Daniel J. Lunt’s research while affiliated with University of Bristol and other places

The origin of pterosaurs, the first vertebrates to achieve powered flight, is poorly understood, owing to the temporal and morphological gaps that separate them from their closest non-flying relatives, the lagerpetids. Although both groups coexisted during the Late Triassic, their limited sympatry is currently unexplained, indicating that ecological partitioning, potentially linked to palaeoclimate, influenced their early evolution. Here we analysed pterosauromorph (pterosaur + lagerpetid) palaeobiogeography using phylogeny-based probabilistic methods and integrating fossil occurrences with palaeoclimate data. Our results reveal distinct climatic preferences and dispersal histories: lagerpetids tolerated a broader range of conditions, including arid belts, enabling a widespread distribution from the Middle to early Late Triassic. Conversely, pterosaurs preferred wetter environments, resulting in a patchier geographical distribution that expanded only as humidity increased in the Late Triassic, probably following the Carnian Pluvial Event. This major environmental disturbance, potentially driven by changes in CO2-related thermal constraints and/or palaeogeography, appears to have had a key role in shaping early pterosauromorph evolution by promoting spatial segregation and distinct climatic niche occupation.

Spatial incompleteness in the fossil record severely diminishes the observed ecological and geographic ranges of clades. The biological processes shaping species distributions and richness through time, however, also operate across geographic space and so clade biogeographic histories can indicate where their lineages must have successfully dispersed through these sampling gaps. Consequently, these histories are powerful, yet untapped tools for quantifying their unobserved ecographic diversity. Here, we couple phylogeographic modelling with a landscape connectivity approach to reconstruct the origins and dispersal of Permian–Triassic archosauromorph reptiles. We recover substantial ecographic diversity from the gaps in their fossil record, illuminating the cryptic first 20 million years of their evolutionary history, a peak in climatic disparity in the earliest Triassic period, and dispersals through the Pangaean tropical dead zone which contradict its perception as a hard barrier to vertebrate movement. This remarkable tolerance of climatic adversity was probably integral to their later evolutionary success.

Stable oxygen isotopes (δ18O) are routinely used to reconstruct sea-surface temperatures (SSTs) in the geological past, with mineral δ18O values reflecting a combination of the temperature and oxygen isotope composition of seawater (δ18Osw). Temporal variation of mean-ocean δ18Osw is usually accounted for following estimates of land-ice volume. Spatial variations in δ18Osw, however, are often neglected or corrected using calibrations derived from the present-day or recent past. Geochemical methods for constraining δ18Osw and isotope-enabled general circulation model (GCM) simulations are still technically challenging. This lack of constraints on ancient δ18Osw is a substantial source of uncertainty for SST reconstructions. Here we use the co-variation of δ18Osw and seawater salinity, together with GCM simulations of ocean salinity, to propose estimations of spatial variability in δ18Osw over the Phanerozoic. Sensitivity tests of the δ18Osw-salinity relationship and climate model, and comparison with results of isotope-enabled GCMs, suggest that our calculations are robust at first order. We show that continental configuration exerts a primary control on δ18Osw spatial variability. Complex ocean basin geometries in periods younger than 66 Ma lead to strong inter-basinal contrasts in δ18Osw. Latitudinal SST gradients may be steeper than previously suggested during most of the Mesozoic and Cenozoic. This work has limitations, with δ18Osw-salinity relationships being less reliable in both low-latitude epicontinental settings and high-latitude regions of deep-water formation. Whilst our calculations are limited use in correcting δ18O measurements for local δ18Osw, they identify the time slices and paleogeographical regions that should be prioritized for future work using isotope-enabled GCMs.

