Fish fossil unfolds clues to vertebrate brain evolution
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Vertebrate paleontology
Living fossil
Brain tissue
Fossil Record
Abstract Treeshrews are widely considered a “living model” of an ancestral primate and have long been called “living fossils”. Actual fossils of treeshrews, however, are extremely rare. We report a new fossil species of Ptilocercus treeshrew recovered from the early Oligocene (~34 Ma) of China that represents the oldest definitive fossil record of the crown group of treeshrews and nearly doubles the temporal length of their fossil record. The fossil species is strikingly similar to the living Ptilocercus lowii , a species generally recognized as the most plesiomorphic extant treeshrew. It demonstrates that Ptilocercus treeshrews have undergone little evolutionary change in their morphology since the early Oligocene. Morphological comparisons and phylogenetic analysis support the long-standing idea that Ptilocercus treeshrews are morphologically conservative and have probably retained many characters present in the common stock that gave rise to archontans, which include primates, flying lemurs, plesiadapiforms and treeshrews. This discovery provides an exceptional example of slow morphological evolution in a mammalian group over a period of 34 million years. The persistent and stable tropical environment in Southeast Asia through the Cenozoic likely played a critical role in the survival of such a morphologically conservative lineage.
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Lineage (genetic)
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The fossil record of vertebrates provides abundant evidence for both the fact and the theory of evolution (Carroll, 1997; Prothero and Schoch, 1994). In support of the fact that evolution has indeed occurred, the vertebrate fossil record clearly documents evolutionary change along lineages , that is, along direct lines of ancestors and descendents. The fossil record also shows step-wise evolutionary changes resulting in the emergence of new kinds of vertebrates from pre-existing kinds—for example, the origin of mammals from the “mammal-like” reptiles. In support of the theory that natural selection, in particular, has been largely responsible for evolutionary change, the fossil record shows that the numerous “transitional” forms that lived in the past—far from being nonviable “monsters”—were functionally integrated organisms that were well adapted to their ecological roles. Finally, the vertebrate fossil record preserves certain large-scale phenomena, such as radiations and trends, which show that evolutionary forces can act over very large time scales.
Fossil Record
Mammal
Vertebrate paleontology
Evolutionary Theory
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Neo-darwinian and population genetics theory assumes that the necessary and sufficient set of conditions for all genetic, therefore evolutionary, change has been identified. Punctuationalists have assumed the opposite and cite the fossil record as evidence for change too rapid to be explained in neo-darwinian theory. Data is given here to provide estimates of the rate of evolution in hominid fossils, in living populations, and of that rate which would qualify as punctuational in the hominid fossil record. Evolution in living populations is orders of magnitude greater than that found in the fossil record and far greater than necessary to create apparently instantaneous saltations in the fossil record. It is suggested that such saltations may not represent more rapid rates of evolution but, rather, the persistence of evolutionary change in a given direction for a longer than normal period.
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Evolutionary Theory
Persistence (discontinuity)
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Fossil Record
Taphonomy
Vertebrate paleontology
Geologic record
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Fossil Record
Multicellular organism
Molecular evolution
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Fossil Record
Marine invertebrates
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Several mutually incompatible theories exist about how and why endothermy evolved in mammals and birds. Some take the primary function to have been thermoregulation, selected for one adaptive purpose or another. Others take the high aerobic metabolic rate to have been primary. None of these theories is incontrovertibly supported by evidence, either from the fossil record of the synapsid amniotes or from observations and experiments on modern organisms. Furthermore, all are underpinned by the tacit assumption that endothermy must have evolved in a stepwise pattern, with an initial adaptive function followed only later by the addition of further functions. It is argued that this assumption is unrealistic and that the evolution of endothermy can be explained by the correlated progression model. Each structure and function associated with endothermy evolved a small increment at a time, in loose linkage with all the others evolving similarly. The result is that the sequence of organisms maintained functional integration throughout, and no one of the functions of endothermy was ever paramount over the others. The correlated progression model is tested by the nature of the integration between the parts as seen in living mammals, by computer simulations of the evolution of complex, multifunctional, multifactorial biological systems, and by reference to the synapsid fossil record, which is fully compatible with the model. There are several potentially important implications to be drawn from this example concerning the study of the evolution of complex structure and the new higher taxa that manifest it.
Fossil Record
Ectotherm
Exaptation
Molecular evolution
Tetrapod (structure)
Adaptive Evolution
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The vastness of the vertebrate fossil record and its literature makes any effort to review it in entirety a difficult task; ‘a review’ is understood to be a work that discusses the evolution and diversity of a group, drawing in knowledge on taxonomy, morphology, ecology and distribution, with representative illustrations. Existing reviews of the entire vertebrate record have mostly been designed with teaching in mind and have focused on groups, trends and processes deemed of interest to students. As goes more specific reviews, some groups (Mesozoic dinosaurs in particular) are frequently reviewed; others are afflicted by their association with idiosyncratic authors, others have only been given partial treatment, and others are woefully under-represented. Biographical information on vertebrate palaeontologists themselves is scattered. An additional issue is that several excellent volumes (notably the Handbook volumes) are prohibitively expensive, rare or otherwise hard to obtain. Cenozoic fishes – in particular actinopterygians, the largest and richest vertebrate radiation – remain essentially untouched and it might not be obvious to non-specialists just how rich the fish record is. Indeed, an enormous number of lineages scarcely known to experts on modern fishes are present in the fossil record. The result of this skewed coverage is that both popular and technical perceptio n of the vertebrate fossil record is biased. Not only are there a huge number of groups that fail to attract students, a large number of research questions relevant to these groups remain un- or under-investigated because so few researchers are aware of their existence.
Fossil Record
Vertebrate paleontology
Taxonomic rank
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The fossil record of vertebrates provides abundant evidence for both the fact and the theory of evolution (Carroll, 1997; Prothero and Schoch, 1994). In support of the fact that evolution has indeed occurred, the vertebrate fossil record clearly documents evolutionary change along lineages , that is, along direct lines of ancestors and descendents. The fossil record also shows step-wise evolutionary changes resulting in the emergence of new kinds of vertebrates from pre-existing kinds, for example, the origin of mammals from the “mammal-like” reptiles. In support of the theory that natural selection, in particular, has been largely responsible for evolutionary change, the fossil record shows that the numerous “transitional” forms that lived in the past — far from being nonviable “monsters” — were functionally integrated organisms that were well adapted to their ecological roles. Finally, the vertebrate fossil record preserves certain large-scale phenomena, such as radiations and trends, which show that evolutionary forces can act over very large time scales.
Fossil Record
Mammal
Vertebrate paleontology
Evolutionary Theory
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Fossil Record
Evolution of mammals
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Citations (20)