3. History of the Jurassic/Cretaceous boundary
• Pioneering work by Newell, Raup, Sepkoski (and his compendia)
• Originally considered to be a ‘major extinction’
• Understood general controls on the fossil record
• Current consensus: NOT a mass extinction
Jon Tennant Background
Raup (1976) Raup and Sepkoski (1982) Hallam (1986)
4. The structure of the fossil record
Jon Tennant Background
Smith and McGowan (2011)
Tennant et al. (2016)
Raw diversity is not a reliable
estimate of ‘true’ or relative diversity
The fossil record is affected by several
levels of sampling filters/’biases’
5. Why the J/K boundary?
Jon Tennant Background
Benson and Butler (2011)
Nicholson et al. (2015)
Zanno and Makovicky (2013)
Bronzati et al. (2015)
Newham et al. (2014)
6. What do we want to know?
1. What is the structure of changes in tetrapod
diversity over the J/K transition? Was there a
‘hidden’ mass extinction?
2. What external factors were responsible for
mediating these changes?
Jon Tennant Methods
7. Data. More data.
• 4907 species
• 15,472 occurrences, 7314 references
• Split into higher taxonomic clades
• Fully aquatic or non-marine
• Palaeocontinents
• Time binning methods
Jon Tennant Methods
Tennant et al. (2016)
9. • Tetrapod SQS diversity
falls in both the non-
marine and marine realms
• Finer clade-level dynamics
obscured
• Bootstrapping provides
constraints to overall
patterns
Jon Tennant Results
10. Dinosaur diversity
Jon Tennant Results
• SQS shows greatest decline in theropods
• Sauropods too poorly sampled in Berriasian
• PDE shows greatest decline in sauropods
• Decline less emphasised in theropods
11. Non-dinosaurian tetrapod diversity
Jon Tennant Results
• Staggered pulses of decline and radiation of new clades
• No singular marked ‘event’ at the boundary itself
• Smaller bodied sized animals generally more poorly sampled
12. Marine tetrapod diversity
Jon Tennant Results
• Earliest Cretaceous very poorly sampled
• Seems to track pattern of a global
eustatic lowstand
• Similar pattern seen in PDE
• Sampling from continuous lineages
great for ‘filling in the gaps’
13. A hidden mass extinction at the J/K
boundary?
• No. A prolonged wave of extinctions through the ‘transition’,
coupled with radiations of new groups
• Extinctions target more ‘basal’ groups, and are highest at the
end of the Jurassic
• Magnitude of diversity loss varies – ~33% for ornithischians
to 75-80% for theropods and pterosaurs
• High Late Jurassic origination rates for different groups do
not confer an extinction survival advantage
Jon Tennant Conclusions
18. What controls Jurassic/Cretaceous diversity?
• Primary driver on a global scale was eustatic sea level
• Palaeotemperature also an important factor
• Sampling over-prints raw diversity estimates
• Subsampling methods appear to alleviate sampling
issues
• Cannot rule out evidence of a local common cause
factor in North America
Jon Tennant Conclusions
19. • Major flood basalt and bolide activity
• Marine revolution in micro-organism communities
• Oligotrophic marine conditions likely related to the sea-level regression across the J/K boundary
• Have to consider all levels of an ecosystem and the environment to build a complete picture