The latitudinal biodiversity gradient (LBG) is a fundamental biological pattern seen across taxa and ecosystems today, but its drivers remain uncertain despite intense study. Palaeontological data may add valuable evidence from diversity distributions during intervals with different Earth system configurations, including potential analogues of future climate regimes. However, accurately characterizing these distributions is challenging because the geographic scope of fossil record coverage varies through time, introducing biases that have not been quantified by most previous studies. Here, we attempt a comprehensive documentation of latitudinal biodiversity distributions of marine invertebrates through the past 540 million years, explicitly accounting for regional variation in diversity and sampling. We demonstrate large uncertainties when using current fossil data at this scale. Nevertheless, some signals are detectable. We show that marine animal biodiversity declined with increasing palaeolatitude and with decreasing temperature during at least some intervals from the Permian onwards (298.9 Ma). Additionally, we find that the LBG was shallower on average when Earth's climate was hotter, although this signal is weak. We also document a strong, systematic bias due to intense sampling of the fossil record in North America and especially Europe, which may have led previous studies to incorrectly infer a mid‐latitude diversity peak during warm intervals of Earth history. Our results provide a baseline for what current fossil databases might tell us about Phanerozoic LBGs of marine animals, and suggests that quantitative evaluation of uncertainties and systematic bias will be central to advancing knowledge of geographic variation in diversity through Earth's history.

The El Niño Southern Oscillation (ENSO) during the Early Eocene Climatic Optimum (EECO, 56–48 million years ago) is investigated using a multi-model ensemble of deep-time climate simulations. We reveal that ENSO sea surface temperature variability during the EECO had significantly longer periodicity and stronger amplitude than present-day conditions. These changes are attributed to intensified ocean-atmosphere feedback processes and enhanced in-phase tropical inter-basin interactions within a broader ocean basin compared to the present-day. Sensitivity experiments in coupled ocean-atmosphere models suggest that tectonic changes, particularly the expansion of the tropical ocean basin, play a dominant role in amplifying ENSO variability and extending its periodicity, while stronger inter-basin connections further enhance ENSO amplitude. Elevated atmospheric CO2 levels, though driving substantial mean-state changes, partially offset the tectonic influence on ENSO variability by modifying feedback processes. These findings underscore the role of tropical ocean basin geometry and atmospheric CO2 levels in shaping ENSO variability, offering insights into past climate dynamics and implications for future projections under sustained global warming.

Plain Language Summary Topography plays a pivotal role in climate systems, particularly in East Asia, where diverse mountain ranges significantly influence regional climate dynamics. The Late Cretaceous period was characterized by a complex topography, including Coastal, Taihang, and Yanshan Mountains, which contributed to distinct climatic regimes. However, the specific climatic impacts of these inland mountain ranges and their interactions with adjacent coastal features remain inadequately characterized. This study aims to bridge this knowledge gap by employing paleoclimate modeling to assess the effects of these mountain configurations on temperature and precipitation patterns. We use two model‐proxy comparison strategies, revealing that the combination of Coastal, Taihang, and Yanshan Mountains had slightly higher accuracy than other configurations. Combined with geological evidence, we propose this mountain configuration for East Asia during the Late Cretaceous. Our results indicate that the joint influence of coastal and inland mountain ranges significantly modifies temperature and precipitation, impacting clouds, atmospheric circulation processes, and monsoon systems. These findings underscore the necessity of integrating topographical influences in paleoclimate simulations, refining our understanding of the intricate interactions between ancient landscapes and climate systems.

