Nautiloids and Ammonoids Flashcards
Class and phylum
Mollusca
Cephalopoda
What is morphology of nautilus?
Coiled conical shell, involuted, septal neck points towards protoconch, chambers within shell sealed by septum, last chamber is body chamber occupied by soft parts. Siphuncle extends through chambers via septal neck to continue gas and water levels for buoyancy
What is involuted coiling?
Inner coils almost hidden by last one, produces narrow umbilicus shown in nautilus
What is evolution coiling?
All earlier could can be seen, wide umbilicus, common in Ammonoids
What is planispiral coiling?
Shell is coiled in a single plane
Describe the morphology of Ammonoids
Evolution coiling, may be ornament such as ribs, keel and sulcus may be present to provide stability, simmilar to nautilus, protoconch, septum creating empty chambers, siphuncle to control gas levels but septal neck to shell aperture
What is Ammonoids mode of life
Nektonic, moved laterally using tentacles and jet propulsion of water from chambers through funnel. Moves vertically by volume of gas in chambers gas is nitrogen rich
Evidence is that Cephalopoda were predatory
When did nautiloids appear?
Upper Cambrian to present
When did Ammonoids evolve?
Clearly distinct from nautiloids by Devonian Relatively unchanged until Triassic when they began to diversify, declined through Cretaceous, wiped out by K-T extinction event.
Why did suture lines change over time?
Suture line is where septum fuses with inside of shell. Changed to increase strength, so greater depth for hunting, anchorage for soft tissue
How did sutures change overtime?
Earlier had simple sutures, nautiloids, straight line to gentle curve
Then goniatitic, in Devonian, angular shape
Then ceratitic in Permian, developed frilly lobes, saddles remained simple
Then ammonitic in Triassic, frilly and complex lobes and saddles
How did the internal structure change?
Septal necks in nautiloids point inwards towards protoconch, septal neck in Ammonoids points outwards to aperture.
Siphuncle of nautiloid in centre of shell, Ammonoids siphuncle closer to the venter
What changes occurred on the external structure?
Nautiloids and honoured smooth shelled, ammonites show variety of ornament such as ribs and tubercles
Had excellent camouflage for protection so invisible in water
What are the heteromorphs?
Unusually formed ammonites from the Cretaceous, many show bite marks from reptiles, often called uncoiled ammonites due to loose coiling and have allowed organism to exploit different ecological niches
