Mammals (21,22) Flashcards
What are the three major groups of amniotes, and how are they distinguished?
Synapsids, Anapsids, and Diapsids; distinguished by the structure of the skull roof
What is the significance of cynodonts in mammalian evolution?
Cynodonts showed features
- heterodont teeth
- secondary palate
- diaphragm; supporting a higher metabolic rate
How did the jaw articulation evolve in mammals?
Early synapsids had a quadrate-articular jaw articulation, which evolved into the dentary-squamosal articulation in mammals, with the quadrate and articular bones becoming the incus and malleus.
Name three major characteristics of modern mammals.
Hair, mammary glands, and endothermy.
What are the two clades of living mammals?
Monotremes and Therians (which include Metatherians and Eutherians).
What is unique about monotreme reproduction?
They are oviparous and lay eggs.
What are the two types of hair in mammals, and their functions?
Guard hairs (protection and coloration) and underhairs (insulation)
What are true horns, and how do they differ from antlers?
True horns are hollow keratin sheaths over bone, found in both sexes, and grow continuously. Antlers are solid bone, shed annually, and typically found only in males.
What type of dentition do mammals have, and how does it differ from reptiles?
Mammals have heterodont dentition (differentiated teeth), whereas reptiles have homodont dentition (uniform teeth)
How do ruminant herbivores digest cellulose?
Through a four-chambered stomach and microorganisms in the rumen.
What feature allows mammals to separate nasal and oral cavities for efficient gas exchange?
A secondary palate.
Describe the pathway of air through the mammalian respiratory system.
Nostrils → Nasal chamber → Pharynx → Glottis → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
What are the four types of estrous cycles in mammals?
Monestrous, diestrous, polyestrous, and menstrual cycles.
How do marsupial placentas differ from those of eutherians?
Marsupials have a choriovitelline placenta, while eutherians have a chorioallantoic placenta
Compare the adaptations in teeth and digestive systems between carnivorous, herbivorous, and omnivorous mammals.
Carnivores have sharp canines and bladelike molars for tearing flesh and a short digestive tract. Herbivores have broad molars for grinding, reduced canines, and long digestive tracts with fermentation chambers for cellulose digestion. Omnivores have versatile dentition, including broad molars for crushing, and moderately developed digestive systems.
Explain the evolutionary advantages of mammalian viviparity and its associated energy trade-offs.
Viviparity allows females to move and access resources during gestation, providing better survival for offspring. However, it requires high energy expenditure during gestation and postnatal care, increasing parental investment.
How did the evolution of mammalian hair contribute to their success in diverse environments?
Hair provided insulation, enabling mammals to maintain body heat in cold environments (endothermy). Modified hairs like vibrissae (whiskers) enhanced sensory functions, and spines provided defense.
Discuss the significance of the evolution of mammary glands in mammals.
Mammary glands allowed mammals to nourish their young with nutrient-rich milk, reducing dependence on environmental food sources and enabling survival in varied habitats. This adaptation likely enhanced reproductive success and offspring survival rates.
Contrast monotreme reproduction with that of eutherian mammals in terms of offspring development and maternal investment.
Monotremes lay eggs, providing less maternal investment pre-hatching, and the young are highly altricial. Eutherians nourish embryos via the placenta, leading to more developed offspring at birth and higher maternal energy investment during gestation.
Amniotes
A group of tetrapods
- presence of an amniotic egg
(which includes reptiles, birds, and mammals)
Synapsids
One of the three major groups of amniotes
- single temporal fenestra in the skull
Pelycosaurs
Early synapsids that were herbivores and carnivores in the Permian period; not closely related to modern reptiles
Therapsids
Advanced synapsids that evolved from pelycosaurs, showing more efficient locomotion and feeding adaptations
Cynodonts
A subgroup of therapsids with traits like heterodont teeth, secondary palate, and a diaphragm, indicating higher metabolic rates
Diphyodont
Having two sets of teeth in a lifetime – deciduous (“baby teeth”) and permanent teeth, as seen in most mammals
Polyphyodont
Having continuous tooth replacement throughout life, a characteristic of ancestral amniotes
Dentary-Squamosal Articulation
A jaw joint found in mammals where the dentary bone of the lower jaw articulates with the squamosal bone of the skull
Incus, Malleus, Stapes
The three bones of the mammalian middle ear, evolved from the jawbones of early synapsids, facilitating acute hearing
Endothermy
ability to maintain a stable internal body temperature through metabolic heat production
Hair (Pelage)
A defining characteristic of mammals, providing insulation and sometimes modified for sensory or defensive purposes (e.g., whiskers, spines)
Guard Hairs
Coarse and long hairs that protect against wear and provide coloration
Heterodont Dentition
A condition where teeth are differentiated into various types (e.g., incisors, canines, premolars, molars) for specialized functions
Monotremes
Egg-laying mammals, such as the platypus and echidnas, found in Australia and New Guinea
Marsupials
Mammals that give birth to underdeveloped young that complete their development in a pouch (marsupium)
Eutherians
Placental mammals with a chorioallantoic placenta, allowing extended gestation and advanced offspring development
Choriovitelline Placenta
A transient placenta found in marsupials, formed by the yolk sac and chorion
Chorioallantoic Placenta
The placenta of eutherians, formed by the fusion of the chorion and allantois, facilitating nutrient exchange and waste removal
Viviparity
Giving birth to live young, with the embryo developing within the mother’s uterus
Estrus Cycle
The reproductive cycle in most female mammals during which they are fertile and receptive to mating
Arrector Pili Muscles
Small muscles attached to hair follicles that make the hair stand upright, aiding in insulation
Ruminant Herbivores
Herbivores with a four-chambered stomach for fermenting plant material, including the rumen, reticulum, omasum, and abomasum.
