525-million-year-old fossil defies textbook explanation for brain evolution
Fossils of a tiny sea creature that died more than half a billion years ago may compel a science textbook rewrite of how brains evolved.
Fossils of a tiny sea creature that died more than half a billion years ago may compel a science textbook rewrite of how brains evolved.
Paleontology & Fossils
Nov 25, 2022
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The explosion of animal life on Earth around 520 million years ago was the result of a combination of interlinked factors rather than a single underlying cause, according to a new study.
Earth Sciences
Sep 19, 2013
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(Phys.org) —A team of European researchers working at École polytechnique fédérale de Lausanne (EPFL) in Switzerland has created an artificial compound eye that is comparable to those in insects such as the fruit fly. ...
An extraordinary find allowing scientists to see through the head of the 'fuxianhuiid' arthropod has revealed one of the earliest evolutionary examples of limbs used for feeding, along with the oldest nervous system to stretch ...
Archaeology
Feb 27, 2013
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(Phys.org)—A team of Canadian researchers has found that one species of barnacles mate by ejecting sperm into seawater while another catches it – a process known as spermcasting. Prior to this research, scientists had ...
Complex brains evolved much earlier than previously thought, as evidenced by a 520-million year old fossilized arthropod with remarkably well-preserved brain structures. Representing the earliest specimen to show a brain, ...
Archaeology
Oct 10, 2012
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Insects and spiders often receive little attention from people, except when we're swatting them away. However, as arthropods—creatures distinguished by a hard exoskeleton and jointed legs— they play an essential role ...
Ecology
Jan 13, 2024
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A team from the University of Leicester, Yunnan Key Laboratory for Paleobiology and the Institute of Paleontology at Yunnan University, Chengjiang Fossil Museum, and the Natural History Museum in London, have redescribed ...
Evolution
Aug 29, 2023
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An international team of researchers led by Prof. Ma Keping from the Institute of Botany of the Chinese Academy of Sciences (IBCAS) has shown that forests with higher tree species richness tend to have greater arthropod diversity.
Ecology
Apr 27, 2023
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Millipede legs grow in an unexpected way, according to new research. Previously, it was thought that when a millipede molts (sheds its exoskeleton), it grows new segments on the end of its body without legs. Then after the ...
Plants & Animals
Apr 19, 2023
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An arthropod is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda (from Greek ἄρθρον árthron, "joint", and ποδός podós "foot", which together mean "jointed feet"), and include the insects, arachnids, crustaceans, and others. Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of α-chitin; the cuticles of crustaceans are also biomineralized with calcium carbonate. The rigid cuticle inhibits growth, so arthropods replace it periodically by molting. The arthropod body plan consists of repeated segments, each with a pair of appendages. It is so versatile that they have been compared to Swiss Army knives, and it has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living animal species, and are one of only two animal groups that are very successful in dry environments – the other being the amniotes. They range in size from microscopic plankton up to forms a few meters long.
Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs and through which their blood circulates; they have open circulatory systems. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.
Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae (bristles) that project through their cuticles.
Arthropods' methods of reproduction and development are diverse; all terrestrial species use internal fertilization, but this is often by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Aquatic species use either internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by scorpions.
The versatility of the arthropod modular body plan has made it difficult for zoologists and paleontologists to classify them and work out their evolutionary ancestry, which dates back to the Cambrian period. From the late 1950s to late 1970s, it was thought that arthropods were polyphyletic, that is, there was no single arthropod ancestor. Now they are generally regarded as monophyletic. Historically, the closest evolutionary relatives of arthropods were considered to be annelid worms, as both groups have segmented bodies. This hypothesis is by now largely rejected, with annelids and molluscs forming the superphylum Lophotrochozoa. Many analyses support a placement of arthropods with cycloneuralians (or their constituent clades) in a superphylum Ecdysozoa. Overall however, the basal relationships of Metazoa are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated.
Arthropods contribute to the human food supply both directly as food, and more importantly as pollinators of crops. Some specific species are known to spread severe disease to humans, livestock, and crops.
This text uses material from Wikipedia, licensed under CC BY-SA