|Fig.1. This canid evolved from mongoose-like ancestors (Credit: Tambako via Flickr, 2014)|
Around 23 million years ago, Earth’s climate cooled considerably, causing a shift in North America’s interior ecosystems. Forests turned into the drier, more open grasslands that remain today. As climate change affected the landscape, animals and plants adjusted to their new surroundings. The fossil record indicates that herbivorous mammals evolved longer legs and teeth more adapted to the increasingly ubiquitous C4 grasses. Although a similar adjustment had not been previously seen in predators, an international team of scientists discovered a link between modern canine hunting habits and the ancient shift in climate.
Evolution Hinges on ElbowsZ. Jack Tseng, a researcher at the American Museum of Natural History in New York, worked with scientists around the world to comb through extensive fossil collections of ancient dog relatives. They examined elbow bones and teeth from canids, or members from the Canidae family, which includes domestic dogs, wolves, foxes, and other dog-like mammals. The bones, from 32 species of canids dating from 40 million to 2 million years ago, showed specific structural changes that would have affected how they hunted. Then modern-day canids and closely related species were compared to the fossils to analyze similarity to extant animals.
Around 40 million years ago, the dog's ancestors looked more like mongooses and were well adapted to a wooded habitat. This was seen in the flexible forelimbs that operated more to grab and wrestle prey. As grasslands started to replace woodlands and herbivores shifted to adapt, the canids’ elbow-joints also changed to a structure specialized for endurance running. In their study published in Nature Communications, Tseng et al. said the newer elbow-joint morphologies were indicative of pounce-pursuit behavior that we see today in animals like foxes or wolves. Additionally, teeth evolved to be more durable over time, possibly due to the need for more scavenging in a grassy ecosystem.
The range in fossil dates of 38 million years encompassed the worldwide cooling and allowed scientists to have an understanding of morphologies before and after the change. Museum specimens from the American Museum of Natural History, Harvard’s Museum of Comparative Zoology, and the Natural History Museum in London recorded the disappearance of “ambushers” more suited to forest floors and the emergence of “pursuit and endurance” canids in cooler and drier times.
Climate Change in the RecordsAnimal fossils are not the only collections that show past climate change. Sediment cores and ice cores yield information on precipitation and temperature variation from millions of years ago. To identify upheavals in ecosystems, however, researchers must be more specific. Core samples can also contain remnants from long-dead plants, either in the form of fossil pollen grains or as silica microfossils, known as phytoliths. These tiny plant remains vary in size and shape and allow scientists to identify the species and their abundance from a particular time or place. Combined with animal remains, such fossils can show a shift in ecosystem makeup over time.
This empirical evidence found in the fossil record for behavioral adaptation is a vital part of addressing the future of biodiversity. By the year 2050, shifts in temperature and precipitation are expected to threaten one quarter or more of all species on land with extinction. Only an understanding of how past species have successfully evolved to deal with climate change will prepare for this future.
Figueirido, B., Martin-Serra, A., Tseng, Z. J., & Janis, C.M. (2015, August 18). Habitat changes and changing predatory habits in North American fossil canids. Nature Communications, vol. 6. doi: 10.1038/ncomms8976
Picture Climate: How Pollen Tells Us About Climate. (n.d.). National Oceanic and Atmospheric Administration: News and Updates. Retrieved from https://www.ncdc.noaa.gov/news/picture-climate-what%E2%80%99s-smaller-pinhead-can-tell-us-about-climate