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Mammalian skull evolutionary changes during Mesozoic + Mixodectes (Paleocene primatomorphan) skeleton (free pdfs)
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Ben Creisler
Mar 11, 2025, 1:14:01 PM (7 days ago) Mar 11
to DinosaurMa...@googlegroups.com
Ben Creisler
New mammal papers:
Julia A. Schultz (2025)
A perspective from the Mesozoic: Evolutionary changes of the mammalian skull and their influence on feeding efficiency and high-frequency hearing
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25652
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25652
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.25652
The complex evolutionary history behind modern mammalian chewing performance and hearing function is a result of several changes in the entire skeletomuscular system of the skull and lower jaw. Lately, exciting multifunctional 3D analytical methods and kinematic simulations of feeding functions in both modern and fossil mammals and their cynodont relatives approach this topic, giving fresh insights into the history of mammalian masticatory behaviors and their evolutionary trends. One crucial transformation in this context is the segregation of postdentary bones (becoming the mammalian middle ear) from the lower jaw, which is posited to have led to the important functional decoupling of the hearing and feeding systems. Evolution of the middle ear is regarded as the key transition that enhanced both mammalian chewing performance and hearing capacity. Three major functional parts undergo substantial evolutionary changes in this process that are anatomically linked to each other: the lower jaw and dentition, middle ear, and inner ear. Sound, transmitted via vibrations of the bony middle ear elements to the inner ear, is converted into movements of the endolymph fluid that shift hair cells of the organ of Corti, triggering neural stimuli perceived as hearing. Structural changes in one part of the system influence the function of the other two. In this review, I highlight recent advances in research focusing on the enhancement of both chewing performance and hearing ability in mammalian history to feature the mechanisms that led to the decoupling of the hearing system (i.e., middle and inner ear) from the feeding system.
Mixodectids are poorly understood placental mammals from the Paleocene of western North America that have variably been considered close relatives of euarchontan mammals (primates, dermopterans, and scandentians) with hypothesized relationships to colugos, extinct plagiomenids, and/or microsyopid plesiadapiforms. Here we describe the most complete dentally associated skeleton yet recovered for a mixodectid, specifically Mixodectes pungens from the early Paleocene of the San Juan Basin, New Mexico. A partial skull with all the teeth erupted and associated axial skeleton, forelimbs, and hind limbs, with epiphyses fused, indicate that it was a mature adult. Results from cladistic analyses incorporating new data robustly support primatomorphan (Primates + Dermoptera) affinities of Mixodectidae, but relationships within Euarchonta are less clear, with Mixodectes recovered as a stem primatomorphan, stem dermopteran, or stem primate. Analyses of postcrania suggest that M. pungens was a relatively large (~ 1.3 kg), claw-climbing arborealist capable of frequent clinging on large diameter vertical supports. With teeth suggesting an omnivorous diet that included leaves, M. pungens occupied a unique ecological niche in the early Paleocene of North America that differed from contemporary, arboreal plesiadapiforms that were smaller and more frugivorous. Euarchontans were thus a more diverse radiation in the early Cenozoic than previously appreciated.
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Free pdf:
Julia A. Schultz (2025)
A perspective from the Mesozoic: Evolutionary changes of the mammalian skull and their influence on feeding efficiency and high-frequency hearing
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25652
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25652
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.25652
The complex evolutionary history behind modern mammalian chewing performance and hearing function is a result of several changes in the entire skeletomuscular system of the skull and lower jaw. Lately, exciting multifunctional 3D analytical methods and kinematic simulations of feeding functions in both modern and fossil mammals and their cynodont relatives approach this topic, giving fresh insights into the history of mammalian masticatory behaviors and their evolutionary trends. One crucial transformation in this context is the segregation of postdentary bones (becoming the mammalian middle ear) from the lower jaw, which is posited to have led to the important functional decoupling of the hearing and feeding systems. Evolution of the middle ear is regarded as the key transition that enhanced both mammalian chewing performance and hearing capacity. Three major functional parts undergo substantial evolutionary changes in this process that are anatomically linked to each other: the lower jaw and dentition, middle ear, and inner ear. Sound, transmitted via vibrations of the bony middle ear elements to the inner ear, is converted into movements of the endolymph fluid that shift hair cells of the organ of Corti, triggering neural stimuli perceived as hearing. Structural changes in one part of the system influence the function of the other two. In this review, I highlight recent advances in research focusing on the enhancement of both chewing performance and hearing ability in mammalian history to feature the mechanisms that led to the decoupling of the hearing system (i.e., middle and inner ear) from the feeding system.
===
Free pdf:
Stephen G. B. Chester, Thomas E. Williamson, Jordan W. Crowell, Mary T. Silcox, Jonathan I. Bloch & Eric J. Sargis (2025)
New remarkably complete skeleton of Mixodectes reveals arboreality in a large Paleocene primatomorphan mammal following the Cretaceous-Paleogene mass extinction
Scientific Reports 15: 8041
doi: https://doi.org/10.1038/s41598-025-90203-z
https://www.nature.com/articles/s41598-025-90203-z
Stephen G. B. Chester, Thomas E. Williamson, Jordan W. Crowell, Mary T. Silcox, Jonathan I. Bloch & Eric J. Sargis (2025)
New remarkably complete skeleton of Mixodectes reveals arboreality in a large Paleocene primatomorphan mammal following the Cretaceous-Paleogene mass extinction
Scientific Reports 15: 8041
doi: https://doi.org/10.1038/s41598-025-90203-z
https://www.nature.com/articles/s41598-025-90203-z
Mixodectids are poorly understood placental mammals from the Paleocene of western North America that have variably been considered close relatives of euarchontan mammals (primates, dermopterans, and scandentians) with hypothesized relationships to colugos, extinct plagiomenids, and/or microsyopid plesiadapiforms. Here we describe the most complete dentally associated skeleton yet recovered for a mixodectid, specifically Mixodectes pungens from the early Paleocene of the San Juan Basin, New Mexico. A partial skull with all the teeth erupted and associated axial skeleton, forelimbs, and hind limbs, with epiphyses fused, indicate that it was a mature adult. Results from cladistic analyses incorporating new data robustly support primatomorphan (Primates + Dermoptera) affinities of Mixodectidae, but relationships within Euarchonta are less clear, with Mixodectes recovered as a stem primatomorphan, stem dermopteran, or stem primate. Analyses of postcrania suggest that M. pungens was a relatively large (~ 1.3 kg), claw-climbing arborealist capable of frequent clinging on large diameter vertical supports. With teeth suggesting an omnivorous diet that included leaves, M. pungens occupied a unique ecological niche in the early Paleocene of North America that differed from contemporary, arboreal plesiadapiforms that were smaller and more frugivorous. Euarchontans were thus a more diverse radiation in the early Cenozoic than previously appreciated.
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