Question

Explain the role of climate change in the origins and evolution of early primates, the earliest anthropoids, and the surviving apes of the late Miocene. Think in terms of warming and cooling and affects on available food resources.  

Name and briefly describe the three hypotheses of primate origins.

Answer 1

Changes which occurred in the global, as well as regional environment, had a very profound effect on the evolutionary history of primates.

The earliest known fossils of the primates (Plesiadapiformes or archaic primates) is known to be found in the Paleocene of North America, Europe and Asia. The average global temperature in the Paleocene period was about 8∘C warmer than the average global temperature today, with ice-free poles. This condition continued for about 15 million years, and this is when the global temperature went up to its highest, i.e., about 12∘C above today's average global temperature, which is known as the Early Eocene Climatic Optimum. The warming of the environment could possibly be the reason for the appearance of the Plesiadapiforms in these regions.

In the Paleocene-Eocene boundary, about 55-56 million years ago, the PETM/Paleocene-Eocene Thermal Maximum was seen. This was a sort, but dramatic increase in the global temperature. This could be attributed to the large amount of greenhouse gases, possibly the release of methane that had been stored as clathrates on the ocean floor. It disrupted the ecosystem, leading to the extinction of benthic foraminifera (single-celled organisms similar to amoeboid organisms in cell structure) in the oceans and terrestrial mammals. This was the first time that the euprimates, both adapiforms (early strepsirhines) and omomyoids (early haplorrhines) appeared nearly simultaneously in North America, Europe, and Asia. This is also the time when several major primate groups like anthropoids, adapiforms, tarsiers, and omomyiforms are seen. These primates share features that are not seen in the Plesiadapiforms. These groups had features that showed they had an increasing dependence on vision rather than smell or tactile senses. Many of these early primates were smaller than the any primates living today.

However, in the middle to late Eocene, North America saw the building of mountains and drying, which proved to be disastrous for the primates, where they were seen to be almost extinct by late Eocene.

The euprimates continued to flourish while the Plesiadapiforms became rarer as the temperatures started dropping towards the cooler side. However, even in the late Eocene, the global temperatures were still warmer than the average global temperature today.

When we talk about the Eocene-Oligocene boundary, the drop in temperature plays a significant role in the growth of the large continental ice-sheets in Antarctica and alteration in the ocean circulation. The end of the Eocene period saw an extinction of mammals, including primates, which is known as the  Grande Coupure/Eocene-Oligocene extinction period in Europe and Mongolian remodelling in Asia.

The end of the Oligocene period had seen the return of the global temperatures to its Eocene levels and remained warm up until the middle of the Miocene period. This led to a marked expansion of the primates in both the Old and New World. A diversification of the catarrhine primates in the African and Arabian peninsula was seen.

The first half of Miocene was warm, and in an event termed the Mid-Miocene Climatic Optimum, the global temperatures peaked. Here, both apes and pliopithecoids spread into Europe, which had been devoid of primates since the Grande Coupure.

The second half of the Miocene period saw the declining of the global temperatures. By the late Miocene, the pliopithecoids and apes became rarer and rarer in Eurasia with increasing extinction of forests.

The Miocene-Pliocene boundary saw a decrease in the temperature but an increase in the variation of the climatic conditions. The Messinian Salinity Crisis is where the Mediterranean Sea became closed and isolated from the Atlantic Ocean occurred just before this period. The cooling and drying effects which continued to occur in the Pliocene period had profound effects for the habitats of the Mediterranean region. The only hominids to survive the Miocene are all located in Africa or the more tropical southeastern portions of Asia.

The availability and exploitation of C4 foods like tropical grasses and animals that eat these plants led to certain implications in the diet of early human ancestors and other early hominins. The shifting of diet trends from C3 plants like hard fruits and nuts to C4 foods shows that the early hominins moved into drier habitats. At least one of the species of genus Homo became an efficient runner and hunter and was able to exploit the open grasslands of Africa.

The extinction of the number of primates during the Holocene period may be contributed to the large rise in sea level about 10,000 years ago. The primates on these small islands were susceptible to extinction. Also, human activity in Madagascar and Caribbean leading to destruction of forestland led to the extinction of the primates during the Holocene period.