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Mammals

Evolution

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EVOLUTION AND CHARACTERISTICS

Mammals belong to the class Mammalia, which includes 4000 species

Most dominant land animals on earth.

EVOLUTION•Like mammals, Therapids have

specialized teeth adapted for specialized functions.

•The earliest mammalian fossil found is from the early Mesozoic era, 200 million years ago

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The remaining group, the “Therian” mammals, which originated during the Jurassic survive today

3 major groups of living mammals (the Therians):

1) Monotremes – egg-laying mammals

2) Marsupials – pouched mammals

3) Placentals – mammals with placenta

DIFFERENTIATED DENTITION

-Mammals needed their teeth to do several different jobs and so mammal teeth evolved into different forms. Mammal teeth can grind, stab, scissor, dig, chisel, sieve and lift (elephants tusks).   -The number, size, organization and shape of the teeth are different in every species of mammal and can be used in taxonomy, especially of fossils. In fact without teeth the fossil record would be much harder to understand.   -Mammals have only two sets of teeth, the first set they get soon after birth, often called the 'milk teeth' and a larger set they acquire as an adult.

- In all other toothed vertebrates teeth just keep coming, no matter how many you lose there is always another one ready to take its place. In other words fish amphibians, reptiles and birds either have no teeth or numerous sets.   

PELVICSlender limbs, more movement in pectoral andpelvic girdles;Cynodonts showed general reduction in bodysize. Early cynodonts were size of large dogs, bymid-Triassic the carnivorous cynodonts weresize of rabbits.– Earliest mammals were small, about 100 mm long, shrew-size.

EVOLUTION OF MAMMALS: EAR AND JAW

•Most reptiles have several bones in the lower jaw, and Dimetrodon shares this characteristic.

• But mammals have only a single lower jawbone, the dentary.

• Throughout synapsid evolution, the gradual reduction of the non-dentary elements of the jaw as they are crowded towards the back and eventually lost.

•The dentary bone, in contrast, gets larger and takes over the entire jaw.

•In the final stage of evolution, the dentary bone expands until it makes direct contact with the skull and develops a new articulation with it.

REPTILES TO MAMMALS: HEARING WITH OUR JAWBONES(AN IMPORTANT EXAMPLE OF SKELETAL MODIFICATION)

Evolution of Ear: stapes acquires “stirrup” shape articular bone in jaw becomes malleus quadrate bone in jaw becomes incus. Sophistication of teeth as mammals have evolved!

MAMMAL JAW EVOLUTION: THE TRANSITION FROM A FOUR-BONED LOWER JAW TO THE MAMMALIAN JAW WITH A SINGLE ELEMENT.

MOST DEVELOPED MAMMALS TEETH STRUCTURE

EVOLUTION OF MAMMALS’ DIAPHRAGM

The diaphragm is made of muscles and tendons and it divides the inside of the torso into 2 sections. On one side are the heart and lungs, and on the other side are organs like the stomach and liver.Mammals are the only animals with a diaphragm, although some reptiles and amphibians share some similar features.

The muscle fibers of the diaphragm originate from the lumbar vertebrae, ribs and sternum and insert into the central tendon. This uniformity among mammals and the absence of this muscle from non-mammalian tetrapods have been an obstacle to comparative anatomy in unraveling the evolutionary origin of the diaphragm.

embryonic positions of forelimb muscle progenitors, which correspond to the position of the brachial plexus, likely played an important role in the evolution of the diaphragm.

 evolution of diaphragm can be conluded as, first, forelimb muscle cells were incorporated into tissues to form a primitive diaphragm in the stem synapsid grade, and second, the diaphragm in cynodonts became entrapped in the region controlled by pulmonary development.

LUMBAR REGION FREE In human anatomy, the five vertebrae in

the lumbar region of the back are the largest and strongest in the movable part of the spinal column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body. In most mammals, the lumbar region of the spine curves outward.

FUSED CLAVICLE RIBS

Clavicle

The pectoral girdle consists of two pairs of bones, the large flat Scapula (shoulder bone) and the much smaller and more slender Clavicle (collar bone). 

The clavicle runs from the far end of the scapular to the sternum in most mammals

In some mammals such as the Anisodactyla, Perissodactyla, Mysticeti and Odontoceti (Horses, Pigs, Deer, Buffaloes, etc. and Whales) the clavicle is absent.

STRONG SPINE ON SCAPULAR

Scapula

In anatomy, the scapula  or shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones the scapulae are paired, with the scapula on the left side of the body being roughly a mirror image of the right scapula.

The scapula forms the back of the shoulder girdle. In humans, it is a flat bone, roughly ttriangular in shape, placed on a posterolateral aspect of the thoracic cage.

LIMBS UNDER BODY The pentadactyl limb is common to humans,

other mammals (although whales and dolphins have lost their hind limbs).

Darwin noted how widespread it was when he wrote On the Origin of Species:

'What could be more curious than that the hand of man formed for grasping, that of a mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should all be constructed on the same pattern and should include similar bones and in the same relative positions?'

LIMBS UNDER BODY There are a few mammals that appear to have

different numbers of digits from us. One of these is the panda, which looks like it has 6 digits.

However, close examination has shown that the extra thumb is actually an outgrowth of one of the wrist bones and not an extra digit at all. The same is true of moles.

The pentadactyl limb is common to most tetrapods (4-limbed creatures).  

