Emergent Mammals II

"The mammals arose within the therapsid radiation in the Late Triassic (252 - 201 mya), initially small and shrewlike. These Mesozoic (252 - 66 mya) animals [co-existed] with a terrestrial fauna then dominated by dinosaurs, especially the sauropsids" (Vertebrates, 2012, p. 122).


(419 - 359 mya)


(201 - 145 mya)


(201 - 145 mya)


(252 - 201 mya)


(adapted from Vertebrates, 2012, p. 123)

1) The mammal possesses a chain of 3 bones in the middle ear, that conduct sound from the eardrum to the inner ear (reptiles have only one primary middle ear bone);

2) Whereas several bones comprise the reptilian lower jaw, mammals posses only a single, dentary, bone; and

3) Whereas reptiles have additional bones to complete the jaw joint, mammals have a joint between the dentary and squamosal  bones of the jaw.

ungulate: one of the 16 Mammalian orders, that refers to hooved animals.

protozoa: unicellular, animal-like protists, including amoebas, foraminiferans, actinopods, ciliates, flagellates, and apicomplexans (Biology, 6th Ed., 2002).

protist: once considered a vast kingdom of eukaryotic organisms, primararily unicellular, or simple multicellular (Biology, 6th Ed., 2002), now 'kingdom protista' no longer considered a clade, but considered to be the first eukaryotes to evolve (Biology, 10th Ed., 2015, p. 533).

flagellate protozoan: also identified as subphylum: mastogophora, a uni-nucleate (single nucleus) protozoan, using one or more flagella (hair-like structures) for locomotion, divided into plant-like or animal-like (zoomastigophorea) classes (

eukaryote: the name of a member of one (Eukarya) of 3 principal taxonomic Domains. Eukaryotes, having 2 main clades - 1) unikonts (having a common ancestor with a single postrerior flagellum); and 2) bikonts (having a common ancestor with 2 flagella) are those organisms whose cells possess nuclei and other membrane-bound organelles, organisms which exist in the kingdoms of Animalia, Protista, Fungi, Plants, and Monera.

vertebrata: also called craniata, the sub-phylum derived from the phylumchordates, having a backbone and bony skull that partly encloses a central nervous system. The hollow, dorsal nerve tube is now replaced by the spinal cord, which is now protected by a segmented vertebral, or spinal, column, composed of cartilage and/or bone, which serves as the axis of the interior skeleton, provides strength and rigidity to the body, and as an attachment for muscles (info The head and brain house paired sense organs, that coordinate movement and sensation. Fish (superclass Pisces), comprised of 4 distinct classes, were the first vertebratesSub-phylum vertebrata includes a total of 8 classes, including 4 classes of fish (agnathans (jawless ostracoderms); gnathans (jawed placoderms)chondrichthyes (cartilagenous sharks); and osteichthyes (bony)), and the additional 4 classes (superclass Tetrapoda): amphibia, reptilia, aves (birds), and mammalia ( All fish have gills, and most have 2 sets of paired fins (pectoral and pelvic girdle), while all tetrapods breath air, with 2 sets of paired limbs for locomotion. Amphibians are an exception, with an earlier aquatic gill phase; and snakes have homologous limbs (

zonation, stratigraphic: Examining the distribution of fossilized remains of extinct, ancient fauna, also called biotic groups, such as trilobites (agnostic and polymerid), graptolites, conodonts, chitinozoa, and acritarchs, geologists have been able to achieve worldwide biostratigraphic accuracy, precision, and consistency, in determining the global, environmental characteristics of Earth's complexly layered, temporal subdivisions, which can become meaningfully labeled as stages, periods, eras, epochs, and ages (The Geologic Time Scale, 2012, p. 490).

protostome: A major, fundamental division of the animal kingdom, specifically one of two divisions of bilateria, importantly distinguished from its counterpart, the deuterostomes, in which the blastopore (the first opening into the embryonic gut) develops into the mouth, and the anus forms secondarily. The coelom (body cavity) develops from a split in the embryonic mesoderm (middle tissue); includes the annelids (worms), arthropods (insects, crabs), and mollusks (clams, snails) (Biology, 6th Ed., 2002; and

echinodermata: a phylum of invertebrate marine animals, evolved from deuterostome coelomates, each organism with a skeleton of calcium plates, and a coelom (body cavity), containing a water-vascular system of fluid-filled vessels. Well-known examples are sea urchins, sand dollars, and sea cucumbers. This phylum, is one of 3 phyla derived from the super-phylum, deuterstomes, the other 2 phyla known as hemichordates (represented by acorn worms), and chordates, from which the vertebrates are derived (see Bibliography for references).

deuterostome: A major division of the animal kingdom, a clade, in which the anus develops from the blastopore (from Biology, 6th Ed., 2002)

chordate: an animal phylum, derived from the deuterostomes of the subkingdom bilateria, these organisms are characterized by 5 defining features: 1) a dorsal nerve tube;  2) lateral gill (or pharyngeal) slits or pouches, originally used to obtain oxygen in aquatic environments, but replaced by lungs during embryonic development, in reptiles and mammals; 3) a notochord, i.e., a rudimentary internal skeleton of stiff cartilage, running dorsally (on the back) adjacent to the single, hollow nerve tube (1); 4) an endostyle; and 5) a post-natal tail; this phylum includes 3 subphyla: 1) cephalochordate, represented by amphioxus, subsumed under lanceletssubphylum 2) urochordata, represented by tunicates (sea squirts); and subphylum 3) vertebrata. Two additional features are elongated, bilaterally symmetrical bodies, and a digestive tube running through the body.

