STATION#5-FOSSILINVERTEBRATES choose Two of the following groupings of fossil fo
ID: 207703 • Letter: S
Question
STATION#5-FOSSILINVERTEBRATES choose Two of the following groupings of fossil forms and their modern representatives to examine, drawldiagram and compare/contrast. Describ how the fossil likely formed. During what geological era and period did the fossil creature live? Lastly, comparelcontrast some of the key similarities and differences you observe between the fossil and the modern form, i.e. note at least 3 physical and/or behavioral characteristics Fossil ammonite and modern Nautilus shell, model, pictures Fossil trilobite (extinct arthropod) & modern horseshoe crab (living arthropod) Fossil sand dollar and modern sand dollar (Echinoidea) Fossil giant barnacles and modern giant barnaclesExplanation / Answer
A. Ammonites and modern day Nautilus
Ammonites are fossils of an extinct group of marine molluscs called Ammonoids. They in the subclass Ammonoidea and class Cephalopoda.
When these sea molluscs died, their shells got buried inside the sand of ocean floors. it was covered with layers and layers of sand and silt over many many years. After millions of years, when the ocean beds became open land due to climate and geological changes, these shells got exposed and shell structure got decomposed and replaced by rock-like materials. This process is called 'permineralization". This retained the original shape of the ammonoid shells and this is how the fossils ammonites are formed.
They lived during Devonian geological era.
These ammonites have sinilarties with modern day Nautilus shells.
Nautilus shell
Nautilus are the sea molluscs belonging to family Nautilidae.
Similarities between Ammonites and Nautilus shells:
1. they are both sea molluscs.
2. they both have spiral shells with septa/chambers
3. they both have sexual dimorphism i.e. variation in the shape and size of the shell according to the gender of the animal. The shell of the male is slightly smaller and wider than that of the female.
Differences between Ammonites and Nautilus shells:
1. Ammonites are extinct and Nautilus are called living fossils which means, they survived millions of years through various geological time frames.
2. Defense bhavior: ammonites had the ability retract into their shells for protection. Aptychus, a flap like structure would close head of their shells to protect the ammonites. Nautiluses lacked this ability.
3. Nautiluses have the ability to color camauflauge their shells.
4. Ammonites loved during Devonialn era, whereas Natiluses were first found during late Cambrian era and still living.
5. Siphuncle is centrally located in Nautilus and laterally located in ammonites
B. Trilobites and modern day Horse shoe crabs
Trilobites are the extinct arthropods.
They havedistinctive three-lobed, three-segmented form.
They were first found during Early Cambrian period (521 million years ago), and they flourished throughout the Paleozoic era and extincted, during the Devonian era.
They are fossilised under sea beds and mostly their exoskeletons are the fossils we get.
Horse shoe crabs:
these are the marine arthropods belonging to the family Limulidae
Similarities between trilobites and horse shoe crabs:
1. they both have similar elliptical shape.
2. they both live in ocean beds
3. they both are invertebrate arthropods.
4. they both have compound eyes.
Differences:
1. trilobites have 3 segments in their body: cephalon, thorax and pygidium
wheras horse shoe crabs are chelicerates, which means they have of two segments in their body, cephalothorax and abdomen
2. trilobites have more apendages compared to horse shoe crabs.
3. trilobites found during Early Cambrian period (521 million years ago) and they were extict by Devonian period. where as horse shoe crabs were first found during late Ordovician period (450 million years ago) and still living.
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