Bio chapter 34
3.Suppose lancelets lacked a gene found in tunicates and vertebrates. Would this imply that the chordates' most recent common ancestor also lacked this gene? Explain.
Not necessarily. It would be possible that the chordate common ancestor had this gene, which was then lost in the lancelet lineage and retained in other chordates. However, it would also be possible that the chordate common ancestor lacked this gene; this could occur if the gene originated after lancelets diverged from other chordates but before tunicates diverged from other chordates
Suppose lancelets lacked a gene found in tunicates and vertebrates. Would this imply that the chordates' most recent common ancestor also lacked this gene? Explain.
Not necessarily. It would be possible that the chordate common ancestor had this gene, which was then lost in the lancelet lineage and retained in other chordates. However, it would also be possible that the chordate common ancestor lacked this gene; this could occur if the gene originated after lancelets diverged from other chordates but before tunicates diverged from other chordates.
endothermic
(birds are endothermic reptiles) capable of maintaining body temperature through metabolic activity
lancelets
(Cephalochordata) The most basal (earliest diverging) group of living chordates -invertebrate chordates (no vertebrae, but have nerve chord
hagfishes and lampreys
(hagfish=Myxini) (lampreys=Petromyzontida)-lack jaws -have cartilaginous vertebrae- no backbone -are sister groups Together, the hagfishes and lampreys form a clade of living jawless vertebrates, the cyclostomes. (Vertebrates with jaws make up a much larger clade, the gnathostomes
Derived Characters of Vertebrates
-2+ sets of Hox genes (due to gene replication) *lancelets and tunicates have only one* -resulting additional genetic complexity may be associated with innovations in the vertebrate nervous system and skeleton, including the development of a skull and a backbone composed of vertebrae. -vertebrae enclose the spinal cord and have taken over the mechanical roles of the notochord
Muscular, Post-Anal Tail
-Chordates have a tail posterior to the anus -In many species, the tail is greatly reduced during embryonic development -The tail contains skeletal elements and muscles -It provides propelling force in many aquatic species
Pharyngeal Slits or Clefts
-In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body Functions of pharyngeal slits: -Suspension-feeding structures in many invertebrate chordates -Gas exchange in vertebrates- become gills (except vertebrates with limbs, the tetrapods) -Develop into parts of the ear, head, and neck in tetrapods
Dorsal, Hollow Nerve Cord
-develops from a plate of ectoderm that rolls into a tube located dorsal to the notochord. The resulting dorsal, hollow nerve cord is unique to chordates -nerve cord of a chordate embryo develops into the central nervous system: the brain and spinal cord.
Describe key adaptations of aquatic gnathostomes.
1. jaws (adapted for feeding) 2. paired fins and tail for swimming 3. streamlined bodies for swimming 4. swim blader/ oily liver for buoyancy
6.Which of the following could be considered the most recent common ancestor of living tetrapods? a. a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates b. an armored, jawed placoderm with two pairs of appendages c. an early ray-finned fish that developed bony skeletal supports in its paired fins d. a salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes
A
lateral line system
Another characteristic of aquatic gnathostomes -organs that form a row along each side of the body and are sensitive to vibrations in the surrounding water. Precursors of these organs were present in the head shields of some jawless vertebrates.
3. Unlike eutherians, both monotremes and marsupials a. lack nipples b. have some embryonic development outside the uterus c. lay eggs. d. are found in Australia and Africa
B
Identify four avian adaptations for flight.
Birds have weight-saving modifications, including the absence of teeth, a urinary bladder, and a second ovary in females. The wings and feathers are adaptations that facilitate flight, and so are efficient respiratory and circulatory systems that support a high metabolic rate
What derived characters do sharks and tuna share? What features distinguish tuna from sharks?
Both are gnathostomes and have jaws, four clusters of Hox genes, enlarged forebrains, and lateral line systems. Shark skeletons consist mainly of cartilage, whereas tuna have bony skeletons. Sharks also have a spiral valve. Tuna have an operculum and a swim bladder, as well as flexible rays supporting their fins.
2. Living vertebrates can be divided into two major clades. Select the appropriate pair. a. the chordates and the tetrapods b. the urochordates and the cephalochordates c. the cyclostomes and the gnathostomes d. the marsupials and the eutherians
C
4. Which clade does not include humans? a. Synapsids b. Lobe-fins c. diapsids d. Osteichthya
C-- diapsids are reptiles with two holes on either side of their head
1. Vertebrates and tunicates share a. jaws adapted for feeding. b. a high degree of cephalization. c. an endoskeleton that includes a skull. d. a notochord and a dorsal, hollow nerve cord.