coelom: the closed, fluid-filled, body cavity, formed within the mesoderm (one of the 3 embryonic "germ" layers, i.e., also endoderm and ectoderm), which, in early phyla, serves as a site for temporary food storage; for the excretion of nitrogen waste; and the maturation of gametes. This cavity develops as the mesodermal sacs or outpocketings of the primitive/embryonic gut of multicellular animals, which, in advanced species, helps the (connective) mesenteric tissue to suspend the contents/viscera of the gut, allowing coelomates to obtain greater body size (adapted from; the fluid-filled body cavity, between the body wall and the digestive tube (Biology, 2002, p. 598)

strepsirrhini: one of two primate suborders, distinguished from haplorrhini, also known as pro-simian ("before apes"), and "wet-nosed", represented by lemurs, galagos (bush-babies), and lorises, are predominantly insect eaters, have longer snouts (with a larger olfactory bulb), have a grooming claw instead of a flat nail on the 2nd toe of each foot, and their lower incisors and canines cluster together forming a tooth-comb, also for grooming. The tarsiers, with a wet nose and lacking a tapetum lucidum (reflective layer of posterior eye, that improves night vision), are an ambiguous member of strepsirrhini, now often grouped with the haplorrhini (monkeys, apes, humans)

haplorhini: the second major division, a semi-order, of the order Primates, distinguished from strepsirrhini, characterized as "dry-nosed", called also "simians" or simiiformes, or anthropoidea - monkeys, apes, humans (with the exception of an ambiguous tarsiformes (tarsiers) group). The haplorhines lack the reflecting tapetum lucidum of the posterior eye, but instead have evolved a retinal fovea for enhanced vision; a hemichorial placenta that allows for maternal-fetal sharing of blood, shed monthly if fertilization fails; and having separated from the strepsirrhini about 60 mya (

platyrrhini: an infra-order of anthropoidea, contrasted with catarrhini (old world monkeys, apes, and humans), literal meaning "flat-nosed" primates (nostrils far apart, and directed forward or sideways), usually with a prehensile tail, having 36 teeth (contrasted with the catarrhines' 32 teeth), the group comprising the New World Monkeys, with geographical habitats exclusively in South America.

bilateria: one of 2 ancient sub-kingdoms of the Animal kingdom (the other is Radiata), which further divides into 2 sub-sub-kingdoms, the 1) protostomes (spiral cleavage, where the embryonic blastopore becomes the mouth), and 2) deuterostomes (radial cleavage, where the embryonic blastopore becomes the anus, which evolves to chordates and vertebrates).

catarrhini: an Infra-order, between Sub-order Anthropoidea and Super-family Hominoidea, that includes Old World Monkeys, Apes, and Humans. Catarrhine tails, unlike New World Monkeys, are not prehensile (i.e., cannot grasp). Their molar teeth are biphondont, i.e., with 4 cusps (bumps), arranged in 2 lophs (ridges), each loph with 2 lobes (projections), characteristic of a diet abundant in chewy leaves. Nostrils face forward and down, there is a narrow nasal septum, they have a divergent opposable thumb, and each jaw quadrant has 2 pre-molars rather than 3 (i.e., 32 teeth). See platyrrhines, from which it is distinguished.

amniotes: a group of limbed vertebrates that includes all living reptiles (class Reptilia)birds (class Aves), mammals (class Mammalia), and their extinct relatives and ancestors. The amniotes are the evolutionary branch (clade) of the tetrapods (superclass Tetrapoda) in which the embryo develops within a set of protective extra-embryonic membranes—the amnion, chorion, and allantois, in contrast to the amphibians, whose eggs require an aquatic environment. This biological development has allowed for land-based fetal development and birth, the protective egg providing a terrestrial-based aquatic environment (from

speciation: The process by which new species form, after a population of animals becomes separated, i.e., geopraphically isolated, from the main population. Such organisms may develop different characteristics, and eventually evolve into a new species. (Redmond, p. 30); "Evolution of a new species" (Biology, 10th edition, 2015, p. G-43).

species"...'groups of actually or potentially interbreeding natural populations that are reproductively isolated groups'..." (Redmond, p. 31). A group of organisms with similar structure, function, and behavior, that can breed with one another (Biology, 2nd edition, 2002, p. 368). One or more populations whose members are capable of interbreeding in nature to produce fertile offspring and do not interbreed with members of other species; this definition represents the biological species concept (Biology, 10th edition, 2015, pp. 418, G-43), in contrast to the phylogenetic species concept, which states that, to be declared a separate species, a population must have undergone evolution long enough for statistically significant differences to emerge (Biology, 10th edition, 2015, pp. 418, G-35).

subduction zone: where the heavier oceanic plate, at the convergent margin, sinks beneath the lighter plate. (Geology, 2001)

regolith: " irregular blanket of loose debris...[that] forms [from] the continuous chemical alteration and mechanical breakdown of rock through exposure to the atmosphere, hydrosphere, and biosphere...soils, muds in river valleys...desert [sands]...rock fragments, and all other unconsolidated debris are part of the regolith...Earth's regolith is unique because it forms as a result of complex interactions of physical, chemical, and biological processes, usually involving water..." (Geology, p. 28), and, unlike regolith that may exist on other cosmic bodies, it is postulated that, thus far, only the Earth's regolith contains soil (

reptile: a member within one of the 8 classes of the sub-phylum Vertebrata, its class comprising turtles, snakes, lizards, crocodiles, and the extinct dinosaurs. Features are cold-bloodedness, i.e., body temperature is regulated by external sources, such as sun-light (ectothermic), dry and scaly skin, and hard and leathery eggs.

rift valley: when the continental crust is stretched, torn, and splits apart (Geology2001).

