Important words and concepts from Chapter 34, Campbell & Reece, 2002 (3/25/2005):

by Stephen T. Abedon ( for Biology 113 at the Ohio State University



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Vocabulary words are found below



(1) Chapter title: Vertebrate Evolution and Diversity

(a)                    [vertebrate evolution and diversity (Google Search)] [index]




(2) Phylum Chordata (chordates)

(a)                    Chordates made their first appearance in fossils dating back approximately 550 million years ago

(b)                    The chordates possess four defining anatomical features that separates them from the other deuterostomes, the echinoderms

(i)                      A notochord

(ii)                    A dorsal, hollow nerve chord

(iii)                   Pharyngeal slits

(iv)                  A muscular, postanal tail

(c)                    See Figure 34.1, Chordata characteristics

(d)                    All chordates possess these features at least during development

(e)                    The chordates consist of the following invertebrate subphyla

(i)                      Urochordata

(ii)                    Cephalochordata

(f)                      The third chordate subphylum is

(i)                      Vertebrata, the vertebrates

(g)                    See Figure 34.1, Clades of extant chordates

(h)                    [phylum Chordata, chordates, evolution of chordates (Google Search)] [index]

(3) Notochord

(a)                    The notochord is a stiffened but still flexible rod found between the ventral (front/bottom) gut and the dorsal (back/top) nerve cord

(b)                    The notochord serves as a primitive internal support structure

(c)                    The notochord persists relatively unmodified in only the more primitive chordates

(d)                    In more modern forms, the notochord exists during development but is modified with development, e.g., into the gelatinous material of the intra-vertebral disks (see these in cross section in the image to the right)

(e)                    See Figure 34.2, Chordata characteristics

(f)                      [notochord (Google Search)] [index]

(4) Dorsal, hollow nerve cord

(a)                    The nerve cord that becomes our brain and spinal cord begins embryologically as an in-folding of the central/dorsally located ectoderm of the developing chordate

(b)                    Because the embryonic origin of this nerve cord is as an in-folding, the resulting nerve cord is hollow

(c)                    See Figure 34.2, Chordata characteristics

(d)                    See Figure 34.6, The neural crest, embryonic source of many vertebrate synapomorphies

(e)                    [dorsal, hollow nerve cord (Google Search)] [index]

(5) Pharyngeal slits

(a)                    The pharynx is the structure that spans from the mouth down toward the stomach in the digestive tract

(b)                    More primitive chordates possess slits in their pharynx which are employed either for trapping food particles or as gills (gas-exchange organs)

(c)                    The slits serve as a water exit thus allowing water into the pharynx without it continuing down into the rest of the gastrointestinal tract

(d)                    These slits are present in the chordate embryo, e.g., such as the embryo of humans

(e)                    See Figure 34.2, Chordata characteristics

(f)                      [pharyngeal slits (Google Search)] [index]

(6) Muscular, postanal tail

(a)                    That is, the digestive system in chordates does not extend the entire length of the animal, but instead terminates well before the posterior end of the animal

(b)                    See Figure 34.2, Chordata characteristics

(c)                    [postanal tail (Google Search)] [index]




(7) Subphylum Urochordata (tunicates, sea squirts)

(a)                    The urochordates include the tunicates, a.k.a., sea squirts

(b)                    The tunicates are mostly sessile, filter feeding animals that look almost nothing like a chordate

(c)                    However, their larval form possesses all of the basic characteristics of a chordate

(d)                    See Figure 34.3, Subphylum Urochordata: a tunicate

(e)                    The tunicate life history suggests to many that the chordate body plan may have evolved as a means of optimizing the larval stage for dissemination

(f)                      Adult tunicate:  and larvae:


(h)                    [subphylum Urochordata, urochordates, tunicates, sea squirts (Google Search)] [index]

(8) Subphylum Cephalochordata (lancelets)

(a)                    The lancelets make up the cephalochordates

(b)                    Lancelets retain their chordate body plan throughout life

(c)                    Lancelets additionally display somites

(d)                    Figure 34.4, Subphylum Cephalochordata: the lancelet Branchiostoma

(e)                    [subphylum Cephalochordata, cephalochordates, lancelets(Google Search)] [index]

(9) Somites

(a)                    Somites are blocks of musculature arranged in segments along the bodies of lancelets and fishes (as well as derivations of this segmentation found in tetrapods)

(b)                    The division of musculature into somites is what gives fish meat its flaky consistency after cooking, i.e., the individual layers (flakes) represent individual somite layers

(c)                    See Figure 34.2, Chordate characteristics

(d)                    The segmentation of somites can also be seen in such features as the segmentation of the vertebrae of fish and tetrapods

(e)                    Note that this segmentation is (perhaps) an analogy (rather than homology) to the segmentation observed in the arthropods and the annelids

(f)                      [Below (left) is a mouse embryo with somites highlighted (a U-shaped series of blocks along the bottom of the image  that is highlighted in green when viewed in color); to the right is a sequence termed somitogenesis (the formation of somites), also in the mouse:

(g)                    ]

(h)                    [somites, somitogenesis (Google Search)] [index]




(10) Superclass Agnatha (jawless fish, hagfish, sea lamprey)

(a)                    The agnathans represent the most primitive extant vertebrates

(b)                    They include the hagfish and the sea lamprey

(c)                    See Figure 34.8, A hagfish

(d)                    See Figure 34.9, A sea lamprey

(e)                    Agnathans lack jaws, like their non-vertebrate, chordate ancestors (and hence are known as jawless fish, i.e., agnathans)

(f)                      Agnathans additionally lack paired fins

(g)                    Jawless fish were the vertebrate forerunners of the jawed fish

(h)                    [Hagfish can tie themselves in knots and hagfish can secrete copious slime:

(i)                      ]

(j)                      [Below are two possible phylogenies of subphylum Agnatha, one in which the agnathans for a monophyletic taxon and the other in which the lampreys and the gnathostomes together form a monophyletic taxon which excludes the hagfish; note regardless that the hagfish in this phylogeny are included among the craniates but not among the vertebrates (see: for a discussion of this topic):

(k)                    ]

(l)                      See Figure 34.7, Phylogeny of the major groups of extant vertebrates

(m)                  [superclass Agnatha, jawless fish, hagfish, sea lamprey (Google Search)] [index]




(11) Subphylum Vertebrata (vertebrates)

(a)                    The vertebrates make their first appearance into the fossil record approximately 500 million years ago, i.e., one-half billion years ago

(b)                    "Vertebrates retain the primitive chordate characteristics while adding other specializations, shared derived features (synapomorphies) that distinguish the subphylum from invertebrate chordates. The evolution of these unique vertebrate structures was probably associated with increasing size and more active foraging for food. These vertebrate adaptations include cephalization, a skeleton that includes a cranium and vertebral column, and anatomical equipment that supports the active metabolism required for a more energetic lifestyle."

