Cranial ontogeny of the extinct tapir Tapirus polkensis with comparison to that of the extant Tapirus bairdii
Location
D.P. Culp Center Ballroom
Start Date
4-5-2024 9:00 AM
End Date
4-5-2024 11:30 AM
Poster Number
152
Name of Project's Faculty Sponsor
Steven Wallace
Faculty Sponsor's Department
Geosciences
Competition Type
Competitive
Type
Poster Presentation
Presentation Category
Science, Technology and Engineering
Abstract or Artist's Statement
The Gray Fossil Site (GFS) of eastern Tennessee, which dates to ~ 5 million years ago preserves many exceptional specimens of prehistoric mammals from North America. Among the taxa recovered is an extinct form of dwarf tapir (Tapirus polkensis) thought to be closely related to one of the extant species, the Central American T. bairdii (Baird’s tapir) of tapir. Yet this taxonomic relationship seems questionable considering there are many morphological differences between the two sister taxa. For example, T. bairdii, and more specifically the cranium, is much larger than T. polkensis. Another example seen in T. bairdii is the large vertical flange that runs from the ventral face of the nasals down into the nasal cavity. This flange is not present in any specimen of T. polkensis. Crania are the focus of this study because of their distinctive morphology, at least compared to the more conservative post-crania typical for the family Tapiridae. In addition, we have chosen to concentrate on the nasal region of the crania, as much of the tapir evolution has centered around their distinctive trunk. Digital images, capturing several standard views of the crania and mandible, were taken for 10 near-complete skulls of T. polkensis from the GFS, representing the full ontogenetic series. These photographs included several of the crania in left lateral and dorsal orientations, and several of the lower jaws, also in left lateral and dorsal orientations. Landmarks were placed on each image, then coordinate of these landmarks were transformed through superimposition into shape coordinates, which were then analyzed for statistical patterns. Principal Component Analysis (PCA), which looks for patterns in the raw (ungrouped) data, helped determine which areas of the cranium and/or jaw are growing faster relative to others. A PCA will also calculate the degree of growth or contraction of the landmarks away from the centroid of the cranium or jaw. Principal components were then used to develop a thin plate spline (TPS), or a visual representation of change through time for these tapirs. This project is still a work-in-progress; 46 skulls of T. bairdii will be collected from the Smithsonian National Museum of Natural History later in May of 2024, with the processing of the digital images and landmarks occurring over the next several months. Once all these landmarks have been analyzed for T. bairdii, we will compare the growth and development of the two taxa. The findings of this study could have serious implications for the current accepted relationships between T. polkensis and T. bairdii. In addition, results will contribute to the current knowledge of T. polkensis and can be used in further research for the tapirs at the GFS, and could provide crucial knowledge regarding the ecology of extant tapirs, all of which are considered endangered species.
Cranial ontogeny of the extinct tapir Tapirus polkensis with comparison to that of the extant Tapirus bairdii
D.P. Culp Center Ballroom
The Gray Fossil Site (GFS) of eastern Tennessee, which dates to ~ 5 million years ago preserves many exceptional specimens of prehistoric mammals from North America. Among the taxa recovered is an extinct form of dwarf tapir (Tapirus polkensis) thought to be closely related to one of the extant species, the Central American T. bairdii (Baird’s tapir) of tapir. Yet this taxonomic relationship seems questionable considering there are many morphological differences between the two sister taxa. For example, T. bairdii, and more specifically the cranium, is much larger than T. polkensis. Another example seen in T. bairdii is the large vertical flange that runs from the ventral face of the nasals down into the nasal cavity. This flange is not present in any specimen of T. polkensis. Crania are the focus of this study because of their distinctive morphology, at least compared to the more conservative post-crania typical for the family Tapiridae. In addition, we have chosen to concentrate on the nasal region of the crania, as much of the tapir evolution has centered around their distinctive trunk. Digital images, capturing several standard views of the crania and mandible, were taken for 10 near-complete skulls of T. polkensis from the GFS, representing the full ontogenetic series. These photographs included several of the crania in left lateral and dorsal orientations, and several of the lower jaws, also in left lateral and dorsal orientations. Landmarks were placed on each image, then coordinate of these landmarks were transformed through superimposition into shape coordinates, which were then analyzed for statistical patterns. Principal Component Analysis (PCA), which looks for patterns in the raw (ungrouped) data, helped determine which areas of the cranium and/or jaw are growing faster relative to others. A PCA will also calculate the degree of growth or contraction of the landmarks away from the centroid of the cranium or jaw. Principal components were then used to develop a thin plate spline (TPS), or a visual representation of change through time for these tapirs. This project is still a work-in-progress; 46 skulls of T. bairdii will be collected from the Smithsonian National Museum of Natural History later in May of 2024, with the processing of the digital images and landmarks occurring over the next several months. Once all these landmarks have been analyzed for T. bairdii, we will compare the growth and development of the two taxa. The findings of this study could have serious implications for the current accepted relationships between T. polkensis and T. bairdii. In addition, results will contribute to the current knowledge of T. polkensis and can be used in further research for the tapirs at the GFS, and could provide crucial knowledge regarding the ecology of extant tapirs, all of which are considered endangered species.