Among extinct tetrapods, many dinosaurs had only 3 toes, and some marine reptiles had more than 5 digits in their paddles.  But no animals living today have more than 5 digits that all developed in the same way.

LIMBS UNDER BODY The fossil record shows evidence of a

few extinct species that had different numbers of digits. Examples are Acanthostega, Ichthyostega, and Tulerpeton.

LIMBS UNDER BODY These are all animals that lived during

the late Devonian period, between 380 and 360 million years ago, when tetrapods first began to move onto land. Some had as many as 8 digits, before the common pattern of 5 digits became established that we have inherited. 

LIMBS UNDER BODYWhale: The similarities between the skeletons

of land mammals and whales are quite clear. The hind limbs have all but disappeared.

The front limbs in all whales, the pectoral fins or flippers, basically contain all the bones that can be found in the front limbs of land mammals.

CHARACTERISTICS Mammalian heart has 4 chambers

Mammals have a muscle , the diaphragm that aids in breathing

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WARM BLOODED

WARM BLOODED It explains that warm-bloodedness most likely

did not evolve for purposes of thermoregulation, but instead evolved slowly as a side-effect of increased metabolism, and longer and longer aerobic (oxygen-consuming) activity. 

In other words, it did not evolve suddenly in one animal, but was a long-developing trend across many species in the diapsid and therapsid dinosaurs.

WARM BLOODED With constant use of energy, but along with

the benefits of longer periods activity both seeking food, and avoiding predators. This all led to slow changes in the structures of the heart and lungs, better oxygenation and carrying capacity of blood, better ability for muscle tissue to use oxygen, more mitochondria for energy production in the cells, etc.

This eventually led to what we today call "warm-bloodednes", where the body is in a constant state of energy usage to maintain a more stable body temperature and metabolic rate. 

FUR / HAIR Mammals were the first animals to

evolve body hair and it is still one of their common features today.

Even mammals like whales and dolphins are born with hair above their mouths, even though the adults are hair-less.

FUR / HAIR Hair is widely believed by Darwinists to have

evolved from scales (Denton, 1986, p. 106).  An alternative view is that hair evolved first as tiny

projecting rods in the hinges between scales and served as tactile devices. 

The "protohairs" could help monitor surface sensory data when an animal was hiding from an enemy or retreating from the weather.

This sensory protohair might then have evolved secondarily into an insulative pelage as mammals become endothermic. Although insulative in modern mammals, hair still retains a sensory function.

FUR / HAIRWhale: Land mammals have some form of hairy fur,

which serves among others as insulation. Whales don't have fur. In water, fur needs a lot of maintenance in order to maintain its insulating properties. Losing the fur gave whales a perfectly streamlined body. In whales, the remnants of the fur can still be seen. Young dolphins have small whiskers and in older animals, the hair follicles can still be seen on the snout. Some dolphin species (e.g. river dolphins) have whiskers throughout their life.

PLACENTAL MAMMALS

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CHARACTERISTICS OF PLACENTALS Placental mammals carry unborn young in

the uterus until young can survive in the wild.

Oxygen and nutrients are transferred from mother’s blood to baby’s blood

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PLACENTAL CHARACTERISTICS The placenta is a membrane providing nutrients and waste & gas exchange between the mother and developing young

Gestation period-is the time which mammals develop in mother’s uterus

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MAMMALS ARE A DIVERSE GROUP LIVING ON LAND AND IN WATER. SOME MAMMALS CAN FLY!

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Walrus

CARNIVORA 250 living species in carnivoria are

distributed worldwide Most of the species mainly eat meat,

which explains the name. About 34 species

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Some members of this order such as bears feed extensively on plant material as well as meat, so they are called omnivores.

Carnivores generally have long canine teeth, strong jaws, clawed toes.

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CETACEA AND SIRENIA 90 species of whales, dolphins, and

porpoises are distributed worldwide. Cetaceans have fishlike bodies with

forelimbs modified as flippers.

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PINNIPEDIA Pinnipedia are water dwelling carnivores and have streamlined bodies

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INSECTIVORA Consists of 400 species Includes shrews and moles

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Mole

Shrew

ARTIODACTYLA AND PERISSODACTYLA

Ungulates-hoofed mammals, classified into two orders: Artiodactyla and Perissodactyla

These two classes are herbivores. They have a storage chamber in their

stomach called the rumen, undergoes double digestion.

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Ungulates with an even amount of toes make up the class Artiodactyla

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Ungulates with an odd number of toes make up the class Perissodactyla.

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PROBOSCIDEA Characterized by a boneless nose or proboscis

Elephants are the largest land dwellers alive today, weighing more than 6 tons.

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A complex brain has enabled anthropoids to develop behaviors and to live in highly organized social groups.

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BIBLIOGRAPHY 1. Evolution of mammals limbs.

https://answers.yahoo.com/question/index?qid=20110624172700AAHnvHe. Retrieved on 19 March 2015.

2. Evolution of mammals. http://www.creationresearch.org/crsq/articles/40/40_4/Bergman.htm. Retrieved on 19 March 2015.

3. Evolution of mammals hair. http://www.nhm.ac.uk/nature-online/evolution/what-is-the-evidence/morphology/body-hair/index.html. Retrieved on 19 March 2015.

4. Evolution. http://www.sarkanniemi.fi/akatemiat/eng_evo.html. Retrieved on 19 March 2015.