These notes summarize the more important points we have covered in The History of Life up to this point. These notes reflect a version from Sunday 10/13 at about midnight. I don’t expect them to change greatly after this version. If anyone spots any errors or other things that need to change, please let me know.

A note about the purpose of these notes:

- I post these notes to help you better understand what we covered in class. I know they are unlikely to answer all your questions, but I hope they will be helpful. Given the informal manner of class, with mixed video, commentary, and discussion, I can imagine that it’s important to have me lay out what I consider to be the essential points.

- Some of these notes may contain a bit of information we talked very little about (if at all); I will do my best to make sure that all midterm questions do not rely on information that was not emphasized.

- The notes may not be comprehensive, and they are not intended to be a replacement for participating in the class. Please integrate these notes with those from class.

- I expect you to be familiar with the diversity of common viewpoints associated with public policy issues that comes from opinions posted on this website and from in-class discussions of pros and cons. If you understood what we talked about in class you’ll be fine.

- You should know the answers to the questions you answered on quiz 1.

Each week, we explored the following:

(Week #:) topic and age

Critical thinking: Question to ask and answers

How things work: Concept(s)

Information to remember

Relevance to modern society: Public policy issues

Week 1: “Hyde Park mastodon” preserved in mud in pond in eastern New York State

age: about 11,000 years old

Question to ask: What makes this find special?

- complete and perfectly preserved mastodon, apparently of an animal that died in the pond

- opportunity to carefully document everything around the skeleton

- human interest story: found in a family’s backyard in the suburbs

Concept: Making a fossil

- fossils form when remains or other evidence of life gets buried

- remains have an opportunity to get buried primarily in aquatic settings

- aquatic settings are special because these are places where sediment – mud and sand – accumulate

- soft parts normally do not preserve because they are eaten by bacteria (rotting), insects, and other organisms

- sediments in ponds 11,000 years old normally have not experienced conditions that would harden them into rock

- bones that are 11,000 years old are geologically young and have not filled with minerals the way, for example, dinosaurs bones (over 65 million years old) normally are

- the kinds of animals that most readily become fossils are those whose bones are most likely to end up being buried in an aquatic setting

- large bones may also have a better fossil record than small, simply because they are most likely to survive weathering before burial than smaller, more fragile bones

- many mastodon skeletons have been found in NY State, because many ponds from the last Ice Age glaciation are found in NY; few of these skeletons, however, are complete or very well preserved, because many are from carcasses that rotted and were gradually washed into the pond and suffered damage and loss before burial

Concept: Looking for and excavating vertebrate animals from ponds

- at this point, it is difficult to go looking for mastodon skeletons in ponds, because of the work involved

- most mastodon skeletons are found by accident, during pond dredging or draining

- the highest quality work documents the spatial location of all bones and other kinds of evidence before removing them

- excavations are the work of teams of people of diverse backgrounds

Concept: Geological age

- the age of the mastodon can be calculated in years using radiometric techniques (in this case, carbon dating)

- the age can also be determined “relatively,” using other fossils and other geological evidence

- in practice, a number of dates, both radiometric and relative, are used to make sure there is no serious error in the date; “confluence of evidence” is the use of accumulated independent evidence to make an argument progressively stronger

Information to remember

- mastodons are a kind of prehistoric elephant that went extinct about 10,000 years ago; compared to mammoths and modern elephants, they were relatively straighter-backed, shorter, longer, and stockier; their diet emphasized brush, often cedar branches, as opposed to grasses

- New York was covered by Ice up to about 15,000 years ago, and then this gradually melted back (northward); by 11,000 years ago continental glaciers had left NY, but a number of ponds and lakes were left behind

- paleontology is the study of fossils; fossils are remains of past life; dictionary definitions say fossils are more than 10,000 years old, but of course this is an arbitrary distinction

Week 2: “Jarkov mammoth” preserved in ice in Siberia

age: about 20,000 years old

Concept: Cases of exceptional preservation

-the vast majority of all fossils are hard parts, the impression of hard parts, or tracks and trails left by the animal

- preservation of soft issue is very rare

- occasionally, in special circumstances, soft tissue is preserved; the most exquisite preservation occurs in ice, but some soft tissues can also be preserved as carbon in rocks in which bacterial decay is slowed, or substances like amber (hardened tree sap), which seal the remains off from the outside environment

- these cases of exceptional preservation can be extremely important for providing an especially clear “window” on past life

Concept: Fossils are found both locally and in exotic places; successful excavations often require cooperation of local residents

- contrast the excavation of the Hyde Park mastodon, found in someone’s backyard in a New York State suburb, with the Jarkov mammoth, found in a remote part of Siberia populated by nomadic reindeer herders. In each case the local people were the ones to first find the remains and provided help make the excavation a success

Concept: An important part of an excavations is doing complete detective work, so that the environment and death of the animal can be reconstructed as fully as possible; the materials studied include:

- plants, as determined from leaves, twigs, seeds, pollen, spores

- animals: bones & teeth, shells, trackways if preserved

- some other indicators of past environments:

- concentration of charcoal are an indicator of past fires and thus aridity;

- stable (non-radioactive) isotopes of carbon, oxygen, and nitrogen give a wide variety of information on variables such as temperature, seasonality, kinds of plants, etc.

