Look over every these pages and examine the various bone specimens in regards to what you read. Later, in the laboratory exam, you"ll it is in asked to recognize various specimens, name their vital features, and also discuss their useful significance. Before you leave lab, you should go over the review on each web page to check out if you"re prepared for the rap exam.

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Before examining this page and also the accompanying specimens in lab, you have to read the Skeleton lab introduction page.

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Objectives:

Identify & surname bird bones equivalent to the mammal bones girlfriend learned earlier.Describe how bird skeletons different from those that mammals and explain the functional meaning of these differences.Discuss why the distinct features of bird skeletons can or might not be considered as adaptations to flight.

Specimens

You should apply the info on this page to the adhering to specimens in lab:

Bird skeletons, including chicken & duckBat & bird wing skeletons (compare the wing of this paris mammal come the soup of a bird)Bird skulls

Warning: these skeletons are unbelievably delicate. You re welcome be gentle through them.

Introduction

Birds and also mammals are the two groups of large-brained, endothermic (“warm-blooded”) animals on Earth. In this lab you’ll to compare bird and mammal skeletons, and also you’ll check out some clean homologies in between these 2 groups. This do not do it be too surprising, because both birds and also mammals are descended indigenous the same at an early stage vertebrate ancestors. Top top the various other hand, you will also see some distinctive differences in between bird and also mammal skeletons. There room two key kinds that explanations because that these differences: ancestry and adaptation. If birds and also mammals both came from the same initial terrestrial vertebrate ancestors, they came from different branches that the vertebrate tree. If bird skeletons have unique features, it might be due to the fact that birds inherited those functions from their current ancestors. Therefore, us can"t translate birds" skeletal attributes without learning something around their phylogeny. Top top the other hand, birds do one thing that is dramatically different from mammals: lock fly. If bird skeletons have distinct features, it can be because birds are adapted to flying. Therefore, we can"t interpret birds" skeletal functions without considering just how the skeleton features in flying and also in other activities.

Both of these factors, ancestry and adaptation, are likely to it is in important; in this laboratory you"ll take into consideration both that them. Together it transforms out, numerous of the unique features of birds have actually traditionally been construed as adaptations come flight. However, some major fossil discoveries have to be made in current years, overturning long-held beliefs about bird evolution. With that in mind, this laboratory isn"t only around the skeletal of birds; it"s about the means that biologists recognize the advancement of human body structures.

Before you begin looking at skeletons, here is some an easy background top top the ancestry and unique features of birds.

Birds are dinosaurs

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Consider this very selective phylogenetic tree showing some major groups of land vertebrates. I put boxes approximately two clades: amniotes and also dinosaurs. "Amniotes" contains all the vertebrates through amniotic eggs (yes, mammals have actually eggs!). Amniotes, uneven frogs or fish, deserve to reproduce on dry land. I will comment on the prominence of amniotic egg in lecture.

Now look at the dinosaurs. Allosaurus, Tyrannosaurus, and Velociraptor are are plainly dinosaurs; after ~ all, dinosaurs like these were featured in the Jurassic Park movies. Notification that over there is no clade that includes all this dinosaurs yet does not include birds. If Dinosauria is a precious taxonomic group (and that is), then it has actually to encompass birds. As it transforms out, no all the dinosaurs came to be extinct; birds room the last enduring dinosaurs. Most world tend come think the the period of dinosaurs ended long ago; however, given that there are over 10,000 types of birds on planet (compared to 5500 species of mammals), one could say the we are still living in the age of dinosaurs.

What sort of proof supports this how amazing conclusion? comparisons of the genomes of life vertebrates have presented their evolutionary relationships quite clearly. For the phylogenetic tree presented above, the relationships among crocodiles, turtles, lizards, birds, and mammals could be identified without even looking at the fossils. Together it transforms out, the conclusions based on DNA evidence agree with those based on fossil evidence. Unfortunately, there is no DNA indigenous the long-extinct dinosaur types (Jurassic Park notwithstanding). Therefore, to understand the relationship of pets known just from fossils, paleontologists must study the fossils themselves.

Dinosaur fossils are old, and also have been studied intensively because the late 1800s. You can think the all the important discoveries would have been made long ago, but some exceptional bird-related fossils have actually been found in recent years. These fossil find have displayed how comparable birds space to several of their extinction dinosaur ancestors. Prior to you review on, take a minute to think about what characteristics make birds different from a Velociraptor or Tyrannosaurus. What provides a bird a bird? below are a few of those traits; you can probably think of others.

Ability to flySmall dimension (compared to bigger extinct dinosaur groups)WingsFeathers (but countless non-flying dinosaurs also had feathers)High metabolic rate (compared to various other extant reptiles)Short tail (the bony part, not the feathers)Beak with no teeth

These characteristics might seem come be distinct to birds, but the surprising thing is that all of them have been uncovered in nonflying fossil dinosaurs. While it"s been clear for numerous years the birds descended from dinosaurs, researchers have only recently learned just how much those primitive dinosaurs resembled birds. Few of these features have traditionally been defined as adaptations come flight, yet if the characteristics first appeared in dinosaurs long prior to the advancement of flight, then they weren"t adaptations to flying.

