Research Program
PDFs are available upon request. Google Scholar page is here. ORCID: 0000-0002-4261-1323
From Organisms to Ecosystems: integrative approaches to biodiversity research in deep-time
My research uses a systems approach to disentangle complex interactions between ecosystems, environments, and evolution in deep time.
My research uses a systems approach to disentangle complex interactions between ecosystems, environments, and evolution in deep time.
I) High-resolution palaeocommunity & palaeoenvironmental dynamics across time and space
A major component of the research in my lab focuses on analyzing trends in vertebrate community structure to test the responses of species and ecosystems to climate perturbations and other environmental conditions. In particular, I'm interested in understanding these patterns in the ancient 'non-analogue' ecosystems of the Cretaceous, as this period in Earth history records greenhouse climate conditions that are similar to some of the projected outcomes for climate change occurring on Earth today. Characterizing how species, ecosystems, and landscapes respond under such conditions may give us important insights about both the underlying differences of greenhouse vs. icehouse environments, as well as providing clues about potential differences in response beyond what we might predict based on our present-day knowledge alone (potentially aiding future conservation plans).
A major component of this research thus far has focused on the 3 million year span of the Belly River Group of Alberta, which records multiple major regional environmental and sea level changes, and uses a dataset of over 60 taphonomically-equivalent sites representing over 100,000 fossil specimens. Ongoing work on these strata involves additional site sampling, taxonomic revisions for more effective palaeocommunity analyses, the integration of functional trait metrics to assess differences in functional diversity vs. biodiversity, and the analysis of a suite of terrestrial palaeoclimate proxies to better understand the fine-scale environmental conditions (and changes) in these systems over time and across landscapes.
Most relevant studies (in addition to in-progress research):
Cullen, TM. and Nanglu, K (2024). Functional diversity and structure of Cretaceous coastal plain ecosystems. Conference Abstract, 2024 North American Paleontology Conference. Ann Arbor, Michigan. June 2024.
Thompson, MGW., Cullen, TM., Evans, DC., Schröder-Adams, C., Ryan, MJ. (2024). Multi-proxy paleoenvironmental and paleoecological reconstruction of the Foremost Formation (Upper Cretaceous, Campanian) of Alberta. Palaios 39(12): 425-443. doi: 10.2110/palo.2022.061
Cullen, TM. and Evans, DC. (2016). Palaeoenvironmental drivers of vertebrate community composition in the Belly River Group (Campanian) of Alberta, Canada, with implications for dinosaur biogeography. BMC Ecology. doi: 10.1186/s12898-016-0106-8
Cullen, TM., Fanti, F., Capobianco, C., Ryan, MJ., and Evans, DC. (2016). A vertebrate microsite from a marine-terrestrial transition in the Foremost Formation (Campanian) of Alberta, Canada, and the use of faunal assemblage data as a palaeoenvironmental indicator. Palaeogeography, Palaeoclimatology, Palaeoecology 444: 101-114. doi:10.1016/j.palaeo.2015.12.015
A major component of this research thus far has focused on the 3 million year span of the Belly River Group of Alberta, which records multiple major regional environmental and sea level changes, and uses a dataset of over 60 taphonomically-equivalent sites representing over 100,000 fossil specimens. Ongoing work on these strata involves additional site sampling, taxonomic revisions for more effective palaeocommunity analyses, the integration of functional trait metrics to assess differences in functional diversity vs. biodiversity, and the analysis of a suite of terrestrial palaeoclimate proxies to better understand the fine-scale environmental conditions (and changes) in these systems over time and across landscapes.
Most relevant studies (in addition to in-progress research):
Cullen, TM. and Nanglu, K (2024). Functional diversity and structure of Cretaceous coastal plain ecosystems. Conference Abstract, 2024 North American Paleontology Conference. Ann Arbor, Michigan. June 2024.
