About

Robert Eagle is an Assistant Professor in the Department of Ecology and Evolutionary Biology at UCLA. His research focuses on the ecology and evolution of marine organisms, as indicated by his involvement with marine biology and field research quarters. He is engaged in studying ecological and evolutionary processes, contributing to the department's academic and research missions. His contact email is robeagle@g.ucla.edu, and he is associated with the Math Sciences lab at UCLA.

Research topics

• Geology
• Environmental science
• Biology
• Computer Science
• Ecology
• Chemistry
• Oceanography
• Materials science
• Meteorology
• Geography
• Environmental chemistry
• Nuclear physics
• Physical geography
• Mineralogy
• Atmospheric sciences
• Chromatography

Selected publications

• Sharks as apex predators in the Late Cretaceous Western Interior Seaway empirically revealed by zinc isotope analyses

  Gondwana Research · 2026-03-01

  articleOpen access

  • Enamel(oid) δ 66 Zn values are well preserved in Late Cretaceous marine vertebrates. • Zinc isotopes reveal significant resource partitioning among Cretaceous marine taxa. • Late Cretaceous sharks occupied top trophic positions comparable to today. Food web structures and trophic interactions among Late Cretaceous marine taxa remain largely ambiguous due to the challenges in reconstructing ecological interactions in the deep-time fossil record. Here we analyse enamel(oid) δ 66 Zn values, a trophic-level proxy, across 16 marine vertebrate taxa from two Turonian–Coniacian boundary localities in New Mexico and Kansas, USA, deposited in what was then the Western Interior Seaway (WIS). Our results demonstrate well-preserved enamel(oid) δ 66 Zn values in both localities, but locality-specific differences in the diagenetic modification of dentine δ 66 Zn values. We highlight significant resource partitioning among the analysed taxa within the WIS, including sharks. For example, Archaeolamna , Cretodus and Cretoxyrhina occupied very high trophic positions, whereas Cretalamna was likely foraging opportunistically across several trophic levels. Our study expands the use of enamel(oid) δ 66 Zn analysis to Mesozoic fossils for the first time and demonstrates that robust reconstructions of food web dynamics and trophic interactions are possible in deep time as far back as 90 million years ago, providing new avenues for palaeobiological and evolutionary research.

  PublisherDOI

• Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters

  2026-04-13

  articleSenior author
  PublisherDOI

• Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters

  2026-03-09

  articleOpen accessSenior author

  Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO 3 ) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.

  PublisherOA PDFDOI

• Dissolution Effects on Clumped Isotope Signatures in Planktic Foraminifera

  Paleoceanography and Paleoclimatology · 2025-10-30 · 1 citations

  articleOpen access

  Abstract The carbonate clumped isotope paleothermometer is becoming more widely used in the geosciences because it is less sensitive to solution δ 18 O and Mg/Ca than other carbonate‐based temperature proxies. Here, we examine the impacts of dissolution on foraminiferal clumped isotope records (Δ 47 ). Dissolution is known to impact carbonate minerals in ocean sediments near and below the carbonate saturation horizon. The effects of dissolution on foraminiferal mass, δ 18 O, and Mg/Ca have been the subject of prior work but have not yet been reported for the carbonate clumped isotope paleothermometer. We examine six planktic foraminiferal species from core‐tops collected at different water depths on the Ontong Java Plateau. Below the carbonate saturation horizon, multiple species exhibit higher Δ 47 values, biasing Δ 47 to cooler temperatures, though all species remain within error of their assumed calcification depth ranges. These effects are observed in Globigerinella siphonifera , Pulleniatina obliquiloculata , and Globorotalia tumida with an ∼0.01‰ difference from above to below the saturation horizon; p < 0.01 corresponding to a temperature bias of ∼4°C at a measured temperature of 28°C and of ∼3°C at a measured temperature of 18°C. Normalizing data for different species yields a pooled slope of −0.0006‰/μmol/kg Δ[CO 3 2− ] ( p < 0.01). Dissolution experiments show that for two species, Trilobus sacculifer and G . tumida , Δ 47 increased with mass loss. We propose multiple mechanisms by which dissolution may impact Δ 47 including intra‐test heterogeneous dissolution, which provide context to enable corrections for the impacts of dissolution on clumped isotope‐based paleo‐records.

