11/12/2022 0 Comments If an animal s described as fossorialMammals have evolved several distinct methods of burrow excavation. As the Aplodontoidea include one of the only horned, fossorial animals ever to evolve, understanding the course of evolution of fossoriality in this group is essential to explain how horns could evolve in a fossorial animal. Although the first mylagaulids were described more than 100 years ago, very little is understood about their ecology. Most of the 29 described species of mylagaulids also have flat skull roofs, a feature used by most fossorial mammals in burrow construction. Mylagaulids, like Aplodontia, are large rodents with distinct postcranial adaptations to a fossorial life habit, including a broad, robust skull, long, spatulate digging claws, short forelimbs with broad joint articulations and heavily built limb girdles (the fossorial adaptations of mylagaulid postcrania have been described in detail previously Fagan 1960). Phylogenetic analysis of the Aplodontoidea (see Hopkins submitted) reveals that mylagaulids are the sister group to the much less speciose Aplodontinae, including Aplodontia rufa, the mountain beaver, which is also a fossorial animal. Mylagaulids are among the most speciose clades of fossorial rodents and are common in North American Miocene faunas. Numerous terrestrial mammals have evolved fossorial adaptations and rodents in particular have repeatedly diversified into underground habitats. Horned mylagaulids, in particular, require more than just analogy to determine the adaptive role of horns because there are no modern analogues for a fossorial (digging) animal with horns. It is rapidly becoming apparent that studies of the evolution of cranial appendages in fossil animals require not just a comparison with modern animals but also study of functional morphology, phylogeny and evolutionary ecology. However, it has proven difficult to apply our knowledge of cranial appendages in extant animals to the diverse horns and cranial adornment in dinosaurs ( Goodwin & Horner 2004), brontotheres ( Stanley 1974 Janis 1982) and even other fossil artiodactyls with cranial appendages of independent origins ( Joeckel 1990). The morphologically and functionally diverse cranial appendages of modern ungulates have been used as analogues for studying the variety of cranial appendages in fossil vertebrates. The evolution of cranial appendages in extinct animals poses a complex problem for palaeontologists. Whereas this suggests an obvious explanation for the horns of this rodent, evidence from functional morphology, anatomy, phylogeny and geologic context indicates that the horns in Ceratogaulus were used for defence, rather than digging, and evolved to offset increased predation costs associated with spending more time foraging above ground as body size increased. Tracing the evolution of fossoriality in aplodontoid rodents (the larger clade to which Ceratogaulus belongs) reveals that Ceratogaulus descended from ancestors who dug by head-lifting. These two adaptations co-occur in mammals extremely rarely: only two fossil genera ( Ceratogaulus and the xenarthran Peltephilus) and no extant mammals are both horned and fossorial. Mammals have evolved adaptations for digging repeatedly horns and other cranial appendages have also evolved numerous times. The function of the large, dorsally projecting nasal horns on this burrowing animal has been the subject of wide speculation among palaeontologists suggested uses range from sexual combat to burrowing. Ceratogaulus, a member of the extinct fossorial rodent clade Mylagaulidae, is the only known rodent with horns and the smallest known horned mammal.
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