Teacher Resource for:

Evidence for mesothermy in dinosaurs

Table of Contents:

I. GENERAL USE OF Science in the Classroom

a. Student Learning Goals (general)

b. Using this Resource

i. Learning Lens

ii. Learning Notes

iii. References

iv. Thought Questions

c. Suggestions for Classroom Use

II. ARTICLE-SPECIFIC MATERIALS

a. Connect to Learning Standards

b. Summary of the Article for the Teacher

c. Discussion Questions

d. Related Multimedia Resources from HHMI|BioInteractive

GENERAL USE OF Science in the Classroom

Student Learning Goals: “One fundamental goal for K-12 science education is a scientifically literate person who can understand the nature of scientific knowledge.”1

The U.S. National Academy of Sciences defines science as: “Any new finding requires independent testing before it is accepted as scientific knowledge; a scientist is therefore required to honestly and openly report results so that they can readily be repeated, challenged, and built upon by other scientists. Proceeding in this way over centuries, the community effort that we call science has developed an increasingly accurate understanding of how the world works. To do so, it has had to reject all dogmatic claims based on authority, insisting instead that there be reproducible evidence for any scientific claim.” An important student learning goal, central to any understanding of “the nature of scientific knowledge,” is to give each student an appreciation of how science is done.

This includes knowing why: Scientists must be independent thinkers, who are free to dissent from what the

majority believes.

Science can deal only with issues for which testable evidence can be obtained.

All scientific understandings are built on previous work

It is to be expected that one scientist’s conclusions will sometimes contradict the conclusions of other scientists.

Science is a never-ending venture, as the results from one study always lead to more questions to investigate.

1 A Framework for K-12 Science Education, National Research Council, 2012

Using This Resource

Learning Lens:

The Learning Lens tool can be found on the right sidebar of each resource and is the source of annotations. Click on the headings to highlight portions of the text of the corresponding research article. A subsequent click on the highlighted text will produce a text box containing more information about that particular piece of text. Below is an example of the Glossary function of the Learning Lens.

An example of the resource with the Glossary, Previous Work, Author’s Experiments, News and Policy Links, and References and Notes tools turned on. The Glossary tool is in use.

Learning Notes:

Learning Notes accompany each figure and are designed to help students deconstruct the methods and data analysis contained within each figure.

References:

The Reference section of each resource is annotated with a short statement about how or why each reference relates to the current research study.

Thought Questions

Thought Questions are located above the Learning Lens in the right sidebar of each resource. These questions were written to be universal and applicable to any primary research paper. Thought questions do not have a single answer, or a correct answer for that matter, and can be used to stimulate discussion among students.

Suggestions for Classroom Use:

In addition to the thought questions discussed above, other resources are provided for use in the classroom. These can be found toward the end of the teacher guides associated with each specific article and include:

1. Discussion questions specific to the article, related to the standards, and/or associated with the figures.

2. Activities tied to the articles.

Some ways to use the Science in the Classroom articles:

1. Assign to student groups to read and discuss during class.

2. Assign small sections of the article to student groups to read and discuss during class, with the expectation that they will present or use jigsaw to teach the entire class what is in their part of the article.

3. Assign to individual students to complete during class or as homework.

4. Assign reading as an extra credit project.

Some ideas for interactive student engagement after reading the article:

1. Students write answers to discussion questions (for example, those linked to the standards or those linked to the diagrams).

2. Go over the abstract, as well as information about the purpose and structure of an abstract, and have students write their own abstracts for the articles in language that could be understood by their peers.

3. Have students edit the article, or parts of the article, to a simpler reading level.

4. Have students, alone or in small groups, use the annotated list of references to explain how the scientists who wrote this article built on the published work of at least one independent group of scientists in making their discoveries. In the

process, did they produce data that supports the findings of the earlier publication that they have cited in the text? In what way does this article support the statement that scientific knowledge is built up as a “community effort”?

5. Use the article and discussion questions linked to the standards and the diagrams for a teacher-led classroom discussion. The discussion can focus on the nature of science and scientific research, as well as on the science in the article itself.

6. Have students give a classroom presentation about the article, parts of the article, or their answers to discussion questions.

ARTICLE-SPECIFIC MATERIALS

Connections to the nature of science from the article

Were dinosaurs slow-metabolizing ectotherms like reptiles or fast-metabolizing endotherms like mammals and birds whose activities were unconstrained by temperature?

How can the resting metabolic rate of extinct species be determined using fossils?

