GEOL 204 Dinosaurs, Early Humans, Ancestors & Evolution:
The Fossil Record of Vanished Worlds of the Prehistoric Past
Spring Semester 2014
Endless Forms: A (very, very simplified) Overview of the Diversity of Life
Animals & Vegetables
Traditionally the living world was divided into animals (which moved) and plants (which did not). But as natural world was studied in more detail, it was recognized that there were immobile animals; that fungi were not plants (they were decomposers, not photosynthesizes); that there will microscopic organisms that didn't fit any of these categories. So it was apparent that the diversity of life was much more expansive than just animals and plants.
So, what is Life? A hard thing to define, especially at the boundaries between life and lifelessness. So, in fact, we are not going to do that for this course! Instead, we'll look at some of the properties of life and its diversity, and some conditions under which it arose. All living things on Earth share certain things in common:
- They use deoxyribonucleic acid (DNA) as their genetic material.
- A second molecule, ribonucleic acid (RNA) reads instructions off a strand of DNA and assembles proteins in a sequence determined by the information, which the body uses to assemble its bits and parts and to run its operations
- They have a cell membrane
The Three Domains (Bacteria, Archaea, Eukarya) and LUCA
Genetics reveals three major branches to the Tree of Life. One (the eukaryotes) contain both unicellular and multicellular forms. The other two branches--the Bacteria (sometimes called Eubacteria) and the Archaea (sometimes called the Archaeobacteria)--are all single-celled, lack nuclei, lack mitochondria, and lack chloroplasts. This condition is called the "prokaryote grade." Many are heterotrophs or are chemoautotrophs (live off of inorganic chemicals); however, some bacteria (most significantly the cyanobacteria, also called "blue green algae") are phototrophs.
Many bacteria and archaeans live in what for eukaryotes would be considered intolerable conditions: extremely high or low temperatures; very high salinities; very acid or alkali conditions; etc. These organisms are called "extremophiles," and many of them occur near the base of their respective branches of the Tree of Life. In particular, most primitive bacteria and archaeans are anaerobic environments (ones where gaseous or dissolved oxygen is lacking.)
Biologists have used this evidence to make predictions about the common ancestor of all living things (LUCA, the last universal common ancestor). This ancestor would have been single-celled and have the prokaryote grade: the eukaryote condition and (later still) multicellularity would have occurred later up the branching Tree of Life. Additionally, LUCA would likely have lived in an environment that eukaryotes would consider "extreme"; it would have definitely have been an anaerobic environment, since before the evolution of phototrophs there would have been very little free oxygen in the atmosphere. In fact, LUCA would not have been very different from some types of bacteria and archaeans today.
Bacteria (also called Eubacteria)
- Prokaryotes, diverse habits (heterotrophs, chemolithotrophs, phototrophs, etc.). Some anaerobic (live without oxygen), some aerobic (require oxygen). Two major group of aerobic bacteria groups:
- Cyanobacteria ("blue-green algae") (Proterozoic-Quaternary): aerobic phototrophs; major oxygen producers. Associated with the formation of stromatolites (although nearly any biofilm former could potentially produce stromatolites). Via endosymbiosis, some cyanobacteria were incorporated as plastids in eukaryotes: most significant, as chloroplasts.
- Alpha-proteobacteria (?Archean-Quaternary): wide variety of habits. Of importance for this course, some are anaerobic phototrophs (including some of the oldest forms of photosynthesizers); others (free-living aerobic heterotrophs) include the ancestors of mitochondria in eukaryotes via endosymbiosis.
The other major prokaryote grade of organisms are the Archaea. These are prokaryotes; many are extremophiles; most are anaerobic. Based on features of their DNA synthesis (among others), archaeans are probably more closely related to Eukaryota than to Bacteria. It is possible that Archaea is paraphyletic with respect to Eukaryota, and that the prokaryotic ancestors of the main cell (but not the mitochondria or plastids) of eukaryotes.
The remaining clade of organisms are the eukaryotes (Eukarya or Eukaryota). These are larger cells, with a nucleus surrounding the genetic material and many additional small structures (organelles) with specialized functions. All eukaryotes are aerobic. Many are heterotrophs, but some are autotrophic photosynthesizers (algae and plants).
Eukaryotes have mitochondria: another type of organelle that are the powerplants of the cells. Mitochondria take in food (basically the sugar glucose) and oxygen and convert it into chemical energy (the molecule adenosine triphosphate, or ATP): ATP is then used by other parts of cells as fuel. Mitochondria turn out to be descendants of alphaproteobacteria, and carry their own genome separate from the nuclear DNA of the main cell.
