vertebrate evolution project part 2 data packet.doc

Anatomical

Evidence

Data

Packet

Fossil Evidence

Times that major groups first appear in the fossil record:

Jawless fish: Ordivician Period

Amphibians: Devonian Period

Reptiles: Late Paleozoic Cretaceous Period

Birds: Mesozoic Jurassic period

Primates: End of Paleocene/early Eocene Epoch

Kangaroos: Oligocene Epoch Humans: Pleistocene Epoch

A

Vertebrate Embryology

Embryo: an organism in its earliest stage of development.

All vertebrate embryos follow a common developmental path due to their common ancestry. All have a set of very similar genes that define their basic body plan. All vertebrate embryos look very similar during

the earlier stages of development, including having gill pouches and tails. Thus, a reptilian embryo, a bird embryo and a human embryo look very similar, even though they develop into very different adult organisms. The best explanation for this similarity in embryos is a shared history of vertebrates—all

vertebrates share a common ancestor that had a tailed embryo with gill pouches.

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B

Shown below are drawings of the embryonic "phylotypic" stage (earliest stage of embryonic development) in the major group of vertebrates. Refer to the key below the drawing.

Jawless fish _{Cartilaginous fish} Bony fish

Amphibian

Reptile Birds

Marsupial Mammal

Placental Mammal

Human = placental mammal

Rhesus monkey = placental mammal Kangaroo = marsupial mammal Snapping turtle = reptile

Bullfrog = amphibian Tuna = bony fish Lamprey = jawless fish

How do these embryos “look” similar?

Fish Evolution--Gills to Jaws

Jaws developed in jawed fish from the gill arches. Jawless fish like the lamprey had gill arches with skeletal rods. The first set of gill arches modified over time to form upper and lower jaws.

Meet Tiktaalik roseae: An Extraordinary Transitional Fossil

Tiktaalik roseae is remarkably well preserved for a 375-million-year old fossil

Tiktaalik roseae, better known as the "fishapod," is a 375 million year old fossil fish which was discovered in the Canadian Arctic in 2004. Its discovery sheds light on a pivotal point in the history

of life on Earth: when the very first fish ventured out onto land.

Tiktaalik looks like a cross between the primitive fish it lived amongst and the first four-legged animals (a group called "tetrapods" from tetra-, meaning four, and -pod, meaning foot. Actually, all

animals that descended from these pioneer amphibians, including us, can be called tetrapods).

Tiktaalik lived about 12 million years before the first tetrapods (which are approximately 363 million

years old). So, the existence of tetrapod features in a fish like Tiktaalik is significant because it marks the earliest appearance of these novel features in the fossil record.

Notice how these tetrapod (animals with four limbs) limbs are similar to one another:  They are all built from many individual bones.

 They are all spin-offs of the same basic bone layout: one long bone (the humerus) attached to two other long bones (the radius and ulna), with a branching series of smaller bones (carpals,

metacarpals and phalanges) on the end.

Here you can see the same bones labeled in these different limbs:

Which limb belongs to which organism? Predict and then check on the back…….

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Which limb belongs to which organism?

We see homologous structures in other animals too….

Frogs, birds, rabbits and lizards all have differently shaped forelimbs, reflecting their different lifestyles. But those different forelimbs all share the same set of homologous bones — the humerus, the radius, and the ulna. These same bones can even be seen in fossils of the extinct lobe-finned fish, Eusthenopteron. Such homologies reveal the common ancestry of all these animals.

Vestigial Features in Humans—

From Hiccups to Hernias

Hiccups—“A Hand-Me-Down From Amphibians”:

Nerves that are inherited from fish and travel from the brain to the diaphragm can become irritated and cause synchronous spasms of the diaphragm. The subsequent sharp inhalation of air closes the epiglottis, a closing of the entryway to the windpipe, and causes what we commonly call hiccups. This action is thought to be a hand-me-down from amphibians that breathe with both lungs and gills.

(Adapted from Scientific American “The Evolutionary Origins of Hiccups and Hernias” by Neil H. Shubin)

The evidence that hiccups are a vestigial reflex is as follows:

A. Amphibians have similar motor pathways that cause similar inhalation (of water into their gills) and closing of the epiglottis (to prevent aspirating water into their lungs).

B. Motor pathways necessary for hiccupping complete embryological development before those of lung functionality do.

C. Both hiccups and amphibian water gulping are inhibited by the detection of high CO2 blood

Hernias—“Part of Our Fishy Past”:

The tube through, which sperm passes, forms a round-about loop that can lead to hernias, a result of major anatomical changes that evolved from fish.