primate: one of 19 orders of Mammalia, omnivorous in diet, initially comprised of small, nocturnal, tree-living (arboreal) species, in the tropical forests of the warming eocene epoch (56-34 mya), that evolved into two phyletic divisions, or semi-orders: 1) the haplorhinnes, or dry-nose simians, which includes the anthropoids, which eventually lead to humans. The 2nd semi-order of strepsirrhines, comprise the pro-simian lemurs, galagos, and lorises. Key primate features include forward facing eyes allowing for 3-dimensional, stereoscopic vision, with the eyeball sitting in a solid, protective orbital ring; the specialized use of their hands with an opposable digit, allowing for a firm grasp; flat nails to protect the sensitive tips of fingers and toes; tiny ridges (fingerprints) on fingertips, unique to each member; the presence of a bony clavicle, that connects the shoulder girdle to the sternum; varied means of locomotion and body size; and relatively larger cerebral hemispheres, which allow for increased intelligence and learning, and for more complex, flexible, high-level social interactions and (cultural) adaptability (from Redmond, p. 11, and Fleagle).

prosimian (prosimii): Primate phyletic division, or semi/sub-order, also called strepsirrhini (distinguished from the lineage of haplorrhini), considered a proto- or primitive primate, existing prior to monkeys, apes, and himans, with nocturnal activity enhanced by the tapetum lucidum (eye reflection), an insect diet, a long face, a moist snout, an enlarged olfactory lobe, prominent whiskers, large mobile ears, and large, slightly sideways-facing eyes, comprising the lemurs, galagos, lorises, pottos, and aye aye. The tarsiers have been re-grouped to align more with the haplorrhini-catarrhini lineage (from multiple sources; see Bibliography).

prokaryote: a cell that lacks a nucleus and other membrane-bounded organelles, which is characterized by the Domain Bacteria, as contrasted with  the eukaryotes (2.2 bya) of Domain Eukarya, which possess membrane-enclosed organelles (nucleus, mitochondria, plastids), multiple chromosoes of DNA and proteins, mitosis and meiosis, and sexual reproduction.

phylogeny: "The branching pattern of successive species that results from numerous cladogenetic events" (source?); The course of evolutionary change within a related group of organisms (Vertebrates, p. 753); the complete evolutionary history of a group of organisms (Biology, p. G-35); The course of evolution, summarized using tree-like, branched connections between groups, such summaries called dendrograms (Vertebrates, p. 20).

monophyletic group: when all descendents are derived from a single ancestor.

mineral: a substance comprised of an orderly arrangement of atoms, organized in regular, repeated, geometric patterns, known as its "crystaline structure". The crystalline structure is a unique structural pattern for a specific mineral, identical in all specimens (Geology).

mid-ocean ridge: forms when an oceanic crust splits apart, and the seafloor spreads.

mantle: the layer beneath the Earth's crust, comprised of an outer, mostly rocky layer (part of the lithosphere), and an inner near-molten layer (Geology  p. 15).

lithosphere: a thin, cold, brittle, rocky layer of the Earth, about 60 miles thick, comprised of the Earth's crust (composed mostly of silicates, oxides - magnetite and hematite, and calcium carbonate - CaCO3) , plus the rocky, outermost part of the 2-layered mantle (the lower, weakened liquid layer is the asthenosphere). The lithosphere makes up the 6 large tectonic plates, which account for continental drift.

isostasy: The state of floating tectonic plates, comprised of the Earth's crust and outer layer of the mantle (the inner layer of the mantle is the hot asthenosphere), combined called the lithosphere; the flotational balance of the lithosphere on top of the asthenosphere (Geology, 2001, p. 277).

hominoidea: a taxonomic "superfamily", the members of which have large size, intelligence, and lack a tail, including homo sapiens, non-human great apes (6 species), and lesser apes (12 species). (Redmond, p. 147)

gneiss: a metamorphic rock, whose original form and mineralology have been altered by high temperatures and/or high pressures (Geology, p. 43).

divergent margins: huge lithosphere fractures, where tectonic plates move apart from one another.

convergent margins: describes 3 types of movement of tectonic plates towards one another: 1) ocean-to-ocean; 2) ocean-to-continent; and 3) continent-to-continent. 

anthropoid: a primate sub-order, sandwiched taxonomically below Haplorhinnes, and above Catarhinnes. Referred to as "simian"; describes the "higher primates", including old and new-world monkeys, apes, and humans. Features include a flatter face, dry nose, small immobile ears, and forward-facing eyes; distinguished from 'lower primates', such as tarsiers, lemurs, lorises, pottos, and galagos. The earliest known anthropoid genus, Eosimias, or the "Dawn Monkey", represents the earliest known anthropoid, from the Eocene epoch, 40 mya (Evolution, Roberts, A., 2011, p. 43).

asthenosphere: the almost-molten, inner portion of the rocky mantle layer, contiguous with, and beneath, the lithoshere. Considered a weakened layer, due to its liquid status, the lithospheric plates float and shift upon it (Geology, 2001).

amphibian: a member of one of the 8 classes of the subphylum Vertebrata. Amphibians are the evolutionary bridge between fish and reptiles, whereby it is speculated that intermediary lobe-finned fishes, through gradual, transitional stages, including the tetrapod-like fish, Tiktaalik (375 mya), became increasingly terrestrial, and thereby less dependent on an aquatic environment for oxygen intake (respiration, breathing) and egg-laying. Amphibia include frogs, toads, newts, salamanders, and caecilians (limbless amphibians, that resemble large worms). Their features are cold-bloodedness (body heat derived from external sources); aquatic larvae (young must breed in water, as opposed to amniotes, where extra-embryonic membranes provide a land-based aquatic environment for the embryo); gill breathing in young; but lung and moist glandular skin breathing in semi-terrestrial adults.


endostyle: one of the 5 defining features of a chordate, a glandular organ that corresponds to the thyroid gland in vertebrates, lying below two levels of gill slits, which, in amphioxus, produces an iodinated tyrosine molecule (

sulcus, lunate: the fissure (the crack between the cerebral gyri) in the cerebri of the brain, that separates the occipital cortex from the neocortex. The size of the sulcus provides evidence for the degree of visual perception in an individual fossil, from the size of its etch-like impression on the interior of the skull. The occipital (visual) cortex enlarged as binocular, stereoscopic vision progressed in primates, but then such growth gave way to the enlarging neocortex, as the hominin brain enlarged, which accompanied hominin adaptation to climate change; the use of tools, fire, and cooking; and the development of language and culture(PBS NOVA, Becoming Human, Episode # 1). 

