Download 214 - S11 - [122] - Evolution

Phylum Porifera
(Sponges)
Cambrian to Recent
Porifera are solitary or colonial animals with no mouth, anus, or digestive cavity. The
body is composed of only two layers of cells separated by a jellylike substance containing
amoeboid cells, which perform the functions of digestion, reproduction, and secretion of
the skeleton. The skeleton is composed of organic fibers (collagen), mineral spicules
(hydrous silica or calcite), and plates of calcium carbonate.
1. Most sponges are marine, but there are a few freshwater forms.
2. Most forms are cylindrical, but there are also encrusting forms.
3. Food consists of bacteria removed from water drawn into the body cavity through
pores.
4. Not common as fossils because of poor preservation potential.
Hydnoceras sp.
Phylum Cnidaria (Coelenterata)
Class Anthozoa
(Corals)
Ordovician to recent
Corals are marine organisms with simple, two-layered structure. They are related to
hydrozoans and jellyfish. Unlike those animals, corals secrete calcareous skeletons, and
they have been important reef-builders throughout their history. Almost all modern
colonial reef-building corals require warm, clear, shallow water because of their
symbiotic relationship with algal cells.
Order Rugosa
Ordovician to Permian
1. Solitary horn corals or colonial.
2. Bilaterally symmetrical; septa arranged in multiples of four.
Favistella alveolata
Calceola sandalina
Order Tabulata
Ordovician to Permian
1. Exclusively colonial.
2. Composed of tubes in which tabulae are generally prominent, but septa are poorly developed
or absent.
Syringopora perelegans
Order Scleractinia
Middle Triassic to Recent
1. Solitary or colonial
2. External skeleton of aragonite.
Coelosmilia cupuliformis
Astrhelia palmata
Phylum Bryozoa
Ordovician to recent
Bryozoans are small colonial animals with a simple U-shaped gut and an external skeleton of
calcite or a flexible organic substance. Ciliated tentacles around the mouth draw food into the
body cavity. Each organism lives in a structure called a zooecium. Each new individual arises
from a “bud” of an existing bryozoan, and is assumed to be genetically identical to others in its
colony. Bryozoans are common and widely distributed in modern oceans.
1. Most are marine; all are benthic, sessile, filter feeders.
2. Colonies may be encrusting, stick-like, massive (mounds), twig-like, or delicated branching
fans.
3. The individual animals in the colonies are much smaller than those of corals. In addition, the
openings in the bryozoan colonies (where the animal lived) lack the
distinctive septa found in corals.
Fenestella althaea
Isotrypa ambigua
Hallopora ramosa
Phylum Brachiopoda
Cambrian to Recent
Brachiopods are bivalved marine invertebrates which filter food by means of a lophophore. The
valves are composed of calcite which fossilize well. The valves are bilaterally symmetrical and
are usually formed joined and closed. All varieties are benthic, although some are faunal and
some are epifaunal. Brachiopods dominate the fossil record in the lower and middle Paleozoic.
Cyclothyris velpertillo
Terebratula wilmingtonensis
Cyrtospirifer sp.
Phylum Mollusca
In the evolutionary sense, molluscs are a single group, however, they have adopted such different
adaptive strategies (including skeletal structures) that the similarities are not obvious.
Class Bivalvia (Pelecypoda)
Ordovician to Recent
Clams, oysters, scallops, mussels
Bivalves are molluscs with two shells which are often mirror images of each other and protect
soft body parts. Fossil (and dead) bivalve shells are commonly found separated because they
automatically spring open at death. Bivalves are found in marine, brackish, and freshwater.
Most occur in shallow water, but there are some deep-water forms. In general, bivalves do not
make good index fossils, however they are good paleoecologic indicators, meaning that there are
many different forms that have different life styles. For example, some are infaunal deposit
feeders, others are epifaunal filter feeders, or sessile filter feeders, or vagile deposit feeders.
Sessile forms may stay in one place or attach themselves to rocks or other shells with cement or
threads. Vagile forms use a foot to crawl or burrow. A few, like pectens, “swim” by rapidly
opening and closing their shells
Ostrea titan
Allorisma sp.