(c)                    Thus, most vertebrates have

(i)                      A head

(ii)                    An endoskeleton

(iii)                   A vertebral backbone

(iv)                  A skull

(v)                    Ribs

(vi)                  Paired, lateral appendages (fins, limbs)

(vii)                 A closed circulatory system (blood returns to heart in vessels)

(d)                    Many of these adaptations allowed a more robust swimming plus allowed a more efficient food acquisition such as a carnivorous subsistence on other, relatively large animals

(e)                    [subphylum Vertebrata, vertebrates (Google Search)] [index]

(12) Chordate through tetrapod phylogeny

(a)                    The chordate taxa, including the vertebrates, may be subdivided as follows (note that not all subdivisions are formally recognized taxa, though they do represent formally recognized clades; no need to memorize information not provided in bold)

(i)                      Chordates

·        Subphylum Urochordata

·        Subphylum Cephalochordata

·        Subphylum Vertebrata

            Superclass Agnatha

            Class Osteostraci (extinct armored, jawless fish)

            Class Myxini (Hagfish) (but probably not vertebrates)

            Class Cephalspidomorphi (Lampreys)

            Superclass Gnathostomata

            Class Placodermi (extinct armored, jawed fish)

            Class Chondrichthyes

            Sharks, Rays, Chimeras

            Class Osteichthyes

            The ray finned fish (subclass/class Actinopterygii­­)

            The fleshy-finned fish (subclass Sarcopterygii)

            The lobe-finned fish (subclass Actinistia)

                 The coelacanths (order)

                 The rhipidistians (order) (to the tetrapod?)

            Lungfish (subclass Dipnoi) (to the tetrapod?)

(b)                    See Figure 34.7, Phylogeny of the major groups of extant vertebrates

(c)                    [An indication of when the various major vertebrate lineages came into existence, how long they persisted, and the extent of their diversity (breadth) through geologic time:  ]

(d)                    [chordate phylogeny, evolution of chordates (Google Search)] [the early vertebrates (a wonderful collection of links that follow the early evolution of the vertebrates) (Biology 404Colorado State University, Fullerton)] [index]




(13) Superclass Gnathostomata (jaws)

(a)                    Superclass Gnathostomata includes the jawed fish and their descendants

(b)                    See Figure 34.10, Hypothesis for the evolution of vertebrate jaws

(c)                    See Figure 34.7, Phylogeny of the major groups of extant vertebrates


(e)                    [superclass Gnathostomata (Google Search)] [index]

(14) Class Placodermi

(a)                    The placoderms were a now-extinct early jawed fish which additionally possessed armor, presumably as protection from predation

(b)                    In addition to jaws, the placoderms possessed paired fins

(c)                    [The placoderms were essentially extinct by 350 million years ago (early Carboniferous period)]

(d)                    Note the jaws (in the first image) and paired fins (in the latter image):


(f)                      [class Placodermi, placoderms (Google Search)] [index]




(15) Modern fish

(a)                    The modern fish consist of two classes

(i)                      Class Chondrichthyes (the cartilaginous fish)

(ii)                    Class Osteichthyes (the bony fish)

(b)                    See Figure 34.7, Phylogeny of the major groups of extant vertebrates

(c)                    ["modern fish" -culture, evolution of fish (Google Search)] [index]

(16) Class Chondrichthyes (cartilaginous fish, sharks, rays)

(a)                    The Chondrichthyes are the sharks and rays

(b)                    Members of this class are named for their cartilaginous skeletons, i.e., unmineralized (or less mineralized/ossified) skeletons

(c)                    See Figure 34.11, Cartilagenous fishes (Class Chondrichthyes)

(d)                    [class Chondrichthyes, cartilaginous fish, sharks, rays (Google Search)] [index]

(17) Class Osteichthyes (bony fish, ossification, swim bladder)

(a)                    The Osteichthyes are the bony fish

(b)                    “Until recently, zoologists combined all bony fishes into a single vertebrate class (Osteichthyes), and we’ll continue to use that name as a general, informal one for the great diversity of bony fishes. However, based on cladistic analysis, most vertebrate systematists now recognize three extant classes of bony fishes, [the ray-finned fish], the lobe-finned fishes, and the lungfishes.” (p. 688, Campbell & Reece, 2002)

(c)                    (however, below I will continue to discuss a subclass Actinopterygii, a subclass Actinistia, and a subclass Dipnoi, the bony fish, lobe-finned fish, and lungfish, respectively; in keeping with the latest edition of your text I will also ignore subclass Sarcopterygii as a separate category, the fleshy-finned fish, i.e., containing both the lobe-finned fish and the lungfish, though I retain the Sarcopterygii below as a supplemental discussion)

(d)                    See Figure 34.7, Phylogeny of the major groups of extant vertebrates

(e)                    The bony fish are all of the fish you are familiar with except the sharks and rays

(f)                     See Figure 34.12, Ray-finned fishes (class Actinopterygii)

(g)                    The skeleton of bony fish displays ossification, i.e., calcium phosphate in addition to the cartilaginous base

(h)                    Bony fish additionally possess flattened scales (unlike those of sharks)

(i)                      Bony fish also secrete mucus onto their skin to aid in reducing their coefficient of drag

(j)                      Bony fish additionally possess a gas-filled swim bladder that allows them to adjust their buoyancy to match that of the water

(i)                      sharks and rays lack a swim bladder and consequently sink when not moving

(ii)                    the swim bladder is derived from lungs, an adaptation by early bony fish to shallow, fresh-water living

(k)                   See Figure 34.11, Anatomy of a trout, a representative bony fish

(l)                      "Whereas sharks arose in the sea, bony fishes probably originated in fresh water. The swim bladder was modified from simple lungs that had been used to augment the gills for gas exchange, perhaps in the stagnant swamps with low oxygen content." (question: what happened to all of these fresh water bony fishes with lungs?)