  PublisherOA PDFDOI

• Magnesium (Mg∕Ca, <i>δ</i> ²⁶ Mg), boron (B∕Ca, <i>δ</i> ¹¹ B), and calcium (Ca ²⁺ ) geochemistry of <i>Arctica islandica</i> and <i>Crassostrea virginica</i> extrapallial fluid and shell under ocean acidification

  Biogeosciences · 2025-06-19 · 4 citations

  articleOpen accessSenior author

  Abstract. The geochemistry of biogenic carbonates has long been used as proxies to record changing seawater parameters. However, the effect of ocean acidification (OA) on seawater chemistry and organism physiology could impact isotopic signatures and how elements are incorporated into the shell. In this study, we investigated the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial fluid (EPF), and the shell – in two bivalve species: Crassostrea virginica and Arctica islandica. Additionally, we examined the effects of three ocean acidification conditions (ambient: 500 ppm CO2, moderate: 900 ppm CO2, and high: 2800 ppm CO2) on the geochemistry of the same three reservoirs for C. virginica. We present data on calcification rates, EPF pH, measured elemental ratios (Mg/Ca, B/Ca), and isotopic signatures (δ26Mg, δ11B). In both species, comparisons of seawater and EPF Mg/Ca and B/Ca, Ca2+, and δ26Mg indicate that the EPF has a distinct composition that differs from seawater. Shell δ11B did not faithfully record seawater pH, and δ11B-calculated pH values were consistently higher than pH measurements of the EPF with microelectrodes, indicating that the shell δ11B may reflect a localized environment within the entire EPF reservoir. In C. virginica, EPF Mg/Ca and B/Ca, as well as absolute concentrations of Mg2+, B, and Ca2+, were all significantly affected by ocean acidification, indicating that OA affects the physiological pathways regulating or storing these ions, an observation that complicates their use as proxies. Reduction in EPF Ca2+ may represent an additional mechanism underlying reduction in calcification in C. virginica in response to seawater acidification. The complexity of dynamics of EPF chemistry suggests boron proxies in these two mollusk species are not straightforwardly related to seawater pH, but ocean acidification does lead to both a decrease in microelectrode pH and boron-isotope-based pH, potentially showing applicability of boron isotopes in recording physiological changes. Collectively, our findings show that bivalves have high physiological control over the internal calcifying fluid, which presents a challenge in using boron isotopes for reconstructing seawater pH.

  PublisherOA PDFDOI

• Metabolic skinflint or spendthrift? Insights into ground sloth integument and thermophysiology revealed by biophysical modeling and clumped isotope paleothermometry

  Journal of Mammalian Evolution · 2025-01-14 · 15 citations

  articleOpen access

  Abstract Remains of megatheres have been known since the 18th -century and were among the first megafaunal vertebrates to be studied. While several examples of preserved integument show a thick coverage of fur for smaller ground sloths living in cold climates such as Mylodon and Nothrotheriops , comparatively very little is known about megathere skin. Assuming a typical placental mammal metabolism, it was previously hypothesized that megatheres would have had little-to-no fur as they achieved giant body sizes. Here the “hairless model of integument” is tested using geochemical analyses to estimate body temperature to generate novel models of ground sloth metabolism, fur coverage, and paleoclimate with Niche Mapper software. The simulations assuming metabolic activity akin to those of modern xenarthrans suggest that sparse fur coverage would have resulted in cold stress across most latitudinal ranges inhabited by extinct ground sloths. Specifically, Eremotherium predominantly required dense 10 mm fur with implications for seasonal changes of coat depth in northernmost latitudes and sparse fur in the tropics; Megatherium required dense 30 mm fur year-round in its exclusive range of cooler, drier climates; Mylodon and Nothrotheriops required dense 10–50 mm fur to avoid thermal stress, matching the integument remains of both genera, and further implying the use of behavioral thermoregulation. Moreover, clumped isotope paleothermometry data from the preserved teeth of four genera of ground sloth yielded reconstructed body temperatures lower than those previously reported for large terrestrial mammals (29 ± 2°–32 ± 3° C). This combination of low metabolisms and thick fur allowed ground sloths to inhabit various environments.

