or members.
The first locality is a previously undescribed site within the Late, Middle Devonian (Givetian) Boyle Formation. The exposure consists of a series of road-cuts located on the west side of KY Rt. 89, approximately two miles south of the town of Mina. The outcrop exposes approximately 6 meters of the Boyle Formation, which is unconformably underlain by Late Ordovician Ashlock Formation, and overlain by 3 meters of the Late Devonian New Albany Shale.
The bone rich bed occurs within a distinct, 10 cm layer that spans portions of the exposure. The lithology of the layer consists of an olive-gray to brownish-gray, fine to medium-crystalline dolomitic limestone. Copious well preserved macro- and micro-vertebrate remains and phosphatic nodules are scattered primarily on the upper surface and within the upper two -to- three centimeters of the layer.
Macro-vertebrate remains include disarticulated arthrodire plates and isolated skeletal elements, as well as sarcopterygian tooth plates and teeth. Micro-vertebrate material consists of abundant conodont elements, acanthodian and paleonisciform actinopterygians scales, chondrichthyan dermal denticles and teeth. Chondrichthyans are represented by the cladoselachids Stethacanthus and Symmorium, by the phoebodontids Phoebodus and Thrinacodus, by members of the genus Protacrodus, as well as several undescribed species.
Stratigraphically, the Mina bone bed layer occurs within the Kiddville Member of the Boyle Formation, yet does not appear to correspond to any bone beds described therein. Surprisingly, the vertebrate fauna appears to be similar to Late Devonian faunas described within the Ohio Shales of Central and Northeastern Ohio. Given this discrepancy, future work will focus on careful lithostratigraphic, sequence stratigraphic, and biostratigraphic analysis, as well as faunal correlation with other Late Devonian faunas in the Midwest.
The second, is a series of three bone-beds that occur within a Middle - Upper Devonian Ohio Shale equivalent that is exposed in a stream bed located southeast of Clay City, KY. The outcrop is a condensed interval of dark, grayish, greenish calcareous shales and calcareous clay-rich sandstones that span the Givetian – Famennian Epochs. The uppermost bone-bed exposes carbonized wood, arthrodire plates and other skeletal material, copious conodont material, and a diverse and rich abundance of chondrichthyan and osteichthyan material. Our lab is currently isolating and identifying the chondrichthyan remains, as well as correlating the fauna with other faunas located in Central and Northeastern Ohio.
The third locality is a previously undescribed Middle to Late Devonian bone bed located near East Liberty, Ohio. Preliminary analysis of this bone bed has revealed copious well preserved macro- and micro-vertebrate remains. Macro-vertebrate remains include disarticulated arthrodire plates and isolated skeletal elements, as well as sarcopterygian tooth plates and teeth. Micro-vertebrate material consists of abundant conodont elements, acanthodian and paleonisciform actinopterygians scales, chondrichthyan dermal denticles and teeth. Chondrichthyans are represented by the cladoselachids Stethacanthus and Symmorium, by the phoebodontids Phoebodus and Thrinacodus, by members of the genus Protacrodus, as well as several undescribed species.
The fourth, perhaps most paleontologically significant site of the four, outcrops along the bank of the English River, near the town of Kalona, IA. Here the Maple Mill Member of the English River is exposed as a two meter section of white siltstone, with a basal bone-bed/tooth layer. The inclusive fauna contains a rich assemblage of chondrichthyan teeth, denticles, and dermal spines. The Maple Mill exposed at this locality grades into the overlying basal Mississippian McCraney Limestone, and thus marks the terminal portion of the Devonian within the Illinois Basin.
Mississippian chondrichthyan faunas found in Kentucky, Indiana, and Iowa are typically found within bone-beds, lithological units that are noted by the high abundance of vertebrate material; bones/bone fragments, teeth, dermal elements, and other phosphatic vertebrate remains. Bone-beds tend to occur at the interface between two lithological units or members. The nature of bone-bed formation, as well as statistical methods to enable determination of accurate diversity and abundance data is in need of careful investigation. Currently, my lab is investigating bone-beds and chondrichthyan bearing horizons found within the Haney, Salem, Big Clifty and Harrodsburg Limestones of east-central Indiana, the Fort Payne, Muldraugh, and Glen Dean Limestones of south-central Kentucky, and the Cedar Fork Member of the Burlington Limestone found within southeastern Iowa and northwestern Illinois. We have also started to investigate the chondrichthyan faunas of northern Alabama, particularly the Pride Mountain Formation, Monteagle and Bangor Limestones, and the Hartselle Sandstone. While chondrichthyan remains are well known to local collectors, little has been written on the systematics and taxonomy of inclusive taxa. Recently we have collected and documented faunas, both elasmobranchs and holocephalians from the Monteagle and Bangor Limestones, and bone-beds found within the Pride Mountain Formation.