(m)                  Two subclasses of bony fish exist, those with ray fins and those with fleshy fins

(n)                    See Figure 34.15, The Origin of Tetrapods

(o)                    [class Osteichthyes, bony fish, fish ossification, swim bladder (Google Search)] [index]

(18) Ray-finned fish (subclass Actinopterygii) (no need to memorize subclass designation)

(a)                    The ray-finned fish are the bony fish most familiar to you

(b)                    The fins of these fish are supported by flexible "rays"

(c)                    See Figure 34.12, Ray-finned fishes (class Actinopterygii)

(d)                    [subclass Actinopterygii, ray-finned fish (Google Search)] [index]

(19) Fleshy-finned fish (subclass Sarcopterygii, lung fish) (supplemental discussion)

(a)                    The fleshy-finned fish include members who never lost their lungs, e.g., the lung fish

(b)                    The fleshy-finned fish additionally include the lobe-finned fish and the lung fish

(c)                    [subclass Sarcopterygii, fleshy-finned fish (Google Search)] [index]

(20) Lobe-finned fish (coelacanths, rhipidistians) (subclass Actinistia) (no need to memorize subclass designation)

(a)                    Lobe fins are supported by musculature and a bony skeleton

(b)                    These lobes are employed for "walking" upon the bottom of bodies of water

(c)                    Two orders of lobe-finned fish are known

(i)                     The coelacanths (one known, extant species)

·        See Figure 34.14, A coelocanth (Latimeria), the only extant lob-finned genus


(ii)                    The rhipidistians (extinct)

(d)                    [“Paleontologists agree that the amphibians must have evolved from one of the 3 groups of lobe-finned fishes (lungfish, coelacanths, or extinct rhipidistians). However, there is disagreement on which group is the most likely ancestor. Most paleontologists consider that amphibians evolved from the rhipidistian fishes, based on the remarkable similarity in the pattern of bones in their skulls and fins/limbs. Other paleontologists, however, believe that the lungfish were ancestral to the amphibians, since the development of the lungs, nostrils and limbs of living lungfish is strikingly similar to those of living amphibians.” (BSC Courseware)]

(e)                    Lobed fins, skeletal detail is shown to the right à

(f)                      [subclass Actinistia, lobe-finned fish, coelacanths, rhipidistians (Google Search)] [index]

(21) Lungfish (subclass Dipnoi) (no need to memorize subclass designation)

(a)                    Lung fish:

(b)                    ["While in the larval stage, Australian lungfish superficially resemble tadpoles. Even their eggs are similar to those of amphibians. This supports the theory that a primitive species of fish, anatomically very similar to amphibians, is thought to be the ancestor of modern day terrestrial vertebrates."]

(c)                    ["Distinctive characteristics of the lungfish that are rather more amphibian than fish-like include the elongate but heavily built body, the single "lung," the gelatinous coating on eggs, a pronounced larval phase, and the fusion of teeth into ridged bony plates."]

(d)                    [subclass Dipnoi, lungfish (Google Search)] [index]




(22) Tetrapods

(a)                    The tetrapods are the terrestrial descendants of some lobe-finned fish, starting with the amphibians

(b)                    “Amphibians were the first tetrapods to spend a substantial portion of their time on land. But if we define tetrapods as vertebrates that have relatively sturdy, skeleton-supported legs instead of paired fins, then the first animals to qualify were highly specialized fishes that lived in shallow aquatic habitats. And for the name tetrapod to identify a monophyletic lineage (clade), with legs as the key derived homology, then we must include those ancenstral fishes.” (pp. 690-691, Campbell & Reece, 2002)

(c)                    See Figure 34.15, The origin of tetrapods

(d)                    See Figure 34.16, Skeleton of Acanthostega, a Devonian tetrapod

(e)                    “During the Devonian period, a diversity of plants and arthropods already inhabited the land, and the evolution of trees and other larger vegetation was transforming these terrestrial ecosystems. Plants rooted at the margins of ponds and swamps and organic material that dropped into the water from the terrestrial ecosystems also created new living conditions and new food supplies for fishes living near water’s edge. A diversity of fishes resembling modern lobe-fins and lungfishes had already evolved… In addition to lungs that supplemented gills for gas exchange at water’s edge, leglike appendages were probably better equipment than fins for paddling and crawling through the dense vegetation in shallow water. Thus, the lungs and appendages of tetrapods evolved in certain specialized fists tens of millions of years before this equipment was used by the earliest amphibians to live on land.” (p. 691, Campbell & Reece, 2002)

(f)                      [tetrapod phylogeny, evolution of tetrapods, class Amphibia, amniotes, synapsids,  class Mammalia, class Sauropsida, sauropsids, subclass Anapsida, anapsids, turtles, subclass Diapsida, diapsids, dinosaurs, order Squamata, squamates, lizards, snakes, order Crocodilia, crocodiles, (Google Search)]

(g)                    [(8) leaving the water, (9) amphibians and reptiles, (10) reptiles and thermoregulation, (11) Triassic takeover, (12) dinosaurs, (13) warm-blooded dinosaurs?, (14) the evolution of flight, (15) the origin of mammals, (16) marine reptiles, (17) why flowers are beautiful, (18) the end of the dinosaurs, (19) Cenozoic mammals: guides and trends, (20) geography and evolution, (21) primates, (22) evolving toward humans, (23) the ice age, (24) humans and the ice age (a wonderful collection of links that follow the evolution of the tetrapod vertebrates),  (Biology 404—Colorado State University, Fullerton)] [index]

(23) Class Amphibia (amphibians, frogs, salamanders)

(a)                    The amphibians were the dominant terrestrial vertebrates during the Carboniferous period, i.e., the same time the seed-less, vascular plants dominated the land

(b)                    The modern amphibians include the frogs and the salamanders

(c)                    Most amphibians are dependent on the water, minimally for reproduction

