Multi-proxy, medium-resolution Holocene and high-resolution late Holocene records from a southern Ontario ombrotrophic peatland examined factors affecting carbon accumulation. These records include radiometric dating, calculation of long-term apparent rate of carbon accumulation (LORCA), determination of peat humification, and analysis of plant macro-remains, charcoal and nitrogen concentration. Coupled with existing paleo-climate reconstructions, these data were integrated to determine how factors, such as climate, autogenic succession and fire, influenced carbon accumulation. Mean LORCA were similar to other northern and temperate peatlands. LORCA was high during the marsh phase and decreased following a transition to fen. Neoglacial cooling and the fen to bog transition did not lead to significant differences in LORCA. The last millennium did not exhibit much variation in LORCA; however, there is evidence for warming associated with the Medieval Climate Anomaly. Recent disturbances did impact LORCA; however, fire did not play a role in peatland dynamics in the pre-industrial Holocene.

Multi-proxy, medium-resolution Holocene and high-resolution late Holocene records from a southern Ontario ombrotrophic peatland examined factors affecting carbon accumulation. These records include radiometric dating, calculation of long-term apparent rate of carbon accumulation (LORCA), determination of peat humification, and analysis of plant macro-remains, charcoal and nitrogen concentration. Coupled with existing paleo-climate reconstructions, these data were integrated to determine how factors, such as climate, autogenic succession and fire, influenced carbon accumulation. Mean LORCA were similar to other northern and temperate peatlands. LORCA was high during the marsh phase and decreased following a transition to fen. Neoglacial cooling and the fen to bog transition did not lead to significant differences in LORCA. The last millennium did not exhibit much variation in LORCA; however, there is evidence for warming associated with the Medieval Climate Anomaly. Recent disturbances did impact LORCA; however, fire did not play a role in peatland dynamics in the pre-industrial Holocene.

A transitional climate and the presence of Thule sites make the Melville Peninsula an area of high importance for paleoenvironmental studies. Lake sediment cores and surface samples from Melville Peninsula were analyzed for diatom assemblages. Fragilarioid diatom species dominate assemblages from the interior of the peninsula since the middle Holocene. The greatest changes in diatom communities occurred during the transition from the Holocene Thermal Maximum to the Neoglacial, and in the post-Little Ice Age period. Species richness reached maximum values in the most recent period, reaching 50.8 species in surface sediments. Diatom-inferred pH reconstruction from two lakes did not indicate substantial change throughout the Holocene despite assemblage changes, showing the complexity of interpreting paleoclimate records dominated by Fragilarioids. Analysis of modern assemblages from the interior and East coast of Melville Peninsula confirm the importance of site size and water chemistry, as determined by bedrock geology, in determining diatom species distributions.

A transitional climate and the presence of Thule sites make the Melville Peninsula an area of high importance for paleoenvironmental studies. Lake sediment cores and surface samples from Melville Peninsula were analyzed for diatom assemblages. Fragilarioid diatom species dominate assemblages from the interior of the peninsula since the middle Holocene. The greatest changes in diatom communities occurred during the transition from the Holocene Thermal Maximum to the Neoglacial, and in the post-Little Ice Age period. Species richness reached maximum values in the most recent period, reaching 50.8 species in surface sediments. Diatom-inferred pH reconstruction from two lakes did not indicate substantial change throughout the Holocene despite assemblage changes, showing the complexity of interpreting paleoclimate records dominated by Fragilarioids. Analysis of modern assemblages from the interior and East coast of Melville Peninsula confirm the importance of site size and water chemistry, as determined by bedrock geology, in determining diatom species distributions.

Pollen assemblages, peat humification and carbon:nitrogen stratigraphy were examined at high resolution in a core from a fen peatland in the Hudson Bay Lowlands, Northern Ontario, to interpret the factors that drive long-term peatland dynamics. Subtle changes in the vegetation community are evident over the record, suggesting both allogenic and autogenic influences, but a fen community appears to have been resilient to external perturbations including isostatic rebound and hydroclimatic changes between 6400 and 100 years BP. Paleoclimatic reconstructions from the fossil pollen assemblages indicate that precipitation increased 3000 years BP at the end of the Holocene Thermal Maximum, and that carbon accumulation in the fen was controlled more by effective surface moisture (precipitation) than by temperature. The pollen record suggests changes over the past century, including increases in shrub Betula, Alnus, Ambrosia, and Cyperaceae and a decrease in Sphagnum spores, consistent with the observed Pan-Arctic shrub increase.

Pollen assemblages, peat humification and carbon:nitrogen stratigraphy were examined at high resolution in a core from a fen peatland in the Hudson Bay Lowlands, Northern Ontario, to interpret the factors that drive long-term peatland dynamics. Subtle changes in the vegetation community are evident over the record, suggesting both allogenic and autogenic influences, but a fen community appears to have been resilient to external perturbations including isostatic rebound and hydroclimatic changes between 6400 and 100 years BP. Paleoclimatic reconstructions from the fossil pollen assemblages indicate that precipitation increased 3000 years BP at the end of the Holocene Thermal Maximum, and that carbon accumulation in the fen was controlled more by effective surface moisture (precipitation) than by temperature. The pollen record suggests changes over the past century, including increases in shrub Betula, Alnus, Ambrosia, and Cyperaceae and a decrease in Sphagnum spores, consistent with the observed Pan-Arctic shrub increase.