Pennsylvanian and Permian Faunas
Pennsylvanian rocks in Ohio, Pennsylvania, and West Virginia are divided into four major groups; the Pottsville, Allegheny, Conemaugh, and Monongahela (oldest to youngest) (Camp, 2006; Feldmann & Hackathron, 1996). Each group contains fossiliferous units throughout. Notably, chondrichthyan teeth, denticles, and spines can be found in abundance within both marine and non-marine deposits (Hansen, 1986; McComas & Mapes, 1998; Morningstar, 1922; Murphy, 1971).
Of particular interest is the presence of shark ichthyoliths in both siliciclastic and carbonate units located in Athens, Columbiana, Coshocton, Guernsey, Hocking, Holmes, Jefferson, Lawrence, Mahoning, Morgan, Muskingum, Noble, Perry, Scioto, Tuscarawas, and Vinton Counties in Ohio (Hansen, 1986). While preliminary work was performed on documenting the diversity and abundance of chondrichthyans within selected outcrops much work needs to be done. Modern statistical techniques need to be applied in order to estimate diversity and abundance, new outcrops need to be located and sampled, old outcrops must be resampled, proposed species need to be formalized, and all localities, both new and old, need to be documented using modern techniques such as digital photography, GPS, GIS, and other geospatial techniques.
While preliminary paleoecological and systematic work has been performed in eastern Ohio, West Virginia, Pennsylvania, Kentucky, Missouri, Kansas, and Nebraska have been largely ignored. Of special interest is the placement of the Pennsylvanian – Permian Boundary. Recording the diversity and abundance of chondrichthyans on either side of the boundary may have profound consequences for studies involving disparity or key evolutionary innovations. Additionally, many of the reported chondrichthyan bearing units and localities have been degraded over time, or removed due to construction. Old outcrops must be located and resampled, new outcrops must be uncovered, and modern geospatial techniques need to be applied, and new species need to be formalized or described.
We are currently involved in describing marine chondrichthyan faunas from the Neva Member of the Grenola Limestone and the Bennett Shale Member of the Red Eagle Limestone, in and around Manhattan, Kansas, as well as related faunas from the Indian Cave Sandstone bed, of the Towle Shale Member, of the Admire Group from northeastern Nebraska. Additionally, the diversity and abundance of brackish–marine faunas from the Late Pennsylvanian and Early Permian from southwestern Oklahoma and west Texas are also being analyzed. These include faunas from the Permian “Red Beds” of Texas such as the Archer City Formation and the Ryan Sandstone from Oklahoma. Marine faunas from the Lueders Limestone, near Abilene, TX are also being investigated. The long term goal of this research is to correlate the Late Pennsylvanian and Early Permian chondrichthyan faunas from the Texas – Oklahoma basin with those of the Mid-Continent, and the Appalachian basin.
Although systematic work of Triassic chondrichthyan faunas from Arizona, New Mexico, and Nevada has been performed (Heckert 2002, 2006), diversity and abundance data is lacking. Along the Triassic Rift Valleys of the Northeastern and Southeastern US, chondrichthyan faunas have been encountered, but little systematic work has been performed. Overall, research among these crucial faunas needs to be performed or revised using modern systematic and statistical techniques. Currently, I am interested in the abundance and diversity of Triassic chondrichthyans from the Southwestern and Eastern US. Not only will research on these crucial North American faunas fill in some of the “missing gaps” concerning chondrichthyan post-Paleozoic evolution, but will allow a comparison among their Gondwanian counterparts.
Cretaceous – Eocene Faunas
While much work has been performed on describing Cretaceous – Neogene chondrichthyan faunas, particularly in the Southeastern and Gulf-Central US, much work remains to be done. As in the cases of the other faunas previously mentioned, diversity, abundance, and paleoecological data is either missing or has been largely ignored. Many new localities remain undescribed. Faunas within carbonates have been largely ignored due to the amount work necessary to isolate chondrichthyan remains. Lithological units are in need of revision and correlation throughout the regions. Currently, my lab is locating previously described localities, recollecting each locality, and applying modern geospatial techniques each locality.
