New Theory on the Origin of Primates
ScienceDaily (Jan. 20, 2010) — A new model for primate origins is presented in Zoologica Scripta, published by the Norwegian Academy of Science and Letters and The Royal Swedish Academy of Sciences. The paper argues that the distributions of the major primate groups are correlated with Mesozoic tectonic features and that their respective ranges are congruent with each evolving locally from a widespread ancestor on the supercontinent of Pangea about 185 million years ago.
New biogeographic reconstruction of primates, flying lemurs, and tree shrews about 185 millions of years in the early Jurassic. (Credit: Image courtesy of Buffalo Museum of Science)
Michael Heads, a Research Associate of the Buffalo Museum of Science, arrived at these conclusions by incorporating, for the first time, spatial patterns of primate diversity and distribution as historical evidence for primate evolution. Models had previously been limited to interpretations of the fossil record and molecular clocks.
"According to prevailing theories, primates are supposed to have originated in a geographically small area (center of origin) from where they dispersed to other regions and continents" said Heads, who also noted that widespread misrepresentation of fossil molecular clocks estimates as maximum or actual dates of origin has led to a popular theory that primates somehow crossed the globe and even rafted across oceans to reach America and Madagascar.
In this new approach to molecular phylogenetics, vicariance, and plate tectonics, Heads shows that the distribution ranges of primates and their nearest relatives, the tree shrews and the flying lemurs, conforms to a pattern that would be expected from their having evolved from a widespread ancestor. This ancestor could have evolved into the extinct Plesiadapiformesin north America and Eurasia, the primates in central-South America, Africa, India and south East Asia, and the tree shrews and flying lemurs in South East Asia.
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Michael Heads
Correspondence to Michael Heads, Buffalo Museum of Science, 1020 Humboldt Parkway, Buffalo, NY 14211-1293, USA. E-mail:michael.heads@yahoo.com
ABSTRACT
The ages of the oldest fossils suggest an origin for primates in the Paleocene (∼56 Ma). Fossil-calibrated molecular clock dates give Cretaceous dates (∼80–116 Ma). Both these estimates are minimum dates although they are often 'transmogrified' and treated as maximum or absolute dates. Oldest fossils can underestimate ages by tens of millions of years and instead of calibrating the time-course of evolution with a scanty fossil record, the geographical boundaries of the main molecular clades of primates are calibrated here with radiometrically dated tectonic events. This indicates that primates originated when a globally widespread ancestor (early Archonta) differentiated into a northern group (Plesiadapiformes, extinct), a southern group (Primates), and two south-east Asian groups (Dermoptera and Scandentia). The division occurred with the breakup of Pangea in the Early Jurassic and the opening of the central Atlantic (∼185 Ma). Within primates, the strepsirrhines and haplorhines diverged with volcanism and buckling on the Lebombo Monocline, a volcanic rifted margin in south-east Africa (Early Jurassic, ∼180 Ma). Within strepsirrhines, lorises and galagos (Africa and Asia) and lemurs (Madagascar) diverged with the formation of the Mozambique Channel (Middle Jurassic, ∼160 Ma). Within haplorhines, Old World monkeys and New World monkeys diverged with the opening of the Atlantic (Early Cretaceous, ∼130 Ma). The main aspects of primate distribution are interpreted as the result of plate tectonics, phylogeny and vicariance, with some subsequent range expansion leading to secondary overlap. Long-distance, trans-oceanic dispersal events are not necessary. The primate ancestral complex was already widespread globally when sea-floor spreading, strike-slip rifting and orogeny fractured and deformed distributions through the Jurassic and Cretaceous, leading to the origin of the modern clades. The model suggests that the topology of the phylogenetic tree reflects a sequence of differentiation in a widespread ancestor rather than a series of dispersal events.
Submitted: 4 September 2009 Accepted: 7 September 2009
DIGITAL OBJECT IDENTIFIER (DOI)10.1111/j.1463-6409.2009.00411.x About DOI
The ages of the oldest fossils suggest an origin for primates in the Paleocene (∼56 Ma). Fossil-calibrated molecular clock dates give Cretaceous dates (∼80–116 Ma). Both these estimates are minimum dates although they are often 'transmogrified' and treated as maximum or absolute dates. Oldest fossils can underestimate ages by tens of millions of years and instead of calibrating the time-course of evolution with a scanty fossil record, the geographical boundaries of the main molecular clades of primates are calibrated here with radiometrically dated tectonic events. This indicates that primates originated when a globally widespread ancestor (early Archonta) differentiated into a northern group (Plesiadapiformes, extinct), a southern group (Primates), and two south-east Asian groups (Dermoptera and Scandentia). The division occurred with the breakup of Pangea in the Early Jurassic and the opening of the central Atlantic (∼185 Ma). Within primates, the strepsirrhines and haplorhines diverged with volcanism and buckling on the Lebombo Monocline, a volcanic rifted margin in south-east Africa (Early Jurassic, ∼180 Ma). Within strepsirrhines, lorises and galagos (Africa and Asia) and lemurs (Madagascar) diverged with the formation of the Mozambique Channel (Middle Jurassic, ∼160 Ma). Within haplorhines, Old World monkeys and New World monkeys diverged with the opening of the Atlantic (Early Cretaceous, ∼130 Ma). The main aspects of primate distribution are interpreted as the result of plate tectonics, phylogeny and vicariance, with some subsequent range expansion leading to secondary overlap. Long-distance, trans-oceanic dispersal events are not necessary. The primate ancestral complex was already widespread globally when sea-floor spreading, strike-slip rifting and orogeny fractured and deformed distributions through the Jurassic and Cretaceous, leading to the origin of the modern clades. The model suggests that the topology of the phylogenetic tree reflects a sequence of differentiation in a widespread ancestor rather than a series of dispersal events.
Submitted: 4 September 2009 Accepted: 7 September 2009
DIGITAL OBJECT IDENTIFIER (DOI)10.1111/j.1463-6409.2009.00411.x About DOI
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