Introduction To The Trilobites Morphology Macroevolution-Books Pdf

Introduction to the Trilobites Morphology Macroevolution
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internal anatomy was more conserved In any event in this lab we will provide extensive. information about their external shells as well as their internal anatomy Further here we will. focus not only on the general type and appearance of trilobites We will also pay special. attention to their significance for our understanding of evolution and the nature of ecology in the. distant past while providing both exercises and numerous illustrations. Figure 1 A Asaphus kowalewskii by Smokeybjb Own work CC BY SA 3 0 http creativecommons org. licenses by sa 3 0 via Wikimedia Commons B Dalmanities limulurus University of Kansas Museum on exhibit. C Isotelus iowensis University of Kansas Museum Invertebrate Paleontology KUMIP 294608 D Phacops milleri. University Of Kansas Museum on exhibit E Olenellus sp University of Kansas Museum Invertebrate. Paleontology KUMIP 369418 F Comura sp by Wikipedia Loves Art participant Assignment Houston One. CC BY SA 2 5 http creativecommons org licenses by sa 2 5 via Wikimedia Commons G Walliserops. trifurcates by Arenamontanus Own work CC BY 2 0 http creativecommons org licenses by 2 0 via Flickr. Sheer Numbers, The sheer variety of trilobites is impressive As mentioned above they belong to the. most diverse phylum the arthropods and when it comes to total variety and diversity trilobites. were no slouches themselves They have been divided into. 10 Orders that include,150 Families assigned to,5 000 Genera that contain perhaps more than. 20 000 Species, Figure 2 Diversity of trilobites number of families through time from the Treatise on Invertebrate Paleontology. used with permission, Figure 3 Size range of the largest trilobites from Sam Gon http www trilobites info lgtrilos htm used with. permission, As already mentioned trilobites show an impressive variation in size from under 1 mm.
to over 70 cm in length although the average trilobite was probably around 5 6 cm Figure 3. nicely illustrates the sizes of the very largest known trilobites. Temporal and Spatial Distribution, 521 Ma Cambrian to 251 Ma Permian 300 million year history. Greatest numbers in Cambrian and Ordovician,Worldwide distribution. The earliest trilobites appear suddenly in rocks of Early Cambrian age 522 530 Ma. from present day Scandinavia and eastern Europe Soon afterwards trilobites also appeared in. China North America Antarctica and Australia and within the Early Cambrian are found. throughout the world The early history of trilobite evolution shows a pattern of biogeographic. differentiation which taken with other evidence suggests that there may have been some. significant period of trilobite evolution before they actually appeared in the fossil record. Current estimates suggest that although the earliest trilobites appeared in the fossil record around. 525 Ma they may have originated 550 600 Ma Lieberman and Karim 2010 Paleontologists. continue to investigate this trend looking for evidence of older trilobites and working to better. constrain the timing of their origins The reasons why the earliest relatives may have been absent. from the fossil record remain unclear but may include the fact that they were small lacked a hard. shell or they were very rare and restricted to environments where they were unlikely to fossilize. The trilobites continued to diversify into the Ordovician but were hit particularly hard by. the end Ordovician mass extinction Trilobites were able to partially recover after the end. Ordovician mass extinction only to be hit again by the Late Devonian mass extinction Trilobite. diversity failed to rebound after the Late Devonian event and the group was eventually wiped out. during the largest mass extinction of all time at the end of the Permian Indeed as we shall. discuss more fully below scientists are exploring the possibility that part of the reason trilobites. are no longer with us today has to do with the fact that they fared particularly poorly during. times of mass extinction Lieberman and Melott 2013. General Anatomy, In small groups identify at least 5 morphological features of trilobites that you think are. important for anatomical description Mark the features on the trilobite diagram below with lines. pointing to them, Consider the variety of body forms shown in Figures 1 and 3 Can you identify any. additional morphological features that may be important for distinguishing groups of trilobites. from one another Add as many as you can identify to your diagram. The name trilobite refers to fact that their body is made up of three longitudinal along. the length of the body sections the central section known as the axial lobe and the two lobes. on either side of the axial lobe known as the pleural lobes Figure 4 and 5 Trilobites are also. separated into three sections from front to back known as tagmata the cephalon or head the. middle section made up of multiple segments known as the thorax and the posterior section or. pygidium plural pygidia Figures 4 and 5 Some trilobites have spines originating at the. genal angle in which case they are called genal spines. How does the commonly accepted anatomical regions of trilobites compare with the important. anatomical features identified by your group, Did you identify the longitudinal sections as important features Did you identify the tagmata as.