Habilis, Homo: One of 23 hominins, known as "Handyman", created crude stone tools, the first documented genus "homo", with a 600 cc brain case (Home sapiens is approx 1600 cc), fossils dated in the Pleistocene epoch, 2.4-1.6 mya.

animal: describes the kingdom of, in most instances, multicellular eukaryotes, the cells organized into tissues of 3 germ (primary cellular) layers - ectoderm, mesoderm, and endoderm -  and organs, with  heterotrophic behavior (consumes/ingests organic molecules from the environment, rather than synthesize them); with means of locomotion, having nervous and muscular systems; reproducing via sexual reproduction, whereby a haploid sperm unites with a haploid egg, to form a diploid zygote (fertilized egg); divided into 1) parazoa (represented by sponges - phylum: porifera - which are multicellular, but not "real" tissues, i.e., not 'specialized' "triploblastic"-derived  tissues, i.e., not evolving from ectoderm, mesoderm, or endoderm), and 2) eumetazoa, which represent true (specialized) tissues in a multicellular organism (Biology, 2002, pp. 595-597).

apatite (crystal): the non-living, calcium phosphate/flourine compound that is the hardest human tissue, that comprises tooth enamel, and is also present in bones, as the bone mineral, hydroxyapatite. Calcite is the compound in mollusks (calcium carbonate - CaCO3) which accounts for marine limestone deposits; and gypsum (calcium sulphate- CaSO4/H2O) is used to make plaster (Geology, 2001;

agnathan: a jawless fish that therefore lacks a biting apparatus, but with  a mouth, the jaw later derived from pharyngeal bars, (synonomous with brachial arches), the earliest vertebrate, from the early Cambrian period 541-485 mya, among the 8 classes of vertebrates, living members today including the (extantlampreys (class: petromyzontiformes); and the hagfishes - having a notochord and skull but no trace of vertebrae, and no paired appendages  (sub-phylum: myxiniformes: see page "Emergence of Chordates I),  both surviving groups known as cyclostomes ('round mouth'), which lack bone and possess a single nostril, although the modern cyclostomes differ in many of their features from their agnathan ancesters, the extinct ostracoderms, jawless fishes with body armor; contrast below with gnathostome (Biology, 2015, pp. 680-681; Vertebrates, 2012, 6th edition, p. 86).

ostracoderms: Earliest known jawless fish. These earliest of vertebrate marine animals, from the Cambrian period and extinct by end of the devonian period, exhibited fossil scales and plates made of bony tissue.  Armored with plates and scales, and jawless (class: agnatha), these bottom-dwellers lacked paired fins, and strained their food from water, similar to extant (existing) hagfishes and lampreys, the latter which have well-developed notochords, and cartilaginous skeletons (Biology 2015, p. 680).

notochord: the flexible, slender, longitudinal rod, running anteriorly-posteriorly, and dorsal to the coelom, that develops from mesoderm, that serves as an internal, structural support, i.e., as an endoskeleton, in the embryos of all chordates, and in some adults, i.e., prior to the evolution of a segmented veretebral column, first seen in vertebrate class: petromyzontiformes (today's lampreys) (Biology, 2002; Vertebrates, 2012, p. 52).

gnathostome: a synonym for jawed animals, including the earliest, extinct groups: acanthodians, and placoderms - both armored fishes with fins, that evolved from agnathans, in the late Silurian and Devonian periods, the jaws developing from a portion of the gill arch skeleton, which allowed fish to become predators, not simply passive suspension-feeder, bottom dwellers, a change which probably contributed to the extinction of ostracoderms (Biology, 2002).

degassing: the process whereby water molecules are released when rocks heat up above 500 degrees C., referring to the release of water during Earth's ocean's early evolution.

hydrosphere: the discontinuous layer of water, at or near the Earth's surface, that includes all liquid and frozen surface waters, groundwaters held in soil and rock, and atmospheric water vapor (; Baron's Earth Science).

stromatolite: rocklike columns composed of minute layers of prokaryotic, cyanobacteria, currently known by  ancient, 3.5 billion year old fossil reefs, and as contemporary, living reefs. The oxygen produced by these organisms initially saturated the oceans as iron oxide, and then seeped into the atmosphere, enormously contributing to the current concentration of 20 % atmospheric oxygen ( Biology, 2002).

clade: A natural evolutionary lineage including an ancestor plus all and only its descendants (Vertebrates, 2012); a group of organisms evolved from a common ancestor, also called a monophyletic group, their evolutionary relationships based on shared patterns of traits or characteristics, which include structural, developmental, behavioral, and molecular features (Biology, 6th ed.,2002, 10th ed., 2015).

scolex: the head of a tapeworm (Vertebrates, 2012, p.16).

choanoflagellates: unikonts (having a single posterior flagellum) that are probably the closest living nonanimal relative of animals, included with fungi in the opisthokont clade (Biology, 10th Ed., 2015)

protist: a primarily unicellular eukaryotic, mostly aquatic, organism within the Eukarya animal Domain (Biology, 6th Edition, 2002, p. G-37).

