Econstudentlog

Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe (3)

Here’s a previous post in the series. In this post I’ll pick up roughly where I left off in my last post, around the time of the ‘Grande Coupure‘ roughly 34 million years ago.

“The extinction of the arboreal primates and the reduction or extinction of several browsing groups […] are strong evidence for the retreat of the forests during the early Oligocene and their replacement by open woodlands or even drier biotopes. […] Among the most distinctive species to enter Europe after the “Grande Coupure” were the first true rhinoceroses [which] achieved a high diversity and were going to characterize the mammalian faunas of Europe for millions of years, until the extinction of the last woolly rhinos during the late Pleistocene. […] the evolution of this group produced the largest terrestrial mammals of any time. The giant Paraceratherium […] was 6 m tall at the shoulders and had a 1.5-m-long skull […]. The males of this animal weighed around 15 tons, while the females were somewhat smaller, about 10 tons.” [Wikipedia has a featured article about these things here].

“One of the most significant features of the early Oligocene small-mammal communities was the first entry of lagomorphs into Europe. The lagomorphs — that is, the order of mammals that includes today’s hares and rabbits — originated very early on the Asian continent and from there colonized North America. The presence of the Turgai Strait prevented this group from entering Europe during the Eocene. […] the most characteristic immigrants during the early Oligocene were the cricetids of the genus Atavocricetodon. The cricetids are today represented in Europe by hamsters, reduced to three or four species […] These cricetids are typical inhabitants of the cold steppes of eastern Europe and Central Asia, and their limited representation in today’s European ecosystems does not reflect their importance in the history of the Cenozoic mammalian faunas of Eurasia. After its first entry following the “Grande Coupure,” this group experienced extraordinary success, diversifying into several genera and species. Even more significantly, the cricetids gave rise to the rodent groups that were going to be dominant during the Pliocene and Pleistocene — that is, the murids (the family of mice and rats) and arvicolids (the family of voles). […] In addition, new carnivore families, like the nimravids, appeared […]. The nimravids were once regarded as true felids (the family that includes today’s big and small cats) because of their similar dental and cranial adaptations. […] one of the more distinctive attributes of the nimravids was their long, laterally flattened upper canines, which were similar to those of the Miocene and Pliocene saber-toothed cats […]. However, most of these features have proved to be the result of a similar adaptation to hypercarnivorism, and the nimravids are now placed in a separate family of early carnivores whose evolution paralleled that of the large saber-toothed felids.” [Actually some of the nimravids were in some sense ‘even more sabertoothed’ than the (‘true’) saber-toothed cats which came later: “Although [the nimravid] Eusmilus bidentatus was no larger than a modern lynx, the adaptations for gape seen on its skull and mandible are more advanced than in any of the felid sabertooths of the European Pliocene and Pleistocene.”]

“About 30 million years ago, a new glacial phase began, and for 4 million years Antarctica was subjected to multiple glaciation episodes. The global sea level experienced the largest lowering in the whole Cenozoic, dropping by about 150 m […]. A possible explanation for this new glacial event lies in the final opening of the Drake Passage between Antarctica and South America, which led to the completion of a fully circumpolar circulation and impeded any heat exchange between Antarctic waters and the warmer equatorial waters. A second, perhaps complementary cause for this glacial pulse is probably related to the final opening of the seaway between Greenland and Norway. The cold Arctic waters, largely isolated since the Mesozoic, spread at this time into the North Atlantic. The main effect of this cooling was a new extension of the dry landscapes on the European and western Asian lands. For instance, we know from pollen evidence that a desert vegetation was dominant in the Levant during the late Oligocene and earliest Miocene […] This glacial event led to the extinction of several forms that had persisted from the Eocene”.

