Question

1. Explain why the earliest evidence of animals in fhe fossil record would come from chemicals as opposed to fossilized imprints.

2. Describe why creating an accurate phylogeny of animal groups (porifera, cnidaria, ctenophora, bilateria and placozoa) is a challenge for taxonomists.

Answer 1

a. Earliest evidence of animals in the fossil record mainly comes from chemicals because body parts of early animals were consisted of mainly soft tissue which decays very easily without leaving any part to be fossilized.. Chemical fossils are derived compounds which have been originated after large biochemical compounds in the early animals have been decayed and form some stable compounds which survived for long geological timescale. Examples of such compounds are some hydrocarbons. These played significant role as fossil mainly for life in the Precambrian period. Often radioisotope methods are employed to measure the exact time of their origin. One example of such chemicals fossil are phytane and pristane. These two compounds in early Precambrian rocks proved the presence of organisms which were able to do photosynthesis.

b. Fossil are formed due to presence of hard or bony parts in the body of the animals. The primitive or early animals were mainly formed of soft tissue which after death decayed easily and no remnants were fossilized. Porifera, Cnidaria , Ctenophora, Placozoa have hardly any hard tissue in their body, so fossil records are not so accurate for them. In addition to this, due to tectonic movement, many fossil have been lost. So accurate phylogeny of such animals is a challenge for taxonomists.