5. lesson Agnathans and Chondrichthyes Flashcards
Conodonts
Predators. 3-10 cm. long.
In the beginning they where really hard to classify, because they only found the pieces of them. There were so many, that geoligist uses them to predict periodes.
But we know they are vertebrates, they got some of the beginning specifics.
Ostracoderms
Big group
Bottom feeders. Around a few cm to 20 cm.
Where the first animal to have BONE. Back then the bone was located on the outer exoskeloton.
They where also the first to have a lateral-line system, which is an inner ear, there runs through the body as a channel. Whit this fish can detect movement, vibrations in the water. “the 6. sense”.
Pteraspidomorpha
Undergroup Ostracorderm
Most of them had bony head shields. The rest of the body was covered by small plates and scales. Some of them had a spine.
They didn´t have paired fines, but instead bony structures, which was used to help them swim through water.
Osteostracans, Anaspids, Thelodonts
Again sub groups to Ostracoderm
Different fishes which lived i the 3D sea. In the different layers, so they looked really different.
But they are all instinct.
Gnathostomes
Vertebrates with jaws
Where did jaws come from? And how did fish breeth.
They came from gill arches, which supported the gill, and where made of cartillage. In the end the additional gill arches help support the jaws for heavier work, and in that chase also helped the beginnig of teeth.
In the beginning they sucked water in through the mouth without breathing. Instead they breathed through the body.
When the gill arches became stronger, the fish was able to use them for breething.
The evolutionary tree (phylogenetic tree) of whit the common ancestor Agnatha
including Gnathostomes, Chondrichthyes, teleostomi, osteichthyes, tetrapoda.
Note that we humans are Gnathostomes, and out history goes through teleostomi (the bony fishes)
Placodermi
Preadtors! The fish was biiig. up to 10 m. Had jaws with bones as teeth and bony plates.
A lot of them lived at the bottom, because of the weight of the bones, but some lived i midwater.
They are the only major group of Aganaths to become extinct whitout any descendants. Therfore they are not a Stem-group.
Chondrichthyes “cartilaginous fishes”
~ 1,200 species
Marine and freshwater
Chondrichthyes has two subclasses, which are Flasmobranchii (sharks, rays, skates and sawfish) and Holocephali (chimaeras).
What is the Devonian time
The age of the fish
What is the specifics of Chondrichthyes skeleton?
Their skeleton is made of cartilage, which make them light. They don´t have any bones!
This means that we don´t have that many fossils, because it preserves badly. Just think of a human cranium.
With other vertebrates, bones are formed around cartilage, like in the case of babies. This phenominum is being used in science today, which looks into creating new bones for people whitout bones. Cartillage also protect tubes and entries, fx nose, ears, throat.
What helps Chondrichthyes to stop sinking?
The skeleton of cartilage is half the density of bones.
In their liver they have oil, which help them to float. The liver is really big.
Pectroal (paired) fins (hydrofolis) and heterocercal tails, which means that the tail of the shark is assymetric, which puches it upward.