an important feature, Use the diagram and descriptions provided in Figures 4 and 5 to label the anatomical elements. highlighted in this photograph of the trilobite Phacops. Figure 4 External trilobite anatomy A Diagram of Phacops from the Treatise on Invertebrate Paleontology used. with permission B Photo of Phacops milleri specimen from the University of Kansas Museum on exhibit. Use the diagram and descriptions provided in Figures 4 and 5 to label some of the same. anatomical elements in this photograph of the morphologically distinct Isotelus iownesis. Figure 5 previous page External trilobite anatomy continued A Diagram of the Ordovician trilobite Isotelus. from the Treatise on Invertebrate Paleontology used with permission B Isotelus iowensis University of Kansas. Museum Invertebrate Paleontology KUMIP 294608, Now that you are familiar with general trilobite anatomy choose one of the trilobites. from Figure 1 Spend 2 minutes writing a description of your trilobite but do not write down. which one you chose Try to be detailed in your observations and use the correct anatomical. terminology where possible, Once you are finished recording your observations switch lab handouts with your. neighbor and try to determine which trilobite they described based on their recorded. observations You may not ask your neighbor for clarification and must rely solely on their. written description, Were you able to match their description with the correct trilobite Were they able to. identify which trilobite you described, What was difficult about identifying you neighbor s trilobite from their description.
What made the task easier How might you change your own description after this exercise. The above photos and diagrams depict the dorsal upper or backside surface of the. trilobite Below is a diagram of the ventral underbelly morphology of a trilobite. An important ventral morphological feature of trilobites is a calcified plate near the mouth. known as the hypostome, The hypostome is thought to have been used in feeding It may be rigidly or flexibly attached to. the shell of the cephalon and can display a variety of shapes including points or fork shaped. projections, Figure 6 Ventral view of a Ceraurus whittingtoni cephalon from the. Treatise on Invertebrate Paleontology used with permission. The shells of trilobites are frequently preserved as fossils due to their mineralized. exoskeletons hardened with calcite Trilobite limbs however are rare in the fossil record. because they lacked a hard mineralized coating of calcite To reconstruct limb morphology we. must rely on exceptionally preserved trilobites those preserving both hard and soft tissues as. fossils This Triarthus eatoni specimen Fig 7 from the Ordovician Beecher s trilobite bed. locality in upstate New York is an example of a pyritized trilobite the limbs are substituted by. the mineral pyrite which contains Iron and Sulfur that preserves soft tissues such as antennae. and appendages Trilobites have biramous appendages each appendage is made up of two. branches These branched appendages are found along the length of the body occurring in. repeating pairs with multiple pairs on the cephalon one pair per thoracic segment and several. small pairs on the pygidium Unlike many modern arthropods with many specialized limbs the. limbs of trilobites are essentially the same from front to back varying only in size The upper. branch or gill branch is a soft filamentous structure used to obtain oxygen from the water The. lower branch is a jointed walking leg used for locomotion The gill branches are located directly. under the trilobite shell, Please answer the following questions using the diagrams and photos provided in Figure 7. Figure 7 Limb morphology A Diagram of the limbs of Triarthus eatoni from the Treatise on Invertebrate. Paleontology used with permission B Photograph of a pyritized specimen of Triarthus eatoni YPM 219 from the. Yale Peabody Museum collections by Bruce Lieberman used with permission. How many pairs of limbs does the cephalon have, How many pairs of limbs does the thorax have hint there are 14 thoracic segments. On the diagrams or photo above Fig 7 draw a line separating the thorax from the pygidium. hint the diagram showing the side view may be the most helpful for this task. Does the pygidium have limbs Y N,Figure 8 Enlarged view of trilobite.
