its original in the Divine Mind, which has gradually fitted the earth
to be the habitation of intelligent beings, and has introduced upon the
stage of time organism after organism, rising in dignity, until all
have found their completion in the human nature, which, in its turn, is
a prophecy of the spiritual and Divine."
Hugh Miller, Sketch-book of Popular Geology (4th Ed, 1869)
preface by Lydia Miller
"The Animal kingdom, one in system from the beginning."
What is a plant and what is an animal? The answer is not easy. From one viewpoint, this difficulty borders on the absurd: everyone knows the difference. But the problem lies in the borderline cases -- in the lower plants and animals. The question arises in the study of fossils: is this fossil an animal or a plant? It is an interesting fact that the 19th century geologists generally did not try to make the distinction -- or perhaps they assumed that the distinction is obvious1.
As obvious as the distinction between plants and animals may seem in daily life, the modern systematists use surprisingly non-intuitive ways to make the distinction. Lynn Margullis, for example, distinguishes between the Plant kingdom (Plantae) and the Animal kingdom (Animalia) based on the nature of the sperm, egg and embryo at fertilization: in plants the embryo is contained in a multicellular ovule at fertilization; in animals, fertilization produces a single-celled zygote, which then forms a multicellular blastula through cell clevage (mitosis). For Margulis, both plants and animals are multi-cellular by definition -- with all single-celled eukaryotes placed into the kingdom Protoctista -- a reasonable move because they never form multi-celled species, although they may form "colonies" that behave as if they were multicellular creatures1.1.
While this distinction between plants and animals may be technically accurate, it does not seem to get at the essence of plants and animals. It is difficult to see why this difference should lead to the vast difference between plants and animals; it seems more an accidental attribute than an essential one.
There are two obvious differences between plants and animals. First, plants do not appear as elaborately organized as animals. Tree branches seem to be somewhat randomly designed, perhaps subject to growth rules, but allowing a broad range of variation within those rules. Animals also have some variation, but an animal body conforms to a much more detailed specification that seems to be determined by placement within an overall body design. We can summarize this difference by referring to plants as algorithmically designed, and to animals as topologically designed.
See also Algorithmic and Topological Body Plans
|The Earliest Fossils of the Protist
Margulis places all single-celled eukaryotes in the kingdom Protoctista, the Protists, which avoids discussion of whether they are plants or animals -- and leads to a clean definition of the plant and animal kingdoms at the embryonic level. Thus, for example, some classification schemes place diatoms (Pr-18) in the Plant kingdom, and place Forams (Pr-3) and Radiolaria (Pr-31) in the Animal Kingdom.
Many Protist (single-celled eukaryotes) phyla are absent in the fossil record, because many are soft-bodied and don't readily fossilize. Exceptions include occasional species (such as the Foraminifera, Pr-3 and Radiolaria, Pr-31) that have skeletons, shells or other hard parts (spicules), and colonies (algal mats, etc.) -- especially when (as in bacterial stromatolyte colonies) they entrap or excrete minerals (calcium, silica, etc.).
The known examples represented in the fossil record are (Using the nomenclature of Margulis):
PR-3 - Granuloreticulosa (Foraminifera). Forams first appeared in the early Cambrian era, about 542 Ma. They secete a mucilage that cements together tiny particles gathered from the sea floor into an agglutinated shell. All species are benthic (bottom-dwelling); however some species moved about on the sea floor while others are stationary either by attaching themselves to the bottom or by burrowing into it. Forams are a commonly found in core samples as agglutinated tubes 3-4 cm (1-1.5") in length2.1.
For images of recent foraminifera, see the H.M.S. Challenger reports: Henry Bowman Brady, Report on the Foraminifera (1884); and W. B. Carpenter, Report on the Orbitolites. (1883).
Pr-04 - Xenophyophora "No proven fossil record" [Margulis p. 143]
Pr-05 - Dinomastigota "Significant fossil record from base of Cambrian" [Margulis] The dinoflagellates are notable because their internal structure is quite peculiar. The chromosomes are formed in a unique way, and mitosis is also peculiar, leading some to speculate that they are half-way between bacteria and eukaryotes02.2. This peculiar structure implies ancient roots, and indeed dinoflagellates appear throughout the geological record, from the cambrian to the present with strong likelihood that their pedigree may include some precambrian fossils.
Pr-18 - Bacillariophyta. This is the phylum that includes the diatoms. Since Margulis classifies all single-celled eukaryotes as protists, the diatoms are not classified as plants (as other naming schemes do), even though they conduct photosynthesis. Diatoms are plankton that can be found in floating algal mats. The name refers to the two-part silicon skeleton.