allopatric speciation, allopatry: occurs when one population of a species becomes geographically separated from the rest of the species, and independently evolves; the absence of overlap in the geographical range of 2 species or populations (Biology, 6th Edition, 2002, p. G-2; Primate Adaptation & Evolution, 3rd Edition, 2013, p. 411).

hominid (or hominidae): comprising the great apes and humans, i.e., humans, orangutans, gorillas, chimpanzees, and bonobos; distinguished from "lesser apes" by their larger size, more robust canine teeth, , broader pre-molars, a very broad ilium, and a robust fibula (Primate Adaptation & Evolution, 2013, pp. 155-157).

gene expression: encompasses the "...transcription of the genetic code in the nucleus [of the cell] to translation of the RNA code and the formation of proteins in the cell cytoplasm...there are approximately 30,000 different genes in each cell...[and] the total number of different proteins least 100,000..." (Textbook of Medical Physiology, p. 27).



geologic time: the entire time that the Earth has existed (Earth Science, 2015, 4th Edition, p, 260).

geologic time scale: "...the framework for deciphering and understanding the long and complex history of...Earth..." (The Geologic Time Scale, 2012, Volume I, p. 1).

atmosphere: the envelope of gases that surround a planet, extending from the land, ocean, and ice-covered surfaces, outward, into space (Geology, 2001, p. 196;

paraphyletic group: contain some, but not all, descendents of a single, common ancestor (Biology, 10th ed., 2015, pp. 535, G-33) (see also monophyletic group).

hemichordate: classified as one of the three divisions (i.e., in addition to echinoderms, and chordates), of the clade 'deuterostomes', these worm-like organisms, typified by acorn worms that live buried in mud, are comprised of a proboscis, collar, and trunk, with a ring of cilia around the mouth (Biology, 10th Ed., 2015, p. 671).

unikont: one of two main clades, also sometimes called a supergroup, of ALL eukaryotes, having a common ancestor with a single flagellum, while a second clade, the bikont, has a common ancestor with two flagella; unikonts further branch into 1) opisthikonts, which comprise fungi, choanoflagellates, and animals, and 2) amoebozoa, which have cytoplasmic projections of pseudopodia, a group which includes amoebas, and plasmodial and cellular slime molds (Biology, 10th Ed., 2015, pp. 549-550).

opisthokont: members of the unikont clade, having a single posterior flagellum, comprising the fungi, choanoflagellates, and animals. See unikont (Biology, 10th Edition, 2015, p. G-32).

tetrapod: a vertebrate with 4 limbs, which often refers  to animals that evolved in transition from fish with scales and fins, to a four-limbed terrestrial organism, beginning with the gradual development of class amphibia, in aquatic environments. Characterized by a "chiridium, a muscular limb with well-defined joints and digits", the earliest tetrapods stepped onto land during the late Paleozoic, after Pangaea split into the continents of northern Laurasia, and southern Gondwana (Vertebrates, p. 104).

tiktaalik: a transitional organism, that lived during the Devonian period, approximately 375 mya, that evolved as a link between fish and subsequent tetrapods (4-limbed vertebrates), that, having the scales and fins of a fish, also developed a mobile neck, and ribs that encased lungs, resembling terrestrial vertebrates (Biology, 10th Ed., 2015, pp. 449, 687).

nucleotide: a molecule within the DNA and RNA strands, composed of one or more phosphate groups, a 5-carbon sugar (ribose or deoxyribose), and one of the 5 nitogenous bases (adenine, guanine cytosine, thymine, or uracil), which, when linked together (polynucleotide), form the backbone of the DNA (helical twin backbone) or RNA molecule (adapted from Biology, 2015, p. G-32). ATP (adenosine triphosphate), also a nucleotiode, is a high-energy compound formed within a cell's mitochondria, and "...used throughout the cell to energize almost all...intracellular reactions..." (Textbook of Medical Physiology, Hall, J., 2016, p. 23).

nucleic acids: the chemical building block and blueprint of all living things, composed of chainlike molecules of polynucleotides, which are essentially strings of nucleotides (adapted from

placoderm: a gnathostome, a jawed, extinct animal, the earliest known jawed fishan armored fish, with paired fins and gills, that evolved from agnathans, or jawless fish, in the late Silurian and Devonian periods, the jaws developing from a portion of the gill arch skeleton, which allowed fish to become predators, not simply passive suspension-feeder, bottom dwellers, a change which probably contributed to the extinction of ostracoderms, the earliest-known jawless fishes (Biology, 6th edition, 2002). Dunkleosteus, the largest of the placoderms, was a powerful predator, with large, bony plates, instead of teeth (from

extinction: a break in the evolving lineage of a species, a finality with no further continuity (Vertebrates, 2012, 6th edition, p. 22). The "...K–T extinction, abbreviation of Cretaceous–Tertiary extinction, also called K–Pg extinction or Cretaceous–Paleogene extinction, a global extinction event responsible for eliminating approximately 80 percent of all species of animals at or very close to the boundary between the Cretaceous and Paleogene periods, about 66 million years ago. The K–T extinction was characterized by the elimination of many lines of animals that were important elements of the Mesozoic Era (252.2 million to 66 million years ago), including nearly all of the dinosaurs and many marine invertebrates. The event receives its name from the German word Kreide, meaning “chalk,” and the word Tertiary, which was traditionally used to describe the period of time spanning the Paleogene and Neogene periods. The K–T extinction ranks third in severity of the five major extinction episodes that punctuate the span of geologic time..." (

plesiomorphic trait: the earlier, ancestral state, or primitive condition of a character (or feature, or trait) of an organism (Vertebrates, 6th edition, p. 24). Compare with synaphomorphic trait, below.

synaphomorphic trait, or shared derived characters: the later, descendant, or derived condition, of a trait, state, character, or feature of an organism, after its transformation through time (Vertebrates, 6th edition, p. 24). Compare with plesiomorphic trait, above.

