1. Fig. 3: Temperature trend through Late
Cretaceous (adapted from [3] )
INTRODUCTION
Fig. 4: Body size disparity in Late Cretaceous (adapted from [1])
Thermal max of Late Cretaceous – Initial radiation
• Thermal inertia supported early ectothermic small
forms (Fig. 4 and 3)
Coniacian cooling, larger forms appear (Fig. 4)
• Larger, less sensitive to temperature change,
possible development of endothermy (Fig. 2,
points circled in green), increase latitude range
Mid-Campanian cooling – lowered diversity (Fig.2)
• Then mosasaurines dominate the end Cretaceous
(Fig. 2 and 3)
Small keeled scales and fibre bundles (Fig. 6)
• May reduce surface deformation and frictional
drag in water
Minimal creasing (Fig. 5) – for smooth body surface
• Shows strong influence of aquatic environment to
improve swimming efficiency
(However, scales may also be useful for concealment
and protection from ectoparasites [5])
Mosasaurs originated during high sea level
(Cenomanian-Turonian highstand, Fig. 7)
• Sea level – associated with tectonic plate
movements and formation of epicontinental
oceans [1]; Potential indirect impact on mosasaur
evolution via productivity?
Thamasha Perera (tp15231@my.bristol.ac.uk) Department of Earth Sciences, University of Bristol
What were the most influential physical drivers of mosasaur evolution?
METHODS 1: Sea Surface Temperature (SST)
• 43 generic and 94 species-level taxa analysed
• Taxonomic diversity and body size compared to
SST in Late Cretaceous
• Temporal ranges and estimates of body size –
taken from the literature [1]
• Lithologic samples – analysed with thin section
petrography & scanning electron microscopy
(SEM) [2]
RESULTS 1: Sea Surface Temperature
DISCUSSION
CONCLUSIONS
REFERENCES
1. Polcyn, M.J., Jacobs, L.L., Araújo, R. et al. (2013) ‘Physical drivers of mosasaur evolution’.
Elsevier. 400(2014):17-27
2. Jacobs, L.L., Polcyn, M.J., Taylor, L.H. and Ferguson, K. (2005) ‘Sea-surface temperatures
and palaeoenvironments of dolichosaurs and early mosasaurs’. Netherlands Journal of
Geosciences. 84(3):269-281
3. Friedrich, O., Norris, R.D. and Erbacher, J. (2012) ‘Evolution of middle to Late Cretaceous
oceans – a 55 m.y. record of Earth’s temperature and carbon cycle.’ Geology. 40:107-110
4. Lindgren, J., Everhart, M. and Caldwell, M.W. (2011) ‘Three-dimensionally preserved
integument reveals hydrodynamic adaptations in the extinct marine lizard Ectenosaurus
(Reptilia, Mosasauridae)’ PLoS ONE. 6(11)
5. Lindgren, J., Alwmark, C., Caldwell, M.W. and Fiorillo, A.R. (2009) ‘Skin of the Cretaceous
mosasaur Plotosaurus: implications for aquatic adaptations in giant marine reptiles’ Biology
Letters.
6.The Geological Society (2012) Upper Cretaceous. [ONLINE] Available at:
https://www.geolsoc.org.uk/Groups-and-Networks/Commissions/Stratigraphy-
Commission/Brief-Summary-of-British-Stratigraphy/Upper-Cretaceous [Last accessed: 1st
November 15]
METHODS 2: Hydrodynamics [4][5]
• Fossilised integument photo-documented with
camera and binocular microscope
• Dermal fibre bundles coated in water to increase
contrast in photographs
• SEM samples affixed to glass slides and studied
under low vacuum
METHODS 3: Sea level
• Same as for Methods 1 – except
taxonomic diversity compared to Sea
Level in Late Cretaceous [1]
RESULTS 2: Hydrodynamics
RESULTS 3: Sea level
Fig. 2: Taxonomic diversity (adapted from [1])
Figure 5: Mosasaur scales
with topographical line
drawings [5]
Origin of mosasaurs
Mosasaurs first appeared 98 million years ago (Ma)
in the Cenomanian stage of the Late Cretaceous
(Fig. 1) [1]. In their relatively short span of 32.5
million years, this group of marine reptiles
exhibited an impressively vast array of taxonomic,
morphological and physiological diversity,
becoming the dominant marine predators for most
of the Late Cretaceous [1]. Mosasaurs went extinct
at the Cretaceous-Palaeogene (K-Pg) boundary
(65.5 Ma) when a bolide impacted Earth [1].
Fig. 7: Sea level estimates and diversity
in Late Cretaceous (adapted from [1])
HYDRODYNAMICS -- biological drivers part-
responsible for scales, scales and fibres from two
specific species, not representative of all clades
SEA-LEVEL – impacts taxonomic diversity, less
influential than temperature
Therefore, SEA SURFACE TEMPERATURE, facilitating a
number of factors across several clades, was likely the
strongest physical driver of mosasaur evolution.
Alternatively: COMBINATION of sea surface
temperature and sea level – strongest physical
influence on mosasaur evolution INDIRECTLY via
driving productivity (biological factor); formation of
epicontinental seas with abundant food, driving
evolution of mosasaurs.
Similar studies on contemporaneous marine reptiles to
identify common evolutionary consequences of
physical drivers should be carried out.
Figure 6: Photo-documented
fibres and keeled scales
(adapted from [4])
FUTURE WORK
Drivers of evolution
A wide variety of factors were responsible for the
aforementioned diversity and success of
mosasaurs, of which the key physical ones will be
considered here.
Figure 1: Stages of the Late (Upper)
Cretaceous [6]