(d)                    This is because their eggs are not desiccation resistant

(e)                    In addition, many amphibians employ their skin for gas exchange, thus requiring that their skin remain moist

(f)                      Thus, amphibians tend to be not as well-adapted to long term, especially multi-generational excursions away from moist habitats

(g)                    See Figure 34.15, The origin of tetrapods

(h)                    See Figure 34.17, Amphibian orders

(i)                      See Figure 34.18, The “dual life” of a frog (Rana temporaria)

(j)                      [class Amphibia, amphibians, frogs, salamanders, evolution of amphibians (Google Search)] [index]




(24) Amniotes

(a)                    The amniotes are a clade within the tetrapods named for their key adaptation to true terrestrial life: the amniote egg

(b)                    "The evolution of reptiles from an amphibian ancestor involved many adaptations that we can interpret as specializations for terrestrial living. The amniotic egg, a reproductive adaptation that enabled terrestrial vertebrates to complete their life cycles on land and sever their last ties with their aquatic origins, was a particularly important breakthrough (Seeds played a similar role in the evolution of land plants)."

(c)                    The amniotes include the reptiles and their descendants including the mammals, the dinosaurs, and the birds

(d)                    See Figure 34.20, A hypothetical phylogeny of amniotes

(e)                    See Figure 34.21, Taxonomic classes of amniotes

(f)                     [amniotes, Amniota, evolution of amniotes (Google Search)] [index]

(25) Amniotic egg (amniota) (not in index)

(a)                    The amniote egg is a shelled egg adapted to desiccation prevention

(b)                    The amniote egg employs extraembryonic membranes to transfer stored nutrients and water, exchange gasses, and remove wastes.

(c)                    See Figure 34.19, The amniotic egg

(d)                    [Amniotic egg, note various extraembryonic membranes: ]

(e)                    [amniotic egg (Google Search)] [index]

(26) Class Reptilia (reptiles)

(a)                    The reptiles gave rise to the dinosaurs, the mammals, the birds, a number of additional classes, and, of course, all extant reptiles

(b)                    The reptiles were the first fully terrestrial vertebrates, achieving true freedom from water except, of course, for the need to drink

(c)                    This freedom was achieved through a number of adaptations that served to increase water retention compared with amphibians

(d)                    These adaptations include

(i)                      The amniotic egg

(ii)                    Achieving gas exchange solely through lungs

(iii)                   Keratinized (i.e., waterproof) skin

(e)                    (as an aside, note that these adaptations are analogous to seeds, stomata, and a waxy cuticle in plants)

(f)                      Modern reptiles includes the lizards/snakes, the crocodiles, the tuatara, and the turtles

(g)                    [Reptilia, reptiles, evolution of reptiles (Google Search)] [index]

(27) Class Aves (birds)

(a)                    Birds are reptiles anatomically modified for flight

(b)                    Compared to their reptile ancestors, birds

(i)                      Have feathers

(ii)                    Have forelimbs modified as wings

(iii)                   Have a bill made of keratin (feathers and hair are also made of keratin)

(iv)                  Have no teeth (reduces weight)

(v)                    Grind their food in a gizzard (since no teeth—seen also in dinosaurs)

(vi)                  Have certain reduced or absent organs (reduces weight)

(vii)                 Have ultra-light bones (reduces weight)

(viii)               Have acute vision (high-speed tree-branch avoidance)

(ix)                  Have larger brains (high-speed 3-D computation)

(x)                    Are bipedal (as were dinosaurs)

(xi)                  Etc.

(c)                    See Figure 34.25, Form fits function: the avian wing and feather

(d)                    See Figure 34.26, A bald eagle in flight

(e)                    See Figure 34.27, Archaeopteryx, a Jurassic bird-reptile

(f)                     See Figure 34.29, A small sample of birds

(g)                    Many of these adaptations are likely true of the non-bird ancestors of birds (e.g., possessing gizzard, bipedalism, etc.)

(h)                    There exists a contentious debate over the reptilian origin of birds with some (the majority and sexiest opinion) arguing that birds evolved from bipedal dinosaurs that also gave rise to such things a velociraptors and Tyranosaurous rex, and the minority arguing that birds arose from non-dinosaur reptiles

(i)                      “Cladistic analysis of fossilized skeletons support the hypothesis that the closest reptilian relatives of birds were the theropods, a group of relatively small, bipedal, carnivorous dinosaurs. (The velociraptors of Jurassic Park fame were theropods.) Most researchers agree that the ancestor of birds was a feathered theropod. However, some scientists place the origin of birds much earlier, from an ancestor common to both birds and dinosaurs.” (p. 699, Campbell & Reece, 2002)

(j)                      [A model showing a Caudipteryx zoui, a flightless dinosaur that lived 120 to 136 million years ago. It offers further evidence that birds descended from dinosaurs.

(k)                    ]

(l)                      Other representations (see for views of the actual fossil, etc.):

(m)                  [Aves, birds, evolution of birds (Google Search)] [index]




(28) Class Mammalia (mammals)

(a)                    "The extinction of the dinosaurs at the close of the Mesozoic era opened many adaptive zones, and mammals underwent an extensive adaptive radiation that filled the void."

(b)                    There are many characteristics of mammals which distinguish them (us) from other reptiles:

(i)                      Hair

(ii)                    Mammary glands

(iii)                   Larger brains

(iv)                  Differentiation of teeth

(v)                    Modified jaws

(vi)                  Etc.

