User:MaksRock/sandbox

= Fossorial =

Definition
“The term fossorial is [...] applied to those species that possess unusual anatomical or physiological adaptations towards burrowing, and that spend a considerable amount of their lives underground.”

Prehistoric Fossorial Evidence
The physical adaption of fossoriality was always widespread among many prehistoric phyla and taxa, such as bacteria and early eukaryotes, but in the phylum Mammalia this trait has only occurred recently, considering the geological timescale of the earth. The oldest examples of such mammals is the Thrinaxodon liorhinus, found in the Karoo of South Africa and is tested to be 251 million years old. Evidence shows, that this adaption occurred due to dramatic mass extinctions in the Permian period.

Todays (Quarterinary) Physical Adaptions
There are seven major external modifications, as described by H.W. Shimer in Adaptations to Aquatic, Arboreal, Fossorial and Cursorial Habits in Mammals, that are shared in all mammalian burrowing species:

Fusiform, as an adaption to the dense subsurface environment below earth. Lesser developed or missing eyesight, considering subsurface darkness. Small or missing external ears, to reduce natural occurring friction during burrowing. Short and stout limbs, since swiftness or speed of movement is less important than the strength to dig. Broad and stout forelimbs (Manus), including long claws, designed to loosen the burrowing material for the hind feet to disperse in the back. Short or missing tail, which also has little to no locomotive or burrowing use to most fossorial Mammals. This is also argued by Jorge Cubo, as he states that the skull is the main tool during excavation, but that the most active parts are the forelimbs for digging and that the hindlimbs are used for stability.

Other important physical features include a subsurface adjusted skeleton: a triangular shaped skull, a prenasal ossicle, chisel shaped teeth, more or less fused and short lumbar vertebrae, well developed sternum and strong forelimb and weaker hind limb bones. Due to the lack of light, one the most important features of fossorial animals are the development of sensory physical traits that allow them to communicate and navigate in the dark subsurface environment. Considering that sound travels slower in air, the use of seismic waves is more advantageous in these environments. Several different uses are well documented and are as follows: as an example, for rodents the cape mole rat or Georychus capensis, uses drumming behaviour for conspecific signaling. The namib destert golden mole or Eremitalpa granti namibensis, can detect termite colonies and similar prey underground due to the development of “a hypertrophied malleus, an adaptation favouring detection of low-frequency signals.” The most likely explanation of the actual transmission of these seismic inputs, captured by the auditory system, is the use of a bone conduction. “Bone conduction refers to the many routes by which vibrations applied to the skull might be transmitted to the inner ear.” The life underground in these subsurface environments also have direct link to the animal’s metabolism and energetics. The weight of the individual specimen here also has direct implications. Animals weighing more than 80g have comparably lower basal rates and animals weighing lower than 60g have comparably high basal rates, considering species that spend only part of their time burrowing. The average fossorial animal has a basal rate between 60% and 90%. Further observations conclude that larger burrowing animals, such as hedgehogs or armadillos have lower thermal conductance’s than smaller animals, most likely to reduce heat storage in their burrows.

Physiological Modifications
One interesting physiological trait, common amongst many fossorial and semi-fossorial mammals that live in temperate zones with partially frozen grounds is hibernation. This is due to the seasonal lack of soft succulent herbage and other sources of nutrition; thus, those species are driven to spend the cold and frozen periods underground. A general conclusion made by W.H. Shimer is that“...it is natural that the majority of fossorial forms should have sprung from primitive and defenceless rodent, insectivores and edentates andthat the carnivores [...] the ungulates [...] and the primates [...] have as a rule failed either to find protection from foes or abundant food by turning into the barred road of fossorial modification.”

Geological and Ecological implications
One important impact on the environment caused by fossorial animals is bioturbation, as defined by Marshall Wilkinson:“ In concert with surface geomorphic processes, bioturbation alters fundamental properties of soil, including particle-size distribution, porosity, the content of carbon and other nutrients, and creep flux rate.” It is measured that small fossorials, such as ants, termites, earthworms and such like displace a massive amount of soil: the total global rates displaced by these animals are equivalent to the total global rates of tectonic uplift. The presence of burrowing animals has also a direct impact on the soils composition, structure and growing vegetation. Impacts of the animals can range from feeding, harvesting, caching and soil disturbances, but can differ considering the large diversity of, especially herbivorous, fossorial species. The net effect usually composes of an alteration of the composition of plant species and increased plant diversity, which can arise issues with standing crops, as the homogeneity of the crops are effected. Burrowing also impacts the nitrogen circle in the effected soil. Mound and bare soils have considerably higher amounts of NH4 and NO3 as well as the nitrification potential and the microbial NO3 consumption than in vegetated soils. The primary mechanism for this occurrences caused by the removal of the covering grassland.