Coprophagy
The re-ingestion of feces to extract additional nutrients, common in some rodents and lagomorphs.
What makes mammalian integument distinct from other vertebrates?
Mammalian integument is thicker and more complex, adapted for terrestrial life with structures like hair and glands.
What keratinized structures are found in mammals?
Hair, hooves, claws, and nails.
What is the typical body temperature range in mammals?
36–38°C.
Name two adaptations mammals have for cold environments
Increased fur thickness and hibernation.
How does fur thickness change in cold environments?
Fur thickness can increase by up to 50%, with underhair acting as the primary insulating layer.
What type of heart do mammals have, and how does it differ from fish and amphibians?
Mammals have a four-chambered heart, while fish have a two-chambered heart and amphibians/reptiles have three chambers.
What is the primary mechanism mammals use for ventilation?
Negative pressure ventilation.
Which muscles are involved in negative pressure ventilation?
The diaphragm and intercostal muscles.
What are the four types of mammalian teeth, and their functions?
Incisors: Biting, cutting, and stripping.
Canines: Seizing, piercing, and tearing.
Premolars and Molars: Grinding and crushing
What are the five functional regions of the mammalian alimentary canal?
Reception, conduction and storage, grinding and early digestion, terminal digestion and absorption, and water absorption/concentration of solids.
Name the four trophic categories of mammals based on feeding specialization.
Insectivores, carnivores, omnivores, and herbivores.
How has the vertebrate brain evolved in mammals?
It has increased in complexity, with deep fissures and intricate structures, culminating in the mammalian brain.
What are two key sensory receptors in mammals and their functions?
Chemoreceptors: Detect chemicals in the environment.
Mechanoreceptors: Detect touch and sound.
What are the three reproductive strategies in vertebrates?
Oviparous: Egg-laying.
Ovoviviparous: Internal egg development with nourishment from yolk.
Viviparous: Live birth with direct nourishment from the mother.
What is unique about the reproductive strategy of monotremes?
They are oviparous mammals that lay eggs.
How does lactation benefit mammalian young?
It provides a nutrient-rich food source, allowing young to rely on their mothers rather than foraging.
Explain the process and benefits of negative pressure ventilation in mammals compared to positive pressure ventilation in amphibians.
Negative pressure ventilation in mammals involves expanding the thoracic cavity using the diaphragm and intercostal muscles, creating a pressure gradient that draws air into the lungs. This system is more efficient, allowing mammals to take in larger volumes of oxygen compared to the forceful air intake used by amphibians in positive pressure ventilation.
Compare the reproductive adaptations in monotremes, marsupials, and eutherians, and discuss how these adaptations support their survival.
Monotremes lay eggs, minimizing maternal investment pre-hatching.
Marsupials give birth to underdeveloped young that complete development in the pouch, enabling shorter gestation and faster reproduction.
Eutherians use a chorioallantoic placenta for extended gestation, allowing young to be born more developed, increasing survival rates.
How do teeth and digestive systems differ among insectivores, herbivores, carnivores, and omnivores?
Insectivores: Pointed teeth for puncturing, short digestive tracts.
Herbivores: Broad molars for grinding cellulose, long alimentary canals, and fermentation chambers.
Carnivores: Sharp canines and short digestive tracts for digesting meat.
Omnivores: Versatile dentition for processing both plant and animal materials, moderately developed digestive systems.