Diatoms have two useful functions: they fix carbon through photosynthesis, and they remove silicic acid from the oceans. In both of these functions, they play a major role. The silicon deposits on the cell wall to form skeletons of amorphous silicon dioixide (SiO2) in beautiful and fantastic shapes which are a favorite object to view under a SEM microscope (Figure 2.3). The details of how diatoms remove silicon from the water are not yet well-understood, but it is thought that the diatom interiors manage to maintain dissolved silicon in a supersaturated condition by an unknown process, which then precipitates the silicon on the cell walls to form the skeletons02.3.
Major diatom deposits date from the Cretaceous era (144-65 Ma) -- forming extensive beds of diatomaceous earth. Diatoms could well originate at a much earlier date, but the silicon crystallizes under pressure, so early examples may not have survived deep burial -- see Sims, et. al.
For images of recent diatoms, see the H.M.S. Challenger report by Conte Abate Francesco Castracane degli Antelminelli, Report on the Diatomaceae (1886).
Pr-25 - Hapatomonada. Single-celled golden-brown algae. The algae have two forms during their life cycle: the "resting state" Coccolithophores with disc-like coccoliths (Calcium Carbonate "scales of renown to paleontologists" which had a major part in creating the world's chalk deposits), and the mobile haptomonad with a single whip-like undulipod (often mis-named a flagellum). The coccoliths are detailed and very distinctive and changes over time make them good markers of geologic time. Coccoliths have been reported in Devonian deposits in China (ca 360 Ma). These are apparently the oldest examples; until this discovery, the earliest fossils came from the Triassic Era (250-200 Ma)02.4.
Pr-28 - Chlorophyta (green algae).
Pr-31 - Actinopoda (Radiolaria). The radiolaria are protists that produce mineral skeletons and spicules (rods). Among the many families the skeletons are formed of various minerals -- silica (SiO2) or opal (hydrated silica - SiO2•nH2O), and strontium sulfate. The skeletons exhibit a fantastic variety of detailed and elaborate forms -- for stunning drawings of radiolaria from the HMS Challenger Expedition, see Ernst Haeckel, Report on the Radiolaria (1887)02.5. One remarkable feature is that the microtubule spicules (at least in some species) appear to be used as oars may be "found rowing in the Mediterranean with the splendor of a Roman galley." [Margulis, p. 207].
Radiolaria fossils have been discovered in China from the lower Cambrian (545 Ma) -- See Figure 2.5, with many others from the Ordovician and later02.6.
For images of recent radiolaria, see the H.M.S. Challenger report by Ernst Haeckel, Report on the Radiolaria, (1887).
Pr-32 - Gamophyta (green algae). green Algae secrete calcium carbonate which assists in fossilization. The fossil record begins in the Cambrian Era, although it is possible that they may have existed prior to that time -- since the body plan is somewhat indefinite, it is hard to classify some earlier candidates with confidence.
Pr-33 - Rhodophyta (red algae). "Unicellular rhodophytes, of which there are a few living today, may go back well into the Precambrian, but since none of the Precambrian fossils in question contain pigments, they cannot be identified confidently as red algae. Multicellular rhodophytes were present in the late Precambrian; the oldest may be as old as 1.25 billion years... Because of their ability to secrete calcium carbonate, calcareous red algae have a better Phanerozoic fossil record than many other groups of algal protists... Most limestone deposits of reef origin consist largely of the skeletons of coralline algae, and because these are often associated with petroleum deposits, there has been a great deal of attention focussed on these fossils. Despite this attention, we still do not fully understand how the rhodophytes precipitate calcium carbonate; the mechanism is not as well studied as those in bone and shell deposition. " -- Rhodophyta: Fossil Record.
|The Animal Phyla: First
Appearances in the Fossil Record03
The known examples represented in the fossil record are (Using the nomenclature of Margulis):
A-3 Phylum Porifera (Spongia). Early Cambrian fossils include a short-lived (about 10My) but prolific blossoming of a sponge Archaeocyathans. They are the first are reef-building animals, conical shaped with a calcium carbonate (calcite) shell -- similar in overall shape to the later rugose corals. Because of their brief span they are an index fossil for the lower Cambrian.
Sponges commonly have needle-like spicules which they use for movement and defense. The following figure shows a number of Cambrian sponges with spicules.
The following Mid-Cambrian fossil sponges are listed by Charles Walcott03.1. Note the surface pores of the sponges indicated in the figures.
For images of recent sponges, see the H.M.S. Challenger reports:
A-4 Phylum Coelenterata (Cnidaria). All Coelenterates have stingers called cnidaria; hence this is an alternative name for the phylum. The phylum includes hydras, medusas, jellyfish and corals. Often the life-cycle of a species may pass through several of these forms.
The Cnidaria are unique among the animal phyla in the presence of their namesake stingers (cnidaria). These stingers are remarkable examples of exquisite design and engineering -- see the box on Cnidaria.
