Post by warsaw on Dec 18, 2011 4:25:35 GMT -9
The evolution of the brain in Canidae (Mammalia: Carnivora)
George A. Lyras
Palaeoneurology is the study of the nervous system of fossil animals. Palaeoneurology
is as old as palaeontology itself: Cuvier (1804) realised that casts of the brain
cavity of fossil vertebrates could be informative concerning the external anatomy of
the brain (Edinger, 1962). To prove this, he peeled away the dorsal surface of the neurocranium
of a fossil mammal to reveal a natural stone cast of the brain, created by the
2 Lyras. The evolution of the brain in Canidae (Mammalia: Carnivora). Scripta Geol., 139 (2009)
sedimentary rock that had fi lled the neurocranium aft er the animal’s death.
Subsequently, the brain has received considerable att ention from vertebrate palaeontologists
(for a review of the literature, see Edinger, 1977), but it was Edinger who
reformed the scope of palaeoneurology from the mere description of incidental fi ndings
of fossil brains into the study of the evolutionary history of the brain, thus founding
modern palaeoneurology (Buchholtz & Seyfarth, 1999). Edinger understood that by
applying methods of comparative neuro-anatomy to endocranial casts of animal groups,
whose evolutionary history is well established through independent phylogenetic and
stratigraphic work, one could reveal the actual evolutionary transformations of brain.
Palaeoneurological data are the only direct evidence available about the brains of
the past. Using only living species to reveal the evolutionary history of the brain has its
limitations, due to the danger of so-called Scalae Naturae (pseudo-evolutionary sequences)
in which a living species is regarded as representative of the ancestral stage of another
species. In such a way, misleading phylogenetic schemes can be constructed, such
as for carnivores (England, 1973; see Preuss, 2000, for a further discussion of this problem).
To avoid the eff ects of parallelisms, the contribution of the fossil record is crucial
(Radinsky, 1971; Lyras & Van der Geer, 2003). While comparative neurology tries to unravel
evolution by comparing the brains of living animals only, palaeoneurology does
so by observations on fossil brains. As Edinger (1962) noted, “paleoneurology introduced
to comparative neurology a fourth dimension: time.”
This palaeoneurological approach is an important contribution to comparative neuro-
anatomy, because it helps us to resolve several misconceptions concerning brain evolution
(Edinger, 1962; Dermitzakis, 2002). These misconceptions result from the way in
which the problem of brain evolution was originally approached. In early theories,
which were based mainly on the study of living species and a few fossil specimens, it
was argued that brains evolve in a linear manner from fi sh to man (for a critique, see
Hodos & Campbell, 1969), and that brain size is correlated with intelligence and, therefore,
with species success (for a critique, see Radinsky, 1982). These theories infl uenced,
and in many cases still infl uence, neuro-anatomical studies (Striedter, 1998). Additionally,
despite the great diversity of living animals, neuro-anatomy is founded on studies
of very few model organisms, mainly rats, cats, pigeons and macaque monkeys, an approach
that further restricts our view of brain evolution (Preuss, 2000).
The present study is a contribution to the study of the evolution of the brain of the
Canidae. This family includes wolves, jackals, foxes and many other less familiar species.
In total there are 35 living species of wild canids (Wozencraft , 2005), that exhibit a
wide range of morphological and ecological diversity, from the insectivorous Otocyon
megalotis to the almost exclusively meat-eating Lycaon pictus. Fossil canids are even more
spectacular. They belong to the oldest carnivore group still extant today and their past
morphological diversity was even greater than currently, as they were not only fi lling
ecological niches that today are occupied by canids, but also those occupied by hyenas,
raccoons (Wang et al., 2004) and, to a certain extent, cats (Van Valkenburgh, 1991).
read more:
dpc.uba.uva.nl/cgi/t/text/get-pdf?idno=m09139a01;c=scripta
George A. Lyras
Palaeoneurology is the study of the nervous system of fossil animals. Palaeoneurology
is as old as palaeontology itself: Cuvier (1804) realised that casts of the brain
cavity of fossil vertebrates could be informative concerning the external anatomy of
the brain (Edinger, 1962). To prove this, he peeled away the dorsal surface of the neurocranium
of a fossil mammal to reveal a natural stone cast of the brain, created by the
2 Lyras. The evolution of the brain in Canidae (Mammalia: Carnivora). Scripta Geol., 139 (2009)
sedimentary rock that had fi lled the neurocranium aft er the animal’s death.
Subsequently, the brain has received considerable att ention from vertebrate palaeontologists
(for a review of the literature, see Edinger, 1977), but it was Edinger who
reformed the scope of palaeoneurology from the mere description of incidental fi ndings
of fossil brains into the study of the evolutionary history of the brain, thus founding
modern palaeoneurology (Buchholtz & Seyfarth, 1999). Edinger understood that by
applying methods of comparative neuro-anatomy to endocranial casts of animal groups,
whose evolutionary history is well established through independent phylogenetic and
stratigraphic work, one could reveal the actual evolutionary transformations of brain.
Palaeoneurological data are the only direct evidence available about the brains of
the past. Using only living species to reveal the evolutionary history of the brain has its
limitations, due to the danger of so-called Scalae Naturae (pseudo-evolutionary sequences)
in which a living species is regarded as representative of the ancestral stage of another
species. In such a way, misleading phylogenetic schemes can be constructed, such
as for carnivores (England, 1973; see Preuss, 2000, for a further discussion of this problem).
To avoid the eff ects of parallelisms, the contribution of the fossil record is crucial
(Radinsky, 1971; Lyras & Van der Geer, 2003). While comparative neurology tries to unravel
evolution by comparing the brains of living animals only, palaeoneurology does
so by observations on fossil brains. As Edinger (1962) noted, “paleoneurology introduced
to comparative neurology a fourth dimension: time.”
This palaeoneurological approach is an important contribution to comparative neuro-
anatomy, because it helps us to resolve several misconceptions concerning brain evolution
(Edinger, 1962; Dermitzakis, 2002). These misconceptions result from the way in
which the problem of brain evolution was originally approached. In early theories,
which were based mainly on the study of living species and a few fossil specimens, it
was argued that brains evolve in a linear manner from fi sh to man (for a critique, see
Hodos & Campbell, 1969), and that brain size is correlated with intelligence and, therefore,
with species success (for a critique, see Radinsky, 1982). These theories infl uenced,
and in many cases still infl uence, neuro-anatomical studies (Striedter, 1998). Additionally,
despite the great diversity of living animals, neuro-anatomy is founded on studies
of very few model organisms, mainly rats, cats, pigeons and macaque monkeys, an approach
that further restricts our view of brain evolution (Preuss, 2000).
The present study is a contribution to the study of the evolution of the brain of the
Canidae. This family includes wolves, jackals, foxes and many other less familiar species.
In total there are 35 living species of wild canids (Wozencraft , 2005), that exhibit a
wide range of morphological and ecological diversity, from the insectivorous Otocyon
megalotis to the almost exclusively meat-eating Lycaon pictus. Fossil canids are even more
spectacular. They belong to the oldest carnivore group still extant today and their past
morphological diversity was even greater than currently, as they were not only fi lling
ecological niches that today are occupied by canids, but also those occupied by hyenas,
raccoons (Wang et al., 2004) and, to a certain extent, cats (Van Valkenburgh, 1991).
read more:
dpc.uba.uva.nl/cgi/t/text/get-pdf?idno=m09139a01;c=scripta