Trilobites were arthropods with soft bodies and many legs that were positioned under a heavily calcified, segmented shell. They first appeared in the Early Cambrian Period (544 million years ago) and thrived through the Middle and Late Cambrian times before their extinction in the Ordovician period (495 million years ago). In their 49 million year existence, they diversified quickly and produced a fossil record that geologists refer to often.
Arthropods are a phylum of hard-shelled creatures with multiple body segments and jointed legs. Trilobites are a class of this phylum that includes eight orders: Agnostida, Asaphida, Corynexochida, Lichida, Phacopida, Proetida, Ptychopariida, and Redlichiida. The trilobites were very diverse, especially in size, ranging from less than 1 millimeter to 70 centimeters. That's almost two feet long! Although they ranged in size, they all shared a standard three-part body: The cephalon (head), thorax, and pygidium (tailpiece). The name "Trilobite" refers to the lobes of the soft body. The axial lobe is centered between the left pleural lobe and the right pleural lobe. The horseshoe crab of today is perhaps the best example to illustrate the physical appearance of a trilobite.
Trilobites occupied only marine environments. Their niches within the marine environment varied from intertidal and nearshore to deep continental slopes. The majority of trilobites were benthic, or bottom dwellers. They crawled on the sea floor and through reefs. They were able to dig into bottom sediments for food or cover. They were adapted to either carnivorous or herbivorous lifestyles depending upon the species. The herbivores fed on algae, some browsed on corals, sponges, and bryozoans. Some were filter feeders ...
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...the late Permian period. Their 49 million year existence is theorized to be halted by a predator known as Anomalocaris. The half-meter long Anomalocaris was an active swimming predator (proto-anthropoda) that was physically capable of swallowing a trilobite whole but may also have bitten out ragged chunks of their prey. Trilobite fossils have been found with such wounds, supporting the extinction by predation theory.
The Trilobites were an interesting as well as important creature. Their large numbers, varied species, and world-wide occupation have made them an integral piece of the geologic puzzle of time.
Sources:
Stanley, Steven M. Earth System History. New York: W.H. Freeman Co., 1999
http://aloha.net/~smgon/trilobite.htm
http://enchantedlearning.com
Fox, R. 2001. Invertebrate Anatomy OnLine: Artemia Franciscana. Lander University. http://webs.lander.edu/rsfox/invertebrates/artemia.html, retrieved February 13, 2011.
T. californicus is found from Alaska to Baja in small, shallow tidepools and tidal flats in the upper spray zone where they cannot avoid the full effect of visible and ultraviolet (UV) radiation. Individuals assemble in areas of lower radiation at midday, yet have no preference to the intensity of light at dawn and dusk (Hartline and Macmillan 1995). These tiny arthropods inhabit all types of marine sediments from sand to fine mud and ooze. Along with plankton, T. californicus eats microscopic algae, protists, bacteria, diatoms, algae and microbes (McGroarty 1958). When the concentrations of the species in their habitats are high, T. californicus will turn to cannibalism for a food source. The nautilus eye present in the species is rich with fatty acids and provides a good food source for the animal.
There is no doubt that arthropods are an extremely successful group of animals, with an estimated 5-10 million species worldwide[1], and this can be attributed to having an exoskeleton; it provides many benefits, such as protection from parasitism and other threats. However, one major disadvantage of having an exoskeleton is the limitations that an inelastic cuticle can place on growth. The exoskeleton provides protection, but when freshly moulted the animal is soft and vulnerable, as well as having limited mobility and use of appendages; many seek shelter before moulting[2]. There are similarities and differences between the moult cycles of all the arthropods, however only crustaceans and insects will be discussed here.
The outer layer of a reef consists of living animals, or polyps, of coral. Single-celled algae called zooxanthellae live within the coral polyps, and a skeleton containing filamentous green algae surrounds them. The photosynthetic zooxanthellae and green algae transfer food energy directly to the coral polyps, while acquiring scarce nutrients from the coral. The numerous micro habitats of coral reefs and the high biological productivity support a great diversity of other life.
