|NPS Paleontology Research Abstract Volume|
Three unidentified fossil fish were found in the paleontological reference collection of Badlands National Park. All collecting data was absent, including information regarding the discoverer and the locality of the find. The fossils have since been identified and a likely source area has been found.
The three fossils represent two families of the Suborder Actinopterygii, Amiidae and Centrarchidae. The first fossil, Amia, is missing the head and so measures 21 cm from gill to tip-of-tail. The remaining two fossils represent the family Centrarchidae (Order Perchiformes). They are basically sunfish and measure 3.5 cm each. Although the occurrence of sunfish is not unexpected, to my knowledge they do represent the only known occurrence of sunfish in White River deposits.
A probable source locality for the fossils has been found in sedimentary lake deposits at an unconformity between the Chadron and Brule formations. The lake deposits have not been positively correlated with either of the formations yet. Petrologic thin sections from both the fish matrix and the lake deposits should indicate the likelihood of their similar origin. It is recognized, however, that until actual fish fossils are found in the probable source area, the correlation of the fish to the lake cannot be claimed with any certainty. This will be the emphasis of future field work.
Microvertebrate fossil remains can potentially unlock many mysteries regarding past faunal diversity and relationships. Unfortunately microfossils will easily erode, transport and redeposit into younger sediments. For this reason, extreme care must be taken to record exact location, stratigraphy, and topography of all microvertebrate finds.
Microvertebrate fossils have been collected from harvester ant mounds across specific basins within Badlands National Park. The nature of the collections from mid-basin areas have then been compared to collections from close proximity to specific buttes and walls. All of the ant mound collections are then compared to collections taken directly from specific source areas on buttes and walls.
Collections from mid-basin are expected to possess the most diverse fauna and include the most recently transported and reworked matter. In fact, some collections are extremely rich in grossular garnets, which have been transported great distances from the Black Hills. The actual results are mixed at this time but will become clearer with more collecting and much more sorting of material.
Hyracodon and Subhyracodon are two rhinocerotoids found in the Oligocene deposits of Badlands National Park. Traditionally Hyracodon is reconstructed as a sub-cursorial runner. However, recently completed work by Hickerson and Wall on Hyracodon locomotor mechanics showed that this animal was not highly specialized for running. These results indicate that competition between Hyracodon and Subhyracodon was not significantly reduced by differences in locomotor abilities. Hyracodon is smaller than Subhyracodon but this distinction alone seems insufficient to account for their coexistence. Our field studies show that these two taxa differ in relative abundance over time. Subhyracodon is more common in the Orellan while Hyracodon is more common in the overlying Whitneyan age rocks. This implies that changes in vegetation due to increasing aridity had a different impact on these two herbivores. We plan to conduct a detailed comparison of feeding mechanics in these two taxa to determine if differences in food habits minimized competition between these rhinocerotoids. Our analysis will center on jaw muscle mechanics, dental wear facets, and incisor and diastema specializations in Subhyracodon.
The fossil record of vertebrates from the lower portion of the Sharps Formation in South Dakota does not exhibit the taxonomic diversity as do the records from superadjacent middle and upper portions of the Sharps and the subadjacent Poleslide Member of the Brule Formation. Channel sandstone deposits in the Cedar Pass area of Badlands National Park, which downcut into the Brule Formation, represent a Lower Sharps age. These channels are rich in fossil mammals and provide new stratigraphic and taxonomic information about the Lower Sharps fauna.
The lack of a lithostratigraphic landmark, coincident with the Whitneyan/Arikareean Land Mammal Age boundary, has created consternation in regards to the placement of this boundary. Review of the Oligocene mammal biostratigraphy indicates that the concurrent ranges of Whitneyan taxa making their last appearance and Arikareean taxa making their first appearance would best serve as the boundary horizon. The fauna of the lower portion of the Sharps Formation best represents this transitional fauna and is suggested as the boundary in South Dakota.
