Evolution Of Hypsodonty Research Articles

Phylogeny, systematics, and evolution of hypsodonty in the Aplodontiinae (Mammalia, Rodentia, Aplodontiidae), with the description of several new species

ABSTRACTWhereas aplodontiid rodents are represented today by a single living species, their fossil record is diverse in number of species (>100), in morphology, and in ecology. Recent phylogenetic efforts are beginning to make sense of the relationships among diverse members of the clade, but there is still much to learn about the relationships within the morphologically coherent subfamilies of this large group. The subfamily Aplodontiinae, including the extant Aplodontia, ranges from the mid-Miocene through recent, including only eight described species. This is the least diverse clade of aplodontiids, even though it is the only extant group. This study describes three new species, increasing the diversity of described fossil aplodontiids by more than a third. The description herein of Liodontia bathypotamos, n. sp., from the late Hemingfordian of Montana, Liodontia dailyi, n. sp., from the late Hemingfordian of Nevada, and Aplodontia minor, n. sp., from the late Hemphillian of Oregon extends the geographic and temporal range of the subfamily. A phylogenetic analysis of all known aplodontiines finds support for slow diversification and possible anagenetic change within lineages while also suggesting substantial missing time in the aplodontiine fossil record. However, the morphological changes, including rapid increases in hypsodonty, along the aplodontiine lineage yield an extant species, Aplodontia rufa, that, despite its early divergence from the rest of crown group Rodentia, is not at all representative of the ‘primitive’ rodent it is commonly assumed to be.

Millions of Years Behind: Slow Adaptation of Ruminants to Grasslands.

The Late Cretaceous appearance of grasses, followed by the Cenozoic advancement of grasslands as dominant biomes, has contributed to the evolution of a range of specialized herbivores adapted to new diets, as well as to increasingly open and arid habitats. Many mammals including ruminants, the most diversified ungulate suborder, evolved high-crowned (hypsodont) teeth as an adaptation to tooth-wearing diets and habitats. The impact of different causes of tooth wear is still a matter of debate, and the temporal pattern of hypsodonty evolution in relation to the evolution of grasslands remains unclear. We present an improved time-calibrated molecular phylogeny of Cetartiodactyla, with phylogenetic reconstruction of ancestral ruminant diets and habitats, based on characteristics of extant taxa. Using this timeline, as well as the fossil record of grasslands, we conduct phylogenetic comparative analyses showing that hypsodonty in ruminants evolved as an adaptation to both diet and habitat. Our results demonstrate a slow, perhaps constrained, evolution of hypsodonty toward estimated optimal states, excluding the possibility of immediate adaptation. This augments recent findings that slow adaptation is not uncommon on million-year time scales.

An Evo-Devo perspective on ever-growing teeth in mammals and dental stem cell maintenance.

A major challenge for current evolutionary and developmental biology research is to understand the evolution of morphogenesis and the mechanisms involved. Teeth are well suited for the investigation of developmental processes. In addition, since teeth are composed of hard-mineralized tissues, primarily apatite, that are readily preserved, the evolution of mammals is well documented through their teeth in the fossil record. Hypsodonty, high crowned teeth with shallow roots, and hypselodonty, ever-growing teeth, are convergent innovations that have appeared multiple times since the mammalian radiation 65 million years ago, in all tooth categories (incisors, canines, premolars, and molars). A shift to hypsodonty, or hypselodonty, during mammalian evolution is often, but not necessarily, associated with increasingly abrasive diet during important environmental change events. Although the evolution of hypsodonty and hypselodonty is considered to be the result of heterochrony of development, little has been known about the exact developmental mechanisms at the origin of these morphological traits. Developmental biologists have been intrigued by the mechanism of hypselodonty since it requires the maintenance of continuous crown formation during development via stem cell niche activity. Understanding this mechanism may allow bioengineered tooth formation in humans. Hypsodonty and hypselodonty are thus examples of phenotypic features of teeth that have both impacts in understanding the evolution of mammals and holds promise for human tooth bioengineering.

Enamel ridge alignment in upper molars of ruminants in relation to their natural diet

Although it is generally thought that dental design reflects mechanical adaptations to particular diets, concrete concepts of such adaptations beyond the evolution of hypsodonty are largely missing. We investigated the alignment of enamel ridges in the occlusal molar surface of 37 ruminant species and tested for correlations with the percentage of grass in the natural diet. Independent of phylogenetic lineage, species that were either larger and/or included more grass in their natural diet showed a higher proportion of enamel ridges aligned at low angles to the direction of the chewing stroke. Possible explanations for this design are a potential alignment of grass blades in parallel to the molar tooth row, a potential increased proportion of a propalinal (anterior-posterior) chewing movement in grazers as opposed to a strictly transversal chewing stroke in browsers, and the general distribution of forces along the occlusal surface during the chewing stroke. The latter will be less heterogenous (with less force peaks) with an increasing proportion of low-angle enamel ridges. While the validity of these explanations will have to be tested in further studies, the enamel ridge alignment represents a clear signal that deviates from arbitrary distribution and hence most likely represents a functional adaptation.