- sediments indicate conditions and direction of water flow

Concept: Geologic time

- geologists typically think about the ordering of events, rather than the number of years; in fact, the geologic time scale was used for a century before anyone knew how old any of the rocks were in years

- geologists try to use events that occur over wide areas to “correlate” layers of rock from one area to the next

- geologists ascribed names to the time intervals between major events (such as big extinctions, or other events), as an easy way to refer to specific time intervals; you can imagine that it’s somewhat like using the “Renaissance” instead of years to refer to an interval

- geologists try to find multiple kinds of evidence to order events in time; the more kinds of independent evidence, the more confidence in the conclusion

- in general, the more recent the time interval, the more detail we know about it; there is an interface between geological history and written records, in which we can verify and calibrate geological records using human records

Concept: the Ice Ages

- sheets of ice covered New York State as recently as 20,000 years ago; these sheets grew and melted about 50 times in the past 2.5 million years

- technically, we are still in the “Ice Ages;” if “global warming” weren’t occurring, we might expect to re-enter an Ice Age time in about 50,000 years, and to be at the height of glaciation in another at 80,000 years from now

- a lot of what we know about Ice Ages comes not from the land, where glaciers themselves destroy some evidence of the previous glaciation, but in the deep sea, where sediment layers reflect the climate at the surface

- oxygen isotopes in shells of tiny plankton shells shows a detailed record of ice sheets; since so much water is tied up in glaciers during glaciations,. the ocean level drops slightly – over a 100 meters

Question: what makes this find special?

- a carcass found in ice gives information that is normally unavailable to paleontologists, including genetic material [some have suggested cloning, though this appears very unlikely]

- opportunities exist to carefully document all clues around the carcass

- human interest story: discovered by nomadic people in Siberia, study is an international adventure

Information to remember

- mammoths are a kind of elephant with a high “domed” skull, a sloping back, and long curved tusks that is now extinct; there have been several species of mammoths that lived in Europe, Asia and North America

public policy issue 1: cloning of ancient animals

context: some scientists have been interested in cloning very well preserved tissues of extinct animals such as mammoths and mastodons; there have been suggestions that DNA might be taken from a frozen mammoth or even from exceptionally well-preserved bone in a mastodon

[Note: various pros and cons of the public policy issues are reflected in the opinions posted on-line and in class discussions]

current scientific status: it is actually not possible now, and perhaps never will be, to clone an ancient animal, because the DNA needs to be whole

public policy issue 2: global warming

context: geological records indicate a close relationship between carbon dioxide (CO2) and temperature; since we can’t experiment with our own atmosphere to find out what will happen to climate in the future with increased CO2, perhaps the geologic record can give us information from Earth history about what happens

current scientific status: the general consensus is that global warming is both likely to occur based on our understanding of CO2 and climate, and is actually occurring; there is no question that global climate change has always occurred naturally; the real question, then, does not seem to be whether climate change will occur, but rather how quickly? and how much?

Week 3: hominid fossils found in rocks in southern and eastern Africa, for example “Lucy” (among others)

age: we discussed fossils about 3.5 to 0.2 million years old

Australopithecus

Homo

Question: what makes these finds significant?

- hominid skeletons are relatively rare, so each skeleton discovered reveals critical new information

- skeletal finds since the 1970s, and including several significant recent finds, shed light on the diversity of past hominids, and the way in which characteristics of our own species, Homo sapiens, were developed

Concept: paleontologists use modern animals as the basis for understanding the anatomy of fossil animals; scientists and artists work together to create depictions of what ancient hominids and other fossil animals looked like; but since fossil animals differ from modern animals in various respects, scientists must make sense of differences from modern animals in shapes of bones and positions of muscle scars in order to reconstruct ancient animals

- skeletons can be reconstructed, either literally or virtually (now with 3-D computer imaging); these days this part of the reconstruction is generally considered to be fairly well-constrained (though reinterpretations of skeletons has been made, especially of 19^th and early 20^th century reconstructions)

- muscles are attached to the skeletal reconstruction; this is somewhat well-constrained based on muscle scar patterns, though the muscles themselves are not preserved

- estimation of skin and fat are attached; our understanding of skin and fat are more poorly constrained; bones say little or nothing about features of fat and skin, so these are estimated based on similarities to similar extant (=animals that are still around) animals

- estimation of hair and color are added; hair and color are especially poorly constrained; hair type and color vary considerably according to environment, so reconstructions normally add hair and color to reflect according generalities known about environmental variations in hair type and color we see today

Concept: hominids are distinct from other primates in their upright posture, increased brain capacity, and flattening of the face, and decrease in the size of teeth and jaw muscles

- several important questions that “paleoanthropologists” ask about trends in hominid evolution that we encountered at least briefly in the hominid videos. They include:

......when did hominids first become nearly 100% bipedal (walking on two legs)?

