Ecology and Diversity of Cambrian Faunas - Lab Report Example

Ecology and Diversity of Cambrian Faunas Introduction This laboratory exercise is based on ecology and diversity of Cambrian faunas which gives an insight into the cause and nature of the ‘Cambrian Explosion’. The practical consists of a series of calculations using data from the Burgess Shale fauna that was exceptionally preserved. Marine faunas that are soft-bodied and from the middle and lower Cambrian, exemplified by the British Columbia Burgess Shale, are a major component in understanding the adaptive radiations that are major at the beginning of the Phanerozoic (“Cambrian explosion”) (Conway et al.,1989). It was required to compare the results with information on modern faunas and normal Cambrian faunas. Also it was required to discuss the representativeness of the former and the differences between the latter and Cambrian faunas. Results and Discussion A. TAXONOIC ASPECTS 1. What proportion of the total fauna is constituted by the commonest species, and to which higher taxon(phylum) does it belong? Answer: 57%, primitive arthropoda. 2. What proportion of the total fauna is constituted by Arthropoda? 89.9% 3. What maximum proportion of Arthropoda is constituted by readily preservable forms (trilobites)? Answer: 0.89% 4. What proportion of the total fauna (in term of percentage of individuals) is constituted by each of Brachiopoda, Annelida, Priapulida, Porifera, Chordata and species not assigned to phylum? Answer Brachiopoda= 0.045% Annelida=2.14% Priapulida=6.35% Porifera=0.55% Chordata=0.23% Species not assigned =0.8% 5. At the level of higher taxa, to what extent is the Burgess Shale fauna likely to be representative of Cambrian marine life as a whole? (Give reasons) Answer: It represents most of deep marine but not shallow or tropical one. The reason for this is that Cambrian rocks only have marine fossils, mainly for species that lived on hard substrates on the sea floor and this includes Burgess Shale fauna 6. How does fauna of Burgess Shale compare with that of Cambrian deposits exhibiting normal (mineralized hard part-only) preservation, in terms of higher taxa represented and their relative proportion? How representative therefore are normal faunas? Answer: In terms of higher taxa representation, Cambrian deposits exhibiting normal (mineralized hard part-only) preservation accounts for only a minor component of the total diversity. Similarly, in most Burgess Shale-types deposits, the Shelly assemblage normally represents a small proportion of the collected specimen. In this case, soft bodied organisms fossilized remains especially from Burgess Shale the Cambrian ecosystem knowledge could be totally limited Burgess fauna consists of many soft bodied animals’ fossils as well as those with hard parts. A completely soft bodied animal normally rot away before it is fossilized. Hard parts are crucial because they are more easily preserved; they are seen to help an organism last for a longer time to become fossilized. Burgess Shale is rich in life most of fauna in it are soft bodies while it contain only 0.89% of mineralized hard parts. 7. How does the fauna of the burgess shale compare with that of modern muddy marine environment in terms of the higher taxa represented and their relative proportions? Burgess Shale, organisms lived in underwater mud banks, the moving water buried living organism in moving sediment. They are therefore found in random orientation. Modern muddy marine invertebrates usually curl up upon dying but fossils of the Burgess Shale locality never exhibit such coiling and there is evidence that this organisms died instantly. B. ECOLOGICAL ASPECTS Histogram showing the % of individuals in: (a) living habit EV - vagrant epifauna ES - sessile epifauna IV- vagrant infauna IS - sessile infauna NK - nekton Histogram showing the % of individuals in: (b) Feeding strategy. S - Suspension feeder D - Deposit feeder P - carnivore/scavenger 9,200 individuals (23%) are accounted by the Hemichordate "Ottoia" tenuis, a sessile infaunal and suspension feeder. 1. Comment on the community structure of the Burgess Shale as revealed by this analysis. In comparison to the conventional fossil deposits, where only the more durable body parts remains are typically preserved, it is observed that Burgess Shale –type deposits give a much more full picture of a normal Cambrian marine community. The highest percentage of the individuals are deposit feeders, this is followed by suspension feeders then carnivore/scavengers 2. How does the fauna of the Burgess Shale compare with that of Cambrian marine deposits exhibiting normal (mineralized hard part-only) preservation, in terms of the living habits and the modes of feeding represented and their relative importance? How representative therefore are normal faunas? The marine deposits organisms burrows opened up new ecological niches that were beneath the floor of the sea and the water and oxygen could reach the sediment layers. The revolution changed the uniform sea floor to heterogeneous patchwork and it opened up a variety of new niches for animals that included those of Burgess Shale. The Cambrian early record is based on Cambrian marine deposits exhibiting normal (mineralized hard part) preservation. Burgess Shale, organisms lived in underwater mud banks, the moving water buried living organism in moving sediment. They included a wide range of feeders that include deposit, suspension and carnivore. In relation to this, the Burgess Shale type deposits give a complete picture of normal Cambrian marine community because both their soft part and hard body parts are fossilized. The deposits are normally found in middle and lower Cambrian rock layers, but could extend up to the Ordovician. In modern marine settings, mineralized animals’ bodies parts contribute to only a minor component of the total diversity (Collins D. et al., 1983).The normal fauna represent a bigger picture of the Cambrian marine community. 3). How does the fauna of the Burgess Shale compare with that of modern muddy marine environments, in terms of the living habits and modes feeding represented and their relative importance? Attempt to interpret differences. Burgess Shale, organisms lived in underwater mud banks, the moving water buried living organism in moving sediment. They are therefore found in random orientation. Modern muddy marine invertebrates usually curl up upon dying but fossils of the Burgess Shale locality never exhibit such coiling and there is evidence that this organisms died instantly. Shale is a type of mudstone originally formed from fine mud deposits mostly made of clay minerals. The processes of preservation in the Burgess Shale environment started with fine grained sediments occasional flow that swept through the given area (Collins D. et al., 1983). References Conway Morris S., Trans. R. Soc. Edinburgh: Earth Sci. 80, 271 (1989). Collins D. et al., Science 222, 163 (1983). Soft-bodied fossils were recently discovered above the Raymond Quarry; D. Collins, personal communication. Read More