(c)                    Mammals date back about 220 million years, though the mammal-like reptiles date back much further

(d)                    See Figure 34.26, The evolution of the mammalian jaw and ear bones

(e)                    ["Transitional fossils between groups have been found. One of the most impressive transitional series is the ancient reptile to modern mammal transition. Mammals and reptiles differ in skeletal details, especially in their skulls. Reptilian jaws have four bones. The foremost is called the dentary. In mammals, the dentary bone is the only bone in the lower jaw. The other bones are part of the middle ear. Reptiles have a weak jaw and a mouthful of undifferentiated teeth. Their jaw is closed by three muscles: the external, posterior and internal adductor. Each reptile tooth is single cusped. Mammals have powerful jaws with differentiated teeth. Many of these teeth, such as the molars, are multi-cusped. The temporalis and masseter muscles, derived from the external adductor, close the mammalian jaw. Mammals have a secondary palate, a bony structure separating their nostril passages and throat, so most can swallow and breathe simultaneously. Reptiles lack this. ¶ The evolution of these traits can be seen in a series of fossils. Procynosuchus shows an increase in size of the dentary bone and the beginnings of a palate. Thrinaxodon has a reduced number of incisors, a precursor to tooth differentiation. Cynognathus (a doglike carnivore) shows a further increase in size of the dentary bone. The other three bones are located inside the back portion of the jaw. Some teeth are multicusped and the teeth fit together tightly. Diademodon (a plant eater) shows a more advanced degree of occlusion (teeth fitting tightly). Probelesodon has developed a double joint in the jaw. The jaw could hinge off two points with the upper skull. The front hinge was probably the actual hinge while the rear hinge was an alignment guide. The forward movement of a hinge point allowed for the precursor to the modern masseter muscle to anchor further forward in the jaw. This allowed for a more powerful bite. The first true mammal was Morgonucudon, a rodent-like insectivore from the late Triassic. It had all the traits common to modern mammals. These species were not from a single, unbranched lineage. Each is an example from a group of organisms along the main line of mammalian ancestry." (Talk.Origins)]

(f)                      Today, the mammals can be subdivided into three major taxa

(i)                      Monotremes

(ii)                    Marsupials

(iii)                   Placentals (Eutherians)

(g)                    See Figure 34.33, Hypothetical cladogram of mammals

(h)                    [Mammalia, mammals, mammal-like reptiles, evolution of mammals (Google Search)] [index]

(29) Monotremes (echidnas, platypuses)

(a)                    The monotremes are the only mammals (possess both hair and mammary glands) which lay eggs and include the platypuses and echidnas (spiny anteaters)

(b)                    "The egg, which is reptilian in structure and development, contains enough yolk to nourish the developing embryo. Monotremes have hair and produce milk, two of the most important trademarks of Mammalia. On the belly of a monotreme mother are specialized glands that secrete milk. After hatching, the baby sucks the milk from the fur of the mother, who has no nipples. The mixture of ancestral reptilian characters and derived characters of mammals suggests that monotremes descended from a very early branch in the mammalian genealogy."

(c)                    This is an echidna and a platypus, respectively:


(e)                    See Figure 34.31a, Australian monotremes and marsupials

(f)                     See Figure 34.33, Hypothetical cladogram of mammals

(g)                    [monotremes, echidnas, platypuses, evolution of monotremes (Google Search)] [index]

(30) Marsupials (kangaroos, koalas, opossums)

(a)                    "Opossums, kangaroos, and koalas are examples of marsupials, mammals that complete their embryonic development in a maternal pouch."

(b)                    "In Australia, marsupials have radiated and filled niches occupied by placental mammals in other parts of the world. Convergent evolution has resulted in a diversity of marsupials that resemble their placental counterparts occupying similar ecological roles."

(c)                    "The opossums of North and South America are the only extant marsupials outside the Australian region."

(d)                    See Figure 34.32, Evolutionary convergence of marsupial and eutherian (placental) mammals

(e)                    See Figure 34.33, Hypothetical cladogram of mammals

(f)                      [marsupials, kangaroos, koalas, opossums, evolution of marsupials (Google Search)] [index]

(31) Placentals (eutherians)

(a)                    The placental mammals diverged from the marsupials about 80 to 100 million years ago.

(b)                    See Figure 34.33, Hypothetical cladogram of mammals

(c)                    Note that there may exist four major extant placental-mammal lineages

(i)                      An African-centered branch that includes elephants, manatees, hyraxes (an elephant relative), and aardvarks

(ii)                    A South-American-centered branch that includes sloths, anteaters, and armadillos

(iii)                   Primates, rodents, rabbits, and tree shrews

(iv)                  Everything else (i.e., ranging from the carnivores—cats, dogs, bears, seals, etc.—through the whales though the ungulates such as deer, pigs, cows, and horses), etc.

(d)                    See Table 34.2, Major orders of mammals

(e)                    [placentals, placental mammals, eutherian, bats, carnivora, rodents, shrews, evolution of placental mammals, evolution of bats, evolution of carnivores, evolution of rodents, evolution of shrews (Google Search)] [index]




(32) Primates (prosimians) (is not in index?)

(a)                    Key to understanding the evolution of primates is understanding that much of primate evolution consisted of adaptation to arboreal living, i.e., in trees (note that the same, to a large extent, can also be said of the birds)

(b)                    Primate ancestors likely first chased insects in trees

(c)                    Being a predator that lives in trees likely is a least somewhat similar to the lifestyle that gave rise to the birds, and has made a similar impact on the primates

(i)                      Primates possess numerous skeletal/musculature adaptations that allow rapid movement through trees, such as having flexible joints (for swinging from branches), i.e., just as birds have modified forelimbs adapted to flying

(ii)                    Primates possess hands rather than paws which are useful for grasping branches, just as the bird hind limbs are adapted also for grasping branches; hands additionally allow skilled manipulation of food (see image to right of various prosimian hands à)

(iii)                   Good eyesight; just as birds need good eyes to keep from running into things while they fly, primates need good eyesight to keep from running into things as they move rapidly through trees; many primates additionally possess overlapping fields of vision that allow a three dimensional characterization of their environment

(iv)                  Big brains; to move rapidly through a complex, three-dimensional environment requires lots of processing power

(d)                    Big brains, good eyesight, and hands allowed the adaptation by primates to becoming "specialists" in the acquisition of high quality foods, such as fruits and other briefly available plant products; that is, rather than morphological adaptation to specific kinds of foods (e.g., cows to grass)

(e)                    Big brains and good memories are crucial to animals that consume large varieties of food that are present in their environments in only limited supplies at limited times of the year and then in only a limited number of locals­­—keeping track of what's growing where and when is not easy and probably drove much of the evolution of increased intelligence among primates

(f)                      The competing, and not mutually exclusive hypothesis as to what drove the evolution of bigger and bigger brains among primates is the high degree of complexity of the social interactions within primate troops; those animals that failed to grasp this complexity were less able to obtain the advantages of group living so were lost from the gene pool

(g)                    There exist two extant primate suborders

(i)                      Suborder Prosimii (the prosimians, i.e., the lemurs, tarsiers, etc.)

