Dinosaur Thermoregulation Were They “Warm Blooded”?

Body temperature in endotherms and ectotherms

Thermogram of ostriches Thermogram of a snake wrapped around a human arm

Thermogram of a python held by people Thermogram of a lion Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Physiology, metabolism, and dinosaurs? Ornithopods Birds Sauropods Dromeosaurs Tyrannosaurus Ceratopsians Pachycephalosaurs Crocodilians Stegosaurs Ankylosaurs Lizards and snakes Lizards

“extant phylogenetic bracket”

Using phylogenetic logic to reconstruct biology of extinct animals.

Features observed in living animals can be traced back to common ancestor. This suggests that extinct clades that fall between are likely to have similar in features even if they cannot be observed directly in the fossils.

Thermoregulation

Maintaining body temperature within limited boundaries regardless of temperature of the surrounding environment.

Endotherm vs. Ectotherm

Endotherms use internal metabolic heat to regulate themselves, ectotherms use external sources of heat (and cool). Mammals and birds are endotherms, most other vertebrates are ectotherms.

Homeotherm vs. Poikilotherm

Homeotherms have a constant body temperature, poikilotherms have a variable body temperature. Mammals are homeotherms, but so are ﬁsh that live in water of constant body temperature. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Endothermic groups In-between groups Mammalia (mammals) Very large animals (inertial Aves (birds) homeotherms) Animals with unusual physiology (tuna are endothermic)

Unknown groups Ecothermic groups Non-avian dinosaurs most fishes Amphibia Pelycosaurs (non-mammalian synapsids) Lepidosauria (lizards and snakes) Crocodilians Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Source of internal heat

Anaerobic metabolism Produces lactic acid Less energy stored in ATP

Aerobic metabolism

Mechanisms for regulating body temperature

Regulate production of heat by changing metabolism • shivering • torpor Regulate amount of blood at surface of body • “counter current” exchange (arteries and veins intertwine in legs and other places so that outgoing blood is cooled by returning blood and vice versa) • dilation and constriction of blood vessels (blushing, shock) Insulation • hair • feathers • subcutaneous fat Evaporative cooling • sweating • panting Behavioral regulation • sunning • moving into shade • denning • lying on cool mud or in water • Expose wing surfaces Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Behavioral thermoregulation in an ectotherm

Changes in body temperature in ectothermic poikilotherm

95F

From Shine, 1991, Australian Snakes, A Natural History, Cornell. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Poikilotherm and variation in body temperature Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Inertial homeothermy probable in large dinosaurs

Large animals retain heat because their surface area is proportionally smaller.

An inertial homeotherm is an ectotherm that is so large that it cannot exchange heat across the surface fast enough to keep up with changing environment temperature. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Metabolic rate is related to body size in ectotherms (mammals)

1.50 /hr/g)

2 1.00

0.50

0.00

-0.50

-1.00

Logmetabolic rate(O -1.50 -4.0 -2.0 0.0 2.0 4.0

Vertebrate dietary categories

Omnivore - mixed diet

Frugivore - diet Herbivore - generalized specializing on fruits (only diet on plant leaves and exists after the stems Cretaceous)

Granivore - diet Piscivore - carnivorous diet specializing on seeds and specializing on fish nuts

Insectivore - diet specializing on insects (and sometimes other Carnivore - generalized diet invertebrates, like of flesh and fat worms) Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Energy value in different food sources

Small ectotherms = high metabolic rate = high calorie diet = small animals must be insectivores and granivores Large ectotherms = lower metabolic rate = lower calorie diet = large animals can be herbivores and frugivores

700

525

350 kcal per 100 g

175

Skeletal evidence for conserving heat

Deterministic growth and physiology

Deterministic growth: rapid growth to fixed adult size (birds and mammals)

Indeterminate growth: slower growth with no maximum size

Structure of mammalian bone Haversian system - blood vessels nourish osteocytes, chondrocytes, and provide minerals for bone deposition in concentric rings around the vessels

Histology of fossil bone Osteons (or Haversian structures

Bone histology and the rate of growth in dinosaurs

How big was Titanoboa?

Regression of SVL on vertebra width P < 0.001, R2 = 0.7

Total body length: 12.82 m +/- 2.18 m (42 ft) Body mass: 1,135 kg (1.27 tons)

Head, J.J., J.I. Bloch, A.K. Hastings, J.R. Bourque, E. Cadena, F. Herrera, P.D. Polly, and C.A. Jaramillo. 2009. Giant boine snake from a Paleocene Neotropical rainforest indicates hotter past equatorial temperatures. Nature, 457: 715-718. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Global Climate for the last 65 million years Present 14 C (57.2 F)

Last Glacial Maximum 9 C (48.2 F)

Miocene Climatic Optimum 21 C (70 F)

Eocene thermal maximum 23-26 C (73-79 F)

Titanoboa’s world

(Zachos et al., 2001. Science, 292: 686-693) (© 2010, Ron Blakey, NAU Geology) Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Climate in the Paleogene circles = no frost intolerant plants squares = palms triangles = cycads, gingers or tree ferns

Eocene Metasequoia stumps, Axel Heiberg Island (photo by Greenwood)

Why was Titanoboa so big? Size, metabolism and temperature in poikilotherms*

mass specific metabolism b is lower in larger organisms, placing limit on maximum size (B = base metabolic rate, M = body mass)

Max size (Lmax) is function of temperature and base metabolic rate Record sizes for living poikilotherms

Relative size is proportional to temperature

Makarieva, A.M, V.G. Gorshkov, and B-L. Li. 2005. Temperature- associated upper limits to body size in terrestrial poikilotherms. Oikos, 111: 425-436. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Reptile paleothermometer Estimated temperatures at Titanoboa site

Minimum MAT from Titanoboa : 32-33°C

Minimum MAT from giant fossil turtle: 32-33°C

dO18 from Forams: 28-31°C

fossil plants: 26-28°C (known underestimate)

Other giant reptiles of the Paleocene Size evolution in relation to climate Palaeophis snake

Gigantophis snake

podocnemidid turtle

Sea-surface temperature today

28°F 87°F

Middle Cretaceous 34°C - 42°C 93°F - 107°F