ERTH 2401 Lecture 19: Dinosaurs Role in Paleogeography
26 Oct 2018
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ERTH 2401 – Lecture 19: Dinosaurs Role in
Paleogeography
• Evolution is closely linked to the changes our planet has gone through, through geological time
• Graph of Number of Genera over time
o Red arrows point out the 5 mass extinction events
o After mass extinctions, Earth is repopulated with life quickly
o In Jurassic there was a spike in diversity, which can be attributed to the separation of
Pangea, showing there is a relationship to paleogeography
o Biased. The older you go back, the more geological processes have gone over those
layers, destroying those fossils, leaving smaller fossil records behind
o The Cretaceous was a tectonically active time, in contrast the further back in time, it was
less tectonically active in the Permian, Triassic, and Lower Jurassic when we had Pangea
o Paleogeography is really driving the ecosystem and evolution
• Dinosaurs achieved a global distribution
o In the Triassic only have some dinosaurs
▪ Pangea still together
o Dinosaurs became more abundant and diverse in the Jurassic
▪ Small land bridge still connecting N. America and S. America
o When we get into the Cretaceous we get so many dinosaurs, immense diversity
• Distribution
o Vertebrates are rarer than invertebrates
▪ Vertebrates have also contributed to reconstruction of the world
o Geographic distribution
o Temporal distribution
o Want to look at how they geographically distributed through time
o Rare fossils of two species together
▪ If we do find this, then we know the two species lived together (sympatric)
▪ Famous fossil of a Proceratops and a Theropod locked together in a fight and
died together so know they lived together in the same area at the same time
o Rare fossils of interspecific behavior
• Geographic distribution
o Endemism – Endemic taxa or Indigenous are concentrated/related to one area. Not
world wide, cosmopolitan distribution
▪ “Restriction to one area”
o Endemic taxa
o Indigenous taxa
o Migration routes are shut down
▪ From Mid-Jurassic onwards, particularly in the Cretaceous, had endemism very
present because of restriction to one area because of water ways in between
▪ In the Triassic into the Early Jurassic, endemism has not developed well
o Continental separation
• Temporal Distribution
o A new dinosaur genus occurred every 4-8 Million years
▪ These numbers are revised with time as more discoveries occur
o Possibly exceeded at time of mass extinctions
▪ Emptying an ecosystem, allowing for a faster evolutionary step, so the numbers
go up more quickly in that time
• Ceratopsian Dinosaurs
o Relatively complete fossil record
o A new species every 1.9 Million years
o Stegosaurs produced 1 new species every 5.6 Million years
• Minimum Divergence Time – Measurement of how fast dinosaurs evolved
▪ Have a measured stratigraphic section, with a certain time for the section. Have
the levels where dinosaurs X and Y were found, and there is 25Ma in between.
Do X and Y have a common ancestor? If we do not know then we are talking
about a Ghost Lineage. For these two dinosaurs the minimum divergence time is
25Ma.
o Used for estimation of fossil completeness
▪ The smaller the number the better (the more complete the fossil record is)
o MDT’s in Ceratopsian dinosaurs
o Good candidate for temporal and geographic distribution studies
• Late Triassic (231-208Ma)
o Time of Pangea
o Heat and aridity (deserts)
o Very continental climate
o Strong seasons
o Low endemism
▪ No restricted migration routes
o Mountain range between Northern and Southern hemisphere as a result as a result of a
collision between the two continental masses
▪ Could have of functioned as a barrier separating southern and northern
dinosaurs
o Lines are spreading ridges where spreading will take place
▪ Pictured: Herrerasaurus, Eoraptor, Plateosaurus, Coelophysis, Stounikosaurus
o Who was around?
▪ Therapsids
▪ Archosaurs
▪ Pterosaurs
▪ Early mammals
▪ Earliest dinosaurs (231-223 Ma)
• Ex. Eoraptor
• Not a large species diversity
▪ Land dwelling crocodiles with long legs which would have been large predators,
small mammals, ancient reptiles, and Pterosaurs
o Eoraptor
Document Summary
Erth 2401 lecture 19: dinosaurs role in. In jurassic there was a spike in diversity, which can be attributed to the separation of. Pangea, showing there is a relationship to paleogeography: biased. Restriction to one area : endemic taxa, migration routes are shut down. Indigenous taxa: from mid-jurassic onwards, particularly in the cretaceous, had endemism very present because of restriction to one area because of water ways in between. Have the levels where dinosaurs x and y were found, and there is 25ma in between. If we do not know then we are talking about a ghost lineage. For these two dinosaurs the minimum divergence time is. 25ma: used for estimation of fossil completeness, the smaller the number the better (the more complete the fossil record is, mdt"s in ceratopsian dinosaurs, good candidate for temporal and geographic distribution studies. Late triassic sea level close to present day.