Additionally, plants (and a few other groups of eukaryotes) have specialized organelles called chloroplasts: these are little solar energy collectors. Chloroplasts contain the substance chlorophyll: plants use their chloroplasts to combine sunlight, water, and carbon dioxide into chemical energy and waste oxygen gas (the latter they release into the atmosphere). Similar to mitochondria, chloroplasts are descendants of once-free-living prokaryotes (in this case, cyanobacteria) incorporated into the eukaryotic cell, and retain their own DNA.
This process--the permanent incorporation of once-free-living cells into the cells of eukaryotes--has been termed endosymbiosis.
Most of the main organisms we will be concerned with in this course are multicellular organisms, but there are some major fossil-forming eukaryotic unicells:
- Diatoms (Jurassic-Quaternary; more abundant in Cenozoic than in Mesozoic; freshwater Paleogene-Quaternary): phototrophs; siliceous shells (called frustrules) accumulate to form diatomite
- Coccolithophorids (Jurassic-Quaternary; amazingly abundant in Cretaceous): phototrophs; calcareous plates (coccoliths) accumulate to form chalk
- Foraminferans ("forams") (Cambrian-Quaternary): heterotrophs; "armored amoebas"; have calcareous shells (test) that grow by addition of new chambers; tests accumulate to form foraminferal ooze, very important index fossils.
Several groups of eukaryotes evolved the ability to form complex bodies made of multiple differentiated cells all with the same genetic information. There are even more groups that form simple colonies, but these all have cells that are essentially identical. True multicellular bodies have different cell types, each with their own function.
Here are some of the benefits to multicellularity:
- Larger body size: competitive space utilization
- Increased energy storage reserves
- Increased feeding surface area
- Functional specialization of different parts of the body
Among the terrestrial realm the major groups of multicellular organisms are animals, plants, and fungi. Each is more closely related to unicellular forms than to any other multicellular group. Brown algae like kelp represent another independent origin of multicellularity.
The Green Kingdom: A Brief Overview of Plants
Plants in the broad phylogenetic sense (Plantae or Primiplantae) represent a major clade of eukaryotes. "Algae" are simply all members of Plantae that do not live on land. Basal members of the various plant groups are often unicellular, but the red algae and some green algae (including land plants) are multicellular. All are phototrophs, and have chloroplast. (In fact, all non-plant phototrophic eukaryotes actually have symbiotic plants rather than just symbiotic cyanobacteria.) Rhodophytes ("red algae") have a fossil record back to Ectasian; green algae not before the Cambrian.
Land plants (technically Embryophyta) show up in the Ordovician (with possible spore evidence in the Cambrian). They are descendants of freshwater green algae. The fossil record contains many stages of plant evolution. All land plants are phototrophs and multicellular.
Basal land plants ("bryophytes": a paraphyletic grouping) (Ordovician-Quaternary): live on land, but have no vascular tissue (and thus no good stalks, stems, roots, etc.). Liverworts, hornworts, true mosses, etc. are living representatives. Reproduce by means of spores.
Vascular plants (technically Tracheophyta) (Silurian-Quaternary): vascular tissue, stems, roots, bark (for larger plants). Two major branches are the club mosses and the eupyllophytes.
Clubmosses (technically Lycophyta) (Silurian-Quaternary): reproduce by spores; covered with small leaflets rather than true leaves. An important fossilizing group is the scale trees (technically Lepidondronales) (Carboniferous): enormous, tree-sized wetlands trees of the coal swamps of the Carboniferous. Much of the coal from the coal swamps is from scale trees.