stromatolites: mats of cyanobacteria - unicellular photosynthetic prokaryotes mixed with calcium carbonate minerals - existing today in aqueous pools in Western Australia, hypothesized to have generated the Earth's earliest oxygen supply, that, after saturating the oceans as iron oxide about 3.5 bya, filtered into the Earth's atmosphere (Biology, 10th edition, 2015, p. 444). The "great oxidation event", about 2.4 bya, describes a surge of atmospheric oxygen to 1-10% of current levels; current atmosheric O2 concentration was achieved about 0.6 bya (Perspectives on Ocean Science, Jeffrey Graham, youtube, 2015).

alleles: Genes governing variation of the same character that occupy corresponding positions (loci) on homologous chromosomes (Biology, 10th edition, 2015, p. G2).

evolution:   "...the process by which populations change over time in response to changes in the environment..." (Biology, 10th edition, p. 23); The accumulation of inherited changes within populations over time; changes in the characteristics of populations over the course of generations. When 2 populations diverge to a certain degree, they become different species (Biology, 2nd edition, 2002, p, 368); Any cumulative genetic changes in a population from generation to generation, leading to changes and differences in populations over time (Biology, 10th edition, 2015, pp. 10, G-16).

chondricthyes: represented by sharks, these are the cartilagenouse descendants of the placoderms, without body armor, and without a bony skeleton (i.e., with a cartilagenous skeleton), having jaws, gills, a vertebral column that has replaced the notochord in the adult organism, 2 pairs of fins, and placoid scales.

parsimony, principle of: The hypothesis that animals evolved only once, based on the similarity in the structure of genes that control development, RNA, and other molecules; animals are, thus, a monophyletic group (Biology, 10th edition, p. 625).

molecular systematics: The science that focuses on the diversity of organisms and on molecular structure, in order to clarify evolutionary relationships ( Biology, 10th edition, 2015, p. 625).

natural selectionThe major mechanism by which evolution proceeds, whereby the environment selects the best-adapted organisms for survival, i.e., organisms that: 1) best obtain and use resources; 2) escape predators; 3) resist disease; and 4) withstand environmental changes. Natural Selection favors those individuals with genes that specify those traits that allow them to respond effectively to those pressures exerted by the environment. These organisms are more likely to survive and reproduce, and, thereby, pass their genetically derived adaptations for survival on to their offspring, which is called: differential reproductionThis occurs when, because of its advantageous characteristics, a greater proportion of these better-adapted organisms will survive and reproduce, thus passing on their survival strengths. Better adapted organisms are more llikely to survive and become parents of the next generation, thus causing a change in population over time, increasing the frequency of favorable traits over successive generations, while decreasing the frequency of less favorable traits. The mechanism of evolution proposed by Charles Darwin...Evolution occurs when natural selection results in changes in allele frequencies in a population (Biology, 2002, p. 372; Biology, 2015, 10th edition, pp. 14, 15, G-30).

differential reproductionThis occurs when, because of its advantageous characteristics, a greater proportion of these better-adapted organisms will survive and reproduce, thus passing on their survival strengths (Biology, 2015, 10th edition, pp. 9-14)

bikont: distinguished from unikonts with a single flagellum, this single-cell organism, from the ancient lineage of early eukaryotes, has a common ancestor with two flagella, and has diverged away from the evolution of the first "animal" (Biology, 2015, p. 550).

biosphere: comprises all the systems of Earth that are inhabited by living organisms: the 1) atmosphere; 2) hydrosphere (water in any form);  3) lithosphere (the Earth's crust); and the 4) regolith (see definition, below) (Biology, 2015. p. 6).

chiridium: a muscular limb with well-defined joints and digits, characteristic of the earliest tetrapods, when they first literally took foot onto land, during the late Paleozoic (Vertebrates, p. 104).

actinopterygii: the first, major group of bony fishes,  or ray-finned fishes (distinguished from sarcopterygii or fleshy-finned fishes), their fin movements controlled by muscles within the body wall. The modern derived forms, or neopterygii, encompass 20,000 living species. It is the latter fleshy-finned fishes from which terrestrial tetrapods developed, their fleshy lobe fins housing the bony digits and joints that foreshadowed the skeletal template of the reptilian, mammalian, primate, and human limbs (Vertebrates, 2012, p. 99).

sarcopterygii: this second, major group of bony fishes, or fleshy-finned fishes (contrasted with the ray-finned actinopterygii), gave rise to the very first terrestrial vertebrates,  tetrapod (four) limbs having evolved from their fins (Vertebrates, p. 101). The only two living species of this group are the Australian lungfish (Neoceratodus), and the Indian Ocean coelacanth (Latimeria) (youtube: the K-Pg extinction).

coelacanth: thought to have become extinct 75 mya,  rediscovered in the 1930's off the coast of southern Africa, this "living fossil", a sarcopterygian (fleshy-finned or lobe-finned) fish, also known as latimeria, its fins resembling limbs, represents an evolutionary transitional organism, linking the aquatic, vertebrate, bony fishes with tetrapod, terrestrial vertebrates. (Vertebrates, p. 46, 102).

magma: underground, molten rock, containing mineral grains and dissolved gas, that, when it reaches the Earth's surface, is called lava. Studied indirectly via lava, magma contains predominantly silicon dioxide (Si02), and has then flowing property of a liquid (Geology, p. 99).

anapsids: branching off from the reptilian subclass known as diapsids, the skull temporal bone openings disappears in turtles, order Testudines (see page 21: "Emergent Reptiles")

angiosperms: descended from the gymnosperms, these are the flowering plants, the phylum of vascular plants that produce flowers and seeds enclosed within a fruit, originating and diversifying in the Cretaceous period, beginning about 130 mya. A shrub, Amborella trichopoda, native to a South Pacific island, may be the nearest living relative to the ancestor of all flowering plants (Biology, 10th Edition, 2015, pp 591-595).

