Research

Last updated: 04.26.22

Our research: Using anatomy to understand ecology and evolution

We use the fossil record to investigate changes in mammalian morphology over millions of years during the Oligocene and Miocene (ca. 30 to 5 Million years ago). Our goal is to understand the evolution of modern mammalian communities and their responses to diverse dramatic climatic and environmental perturbations. We combine comparative anatomy, museum work, and biostatistics to infer the taxonomic and ecological affinities of extinct taxa and shed light on the tempo and mode of mammalian evolution.

We contribute to the study of systematics and evolutionary ecology across a broad swath of mammals representing some of the most diverse clades, but we focus much of our work on burrowing (=fossorial) rodents. Burrowing requires profound morphological and physiological adaptations and has led to some remarkable convergences among rodent lineages separated by tens of millions of years and thousands of kilometers; burrowing rodents have evolved on every continent but Antarctica. Much of this work is undertaken in collaboration with students and colleagues, including Dr. Samantha Hopkins.

We seek to answer three main questions:

1. Did burrowing rodents evolve through adaptive radiations?

2. Do the constraints of burrowing lead to convergent evolution?

3. Does burrowing lead to an evolutionary dead-end?

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1. Did burrowing rodents evolve through adaptive radiations?

Introduction:

Adaptive radiations are sudden bursts of diversity arising from a common ancestor enabled by the appearance of novel adaptations. These bursts in taxonomic richness are associated with ecological diversifications and the exploitation of new niches. They are characterized by: (1) the common ancestry of the species studied, (2) an extraordinary diversification, (3) fitness-enhancing apomorphic trait(s), and (4) an association between the trait(s) and environmental change. Many mammal radiations are associated with locomotor ecology: the evolution of echolocation was critical to bat adaptive radiation, and body elongation enabled burrow use and the radiation of some musteloids. We aim to determine how pervasive adaptive radiations are throughout the evolutionary history of burrowing rodents. To this end, we have been building phylogenetic trees for a range of burrowing rodent clades in addition to exploring their systematics and morphology.

Current projects:

  • We are developing a phylogenetic framework for the extinct pocket gophers of the subfamily Entoptychinae.
  • We are studying the cranial and dental variation within and across species of modern as well as extinct pocket gophers to refine our understanding of the rise and demise of the dominant burrowing rodent group ca. 28 to 23.5 million years ago.
  • We are also working towards resolving the phylogenetics of the clade Geomorpha, which includes pocket gophers, the living family Heteromyidae, and numerous extinct taxa liek the family Florentiamyidae.

Relevant publications:

Calede, J.J.M. and Brown, A. 2021. Sexual dimorphism in cranial shape and size in geomyoid rodents: multivariate and evolutionary perspectives. Current Zoology doi:10.1093/cz/zoab070: 1-18.

Calede, J., and Samuels, J. X. 2020. A new species of Ceratogaulus from Nebraska and the evolution of nasal horns in Mylagaulidae (Mammalia, Rodentia, Aplodontioidea). Journal of Systematic Palaeontology 18: 1395-1414.

Calede, J., and Rasmussen, D.L. 2020. New gophers (Rodentia: Geomyidae) from the Cabbage Patch beds of Montana (Renova Formation) and the phylogenetic relationships within Entoptychinae. Annals of Carnegie Museum 86: 107-167.

Calede, J. and Glusman, J. 2017. Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia: Geomyidae). Palaeontology 60: 281-307.

Davis, E. B., and Calede, J. 2012. Extending the utility of artiodactyl postcrania for species-level identifications using multivariate morphometric analyses Paleontologia Electronica 15.1.1A. → Full text/PDF

Calede J., and Hopkins, S.S.B. 2012. Intraspecific versus interspecific variation in Miocene Great Basin mylagaulids: implications for evolutionary history. Zoological Journal of the Linnean Society 164:427–450.

Calede, J., and Hopkins, S.S.B. 2012. New material of Alphagaulus pristinus (Mammalia: Rodentia: Mylagaulidae) from the Deep River Formation (Montana, USA): implications for ecology, ontogeny, and phylogeny. Journal of Vertebrate Paleontology 32:151–165.

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2. Do the constraints of burrowing lead to convergent evolution?

Introduction:

Burrowing is expected to cause convergent morphologies. Indeed, with increased specialization, there should be an increasingly narrow set of derived morphologies for asymmetric selection to act upon, leading to a limited set of phenotypes in descendants. This pattern is shown in several mammalian clades that evolved specialized diets. The limited sets of phenotypes associated with the similar constraints that different clades of burrowing rodents experience should lead to convergent morphologies. Although such convergence has been suggested before, it has also been challenged. We use phylogenies and ecomorphological data to assess the degree to which the constraints of burrowing evolution lead to the repeated evolution of similar morphologies across clades.

Current projects:

  • We are studying the locomotion of a fossil beaver from Montana using the morphology of its ankle bones and comparisons with modern rodents.
  • We are working on the bite force and procumbency of pocket gophers and their relatives.
  • We are working with Drs. Nicholas Famoso and Samantha Hopkins on better understanding the changes in tooth morphology in mylagaulids with environmental change.

Relevant publications:

Scarpitti, E.A. and Calede, J.J.M. 2022. Ecological correlates of the morphology of the auditory bulla in rodents: applications to the fossil record. Journal of Anatomy 240:647-668. http://doi.org/10.1111/joa.13579

Calede, J., Samuels, J.X., and Chen, M. 2019. Locomotory adaptations in entoptychine gophers (Rodentia: Geomyidae) and the mosaic evolution of fossoriality. Journal of Morphology 280: 879-907.

Calede, J. 2014. Skeletal morphology of Palaeocastor peninsulatus (Rodentia, Castoridae) from the Fort Logan Formation of Montana (Early Arikareean): ontogenetic and paleoecological interpretations. Journal of Mammalian Evolution 21: 223-241.

Calede, J., and Hopkins, S.S.B. 2012. New material of Alphagaulus pristinus (Mammalia: Rodentia: Mylagaulidae) from the Deep River Formation (Montana, USA): implications for ecology, ontogeny, and phylogeny. Journal of Vertebrate Paleontology 32:151–165.

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3. Does burrowing lead to an evolutionary dead-end?

Introduction:

The presence and distribution of burrowing rodents is strongly soil dependent. Soil properties control the distribution of burrowing rodents and changes in soil conditions lead to changes in spatial distribution. On a larger scale, such patterns can lead to extinctions if runaway habitat specialization increases extinction risk. Competition among burrowing rodent clades may also play a role in extinction dynamics, leading to taxon succession. Whatever the cause of its extinction, we expect the demise of a clade to be concurrent with the rise of others taking advantage of the novel environment. We seek to explore the decline and replacement of burrowing rodent clades to determine if the timing of increased extinction rates in burrowing rodents coincides with the appearance of competing lineages or changes in the environment.

Current projects:

  • We are studying rates of evolution and biogeography of entoptychine gophers through the Oligocene and Miocene.
  • We are working to expand our analysis to the clade Geomorpha.