A model of wear in curved mammal teeth: controls on occlusal morphology and the evolution of hypsodonty in lagomorphs

Cheek teeth of some mammalian herbivores exhibit pronounced changes in occlusal size and shape through wear, purportedly caused by strong curvature. Such changes are extreme in the upper cheek teeth of extinct, dentally archaic lagomorphs. Morphologic and taxonomic turnover in lagomorphs suggests that these dentally archaic forms may have been unable to develop hypselodont (ever-growing) cheek teeth. This study investigates how the interaction of tooth shape and wear can cause occlusal size and shape changes, and potentially impose structural constraints on crown height. These constraints may help explain extinction of mammals with teeth like archaic lagomorphs, evolution and diversification of other mammalian herbivores during the late Miocene, and the relative paucity of hypsodont cheek tooth shapes in extant mammals.I first quantify two-dimensional curvature accounting for shape differences observed in hypsodont teeth, P4s of the archaic lagomorphs Russellagus and Hesperolagomys, which exhibit pronounced change with wear, and Ondatra lower incisors, which show minimal change with wear. Using this quantification, I generate theoretical curvature morphologies and describe a geometric model of tooth wear that generates values for qualitative and quantitative aspects of the occlusal surface at different wear stages. Modeled results of wear surface topography and dimensions closely correspond to observed patterns in Russellagus, Hesperolagomys, and Ondatra. Model results on wear in theoretical tooth morphologies identify two major shape factors influencing wear: orientation of the wear surface (incisor-like or cheek-tooth-like), and tooth curvature (“concentric” or “nonconcentric”). Modeled wear also suggests two geometric constraints on crown height. Teeth with nonconcentric curvatures can have crown height limited by potential tooth area. “Incomplete wear” in any tooth can present severe constraints on increasing crown height, causing structurally untenable morphologies in very tall-crowned to hypselodont teeth.

Evolution of hypsodonty in equids: testing a hypothesis of adaptation

The independent acquisition of high-crowned cheek teeth (hypsodonty) in several un- gulate lineages (e.g., camels, equids, rhinoceroses) in the early to middle Miocene of North America has classically been used as an indication that savanna vegetation spread during this time. Implicit in this interpretation is the untested assumption that hypsodonty was an evolutionary response to feeding in open habitats, either due to a change in food source (from browse to graze) or to in- creased incorporation of airborne grit in the diet. I examined the adaptive explanation for hypso- donty in equids using criteria pertaining to process and pattern of adaptations set up in the com- parative-methods literature. Specifically, I tested whether hypsodonty appeared coincident with or just after the spread of open, grass-dominated habitats in the Great Plains of North America. Phytolith (plant opal) analysis of 99 phytolith assemblages extracted from sediment samples from Montana/Idaho, Nebraska/Wyoming, and Colorado were used to establish the first contin- uous record of middle Eocene-late Miocene vegetation change in the northern to Central Great Plains. This record was compared with the fossil record of equids from the same area in a phy- logenetic framework. The study showed that habitats dominated by C 3 grasses were established in the Central Great Plains by early late Arikareean ($21.9 Ma), at least 4 Myr prior to the emergence of hypsodont equids (Equinae). Nevertheless, the adaptive hypothesis for hypsodonty in equids could not be rejected, because the earliest savanna-woodlands roughly co-occurred with members of the grade constituting the closest outgroups to Equinae (''Parahippus'') showing mesodont dentition. Expla- nations for the slow evolution of full hypsodonty may include weak and changing selection pres- sures and/or phylogenetic inertia. These results suggest that care should be taken when using func- tional morphology alone to reconstruct habitat change.