For images of recent Coelenterata, see the H.M.S. Challenger reports:
A-5 Ctenophora. Comb jellies. Ediacaran (Australia) fossil beds show abundant remains of an early animal named Funisia dorothea (Figure 3.6) viewed by some as a comb jelly, and by others as a kind of sponge. Consistent with the view that they are early comb jellies is the view of one line of research (based on cladistic studies of gene structure) that the comb jelly was the earliest form of complex life, earlier than the sponge. Thus "the relatively complex comb jelly at the base of the tree of life suggests that the first animal was probably more complex than previously believed."03.2
The earliest known Ctenophore (if Funisia is classified as a sponge) is an embryonic comb jelly of the lower Cambrian03.3.
A-6 Gnathostomulida. Early Cambrian "protoconodonts" are currently believed to be the unrelated remains of chaetognaths (or "arrow worms"). Margulis classifies Conodonts in Phylum A-37 (Craniata).
A-7 to A-19 are mostly soft-bodied and many are worms.
A-11 Nematoda. (Nematodes).
H.M.S. Challenger Expedition (1873-1876) Reports of Species in Phylum Nemertina (A-10)
A-12 Nematomorpha (horsehair worms). A lower Cambrian worm of phylum Nematomorpha, in quite remarkable preservation, was discovered in 1999 in the Chengjiang Maotianshan Shales of China (Figure 3.8).
A-20 Phylum Chelicerata. The Chelicerates include horseshoe crabs, scorpions, spiders and mites. Some classification systems combine chelicerata with crustaceans and mandibulata into a single arthropod phylum [Margulis, p. 294]. The shells are somewhat soft and may not fossilize well.
The Cambrian fossils that are classified as Chelicerates lack the Chelicera (front pair of clawed, jointed "legs")03.4-- but otherwise appear to be the proper form.
The oldest horseshoe Crab fossil comes from the Ordovician Era, about 445 Ma (Figure 3.9).
Extinct Phylum Trilobita. The Trilobite is perhaps the most remarkable Cambrian fossil. It appeared suddenly as a fully formed arthropod, and lasted for over 200 My, becoming extinct in the Permian Extinction (about 250 Ma). Trilobite fossils represent the earliest clearly defined occurrence of compound eyes. In most classification schemes the trilobite is placed in its own phylum because of its unique body structure which consists of multiple segments each with three lobes (left to right). The only comparable animal is a newly-hatched trilobite larva of the horseshoe crab (a Chelicerate), so-named because its body plan resembles a trilobite. The Cambrian trilobites are mostly small, but in later times some fossils are quite large -- up to 28 inches. See Chapter 9 for further remarks on the trilobite, particularly the trilobite eyes.
H.M.S. Challenger Expedition (1873-1876) Reports of Species in Phylum Arthropoda (Chelicerata and Mandibulata)
Pelagic Hemiptera: Part XIX
Pycnogonida: Part X
Brachyura: Part XLIX
Anomura: Part XLIX
Macrura: Part LII
Schizopoda: Part XXXVII
Stomatopoda: Part XLV
Cumacea: Part LV
Phyllocarida: Part LVI
Isopoda: Parts XXXIII, XLVIII
Amphipoda: Part LXVII
Cirripedia: Parts XXV, XXVIII
Copepoda: Part XXIII
Ostracoda: Part III
A-21 Phylum Mandibulata. This phylum includes the classes Hexapoda (Insecta) -- insects and spiders, Crustacea -- crabs, shrimp and lobsters, and Myriapoda -- centipedes and millipedes.
A-22 Phylum Annelida. segmented worms -- Earthworms, etc.
Spriggina is a possible pre-Cambrian annelid. It is a segmented worm about 3 cm in length. It appears to be armored with interlocking plates. There are no Cambrian examples.
H.M.S. Challenger Expedition (1873-1876) Reports of Species in Phylum Annelida:
Annelida: Part XXXIV
A-26 Phylum Mollusca. A Cambrian fossil Mollusc (class Monoplacophora) is named Knightoconus. This was thought to be extinct, until ten living species were discovered in 1952. Since that time a number of other specimens have been found. Modern species live on the ocean bed in deep water. "All extant classes of molluscs, except Scaphopoda, began at various times during the Cambrian."03.6
H.M.S. Challenger Expedition (1873-1876) Reports of Species in Phylum Mollusca
Brachiopoda: Part I
Polyzoa: Parts XXX, L, LXXIX
Cephalodiscus: Part LXII
Phoronis: Part LXXV
Cephalopoda: Part XLIV
Pteropoda: Parts LVIII, LXV, LXVI
Nudibranchiata: Part XXVI
Marseniadæ: Part XLI
Heteropoda: Part LXXII
Scaphopoda & Gasteropoda: Part XLII
Polyplacophora: Part XLIII
Lamellibranchiata: Part XXXV
Anatomy of Deep-Sea Mollusca: Part LXXIV
A-27 Phylum Tardigrada. Tardigrades are microscopic animals that range from 100 µm to 1,500 µm in size
A-28 Phylum Onychophora. This phylum includes the lobopods or velvet worms. Lobopods are segmented and typically bear legs with hooked claws on their ends.