+ leg joints and opening in the bottom (instead of back) of the skull, together with footprint, suggest a fairly highly developed ability for walking on two legs

+ recent finds of foot bones from South Africa suggest that early Australopithecus from about 3 million years ago still had elements of an opposable big to and relatively long arms compared to legs, characteristics useful to apes for climbing trees

what was the motivating force behind bipedalism?

+ in recent decades it has been suggested that climate change and greater aridity in eastern Africa led to grasslands and need for covering longer distances between forested patches, and/or in the long-run general adaptation to living on savanna

when did increased brain size occur relative to other anatomical changes?

+ evidence in recent decades suggests that some of the major trends in hominid evolution, such as bipedalism, occur before large changes in brain size

from which populations did Homo sapiens arise? Two contrasting ideas:

(a) Homo erectus is found all over Africa and Eurasia; Homo sapiens evolved independently (but with population intermixing) from H erectus populations in each location (Asia, Africa, etc.)

(b) though Homo erectus is found all over Africa and Eurasia, these populations are not the origin of modern humans; H sapiens arose in one locality in Africa and spread around the world; this idea is favored by many

Information to remember:

- hominids are human-like primates; they include Australopithecus and Homo, among others

- hominids first occur about 4+ million years ago, and possibly earlier

- today there is one species of Homo (Homo sapiens), but in the past there have been two or three or more species of hominids alive at one time.

public policy issue 3: hominid (including H. sapiens) remains:

context: some hominid remains that are being used to understand prehistory have been claimed by native peoples; note, however, that most of these cases concern remains up to about 10,000 years old, whereas our discussions in class were largely of remains about 3+ million to 100,000 years old.

current scientific status: a lingering question is how to identify remains as belonging to a certain group of modern peoples, for example whether bones older than a certain age (say, a thousand years old) can be ascribed to native peoples who live in a given region today, because of movement of human populations

Week 4: very large mammals found in middle and late parts of Cenozoic Era, some much larger than today

age: we discussed large mammals about 30 million to 10,000 years old

Indricotherium was the huge hornless rhinoceros – the largest land mammal known

Question to ask: Why are these animals especially interesting?

- to the general public, because of the intrinsic fascination with large prehistoric vertebrate animals

- to scientists, to the way in which size gradually increased in both herbivores and carnivores, which also occurred in dinosaurs and some other kinds of animals

- scientists are also interested in the phenomenon between 50,000 and 10,000 years ago, in which large land vertebrates (“megafauna”) died out; gradually the confluence of evidence is suggesting that spread of humans with Clovis spear points is correlated with these extinctions

Concept: Extinction

- Species of animals have been arising and going extinct throughout the history of animals (the past 600 million years).

- Based on what we see in the fossil record, most species of animals that have ever existed are already extinct.

- Really large extinctions in which many kinds of organisms go extinct nearly simultaneously are called “mass extinctions”; some call the extinctions since the megafaunal extinctions part of a 6^th mass extinction

Concept: the ecological significance of size

- mammals increased in size considerably from the beginning of the Cenozoic Era to the middle part of the era; even geologically recently (before the megafaunal extinction) there were many very large mammals on continents around the world

- increase in size is a phenomenon seen in many independent times and environments: dinosaurs, sea reptiles, whales, land mammals (among others) all originated as smaller animals that then diversified, some of which became enormous

- size has both pros and cons ecologically:

pros: it makes animals more effective predators or more effective at avoiding predation, greater body mass helps hold heat

cons: it makes gestation periods small, decreases number of offspring, and makes large quantities of food necessary, all of which means that populations are relatively small

Concept: behavior and physiology of past animals is based on modern animals

- behavior is not preserved directly, so clues must be sought

- documentaries depict fossil animals behaving as we might expect given our understanding of modern animals and on adaptations these animals clearly had, but this behavior is not necessarily well-known

Information to remember

- The Cenozoic Era is known as the Age of Mammals, because mammals are the most abundant and ecologically dominant vertebrate land animals during this interval.

