Placoderms were among the first jawed fish ; their jaws likely evolved from the first of their gill arches.

Thought to have arisen in the first jawed vertebrates, the adaptive or " specific " immune system is activated by the “ non-specific ” and evolutionarily older innate immune system ( which is the major system of host defense against pathogens in nearly all other living things ).

However, this fails to explain why the lichid trilobites, especially those of the family Odontopleuridae, first began evolving large spines ( and in some cases, spiny spines ) during the start of the Ordovician period, long before the advent of jawed vertebrates.

The first vertebrates appeared over 500 million years ago ( Mya ), during the Cambrian period, and may have resembled the modern hagfish in form.

Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into reptiles, the first fully terrestrial vertebrates.

Dinosaurs, as the largest vertebrates, were the first affected by environmental changes, and their diversity declined.

Large piscivore amphibians were the first vertebrates to conquer land, they evolved 400 million years ago.

In response to Haeckel ’ s evolutionary claim that all vertebrates are essentially identical in the first month of embryonic life as proof of common descent, His responds by insisting that a more skilled observer would recognize even sooner that early embryos can be distinguished.

Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period.

The first vertebrates appeared in the form of primitive fish, which greatly diversified in the Silurian and Devonian.

The gene spans 20 kb, with a non-coding exon 1 and a very long first intron of 10 kb. The coding sequence contains five regions showing a high degree of conservation in vertebrates, predominantly in exons 2, 5, 6, 7 and 8, but the sequences found in invertebrates show only distant resemblance to mammalian TP53.

The first true mammals also evolved during this period, as well as the first flying vertebrates, the pterosaurs.

Later on, as a young adult, he made himself an expert of knowledge on the topic of first on invertebrates, and later on vertebrates, all self-taught.

The homeobox domain was first identified in a number of drosophila homeotic and segmentation proteins, but is now known to be well-conserved in many other animals, including vertebrates.

The superclass tetrapoda ( Ancient Greek τετραπόδηs tetrapodēs, " four-footed "), or in semi-anglicized form the tetrapods, comprises all of the descendants of the first four-limbed vertebrates which emerged from aquatic environments to colonize land.

The evolution of the first tetrapods marked the moment when the two basic forms of vertebrates, fishes and tetrapods, diverged.

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds.

It is believed that the first lungs, simple sacs connected to the gut that allowed the organism to gulp air under oxygen-poor conditions, evolved into the lungs of today's terrestrial vertebrates and some fish ( e. g. lungfish, gar, and bichir ) and into the swim bladders of the ray-finned fish.

These fins evolved into legs of the first tetrapod land vertebrates, amphibians.

The first tetrapodomorphs, which included the gigantic rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the late Devonian epoch ( 385-359 Ma ), with the appearance of tetrapods ( four-legged vertebrates ).

The Devonian Period ( 395 to 345 Ma ) brought in the changes that allowed primitive air-breathing fish to remain on land as long as they wished, thus becoming the first terrestrial vertebrates, the amphibians.

Electrical synapses were first demonstrated between escape-related giant neurons in crayfish in the late 1950s, and were later found in vertebrates.

The development of the meninges and the existence of a defined pia mater was first noted in the vertebrates, and has been more and more significant membrane in the brains of mammals with larger brains.

This response was later recognized as the first stage of a general adaptation syndrome that regulates stress responses among vertebrates and other organisms.

These narratives of coarse action and crude language appeared first in local newspapers, as a rule, and later found their way between book covers, though rarely into the planters' libraries beside the morocco-bound volumes of Horace, Mr. Addison, Mr. Pope, and Sir Walter Scott.

approaching shore their masts appeared first.

and, `` I do think that families are the most beautiful things in all the world '', burst out Jo some five hundred pages later in that popular story of the March family, which had first appeared when Henrietta was eight ; ;

Four years after the publication of The History Of England, the first volume of Trevelyan's Queen Anne trilogy appeared.

Perhaps Patchen was once involved in a train accident, and this passage from First Will And Testament may have been how the accident appeared to the poet when he first saw it -- if he did: ``

When this second dilemma first became obvious -- during the mid to late '50's -- the United States appeared to have three choices.

The first report in this continuing series appeared in the September 1960 issue of the Journal.

He appeared in the hopples about November 14, was treated for worms on the 18th, the latter date being the first time he struck a real pace.

The first eight of these eighteen statements, which received at least one-half of the votes, were duplicated to form an analysis checklist for the particular manager, and when this particular manager roleplayed in other situations, the members checked any items that appeared.

In January, 1958, the Minister of the Interior announced that an election law was ready to be submitted to the King, the rumors of election dates appeared once again, first for spring of 1958 and later for the summer.

In the orchestra we hear first a hushed, hesitant pizzicato figure, then the insistent `` police '' motif as it appeared in the opening scene.

The first section of this publication appeared in 1948 and the last supplement in 1960.

Although slab stock appeared first, it soon became apparent that for the production of cushions with irregular shapes, crowned contours, or rounded edges, the cutting of slab stock is a wasteful and uneconomical process.

From the lioness' point of view, this strange creature on the back of another creature, lashing out with its long thin paw, very likely appeared as something she could not at first cope with.

The size of Saud's family was still being debated when the King appeared for his first meeting with Eisenhower.

About all that remains to be said is that the present selection, most of which appeared first in The New Yorker, comprises ( as usual ) a slightly unstrung necklace, held together by little more than a slender thread cunningly inserted in the spine of the book.

Alvin Ailey and Carmen De Lavallade appeared in the first New York performance of Mr. Ailey's `` Roots Of The Blues '', a work given its premiere three weeks ago at the Boston Arts Festival.

Nevertheless, in spite of Rutherford's estimation that gold had a central charge of about 100 ( but was element Z = 79 on the periodic table ), a month after Rutherford's paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electrons in an atom was exactly equal to its place in the periodic table ( also known as element number, atomic number, and symbolized Z ).

Even his old literary home, Punch, where the When We Were Very Young verses had first appeared, was ultimately to reject him, as Christopher Milne details in his autobiography The Enchanted Places, although Methuen continued to publish whatever Milne wrote, including the long poem ' The Norman Church ' and an assembly of articles entitled Year In, Year Out ( which Milne likened to a benefit night for the author ).

Aphrodite figures as a secondary character in the Tale of Eros and Psyche, which first appeared as a digressive story told by an old woman in Lucius Apuleius ' novel, The Golden Ass, written in the second century AD.

Peasant parties first appeared across Eastern Europe between 1860 and 1910, when commercialized agriculture and world market forces disrupted traditional rural society, and the railway and growing literacy facilitated the work of roving organizers.

The quantum number n first appeared in the Bohr model where it determines the radius of each circular electron orbit.

" Amazing Grace ", with the words written by Newton and joined with " New Britain ", the melody most currently associated with it, appeared for the first time in Walker's shape note tunebook Southern Harmony in 1847.

It was originally one of between 50 to 70 verses of a song titled " Jerusalem, My Happy Home " that first appeared in a 1790 book called A Collection of Sacred Ballads:

Moody and Sankey began publishing their compositions in 1875, and " Amazing Grace " appeared three times with three different melodies, but they were the first to give it its title ; hymns were typically published using the first line of the lyrics, or the name of the tune such as " New Britain ".