To be a Hippo

A Question of Hippos

During the Pleistocene (around 11,700-2.6 million years ago) multiple hippopotamus species were present in Europe. Today, as we know, their occurrence is restricted to sub-Saharan Africa (Schreve, 2009). The reason we are discussing the hippopotamus is because during the Last Interglacial the modern African hippo came as far North as Britain, and that's quite something... We will examine their presence and movement in Europe during previous interglacials, including what facilitated their spread, and why they aren’t here now. We will also discuss another hippopotamus species which is now extinct, but with emphasis on the surviving African hippo.

Today we will look at the two main forms of Hippo during the Quaternary:

       1. Hippopotamus antiquus (European Hippopotamus)

       2. Hippopotamus amphibious (alive in Africa today) 

Hippopotamus antiquus (extinct)

Hippopotamus amphibious (extant)

A British Context

Britain contains some fantastic records of Quaternary animals, including well-documented sites of Hippopotamus appearance found in British lake and river sediments (Schreve, 2009). During the Pleistocene, the British Isles were joined to the mainland (van der Geer et al, 2014). In this time Britain experienced  a single occurrence of the species Hippopotamus amphibious during the Last Interglacial (Marine Isotope Stage 5e 'MIS5e'), which represents the time period between around 128-116,000 years before present. During this interglacial mean summer temperature in the South was around 4^oC warmer than contemporary values (Schreve, 2001, Schreve 2009). Today this species possesses a low-latitude distribution surviving only on the continent of Africa. In contrast, Hippopotamus antiquus appeared between round 2-1.6 million years ago in Europe (Madurell-Malapeira, 2012). It was widespread and common until its extinction in the latter part of the Pleistocene. Hippopotamus antiquus has been recorded during multiple interglacials across most of Europe, and was a common feature during warm phases (Owen-Smith, 1992). 

Climatic importance & aids to dispersal?

Hippopotamus amphibious is of particular interest. It was only present in Britain during the Last Interglacial. This suggests that it must have undergone extensive spread throughout Europe in order to reach the British Isles as its presumed most northern point. Hippopotamus amphibious dispersal during MIS5e into Britain was likely allowed following the abrupt rise in temperatures during the onset of the Last Interglacial (Stuart, 1975). Though,  Hippopotamus amphibious from a French site is found to occur during both Marine Isotope Stages 11 and 7, but not during substage 5e. We all know that the hippopotamus is a warm adapted genus, for that reason it is questionable as to why this particular species was not around during another warm period at this site. So maybe climate was not the only factor allowing hippopotamus to spread into Britain? Animals present in Britain apparently show greater similarities with those in Germany during this timeframe, rather than the French fauna (Schreve et al, 2007; Schreve, 2009). This could mean that, yes, climate has allowed hippopotamus species to spread this far North, but it could be that the River Rhine (Germany) and the River Thames (England) facilitated the spread of the hippopotamus into Britain at this time (Schreve, 2009). The importance of this is to understand that a lot of the time no one factor can explain the spread of a species. In this case, it may be a combination of factors which allowed the first and only survival of Hippopotamus amphibious in Britain.

Extinction & Range Reduction

Hippopotamus presence in Europe is thought to have lasted into the early part of MIS3, which began around 60,000 years ago. Here, remaining populations of the genus survived in southern Italy (Pandolfi and Petronio, 2015). Although we know that Hippopotamus amphibious survives today in suitable African habitats, the story of Hippopotamus antiquus is less obvious. Though, climatic and environmental changes are considered likely the cause of their disappearance. Still, varieties of dwarf hippo (due to isolation) which possibly derived from both of these species occurred on the Mediterranean Islands, and may have survived up until as late as 8,000 years ago (Owen-Smith, 1987).

 In Summary

The importance of this post is to understand that multiple factors can lead to the spread of animals, and that the reason for their disappearance is not always well documented. In the case of hippopotamus species, the story is not entirely clear.

Soon we will be discussing some of the smaller animals of the Quaternary.