The importance of this scientific research

This research furthers the understanding of how dinosaurs regulated their body temperature in comparison to known ectotherms and endotherms. It determines the resting metabolic rate of dinosaurs using maximum growth rate as measured by bone growth rings.

The actual science involved

Thermodynamics Paleontology

Connect to Learning Standards:

The Next Generation Science Standards

Science and Engineering Practice 2: Developing and using models Science and Engineering Practice 6: Constructing explanations (for science) and

designing solutions (for engineering)

The AP Biology Standards

Essential knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics.

Essential knowledge 2.A.1: All living systems require constant input of free energy. Essential knowledge 2.C.2: Organisms respond to changes in their external

environments. Essential knowledge 2.D.2: Homeostatic mechanisms reflect both common ancestry

and divergence due to adaptation in different environments.

Common Core English Language Arts

11.12.8: Evaluate the hypotheses, data, analyses, and conclusions in a science or technical test, verifying the data when possible and corroborating or challenging conclusions with other sources of information.

Summary of the Article for the Teacher:

It is recommended that this not be used by students in place of reading the article.

General Overview:

Dinosaurs were once thought to be slow, lumber giants with slow ectothermic metabolic rates. More recently, the skeletal structure of some dinosaur bones have lead scientists to conclude that dinosaurs were more agile and faster-growing than once thought. Fast resting metabolic rates (RMRs, a measure of energy expenditure) are typical of endothermic organisms like birds and mammals, which can maintain a constant body temperature higher than the ambient temperature. In contrast, ectotherms, such as amphibians, reptiles, and most fish, have slower RMRs and do not generate enough excess heat from metabolism to maintain a constant body temperature. Whether dinosaurs had energetic systems closer to endotherms or ectotherms is a difficult one to tackle, because the metabolic rate of extinct animals is not directly measurable. However, limited evidence from earlier studies suggests a relationship between the metabolic rate of an organism and its growth rate, which in turn can be determined from fossil bones. So what is this relationship, and how can it help us determine the metabolic rate of extinct species?

The researchers analyzed large, updated data sets on growth rate from both living and extinct vertebrates, using a method that considers body temperature and body size. This enabled the scientists to develop a mathematical model that predicts the relationship between metabolic rate, growth rate, and body size in living vertebrates.

Using these equations and reliable published data on growth rate and body size of dinosaurs, the researchers calculated the RMRs of 21 dinosaur species. The growth rate and age of an extinct animal can be estimated from growth rings in bones that, similarly to tree rings, are laid down annually. Overall bone dimensions, on the other hand, are a great indicator of the animal’s size.

The results placed dinosaurs squarely in an intermediate category in between living endotherms and ectotherms, known as “mesothermy.” The earliest birds—direct descendants of dinosaurs— plotted as mesotherms, too. Mesotherms, which include living tuna and leatherback turtles, use heat from metabolism to maintain an internal temperature higher than the outside temperature, but they do not “defend” a set temperature.

See also this In Depth feature, which concisely summarizes the findings of the paper: http://science.sciencemag.org/content/344/6189/1216.full

Topics Covered: Thermoregulation Metabolic rate Phylogeny Paleontology

Why this research is important:

For several decades, researchers have struggled to determine whether dinosaurs had energetic systems closer to those of rapidly metabolizing mammals and birds, or to those of slower reptiles that do not internally regulate their body temperature. Much of the previous research on this topic has been constrained by a lack of reliable comparative data and the difficulty of estimating metabolic rates of extinct species. Grady and colleagues used a new approach and updated data sets to determine the metabolic rates of 21 dinosaur species, placing them in an intermediate thermoregulation category called “mesothermy.” The findings suggest that the current dichotomy of endothermic versus ectothermic may be far too simplistic.

The study can also help us understand the ecological role dinosaurs played in their environment and why they were so successful, ruling Earth nearly uncontested until the asteroid struck. The climate at the time was overall hotter than today, and being a “full” endotherm to be active and fast-growing was not as necessary as in colder climates. In fact, some studies suggest that during the Mesozoic, mammalian endotherms kept their bodies at a lower set temperature than today. So mesothermy may have allowed dinosaurs to grow large and active at relatively low energetic costs compared with endotherms, filling the "large-animal” ecological niche before small, energy-craving endothermic mammals could evolve to become bigger themselves. In addition, being mesothermic probably meant that dinosaurs could easily outcompete the lethargic, ectothermic reptiles.

