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M. Cunniffe Stanford IISME Fellow, 2013
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The Trilobite: An extinct Arthopod CheliceratesCrustaceansMyriapodsHexapodsTrilobites
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Trilobites were marine organisms that lived on Earth for over 270 million years and are considered known to be one of the most successful early animal groups Trilobites are a member of the Arthropods. Of the five types of Arthropods, only the trilobites are extinct. The four extant Arthropod groups include: Chelicerates (spiders, scorpions) Crustaceans (lobsters, crabs, barnacles, shrimp) Myriapods (millipedes, centipedes) Hexapods (insects) Trilobites are a highly diverse and geographically dispersed species with new species of fossil specimens discovered every year What is a Trilobite?
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Trilobite Fossil Distribution
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Trilobites first appeared in the Early Cambrian. The height of their diversity occurred in the early Paleozoic. Adaptive radiations occurred in the Ordovician, Silurian, and Devonian periods. After the Devonian mass extinction, only two families in one single order of trilobites remained. At the Permassian-Triassic mass extinction event, no trilobites were left. Evolutionary History of Trilobites
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Patterns of Marine Animal Diversification Raup & Sepkoski, Science 1982
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Trilobite Diversity Treatise of Invertebrate Paleontology (1997) figure p. 269 modified, S. Gonn website www. trilobites.info Extent of the Trilobite Orders over Geological Time
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Ecospace coding for trilobites and other groups is based upon three ecological areas of interest: Tiering: where in the ocean did they live? Motility: did they move and if so, how freely were they able to move? Feeding Mechanism: how did they get their nutrition? Ecospace Coding
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1. Pelagic (out in the water column) 2. Erect (benthic, extending into water mass) 3. surficial (benthic, not extending upward) 4. Semi-infaunal (partly infaunal, partly exposed) 5. Living in the top ~5 cm of sediment 6. Living more than ~5 cm deep in sediment Tiering
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1. Freely, fast moving (regularly moving, unencumbered) 2. Freely, slow (as above but with strong bond to substrate) 3. Facultative, unattached (moving only when necessary, free-lying) 4. Facultative, attached (moving only when necessary, attached) 5. Non-motile, unattached (not capable of movement, free- lying) 6. Non-motile, attached (not capable of movement, attached) Motility
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1. Suspension (capturing food particles from the water) 2. Surface deposit (capturing loose particles from a substrate) 3. Mining (recovering buried food) 4. Grazing (scraping or nibbling food from a substrate) 5. Predatory (capturing prey capable of resistance) 6. Other (photo- or chemo- symbiosis, parasites) Feeding Mechanism
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Ecospace Coding Sea Star (echinoderm) Tiering: 4 Movement: 2 Nutrition: 5
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Ecospace CubeTemplate
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Ecospace Cubes
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Ecospace vs. Niche Niche The range of conditions and resources within which individuals of a species can persist Is specific to each individual species Competition and predation restrict the distribution of a species across its fundamental niche resulting in a species’ realized niche Ecospace A more general way of looking at species specialization and interaction within a community Unlike niches, more than one type of organism can inhabit the same ecospace
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For higher diversity in a community, there must be less competition between species How? Greater resources available Reduced resource demand (general predation) Intensified predation of a species subset (camoflauge in moth population) Greater inter- and/or intraspecial ecological specialization of organisms Morphology (species diversity) can be used as an indicator of niche diversity (Structure Function) More on Niches
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Trilobite Fossils Trilobite easily fossilized due to their easily preserved exoskeletons Soft parts such as eyes can also be found due to the nature of the materials that surround the fossils Trace fossils can be either resting or sediment furrows: Hard fossils indicate protection, hunting, resting Furrows in sediment suggest movement Trilobite fossils can be used as index (aka guide, zone, or indicator) fossils to determine the age of surrounding rocks Geologists and oil companies in particular use this process known as biostratigraphy
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The Paleozoic Era consists of 6 time periods: Cambrian ~541-485 mya Ordovician ~485-443 mya Silurian Devonian Carboniferous Permian ~298-252 mya The Paleozoic Era
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The Geologic Clock
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Geologic time periods
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Anatomy of a Trilobite Trilobites are arthropods and have segmented bodies, An exoskeleton Jointed appendages In addition, trilobites have complex and diverse eyes and a variety of mouthparts known as hypostomes
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Trilobite Feeding Trilobites used their hypostomes to prepare food for digestion. Conterminant hypostomes are firmly attached to the body and allowed for the digestion of a different type of prey than natant hypostomes, which did not have extra reinforcement for crushing moving prey
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Extension: Body Size Data Body size in organisms is a biologically important data set The study of allometry relates body size to other biological significant factors such as: Body shape Anatomy Physiology Metabolism Behavior All trilobite body size data is included on the original spreadsheet (see Attachment #7). By sharing the spreadsheet with students electronically, students can reorganize data to create graphs for a variety of data groupings: body size vs. ecospace designation ecospace designation throughout various geologic time periods
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