A-29 Phylum Bryozoa. Bryozoans are sometimes called "moss animals". Individuals are small and tubular in shape with a looped digestive tract so that the mouth and anus are both located at one end. The individuals usually live in colonies. Until recently, this phylum was thought to begin in the Ordivician Era; however, in 2010, a Cambrian bryozoan was reported03.8.
According to Wikipedia, The genus Lingula (Bruguiere, 1797) is "among the oldest known animal genus that has extant species.... Shells of living specimens found today in the waters around Japan are almost identical to ancient Cambrian fossils."
A-33 Phylum Hemichordata. The Hemichordates (acorn worms) are marine worms -- often live planktonic lives as larvae and benthic (ocean floor) lives as adults. The name "half-chordate" is a misnomer [Margulis] since they do not have a notochord.
A-34 Phylum Echinodermata. The Echinoderms include starfish, sea lilies, sea urcins, and sea cucumbers. Most of these appear later in the Ordovician Era. The sea lilies (Crinoids), or at any rate, crinoid-like fossils, occur in the Cambrian Era. Gogia is the most common example.
Holothurioidea: Parts XIII, XXXIX
Echinoidea: Part IX
Ophiuroidea: Part XIV
Asteroidea: Part LI
Crinoidea: Parts XXXII, LX
Myzostomida: Parts XXVII, LXI
A-35 Phylum Urochordata (Tunicata). Urochords are the only animals that can produce cellulose [See note 1.3].
A-36 Phylum Cephalachordata.
Cambrian - Pikaia a "pre-vertebrate cephalochordate from the Cambrian Burgess Shale"
A-37 Phylum Craniata. The craniates have a central, hollow, fluid-filled nerve cord ending in a brain that is enclosed in a cranium (brain-case). In the embryo, all craniates have a flexible rod called a notochord, which in vertebrates is replaced in maturity by a bony or cartilaginous backbone.[Margulis]
The earliest (probable) chordate is Haikouichthys, a 2-3 cm. length fish-like Cambrian fossil from China reported in 1999, with additional fossils reported in 2003 that show well-developed eyes, and other sensory structures characteristic of the cratiates, as well as the muscle blocks typical of early vertebrates 03.10. Bony fish officially date to the Ordovician Era.
Conodonts, also classified as Craniates (based on living species) may also date from the mid-Cambrian -- see the box on Conodonts in Chapter 9.
H.M.S. Challenger Expedition (1873-1876) Reports of Species in Phylum Vertibrata (Craniata)
Human Skeletons: Parts XXIX, XLVII
Seals: Part LXVIII
Bones of Cetacea: Part IV
Marsupialia: Part XVI
Birds: Part VIII
Anatomy of Petrels: Part XI
Anatomy of Spheniscidæ: Part XVIII
Fishes: Parts VI, LVII, LXXVIII
Phyla: First Appearances in the Fossil Record
Moving to land began seriously about 470 My ago, some 100 My after the Cambrian explosion. By this time corals, mollusks, and other sea creatures were long established. Some early fungi appeared at about 500 My and mosses about 470 My, both in the Ordovician era. The evidence for this is not found in actual plant fossils but in spores which appear at this time, and are markers of plant life (see the box). These early colonizers of the land lack real roots, so they can only be small and can only grow in water or wet surroundings. However, they could move from shorelines to the interior of land masses, provided the necessary bacteria had preceeded them to supply food and nitrogen, and the spores have the ability to go into a dormant state during dry periods.Unlike the animal phyla, the various plant phyla appear on earth over a long period of time, with the crowning achievement, the flowering plants, first appearing in the fossil record around 145 Ma. There is a clear reason for this: all animals first arose in the oceans; plants live in (or near to) the atmosphere -- that is, on dry land or adjacent shallow water. Although permanent dry land first appeared around 2 Ga, as a result of plate tectonics, hard cosmic and solar radiation sterilized it. This condition continued until the oxygen in the atmosphere could build up an adequate outer-atmosphere ozone layer. Only microbes and simple plants and animals with high reproduction rates could survive the race against destruction by radiation. Once that ozone layer built up, dry land was open to colonization.
Cosmic and solar radiation at this time was still severe, but for these simple plants, that was only an inconvenience, because every plant zapped by radiation became food for other plants. Various means could be used to minimize the effects of radiation, including the use of shelter, damp locations and subterranean growth. As long as plant reproduction could keep ahead of the destruction, they were able to cope.
The really serious issue was water, more precisely, the retention of water in the plants that were exposed to dry land and air. By the start of the Silurian age, 430 My ago, the algae and mosses appear with waxy coats that prevent drying out, and stomata which controlled the plant respiration and moisture content. From this time plants spread all over the dry land. The waxy coating and stomata are characteristic of all land plants from this time on.
