Los paleontólogos han dicho desde hace mucho tiempo que los caballos son un clásico ejemplo de evolución mediante selección natural. Sin embargo, la teoría era difícil de probar ya que la mayoría de las especies equinas se han extinguido
Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias y Gina M. Semprebon han utilizado fósiles para comprobar dicha teoría. Han examinado los dientes de 6.000 caballos fósiles representativos de 222 poblaciones diferentes de 70 especies extintas de caballos. Los fósiles que abarcan un periodo de 55 millones de años, indican un intervalo de tiempo "crítico" entre la evolución de los dientes del caballo y los cambios en la dieta debidos a cambios climáticos.
Para ello han desarrollado una metodología, que utiliza la agudeza y relieve del desgaste de los ápices de los dientes como medida de la abrasión, para reconstruir las dietas de especies extinguidas. El proceso fue empleado para investigar las pautas de desgaste de los molares de miles de dientes fósiles. Después, estos datos fueron analizados junto con registros de los cambios climáticos de Norteamérica que podrían haber obligado a cambiar la dieta de los animales, de frutas de la selva y hojas a las dietas más abrasivas de las sabanas.
Según Mihlbachler, "el intervalo de tiempo en la evolución de los dientes de caballo en comparación con los cambios dieteticos es crítico" y añade "hemos encontrado que los cambios evolutivos en la anatomia del diente van retrasados a los cambios dietéticos en un millón de años o más". Es decir, los cambios dentales de los caballos siguen sus cambios de dieta, un hecho consistente con la evolución por adaptación, que ha conducido finalmente a los caballos tal como los conocemos hoy día.
Paleontologists have long held horses as classic examples of evolution through natural selection. However, the theory has been difficult to test because the majority of horse species are extinct.
Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias and Gina M. Semprebon have used fossil records to verify the above theory. They examined the teeth of 6,500 fossil horses representing 222 different populations of 70 extinct horse species. The records, spanning the past 55 million years, indicate a "critical" lag time between the evolution of horse teeth and dietary changes resulting from climate change.
For it they have developed a methodology that uses the sharpness and relief of the worn cusp apices of teeth as a measure of dietary abrasion, to reconstruct the diets of extinct species by measuring food-related wear and tear on fossil teeth. The process was used to investigate wear patterns on the molars of thousands of fossil horses. Later these data were analyzed alongside records of North American climate changes that would have shifted the animals' diets from rainforest fruits and woody, leafy vegetation to the more abrasive diets found in grasslands.
"Lag time in the evolution of horse teeth in comparison to dietary changes is critical," Mihlbachler explained. "We found that evolutionary changes in tooth anatomy lag behind the dietary changes by a million years or more" : dental changes in horses follow their dietary changes, a fact that is consistent with evolution due to adaptation and led finally to the horses as we know them today
Tomado de/Taken from Science Daily
Resumen de la publicación científica/Abstract of the paper
Dietary Change and Evolution of Horses in North America
Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias and Gina M. Semprebon
Science 4 March 2011
Vol. 331 no. 6021 pp. 1178-1181
DOI: 10.1126/science.1196166
Abstract: The evolution of high-crowned molars among horses (Family Equidae) is thought to be an adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion. We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global cooling and associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse paleopopulations had highly variable amounts of dietary abrasion, suggesting that selective pressures for crown height may have been weak much of the time. However, instances of higher abrasion were observed in some paleopopulations, suggesting intervals of stronger selection for the evolution of dentitions, including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.