biramous limb morphology showing the,jointed walking leg and filamentous gill. branch A Close up of Middle,Cambrian Olenoides serratus from. Treatise on Invertebrate Paleontology,used with permission B Limb. reconstruction from the Treatise on,Invertebrate Paleontology used with. permission, Using the diagram as a guide circle and label a walking leg and a gill branch on the close up.
photo provided in Figure 8, What was the gill s function How did the gill s feathery construction help it perform this. What factors constrain the placement of the gills For instance would gills placed under the. walking leg be more or less effective Why, Many different clades of trilobites are capable of flexing the thoracic segments to rest the. cephalon on the pygidium The process of flexing into a ball is known as enrollment Some. trilobites even have structures that allow the cephalon and pygidium margins to interlock for a. Figure 9 Fully enrolled trilobites Flexicalymene meeki Upper Ordovician University of Kansas Museum. Invertebrate Paleontology KUMIP 241339 241344 and University of Kansas Museum Invertebrate Paleontology. KUMIP 241347 241349, Given what you just learned about the structure of trilobite limbs what do you think the benefit. of enrollment was What might cause a trilobite to roll up into a ball. Looking at the range of morphologies illustrated in Figure 1 what other structures can you see in. the photos that likely served the same function as enrollment. Trilobites had compound eyes made up of numerous calcite lenses Eyes in which. individual lenses are not separated are known as holochroal Fig 10A All of the lenses in a. holochroal eye share a single cornea or covering Eyes in which individual lenses were separated. by exoskeleton material are known as schizochroal Fig 10B In a schizochroal eye each lens. had its own cornea Holochroal and schizochroal eyes may have been equally adept at allowing. trilobites to see static objects but schizochroal eyes were more adept at detecting movement. Figure 10 A Holochroal eye of Paralejurus brongniarti Devonian Bohemia lateral view 7 Clarkson 1975 pl. 1 g 1 from the Treatise on Invertebrate Paleontology used with permission B Schizochroal eye of Phacops. rana University of Kansas Museum Invertebrate Paleontology KUMIP 240295. The holochroal style of eyes evolved first whereas the schizochroal style of eyes evolved. in only one group of trilobites the Order Phacopida and presumably evolved sometime in the. Late Cambrian, Figure 11 A Erbenochile erbenii by Moussa Direct Ltd Own work CC BY SA 3 0 http creativecommons. org licenses by sa 3 0 via Wikimedia Commons B Ellipsocephalus hoffi by TheoricienQuantique Own work. Public domain via Wikimedia Commons C Asaphus kowalewskii by Smokeybjb Own work CC BY SA 3 0. http creativecommons org licenses by sa 3 0 via Wikimedia Commons D Phacops milleri University of. Kansas Museum on exhibit, Describe the visual capabilities of the trilobites in Figure 11 Things to consider presence or.
absence of an eye the size of the eye the position of the eye on the cephalon the field of vision. the trilobite may have had in which directions can the trilobite see whether the eye is. schizochroal or holochroal,Ecological Niches, As mentioned above trilobites are only found in rocks representing marine environments. but they were present at all depths and in all marine environments Trilobites filled many. different ecological niches and were capable of a wide range of behaviors Paleontologists. reconstruct these behaviors and modes of life using a combination of evidence including. morphology occurrence with other organisms types of sediments in which trilobites are. Introduction to the Trilobites Morphology Macroevolution and More By Michelle M Casey1 and Bruce S Lieberman1 2 1Biodiversity Institute and 2Department of Ecology and Evolutionary Biology University of Kansas Lawrence KS 66045 Undergraduate laboratory exercise for sophomore junior level paleontology course Learning Goals and Pedagogy

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