(ii)                    Suborder Anthropoidea

(h)                    See Figure 34.35, A phylogenetic tree of primates

(i)                      [primates, order Primata, suborder Prosimii, prosimians, evolution of primates (Google Search)] [tai forest monkey project (under construction) (MicroDude)] [index]

(33) Suborder Anthropoidea (monkeys)

(a)                    Monkeys as well as the apes and hominids make up suborder Anthropoidea

(b)                    Compared with the prosimians, the monkeys

(i)                      are diurnal (daylight)

(ii)                    have color vision (color)

(iii)                   have opposable thumbs (thumbs)

(iv)                  have expanded brains (smart)

(v)                    have extended child development (childhood)

(vi)                  have complex social structures (clans)


(d)                    See Figure 34.36, New World monkeys and Old World monkeys compared

(e)                    [suborder Anthropoidea, monkeys, evolution of monkeys, evolution of anthropoids (Google Search)] [index]




(34) Superfamily Hominoidea (apes, hominoids,  gibbons, orangutans, gorillas, chimpanzees)

(a)                    Superfamily Hominoidea consists of the apes

(b)                    Compared with the monkeys, the apes

(i)                      Have larger bodies

(ii)                    Have larger brains (relative to body size)

(iii)                   Have no tails

(c)                    See Figure 34.37, Apes

(d)                    Superfamily Hominoidea includes the

(i)                      Gibbons (below is an animated gif of a gibbon brachiating)



(ii)                    Orangutans

(iii)                   Gorillas

(iv)                  Chimpanzees

(v)                    Hominids

(vi)                  A large number of extinct genera

(e)                    The gorillas, chimpanzees, and humans in particular are much less arboreal than their ancestors and are all more closely related to each other than either is to the other extant apes

(f)                      "If it were not for the vanity of human beings, we would be classified as an ape. Our closest relatives are, collectively, the chimpanzee and the pygmy chimp. Our next nearest relative is the gorilla." (Talk.Origins)

FAQ: I've been on an AOL message board recently where a number of posters insist that "humans are apes." The way I heard it humans and apes shared a common ancestor, but are not the same animal.  It seems to me that saying humans are apes is like saying dogs are wolves or mice are rats.  But I have very little training in biology. Does the formal definition of hominoidea make it "apes" or "apes and humans? I'd be grateful for any information.


"Wolves are dogs" might be a closer analogy to "Humans are Apes" with dogs a more global classification (e.g., including wolves, domestic dogs, coyotes, etc.). "Dogs are wolves", also works, however, since dogs are in fact domesticated descendants of wolves. The key in all of these musings is going to be two things: blood relationships and the associated concept of common ancestry. In particular, well before anyone had heard of evolutionary biology it was well understood that animals and plants could be grouped together based on their similarities. Thus, domestic dogs are similar to wolves, and vice versa. From this we infer common ancestry. If the similarity is even greater, then we assume that the common ancestor lived later (closer to the present) while if the similarity is less than we assume that the common ancestor lived earlier (farther from the present). The more ways that we can test similarity, the more confidence we have in concluding shared ancestry. Pushed to the extreme, it appears that all living things (on Earth!) share a common ancestry, an inference based upon significant biochemical similarity such as a core group of 20 translated amino acids, a common genetic code, common biochemical pathways, use of DNA as the molecule of heredity, and of RNA as a go-between between genotype and phenotype, etc.


Note that "Mice are rats" does not work. This is because mice are not rats and rats are not mice. However, you have put your finger on an important point, perhaps inadvertently: Mice and rats are similar and, in fact, are more similar to each other than either is to dogs, wolves, humans, or apes. We can describe mice as consisting of a group of animal species that have certain characteristics (small, fury tails, etc.). We can describe rats also as consisting of a group of animals species that have certain, but different characteristics (medium-small, naked tails, etc.). We can also describe a larger taxon (grouping of species) called order Rodentia, the rodents, that includes a number of relatively similar species including mice and rats. Note the hierarchy: Mice species are similar to other mice species, but less similar to rat species. At a higher level mice species are similar to rat species, but less similar to non-rodents. At an even higher level, class mammalia, we can group together mice, rats, dogs, wolves, and humans, which are all more similar to each other than any are to, say, a trout. Note, and this is important: The last common ancestor to all mice lived later (i.e., closer to the present) than the last common ancestor to all rodents. Older still was the last common ancestor to all mammals. And we can keep working our way back through time to the last common ancestor between all amniotes (reptiles and their descendants including mammals), all tetrapods (amphibians and their descendants including reptiles), etc. As the taxon becomes more inclusive, the members, as a whole, become less similar and the last common ancestor lived farther back in the past. Still, all members of a given taxa are blood relatives, literally with more-similar species less-distant cousins and less-similar species more-distant cousins.


Though the classification of organisms into clades--a group consisting of a common ancestor along with all descendant species--is non-arbitrary, determination of how to rank a given clade, e.g., genus versus family versus order versus class, can be quite arbitrary. Your concern, I believe, is a consequence of your confusion between your understanding of human evolution in terms of clades and your understanding of human evolution in terms taxonomic rank. What is unquestionably clear is that humans and apes such as chimpanzees share more features in common with each other than, for example, do domesticated cats with lions. Because our own lineage apparently has been subject to rapid morphological evolution, it might seem strange to argue that humans and chimps are that similar, but at all levels except perhaps the ones we humans hold most dear (i.e., that which we can see with our unaided eyes or create using our over-sized capacity for culture), humans and chimpanzees are nearly, though not quite, identical. Based upon this similarity we can infer that humans and chimpanzees are both members of the same clade with a last common ancestor that lived relatively recently, particularly when compared to the last common ancestor between, for example, humans and dogs, or even domesticated cats and lions.