Climate-model simulations are important tools for testing hypotheses about the drivers of shifts in climate and ecosystem distributions throughout the Phanerozoic. Initial simulations of Phanerozoic climates have been carried out using the HadCM3L climate model, with 109 time slices across the 540 million years. Each time slice represents a distinct stage, with CO 2 concentrations prescribed to align the modeled global mean surface temperatures (GMST) with estimates of past GMST. However, these simulations utilized modern plant functional types (PFT) and globally homogeneous surface properties across all Phanerozoic timescales. In reality, vegetation has evolved through time. So, use of modern PFT may introduce significant errors in climatically relevant variables (e.g., albedo). Consequently, the estimated values of modeled temperatures through time may be inaccurate. The aim of this project is to implement more realistic representations of vegetation in the simulations, by utilizing PFTs that are appropriate for each time slice. For example, the early Ordovician would be characterized by low-lying, sparse vegetation dominated by bryophyte-like plants, which likely exhibited simple anatomy and physiology, were restricted to moist lowland habitats, and lacked deep anchoring structures. As a first step towards this aim, we have set up a series of simulations that are simple continuations of the existing simulations, run for 110 years, but including more vegetation-specific outputs. Our analysis included visualizations of the Phanerozoic vegetation fraction, which pointed out clear inaccuracies, such as the unrealistic representation of vegetation during the early Phanerozoic. These findings emphasize the limitations of the original model's assumptions about vegetation. Furthermore, we demonstrated that vegetation significantly influences surface temperature and found strong relationships between climate variables (such as precipitation and surface air temperature) and vegetation distribution. Our results underscore the need to make realistic adjustments to vegetation parameters in HadCM3L simulations.

A tuned version of HadCM3 (HadCM3t) is used to simulate the climate of the mid‐Pliocene warm period (mPWP) and is compared with the original untuned version of HadCM3 (HadCM3u). After the tuning, HadCM3t performs as well as HadCM3u in simulating the preindustrial climate, but aligns better with the reconstructed mPWP sea surface temperature anomalies, primarily due to a better representation of high latitude warming. Regarding the mPWP climate anomaly relative to the preindustrial, compared to HadCM3u, HadCM3t produces stronger mid‐to‐high latitude warming with polar warming 2.2 times the global mean, which is higher than the 2.0 of HadCM3u. The warming of the mPWP is primarily explained by an increase in emissivity and surface albedo. The warming of the polar regions induced by emissivity and surface albedo from HadCM3t is higher by 0.6° ${}^{\circ}$C and 0.7° ${}^{\circ}$C respectively, than that from HadCM3u, leading to warmer mPWP high latitudes. The increase in shortwave radiation over the Polar Regions is driven mainly by changes in surface albedo, which lead to a temperature rise of +0.7° ${}^{\circ}$C, and by changes in cloud cover, which contribute an additional +0.1° ${}^{\circ}$C to the temperature increase. Here, the increased cloud‐induced shortwave radiation change is due to decreased cloud fraction and decreased cloud scattering effect; the increased surface albedo‐induced radiative effects result from the increased ice loss due to warm high latitudes. This tuning allows models like HadCM3 to better align with proxy data, offering a more reliable baseline for projecting future scenarios under similar conditions.

The Miocene (∼23–5 Ma) is a past warm epoch when global surface temperatures varied between ∼5 and 8°C warmer than today, and CO2 concentration was ∼400–800 ppm. The narrowing/closing of the tropical ocean gateways and widening of high‐latitude gateways throughout the Miocene is likely responsible for the evolution of the ocean's overturning circulation to its modern structure, though the mechanisms remain unclear. Here, we investigate early and middle Miocene ocean circulation in an opportunistic climate model intercomparison (MioMIP1), using 14 simulations with different paleogeography, CO2, and vegetation. The strength of the Southern Ocean‐driven Meridional Overturning Circulation (SOMOC) bottom cell is similar in the Miocene and Pre‐Industrial (PI) but dominates the Miocene global MOC due to weaker Northern Hemisphere overturning. The Miocene Atlantic MOC (AMOC) is weaker than PI in all the simulations (by 2–21 Sv), possibly due to its connection with an Arctic that is considerably fresher than today. Deep overturning in the North Pacific (PMOC) is present in three simulations (∼5–10 Sv), of which two have a weaker AMOC, and one has a stronger AMOC (compared to its PMOC). Surface freshwater fluxes control northern overturning such that the basin with the least freshwater gain has stronger overturning. While the orography, which impacts runoff direction (Pacific vs. Atlantic), has an inconsistent impact on northern overturning across simulations, overall, features associated with the early Miocene—such as a lower Tibetan Plateau, the Rocky Mountains, and a deeper Panama Seaway—seem to favor PMOC over AMOC.