proboscis: the anterior "head" of a marine (aquatic) invertebrate, such as the burrowing acorn worm, an enteropneust (burrowing) hemichordate (marine worms of deuterostome origin, distinguished from chordates and echinoderms), that promotes the flow of water across a mucosal surface into  the organism, for suspension feeding, facilitated by an apron of circumoral (around the mouth) cilia. The outer, muscular wall of the proboscis helps to anchor the organism in its burrow, while ingesting loosened sediment through its simple gut (Vertebrates, p. 56).

autotrophs: organisms that produce their own food from simple raw materials, usually via photosynthesis; see heterotrophs, to compare (Biology, 10th edition, p. 9).

photosynthesis: The process whereby autotrophs use C02, HOH, and light energy, to synthesize glucose and oxygen (Biology, 10th edition, p. 9, 10).

acritarchs: "...spherical to polygonal, organic walled microfossils...", the emergence of which in the late Proterozoic era, help geologists, through stratigraphy, to specify the stages of deep geologic time (The Concise Geologic Time Scale, 2008, p. 24).



adaptive radiation: the evolution of a large number of related species from an unspecialized ancestral organism (Biology, 2015, p. G-1).

Ediacaran (period): formally ratified as an addition to the geologic time scale in 2004, this period (635-541 mya) marks the end a trend of massive global glaciations, preceding the Cambrian period, with increasing oxygenation of the deep ocean environment, and the appearance of soft-bodied biota. The Ediacaran "...marks a pivotal position in the history of life, between the microscopic, largely prokaryotic assemblages that had dominated the classical "Precambrian" and the large, complex, and shelly animals that dominated the Cambrian...The earliest abundant bilaterian burrows and impressions (555Ma) and calcified animals (550 Ma) appear towards the end of the Ediacaran Period..."  (The Geologic Time Scale 2012, p. 413).

stratigraphy: "the science of the layering of strata and its content, in radiogenic and stable isotopes chronology, and in age and duration calculations using orbital tuning models" (The Geologic Time Scale, 2012, p. xv); "from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history" (

conodonta or conodontophora: an extinct marine, fish-like chordate, with gill arches, muscular segments, and fins, abundant from the Precambrian to the LateTriassic periods, having a long wormlike body, numerous small, hook-like teeth, and a pair of large eyes, believed to possibly be the earliest vertebrate (Biology, 10th ed., p. 680, G-10).

hagfish: an existing, jawless, marine vertebrate, class Myxini, that lacks paired appendages, and lacks vertebrae, axial support only by a notochord (Biology, 2015, p. 681).

benthic: characterizes an animal that lives on or within a bottom marine substrate (Vertebrates, p. 55). Marine biota, such as benthic organisms (mainly foraminifera, an order of marine protozoa) provide excellent measurements of global environmental changes of paleo-environments, due to their sensitivity to local, regional, and global environmental changes (The Geologic Time Scale, 2012, p. 625).

postorbital bar: a bony strut around the eye socket of strepsirrhine primates, contrasted with the fully enclosed eye sockets of haplorhine primates, the haplorhines, or "dry-nosed", primates splitting off from the strepsirrhines about 60 mya, leading to the anthropoid lineage, an ancestor to the human (homo) genus (wikipedia).

ecdysozoan: the group of animals that molt, i.e., undergo ecdysis, which is the shedding of an exoskeleton, in order to grow larger, one of two branches of the protostomes known as pseudo-coelomates (having a body cavity incompletely lined with mesoderm), that includes the phyla nematodes (round worms), and the arthropods: insects, crustaceans, and spiders. See lophotrochozoan, the 2nd branch of protostomata (youtube: Ecdysoza, 2010). 

cynodont: an especially successful group of therapsids, the mammal representing the only surviving lineage following the great dinosaur extinction, after the Cretaceous period (Vertebrates, 2012, p. 122).

lophotrochozoa: a branch of animals known as a clade, descending as one of two branches (contrast 'ecdysozoa') of the protostomes, that contains three sub-branches: 1) brachiopods; 2) worms (marine, ribbon, flat, & earth); and 3) mollusks (clams, snails, and squid) (derived from multiple sources - see Bibliography).

multituberulates, or multituberulata: " [a] diverse lineage of Mesozoic to early Cenozoic mammals that occupied a rodent-like niche...[and] appear first in the late Jurassic and are last known from the early Oligocene..." (

conodonts, conodont element or microfossil: "...the phosphatic tooth and jaw elements of eel-like chordates, [that] provide both a standardized global biostratigraphic framework...and a record of oceanic oxygen-18 values for sea-surface temperatures..." (A Concise Geologic Time Scale, 2016, p. 87); the tooth-like, phosphatitic, feeding apparatus of an extinct, hag-fish-like vertebrate, composed of calcium carbonate fluorapatite, found in marine deposits, that is helpful in dating early, paleozoic (Cambrian, Ordovician, Silurian, and Devonian periods) strata (

arthropoda: a phylum within the ecdysozoan branch of the protostome clade (contrast with deuterostome (the other branch called lophotrochozoans), that has a fluid-filled, pseudocoelom skeleton, also grouped with the nematodes (roundworms). An invertebrate (vertebrates develop from deuterostome-derived chordates), organisms in this phylum  (the largest phylum of the animal kingdom)  have a hard exoskeleton, a segmented body, and paired appendages (from multiple sources, see "Emergence of Animals II":

foramen magnun: the large oval hole in the occipital bone, through which the brainstem passes inferiorly, into the vertebral canal (Human Osteology, 3rd Edition, White, T., et al, 2012, p. 71).