Finding that humans and chimpanzees are members of a relatively recent clade is the scientific part of the above exercise. Where to rank that clade is much (much) more arbitrary, and really more a matter of personal opinion than based on hard scientific fact or inference. In fact, as a consequence of the visual dissimilarity between humans and chimpanzees, there has been significant controversy over the years not only where to rank this clade but also how to name it and even over what to include in it. Thus, for a long time "apes" were classified as a taxon that did not include humans. In good cladistic terms apes therefore represented a hypothesis positing that the last common ancestor to chimpanzees and gorillas and orangutans lived later (closer to the present) than the last common ancestor to humans and chimpanzees and gorillas and orangutans. By this assertion humans clearly are not apes. Unfortunately for that argument, however, there is overwhelming evidence that its basic premise is incorrect. That is, humans and chimpanzees, based upon similarity, appear to form a clade whose last common ancestor lived later (i.e., closer to the present) than the last common ancestor to humans, chimpanzees, and gorillas. In turn, the last common ancestor to humans, chimpanzees, gorillas, and organgutans lived even farther back in time.


If we are going to insist on calling chimpanzees, gorillas, and orangutans (as well as the gibbons) apes, then as good cladists we must include humans in this group. Humans--even though we clearly are not the same species as chimpanzees or gorillas, etc.--therefore still, clearly, are apes! That is, as you ask, superfamily Hominoidea (the apes) includes humans and all other apes. Family Hominidae (the hominids), on the other hand, forms a clade that includes humans, but not chimpanzees. Genus Homo, in turn, contains upright walking apes with relatively large brains, i.e., humans and human-like apes.


By the way, if you have an interest in throwing creation-myth into the above arguments, consider that a god or gods created humans in manner such that we are all more biologically similar to chimpanzees than chimpanzees are to gorillas. Same argument, same conclusion, different creative force. Humans still are apes, though apes, of course, are not necessarily human.

(g)                    [superfamily Hominoidea, hominoids, gibbons, orangutans, gorillas, chimpanzees, evolution of hominoids, evolution of apes, evolution of gibbons, evolution of orangutans, evolution of gorillas, evolution of chimpanzees (Google Search)] [index]




(35) Family Hominidae (hominids, bipedalism, knuckle walking)

(a)                    Family Hominidae includes the bipedal hominoids, but recently has also come to include the closest relatives to the bipedal apes among the Hominoids, i.e., the chimpanzees, the gorillas, and the orangutans, i.e., the great apes

(b)                  [“Hominidae: chimpanzees, gorillas, orangutans, humans. Until recently, most classifications included only humans in this family; other apes were put in the family Pongidae (from which the gibbons were sometimes separated as the Hylobatidae). The evidence linking humans to gorillas and chimps has grown dramatically in the past two decades, especially with increased use of molecular techniques. It now appears that chimps, gorillas, and humans form a clade of closely related species; orangutans are slightly less close phylogenetically, and gibbons are a more distant branch. …Chimps, gorillas, humans, and orangutans make up the family Hominidae; gibbons are separated as the closely related Hylobatidae.”]

(c)                    [The traditional view has been to recognize three families of hominoid: the Hylobatidae, the Hominidae, and the Pongidae. The Hylobatidae include the so-called lesser apes of Asia, the gibbons and siamangs. The Hominidae include living humans and typically fossil apes that possess a suite of characteristics such as bipedalism, reduced canine size, and increasing brain size such as the australopithecines. The Pongidae include the remaining African great apes including gorillas, chimpanzees, and the Asian orangutan.  Under the new classification model, hominoids would remain a primate superfamily, as has always been the case. Under this hominoid umbrella would fall orangutans, gorillas, chimps, and humans, all in the Family Hominidae.  ¶ In recognition of their genetic divergence some 11 to 13 million years ago, the orangutans would be placed in the sub-family Ponginae and the African apes, including humans, would all be lumped together in the sub-family Homininae. The bipedal apes—all of the fossil species as well as living humans—would fall into the tribe Hominini (thus hominin). All of the fossil genera, such as Australopithecus, Ardipithecus, Kenyanthropus, and Homo, would fall into this tribe. – Lee R. Berger writing for National Geographic News]

(d)                    Family Hominidae, the strictest sense, includes at least two genera of bipedal apes:

(i)                      Genus Australopithecus

(ii)                    Genus Homo

(e)                    Both diverged from a common ancestor with the chimpanzee about 5 million years ago (and from the common ancestor to the rest of the African apes a few million years earlier)

(f)                      Bipedalism is a derived character from a presumably ancestral knuckle walking ancestor, as is still employed by the gorillas and chimpanzees

(g)                    See Figure 34.38, A timeline for some hominid species

(h)                    See Figure 34.39, Upright posture predates an enlarged brain in human evolution

(i)                      The environmental cause of the divergence may have been the opening of the East African rift valley and the corresponding drying of Eastern Africa


(k)                    See for a fun tour of the reconstructed faces of the various bipedal hominids

(l)                      [family Hominidae, homonids, bipedalism, knuckle walking, East African rift valley, evolution of hominids, evolution of bipedalism (Google Search)] [index]

(36) Genus Australopithecus (australopithecines)

(a)                    The Australopithecines are an extinct genera consisting of bipedal but relatively small-brained apes (larger brains than chimps, smaller brains than members of genus Homo)

(b)                    The australopithecines were not obligate tool users

(c)                    Genus Australopithecus was ancestral to genus Homo

(d)                    The divergence between these two genera occurred approximately 2.5 million years ago

(e)                    The last Australopithecine went extinct approximately 1 million years ago

(f)                      [These are skulls of A. africanus and A. afarensis (i.e., Lucy’s kin), respectively: ]

(g)                    [This is a reconstruction of the Taung child (A. africanus infant; left) and a comparison of Australopithecus with a human (right):

(h)                    ]

(i)                      [genus Australopithecus, australopithecines (Google Search)] [index]




(37) Genus Homo (obligate tool users)

(a)                    Members of genus Homo are essentially larger-brained australopithecines

(b)                    Members of genus Homo additionally were/are obligate tool users; that is, they likely derived a huge advantage from their technology versus their morphological (i.e., evolutionary) adaptations

(c)                    The first member of genus Homo arose approximately 2.5 million years ago

(d)                    One factor which may have driven the evolution of genus Homo from the ancestral australopithecine is the scavenging of meat

(e)                    In order of their appearance, the commonly accepted members of genus Homo who were ancestral to modern humans includes

(i)                      Homo habilis

(ii)                    Homo erectus

(iii)                   Homo sapiens archaic

(f)                      [genus Homo, evolution of genus homo, "tool use" homo (Google Search)] [index]

(38) Homo habilis

(a)                    "Handy man," Homo habilis was a relatively early ape who was an obligate tool user (~2.5 to ~1.6 mya) [CHECK DATES]

(b)                    [This is the skull (left) of H. habilis (or, more correctly, is the skull of Homo rudolfensis), a portrait (right), and the details of a reconstruction (below):

(c)                    ]

(d)                    [Homo habilis, evolution of Homo habilis (Google Search)] [index]

(39) Homo erectus

(a)                    In terms of the longevity of the species, Homo erectus was/is the most successful member of genus Homo (~1.8 to 0.5 mya) [CHECK DATES]

(b)                    Humanity had truly almost arrived as H. erectus replaced H. habilis as the dominant Homo species.