D
5.As hominins diverged from other primates, which of the following appeared first a. reduced jawbones b. an enlarged brain c. the making of stone tools d. bipedal locomotion
D
Identify at least five derived traits of primates
Hands and feet adapted for grasping, flat nails, large brain, forward-looking eyes on a flat face, parental care, and movable big toe and thumb
Identify some characters that distinguish hominins from other apes.
Hominins are a clade within the ape clade that includes humans and all species more closely related to humans than other apes. The derived characters of hominins include bipedal locomotion and relatively larger brains
3.Suggest key roles that mineralized bone might have played in early vertebrates.
In armored jawless vertebrates, bone served as external armor that may have provided protection from predators. Some species also had mineralized mouthparts, which could be used for either predation or scavenging
Provide an example in which different features of organisms in the hominin evolutionary lineage evolved at different rates.
In hominins, bipedal locomotion evolved long before large brain size. Homo ergaster, for example, was fully upright, bipedal, and as tall as modern humans, but its brain was significantly smaller than that of modern humans.
2.You are a chordate, yet you lack most of the main derived characters of chordates. Explain.
In humans, these characters are present only in the embryo. The notochord becomes disks between the vertebrae; the dorsal, hollow nerve cord develops into the brain and spinal cord; the pharyngeal clefts develop into various adult structures, and the tail is almost completely lost.
You are a chordate, yet you lack most of the main derived characters of chordates. Explain.
In humans, these characters are present only in the embryo. The notochord becomes disks between the vertebrae; the dorsal, hollow nerve cord develops into the brain and spinal cord; the pharyngeal clefts develop into various adult structures, and the tail is almost completely lost.
How are differences in the anatomy of lampreys and conodonts reflected in each animal's feeding method?
Lampreys have a round, rasping mouth, which they use to attach to fish. Conodonts had two sets of mineralized dental elements, which may have been used to impale prey and cut it into smaller pieces
ray-finned fishes
Nearly all the aquatic osteichthyans familiar to us are among the over 27,000 species -Named for the bony rays that support their fins
Develop a hypothesis to explain why the diversity of mammals increased in the Cenozoic. Your explanation should consider mammalian adaptations as well as factors such as mass extinctions and continental drift.
Mammals are endothermic, enabling them to live in a wide range of habitats. Milk provides young with a balanced set of nutrients, and hair and a layer of fat under the skin help mammals retain heat. Mammals have differentiated teeth, enabling them to eat many different kinds of food. Mammals also have relatively large brains, and many species are capable learners. Following the mass extinction at the end of the Cretaceous period, the absence of large terrestrial dinosaurs may have opened many new ecological niches to mammals, promoting an adaptive radiation. Continental drift also isolated many groups of mammals from one another, promoting the formation of many new species.
Scientists think that amphibian populations may provide an early warning system of environmental problems. What features of amphibians might make them particularly sensitive to environmental problems?
Many amphibians spend part of their life cycle in aquatic environments and part on land. Thus, they may be exposed to a wide range of environmental problems, including water and air pollution and the loss or degradation of aquatic and/or terrestrial habitats. In addition, amphibians have highly permeable skin, providing relatively little protection from external conditions, and their eggs do not have a protective shell.
tunicates
Members of the subphylum Urochordata, sessile marine chordates that lack a backbone. -9 hox genes- usual chordates have 13 -thought to be more closely related to other chordates than are lancelets. -loss of chordate characters in the adult stage of tunicates appears to have occurred after the tunicate lineage branched off from other chordates
Contrast monotremes, marsupials, and eutherians in terms of how they bear young.
Monotremes lay eggs. Marsupials give birth to very small live young that attach to a nipple in the mother's pouch, where they complete development. Eutherians give birth to more developed live young
operculum
Most fishes breathe by drawing water over four or five pairs of gills located in chambers covered by a protective bony flap called the operculum -Water is drawn into the mouth, through the pharynx, and out between the gills by movement of the operculum and contraction of muscles surrounding the gill chambers.
Some amphibians never leave the water, whereas others can survive in relatively dry terrestrial environments. Contrast the adaptations that facilitate these two lifestyles
Some fully aquatic species are paedomorphic, retaining larval features for life in water as adults. Species that live in dry environments may avoid dehydration by burrowing or living under moist leaves, and they protect their eggs with foam nests, viviparity, and other adaptations
.In several different animal lineages, organisms with a head first appeared around 530 million years ago. Does this finding constitute proof that having a head is favored by natural selection? Explain.
Such a finding suggests that early organisms with a head were favored by natural selection in several different evolutionary lineages. However, while a logical argument can be made that having a head was advantageous, fossils alone do not constitute proof
Describe the origin of tetrapods and identify some of their key derived traits
Tetrapods are thought to have originated about 365 million years ago when the fins of some lobe-fins evolved into the limbs of tetrapods. In addition to their four limbs with digits—a key derived trait for which the group is named—other derived traits of tetrapods include a neck (consisting of vertebrae that separate the head from the rest of the body), and a pelvic girdle that is fused to the backbone.