- Mammals at the beginning of the interval are small; large mammals become more common as climate cools and grasslands expand, though other factors may play a role in increasing size.

public policy issue 4: extinction

context: many large mammals in various parts of the world apparently went extinct roughly at the time that humans with Clovis-spear points migrated in;

- thus, although large mammals today such as elephants appear to be a rare exception, in fact there have been many more elephant-sized mammals around the world since the middle of the Cenozoic, and geologically speaking they were around quite recently

- the possibility exists that human-induced extinction that we often think of as occurring in the 20^th century actually began with human ingenuity tens of thousands of years ago

current scientific status: although climate change at the end of the last glaciation may have caused some species to have unstable populations, the general consensus today is that human hunting had something to do with late Pleistocene epoch megafaunal extinction

Week 5: whales found in throughout Cenozoic Era

from land animals with whale-like characteristics to whales with land mammal characteristics

age: we discussed fossils about 50 million to 30 million years old (and of course their descendents continue afterward)

Concept: Adaptation

- animals that adapt to life in water adopt a certain number of traits, that develop in a step-like pattern

features of aquatic animals include streamlined body, including long and narrow head, teeth sometimes adapted for catching fish, limbs in the shape of paddles, development of a significant tail and dorsal fin, and adaptation to pressure in ears (among other organs)

“vestigial” features of life on land are common, such as possession of small tail limbs inside the flesh

Concept: fossilization potential of various kinds of animals

- different animals have different potentials for fossilization, and so we know a lot more about the history of some kind of animals than others

animals that live in or near water have a much better chance of being fossilized, because fossilization usually occurs in through being buried in sediment, which accumulates under water

animals with bigger, more robust skeletons have a better chance of withstanding weathering and other damage than small thin skeletons

animals that live in aquatic sediments that are easy to sample by paleontologists, such as along coastlines or shallow flooding on land by seas, are more likely to be collected

- the best fossil record is of shelly animals that live in and on sediment in water; the worst fossil records are of animals with fragile skeletons that live at high altitudes with dry climates, where very little sediment accumulates

- thus, one might imagine that whales have a pretty decent fossil record, especially smaller whales that lived in big rivers or along coastlines; big mammals that lived around ponds and lakes (watering holes) also have a pretty good chance at fossilization; hominids have a more sketchy fossil record, though it is considerably better because of intense interest in collecting

Information to remember:

- the first whale-like animals occur in sedimentary rocks from fresh-water settings fairly early in the Cenozoic Era, about the time many other modern groups of mammals first appear; these animals are rather crocodilian in shape and life-style

- later whales adapt to ocean habitats and become larger, but continue to be oriented around active hunting (we saw Basilosaurus in the video)

- eventually whales split into two groups, so-called toothed whales and baleen whales (which specialize on small shrimp like animals, krill, that live in plankton) – [we didn’t get to this in class]

public policy issue 5: hunting whales

context: many kinds of whales are now nearing extinction

- some of these have been hunted by native peoples for hundreds of years (or longer)

- whales, however, have an evolutionary history tens of millions of years long, and represent perhaps the largest animals that have ever lived

Week 6: Escalation in adaptation of predator and prey to each other

some predator-prey relationship today, the first marine animals (550-500 million years ago), the first dinosaurs (220-200 million years ago)

Why is interpreting ancient ecology interesting?:

- The history of animals and plants is in part the history of their relationships to each other

- Understanding how animals have adapted to their environment means in part understanding how they have adapted to each other; this, it turns out, is a “dynamic” relationship, always changing

Concept: Interpreting ancient ecology of the past

- We can’t see ecology happen, yet it leaves behind evidence

some evidence is detailed, from specific fossils, such as marks of predation left behind on bones and shells that are preserved

more speculative evidence is left behind by patterns of evolution: gradually increasing size, speed, thickness and spininess of shells, etc.

- the relationship of predators and prey is just one of many kinds of relationships among organisms (others could include parasitism, changing of the physical habitat, and so on), but it is direct and so a good example for considering ecology of the past

.....some kinds of predator-prey relationships fossilize well

larger size preserved as larger skeletons or larger shells

armor in dinosaurs, or spines and thicker shells among snails and clams; conversely, larger size, teeth adapted for crushing among predators

some kinds of predator-prey relationships preserve, but may be more speculative

greater speed, based on understanding of mechanics of skeletons, but problems can arise if no animals today are similar to animal of past (such as T. rex – how fast was it really?)

some kinds of predator-prey relationships may be difficult to establish due to lack of fossil evidence

increase in camouflage and predator ability to detect camouflage

Information to remember:

- the first sea animals are relatively small and weakly (or not) shelled; the first dinosaurs are small; so are the first mammals and the mammals at the start of the Cenozoic Era; size increase, diversification in kinds of predator and prey, and “escalation” occur through time