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Megafaunal Extinction during the Pleistocene-Holocene transition in North America
Megafaunal Extinction during the Pleistocene-Holocene transition in North America
Today, there is a contentious debate surrounding the validity of a sixth mass extinction; not up for debate is the clear decline of the last remaining megafauna in Africa. In collaboration with Drs. Felisa Smith, Kate Lyons, and Seth Newsome, we are investigating the temporal and spatial consequences of the Pleistocene-Holocene megafaunal collapse in North America on the remaining mammalian communities, including humans.
Today, there is a contentious debate surrounding the validity of a sixth mass extinction; not up for debate is the clear decline of the last remaining megafauna in Africa. In collaboration with Drs. Felisa Smith, Kate Lyons, and Seth Newsome, we are investigating the temporal and spatial consequences of the Pleistocene-Holocene megafaunal collapse in North America on the remaining mammalian communities, including humans.
Numerous cave sites across southern and central Texas have an incredible fossil record and can be used as a test case to explore the ecological consequences of megafaunal extinction. We use both bulk and compound-specific stable isotope analysis to elucidate food web dynamics. Our team also uses morphological analyses of skeletal material to examine the effect of megafaunal loss on dietary behavior and niche partitioning.
Numerous cave sites across southern and central Texas have an incredible fossil record and can be used as a test case to explore the ecological consequences of megafaunal extinction. We use both bulk and compound-specific stable isotope analysis to elucidate food web dynamics. Our team also uses morphological analyses of skeletal material to examine the effect of megafaunal loss on dietary behavior and niche partitioning.
Recently, in collaboration with Joshua Porter, at the University of Arkansas, we've expanded the scope of this project and are exploring how movement patterns of large mammals have changed after megafauna went extinct. To do this, we're examining the strontium isotopes from large mammals like mammoths, as well as from species that survived the extinction, like bison.
Recently, in collaboration with Joshua Porter, at the University of Arkansas, we've expanded the scope of this project and are exploring how movement patterns of large mammals have changed after megafauna went extinct. To do this, we're examining the strontium isotopes from large mammals like mammoths, as well as from species that survived the extinction, like bison.
Community assembly and disassembly across deep time
Community assembly and disassembly across deep time
The present is often called the key to the past, but paleontological research in the last decades has proven that the opposite is also true. As a research associate at the NMNH, I joined the Evolution of Terrestrial Ecosystems group to collaborate with an integrative group of senior researchers and students in Paleobiology.
The present is often called the key to the past, but paleontological research in the last decades has proven that the opposite is also true. As a research associate at the NMNH, I joined the Evolution of Terrestrial Ecosystems group to collaborate with an integrative group of senior researchers and students in Paleobiology.
During my tenure, the group published papers exploring patterns of plant and animal community assembly and disassembly through time (Blois et al., 2014) and demonstrated that the present is quite different in its ecological structure than anything in the past (Lyons et al., 2016). The group has also made contributions in understanding the role of biotic interactions in deep time (Fraser et al., 2021).
During my tenure, the group published papers exploring patterns of plant and animal community assembly and disassembly through time (Blois et al., 2014) and demonstrated that the present is quite different in its ecological structure than anything in the past (Lyons et al., 2016). The group has also made contributions in understanding the role of biotic interactions in deep time (Fraser et al., 2021).
Recently, the group has moved on to asking why present plant and animal communities differ from those in the past ~350 million years as well as whether other community ecology metrics show a pattern of recent assembly change (Toth et al., 2019; Pineda Munoz et al., 2021). Dr. Danielle Fraser (the Canadian Museum of Nature) and I also lead a project exploring community composition changes across Pleistocene to modern North America (Fraser et al., 2022).
Recently, the group has moved on to asking why present plant and animal communities differ from those in the past ~350 million years as well as whether other community ecology metrics show a pattern of recent assembly change (Toth et al., 2019; Pineda Munoz et al., 2021). Dr. Danielle Fraser (the Canadian Museum of Nature) and I also lead a project exploring community composition changes across Pleistocene to modern North America (Fraser et al., 2022).
Figure below from Fraser et al., 2022: Mammal communities begin to homogenize (become more similar to others around them) as recently as ten thousand years ago. This phenomenon accelerates toward the present and is even more pronounced among mammals greater than 5kg.
Figure below from Fraser et al., 2022: Mammal communities begin to homogenize (become more similar to others around them) as recently as ten thousand years ago. This phenomenon accelerates toward the present and is even more pronounced among mammals greater than 5kg.
Hominin Distribution in Pliocene Eastern Africa And the Importance of Woody Cover
Hominin Distribution in Pliocene Eastern Africa And the Importance of Woody Cover
At least three hominin species are found across eastern and central Africa at 3.5 Ma. The most widespread and well known species, Australopithecus afarensis, is associated with 3.4-million-years-old cut-marked bones in Ethiopia’s Afar Basin and is anatomically distinct from a contemporaneous northern Kenyan hominin, Kenyanthropus platyops, which is associated with the oldest known stone tools at 3.3 Ma. Isotopes from enamel show that both species also incorporated resources from both grasslands and woodlands or shrublands during the middle Pliocene (~3.8-3.2 million years ago). Though the two share ecological similarities, there are no studies comparing the ecology of their contemporaneous sites.