Describe three key amniote adaptations for life on land.
The amniotic egg provides protection to the embryo and allows the embryo to develop on land, eliminating the necessity of a watery environment for reproduction. Another key adaptation is rib cage ventilation, which improves the efficiency of air intake and may have allowed early amniotes to dispense with breathing through their skin. Finally, not breathing through their skin allowed amniotes to develop relatively impermeable skin, thereby conserving water
1.Identify four derived characters that all chordates have at some point during their life.
The four characters are a notochord; a dorsal, hollow nerve chord; pharyngeal slits or clefts; and a muscular, post-anal tail
Paedomorphosis
The retention in an adult of juvenile features of its evolutionary ancestors.
Factors that lead to gnathostomes' success
Their success probably resulted from a combination of anatomical features: Their paired fins and tail (which were also found in jawless vertebrates) allowed them to swim efficiently after prey, and their jaws enabled them to grab prey or simply bite off chunks of flesh
Some genetic studies suggest that the most recent common ancestor of Homo sapiens that lived outside of Africa left Africa about 50,000 years ago. Compare this date with the dates of fossils given in the text. Can both the genetic results and the dates ascribed to the fossils be correct? Explain
Yes, both can be correct. Homo sapiens may have established populations outside of Africa as early as 115,000 years ago, as indicated by the fossil record. However, those populations may have left few or no descendants today. Instead, all living humans may have descended from Africans that spread from Africa roughly 50,000 years ago, as indicated by genetic data.
Imagine that we could replay the history of life. Is it possible that a group of vertebrates that colonized land could have arisen from aquatic gnathostomes other than the lobe-fins? Explain.
Yes, that could have happened. The paired appendages of aquatic gnathostomes other than the lobe-fins could have served as a starting point for the evolution of limbs. The colonization of land by aquatic gnathostomes other than the lobe-fins might have been facilitated in lineages that possessed lungs, as that would have enabled those organisms to breathe air
Are snakes tetrapods? Explain.
Yes. Although snakes lack limbs, they descended from lizards with legs. Some snakes retain vestigial pelvic and leg bones, providing evidence of their descent from an ancestor with legs.
cloaca
a common chamber that has a single opening to the outside
Identify four derived characters that all chordates have at some point during their life.
a notochord, a dorsal hollow nerve cord, gill slits, muscular post-anal tail
The increased efficiency of rib cage ventilation may have allowed amniotes to
abandon breathing through their skin and develop less permeable skin, thereby conserving water.
ectothermic
absorb external heat as their main source of body heat. By warming themselves directly with solar energy rather than through the metabolic breakdown of food, an ectothermic reptile can survive on less than 10% of the food energy required by a mammal of the same size
Chordates
an animal phylum that has a notochord, a dorsal hollow nerve cord, and gill slits, muscular post-anal tail -cordates are bilaterian (bilaterally symmetrical) animals, and within Bilateria, they belong to the clade of animals known as Deuterostomia
acanthodians
another group of jawed vertebrates that radiated during the silurian and devonian periods -extinct
Vertebrates
chordates with backbones
The earliest known mineralized structures in vertebrates
conodont dental elements—were an adaptation that may have allowed these animals to become scavengers and predators.
In contrast to the shell-less eggs of amphibians, the amniotic eggs of most reptiles and some mammals have a shell. A shell slows
dehydration of the egg in air, an adaptation that helped amniotes to occupy a wider range of terrestrial habitats than amphibians, their closest living relatives. (Seeds played a similar role in the evolution of land plants
placoderms
earliest gnathostomes in the fossil record that are an extinct lineage of armored vertebrates
Most mammals have dispensed with the..
eggshell over the course of their evolution, and the embryo avoids desiccation by developing within the amnion inside the mother's body
The gnathostome forebrain is
enlarged compared to that of other vertebrates, and it is associated with enhanced senses of smell and vision
Most fishes can maintain a buoyancy equal to the surrounding water by
filling an air sac known as a swim bladder. (If a fish swims to greater depths or towards the surface, where water pressure differs, the fish shuttles gas between its blood and swim bladder, keeping the volume of gas in the bladder constant.)