Amnigenia sp.
Inoceramus sp.
Class Gastropoda
Cambrian to Recent
Snails, slugs, limpets
The basic gastropod skeleton is a hollow, tapering, calcite tube, which may be straight, or coiled.
They have a well developed head with sensory organs and a foot for locomotion. This group is
the most adaptable of the molluscs as they can be herbivores, scavengers, and predators.
Gastropods are found in marine, brackish, freshwater, and terrestrial environments.
Pleurotomaria conidea
Maclurea magna
Olivia litterata
Pterocerella sp.
Buccinum clathratum
Class Cephalopoda
Late Cambrian to Recent
Squid, octopus, chambered nautilus, ammonites, belemnoids
In the past, cephalopods were an important and very successful group of marine predators and
scavengers, and are the most advanced or all molluscs. Cephalopods are swift and agile
swimmers with a defined head, elaborate sensory organs, and well developed eyes. They may or
may not secrete a shell.
Subclass Nautiloidea
Nautiloids have straight, curved, or coiled calcite tubes that are divided into chambers by simple
walls (septa). The joint where the septa and external wall meet is called the suture, which form
rings around the shells. Nautiloids were common throughout the Paleozoic, however today
Nautilus is the only living representative.
Bickmorites bickmoreanum
Nautilus lineatus
Subclass Ammonoidea
Ammonoid shells are similar in structure to nautiloid shells, however the suture patterns are
more complex. Ammonoids frequently have external knobs, ridges, or other ornament. There
are no living representatives of this class.
Discoscaphites nebrascensis
Muensteroceras oweni
Subclass Coleoidea
Squid, cuttlefish, octopus, belemnoids
Coleoids have greatly reduced internal or missing skeletons. Fossil coleoids (belemnoids) had
stout, cigar-shaped internal skeletons consisting of a chambered shell surrounded by a
counterweight.
Hibolites semihastatus
Phylum Arthropoda
Trilobites, insects, spiders, crustaceans, ostracodes
Class Trilobita
Early Cambrian to Late Permian
Trilobites are members of the phylum arthropoda, which means they have segmented bodies,
jointed appendages, and jointed external skeletons, and grow by molting. They are a class of
extinct arthropods in which the body is divisible into three parallel lobes. Trilobites are the
earliest known arthropods and were exclusively marine. Most were benthic, vagile, epifaunal
scavengers and deposit feeders. They are the first organisms known to have eyes, and were the
dominant invertebrates in the Paleozoic. Trilobites are useful for biostratigraphy and world-wide
correlation.
Ptychagnostus praecurrens
Agraulos ceticephalus
Olenellus getzi
Ellipsocephalus hoffi
Calymene blumenbachi
Phylum Echinodermata
Cambrian to Recent
Sea Urchins, Star fish, Crinoids
Echinoderms are marine animals characterized by five-fold symmetry and a skeleton composed
of individual plates. This group is highly diversified and successful
Class Crinoidea
Cambrian to Recent
Crinoids, sea lilies
Most crinoids are epifaunal, filter feeders that were sessile, and attached to the seafloor by a
stem. The stem is composed of button-like discs that were stacked and held together by ligament
fibers. The plates of the skeleton disarticulate upon death so complete skeletons are rare. Stems
are more common than crowns. Crinoids were especially common in the Mississippian and
much less common in the Mesozoic and Cenozoic.
Barycrinus hoveyi
Pachylocrinus aequalis
Class Blastoidea
Ordovician to Permian
All blastoids are attached by stems and lived in shallow water in reefs. Blastoids have well
developed 5-fold symmetry and were most abundant in the Mississippian. Crowns are found
more often than stems.
Pentremites sulcatus
Deltoblastus verbeeki
Phylum Chordata
Class Graptolithina
Cambrian to Mississippian
Graptolites are small, extinct colonial invertebrates which had chitinous skeletons. They may
have distant affinities to vertebrates. Graptolites are most commonly found as carbon
impressions in black shales.
Diplograptus foliaceus
Didymograptus denticulatus