Publicação
New mammaliaform from the Upper Triassic of Kap Stewart Group of East Greenland
| Resumo: | The earliest mammaliaforms (the group that includes Mammalia) emerged in the Late Triassic. Due to a lack of fossils from this time period, many questions remain regarding their origin and emergence. Greenland provides pivotal evidence for the earliest mammaliaforms, and the landmass’s position between Europe and the Americas provides key biogeographical information. Within Greenland’s fossil record, mammaliaforms have been found exclusively in the Fleming Fjord Formation. A new specimen, NHMD 1184958, is the first mammaliaform identified from the Kap Stewart Group, which spans the Late Triassic to Early Jurassic boundary. This specimen comprises an incomplete dentary with a single preserved molar (m2?), and was previously attributed to the order Docodonta. However, it was not fully prepared and studied until now. For this thesis, specimen NHMD 1184958, was manually prepared, and fully digitally visualized using micro CT scans, to reveal details of its anatomy. It was described, and comparisons made with known early mammaliaforms groups, to assess its taxonomic placement. This specimen somewhat resembles the French early mammaliaform Delsatia, suggested to be an early docodontan, as well as posessing features also seen in members of the clade Docodonta, especially the British docodont Dobunnodon. A phylogenetic analysis incorporating most known genera of docodontans was performed to determine the phylogenetic position of NHMD 1184958. Results place it as a basal member of Docodonta, or close sister taxon, closer than other proposed early docodontans such as Delsatia, Gondtherium or Tikitherium. This would make NHMD 1184958 one of the oldest known docodontans, pushing the origin of the group back to the Late Triassic. Its presence in Greenland supports the proposal that docodontans have their origins in the region that now includes Europe and Greenland, and later dispersed across the rest of Laurasia. This specimen provides important new anatomical characters that help us understand the emergence of docodontan dental complexity, a key feature for the clade that set the scene for their impressive diversification in the Middle to Late Jurassic. |
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| Autores principais: | Patrocínio, Sofia Alexandra Mendes |
| Assunto: | Mammaliamorph Jameson Land Basin Rhatelv Formation Taxonomy Image segmentation Phylogeny |
| Ano: | 2024 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade Nova de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório Institucional da UNL |
| Resumo: | The earliest mammaliaforms (the group that includes Mammalia) emerged in the Late Triassic. Due to a lack of fossils from this time period, many questions remain regarding their origin and emergence. Greenland provides pivotal evidence for the earliest mammaliaforms, and the landmass’s position between Europe and the Americas provides key biogeographical information. Within Greenland’s fossil record, mammaliaforms have been found exclusively in the Fleming Fjord Formation. A new specimen, NHMD 1184958, is the first mammaliaform identified from the Kap Stewart Group, which spans the Late Triassic to Early Jurassic boundary. This specimen comprises an incomplete dentary with a single preserved molar (m2?), and was previously attributed to the order Docodonta. However, it was not fully prepared and studied until now. For this thesis, specimen NHMD 1184958, was manually prepared, and fully digitally visualized using micro CT scans, to reveal details of its anatomy. It was described, and comparisons made with known early mammaliaforms groups, to assess its taxonomic placement. This specimen somewhat resembles the French early mammaliaform Delsatia, suggested to be an early docodontan, as well as posessing features also seen in members of the clade Docodonta, especially the British docodont Dobunnodon. A phylogenetic analysis incorporating most known genera of docodontans was performed to determine the phylogenetic position of NHMD 1184958. Results place it as a basal member of Docodonta, or close sister taxon, closer than other proposed early docodontans such as Delsatia, Gondtherium or Tikitherium. This would make NHMD 1184958 one of the oldest known docodontans, pushing the origin of the group back to the Late Triassic. Its presence in Greenland supports the proposal that docodontans have their origins in the region that now includes Europe and Greenland, and later dispersed across the rest of Laurasia. This specimen provides important new anatomical characters that help us understand the emergence of docodontan dental complexity, a key feature for the clade that set the scene for their impressive diversification in the Middle to Late Jurassic. |
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