We are currently describing the diverse and abundant elasmobranch fauna found within the Santonian age Eutaw Formation that outcrops along Luxapalila Creek in Columbus, Mississippi, as well as revising the lithological description and describing the Eocene elasmobranch fauna found along the Conecuh Point “A” Dam, in River Falls, Alabama. Additionally, we are investigating new Cretaceous – Cenozoic chondrichthyan localities in Virginia, North and South Carolina, Georgia, Alabama, and Mississippi, including a bone-bed that contains a diverse, and extremely abundant vertebrate fauna found along Clapp Creek in Kingstree, SC.
Oligocene – Pleistocene Faunas
The evolutionary origin of the great white shark (Carcharodon carcharias) is unclear, with debate centering around two principal hypotheses. The first, based on similarity in tooth shape, claims that C. carcharias originated from a group of extinct mako sharks that includes Isurus hastalis. The second hypothesis, based mostly on piecemeal cladistic evidence, claims that C. carcharias originated from the same lineage as the giant megatoothed sharks, sharing a close evolutionary ancestor with the extinct Carcharodon megalodon. To distinguish between the two hypotheses we performed several morphometric analyses. In the first analysis, we used Procrustes method and principal components analysis (PCA) to quantify variation between C. carcharias, I. hastalis, and C. megalodon in four different positions within the dentition. The results indicate no significant difference in tooth shape between C. carcharias and I. hastalis. In the second analysis, correlating tooth size with age, we analyzed teeth from upper anterior and lower anterior positions. For both tooth positions, we show that the growth rate of C. carcharias is more congruent with the growth rate of I. hastalis than that of C. megalodon. Finally, we used scanning electron microscopy to show that the tooth serrations of C. carcharias are distinct from those of the megatooths and more similar in size to those of slightly serrated mako teeth. Taken together, these results indicate that C. carcharias originated from an extinct group of mako sharks.
Our analysis indicates that the teeth of C. carcharias look drastically different in every position in the mouth than that of Megalodon (of course given that we know the exact positions of each tooth in Megalodon’s mouth, which is not truly the case), but look nearly identical to the broad toothed Mako. This is visibly quite obvious, and this is backed up morphometrically. So what will convince the handful of disbeliever? DNA analysis. Well, maybe. This leads to our proposed “two-pronged” approach to further strengthen the obvious.
Prong 1: Collect as many samples of Meg teeth that have not been aerially exposed, which of course need only be fragments that include portions of the root. Once the samples are brought to the surface they will be placed in 95% ethanol and sealed until they reach the lab. We will sample the root and blade-root interface. Once the samples are taken, we will use mitochondrial cytochrome c primers to hopefully amplify any DNA present. The best aspect of this research is that if we get confirmation of DNA in the samples, we will not have to worry about contamination or “noise”. The lab does not work on living sharks, so contamination is not an issue, and it would be hard to believe that shark DNA would come from the waters where the fossil teeth originate. With even partial mitochondrial DNA sequences, a molecular phylogeny comparing Megalodon versus C. carcharias would be a performed.
Prong 2: A very complete and thorough ontogenetic analysis of tooth morphology using copious “embryonic” and juvenile teeth of C. carcharias and Megalodon. Currently, I have access to a large number of “embryonic” and juvenile Megalodon teeth. Of course, there is no problem acquiring a large number of small C. carcharias teeth. We will also use larger teeth as well to assemble whole growth series, for several tooth positions. This will allow us to ‘fill-in” the gaps in our first paper where we performed several growth series analyses.
A current research focus of the lab is the abundance, diversity, and paleoecological relationships of Miocene chondrichthyans found within phosphate deposits in the continental United States. Specifically, we are focusing on the Pungo River Formation exposed in east-central North Carolina within the PCS “Lee Creek” mine, the Temblor Formation exposed at “Shark Tooth Hill” near Bakersfield, CA, and the Bone Valley Formation exposed in central Florida. The main thrust of the project focuses upon the isolation and analysis of chondrichthyan micro-fauna found within the fossiliferous matrix exposed at each locality.
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