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Late Cretaceous Dinosaur Diversity (Hell Creek Formation, West N. America,…
Late Cretaceous Dinosaur Diversity
Diversity Msmts
Number of species corrected for sampling
Morphological disparity
Anatomical diversity
Short-Term Diversity Decline Consequences
Decreased diversity (large bodied plant-eaters) at very end Cretaceous
Fewer plant-
eaters at base
Food web foundation = weaker
(Food webs = more robust
if have more plant-eaters at base)
Computer simulation Mitchell et al 2012
Meat-eaters remain constant
Possible Causes Diversity Decline
Paleogeography?
N. American
Seaway open before
spliting American continent in 2 from N-S
promoted greater diversity
Decline
perhaps due to
during REGRESSION sea level
Continents reconnecting
more uniform to dino diversity
Hell Creek Formation, West N. America
Only place with very good dinosaur preservation around K-T boundary
Last gasp of dinosaurs
14 species
Tyrannosaurs
Triceratops
Pachycephalosaurus
Terminal Cretaceous ~ 67.5 - 66 Ma
Confirms
No major extinctions before asteroid impact
Dinosaur remains abundant & diverse up till boundary
(triceratops 13 m below boundary)
Dinosaur species occurrence unrelated to volcanism / sealevel regression / temp change
This is ecosystem after plant eater decline
Europe in Latest Cretaceous
Flooded island continent
warm & humid
inhabited by dinosaurs
High global sea level
Dinos dominated 2 islands
now in Spain/France & Romania
Tremp Basin, Spain
Less data available
Fewer
radiometric dates
No boundary outcrop thus no iridium spike observed
Only palaeomagnetic dates
Dating uncertain
Fewer species/findings
Dino Diversity
Dinos remain diverse & abundant to boundary
meat-eating, long-neck, ornithiscians (duckbilled)
Turnover Event
~69 Myr
Some groups
disappear
from before
Armoured dinos & smaller primitive duckbilled
Appearance larger & more derived
duck-billed dinosaurs
larger, more diverse
Plant-eaters exhibit change
Plant-eaters = ecologically v important
Transylvania, Romania
Dino bones exposed in fast eroding rivers
Balaur
poodle sized meat-eating dino with 2 claws
more dangerous than velociraptor
Age is uncertain
No iridium layer / boundary to exposed
Ash dates are appearing which contribute
Think they lived up till boundary
Dwarf dinosaurs of Romanian Island Fauna
characteristic of island fauna
extends to Late/End Cretaceous
Late Maastrichtian
(Final Subdivision Late Cretaceous)
Highly diverse faunas