Presented By: Earth and Environmental Sciences
Sanaa El-Sayed Dissertation Defense
Teleost Fish Evolution in the Cenozoic: New insights from Paleogene Ichthyofaunas from the Eastern Desert of Egypt
Zoom link: https://umich.zoom.us/j/98521134857
Password: MUVP!
The Cretaceous–Paleogene (K–Pg) mass extinction reshaped marine fish faunas, but the timing, geography, and environmental context of this change remain poorly resolved. This stems from the scarcity of articulated Maastrichtian–Paleocene fish skeletons, a paleontological hiatus termed Patterson’s Gap. It is exacerbated by the limited paleoenvironmental context available for fossil-bearing low-latitude sections, especially the scarcity of direct paleotemperature records from settings that preserve marine fish assemblages. As a result, it remains difficult to evaluate how marine fish communities persisted through the dynamic climatic events of the early Paleogene. This dissertation addresses these problems using new fossil and geochemical data from Egypt, a paleotropical region on the southern Tethyan margin.
I first document Qreiya 3, a new early Paleocene marine Lagerstätte from the Eastern Desert of Egypt. Qreiya 3 is dated to approximately 62.2 Ma, occurs within the Late Danian Event horizon, and represents an offshore outer-neritic to upper-bathyal setting. The locality preserves abundant articulated and associated vertebrate material, including at least 21 actinopterygian taxa and rare chondrichthyans and non-fish vertebrates. The assemblage includes pycnodontiforms, clupeiformes, anguilliforms, osteoglossiforms, lampriforms, zeiforms, syngnathiformes, scombriforms, carangiforms, and additional acanthomorph and percomorph morphotypes, providing new fossil data from deep within Patterson’s Gap.
I then place Qreiya 3 within a broader comparative framework for marine fish turnover. Quantitative comparisons show that Qreiya 3 is the oldest known majority-percomorph marine assemblage and exceeds the diversity of all other Danian skeletal assemblages combined. It lacks several major Cretaceous predatory lineages but preserves early records of groups that became important components of Cenozoic and Recent marine faunas, including the oldest skeleton-based records of scombrids, carangids, menids, trichiuroids, syngnathids, and veliferids. Qreiya 3 therefore shows that substantial faunal restructuring had occurred in the tropical Tethys less than four million years after the K–Pg extinction. Comparisons across sites further indicate that percomorphs were more common at lower paleolatitudes in the Paleocene before expanding into higher paleolatitudes by the Eocene.
To evaluate the pre-extinction context for this transition, I also describe the Campanian–Maastrichtian actinopterygian assemblage of the Duwi Formation in the Western Desert of Egypt. This fauna retains a distinctly Mesozoic composition, including pachycormids, saurodontid, and aulopiforms such as enchodontids, dercetids, and cimolichthyids, showing that large-bodied, predatory teleost total-group lineages remained important components of southern Tethyan ecosystems shortly before the K–Pg extinction. Quantitative comparisons indicate broad higher-level similarity among Campanian–Maastrichtian assemblages and possible modest geographic structure, while uneven sampling, taphonomic differences, inconsistent stratigraphic resolution, and contrasting collecting histories strongly limit tests of latest Cretaceous fish provinciality.
Finally, I place these new Egyptian fossil assemblages within a regional environmental framework using clumped isotope analyses of mollusk shells spanning the Campanian through Paleocene. These data provide the first low-paleolatitude marine temperature record across this interval and indicate persistent southern Tethyan warmth, with mean temperatures of approximately 28 °C in the latest Cretaceous and 30 °C in the Paleocene. In this context, diverse early Paleogene fish assemblages suggest that survivorship during hyperthermals may have involved physiological accommodation to sustained warmth and ecological buffering through deeper, thermocline-influenced habitats.
Together, these results show that the K–Pg transformation of marine fish faunas was rapid, geographically structured, and environmentally complex. By linking fossil assemblages with direct environmental proxies, this dissertation demonstrates that undersampled low-latitude records from the southern Tethys are essential for resolving how modern marine fish communities emerged and persisted during the early Cenozoic.
