Topic 1: Elasmobranch Evolution Flashcards
What is an Elasmobranch?
Group of specialized fish with a cartilaginous skeleton, specialized scales, and 5-7 gill slits.
What is under Class Chondrichthyes?
Subclass Elasmobranchii
What does subclass elasmobranchii contain?
Sharks (>440sp), skates, and rays (~500 sp)
Why are fossilized sharks hard to find? What is usually found?
because they are made up of cartilage
L> scales…placoid
, and _ all have the same parts but _ and _ are flat.
sharks,skates and rays
- skates and rays
What does neoselachians contain?
modern sharks
A lot of morphology of ancient sharks are based on speculation based on?
similarities seen in modern day sharks
What eras are in the eon Phanerozoic (3)
Cenozoic
Mesozoic
Paleozoic
What eras are in the eon Proterozic ?
Late, middle and early proterozic (2500 mya)
What eras are in the eon Archaen?
Late, middle and early arcane (3800mya ?)
What two periods are in the Cenozoic era?
- Quanternary ( 1.6 mya)
2. Tertiary ( 66 mya)
What three periods are in the Mesozoic era?
- Cretaceous ( 138 mya)
- Jurassic (205mya)
- Triassic ( 240 mya)
What seven periods are in the Paleozoic era?
- Permian ( 290 mya)
- Pennsylvanian (330 mya)
- Mississippian (360 mya)
- Devonian (410 mya)
- Silurian (435 mya)
- Ordovician (500 mya)
- Cambrian (570 mya)
What are the seven possible fossilized remains of a shark?
- Which is the most abundant?
- Which is not very common and why
- vertebrae
- fin spine
- rostral node
- teeth ** most abundant
- cartilage ( usually found in the jaw present if the right conditions are met)
- dermal denticle
- coprolite (poop) –> not exclusive to sharks.. all animals can deposit this…but usually with sharks it liquidized and disperses in the water so its not very common
Shark evolution dates back to what period?
Paleozoic era—-> Ordovician period (450-420mya)
Back in the Ordovician what fossilized records of sharks were found?BUT ?
- scales
L> Not all agree the oldest are from true sharks
What is the oldest named shark found back in the Ordovician period?When was it named?
Tantalepis gatehousie (named in 2012)
All evidence of sharks back in the ordovician were scales and what is the issue with them?
- not sure if they are from sharks or they are just shark LIKE.
The oldest undisputed shark scale is from the ___ period in Siberia 420mya.
L> what was the sharks name….description of its morphology?
- Silurian period
- Elegestolepis: no idea what it looked like
L> only scales were found
Fossil records for sharks became much richer in what period? (hint: 410-358mya)
Devonian
The Devonian period was called the age of ____ and the first ___ appeared. In terms of fossils which came first?Second? Did they look more like fish or sharks?
- Fishes
- tetrapods
- Teeth
- complete fossils
- FISH
In the devonian period there was massive radiation of many types of fishes including boney fishes and tetrapods. In this period the ____ predators dominated. The age of the ___ has not yet occurred. Early sharks looked more like a typical ___.
- large marine
- reptiles
- boney fish
The earliest shark teeth are from the ____ period 400nya. They were described as ___ and ___.
- Devonian
- two-pronged and puny
The two pronged and puny teeth found in the devonian period may have belonged to ___ and is similar to Xenacanthus what can we deduce?What was also found to be present?
- Leonodus a xenacanths (freshwater shark)
- likely fed on similar prey
- claspers
Comparisons of teeth from the devonian period with similar shark teeth structure can mean what two things?
- hunt the same prey
- or came from the same ancestor
The Leonodus found in the devonian period had an important feature. What was it?
- claspers…they are unique to sharks! no other organisms have it!
L>its used for reproduction
What can we tell from the claspers of a shark?
- its age via the structure of the clasper and if it has mated!
The Leonodus found in the devonian period had what kind of body?
- eel like than the typical shark…long and slender
Where was the oldest complete shark fossil from early Devonian (409mya) found?What was it?
- Campellton, NB
L>brain case found xenacanth… Antarctilamna
L> articulated remains from Antarctica and Australia
Describe Cladoselache! L> period? L> how many gill slits L> explain jaw and swim speed L> teeth? L> scales? L> spines? L> claspers?
- Devonian, 370mya
- 5-7 gill slits
- weak jaw, fast swimmer
- multi-cusped teeth
- few scales
- spines different
- lacked claspers….so how did it reproduce?
Cladoselache is very similar to _____. Its caudal tail is the morphology of a slow/fast swimmer. Explain its spine situation?
- largest dog fish
- fast
- it did possess spines but they were structurally different than modern sharks
Is it likely or unlike that they found a Cladoselache female fossil since it doesn’t have claspers?
UNLIKELY
SO Y NO CLASPERS?
With the Cladoselache they found what is the alternative explanation for the absence of claspers?
- reproduction morphology of some birds possibly….
With the Cladoselache how did it eat its prey?
- swallowed tail first….therfore fast chases??
When was Ctenacanths found?
- the same time as the cladoselache!
Length of the Ctenacanths?
less than 2m
What features did Ctenacanths develop that were more advanced features than Cladoselache?
- pectorals supported by cartilage like modern sharks
- spines long and cylindrical
- more advanced structural support….reinforced cartilage which is a trait of modern sharks….
