Lesson 8: Evolution

Question 1

The theory of evolution was first conceived by the British naturalist ___ ___. His theory explains how new species come into existence, how organisms become adapted to their environments, and why specific groups of organisms share specific traits. It also correctly postulated that all life on Earth is related and shares a single common origin.

Answer 1

Charles Darwin.

Question 2

What are the 4 basic principles of life?

Answer 2

The differential success (3) of certain variations (2) of a heritable trait (1), because of competition for limited resources (4), leads to the change over time (evolution) of that trait in a population.

Question 3

What does heritable mean?

Answer 3

Heritable means that the trait is part of an organism’s genetic code and, therefore, either will be, or (depending on the type of reproduction) has a chance to be, copied to the organism’s offspring.

Question 4

What does variation mean?

Answer 4

Sometimes organisms have heritable traits that are new, not copied from the organism’s parent(s), i.e. random genetic mutation. In order for selection to occur on any given trait, there must be variation in that trait in a population.

Question 5

What does advantage (or, differential success) mean?

Answer 5

An organism’s traits affect how successfully that organism is able to reproduce (or survive and reproduce). One variation of the trait must provide an advantage (or, differential success) over the other variations in order for evolution to occur.

Question 6

What does competition mean?

Answer 6

Some of the versions of a given trait must be ‘selected out’ of a population in order for evolution to occur, and this must occur because of competition for limited resources.

Question 7

The organisms that have accumulated new traits are so different from their ancestors that they constitute a new ___.

Answer 7

Species.

Question 8

The competitive selective process by which detrimental traits are competitively discarded and advantageous traits are retained is called ___ ___.

Answer 8

Natural selection.

Question 9

Evolution provides a framework that modern taxonomy uses to categorize organisms. Organisms are grouped together based on their …?

Answer 9

Most recent shared common ancestors.

Question 10

These ornithischians and the saurischians share a more recent ancestor (a single species of amniote tetrapod)with each other than they do with all other amniotes, and we call this group ___.

Answer 10

Dinosauria.

Question 11

What is a character?

Answer 11

A character is any heritable trait that can be described and labeled.

Question 12

What is a shared derived character (synapomorphy)?

Answer 12

A shared derived character is a character that is present in two or more groups and their common ancestor, but is not present in any more distantly related groups.

Question 13

What is convergent evolution? Give an example.

Answer 13

The evolution of similar traits in two different lineages is termed convergent evolution. The sail (long processes on back) in Spinosaurus (a theropod with a long snout, sharp teeth, clawed fingers) and in Ouranosaurus (an iguanodont with a beak and grinding teeth, hoofed toes).

Question 14

Birds, pterosaurs, and bats all evolved wings from the forelimbs, but did so in different ways (convergent). Describe them.

Answer 14

Pterosaurs have a wing made of a membrane supported by just one long finger. Bats (which are mammals) have a wing made of a membrane supported by several fingers. And birds have a wing made of feathers, and have fused the hand bones into a single unit.

Question 15

What is parsimony (Occam’s razor)?

Answer 15

The idea that “all other things being equal, the simplest answer is usually the right one”.

Question 16

What are phylogenetic trees?

Answer 16

Based on the character matrix, the computer program applies the principle of parsimony to arrange the organisms in a sequence of relationships that requires the fewest instances of convergent evolution.

Question 17

What does the node on a phylogenetic tree represent? The branches?

Answer 17

A node is where two branches diverge, and shows the point at which two linages shared a common ancestor. After a node, the pattern of subsequent branches and nodes shows how the descendants of that common ancestor continued to diverge from each other.

Question 18

What is a clade?

Answer 18

A group of species that share a common node. Can be small (2 species) or large and must contain the ancestor of a group and all of its descendants.

Question 19

What is the Linnean Hierarchy? What is wrong with it?

Answer 19

Classifies organisms as belonging to a Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Mammalia (mammals), Aves (birds), Pisces (fish), and Amphibia (amphibians, lizards, snakes, crocodiles, and turtles, but also sharks, rays, and some fish!) were all classified at the equivalent rank of Class. But we can trace all four-limbed animals (the tetrapods, including mammals, reptiles, birds, and amphibians) back to a fish ancestor – Class Mammalia, Aves, and Amphibia are all a subset of Class Pisces (now called Osteichthyes).

Question 20

Who is Thomas Henry Huxley?

Answer 20

Was a close colleague of Charles Darwin and one of the earliest advocates for the theory of evolution. Huxley was also the first scientist to recognize that birds evolved from dinosaurs, and he cited the newly discovered specimens of Archaeopteryx as fossils of a “missing link” between dinosaurs and birds.

Question 21

Specimens of Archaeopteryx had been found exquisitely preserved in fossil lake deposits. What did they show?

Answer 21

These specimens clearly show that Archaeopteryx has long wing-feathers and tail feathers just like a bird, but they also show that Archaeopteryx had teeth, clawed fingers, and a long series of tail vertebrae just like a dinosaur. With the help of Archaeopteryx, Thomas Henry Huxley showed that transitional forms do exist in the fossil record, just as the theory of evolution predicted, and also showed that birds are a branch of the dinosaur family tree.

Question 22

What did the specimen of the little dinosaur Sinosauropteryx show?

Answer 22

Sinosauropteryx was the first non-avian (non-bird) dinosaur to be discovered with feathers. The feathers of Sinosauropteryx had a simple structure compared to the feathers of modern birds and were used for insulation, not for flight, but they were feathers just the same.

Question 23

Many other small theropod specimens have since been found with feathers, some with complex flight feathers. Recently, feathers have also been found on specimens of the large tyrannosauroid ___, showing that some large dinosaurs had them as well.

Answer 23

Yutyrannus.

Question 24

___ are the only clade of dinosaurs alive today.

Answer 24

Birds.

Question 25

Many palaeontologists use Aves to refer to the crown group of birds, which includes all living birds as well as extinct taxa like the dodo and moa. Another clade name, Avialae, is generally equivalent to ‘flying dinosaurs’, which includes extinct species that looked very similar to modern birds, including Archaeopteryx. However, ‘birds’ can be defined in several ways. Name 4 and their problems.

Answer 25

• Definition 1: Archaeopteryx and all of its descendants. Problem: New phylogenetic analyses sometimes show that Archaeopteryx is more closely related to the dromaeosaurid theropods than to modern birds.
• Definition 2: Feathered dinosaurs. Problem: As more and more feathered dinosaur fossils, like Yutyrannus, are found, more dinosaur are included in this definition. For instance tyrannosaurs would now be considered birds!
• Definition 3: Flying dinosaurs. Problem: It is difficult to determine exactly which dinosaurs were capable of flying (as opposed to simply gliding).
• Definition 4: Crown dinosaurs. This a somewhat technical term that means the last common ancestor of all extant birds and its descendants. Problem: This definition fails to recognise many feathered and flying dinosaurs that are more closely related to modern birds than to Archaeopteryx as birds. However, this is the definition favoured by many palaeontologists. We then use the name Avialae for the clade containing Archaeopteryx and all of its descendants.