Thompson, MGW., Cullen, TM., Evans, DC., Schröder-Adams, C., Ryan, MJ. (2024). Multi-proxy paleoenvironmental and paleoecological reconstruction of the Foremost Formation (Upper Cretaceous, Campanian) of Alberta. Palaios 39(12): 425-443. doi: 10.2110/palo.2022.061
Cullen, TM. and Evans, DC. (2016). Palaeoenvironmental drivers of vertebrate community composition in the Belly River Group (Campanian) of Alberta, Canada, with implications for dinosaur biogeography. BMC Ecology. doi: 10.1186/s12898-016-0106-8
Cullen, TM., Fanti, F., Capobianco, C., Ryan, MJ., and Evans, DC. (2016). A vertebrate microsite from a marine-terrestrial transition in the Foremost Formation (Campanian) of Alberta, Canada, and the use of faunal assemblage data as a palaeoenvironmental indicator. Palaeogeography, Palaeoclimatology, Palaeoecology 444: 101-114. doi:10.1016/j.palaeo.2015.12.015
II) Isotope approaches to characterize environmental & ecological interactions in ancient systems
Another primary focus of research in my lab involves applying isotopic and elemental analyses to reconstruct diet, environmental conditions, trophic interactions, and habitat preferences in extant and ancient systems. One of the conventional issues in using fossil data is that there are many aspects of the biology which do not fossilize (e.g. behaviour, specifics of diet, variations in movement patterns through life, etc.), but which we are still interested in understanding. Geochemical proxies are useful in this regard as they involve the measurement of particular naturally occurring isotopes or the ratios of certain trace elements (often metals) which have been ingested by an animal during its life and incorporated into its soft and hard tissues (particularly the tooth enamel and bones, both of which do readily fossilize). In this way, animals 'are what they eat', and a record of their diet, behaviour, and movements can all be recorded permanently in their fossilized remains for us to measure many millions of years later.
A major focus so far has been on Late Cretaceous coastal floodplain ecosystems and their modern near-analogue environments, providing a finer-resolution complement to the ecosystem-scale / macroecological approach listed in section [I] above. The goals of this research are two-fold: 1) to understand the community structure and food webs of the Late Cretaceous, and their relation to various environmental parameters, given that there are a number of unusual biogeographic and ecological patterns documented via fossil occurrence data which suggest differences in baseline ecosystem function in these greenhouse environmental systems compared to large vertebrate communities today; and 2) to use the Cretaceous as as a baseline model both for understanding ecological processes in non-analog greenhouse systems and apply those insights to form predictions of future ecological shifts as the Earth transitions from icehouse to greenhouse conditions as a result of ongoing climate change (again, in concert with similar goals for analyses in section [I]).
Most relevant papers (in addition to in-progress research):
Cullen, TM., Cousens, B. (2024). New geochemical insights in Mesozoic terrestrial paleoecology and evidence for omnivory in troodontid dinosaurs. GSA Bulletin. doi: https://doi.org/10.1130/B37077.1
Cullen, TM., Longstaffe, FJ., Wortmann, UG., Huang, L., Evans, DC. (2023). Anomalous 13C-enrichment in Mesozoic vertebrate enamel reflects environmental conditions in a ‘vanished world’ and not a unique dietary physiology. Paleobiology: 1-15. doi: 10.1017/pab.2022.43
Cullen, TM., Zhang, S., Spencer, J., Cousens, B. (2022). Sr-C-O isotope signatures reveal herbivore niche-partitioning in a Cretaceous ecosystem. Palaeontology. doi: https://doi.org/10.1111/pala/12591
Cullen, TM., Longstaffe, FJ., Wortmann, UG., Huang, L., Fanti, F., Goodwin, MB., Ryan, MJ., Evans, DC. (2020). Large-scale stable isotope characterization of a Late Cretaceous dinosaur-dominated ecosystem. Geology 48(6): 546-551.
A major focus so far has been on Late Cretaceous coastal floodplain ecosystems and their modern near-analogue environments, providing a finer-resolution complement to the ecosystem-scale / macroecological approach listed in section [I] above. The goals of this research are two-fold: 1) to understand the community structure and food webs of the Late Cretaceous, and their relation to various environmental parameters, given that there are a number of unusual biogeographic and ecological patterns documented via fossil occurrence data which suggest differences in baseline ecosystem function in these greenhouse environmental systems compared to large vertebrate communities today; and 2) to use the Cretaceous as as a baseline model both for understanding ecological processes in non-analog greenhouse systems and apply those insights to form predictions of future ecological shifts as the Earth transitions from icehouse to greenhouse conditions as a result of ongoing climate change (again, in concert with similar goals for analyses in section [I]).
Most relevant papers (in addition to in-progress research):
Cullen, TM., Cousens, B. (2024). New geochemical insights in Mesozoic terrestrial paleoecology and evidence for omnivory in troodontid dinosaurs. GSA Bulletin. doi: https://doi.org/10.1130/B37077.1
Cullen, TM., Longstaffe, FJ., Wortmann, UG., Huang, L., Evans, DC. (2023). Anomalous 13C-enrichment in Mesozoic vertebrate enamel reflects environmental conditions in a ‘vanished world’ and not a unique dietary physiology. Paleobiology: 1-15. doi: 10.1017/pab.2022.43
Cullen, TM., Zhang, S., Spencer, J., Cousens, B. (2022). Sr-C-O isotope signatures reveal herbivore niche-partitioning in a Cretaceous ecosystem. Palaeontology. doi: https://doi.org/10.1111/pala/12591
Cullen, TM., Longstaffe, FJ., Wortmann, UG., Huang, L., Fanti, F., Goodwin, MB., Ryan, MJ., Evans, DC. (2020). Large-scale stable isotope characterization of a Late Cretaceous dinosaur-dominated ecosystem. Geology 48(6): 546-551.
