Body size variation in Quaternary mammals

We are investigating the causes of variation in mammal body size during the Quaternary period by comparing ice-age mammal species from the past 750,000 years in Britain.

The Quaternary is the most recent geological period, and many of the mammal species targeted in our study are alive today. Body mass is a fundamental parameter for understanding the adaptations, ecology and life-history of mammals, so our results will contribute to understanding the effects of current and future climate change on mammal species.

Our research will test current hypotheses to explain body size variation in ice-age mammals, including:

• Temperature: Large animals are better adapted to cold periods as they conserve heat more effectively. Small animals are more able to lose heat during warm periods.
• Vegetation: The quality and quantity of vegetation determines herbivore body size, and therefore carnivore size.
• Competition: Body size is affected by the presence or absence of related, competitor species.

Methods

The mammal fossils we are studying:

• represent around 20 mammal species
• include carnivores and herbivores
• derive from 50 sites across southern Britain
• date from 750,000 to 10,000 years ago

Our previous work on mammal fossils has produced valuable resources for the study of body size variation, in particular a large database of mammal bone measurements from key Pleistocene sites in Britain.

Palaeotemperature and vegetation

To estimate palaeoenvironmental conditions, we use:

• data from associated invertebrate flora and fauna, such as beetles or ostracods
• floral and faunal lists, using models based on modern distributions
• associated pollen or plant macrofossil data, from which vegetation spectra are obtained and simple metrics such as degree of wooded cover can be derived

Determining body size variation

We are converting bone measurement data to body mass, using regression equations based on living species. A mean body mass for each species is obtained for each fossil site or horizon.

Mammal body masses are compared to palaeoenvironmental indices using a multivariate statistical approach. This is enabling us to:

• resolve the effects of temperature and vegetation on the body sizes of different mammal species
• understand any effects of the mammals on each other