Tetrapods
gnathostomes that have limbs -Limbs support a tetrapod's weight on land, while feet with digits efficiently transmit muscle-generated forces to the ground when it walks.
amniotes
group of tetrapods whose extant members are the reptiles (including birds, as we'll discuss in this section) and mammals -have amniotic egg, which contains four specialized membranes: the amnion, the chorion, the yolk sac, and the allantois-- It allowed the embryo to develop on land in its own private "pond," hence reducing the dependence of tetrapods on an aqueous environment for reproduction -use their rib cage to ventilate their lungs. This method is more efficient than throat-based ventilation, which amphibians use as a supplement to breathing through their skin
Osteichthyes
have an ossified (bony) endoskeleton with a hard matrix of calcium phosphate -The vast majority of vertebrates belong to the clade of gnathostomes called Osteichthyes -include tetrapods along with bony fishes in the clade Osteichthyes
all nonmammalian aquatic vertebrates
have no eardrums, structures that terrestrial vertebrates use to transmit sound waves in air to the auditory organs
gnathostomes
hinge jawed vertebrates
Benefits of a hinged jaw
hinged jaws, especially with the help of teeth, enable gnathostomes to grip food items firmly and slice them.
reptile
includes tuataras, lizards, snakes, turtles, crocodilians, and birds, along with a number of extinct groups, such as plesiosaurs and ichthyosaurs -reptiles have scales that contain the protein keratin help protect the animal's skin from desiccation and abrasion. -most reptiles lay their shelled eggs on land. Fertilization occurs internally, before the eggshell is secreted. -do not use their metabolism extensively to control their body temperature. However, they do regulate their body temperature by using behavioral adaptations.
notochord
longitudinal, flexible rod located between the digestive tube and the nerve cord. It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue. Provides: skeletal support
Osteichthyans in many early-branching lineages have
lungs, which they use to breathe air as a supplement to gas exchange in their gills. This suggests that lungs arose in early osteichthyans; later, swim bladders evolved from lungs in some lineages.
Lamprey
parasitic -jawless vertebrates -marine and freshwater -cyclostome -larval stage resembles lancelet-- spends much of its time burried in sediment
amphibians
represented today by about 6,150 species in three clades: salamanders (clade Urodela, "tailed ones"), frogs (clade Anura, "tailless ones"), and caecilians (clade Apoda, "legless ones").
Hagfish
scavengers, bottom feeders -feed on worms/ sick or dead fish -jawless vertebrates -marine -cyclostome
Living gnathostomes are a diverse group that includes
sharks and their relatives, ray-finned fishes, lobe-finned fishes, amphibians, reptiles (including birds), and mammals.
Chondrichthyans
sharks, rays, and their relatives. have a skeleton composed primarily of cartilage -the biggest and most successful vertebrate predators in the oceans.
conodonts
slender, soft bodied vertebrates that lacked jaws and internal skeleton composed of cartilage, with prominent eyes that were controlled by numerous muscles and armored; extinct
shark gains buoyancy by
storing a large amount of oil in its huge liver, the animal is still more dense than water, and if it stops swimming it sinks. Continual swimming also ensures that water flows into the shark's mouth and out through the gills, where gas exchange occurs.
The largest sharks and rays are
suspension feeders that consume plankton. Most sharks, however, are carnivores that swallow their prey whole or use their powerful jaws and sharp teeth to tear flesh from animals too large to swallow in one piece
The reproductive tract of the shark empties along with
the excretory system and digestive tract into the cloaca
tunicates lack many genes that in vertebrates are associated with
the long-range transmission of nerve impulses. This result suggests that such genes arose in an early vertebrate and are unique to the vertebrate evolutionary lineage.
lobe-fins
the other major lineage of osteichthyans -presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins -coelacanths (Actinistia) and Lungfishes -tetrapods—a lineage that includes humans
decline in amphibian populations in locations throughout the world is caused by
the spread of a disease-causing chytrid fungus, habitat loss, climate change, and pollution
The same Hox genes that organize major regions of the forebrain, midbrain, and hindbrain of vertebrates express themselves in a corresponding pattern in this small cluster of cells in the lancelet's nerve cord. This suggests....
the vertebrate brain is an elaboration of an ancestral structure similar to the lancelet's simple nerve cord tip
viviparous
the young develop within the uterus and obtain nourishment prior to birth by receiving nutrients from the mother's blood through a yolk sac placenta, by absorbing a nutritious fluid produced by the uterus, or by eating other eggs
descendant of acanthodians and placoderms
they had diverged into the three lineages of jawed vertebrates that survive today: chondrichthyans, ray-finned fishes, and lobe-fins
oviparous
they lay eggs that hatch outside the mother's body
ovoviviparous
they retain the fertilized eggs in the oviduct. Nourished by the egg yolk, the embryos develop into young that are born after hatching within the uterus
With a skeletal system and a more complex nervous system than that of their ancestors, vertebrates became more efficient at
two essential tasks: capturing food and avoiding being eaten
The common ancestors of all gnathostomes
underwent an additional duplication of Hox genes, such that the single set present in early chordates became four. In fact, the entire genome appears to have duplicated, and together these genetic changes likely enabled the origin of jaws and other novel features in gnathostomes.