When the flowering plants arrived, the colonization by animals took place in parallel. There was a close symbiosis between the development of new plant types and animal types -- particularly the insects -- that need each other for food and fertilization.
For following table see:
Mansfield State (Ohio) Evolution of Plants.
The Plant Phyla in the Fossil RecordSpores. Spores provide the earliest evidence of plant life in the fossil record. Terrestrial plants produce extremely resistent spores and pollen which are easily transported by wind and water. Trilete spores which are unique to plants, appear in the MId-Ordovician Age (~470 Ma), and are taken as the earliest evidence of life on land [Wiki]. These spores are produced during sexual reproduction (meiosis) whereby the mother (diploid) cell divides to form 4 haploid cells04.4.
Description and First Appearances of the Plant Phyla
These spore indications of plant life preceed actual plant fossils by 50 My. See the box on spores and seeds. Figure 4.3a shows trilete spores and Figure 4.3b shows a fossil (!) spore capsule ejecting sperm cells. Both of these figures come from the Rhynie Chert (early Devonian).
The known examples represented in the fossil record are (Using the nomenclature of Margulis):
extinct phylum Rhynophyta. Cooksonia is often regarded as the earliest known fossil of a vascular land plant, and dates from 425 Ma, in the late Silurian Age. This phylum became extinct in the mid-Devonian (about 380 Ma). It was a small plant, only a few centimetres high. Many more examples of this phylum exist in the Rhynie Chert. They are the "oldest known anatomically preserved vascular land plants." The fine-grained quartz rocks preserve the fossils in exquisite detail, and also include many co-existing fossils of early animals (protists and arthropods) in the actual life positions. Figure 4.5 shows a thicket of Rhynia preserved in life position in the chert (size ~ 5 x 8 cm). The leafless stems had stomata.
The following nomencature follows Margulis.
(Subkingdom Bryata, Phyla Pl-1 to Pl-3)
Margulis suggests of the first three plant phyla that "Hornworts, mosses and liverworts probably evolved independently of one another ... and give rise to no other plant lineage." These phyla include all non-vascular plants -- that is, they do not have an organized way (xylem and phloem) to move liquids throughout the plant. As a result the plants are small in size and require dampness to grow (although they may have remarkable abilities to survive dessication).
Because these plants are small and soft-bodied, early fossil evidence is problematic and depends on special fossilizing conditons.
Pl-1 Bryophyta. Mosses are non-vascular, so they are necessarily small and must live in wet or damp areas. Reproduction must occur in the presence of water so that the male sperm can swim to the female sex organ. The fertilized spores generally disperse in wind currents. Some mosses are also capable of asexual reproduction.
The mosses are soft-bodied and small, and so fossils are rare. Figure 4.6 is the oldest fossil moss, Pallavicinites devonicus, from the Upper Devonian (ca. 370 Ma) of New York.
Bryophytes in Amber. The Dominican amber is one of very few sources of fossil mosses04.8. The amber was fossilized in the Eocene era (56-34 Ma) from an extinct species of Hymenaea, a large tree found in forest areas from Mexico to Brazil.
Pl-2 Hepatophyta. Liverworts. Non-vascular. The name comes from the liver-shaped head of the male spore-producing stalk. Compared with mosses, liverworts have flattened leaf-like body attached in a ribbon-like branching structure and rhizoids which function much like roots for attachment and food uptake. The earliest liverwort fossils are mid-Devonian (Hernick et al., Earth's oldest liverworts, Review of Palaeobotany and Palynology, Volume 148, Issues 2-4, January 2008, Pages 154-162). Liverworts are the only plants that do not have proper stomata, although some have pores which, however, cannot close as do stomata.
Pl-3 Anthocerophyta. Hornworts. Non-vascular. The name comes from the horn shape of the male spore-producing stalk. Some varieties are host to nitrogen-fixing bacteria, so that they can derive nitrogen from the air and live on bare rock. This makes the hornwarts one of the first successful invaders of sterile land.
The hornworts are relative late-comers in the fossil record, first appearing in the Cretaceous Era (144-65 Ma) contemporary with the flowering plants and grasses. This seems very late from an evolutionary point of view. The "horn" is unusual because -- like grasses -- it grows from the base -- an undifferentiated "stem cell" called the meristem: most plants grow from their tips.
The earliest unambiguous fossil hornwort was preserved in Dominican Amber, dated to about 15 Ma04.9.
Subkingdom Tracheata, Phyla Pl-4 to Pl-12).
All vascular plants have vascular tissue which transports nutrients and water throughout the plant. Because of this specific provision for circulation, the vascular plants can (in principle) grow much larger than the non-vascular plants -- although other changes have to accompany the provision of vascula -- such as ways to preserve and control moisture content, strengthening of cell walls for support, and ways to promote vascular flow in the face of gravity.
