Heteromys

Abstract: The New World rodent family Heteromyidae shows a marvelous array of ecomorphological types, from bipedal, arid-adapted forms to scansorial, tropical-adapted forms. Although recent studies have resolved most of the phylogenetic relationships among heteromyids at the shallower taxonomic levels, fundamental questions at the deeper taxonomic levels remain unresolved. This study relies on DNA sequence information from 3 relatively slowly evolving mitochondrial genes, cytochrome c oxidase subunit I, 12S, and 16S, to examine basal patterns of phylogenesis in the Heteromyidae. Because slowly evolving mitochondrial genes evolve and coalesce more rapidly than most nuclear genes, they may be superior to nuclear genes for resolving short, basal branches. Our molecular data (2,381 base pairs for the 3-gene data set) affirm the monophyly of the family and resolve the major basal clades in the family. Alternative phylogenetic hypotheses of subfamilial relationships are examined statistically and the Perognathinae and Heteromyinae are found to represent sister clades relative to the Dipodomyinae. The 3 traditional subfamilial groupings are supported; the controversial placement of Microdipodops as a sister clade to Dipodomys in the Dipodomyinae is affirmed, Perognathus and Chaetodipus are distinct sister clades within the Perognathinae, and species of Liomys and Heteromys form the resolved clade Heteromyinae. However, Liomys is found to be paraphyletic relative to Heteromys and, given that this finding corroborates earlier studies, we present a formal taxonomy of Heteromys wherein we place Liomys in synonymy. Semiparametric and parametric methods are used to estimate divergence times from our molecular data and a chronogram of the Heteromyidae, calibrated by the oldest known fossils of Dipodomys and Perognathus ,i s presented. Our time estimates reveal subfamilial differentiation in the early Miocene (22.3‐21.8 million years ago) and pose testable times of divergence for the basal heteromyid nodes. With the basal heteromyid clades resolved and cladogenic events positioned in a time framework, we review the major geological and paleoecological events of the Oligocene and Miocene associated with the early historical biogeography of the family.

Abstract: Middle and inner ear structure and auditory sensitivity have been studied in all five genera of the rodent family Heteromyidae. In the most xericc genera ( Dipodomys and Microdipodops ) the middle ears are greatly inflated the tympano-ossicular system very efficient the organ of Corti extremely modified and low-frequency sensitivity extremely acute. In the most mesic genera ( Heteromys and Liomys ) the middle and inner ears show few modifications and the low frequency sensitivity is rather poor. Perognathus is intermediate in habitat structure, and low frequency sensitivity. Experimental data demonstrate that the low frequency sensitivity in Dipodomys is adaptive in predator avoidance.

Abstract: The rodent superfamily Geomyoidea is an old, undoubtedly monophyletic lineage having only obscure affinities with other rodent groups. Geomyoid rodents, autochthonous in North America, experienced major evolutionary diversification in the Mio-Pliocene coincident with the development of the Madro-Tertiary Geoflora and the climatic trend toward increasing aridity and coolness. Extant geomyoids are divisible into two groups: (1) the Geomyidae, all members of which are fossorial, and (2) the Heteromyidae, whose members display an adaptive continuum from bipedal, xeric-adapted forms to scansorial, mesic-adapted forms. These moieties, although recognizable on biochemical criteria, become particularly difficult to distinguish when paleontological data are considered. Nevertheless, most lines of evidence indicate that the families Heteromyidae and Geomyidae are distinct, monophyletic lineages. The extant heteromyids comprise three main lineages (including six genera) that diverged during the Eocene: (1) subfamily Perognathinae ( Chaetodipus and Perognathus ); (2) subfamily Dipodomyinae ( Dipodomys and Microdipodops ); and (3) subfamily Heteromyinae ( Liomys and Heteromys ). Protein differentiation has occured at heterogeneous rates among these major lineages. Based on available karyotypic data, the main direction of chromosomal evolution in the Heteromyuidae appears to be toward increasing chromosome number. Cladistic analysis of morphological characters used in previous studies aupports biochemical evidence allying Microdipodops with Dipodomys . A model is introduced to describe how heterochronic changes in ontogeny may explain the great breadth of morphological diversification within the superfamily. Taxonomic recommendations at the subfamilial, generic, and sub-generic levels are provided.