“Among the carnivores, the late Oligocene saw the decline and local extinction of the large nimravids [Key word: local. They came back to Europe later during the early Miocene, and “the nimravids maintained a remarkable stability throughout the Miocene, probably in relation to a low speciation rate”]. In contrast, the group of archaic feloids that had arisen during the early Oligocene […] continued its evolution into the late Oligocene and diversified into a number of genera […] The other group of large carnivores that spread during the late Oligocene were the “bear-dog” amphicyonids, which from that time on became quite diverse, with many different ecological adaptations. […] The late Oligocene saw, in addition to the bearlike amphicyonids, the spread of the first true ursids […]. The members of this genus did not have the massive body dimensions of today’s bears but were medium-size omnivores […] Another group of carnivores that spread successfully during the late Oligocene were the mustelids, the family that includes today’s martens, badgers, skunks, and otters. […] In contrast to these successes, the creodonts of the genus Hyaenodon, which had survived all periods of crisis since the Eocene, declined during the late Oligocene. The last Hyaenodon in Europe was recorded at the end of the Oligocene […], and did not survive into the Miocene. This was the end in Europe of a long-lived group of successful carnivorans that had filled the large-predator guild for millions of years. However, as with other Oligocene groups, […] the hyaenodonts persisted in Africa and, from there, made a short incursion into Europe during the early Miocene”.

“After a gradual warming during the late Oligocene, global temperatures reached a climatic optimum during the early Miocene […] Shallow seas covered several nearshore areas in Europe […] as a consequence of a general sea-level rise. A broad connection was established between the Indian Ocean and both the Mediterranean and Paratethys Seas […] Widespread warm-water faunas including tropical fishes and nautiloids have been found, indicating conditions similar to those of the present-day Guinea Gulf, with mean surface-water temperatures around 25 to 27°C. Important reef formations bounded most of the shallow-water Mediterranean basins. […] Reef-building corals that today inhabit the Great Barrier Reef within a temperature range of 19 to 28°C became well established on North Island, New Zealand […] The early Miocene climate was warm and humid, indicating tropical conditions […]. Rich, extensive woodlands with varied kinds of plants developed in different parts of southern Europe […] The climatic optimum of the early Miocene also led to a maximum development of mangroves. These subtropical floras extended as far north as eastern Siberia and Kamchatka”.

“Despite the climatic stability of the early Miocene, an important tectonic event disrupted the evolution of the Eurasian faunas during this epoch. About 19 million years ago, the graben system along the Red Sea Fault, active in the south since the late Oligocene, opened further […] Consequently, the Arabian plate rotated counterclockwise and collided with the Anatolian plate. The marine gateway from the Mediterranean toward the Indo-Pacific closed, and a continental migration bridge (known as the Gomphothere Bridge) between Eurasia and Africa came into existence. This event had enormous consequences for the further evolution of the terrestrial faunas of Eurasia and Africa. Since the late Eocene, Africa had evolved in isolation, developing its own autochthonous fauna. Part of this fauna consisted of a number of endemic Oligocene survivors, such as anthracotheres, hyaenodonts, and primates, for which Africa had acted as a refuge […] The first evidence of an African–Eurasian exchange was the presence of the anthracothere Brachyodus in a number of early Miocene sites in Europe […] a second dispersal event from Africa, that of the gomphothere and deinothere proboscideans, had much more lasting effects. […] Today we can easily identify any proboscidean by its long proboscis and tusks. However, the primitive proboscideans from the African Eocene had a completely different appearance and are hardly recognizable as the ancestors of today’s elephants. Instead, they were hippolike semiamphibious ungulates with massive, elongated bodies supported by rather short legs. […] The first proboscideans entering Europe were the so-called gomphotheres […] which dispersed worldwide during the early Miocene from Africa to Europe, Asia, and North America […]. Gomphotherium was the size of an Indian elephant, about 2.5 m high at the withers. Its skull and dentition, however, were different from those of modern elephants. Gomphotherium’s skull was long […] and displayed not two but four tusks, one pair in the upper jaw and the other pair at the end of the lower jaw. […] Shortly after the entry of Gomphotherium and Zygolophodon [a second group of mastodons], a third proboscidean group, the deinotheres, successfully settled in Eurasia. Unlike the previous genera, the deinotheres were not elephantoids but represented a different, now totally extinct kind of proboscidean.”

