Lecture 5 Mammal Zoogeography. Triconodontidae. Multiturberculata. Spalacotheriidae. Paurodontidae. Dryolestidae. Amphilestidae. Docodontidae. Amphitheridae. Shuotherium. Sinoconodontidae. Morganucodontidae. Haramiyoidea. Phylogeny of Mesozoic Mammals. 0 Yrs. CENOZOIC. MONOTREMES.
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HaramiyoideaPhylogeny of Mesozoic Mammals
(from Carroll 1988, pp. 415)
Zoogeography is the study of the geographical distributions of animals
Zoogeography seeks answers to questions like:
Why are there marsupials in Australia and South America?
Why are members of the camel family (Camelidae) found in north Africa and South America?
Why are there primates from Japan to Africa, as well as South but not North America?
all species have a limited distribution on a world scale. Some mammals are very well dispersed - eg. Humans, their stock, and commensuals like the house mouse (Mus domesticus), whereas others have a very limited distribution.
Endemism (occurring nowhere else), or being endemic - a taxon is restricted to a limited geographical area.
Endemism depends on the scale you are referring to - it might be a small area like an island, or an entire continent.
Endemism can refer to a single species, genus, family, order, or other grouping.
when groups of mammals become geographically isolated, they usually diverge - meaning they adapt (over a long time span) to the specific climatological, geological and ecological situation they are faced with.
However - sometimes convergence occurs - convergence occurs when distantly related lineages inhabiting regions with similar climatological, geological and ecological situations evolve similar morphologies, life history patterns or niche characteristics.
Numerous examples of convergence exist among mammals
Giant anteater (Myrmecophaga)
Mammals on Islands
160Principles of Ecological Zoogeography
Species diversity of mammals (and most other life forms) increases along a gradient from the poles to the Equator
Plate Tectonics - theory that the earth’s crust, including the continents and ocean floors, is made up of a series of plates, as plates collide volcanoes occur, and may result in oceanic islands, mountain ranges etc.
Continental Drift - movement over geological time of the earths large land masses as a result of plate tectonics
Marsupials evolved in North America (diverse fossil evidence from southern Canada & western USA)
Dispersed south to South America, Antactica and Australia, and East to Europe & north Africa
Gondwana split from Pangaea, and marsupials underwent extensive radiation in relative isolation
Marsupials in North America and Europe went extinct, possibly due to radiation and expansion of the Eutherians
Antartica drifted south - massive extinction. Australia drifted east, enormous radiation
Passive Dispersal - movements in which the dispersing organism plays no active role in the movement Eg. rafting, or being transported by humans
Active Dispersal - involves an accumulation of ecological dispersal events in which individuals move by terrestrial locomotion or flight
active long-term species dispersal movements, also called faunal interchanges, occur via several routes.
Corridor Route - minimal resistance to the passage of animals (eg. present interconnection of Asia and Europe)
Filter Route - allows only certain species to pass through - eg. Beringia. Only mammals adapted to the cold climate could successfully cross between the continents.
Sweepstake Route - most restrictive pathway. Involves movement of animals by swimming, flying, rafting or other means . Unlikely to be crossed by large numbers of a given type of animal, but occasional one will make it. Eg. New Guinea to Australia to New Zealand
During the Pleistocene several cool, dry glacial periods, interspersed with warmer and wetter interglacial periods have had a substantial effect of mammal distributions
There have been 4 glacial periods in the last 600,000 years, with the most recent one ending approx. 12,000 years ago. We are currently in an interglacial (warm, wet) period
During each glacial period, ice sheets expanded and many species were displaced, some driven to extinction. During glacial periods, however, the sea level was lower and some land bridges formed (eg. Bering land bridge)
During the interglacial periods, episodes of recolonisation and resettlement occurred, and sea level rose, isolating some species
Beringia was a land mass which was largely ice-free during the last glacial period (90,000 - 10,000 years ago) due to its arid climate
It acted as a refugium for several mammals, as well as a land bridge for animals to cross between Eurasia and North America
(from Pringle 1999)
Land bridge was submerged again approx. 11,000 years ago (to the present)
Steppe bison (Bison priscus)
American lion (Panthera leo atrox)
short-faced bears (Artodus)
mastodon (Mammut americanum)
woolly mammoth (Mammuthus primigenius)
Scimitar cat (Hometherium serum)
camels (several genera)
first humans in North America
Jefferson’s ground sloth
(from Pringle 1999)
470,000 years ago
Synaptomys (bog lemming)
Microtus pennsylvanicus (meadow vole)
M. montanus (montane vole)
Cervalces (extinct stag moose)
Oreamnos (mountain goat)
Ovibos (musk ox)
Bootherium (extinct bovid)
1.2 million years ago
Clethrionomys (red-backed vole)
Synaptomys (bog lemming)
Smilodon (saber-tooth cat)
70,000 years ago
Clethrionomys rutilis (red-backed vole)
Microtus oeconomus (tundra vole)
170,000 years ago
Dicrostonyx (collared lemming)
Microtus (vole)Beringia Immigrants
Stopped by Filter
Stopped by Filter
Cannot Recross Filter
Camelidae - Bactrian camels (Camelus bactrianus) and dromedaries (C. dromedarius) occur in north Africa, and llama (Lama glama), alpaca (L. pacos), guanaco (L. guanicoe) and vicuna (Vicugna vicugna) occur in South America
Camelids arose and diversified in North America, with some forms eventually dispersing across the Bering Land Bridge (Beringia) to Eurasia and Africa, and the Panamanian Land Bridge to South America
North American camelids went extinct towards the end of the last glaciation