Password: MUVP!
The Cretaceous–Paleogene (K–Pg) mass extinction reshaped marine fish faunas, but the timing, geography, and environmental context of this change remain poorly resolved. This stems from the scarcity of articulated Maastrichtian–Paleocene fish skeletons, a paleontological hiatus termed Patterson’s Gap. It is exacerbated by the limited paleoenvironmental context available for fossil-bearing low-latitude sections, especially the scarcity of direct paleotemperature records from settings that preserve marine fish assemblages. As a result, it remains difficult to evaluate how marine fish communities persisted through the dynamic climatic events of the early Paleogene. This dissertation addresses these problems using new fossil and geochemical data from Egypt, a paleotropical region on the southern Tethyan margin.
I first document Qreiya 3, a new early Paleocene marine Lagerstätte from the Eastern Desert of Egypt. Qreiya 3 is dated to approximately 62.2 Ma, occurs within the Late Danian Event horizon, and represents an offshore outer-neritic to upper-bathyal setting. The locality preserves abundant articulated and associated vertebrate material, including at least 21 actinopterygian taxa and rare chondrichthyans and non-fish vertebrates. The assemblage includes pycnodontiforms, clupeiformes, anguilliforms, osteoglossiforms, lampriforms, zeiforms, syngnathiformes, scombriforms, carangiforms, and additional acanthomorph and percomorph morphotypes, providing new fossil data from deep within Patterson’s Gap.
I then place Qreiya 3 within a broader comparative framework for marine fish turnover. Quantitative comparisons show that Qreiya 3 is the oldest known majority-percomorph marine assemblage and exceeds the diversity of all other Danian skeletal assemblages combined. It lacks several major Cretaceous predatory lineages but preserves early records of groups that became important components of Cenozoic and Recent marine faunas, including the oldest skeleton-based records of scombrids, carangids, menids, trichiuroids, syngnathids, and veliferids. Qreiya 3 therefore shows that substantial faunal restructuring had occurred in the tropical Tethys less than four million years after the K–Pg extinction. Comparisons across sites further indicate that percomorphs were more common at lower paleolatitudes in the Paleocene before expanding into higher paleolatitudes by the Eocene.
To evaluate the pre-extinction context for this transition, I also describe the Campanian–Maastrichtian actinopterygian assemblage of the Duwi Formation in the Western Desert of Egypt. This fauna retains a distinctly Mesozoic composition, including pachycormids, saurodontid, and aulopiforms such as enchodontids, dercetids, and cimolichthyids, showing that large-bodied, predatory teleost total-group lineages remained important components of southern Tethyan ecosystems shortly before the K–Pg extinction. Quantitative comparisons indicate broad higher-level similarity among Campanian–Maastrichtian assemblages and possible modest geographic structure, while uneven sampling, taphonomic differences, inconsistent stratigraphic resolution, and contrasting collecting histories strongly limit tests of latest Cretaceous fish provinciality.
Finally, I place these new Egyptian fossil assemblages within a regional environmental framework using clumped isotope analyses of mollusk shells spanning the Campanian through Paleocene. These data provide the first low-paleolatitude marine temperature record across this interval and indicate persistent southern Tethyan warmth, with mean temperatures of approximately 28 °C in the latest Cretaceous and 30 °C in the Paleocene. In this context, diverse early Paleogene fish assemblages suggest that survivorship during hyperthermals may have involved physiological accommodation to sustained warmth and ecological buffering through deeper, thermocline-influenced habitats.
Together, these results show that the K–Pg transformation of marine fish faunas was rapid, geographically structured, and environmentally complex. By linking fossil assemblages with direct environmental proxies, this dissertation demonstrates that undersampled low-latitude records from the southern Tethys are essential for resolving how modern marine fish communities emerged and persisted during the early Cenozoic.
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