...ories of why dinosaurs went extinct abound, and as there is no theory yet to be truly confirmed as the “right one”, my theory of dinosaur cannibalism is also purely anecdotal. The discovery of the cannibalistic Majungatholus atopus in Madagascar is an important scientific find because it confirms a long-standing theory of cannibalism among certain carnivorous dinosaurs. Behavioral patterns of extinct animals are difficult to establish; however, these bones give authentication to previous unfounded beliefs about the ancient feeding practices of some dinosaurs.
...however, with further research, it came to light that this was not just a “unique species” but an entire phyla that was new to science (Adler 2013). Why a new phyla? “What made the creatures seem new is they have no living descendants. They represent entire lineages, major branches on the tree of life, left behind by evolution…” (Adler 2013). While other lineages did survive-actually a collateral predecessor of the vertebrates, and that means us! (Adler 2013).
Daphnia, commonly known as water fleas, are tiny crustaceans which live in water. The diameter of adult female bodies is approximately 3-5 mm. The upper skeleton is transparent, making the internal organs visible. This allows the heart rate of the Daphnia to be calculated by observing them under a microscope.
could either survive through adaptation or die off due to an inability to adapt rapidly enough. All different types of animals, carnivorous and herbivorous mammals, birds, and reptiles, lived during the Pleistocene epoch and thanks to preservations such as the La Brea tar pits, we are able to observe and study the life forms of millions of years ago.
The concept of transitional species is an important and complex notion in evolutionary biology. To begin with, there is no such thing as transitional species since all living things were always evolving in the past, not stopping at one stage or another, and they will continue to evolve in the future. In terms of evolutionary biology, we use the concept of transitional species as a way to dim ambiguity. Much like the use of the Linnean taxonomic system of species, we come up with concepts like transitional species to organize and classify species in order to understand their evolutionary roots and how those species changed through life’s history to become what they are today. “In the same way that the concept of species can be provisionally meaningful to describe organisms at a single point in time, the concept of transitional species can be provisionally meaningful to describe organisms over a length of time, usually quite a long time, such as hundreds of thousands or millions of years” (111). Though it can be difficult to distinguish what can be considered an ancestral species from another, the fossil record can show us how species change through time as they develop ways to adapt to stresses found in their environments. “In the modern sense, organisms or fossils that show intermediate stages between ancestral and that of the current state are referred to as transitional species” (222). The concept of transitional species is, in essence, fairly straight forward. This paper will outline the concept of transitional (or sometimes termed intermediate) species and the latter’s role in evolutionary biology, as well as go in depth about several common transitional species: Tiktaalik, an animal at the cusp between life in the water and ...
...nder, C., Tsai, C., Wu, P., Speer, B. R., Rieboldt, S., & Smith, D. (1998/1999/2002). The permian period. Informally published manuscript, Biology 1B project for Section 115, University of California Museum of Paleontology, CA, Retrieved from http://www.ucmp.berkely.edu/permian/permian.php
.... (2011). A New Arthropod Jugatacaris agilis n. gen. n. sp. from the Early Cambrian Chengjiang Biota, South China. Journal of Paleonotology, 85(3), 567-586. doi:10.1666/09-173.1
To begin with, the horseshoe crab, one the world’s oldest living creatures, are quite active. This fascinating crab has ten small walking legs under a strong, sturdy exoskeleton, a long spine in the abdomen, and a long pointy tail in the back used to push itself back up after being flipped on its back (Swinton, 99). Furthermore, horseshoe crabs got their name in an interesting way. The crab’s arc shaped exoskeleton, or shell, was compared to a horse’s shoe (Horseshoe Crab: Saint Louis Zoo). As mentioned before horseshoe crabs aren’t actually crabs. Though it may look like one, they are actually part of a family called Limuli. Some reasons it could have been misconceived as a crab are because its shell is comparable to a crab’s, the legs look a bit similar, and they are found on the Atlantic coast like other crabs. Also we can find horseshoe crab right here in North America along the hot, sandy Atlantic
Diplopoda is a class, belonging to the subphylum of Arthropoda Myriapoda, consisting of about 10 000 species of animals which have two pairs of legs for each body segment and are often known as Millipedes. Hence the name, they do not have one thousand legs.