The vascula consist of the Xylem and Phloem. The xylem draws dissolved nutrients and water up from the soil, and the phloem moves food (mostly sugars) from the place of photosynthesis throughout the plant.
Pl-4 Lycophyta. Lycopods -- club mosses. All living lycopods are herbaceous; all woody lycopods (lepidodendrids) are extinct. Fossil woody lycopods reached over 100 ft. in height and were common in the Carbonaceous. The woody material was formed by defunct tracheids (xyla) constructed with lignin04.10.
The lycopod Baragwanathia (Figure 4.8) from the late Silurian was the first plant that had true leaves with vascular tissue04.11. It reached 30 cm. in height.
Pl-5 Psilophyta. Whisk Ferns. There is no fossil record of this phylum04.11a.
Pl-6 Sphenophyta. Horsetails. Modern horsetails are only a dim shadow of their resplendent past which reached a peak in the Carboniferous Age (359.2 to 299.0 Ma). They first appear in the late Devonian age.
The modern horsetail fern is a genuine "living fossil" on the same order of the Gincko tree. These small plants are commonly found in woods. Like true ferns, they reproduce by spores.
The first fossils that can be unambiguously placed in the Sphenophyta are Late Devonian in age04.12. They were abundant during the Carboniferous Era (450 Ma), the giant Calamites growing to heights of over 100 ft. They became extinct in the early Permian04.13.
Pl-7x Seed Ferns (Extinct) -- the First Seed Plants. Seed-bearing ferns are a phylum of plants -- the Pteridosperms -- that is now extinct. Ferns today are seedless -- Phylum Pl-7 Filicinophyta (Pteridophyta), the seedless ferns. This is the first appearance of seeds, and it is thought by many biologists that all seed plants descended from this phylum. Prior to the appearance of this phylum, all plants propagated sexually with spores. These are the first extinct phylum of vascular plants identified solely by examining the fossil record04.14. The Carboniferous era has been called the age of ferns -- actually, the age of seed ferns which often grew to the size of large trees.
Pl-7 Filicinophyta -- true ferns. Ferns, Pterophyta. The earliest fossils of true ferns occur in the Carboniferous era, contemporary with the seed ferns (see above). Ferns similar to modern families rose later, in the Cretaceous era (145 to 65 Ma) during the heyday of dinosaurs, and also the era of the earliest flowering plants (angiosperms).
Pl-8 Cycadophyta -- Cycads. Cycads are gymnosperms -- "naked" seed plants; that is, they lack the food (derived from the ovaries) that surrounds other seeds. This phylum first appeared in the early Permian Era (299-251 Ma). "The Cycad fossil record is generally poor." -- Wikipedia. Cycads resemble ferns, but typically have fern-like leaves that surround a central seed cone. One variety is the Sago Palm (actually not a palm but a Cycad).
Pl-9 Ginkgophyta -- Ginkgo tree. The modern Ginkgo Balboa tree is the only living species of this phylum which has a fossil record from the Permian Era. Note the leaf varieties in the fossil species, compared with the varieties in the modern Ginkgo Balboa -- all varieties can show up on a single tree (a similar variation occurs in sassafras trees).
Pl-10 Coniferophyta -- Conifers. Conifers are woody gymnosperm plants that first appear in the upper Carbonaceous era but flourish in the Mesozoic Era (250-67 Ma) between the Permian Extinction (251 Ma) and the Chicxulub extinction (65 Ma), the K-T boundary which defined the end of the Cretaceous era and the start of the Tertiary Period. The Mesozoic Era begins with the Triassic Era (250-200 Ma) and ends with the Cretaceous Era.
Pl-11 Gnetophyta. Gnetophytes are also gymnosperms. Many of them are woody climbers. The earliest clearly identifiable fossils are from the Cretaceous, but some fossils with possible identity as Gnetophytes go back to the Permian.
Pl-12 Anthophyta -- Angiosperms = flowering plants. Flowering plants arose in conjunction with the arrival of bees and insects that are adapted specifically in pollenation04.15. This period is characterized by the appearance of very large animals -- it is still a feature today that the largest land animals feed on plants (perhaps because plants must be eaten in bulk in order to provide sufficient nourishment).
Flowering plants appear to have developed concurrently with insects that could aid in pollination. "prior to the evolution of bees [angiosperms] didn't have any strong mechanism to spread their pollen, only a few flies and beetles that didn't go very far."
Grasses. only appear after 65Ma. A remarkable characteristic of grasses (and whisk ferns, Pl-5) is that they grow from their base rather than from the tip. Thus damage to the blades by grazing animals do not kill the grasses, because they continue to grow from the base of the blade. Other plants, such as trees, grow from the stem and branch tips.
The Cnidaria are relatively simple animals -- they have few of the body parts of higher animals. But a defining feature of the phylum is the presence of stingers (nematocysts) used for food-gathering and other tasks. The nematocysts are complex marvels of engineering sophistication.