  PublisherOA PDFDOI

• Supplementary material to "The influence of irradiance and interspecific differences on δ ¹¹ B, δ ¹³ C and elemental ratios in four coralline algae complexes"

  2025-07-03

  preprintSenior author
  PublisherDOI

• The influence of irradiance and interspecific differences on <i>δ</i> ¹¹ B, <i>δ</i> ¹³ C and elemental ratios in four coralline algae complexes from Aotearoa, New Zealand

  Biogeosciences · 2025-12-05

  articleOpen accessSenior authorCorresponding

  Abstract. Coralline algae are a cosmopolitan group of important foundational species. The calcium carbonate they produce is increasingly being used as paleoenvironmental archives, as well as used to trace physiological responses of these important macroalgae to environmental change. In this context, evaluating the effect of oceanic change and photo-physiological parameters on geochemical proxies is critical, as such gaps may lead to erroneous paleoenvironmental reconstructions, misattributed drivers of calcification responses, and ultimately compromise conservation strategies. Here we address the impact of light (irradiance) on four species complexes of coralline red algae including two morphologies; geniculate (branching) and non-geniculate (encrusting). The four complexes up-regulated their δ11B derived pHCF relative to seawater by 0.6 to 0.8 pH unit. δ11B was not measurably affected by varying irradiance despite evidence of increasing photosynthesis. All complexes were able to maintain and elevate their pHCF relative to seawater for all treatments. Non-geniculate and geniculate complexes had distinct geochemical signatures of δ11B, δ13Cmineral and trace elements. These differences in geochemical signatures indicate a variety of calcification mechanisms exist within coralline algae. We propose that different sources of dissolved inorganic carbon (DIC) are necessary to explain the observed δ13Cmineral. As geniculate species have higher photosynthetic activity (i.e. gross photosynthesis), the DIC sources allocated to calcification might be limited due to greater CO2 drawdown. This is supported by B/Ca and U/Ca ratios suggesting modulation of carbonate chemistry and especially lower DICCF in geniculate relative to non-geniculate complexes. DIC sources might come from direct CO2 diffusion or better recycling of metabolic CO2 which would explain the depleted δ13Cmineral. This strategy likely arises from the different energy needs of the organisms, with non-geniculate using relatively more energy to support calcification. We suggest the different calcification mechanisms between morphologies are linked to different interactions between photosynthesis and carbon allocation. While photosynthesis can provide energy to geniculate complexes to maintain their metabolic needs, their calcification may be limited by DIC. In contrast, non-geniculate forms may benefit from more limited DIC drawdown due to lower photosynthetic activity, therefore maintaining higher internal DIC concentrations ultimately supporting faster calcification.

  PublisherOA PDFDOI

• Dissolution effects on clumped isotope signatures in planktic foraminifera

  2025-01-31

  preprintOpen access

  The carbonate clumped isotope paleothermometer is becoming more widely used in the geosciences because it is less sensitive to solution δ 18 O and Mg/Ca than other carbonate-based temperature proxies. Here, we examine the impacts of dissolution on foraminiferal clumped isotope records (∆ 47 ). Dissolution is known to impact carbonate minerals in ocean sediments near and below the carbonate saturation horizon. The effects of dissolution on foraminiferal mass, δ 18 O, and Mg/Ca have been the subject of prior work but have not yet been reported for the carbonate clumped isotope paleothermometer. We examine six planktic foraminiferal species from core-tops collected at different water depths on the Ontong Java Plateau. Below the carbonate saturation horizon, multiple species exhibit higher ∆ 47 values, likely due to dissolution, biasing ∆ 47 to cooler temperatures. The largest effects are observed in G. siphonifera , P. obliquiloculata , and G. tumida with an ~0.01 ‰ difference from above to below the saturation horizon; p &lt; 0.01 corresponding to a temperature bias of ~4 °C at a measured temperature of 28 °C and of ~3 °C at a measured temperature of 18 °C. Normalizing data for different species yields a pooled slope of -0.0006 ‰/µmol/kg ∆[CO 3 2- ] (p &lt; 0.01). Dissolution experiments show that for two species, T. sacculifer and G. tumida , ∆ 47 increased with mass loss. We propose multiple mechanisms by which dissolution may impact ∆ 47 including intra-test heterogeneous dissolution, which provide context to enable corrections for the impacts of dissolution on clumped isotope-based paleo-records.

