On the Genera of Rodents: An Attempt to bring up to Date the current Arrangement of the Order

Evolutionary Relationships among Rodents

Rodents are defined by their unique masticatory apparatus and are frequently separated into three nonmonophyletic groups--sciuromorphs, hystricomorphs, and myomorphs--based on the morphology of their masticatory muscles. Despite several comprehensive dissections in previous work, inconsistencies persist as to the exact morphology of the rodent jaw-closing musculature, particularly, the masseter. Here, we review the literature and document for the first time the muscle architecture noninvasively and in 3D by using iodine-enhanced microCT. Observations and measurements were recorded with reference to images of three individuals, each belonging to one of the three muscle morphotypes (squirrel, guinea pig, and rat). Results revealed an enlarged superficial masseter muscle in the guinea pig compared with the rat and squirrel, but a reduced deep masseter (possibly indicating reduced efficiency at the incisors). The deep masseter had expanded forward to take an origin on the rostrum and was also separated into anterior and posterior parts in the rat and squirrel. The zygomaticomandibularis muscle was split into anterior and posterior parts in all the three specimens by the masseteric nerve, and in the rat and guinea pig had an additional rostral expansion through the infraorbital foramen. The temporalis muscle was found to be considerably larger in the rat, and its separation into anterior and posterior parts was only evident in the rat and squirrel. The pterygoid muscles were broadly similar in all three specimens, although the internal pterygoid was somewhat enlarged in the guinea pig implying greater lateral movement of the mandible during chewing in this species.

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Reviewing the morphology of the jaw-closing musculature in squirrels, rats, and guinea pigs with contrast-enhanced microCT.

The bushlike radiation of muroid rodents is exemplified by the molecular phylogeny of the LCAT nuclear gene.

Recent molecular studies in gerbils found multiple instances of discordance between molecular and morphological phylogenies. In this study, we analyse the largest molecular data set to date of gerbils and their sister group the deomyines to estimate their phylogenetic relationships. Maximum-likelihood and Bayesian analyses were largely concordant, and both generally had high levels of node support. For gerbils, the results were generally concordant with previous molecular phylogenies based on allozymes, chromosomes, DNA/DNA hybridization and DNA sequences, and discordant with morphological phylogenies. None of the traditional gerbil tribes and subtribes were monophyletic. In addition, paraphyly was found in the genera Gerbillus, Gerbilliscus and Meriones as well as in five subgenera within Dipodillus, Gerbillurus and Meriones. Short branches separating taxa in small clusters within Dipodillus and Meriones suggest synonymy. Within deomyines, all genera and subgenera were monophyletic; however, two species groups within Acomys appear to contain synonymous taxa. We also find support for the discordance between molecular and morphological phylogenies in gerbils being partly due to convergent adaptations to arid environments, primarily in the suite of traits associated with inflation of the tympanic bullae. Relative bullar size does appear to be a desert adaptation and is correlated with aridity independent of phylogeny. Further, it varies more strongly along bioclimatic clines than between binary habitat classifications (desert versus mesic).

Molecular systematics of gerbils and deomyines (Rodentia: Gerbillinae, Deomyinae) and a test of desert adaptation in the tympanic bulla

In this paper, the rodents from the composite section of Torrent de Vallparadis (Terrassa, northeastern Spain) are described, with particular emphasis on the arvicolines. Due to their wide geographical distributions and rapid evolutionary rates, arvicolines are especially useful for biostratigraphical purposes. Eight stratigraphic layers have yielded rodent remains, including representatives of the genera Mimomys, Allophaiomys, Stenocranius, Iberomys, Microtus, Arvicola, Apodemus, Eliomys, and Hystrix. The presence of different rodent species, together with the available magnetostratigraphic data, allows a precise determination of the age of each layer and a detailed correlation with other Spanish Pleistocene sites, particularly those of the Sierra de Atapuerca. The complete studied sequence ranges from the pre-Jaramillo Biharian (1.4–1.2 Ma) to the early Toringian (less than 0.6 Ma.), constituting one of the most complete sequences of the Spanish Pleistocene and covering a time span of especial ...

https://bioone.org/journals/journal-of-vertebrate-paleontology/volume-31/issue-4/02724634.2011.576730/Pleistocene-Rodents-from-the-Torrent-de-Vallparad%c3%ads-Section-Terrassa-Northeastern/10.1080/02724634.2011.576730.pdf

Pleistocene rodents from the Torrent de Vallparadís section (Terrassa, northeastern Spain) and biochronological implications

/pdf/on-the-genera-of-rodents-an-attempt-to-bring-up-to-date-the-2jwiub9fde.pdf

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