This rap is about living birds, not extinct dinosaurs, so i will describe just two of the unusual functions that bird inherited from their dinosaur ancestors: feathers and also pneumatic bones. If you"d prefer to learn more about why birds space classified together dinosaurs, see the references under bird development at the bottom that this page.

Feathers

Feathers are essentially a highly modified kind of the scales uncovered on other reptiles. Feather aren"t component of the skeleton, yet they can aid maintain the structure of the body comparable to the method the skeleton does. Because that example, compare the wing of a bird come the wings of a bat. In bats, the "hand" part of the skeleton supports the flaps that skin, making a practical wing. In birds, the "hand" part is proportionally lot shorter. The guideline of the soup is composed just of the huge primary flight feathers. Together a result, the variety of bones in the bird forelimb has actually been reduced compared to their ancestors. In fact, bird skeletons generally have numerous bones eliminated, decreased in size, or unify together compared to mammals, to the level that a bird"s feathers typically weigh more than that is bones.

Since feather play an important role in bird flight, it"s tempting to think that feathers originally advanced as an adaptation come flight. However, this idea transforms out to be wrong. We recognize this since feathers advanced long before birds began to fly. Countless fossils discovered in the last decade or for this reason have evidenced that a great many dinosaur species had feathers, long prior to the advancement of flight. If feathers existed before flying, climate feathers did not arise together an adaptation come flying.

This doesn"t typical that feather aren"t pertinent to flight; the simply method that feathers an initial evolved for other reasons and later became adjusted to flight. If this is the case, then how did feathers duty in nonflying dinosaurs? In contemporary birds, feather are likewise important for insulation, mating displays, and as aerodynamic aids as soon as running. Every these may have been components in the development of feather in the dinosaur ancestors the birds; the is a issue of part debate amongst paleontologists regarding which factors were most important.

Feathers didn"t evolve every at once. Numerous feathered dinosaur fossils have actually been found, through feathers varying from an easy hairlike structures to complicated asymmetrical flight feathers the same, similar thing those of modern birds. Functionally, these feathers didn"t all execute the exact same thing, for this reason it"s likely that a variety of forces acted on the at an early stage evolution of feathers. Birds may be the only living group of pets with feathers, however that wasn"t constantly true; birds are merely the last enduring members the a large group the feathered dinosaurs. For more information, see recommendations under the development of feathers, below.

Pneumatic bones

Find an isolated bird bone and also compare it come a mammal bone of comparable size.

Birds have actually pneumatic (air-filled) bones; the air spaces may comprise the majority of the bone"s volume. In mammals, bones are typically solid, or else filled with marrow. Why do birds have pneumatic bones? The classic explanation is that pneumatic skeletal evolved because it provides the skeleton lighter, allowing birds to paris better. There space two difficulties with this explanation. First, plenty of large, nonflying dinosaurs additionally had pneumatic bones. If pneumatic skeletal evolved before flight, lock didn"t evolve because of flight. Second, bird don"t necessarily have lighter skeletons 보다 mammals of indistinguishable size. Back birds" bones contain air spaces, the bone tissue is denser, therefore it their pneumatic skeletal aren"t have to lighter than the solid bones of a mammal through the very same mass. This doesn"t say that pneumatic skeletal aren"t relevant to flight, though. The hollow, dense building of bird bones does offer them higher rigidity than similar mammal bones. However, just because pneumatic bones function well because that flying, that doesn"t median that castle originally advanced as a result of natural choice for boosted flight.

Why walk non-flying dinosaurs have pneumatic bones? The wait spaces in bones don"t only influence the mass and stiffness of the bones. This air spaces are associated to the device of air sacs that runs throughout the bird"s body. Together you learned in lecture (I hope), birds have one-way air flow through your lungs, aided by air sacs that assist to pump the wait in and also out. This air sacs extend into the bones, and also air can move in and also out that the bones as it move through various other parts that the system. That"s exactly how it works in birds, and it seems likely that at least some dinosaurs had a similar system of air sacs and 1-way ventilation v the lungs. In this respect, birds seem to have simply maintained the pneumatic bone structure inherited from your dinosaur ancestors. Still, one important question remains: Air bag may assist pump air through the lungs, but why have actually them in the bones? walk this aid with gas exchange or some other process? Frankly, i don"t recognize the answer come this one.

Overall, we can say that pneumatic skeleton are an essential feature of bird skeletons, inherited native older dinosaurs, and adjusted to duty in a tiny flying animal. For an ext on this topic, see the referrals under pneumatic bones in birds and also other dinosaurs at the bottom of this page.

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Bird skeleton

Here is a straightforward diagram that a bird skeleton (from Wikimedia Commons). Countless of the bones are clearly homologous come those in mammals, however there room a couple of important differences.