Paleomagnetic measurements at Cedar Pass indicate a polarity transition from normal in the Poleslide Member of the Brule Formation to reversed within the overlying Lower Sharps Formation. The transition occurs within the basal Rockyford Ash Member of the Sharps. This polarity shift can serve as a boundary marker, for the Whitneyan/Arikareean Land Mammal transition, given the lack of a lithostratigraphic landmark. Further, the paleomagnetic samples from channel sediments downcutting into the Brule (reversed polarity) support a Lower Sharps age (normal polarity) for the channel and the associated fossils.
The genus Palaeocastor is one of the most commonly collected fossil vertebrates from the Late Oligocene channel sandstone deposits at Cedar Pass in Badlands National Park. Palaeocastor has previously been considered a good index fossil for the Arikareean Land Mammal Age. Collections from the Poleslide Member of the Brule Formation in Badlands National Park and other Whitneyan localities indicate that the range of this genus is extended into the Whitneyan and should not be considered a definitive Arikareean indicator.
The numerous Oligocene beaver specimens within the Frick Collection at the American Museum of Natural History were examined. All specimens incorporated into the database included detailed stratigraphic information. The study involved a morphometric evaluation of a few dental characters that are typically considered in the identification and description of new beaver taxa. The following measurements were obtained in 57 White River Oligocene beavers: (1) anterio-posterior length of P4-M2; (2) anterio-posterior length of P4; (3) width of P4; (4) anterio-posterior length of M1; (5) width of M1; (6) anterio-posterior length of M2; (7) width of M2; (8) anterio-posterior length of M3; (9) width of M3.
In addition, the ratio between the anterio-posterior length and the width of each tooth was used to establish an index to assess the dental morphology. Indices greater than one (>1.0) indicate a tooth with an anterio-posterior length greater than the width. Indices less than one (<1.0) indicate a tooth with a width greater than the anterio-posterior length. An index of one (1.0) indicates a tooth with an anterio-posterior length equal to the width (a rounded or squared tooth).
The dental morphometry data of Palaeocastor indicates that the age of an individual beaver, with an increasing wear pattern with greater age, is the most significant determinant of dental morphology. Any observable stratigraphic variations in dental morphology are masked by the extent of wear on the teeth.
A more comprehensive study of dental morphology could be accomplished by considering a series of five age classes: (1) specimens that possess a deciduous P4; (2) specimens that lost deciduous P4, but permanent P4 not yet fully erupted; (3) specimens with a fully erupted P4 exhibiting the earliest stages of wear; (4) specimens with an intermediate stage of wear on P4; and (5) specimens with an advanced stage of wear on P4. The general pattern observed indicates that heavier wear yields a more squared tooth (index closer to 1.0).
A systematic revision of the castorids has not been accomplished since Stirton's work in 1935. Dental morphology should be implemented in this study.
Preliminary work on microvertebrates collected by Georgia College field crews in Badlands National Park yields the following information. Three mammalian taxa, Paleolagus, a rabbit, Ischyromys, a primitive rodent, and Eumys an early mouse, are common throughout Orellan age rocks. Exposures of the Scenic Member of the Brule at Cottonwood Pass in the Southern Unit of the park contain the highest concentration of microvertebrates we have found. Four complete skulls and jaws of the burrowing lizard Rhineura hatcheri are probably the most important finds from this locality. Peltosaur lizards are also more frequently found here. Significant mammalian finds in this region are: a complete skull and jaws of the marsupial Peratherium, numerous skulls of the insectivore-like Leptictis, jaws and a partial skull of the earliest beaver Agnotocastor, and several partial skulls of Protosciurus an early relative of squirrels. Our only other significant Orellan microvertebrate locality is in the southern end of Big Corral Draw. Major finds at this locality include a skull and jaws of the insectivore Centetodon and partial skulls of two eomyid rodents, Adjidaumo and Pseudoadjidaumo. Our fieldwork in Whitneyan exposures in the Palmer Creek area of the park has not yielded comparable diversity or abundance. Jaws of the beaver Palaeocastor are most common but more interesting are two jaws of an as yet undescribed rodent.
|United States Department of the Interior, National Park Service|