Methods used in the Research:

Comparative approach by determining the relationship between maximum growth rate and RMR in extant (living) species

Ontogenetic growth curve to determine maximum rate of growth Mathematical modeling Statistic analysis of existing data found in the literature

Conclusions:

High RMR correlates with fast growth rate. Therefore, an organism’s maximum growth rate can be used to predict its resting metabolic growth rate.

Endotherms have higher RMRs and growth rates, whereas ectotherms have lower RMRs and growth rates.

Dinosaurs had intermediate growth rates that correspond to intermediate metabolic rates similar to living mesotherms, such as the great white shark, tuna, and leatherback turtle.

Areas of Further Study:

How can analysis of fossil isotopes, which can shed light on body temperatures, be used to test the hypothesis that dinosaur species exhibited a range of mesothermy?

Using this method to determine metabolic rates in newborn and juvenile dinosaurs found in seasonally cool environments can give scientists more insight into Mesozoic ecosystems. The technique should be particularly useful in determining the energetic systems of certain groups of dinosaurs (pterosaurs and therapsids) and Mesozoic birds and might provide insights into phylogenetic relationships from a different perspective.

Discussion Questions:

Discussion questions associated with the learning standards

Essential knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics.

What is the mathematical equation derived by Grady and his colleagues to determine RMR from an organism’s maximum growth rate?

Essential knowledge 2.A.1: All living systems require constant input of free energy.

Compare the food requirements of an endotherm, mesotherm, and ectotherm of the same size.

Explain why a high RMR would support a fast maximum growth rate.

Essential knowledge 2.C.2: Organisms respond to changes in their external environments.

Predict what would happen with the metabolic rate of an endotherm, mesotherm, and ectotherm if these animals moved to a cooler environment than they live in now.

Essential knowledge 2.D.2: Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different environments.

How could a mesothermic metabolism have benefited the dinosaurs?

Which likely evolved first in the ancestors of modern birds: feathers or a high metabolic rate to support endothermy? Provide evidence to support your claim.

Is endothermy a shared homology between birds (paleognathae) and mammals (placentalia)? Provide evidence to support your claim.

The Science and Engineering Practices contained in the Next Generation Science Standards

Practice 2: Developing and using models

What information did Grady and colleagues use to develop a way to determine the RMR of dinosaurs?

Identify the variables the researchers controlled for when selecting data to use to develop the growth rate/RMR model.

Practice 6: Constructing explanations (for science) and designing solutions (for engineering)

Provide evidence and reasoning for the researchers’ claim that “some dinosaurs were mesotherms.”

The Common Core English and Language Arts Standards

Integration of Knowledge and Ideas: CCSS.ELA-Literacy.RST.11.12.8: Evaluate the hypotheses, data, analyses, and conclusions in a science or technical test, verifying the data when possible and corroborating or challenging conclusions with other sources of information.

What conclusions from prior studies did the researchers challenge? What justification do they provide for the validity of their own conclusions?

Discussion questions associated with the figures in the paper

Figure 1 Across the types (guilds) of thermoregulation, describe the relationship between a

species’s mass and its maximum growth rate.

In general, which type of thermoregulation has the highest growth rate at any given body mass?

According to graph B, dinosaurs had a growth rate most similar to which group of organisms? According graph A, to which thermoregulation type do these organisms belong?

Logarithmic scale graphs What is the bottom and top value for each of the following intervals?

a. 100 and 102 b. 104 and 106

Using graph B, how much greater is the growth rate of a mammal that has an adult mass of 108 g versus a mammal that is 102 g?

Figure 2 Compare and contrast mass-independent metabolic rates and growth rates of

endotherms versus ectotherms.

Which two groups of endotherms do not fall on the established theoretical prediction (solid line)?

Describe why a high metabolic rate would support an endotherm’s thermoregulation. (Hint: Apply the second law of thermodynamics.)

Which variable in Figure 2B can be measured in dinosaurs, and how is it measured?

If an organism had a mass-independent growth rate of 10-2 (g1/4d-1) what do you predict its mass-independent metabolic rate would be?

If an organism had a mass-independent growth rate of 10-3, what thermoregulation type would you predict it to be?

Figure 3 Using Figure 3B, describe the relationship between the mass of a species and its

metabolic rate.

Describe what Figure 3B illustrates regarding the metabolic rates of endotherms, mesotherms, and ectotherms.

What do you think? How would the amount of food required to support a 10-gram endotherm compare to the amount needed to support a 10-gram ectotherm?