heterodonty: characterizes the dentition of animals with different kinds of teeth, much like a division of labor, for chewing diverse nutrients, characteristic of primates, which have acquired an omnivorous diet (Essentials of Physical Anthropology, p.157)

brachiopods: grouped under lophophorates (marine animals adapted for life on the ocean floor), these coelomate, suspension-feeders have a ring of ciliated tentacles around the mouth (lophophore), without a distinct head. A solitary, cold-water, marine animal resembling mollusks,  these animals differ with bivalve mollusks in the orientation of their two shells (or shell valves) (Biology, 10th Edition, 2015, p. 653).

mammal: Having arisen within the therapsid radiation in the late Triassic period, initially small and shrew-like, any member of the class, Mammalia, comprised of 19 orders, including that of Primates, that is warm-blooded or endothermic, that has a body covered with hair or fur, mammary glands to nourish its young with milk, and bearing live offspring, but for the egg-laying monotremesMammals are also distinguished by red blood cells without nuclei, and 3 middle ear bones, 2 bones having migrated during evolution, from the reptilian jaw (The Princeton Field Guide to Prehistoric Mammals, Prothero, D., 2017, p.15; Vertebrates, Kardong, K., 2012, p. 122).

archonta, or euarchonta: a superorder of 4 orders of mammals, that include: 1) primates; 2) plesiadapaformes; 3) scandentia (tree shrews); and 4) dermoptera (colugos, or flying lemurs) (The Princeton Field Guide to Prehistoric Mammals, Prothero, D., 2017, pp. 80-93).

 magnetosphere: "...The region of space around a planet within which the motion of charged particles is controlled by the planetary magnetic field..." (Universe, 2015, p. 506), which  has  served to protect the evolution of living things on Earth, as it deflects the solar wind, the stream of fast-moving charged particles, predominantly electrons and protons, generated by the sun (ibid., p. 508). Earth's iron core, formed at Earth's center 4.57 billion years ago, generates giant magnetic fields encircling the Earth, shielding the planet from the deadly solar wind, deflecting the sun's charged particles, diverting some to the poles, forming the Northern and Southern Lights, and some to other magnetosphere regions, known as the Van Allen radiation belts.  The Earth's magnetic fields self-perpetuate (magnetic dynamo), as the electrically-conductive iron core moves through the magnetic field by way of its own convection motion, and its molten surroundings (Earth Science, 2015, pp. 206-207). 

isotope: a property of most elements, that are varieties of the same element, whose atoms differ slightly in atomic mass, i.e., the number of neutrons, and/or atomic number, i.e., the number of protons. Some isotopes are unstable - radioisotopes - and undergo radioactive decay, whereby its neutrons and/or protons are emitted at a regular rate from the nucleus, to form a new, decay product, which may be a more stable isotope of the same element, or a completely different element of lower atomic number and/or atomic mass. The predictable rate of decay of a radioactive isotope is measured as a half-life, i.e., the time required for 1/2 of the number of atoms of the unstable radioisotope to degrade into a stable decay product (Earth Science, 2015, pp. 265-267). Some texts are not clear about precisely what is emitted when atoms decay: protons and/or neutrons? or alpha particles  (two protons and two neutrons)? or beta particles (formed by breakdown of a neutron into its proton-electron components); and gamma rays

(see: )

ionosphere: "...In 1839, the German mathematician Carl Friedrich Gauss speculated that an electrically conducting region of the atmosphere could account for observed variations of Earth’s magnetic field. The notion of a conducting region...was explain the transmission of radio signals around the curve of Earth’s surface before definitive evidence was obtained in 1925...the ion-rich region was referred to as the Kennelly-Heaviside layer...The name “ionosphere” was formally defined in 1950 by a committee of the Institute of Radio Engineers as “the part of the earth’s upper atmosphere where ions and electrons are present in quantities sufficient to affect the propagation of radio waves” engineers...need[ed] to define the factors influencing long-range radio communication...[and, for other scientists,] on understanding the ionosphere as the environment for Earth-orbiting satellites and, in the military arena, for ballistic missile flight..." (

trilobite: a paleozoic arthropod, the most widely used fossil group for biostratigraphic zonation of the Cambrian period, divided into 2 genera/species: 1) polymerid and 2) agnostoid. Because of their extreme diversification and evolutionary turnover, these organisms have allowed geologists to map the continental shelf and platform regions (polymerid species), and to map the open shelf-to-shelf margins intercontinentally (agnostoid species), thus mapping the fine zonations of strata among the major paleo-continents, as they existed 500 mya: "...zones based on the first appearances of characteristic species have been replacing the older, regional concepts of zones. Particularly where widespread species, such as agnostoids, are the characteristic species of zones, this practice has lead to the precise correlation regionally and intercontinentally..." (my italics) (The Geologic Time Scale, 2012, p. 467).

synapsida: includes ancestors of mammals, and all of their mammalian descendants, incorrectly called "mammal-like  reptiles"; correctly referred to as protomammals, or stem mammals, these animals, that split off from the reptiles 315 mya, during the Early Carboniferous period (359 - 299  mya), had a distinctive, single hole, the temporal fenestra , low on the side of the skull, below the bone behind the eye socket (most reptiles, or diapsids, have 2 temporal fenestra). Dimetrodon and Edaphosurus were part of the first great evolutionary radiation of synapsids, and are sometimes called pelycosaurs. The synapsids, after a second evolutionary wave, were replaced by therapsids, more advanced mamlmals, that, after the massive Permian (252 mya) extinction, further advanced into the cynodonts, with an upright posture (rather than the sprawling pelycosaur posture), more specialized teeth (incisors, canine and cheek), a complete secondary palate that allows for simultaneous chewing and breathing, and many other mammalian features (Prehistoric Mammals, 2017, p. 20-22).