At least three hominin species are found across eastern and central Africa at 3.5 Ma. The most widespread and well known species, Australopithecus afarensis, is associated with 3.4-million-years-old cut-marked bones in Ethiopia’s Afar Basin and is anatomically distinct from a contemporaneous northern Kenyan hominin, Kenyanthropus platyops, which is associated with the oldest known stone tools at 3.3 Ma. Isotopes from enamel show that both species also incorporated resources from both grasslands and woodlands or shrublands during the middle Pliocene (~3.8-3.2 million years ago). Though the two share ecological similarities, there are no studies comparing the ecology of their contemporaneous sites.
To address this gap in our knowledge, I use taphonomically informed methods and extensive catalogue data (published and unpublished) to examine differences in the ecology and community structure of Australopithecus afarensis and Kenyanthropus platyops . Specifically, I've analyzed how their local environments may have affected hominin abundance across multiple sites in eastern Africa (Villaseñor et al., 2020).
To address this gap in our knowledge, I use taphonomically informed methods and extensive catalogue data (published and unpublished) to examine differences in the ecology and community structure of Australopithecus afarensis and Kenyanthropus platyops . Specifically, I've analyzed how their local environments may have affected hominin abundance across multiple sites in eastern Africa (Villaseñor et al., 2020).
The image below from Villaseñor et al., 2020 shows the relative abundance of our ancestors (hominins) versus baboon-sized animals at four different sites within Kenya and Ethiopia. Hominins are rare in the Lower Omo of Ethiopia.
Woody Cover, Savanna Dynamics, and Human Evolution in Pliocene Eastern Africa
Woody Cover, Savanna Dynamics, and Human Evolution in Pliocene Eastern Africa
Savannas are one of the dominant ecosystems within tropical and sub-tropical environments today. They are home to many of Earth's remaining megafauna. Complicated and dynamic systems, they are defined by a state of disequilibrium: neither grassland nor forest. Savannas may have also characterized the environments of our Pliocene ancestors. The savanna hypothesis, suggesting that hominins became tool-using bipeds in response to more open environments has waned and waxed in importance and relevance in human evolutionary studies. While mixed-grassland and woodland conditions clearly existed in the past, it remains unclear whether these mosaic grassland-woodland environments are similar biomes to the savannas of modern Africa, which are characterized by warm, seasonal, environments with regular burning.
Savannas are one of the dominant ecosystems within tropical and sub-tropical environments today. They are home to many of Earth's remaining megafauna. Complicated and dynamic systems, they are defined by a state of disequilibrium: neither grassland nor forest. Savannas may have also characterized the environments of our Pliocene ancestors. The savanna hypothesis, suggesting that hominins became tool-using bipeds in response to more open environments has waned and waxed in importance and relevance in human evolutionary studies. While mixed-grassland and woodland conditions clearly existed in the past, it remains unclear whether these mosaic grassland-woodland environments are similar biomes to the savannas of modern Africa, which are characterized by warm, seasonal, environments with regular burning.
My research seeks to characterize Pliocene environments using stable isotopes to reconstruct woody cover. Moreover, as a result of human activities, the 21st century has seen global atmospheric pCO2 levels and temperature conditions shift back toward Pliocene levels, making it increasingly important to explore the local to regional ecological conditions of these past periods, which may hold insight into the ecosystems of the future.
My research seeks to characterize Pliocene environments using stable isotopes to reconstruct woody cover. Moreover, as a result of human activities, the 21st century has seen global atmospheric pCO2 levels and temperature conditions shift back toward Pliocene levels, making it increasingly important to explore the local to regional ecological conditions of these past periods, which may hold insight into the ecosystems of the future.
In collaboration with the Stable Isotope Laboratory at the University of Arkansas and the Tallgrass Prairie Preserve in northern Oklahoma, we are exploring new ways to understand the stable carbon and oxygen isotope signals derived from pedogenic carbonates.
In collaboration with the Stable Isotope Laboratory at the University of Arkansas and the Tallgrass Prairie Preserve in northern Oklahoma, we are exploring new ways to understand the stable carbon and oxygen isotope signals derived from pedogenic carbonates.
A cow staring down our game camera at the experimental research station at the University of Arkansas (Above). University of Arkansas honor's undergraduate, Gisell Maldonado, collecting tissue samples from bison on the TGP for her thesis (Below).
What is the functional role of large mammals Today?
What is the functional role of large mammals Today?
We have a lot of questions about the roles of large mammals in their ecosystems both is the past and today.
We have a lot of questions about the roles of large mammals in their ecosystems both is the past and today.
What are the roles of large mammals in an ecosystem and how important are these roles? Can extinct species' ecological roles be replicated among living species? Would an ecosystem collapse without these large creatures?
What are the roles of large mammals in an ecosystem and how important are these roles? Can extinct species' ecological roles be replicated among living species? Would an ecosystem collapse without these large creatures?
Many members of the lab are addressing the basic question of roles large mammals play in the ecosystem in both life and death.
As humans occupy and modify more and more of the planet's environments, these questions become extremely pressing.
In the Ozarks of the United States, we have the unique opportunity to explore some of the few Tallgrass Prairie (TGP) fragments and the role of large mammals within them.
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