III) Osteohistology to study growth variability, body-size evolution, and autecology
Another major component of research in my lab is the use of bone cross-sections to study age and growth in vertebrates. Similar to the purpose of applying isotope approaches, I examine bone cross-sections as a way to learn about growth in extinct (and extant animals), where we are not able to simply observe an animal growing in-life and taking ongoing measurements of its weight and dimensions (as one might do for a zoo animal, for example). By using these approaches we can gain similar amount of information for animals which have been extinct for tens of millions of years.
This research involves quantifying the variability present in multiple growth proxies (e.g. tissue organization, presence of annual growth marks, etc) found in bone microstructure and reconstructing the growth curves and body size evolution of different species. A major component of this research focuses on testing if hypothesized indicators of ontogenetic age and growth are recorded similarly across different bones of the same skeleton, different individuals of the same species, and across different species, to what extent each varies, and if that variation follows any particular pattern and/or introduces a sufficient amount of 'noise' to overprint the 'signal' of growth. Based on these data, I have also examined questions of macroevolution, in particular testing differences in growth pattern across dinosaur groups which have independently evolved 'gigantic' body size.
In my current research, I am also combining these approaches with isotopic analyses to investigate events and ecology recorded during the life history of individual animals to reconstruct climate conditions at very fine scales and to test questions such as I) how did seasonal and multi-year patterns of environmental change impact growth of organisms, II) how did diets shift through life, III) how did migration and range-size differ in juveniles vs. adults of a species, and IV) what can we learn about particular behaviors such as parental care in extinct animals?
Most relevant papers (in addition to in-progress research):
Cullen, TM., Brown, CM., Chiba, K., Brink, KS., Makovicky, PJ., Evans, DC. (2021). Growth variability, dimensional scaling, and the interpretation of osteohistological data. Biology Letters 17: 202110383. doi: https://doi.org/10.1098/rsbl.2021.0383
Cullen, TM., Canale, JI., Apesteguía, S., Smith, NS., Hu, D., Makovicky, PJ. (2020). Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution. Proceedings of the Royal Society B 287: 20202258. http://dx.doi.org/10.1098/rspb.2020.2258.
Cullen, TM., Ryan, MJ., Currie, PJ., Kobayashi, Y., and Evans, DC. (2014). Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae). BMC Evolutionary Biology. doi: 10.1186/s12862-014-0231-y.
This research involves quantifying the variability present in multiple growth proxies (e.g. tissue organization, presence of annual growth marks, etc) found in bone microstructure and reconstructing the growth curves and body size evolution of different species. A major component of this research focuses on testing if hypothesized indicators of ontogenetic age and growth are recorded similarly across different bones of the same skeleton, different individuals of the same species, and across different species, to what extent each varies, and if that variation follows any particular pattern and/or introduces a sufficient amount of 'noise' to overprint the 'signal' of growth. Based on these data, I have also examined questions of macroevolution, in particular testing differences in growth pattern across dinosaur groups which have independently evolved 'gigantic' body size.
In my current research, I am also combining these approaches with isotopic analyses to investigate events and ecology recorded during the life history of individual animals to reconstruct climate conditions at very fine scales and to test questions such as I) how did seasonal and multi-year patterns of environmental change impact growth of organisms, II) how did diets shift through life, III) how did migration and range-size differ in juveniles vs. adults of a species, and IV) what can we learn about particular behaviors such as parental care in extinct animals?
Most relevant papers (in addition to in-progress research):
Cullen, TM., Brown, CM., Chiba, K., Brink, KS., Makovicky, PJ., Evans, DC. (2021). Growth variability, dimensional scaling, and the interpretation of osteohistological data. Biology Letters 17: 202110383. doi: https://doi.org/10.1098/rsbl.2021.0383
Cullen, TM., Canale, JI., Apesteguía, S., Smith, NS., Hu, D., Makovicky, PJ. (2020). Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution. Proceedings of the Royal Society B 287: 20202258. http://dx.doi.org/10.1098/rspb.2020.2258.
Cullen, TM., Ryan, MJ., Currie, PJ., Kobayashi, Y., and Evans, DC. (2014). Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae). BMC Evolutionary Biology. doi: 10.1186/s12862-014-0231-y.
IV) Other research topics (collaborative & side-projects contributing to primary research)
I am also actively involved in collaborative research examining: I) sources of preservational, sampling, and analytical biases in studies of the fossil record, II) taphonomic/sedimentological analysis, III) dinosaur biodiversity, anatomy, and taxonomy, IV) morphological variability, sexual dimorphism, and evolution in mammals, and V) the value of natural history data & museums for science and education.