Based on dental, cranial, and postcranial anatomy, members of the Permo-Carboniferous clade Diadectidae are generally regarded as the earliest tetrapods capable of processing high-fiber plant material; presented here is a review of diadectid morphology, phylogeny, taxonomy, and paleozoogeography. Phylogenetic analyses support the monophyly of Diadectidae within Diadectomorpha, the sister-group to Amniota, with Limnoscelis as the sister-taxon to Tseajaia + Diadectidae. Analysis of diadectid interrelationships of all known taxa for which adequate specimens and information are known—the first of its kind conducted—positions Ambedus pusillus as the sister-taxon to all other forms, with Diadectes sanmiguelensis, Orobates pabsti, Desmatodon hesperis, Diadectes absitus, and (Diadectes sideropelicus + Diadectes tenuitectes + Diasparactus zenos) representing progressively more derived taxa in a series of nested clades. In light of these results, it is recommended herein that the species Diadectes sanmiguelensis be referred to the new genus Oradectes, Diadectes absitus be referred to the new genus Silvadectes, and Diasparactus be synonymized with Diadectes to produce Diadectes zenos. The phylogenetic hypothesis also reveals an evolutionary history leading to more efficient oral processing within the lineage, with successive nodes characterized by features indicative of a high-fiber diet. Within Diadectomorpha, diadectids constitute the majority of the species, suggesting that the advent of herbivory resulted in a relatively rapid radiation of species within the group, producing a clade that is markedly more species-rich than other, non-herbivorous diadectomorph taxa. An extensive review of Permo-Carboniferous tetrapod-bearing localities does, however, indicate that diadectids were not a key component of the fauna, discovered at fewer than 50 percent of the sites reviewed. These results counter suggestions that the evolution of Diadectidae led to the formation of the modern terrestrial ecosystem—where a large crop of herbivores supports a much smaller number of carnivores—during the Late Carboniferous and Early Permian.

Rapidly changing climates in northern Canada make the western Hudson Bay region an area of high importance for paleoenvironmental studies. Long-term changes in assemblages of diatoms (microscopic algae) were analyzed from lake sediment cores from Baker Lake, Nunavut, and Lake AT01, northern Ontario, to track responses to past environmental changes. Diatom assemblages dating to 6700 years ago in AT01 were initially characterized by cold- tolerant Fragilarioid assemblages, but shifted to an assemblage dominated by large benthic species and Cymbella diluviana consistent with the timing of the Holocene Thermal Maximum after 6300 years BP. A possible drainage event in Lake AT01 may have added significant hydrologic control on the diatom assemblages. The post-industrial period is marked by the largest compositional shifts in both records. Assemblages during the 20th century are indicative of reduced ice cover and enhanced thermal stratification linked to a climate regime shift noted in Hudson Bay since the mid-1990’s.

Rapidly changing climates in northern Canada make the western Hudson Bay region an area of high importance for paleoenvironmental studies. Long-term changes in assemblages of diatoms (microscopic algae) were analyzed from lake sediment cores from Baker Lake, Nunavut, and Lake AT01, northern Ontario, to track responses to past environmental changes. Diatom assemblages dating to 6700 years ago in AT01 were initially characterized by cold- tolerant Fragilarioid assemblages, but shifted to an assemblage dominated by large benthic species and Cymbella diluviana consistent with the timing of the Holocene Thermal Maximum after 6300 years BP. A possible drainage event in Lake AT01 may have added significant hydrologic control on the diatom assemblages. The post-industrial period is marked by the largest compositional shifts in both records. Assemblages during the 20th century are indicative of reduced ice cover and enhanced thermal stratification linked to a climate regime shift noted in Hudson Bay since the mid-1990’s.

Based on dental, cranial, and postcranial anatomy, members of the Permo-Carboniferous clade Diadectidae are generally regarded as the earliest tetrapods capable of processing high-fiber plant material; presented here is a review of diadectid morphology, phylogeny, taxonomy, and paleozoogeography. Phylogenetic analyses support the monophyly of Diadectidae within Diadectomorpha, the sister-group to Amniota, with Limnoscelis as the sister-taxon to Tseajaia + Diadectidae. Analysis of diadectid interrelationships of all known taxa for which adequate specimens and information are known—the first of its kind conducted—positions Ambedus pusillus as the sister-taxon to all other forms, with Diadectes sanmiguelensis, Orobates pabsti, Desmatodon hesperis, Diadectes absitus, and (Diadectes sideropelicus + Diadectes tenuitectes + Diasparactus zenos) representing progressively more derived taxa in a series of nested clades. In light of these results, it is recommended herein that the species Diadectes sanmiguelensis be referred to the new genus Oradectes, Diadectes absitus be referred to the new genus Silvadectes, and Diasparactus be synonymized with Diadectes to produce Diadectes zenos. The phylogenetic hypothesis also reveals an evolutionary history leading to more efficient oral processing within the lineage, with successive nodes characterized by features indicative of a high-fiber diet. Within Diadectomorpha, diadectids constitute the majority of the species, suggesting that the advent of herbivory resulted in a relatively rapid radiation of species within the group, producing a clade that is markedly more species-rich than other, non-herbivorous diadectomorph taxa. An extensive review of Permo-Carboniferous tetrapod-bearing localities does, however, indicate that diadectids were not a key component of the fauna, discovered at fewer than 50 percent of the sites reviewed. These results counter suggestions that the evolution of Diadectidae led to the formation of the modern terrestrial ecosystem—where a large crop of herbivores supports a much smaller number of carnivores—during the Late Carboniferous and Early Permian.