What is the advantage and disadvantage of being an endotherm versus an ectotherm?

How was the predicted metabolic rate of the dinosaurs determined?

How does Figure 3A contribute to the validity of the dinosaur prediction?

What do you think? How could a mesothermic metabolism have benefited the dinosaurs?

Figure 4 According to Figure 4, which group of organisms do dinosaurs share a more

recent common ancestor with: fish (sharks, groupers, tuna), mammals (placentalia, echidna), reptiles (turtles, crocodiles), or birds (paleognathae)?

Which likely evolved first in the ancestors of modern birds: feathers or high metabolic rate to support endothermy? Provide evidence to support your claim.

Is endothermy a shared homology between birds (paleognathae) and mammals (placentalia)? Provide evidence to support your claim.

Multimedia Resources from HHMI’s BioInteractive (www.BioInteractive.org)

eBook (iTunes)Mass Extinctions: Lessons from the Past (https://itunes.apple.com/us/book/mass-extinctions/id1087203609?mt=13). This free book showcases the work of HHMI BioInteractive, including interactive graphics, animations, and videos, designed to examine the evidence and causes of mass extinctions and what we can learn about how humans are affecting the planet.

Short Films and VideosGreat Transitions: The Origin of Birds (http://www.hhmi.org/biointeractive/great-transitions-origin-birds). In the second film of the Great Transitions trilogy, paleontologist Julia Clarke takes us on a journey to uncover the evidence that birds descended from dinosaurs. Also available as interactive video with embedded quiz: http://www.hhmi.org/biointeractive/origin-birds-quiz.

The Day the Mesozoic Died (http://www.hhmi.org/biointeractive/day-mesozoic-died). The disappearance of the dinosaurs at the end of the Cretaceous period posed one of the greatest, long-standing scientific mysteries. This three-act film tells the story of the extraordinary detective work that solved it. Also available as interactive video with embedded quiz: http://www.hhmi.org/biointeractive/mesozoic-film-quiz.

Scientist at Work: How To Find a Dinosaur (http://www.hhmi.org/biointeractive/how-find-dinosaur). Paleontologist Tyler Lyson describes dinosaur digs and his focus on prehistoric turtle fossils.

Feature FilmMass Extinctions: Life at the Brink (http://www.hhmi.org/biointeractive/mass-extinction-life-brink and http://www.smithsonianchannel.com/shows/mass-extinction-life-at-the-brink/0/3413789). Mass extinctions have ocurred at least five times in the past, and some experts believe a manmade mass extinction could be next. Is our planet in trouble? And if so, is

there anything we can do to stop the sixth mass extinction? Experts are traveling the world, performing groundbreaking scientific detective work to answer these very questions.

CollectionExtinctions (http://www.hhmi.org/biointeractive/explore-extinctions). A variety of engaging videos, films, lectures, online interactives, posters, and classroom activities to teach key concepts related to extinctions past and present.

Online InteractivesMass Extinctions Interactive (http://www.hhmi.org/biointeractive/mass-extinctions-interactive). Discover the environmental factors that caused the five big mass extinctions in Earth’s history and which species they impacted. Also available as poster: The Making of Mass Extinctions http://www.hhmi.org/biointeractive/making-mass-extinctions

Comparative Anatomy of the Domestic Chicken (http://www.hhmi.org/biointeractive/comparative-anatomy-domestic-chicken). Trace the evolutionary history of birds by comparing the shapes and structures of certain bones in a chicken to those of some of its extinct and living relatives.

Image of the WeekYour Turkey’s Ancestors (http://www.hhmi.org/biointeractive/your-turkey-s-ancestors). A reconstruction of Anchiornis huxleyi, a feathered dinosaur that is part of the ancestral lineage of birds.

Classroom ActivitiesHow Did Dinosaurs Regulate Their Body Temperature? (http://www.hhmi.org/biointeractive/how-did-dinosaurs-regulate-their-body-temperature). This activity uses data from Grady et al. (2014) to explore thermoregulation in living and extinct animals, including dinosaurs. Students learn about the methods used to determine the metabolic rates of these animals, and they will analyze, interpret, and graph scientific data.

Living Dinosaurs: Fact or Fiction? (http://www.hhmi.org/biointeractive/living-dinosaurs-fact-or-fiction). Students evaluate and discuss statements about the evolutionary relationship between birds and dinosaurs and other facts about these groups, before and after watching the short film Great Transitions: The Origin of Birds.