  PublisherOA PDFDOI

• Dietary niche partitioning among large sharks in the Late Cretaceous Western Interior Seaway of North America documented by zinc isotopes

  2025-03-14

  preprintOpen accessCorresponding

  The Western Interior Seaway (WIS) was a major epicontinental sea that divided North America during the Late Cretaceous with a rich ecosystem that hosted a wide variety of marine life. The seaway was home to a diverse range of species, from microscopic planktonic organisms to giant reptiles and sharks. However, food web structures and trophic interactions among Late Cretaceous marine taxa remain largely ambiguous due to the challenges in reconstructing ecological interactions in the fossil record. Fossil evidence of predator-prey interactions such as preserved bite marks, stomach content or faeces is limited. For sharks, trophic interactions can be inferred from morphological comparisons of teeth with modern counterparts. Yet, none of these methods alone can decisively identify the overall diet nor can they quantify a species&amp;#8217; trophic position. Thanks to recent methodological advancements, an animal&amp;#8217;s trophic position can now be reconstructed on geologic timescales by analysing geochemical proxies preserved in dental enamel(oid). Among these novel proxies are zinc isotope ratios (66Zn/64Zn), reported as &amp;#948;66Zn value, a trophic-level proxy that is increasingly applied to address archaeological and palaeobiological research questions.Here we use enamel(oid) &amp;#948;66Zn values to investigate the food web structures and trophic positions among lamniform sharks within the WIS. We focus on specimen from two Upper Cretaceous localities in the U.S., the Tocito Sandstone-Mulatto Tongue of the Mancos Shale in New Mexico and the Codell Sandstone Member of the Carlile Shale in Kansas. The fossil assemblages are dated to the Turonian-Coniacian transition, just prior to the radiation of Mosasauroidea (extinct marine lizards) to becoming the dominant marine predator of the WIS. Our results demonstrate well-preserved enamel(oid) &amp;#948;66Zn values in both localities, but locality-specific differences in the diagenetic modification of dentine &amp;#948;66Zn values. We highlight significant resource partitioning among the 16 analysed taxa within the WIS. Archaeolamna cf. A. kopingensis, Cretodus sp. and Cretoxyrhina mantelli occupied very high trophic positions, whereas Cretalamna cf. C appendiculata was likely foraging opportunistically across several trophic levels. We expand the use of enamel(oid) &amp;#948;66Zn analyses to Mesozoic fossils and demonstrate that the analyses of enameloid &amp;#948;66Zn values of multiple taxa within fossil assemblages enables robust reconstructions of food web dynamics and trophic interactions, providing new avenues for palaeobiological and evolutionary research in deep time.

  PublisherDOI

Recent grants

• Collaborative Research: A combined boron isotope, pH microelectrode and pH-sensitive dye approach to constraining acid/base chemistry in the calcifying fluids of corals

  NSF · $271k · 2014–2018

Frequent coauthors

• Aradhna Tripati

  Planetary Science Institute

  321 shared

• Maxence Guillermic

  University of California, Los Angeles

  162 shared

• Yi‐Wei Liu

  Shandong University

  160 shared

• Jill Sutton

  Université de Bretagne Occidentale

  98 shared

• John Trowsdale

  University of Cambridge

  88 shared

• Justin B. Ries

  Northeastern University

  83 shared

• Jamie Lucarelli

  Center for Creative Leadership

  73 shared

• Insiya Jafferji

  The University of Texas MD Anderson Cancer Center

  73 shared

Labs

• 2023-2024 Undergraduate Research Lab AvailabilityPI

Education

• Ph.D., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2005

• M.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2001

• B.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  1999