1. The study analyzed tetrapod diversity over the Jurassic-Cretaceous boundary using subsampling methods to account for biases in the fossil record. 2. Results showed a prolonged decline in tetrapod diversity through the transition period rather than a single mass extinction event. Extinctions targeted more basal groups and were highest in late Jurassic. 3. Primary drivers of global diversity changes were found to be eustatic sea level changes and paleotemperature, though sampling effects could not be fully ruled out.

1. A hidden extinction in
tetrapods at the Jurassic-
Cretaceous boundary
Jonathan Tennant

2. Thanks! • NERC
• PALASS
• SVP

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)

8. Methodological approach
•Subsampling (SQS) and
phylogenetic diversity
estimates (PDE)
•Model-fitting of extrinsic
parameters
Jon Tennant Methods

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

14. What controls global J/K diversity?
Jon Tennant Results
Group
Non-marine
rho p-value
Adjusted
p-value
r p-value
Adjusted
p-value
Aves 0.321 0.498 0.988 -0.174 0.708 0.865
Choristoderes -0.500 1.000 1.000 -0.509 0.660 0.865
Crocodyliformes 0.273 0.448 0.988 0.015 0.967 0.967
Lepidosauromorphs 0.050 0.912 1.000 0.317 0.406 0.757
Lissamphibians 0.000 1.000 1.000 -0.340 0.371 0.757
Mammaliaformes 0.079 0.838 1.000 -0.292 0.413 0.757
Ornithischians 0.209 0.539 0.988 0.424 0.539 0.847
Pterosaurs 0.521 0.123 0.451 0.309 0.387 0.757
Sauropodomorphs 0.736 0.024 0.264 0.733 0.031 0.171
Testudines -0.117 0.776 1.000 -0.094 0.810 0.891
Theropods 0.531 0.079 0.435 0.790 0.004 0.044
Marine
Chelonioides -0.500 1.000 1.000 -0.474 0.686 0.842
Crocodyliformes 0.690 0.069 0.138 0.740 0.036 0.144
Ichthyopterygians 0.612 0.060 0.138 0.479 0.166 0.332
Sauropterygians 0.335 0.263 0.351 0.061 0.842 0.842
Spearman's rank Pearson's PMCC
Tetrapod-bearing
Collections
No correlations with
Formations
Raw diversity is over-
printed by sampling

15. What controls regional subsampled diversity?
(Europe)
Jon Tennant Results
rho p-value
Adjusted
p-value
r p-value
Adjusted
p-value
Raw richness 0.671 0.006 0.034 0.513 0.042 0.167
Collections 0.468 0.070 0.140 0.474 0.064 0.167
Occurrences 0.512 0.045 0.135 0.446 0.084 0.167
Good's u -0.147 0.616 0.660 -0.348 0.223 0.267
Formations 0.326 0.173 0.259 0.328 0.171 0.256
Global sea-level -0.115 0.660 0.660 -0.153 0.557 0.557
Subsampled richness
Crocodyliformes 0.036 0.964 0.964 0.381 0.400 0.599
Lepidosauromorpha 0.657 0.175 0.525 0.449 0.372 0.599
Ornithischia 0.091 0.811 0.964 0.323 0.363 0.599
Pterosauria -0.107 0.840 0.964 0.277 0.547 0.657
Testudines -0.257 0.658 0.964 0.034 0.949 0.949
Theropoda 0.527 0.123 0.525 0.605 0.064 0.383
Europe
Pearson's PMCCSpearman's rank
• Raw tetrapod diversity
strongly correlates with
outcrop area (non-marine)
• SQS diversity for individual
clades shows no relationship
• No correlations with outcrop
area in the marine realm

16. What controls regional subsampled diversity? (N.
America)
Jon Tennant Results
rho p-value
Adjusted
p-value
r p-value
Adjusted
p-value
Raw richness 0.346 0.206 0.309 0.278 0.315 0.464
Collections 0.446 0.097 0.292 0.561 0.030 0.089
Occurrences 0.386 0.157 0.309 0.388 0.153 0.305
Good's u -0.073 0.839 0.965 -0.290 0.387 0.464
Formations -0.012 0.965 0.965 -0.146 0.589 0.589
Global sea-level 0.581 0.016 0.098 0.630 0.007 0.040
Subsampled richness
Ornithischia 0.150 0.708 0.708 0.268 0.485 0.485
Theropoda -0.452 0.268 0.536 -0.404 0.321 0.485
North America
Pearson's PMCCSpearman's rank
rho p-value
Adjusted
p-value
r p-value
Adjusted
p-value
Raw richness 0.429 0.113 0.332 0.509 0.053 0.133
Collections 0.154 0.584 0.683 0.454 0.089 0.133
Occurrences 0.146 0.602 0.683 0.474 0.074 0.133
Good's u 0.300 0.683 0.683 0.298 0.626 0.626
Formations 0.479 0.166 0.332 0.457 0.185 0.221
Global sea-level 0.463 0.063 0.332 0.702 0.002 0.010
North America
Spearman's rank Pearson's PMCC
Non-marine
Marine
• Outcrop area correlates
with sea level in marine
and non-marine realms
• Therefore cannot rule
out regional level
‘common cause’

17. Environmental factors governing diversity
Jon Tennant Results
Likelihood Weight rho
adjusted
p-value
r
adjusted
p-value
Crocodyliformes (marine) Palaeotemp. 22.741 0.237 -0.524 0.634 -0.522 0.678
Crocodyliformes (non-marine) Sea level 26.285 0.969 0.750 0.175 0.846 0.028
Lissamphibia Palaeotemp. 38.260 0.796 0.700 0.301 0.742 0.154
Mammaliaformes Sea level 51.394 0.931 -0.450 0.537 -0.666 0.301
Ornithischia Sea level 60.106 0.391 0.200 0.681 0.047 0.898
Pterosauria Sea level 33.261 0.872 0.714 0.406 0.647 0.581
Sauropodomorpha Sea level 41.191 0.501 0.310 0.810 0.457 0.564
Sauropterygia Sea level 41.820 0.409 0.055 0.906 0.065 0.985
Testudines Palaeotemp. 50.648 0.258 0.343 0.880 0.462 0.891
Theropoda Sea level 72.931 0.534 -0.018 0.968 0.037 0.954
AICc Pearson's PMCCSpearman's rank
Group Parameter

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