(c)                    H. erectus

(i)                      lived in large groups

(ii)                    controlled fire

(iii)                   had a much more sophisticated "tool kit" than all animals that came before her

(iv)                  spread her kind throughout the old world

(d)                    She was also the most culturally advanced creature of any previous.

(e)                    [This is a skull (left) of H. erectus and a portrait (right):

(f)                      ]

(g)                    See for a fun tour of the reconstructed faces of the various bipedal hominids

(h)                    [Homo erectus, evolution of Homo erectus (Google Search)] [index]

(40) Homo sapiens

(a)                    Homo sapiens was one of perhaps many species which descended from H. erectus, certainly one of many sub-species of a species that descended from H. erectus

(b)                    Homo sapiens are first defined as archaic forms which likely are simply anatomically diverse, not-necessarily-the-same-species descendants of H. erectus

(c)                    Modern H. sapiens are first found in the fossil record only from about 100,000 years ago

(d)                    By contrast, H. erectus survived on this earth for nearly 1,000,000 years

(e)                    H. sapiens possess the largest brain size to body size ratio of any animal, though some archaic forms of H. sapiens possessed even larger brains

(f)                      H. sapiens additionally, and correspondingly, have better exploited cultural evolution than any previous animal

(g)                    This, of course, is the skull of a modern human:

(h)                    [Homo sapiens, evolution of Homo sapiens (Google Search)] [index]




(41) Cultural evolution (culture)

(a)                    Lot's of animals participate in cultural evolution

(b)                    Culture simply represents behavior learned from others

(c)                    An organism that can learn new behavior from others need not

(i)                      Code all of their behavior in their genes

(ii)                    Learn all of their learned behavior de novo each generation

(d)                    Culture

(i)                      May be passed down from generation to generation

(ii)                    May be passed down imperfectly (e.g., with mistakes or with modification)

(iii)                   May underlie differential survival

(e)                    Thus, even if individuals are not consciously attempting to modify their culture, culture can and will change with time as novel ideas are introduced and as individuals (or groups) with bad ideas (in a Darwinian fitness sense) are culled

(f)                      Thus, cultures can evolve, often faster and differently from the evolution of genes (i.e., identical individuals in identical environments can vary in their fitness as a consequence of the learned behaviors they employ)

(g)                    Humanity represents the ultimate application of culture towards the enhancement of the Darwinian fitness of a species

(h)                    Unfortunately, despite our cultural prowess, we as a species are still locked into a pattern of enhancing our own short-term fitness (e.g., our immediate comfort and personal reproductive output) at the expense of the fitness of our descendants, our species, and our planet—with every hedonistic evolutionary impulse further converting our metaphorical Garden of Eden, a.k.a., planet Earth, into one big, polluted, weedy, desertified mess

(i)                      [cultural evolution, culture, memes (Google Search)] [index]




(42) Vocabulary [index]

(a)                    Amniotic egg

(b)                    Amniotes

(c)                    Amphibians

(d)                    Apes

(e)                    Australopithecines

(f)                      Bipedalism

(g)                    Birds

(h)                    Bony fish

(i)                      Cartilaginous fish

(j)                      Chimpanzees

(k)                    Chordate through tetrapod phylogeny

(l)                      Chordates

(m)                  Class Agnatha

(n)                    Class Amphibia

(o)                    Class Aves

(p)                    Class Chondrichthyes

(q)                    Class Mammalia

(r)                     Class Osteichthyes

(s)                     Class Placodermi

(t)                      Class Reptilia

(u)                    Coelacanths

(v)                    Cultural evolution

(w)                  Culture

(x)                    Dorsal, hollow nerve cord

(y)                    Echidnas

(z)                     Eutherians

(aa)                 Family Hominidae

(bb)                Frogs

(cc)                 Genus Australopithecus

(dd)                Genus Homo

(ee)                 Gibbons

(ff)                    Gorillas

(gg)                 Hagfish

(hh)                 Hominids

(ii)                     Hominoids

(jj)                    Homo erectus

(kk)                Homo habilis

(ll)                     Homo sapiens

(mm)             Jawless fish

(nn)                 Jaws

(oo)                Kangaroos

(pp)                Knuckle walking

(qq)                Koalas

(rr)                   Lancelets

(ss)                  Lobe-finned fish

(tt)                    Mammals

(uu)                 Marsupials

(vv)                 Modern fish

(ww)             Monkeys

(xx)                 Monotremes

(yy)                 Muscular, postanal tail

(zz)                  Notochord

(aaa)             Obligate tool users

(bbb)            Opossums

(ccc)             Orangutans

(ddd)            Ossification

(eee)             Pharyngeal slits

(fff)                  Phylum chordata

(ggg)             Placentals

(hhh)             Platypuses

(iii)                   Primates

(jjj)                  Rays

(kkk)            Ray-finned fish

(lll)                   Reptiles

(mmm)       Rhipidistians

(nnn)             Salamanders

(ooo)            Sea lamprey

(ppp)            Sea squirts

(qqq)            Sharks

(rrr)                Somites

(sss)               Suborder Anthropoidea

(ttt)                  Subphylum Cephalochordata

(uuu)             Subphylum Urochordata

(vvv)             Subphylum Vertebrata

(www)       Superclass Gnathostomata

(xxx)             Superfamily Hominoidea

(yyy)             Swim bladder

(zzz)               Tetrapods

(aaaa)          Tunicates

(bbbb)        Vertebrates