Important words and concepts
from Chapter 34, Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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(1) Chapter title: Vertebrate Evolution and
Diversity
(a)
[vertebrate evolution and
diversity (Google Search)] [index]
CHORDATE CHARACTERISTICS
(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]
(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]
(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]
(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]
(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]
PRIMITIVE CHORDATES
(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:
(g)
(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]
(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]
CRANIATA &
MOST-PRIMITIVE VERTEBRATA
(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: http://128.223.21.97/classes/bi355f99/lectures/l16b.html
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]
SUBPHYLUM VERTEBRATA
(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
Class Osteostraci (extinct armored, jawless fish)
Class Myxini (Hagfish) (but probably not vertebrates)
Class Cephalspidomorphi (Lampreys)
Class Placodermi (extinct armored, jawed fish)
Sharks, Rays, Chimeras
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 404—
SUPERCLASS GNATHSTOMATA
(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
(d)
(e)
[superclass Gnathostomata
(Google Search)]
[index]
(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):
(e)
(f)
[class Placodermi, placoderms (Google Search)]
[index]
MODERN FISH
(a)
The modern fish consist of two classes