Continuously growing rodent molars result from a predictable quantitative evolutionary change over 50 million years.
The fossil record is widely informative about evolution, but fossils are not systematically used to study the evolution of stem-cell-driven renewal. Here, we examined evolution of the continuous growth (hypselodonty) of rodent molar teeth, which is fuelled by the presence of dental stem cells. We studied occurrences of 3,500 North American rodent fossils, ranging from 50 million years ago (mya) to 2 mya. We examined changes in molar height to determine whether evolution of hypselodonty shows distinct patterns in the fossil record, and we found that hypselodont taxa emerged through intermediate forms of increasing crown height. Next, we designed a Markov simulation model, which replicated molar height increases throughout the Cenozoic and, moreover, evolution of hypselodonty. Thus, by extension, the retention of the adult stem cell niche appears to be a predictable quantitative rather than a stochastic qualitative process. Our analyses predict that hypselodonty will eventually become the dominant phenotype.
Department of Orofacial Sciences and Program in Craniofacial Biology, University of California San Francisco, San Francisco, CA 94143, USA.
Vagan
V
Tapaltsyan
Department of Geosciences and Geography, University of Helsinki, PO Box 64, 00014 Helsinki, Finland; Senckenberg Research Institute and Nature Museum, Biodiversity and Climate Research Centre LOEWE BiK-F, Senckenberganlage 25, 60325 Frankfurt am Main, Germany.
Jussi T
JT
Eronen
Department of Ecosystem Science and Management, Texas A&M University, College Station, TX 77843, USA.
A Michelle
AM
Lawing
Department of Orofacial Sciences and Program in Craniofacial Biology, University of California San Francisco, San Francisco, CA 94143, USA.
Amnon
A
Sharir
Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA.
Christine
C
Janis
Developmental Biology Program, Institute of Biotechnology, University of Helsinki, PO Box 56, 00014 Helsinki, Finland. Electronic address: jernvall@fastmail.fm.
Jukka
J
Jernvall
Department of Orofacial Sciences and Program in Craniofacial Biology, University of California San Francisco, San Francisco, CA 94143, USA; Department of Pediatrics and Institute for Human Genetics, University of California San Francisco, San Francisco, CA 94143, USA. Electronic address: ophir.klein@ucsf.edu.
Ophir D
OD
Klein
D000818:Animals; D001683:Biological Clocks; D005075:Biological Evolution; D016208:Databases, Factual; D005580:Fossils; D008390:Markov Chains; D051379:Mice; D008962:Models, Theoretical; D008963:Molar / Q000000981:diagnostic imaging / Q000502:physiology*; D014057:Tomography, X-Ray Computed