Mammals: Diagnostic Characteristics

Question 1

Hairs

Answer 1

Unique epidermal structures
Protein filaments grow from follicles found in the dermis but are derived from the epidermis by invagination.
Present with cutaneous glands and muscles.

Question 2

Epidermis of mammals are different to that of the integument of sauropsids

Answer 2

Bird feathers and reptile scales are mainly beta keratin whilst mammals are alpha keratin.
It lacks glands except for the uropygial gland in birds.

Question 3

Origin of hair

Answer 3

The epidermal projections at scale hinges in cynodonts associated with specialized mechanoreceptors possibly elongated and thickened as endothermy developed.
Allowed protomammals to occupy nocturnal niches safe from dinosaurs.
Evolution of hair involved the cooption of preexisting structural proteins present in ancestral amniotes.
First fossil evidence dates back to 164 mya.
Alpha keratin proteins encoded in the genomes of chickens and lizards.

Question 4

Epidermal glands

Answer 4

For neural and hormonal control.

There are two types of sweat glands, namely eccrine and apocrine sweat glands.

Question 5

Eccrine sweat glands

Answer 5

Opens directly onto the skin.
Allows for evaporative cooling.
Present on the soles of feet.
Improves adhesion and tactile

Question 6

Apocrine sweat glands

Answer 6

Opens into hair follicles.
Viscous, milky secretions.
Activated at puberty.
Allows for chemical communication.
Used for evaporative cooling, some ungulates.

Question 7

Ungulates

Answer 7

Animals with hooves.

Question 8

Sebaceous glands

Answer 8

Open into the hair follicles.

Sebum conditions and waterproofs fur and epidermis.

Question 9

Scent glands

Answer 9

Has some properties of apocrine sweat and sebaceous glands.
Used for territorial marking, as well as chemical communication within species.m
Also used for warning and defense against enemies.

Question 10

Mammary glands

Answer 10

Resembles both sebaceous and apocrine sweat glands by the structure, distribution and composition of secretions.
Developed as a composite gland associated with hair follicles.
Association seen in monotremes.

Question 11

Lactation

Answer 11

Evolution of mammary glands are linked to hair. As it has properties of sebaceous/apocrine glands that open into hair follicles.

Question 12

When did lactation evolve?

Answer 12

Fossil evidence of skins suggests cynodont 200mya could secrete from their abdominal skin glands.

Question 13

Comparative genomics of lactation

Answer 13

Major milk resource genes, caseins, which have similar functional properties as vitellogenins, appeared in the common mammalian ancestor approximately 200-310mya.

Question 14

Evolutionary advantages of lactations

Answer 14

Production of young decoupled from seasonal food supply.
The mother is less dependent on paternal care for rearing young.
It reduces the energetic cost of gestation by is offset by the high costs of lactation.
It allows for a longer maternal bond, which causes an opportunity for more learning and thus greater intelligence.

Question 15

How lactation evolved? Theory 1

Answer 15

Synapsids had parchment shelled eggs like monotremes, which were semi permeable which regulated the gain/loss of water. Synapsids had glandular skins. The apocrine sweat glands and sebaceous secreted sebum and fluids to provide water, and later provided nutrients. There was a progressive decrease in egg size and the glands concentrated in a patch as in extant monotremes. Initial secretions of ancestral sebum/mammary glands to protect then nourish the young. The nutritional components of milk was synthesized by enzymes also found in the sebum.
Anti microbial enzymes protect eggs against microbial attacks. Secretions increased in volume and nutritive value to supplement, and eventually supplant, the egg yolk.

Question 16

How lactation evolved? Theory 2

Answer 16

Initial secretions of ancestral sebum/mammary glands to protect and then nourish young. There are many components of milk that are also present in sebum. The nutritional components of milk synthesized by enzymes are also found in sebum. The anti microbial enzymes, in all mammalian milks, possibly protected the eggs against microbial attacks. The secretions increased in volume and nutritive volume to supplement, and eventually replace, the egg yolk.

Question 17

Reproductive modes

Answer 17

Three patterns which tends to display the degree of maternal-foetal intimacy.
Monotreme strategy
Therian strategy
Metatherian strategy
Eutherian strategy

Question 18

Monotreme reproduction

Answer 18

Eggs are very large at ovulation.
Fertilized in the oviduct.
Coated with albumin and the shell is laid down by a shell gland.
Takes 2-3 weeks in the uterus then is laid.
Intra uterine growth is supported entirely by the yolk.
Retains primitive amniote pattern (oviparity) but has a period of lactation.

Question 19

Oviparity

Answer 19

Animals that lay eggs with little or no development within the mother.

Question 20

Marsupial

Answer 20

Shell membrane present for two thirds of the gestation which prevents rejection by the maternal immune system. The tr

Question 21

Trophoblast

Answer 21

A layer of tissue on the outside of a mammalian blastula, supplying the embryo with nourishment and later forming the major part of the placenta.

Question 22

Blastula

Answer 22

A hollow sphere of cells, surrounding an inner fluid filled cavity called the blastocoele formed during