In the case of the spermatic cord, human gonads begin development in a similar way to those of sharks, fish and other vertebrates. The gonads—ovaries in females and testes in males—originally form high up in the human body, near the liver. In adult sharks and fish, the gonads typically remain up near the liver. They probably stay in this ancestral configuration because their sperm can develop within the confines of the body cavity itself.

Mammals like us do things differently from our fish ancestors. As a male fetus develops, the gonads descend. In females, the ovaries move down from the midsection to lie near the uterus and fallopian tubes. This movement ensures that the egg does not have far to travel to be fertilized. In males, the gonads descend farther, all the way to the scrotal sac, which extends from the body. This feature is quite important for the production of healthy sperm. One possible reason is that mammals are warm-blooded and that the quantity and quality of sperm are dependent on developing in a cooler temperature than the rest of the body. Accordingly, the mammalian scrotum is a sac separated from the warm body that can rise and fall to control the temperature at which the sperm develops—think “cold-shower effect.”

And therein lies the problem. For the testes to sit in this sac, they have to descend a long way, thereby causing the spermatic cord to take a roundabout loop. Unfortunately, for males the loop causes a weakness within the body wall near its apex. Several types of hernias can result when a little bit of gut pokes through this weak spot. These hernias can be congenital: some intestinal pieces travel with the gonads and descend through the body wall. Or they can develop later in life because of this zone of weakness. So the propensity to acquire certain kinds of hernias reflects layers of human history: our fishy past and mammalian present.

(Adapted from Scientific American “The Evolutionary Origins of Hiccups and Hernias” by Neil H. Shubin)

Mammal Transitional Fossil

“Reptiles have a jaw full of ear bones from mammals and mammals have an ear full of jawbones from reptiles.”

News Blurb from 2007:

Ancient Mammal Fossil Gives Clues to Ear

Evolution

(adapted from various sources)

Scientists have discovered a mammal the size of a gerbil, living at the time of the dinosaurs 125 million years ago. It reveals clues about how mammal ears evolved from reptile jaw bones.

Fossils from the mammal's skull show a key feature of early middle ear evolution, at an intermediate stage between modern mammals and ancient mammal relatives.

The mammal is called Yanoconodon allini, after the Yan Mountains in China where it was found, and after Edgar Allin for his studies of mammalian ear evolution. The fossils show incredible detail because they are so well preserved.

Mammals have highly sensitive hearing, far better than the hearing capacity of all other vertebrates, scientists have found. Mammalian hearing adaptation is made possible by a sophisticated middle ear of three tiny bones, known as the hammer (malleus), the anvil (incus) and the stirrup (stapes), plus a bony ring for the eardrum (tympanic membrane). Consequently, paleontologists and evolutionary biologists have been searching for more than a century for clues to the evolutionary origins of mammal ear structure. Mammals have one lower jaw bone called the dentary. Reptiles, amphibians and birds have, today and in the past, lower jaws composed of several different bones. Fossils from ancestors of mammals, such as the mammal-like reptiles, allow us to trace an early evolutionary reduction from a jaw bone with several bones to a single bone. The bones didn't disappear. They reduced in size and migrated to the ear region, becoming the middle ear in modern mammals.

The mammal middle ear bones evolved from the bones of the jaw hinge in their reptilian relatives. However, paleontologists long have attempted to understand the evolutionary pathway via which these precursor jaw bones became separated from the jaw and moved into the middle ear of modern mammals. Now they have an answer. Yanoconodon clearly shows an intermediate condition in the evolutionary process of how modern mammals acquired their middle ear structure--Yanoconodon's stirrup, anvil and hammer bones are still connected to the jaw by another bone, which is gone from modern mammals. This means that the proportion of the ear bones is like those of modern mammals but the reptilian connection to the jaw is retained.

Biogeography

The distribution of living things on the globe provides information about the past histories of both living things and the surface of the Earth. This evidence is consistent not just with the evolution of life, but

also with the movement of continental plates around the world-otherwise known as plate tectonics.

Marsupial mammals are found in the Americas as well as Australia and New Guinea, shown in brown on the map at right. They are not found swimming across the Pacific Ocean, nor have they been discovered wandering the Asian

mainland. There appear to be no routes of migration between the two populations. How could marsupials have gotten from their place of origin to locations half a world away?

Fossils of marsupials have been found in the Antarctic as well as in South America and Australia. During the past few decades scientists have demonstrated that what is now called South America was part of a large land mass called Gondwana, which included Australia and Antarctica. Click on the map below for a short animation that shows how Gondwana split apart 160–90 million years ago. Marsupials didn’t need a migration route from one part of the world to another; they rode the continents to their present positions.

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