The Cnidaria are relatively simple animals -- they have few of the body parts of higher animals -- no enclosed digestive tract, nerve network, circulatory system, vision, skeletal structure, or appendages to aid in movement -- but they have a means of communication to coordinate actions. They are radially symmetric and digest food in an open interior sac. The phylum includes corals and jellyfish (= medusas).They are soft-bodied, but corals secrete calcium carbonates that form the hard coral reefs that house millions of individual animals. A few corals show up in the Cambrian era (520 Ma) , but become abundant about 100 My later, in the Ordovician era . The modern corals date from the Devonian era (about 240 Ma).
There are a large variety of nematocysts, which may even vary geographically for the same or similar species. This implies that there is a robust evolutionary mechanism at work which supports variability around a basic gene package. I conjecture that this evolutionary variation occurs primarily in the parameters of gene expression.
The geologist Buckland once marvelled at the exquisite attention to engineering detail that is revealed in ancient fossils.
Our own fascination is with the Cnidarians - Phylum A-4, which includes corals and medusas. All species in this phylum are radially symmetric and have stingers, called nematocytes. The cnidarians are (relatively) immobile, and gather food with stingers which inject neuro-poisons (hypnotoxin) to immobilize their victims.
The nematocysts have been called the "most complex organelles of animal cells".05.00 They are small -- about the size of an average bacterium (up to 60 µm in length).
A cnidarian may have many thousands of these nematocysts with various specialized functions. When fully mature they appear able to function somewhat independently of the host. Some species eat cnidarians and preserve immature nematocysts (called "kleptocnidae") for their own defensive use05.01.
The engineering challenges are as follows05.02:
• The cell wall is super-strong, to resist extreme pressure without bursting. One scientist estimated that "the tip of the nematocyst thread is forced out of the capsule [by hydrolic pressure, although some authors assert that electrical repulsion initiates the explosion - dcb] at the astounding acceleration of 40,000g!" This is over 30 times the water pressure at the deepest part of the ocean (16,000 psi ~ 1,100 atm) and is strong enough to penetrate almost any biological structure, including shells and exoskeletons. Despite this, water can pass through the cell wall05.03.
• A hollow tube is tightly coiled under tension inside the cell, which leads to the question: how does the coil get packed into the cell? (An analogous packing problem exists for packing of viral dna inside its capsule). This tube is packed inside-out with barbs along the inner surface (which will be the outer surface once the tube is discharged). The venom may be stored in the tube[CHECK].
• The propulsion is provided by a concentrate of calcium ions that are stored in a water-tight sac. When the cyst is triggered, these ions rush into the cell, and immediately cause a severe osmotic imbalance so that water rushes into the cell, swelling it rapidly to the point of explosion directed through the lid. The hollow piercing barb penetrates the victim's skin; the coiled tube passes through the tube and poison is ejected through the tip of the tube or through the tube wall.[GET REFS -- is this consistent with Fig below??]
• The activation time is the fastest in the animal kingdom: the entire process is complete in 3 ms05.04. Electric triggering causes the cell volume to increase by 10%, which opens the lid, and the dart ejects in a few µs, propelled by hydrostatic (osmotic) pressure."
• The triggering mechanism is generally a combination of mechanical and chemical response, so that discharge occurs when the trigger is touched by the right prey[FOOTNOTE: REF??]. Either mechanical or chemical response alone is not sufficient.[GET REF]
At present, the details of the nematocyst's life cycle are uncertain. Figure 5.02 summarizes one current view (expressed in general terms with some details missing). Ultimately, of course, every detail must be explained in terms of ordinary chemistry, but many questions remain.
There does not appear to be full concensus on the details of the discharge mechanism -- how the remarkably rapic high pressure impulse is created. The wikipedia article credits "a large concentration of calcium ions"; the above references assume electrical repulsion and osmotic pressure; other discussions assume a role for spring tension in the coil. It seems fair to conclude that this is still an unsettled question.
Similarly the storage of the toxins, or how it enters the victim does not appear to be fully settled.
Ordovician (488 - 443 Ma) to Lower Carboniferous (Mississippian) (359 - 316 Ma) Eras.
Marine plants first appear late in the Ordovician Era, but the Devonian era (416 to 359 Ma) saw the true "greening" of the land. The massive invasion of plants onto the continents had to wait until the ozone layer first grew to a level that could filter out the most harmful cosmic rays. This is a time in which many major innovations in plants occurred.
Plants may have both sexual (requiring fertilization of a male and female cell) and asexual means of reproduction -- as is also the case with most single-celled species of life. Sexual reproduction of plants involves spores or seeds. The primary distinction between spores and seeds, is that spores fertilize outside the parent's body, whereas seeds fertilize and mature within or on the parent's body. [CHECK!!!] Seed plants may disperse a powder-like Pollen of male cells to provide cross-fertilization between plants, with the actual fertilization occurring within plant ovaries. This accomplishes the cross-fertilization that spores also provide.