DNA Data Support a Rapid Radiation of Pocket Gopher Genera (Rodentia: Geomyidae)

In this study, we address the question of phylogenetic relationships in the Geomyidae, focusing primarily on intergeneric relationships within the tribe Geomyini. Our study makes use of DNA sequences from two mitochondrial and two nuclear genes, and we use model-based methods of phylogenetic analysis to infer relationships and determine the level of support for each proposed relationship. Relationships among geomyine pocket gopher genera remain only partially resolved despite a number of earlier attempts to reconstruct their phylogenetic history and despite the newly generated sequence data analyzed in this study. This lack of resolution does not appear to result from insufficient or inappropriate DNA data, nor is it caused by inadequate sampling of taxa. Rather, molecular data and fossil data together lead to the conclusion that diversification within the Geomyini likely occurred during a geologically brief period in the Blancan. Rapid climate change during the Blancan, the origin of patchily distributed grasslands, and the evolution of hypsodonty may have triggered the rapid diversification that eventually produced the five extant genera of the Geomyini.

Climate stability across the Eocene-Oligocene transition, southern Argentina

Research Article| July 01, 2004 Climate stability across the Eocene-Oligocene transition, southern Argentina Matthew J. Kohn; Matthew J. Kohn 1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA Search for other works by this author on: GSW Google Scholar Jennifer A. Josef; Jennifer A. Josef 1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA Search for other works by this author on: GSW Google Scholar Richard Madden; Richard Madden 2Department of Biological Anthropology and Anatomy, Duke University, Durham, North Carolina 27710, USA Search for other works by this author on: GSW Google Scholar Richard Kay; Richard Kay 2Department of Biological Anthropology and Anatomy, Duke University, Durham, North Carolina 27710, USA Search for other works by this author on: GSW Google Scholar Guiomar Vucetich; Guiomar Vucetich 3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina Search for other works by this author on: GSW Google Scholar Alfredo A. Carlini Alfredo A. Carlini 3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Matthew J. Kohn 1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA Jennifer A. Josef 1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA Richard Madden 2Department of Biological Anthropology and Anatomy, Duke University, Durham, North Carolina 27710, USA Richard Kay 2Department of Biological Anthropology and Anatomy, Duke University, Durham, North Carolina 27710, USA Guiomar Vucetich 3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina Alfredo A. Carlini 3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina Publisher: Geological Society of America Received: 05 Jan 2004 Revision Received: 24 Mar 2004 Accepted: 25 Mar 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (7): 621–624. https://doi.org/10.1130/G20442.1 Article history Received: 05 Jan 2004 Revision Received: 24 Mar 2004 Accepted: 25 Mar 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Matthew J. Kohn, Jennifer A. Josef, Richard Madden, Richard Kay, Guiomar Vucetich, Alfredo A. Carlini; Climate stability across the Eocene-Oligocene transition, southern Argentina. Geology 2004;; 32 (7): 621–624. doi: https://doi.org/10.1130/G20442.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Fossil mammal teeth from mid-latitude southern Argentina (∼46°S) that closely bracket the Eocene-Oligocene transition show no resolvable change in oxygen isotope compositions. In combination with paleofloral observations and geographic considerations, this finding implies not only that climate was essentially constant, despite interpretations elsewhere for major mid- and high-latitude cooling, but also that evolution of hypsodonty did not coincide with climate change during the Eocene-Oligocene transition. One possible explanation for Eocene-Oligocene transition climatic stability is that southern high-latitude cooling increased latitudinal temperature gradients and strengthened ocean circulation gyres, including the southward-flowing Brazil Current in the western South Atlantic. Regionally increased heat transport in the western Atlantic offset global cooling, producing a nearly constant temperature in southern South America. A more radical interpretation, supported by some marine data, is that the paradigm of major global cooling at the Eocene-Oligocene transition is largely false, in that mean sea-surface temperatures changed very little. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The origin and spread of grass-dominated ecosystems in the late Tertiary of North America: preliminary results concerning the evolution of hypsodonty

Sediment samples were collected in northwestern Nebraska from the following lithologic units: (1) the upper Oligocene Monroe Creek Formation, the lower Miocene Harrison Formation and ‘upper Harrison’ beds of the Arikaree Group; and (2) the lower Miocene Runningwater Formation and the Dawes Clay Member (Box Butte Formation) of the Ogallala Group. The samples were processed using heavy liquid extraction and analyzed for siliceous plant microfossils (phytoliths). All samples yielded well preserved and diverse assemblages dominated by grass phytoliths, but included phytoliths produced by woody and herbaceous dicotyledons, palms, and sedges. The abundance of woody dicotyledons and palms decreased up section. The grass assemblages consisted mainly of Festucoid (C 3) phytolith morphotypes. An index assessing the amount of tree cover ( d:p, the ratio of dicotyledon phytoliths to grass phytoliths) was employed to interpret the data. According to this analysis, there was open C 3-dominated grassland in the study area between 25 and 17 Ma, at least 7 Ma before supposed adaptations to grasslands in ungulates (hypsodonty) originate.