Most relevant papers (in addition to in-progress research):
Nanglu, K., de Carle, D., Cullen, TM., Anderson, E., Arif, S., Castañeda, RA., Chang, LM., Iwama, RE., Fellin, E., Manglicmot, RC., Massey, MD., Astudillo-Clavijo, V. (2023). The nature of science: the fundamental role of natural history in ecology, evolution, conservation and education. Ecology & Evolution 13(10): e10621. doi: https://doi.org/10.1002/ece3.10621
Nanglu, K., Cullen, TM. (2023). Across space and time: a review of sampling, preservational, analytical, and anthropogenic biases in fossil data across macroecological scales. Earth Science Reviews 244. https://doi.org/10.1016/j.earscirev.2023.104537
Cullen, TM., Larson., DW., Witton, MP., Scott, D., Maho, T., Brink, KS., Evans, DC., Reisz, R. (2023). Theropod dinosaur facial reconstruction and the significance of soft tissues in paleobiology. Science 379 (6639): 1348-1352.
Canale, JI., Apesteguía, S., Gallina, PA., Mitchell, J., Smith, ND., Cullen, TM., Shinya, A., Haluza, A., Gianechini, FA., Makovicky, PJ. (2022). New giant carnivorous dinosaur from the Late Cretaceous of Argentina reveals convergent evolutionary trends in theropod arm reduction. Current Biology 32, 1-8. https://doi.org/10.1016/j.cub.2022.05.057
Benson, R., Brown, CM., Campione, N., Cullen, TM., Evans, DC., Zanno, L. (2022). Comment on the influence of juvenile dinosaurs on community structure and diversity. Science 375(657821). doi: https://doi.org/10.1126/science.abj5976
Cullen, TM., Zanno, L., Larson, DW., Todd, E., Currie, PJ., Evans, DC. (2021). Anatomical, morphometric, and stratigraphic review of theropod biodiversity in the Dinosaur Park Formation (Late Cretaceous; Campanian) of Alberta. Canadian Journal of Earth Sciences 58(9): 870-884.
Cullen, TM., Fraser, D., Rybczynski, N., and Schroder-Adams, C. (2014). Early evolution of sexual dimorphism and polygyny in Pinnipedia. Evolution 68-5: 1469–1484. doi: https://dx.doi.org/10.1111/evo.12360
Most relevant papers (in addition to in-progress research):
Nanglu, K., de Carle, D., Cullen, TM., Anderson, E., Arif, S., Castañeda, RA., Chang, LM., Iwama, RE., Fellin, E., Manglicmot, RC., Massey, MD., Astudillo-Clavijo, V. (2023). The nature of science: the fundamental role of natural history in ecology, evolution, conservation and education. Ecology & Evolution 13(10): e10621. doi: https://doi.org/10.1002/ece3.10621
Nanglu, K., Cullen, TM. (2023). Across space and time: a review of sampling, preservational, analytical, and anthropogenic biases in fossil data across macroecological scales. Earth Science Reviews 244. https://doi.org/10.1016/j.earscirev.2023.104537
Cullen, TM., Larson., DW., Witton, MP., Scott, D., Maho, T., Brink, KS., Evans, DC., Reisz, R. (2023). Theropod dinosaur facial reconstruction and the significance of soft tissues in paleobiology. Science 379 (6639): 1348-1352.
Canale, JI., Apesteguía, S., Gallina, PA., Mitchell, J., Smith, ND., Cullen, TM., Shinya, A., Haluza, A., Gianechini, FA., Makovicky, PJ. (2022). New giant carnivorous dinosaur from the Late Cretaceous of Argentina reveals convergent evolutionary trends in theropod arm reduction. Current Biology 32, 1-8. https://doi.org/10.1016/j.cub.2022.05.057
Benson, R., Brown, CM., Campione, N., Cullen, TM., Evans, DC., Zanno, L. (2022). Comment on the influence of juvenile dinosaurs on community structure and diversity. Science 375(657821). doi: https://doi.org/10.1126/science.abj5976
Cullen, TM., Zanno, L., Larson, DW., Todd, E., Currie, PJ., Evans, DC. (2021). Anatomical, morphometric, and stratigraphic review of theropod biodiversity in the Dinosaur Park Formation (Late Cretaceous; Campanian) of Alberta. Canadian Journal of Earth Sciences 58(9): 870-884.
Cullen, TM., Fraser, D., Rybczynski, N., and Schroder-Adams, C. (2014). Early evolution of sexual dimorphism and polygyny in Pinnipedia. Evolution 68-5: 1469–1484. doi: https://dx.doi.org/10.1111/evo.12360