Spores. Spores appear first in the fossil record during the middle Ordovician Era (~470 Ma). Spores form in groups of four called spore tetrads. There are two types of spore anatomy: monolete and trilete which differ in the way the original mother spore (sporophyte) divided into four[FOOTNOTE: The sporophyte is diploid (double strand chromosomes). The sporophyte divides once and then each part forms two haploid (single strand chromosomes) spores, hence four spore form togeether[FOOTNOTE: See the New World Encyclopedia entry on Spore Formation Note that ?? these spores are haploid - only half of a chromosome?? --- add Meiosis_overview pic to show 4 spores after meiosis] If they divide like orange slices, the result is a monolete spore with a single scar marking the joining point. If they divide like a tetrahedron, the result is a trilete spore with three scars marking the joining point with the other spores.
[FOOTNOTE: For further images of pollen and spores see ref. Eckart Schrank below.]
Seeds. Seeds made it possible for plants to live away from moist environments during reproduction. [Rich p386].
All seeds are the product of fertilization and are diploid combinations of the haploid male sperm and female egg. In contrast, spores may be haploid or diploid -- that is they may form before (generally) or after fertilization [CHECK].
How long can pollen, spores and seeds survive?
Spores -- note two classes of spores mono and tri. etc. intexine and exoexine
See http://www.benbest.com/misc/DNAamber.html Claims to get dna from amber appear to be false -- due to contamination. Not reproducible. ... There are sound theoretical reasons for believing that DNA could not survive hydrolysis & oxidation under such conditions for more than 50,000 to 100,000 years [NATURE; 365:700 (1993) and NATURE; 366:513 (1993)]. But deep ice cores taken from Greenland permafrost have revealed DNA sequences from plants and insects verified to be between 450,000 and 800,000 years old [SCIENCE; Willerslev,E; 317:111-113 (2007)]. Ice cores taken from Antarctica have the potential to reveal DNA samples that are much older. The entire human genome was sequenced from 4,000-year-old hair recovered from permafrost in Greenland [NATURE; Rasmussen,M; 463:757-762 (2010) and NATURE; Lambert,DM; 463:739-740 (2010)].Despite the discovery of lucite & epoxy resins, it has not yet been possible to artificially synthesize amber, the hardest natural resin known.
Compare viable dna from animals trapped in resin.
Wiki: Early land plants reproduced in the fashion of ferns: sporessporophyte ???
Seeds = complete (fertilized) plants, with food & protective shell [describe how]. You can see the miniature plant in, for example, lima bean seeds: split the seed in half lengthwise and you will see two miniature leaves. germinated into small gametophytes, which produced sperm. These would swim across moist soils to find the female organs (archegonia) on the same or another gametophyte, where they would fuse with an ovule to produce an embryo, which would germinate into a
GO INTO THE PROTECTIVE, DISPERSAL FEATURES OF SPORES AND SEEDS. LONG LIVED DORMANCY.
Another difference is that self-fertilization is more likely in the process of spore-based reproduction than in the pollination of a flowering plant. The seed-based process, therefore, has more possibilities for genetic adaptation and evolution."
Remarkable exanmple: Seed Ferns vs modern ferns.
See Dr. Gerhard Leubner's website, The Seed Biology Place -- Seed Evolution for further information on seed evolution. (nte 4.14)
Development Biology of fern gametophytes -- Morphogenesis of spore maturation
plants: Alternation of Generations 26:seedless plants (.doc)
haplodiplontic = diplohaplontic = diplobiontic = dibiontic
Some of the following are primitive tasks in themselves, others are composite tasks that can in turn be described as a combination of primitive tasks.
• Electric potential gradients. This is a prime mover for molecular reconfiguration, conbination, motion, etc. Example: The movements of the Kinesis molecular motor. Reaction pockets within molecules based on local electrical gradients.
• Solute concentration gradients. Note that different solutes may operate independently to an extent. Example: operation of xylem and phloem in plants.
• Acidity gradients. This is excess/deficiency of H+ ions (== ph).
• Osmotic pressure across membranes. Classical examples: The cnidocyst discharge; xylem and phloem movement between cells.
• Capillary Action. xylem and phloem.
• Condensation and evaporation. Leaf transpiration via stomata "breathing."
• Semi-permeable membrane differentiation.
• Mechanical transport with specialized motor molecules. Kinesin, ATPase, Nitrogenase, etc.
• Mechanical reconfiguration. Membrane gate-keepers (e.g. in nuclear membrane, cell wall).
• Key-matching. E.g. t-rna, etc.
Mid Cambrian Trilobite
Paradoxides, length 10"
Trilobites are the prototypical symbol of the
Age of Fossils.