“The dispersal of not only the African proboscideans but also many eastern immigrants contributed to a significant increase in the diversity of the impoverished early Miocene terrestrial biotas. The entry of this set of immigrants probably led to the extinction of a number of late Oligocene and early Miocene survivors, such as tapirids, anthracotherids, and primitive suids [pigs] and moschoids. In addition to the events that affected the Middle East area, sea-level fluctuations enabled short-lived mammal exchanges across the Bering Strait between Eurasia and North America, permitting the arrival of the browsing horse Anchitherium in Eurasia […] Widely used for biostragraphic purposes, the dispersal of Anchitherium was the first of a number of similar isolated events undergone by North American equids that entered Eurasia and rapidly spread on this continental area.”

“A new marine transgression, known as the Langhian Transgression, characterized the beginning of the middle Miocene, affecting the circum-Mediterranean area. Consequently, the seaway to the Indo-Pacific reopened for a short time, restoring the circum-equatorial warm-water circulation. […] tropical conditions became established as far north as Poland in marine coastal and open-sea waters. After the optimal conditions of the early Miocene, the middle Miocene was a period of global oceanic reorganization, representing a major change in the climatic evolution of the Cenozoic. Before this process began, high-latitude paleoclimatic conditions were generally warm although oscillating, but they rapidly cooled thereafter, leading to an abrupt high-latitude cooling event at about 14.5 million years ago […] Increased production of cold, deep Antarctic waters caused the extinction of several oceanic benthic foraminifers that had persisted from the late Oligocene–early Miocene and promoted a significant evolutionary turnover of the oceanic assemblages from about 16 to 14 million years ago […] This middle Miocene cooling was associated with a major growth of the Eastern Antarctic Ice Sheets (EAIS) […] Middle Miocene polar cooling and east Antarctic ice growth had severe effects on middle- to low-latitude terrestrial environments. There was a climatic trend to cooler winters and decreased summer rainfall. Seasonal, summer-drought-adapted schlerophyllous vegetation progressively evolved and spread geographically during the Miocene, replacing the laurophyllous evergreen forests that were adapted to moist, subtropical and tropical conditions with temperate winters and abundant summer rainfalls […] These effects were clearly seen in a wide area to the south of the Paratethys Sea, extending from eastern Europe to western Asia. According to the ideas of the American paleontologist Ray Bernor, this region, known as the Greek-Iranian (or sub-Paratethyan) Province, acted as a woodland environmental “hub” for a corridor of open habitats that extended from northwestern Africa eastward across Arabia into Afghanistan, north into the eastern Mediterranean area, and northeast into northern China. The Greek-Iranian Province records the first evidence of open woodlands in which a number of large, progressive open-country mammals—such as hyaenids, thick-enameled hominoids, bovids, and giraffids — diversified and dispersed into eastern Africa and southwestern Asia […] the peculiar biotope developed in the Greek-Iranian Province acted as the background from which the African savannas evolved during the Pliocene and Pleistocene.”

“The most outstanding effect of the Middle Miocene Event is seen among the herbivorous community, which showed a trend toward developing larger body sizes, more-hypsodont teeth, and more-elongated distal limb segments […]. Increasing body size in herbivores is related to a higher ingestion of fibrous and low-quality vegetation. Browsers and grazers have to be large because they need long stomachs and intestines to process a large quantity of low-energy food (this is why they have to eat almost continuously). Because of the mechanism of rumination, ruminants are the only herbivores that can escape this rule and subsist at small sizes. Increasing hypsodonty and high-crowned teeth are directly related to the ingestion of more-abrasive vegetation […] Finally, the elongation of the distal limb segments is related to increasing cursoriality. The origin of cursoriality can be linked to the expansion of the home range in open, low-productive habitats. […] At the taxonomic level, this habitat change in the low latitudes involved the rapid adaptive radiation of woodland ruminants (bovids and giraffids). […] Gazelles dispersed into Europe at this time from their possible Afro-Arabian origins […] Not only gazelles but also the giraffids experienced a wide adaptive radiation into Africa after their dispersal from Asia. […] Among the suids [pigs], the listriodontines evolved in a peculiar way in northern Africa, leading to giant forms such as Kubanochoerus, with a weight of about 500 kg, which in some species may have reached 800 kg.”

March 8, 2015 - Posted by | biology, books, climate, Geology, Paleontology, Zoology

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