From about 300-150mya most fossil sharks can be assigned into what two groups?
- Xenacanths: fresh water sharks (450-220mya)
2. Hybodonts: marine sharks ( 320mya throughout Jurassic )
The Hybodonts were ousted by?
- modern forms began to emerge and outlasted the hybodonts
- ended with the dinosaurs
The xenacanths faded out slightly in the ___ period because they were evolutionary dead
Devonian
Sharks have undergone a lot of what?
evolutionary experimentation
Sharks survived changes in ____ and ___.
- environmental changes and mass extinctions
The first major radiation of sharks occurred during the __ period. (360-286mya). How many families of sharks emerged?Specific example?
- carboniferous period
- 45
- Stethacanthids (60cm)
What two periods occurred in the carboniferous period?
- pennsylvanian and mississippian
Explain the stethacanthids (60cm) found in the carboniferous period!
- very small
- bizarre shape
- the function of its weird body is possibly for mating rituals….ex: some modern sharks do head butts or it could function as a way to latch on to other larger animals
Falcatus is a ____. How long is it? Is its coloration fact based? Describe the main morphological difference in the male?
- Stethacanthids.
- 15 cm
- not fact based
- has a hook structure coming off of its head!
- basically it is a handle…in modern sharks males bite on the female… which have a outer outer skin and heal faster but…its the opposite here.
Explain helicoprion and edestus teeth structure??
- its spiral teeth structure…. is a precursor to multiple rows of tooth like structures seen in modern day sharks….its like a converter belt like function….this is in devonian.
At the end of Permian a mass extinction occurred in which __% of marine species were wiped out. Some __ lineages survived which gave rise to?
99%
- shark
- modern sharks
** this was a massive extinction all across the planet not just marine.
L> no one knows what caused it.
**nor do we know which species gave rise to modern sharks
The second major radiation in shark evolution occurred during the __ period. (208-144mya)What appeared here?
- Jurassic
- modern sharks
L> the group that did this is unknown
Issue with the modern sharks during the jurassic period?
they had to compete with dinosaurs…..they were not top dogs until the dines were wiped out
Did hybodonts give rise to any modern sharks?Length? Describe their teeth?
- NO
- 2.5 m
- grasping canines and crushing molars
They believe that hybodonts with grasping canines and crushing molars may have given rise to?
bullhead sharks or very similar to them but in general they were an evolutionary dead end.
___ may have given rise to modern sharks.. they date back to the __ period. This is relation is based on what structure? What are these sharks classified as?
- Mcmurdodous
- devonian
- tooth structure
- Neoselachian
When did neoselachian radiate?
during the mid cretaceous period about 100 mya
When did Batoids appear? What are they?
- Jurassic period
- skates and rays
Batoids are mostly represented by __ and __. The oldest articulated skeleton dated back to __ mya. Stingrays found back __mya. (__period)
- teeth and spine
- 150
- 60
- late cretaceous
Do we have an ira what the first batoid looked like?
NO
Are fatalities high via poison from stingrays?
NOPE
When did shark filter feeding species appear?
during the mid tertiary period (65-35mya)
What type of sharks are the most recent to have appeared?
- hammerheads ….50-35 mya
What type of sharks have left a rich fossil history?
- Lamnoids
L> 155mya
Lamnoids are called the __ sharks.
typical
L> very streamline…fast swimming
When did the C.mantelli (lamnoid) appear? How long was it?
100 mya
- 4.5 to 5.5 m
Lamnoids: - Squalicorax L> length? - appeared in what period? - its known for their?
- 5m
- late cretaceous period
L> 100-65 mya - distinct teeth
Lamnoids:
- Squalicorax
L> Their teeth are very distinctive. This is the first group that have this type of dentition which is only found in ___ sharks.What are they designed for?
tiger
L> pure shearing power…modern day tiger sharks with these teeth can break through turtle shells for instance.
White sharks ancestors can be traced back to - mya. Modern day great white shark evolved about _ mya.
- 65-55mya
- 11 mya
The dentition of great whites changed over time because ?
- changes in diet…especially isnce marine animals were also changing over time….
Four species of white sharks evolving in order over time?
- Isurolamna inflata
- Macrohizodus praecursor
- Cosmopolitodus hastalis
- Carcharodon carcharias
The Megalodon is related to ?
Great white
When did the megalodon first appear via fossil record?Disappeared?
about 16 mya and disappeared about 1.6 mya.
Reasons why the megalodon disappeared 11,000 years ago??
Changing environmental conditions……. cooling climates possibly at about 1.6 mya the ocean started to cool and became very productive…seas started to deepen and the theory is that whales the primary food source started to mover to the pools away from the warm areas they hunted….BUT if they are related to GW why didn’t they follow via thermoregulation ?
—> also think that their pups were hunted off due to loss of habitat
What proof do we have that the megalodon is related to great white?
- Tooth structure similarities !
L> they both have robust root, regular serrations, no cusps on adult teeth, broad crown BUT the megalodon upper tooth has w wide bourlette which the GW does not have.
Medial side of tooth?
-inside of tooth… distal = outside
Basal ?
rooted in jaw
Lingual side of tooth?
- tongue side
What can we estimate from a sharks anterior teeth?
- total length…but you can only know if it is anterior without the full jaw.
What proof do we have that megalodon hunted whales?
- ancient whale vertebrae…found broken which matches Megalodon tooth dentation