Euphyllophyta (Devonian-Quaternary): plants with true leaves. Two major divisions within this group are:
- Ferns (technically Pteridophyta) (Devonian-Quaternary): Still reproduce by spores. Major fossilizers include:
- Horsetails (technically Sphenopsida) (Carboniferous-Quaternary): tough stems; reproduce by shoots. The Carboniferous segmented tree Calamites was a horsetail the size of a small tree
- "Tree ferns" (various groups) (Carboniferous-Quaternary): not a single group, but several types of true ferns convergently evolved a tree-like form at different points in plant history
- Woody plants (technically Lignophyta) (Devonian-Quaternary): have specialized highly vascular tough lignin-rich tissue (wood) allowing them to grow tall. The most primitive woody plants—such as Devonian Archaeopteris—still reproduced by spores. All more advanced woody plants were seed plants
Seed plants (technically Spermatophyta) reproduce by pollen (containing the sperm cells) fertilizing specialized female organs containing the egg cells: the embryo produced is protected by a seed. The oldest seed plants are Devonian. Current evidence points to the living non-flowering seed plants (conifers, cycads, ginkgos, gnetophytes) forming a monophyletic clade Acrogymnospermae instead of the traditional interpretation of these "gymnosperms" are a paraphyletic grouping with respect to the flowering plants. There definitely do appear to be fossil gymnosperms (that is, non-flowering seed plants) which are more closely related to flowering plants than to any living group of gymnosperm regardless of the monophyly or not of acrogymnosperms. The major groups of fossilizing seed plants are:
- "Seed ferns" (various groups) (Devonian-Cretaceous): not a clade, but rather a grade of any seed plant that isn't clearly a flowering plant or one of the "classic" gymnosperm groups. Typically have fern-like leaves (hence the name). Some seed ferns (such as the Devonian-Carboniferous medullosans) branched off the seed plant line before classic gymnosperms and flowering plants diverged; others (including the famous Permian Glossopteris) are early members of the flowering plant-branch.
- Acrogymnospermae (Devonian-Quaternary):
- Cordaites (technically Cordiatales) (Devonian-Permian; most abundant in Carboniferous): close relatives of the conifers; first major upland trees and shrubs. Some grew in excess of 30 m tall.
- Conifers (Pinophyta or Coniferophyta) (Carboniferous-Quaternary): includes pines, cypresses, redwoods, junipers, etc., etc.
- Ginkgos (Ginkgophyta) (Permian-Quaternary; most abundant in Jurassic-Cretaceous)
- Cycads (Cycadophyta) (Permian-Quaternary)
- Bennettitaleans (Bennettitales) (also called "cycadeoids") (Triassic-Cretaceous): superficially resemble cycads, but more closely related to flowering plants
- Angiosperms (Angiospermae or Anthophyta, "flowering plants") (Cretaceous-Quaternary; possible body fossils from Jurassic and possible pollen from Triassic): have specialized organs (flowers) that attract pollinators, who carry pollen to other flowers to fertilize them. Seeds are wrapped in nutty or succulent fruit. Dominate modern floras. Two important angiosperm groups of note:
- Grasses (Poaceae or Gramineae) (Cretaceous-Quaternary): grow from base of leaf rather than tip; leaves contain bits of silica
- Composites (also called "asteraceans", Compositae or Asteracea) (Paleogene-Quaternary, but most abundant Neogene-Quaternary): daisies, sunflowers, garden vegetables of most types, etc.; flowers of the meadows
Animals (formally the Metazoa) are multicellular heterotrophs. Their closest relatives are choanoflagellates (a group of zooplankton).
Key attributes of metazoans:
- Aerobic heterotrophs
- Sexual reproduction in nearly all forms, in at least some life stage
- Many are capable of extracellular deposits of calcareous minerals (in other words, they can build shells)
- Nearly all basal members of nearly all lineages are suspension feeders: organisms who feed on particles of food (feces, decayed matter, remains from carrion, plankton, etc.) floating in the water
The sponges ("poriferans") (Ediacaran-Quaternary) are the most primitive types of animals. They are suspension feeders in which water comes in through pores on the inside to be picked up by flagellated cells on the inside; essentially living sacs. Shape of sac is held together by spicules that might be siliceous, calcareous, or made of the protein sponging. Recent work has shown that sponges are not a monophyletic group: some are more closely related to eumetazoans (advanced animals) than they are to the other sponge groups. Major fossilizing sponges include:
Glass sponges (technically "Hexactinellida") (Ediacaran-Quaternary): siliceous spicules with three rays (like jacks). Oldest known animals; far more common in Ediacaran-Devonian than later in Earth History.
Archaeocyathids (Cambrian; nearly all from Early Cambrian): calcareous skeleton, shaped like one small ice cream cone inside a slightly larger cone, held together by septa (partitions). Major reef formers of the Early Cambrian.
Stomatoporoids (Cambrian-Devonian; most common in Silurian-Devonian): calcareous skeletons, forming mound-like masses. Major reef formers of the middle Paleozoic (along with tabulate corals). Post-Devonian "stromatoporoids" turn out to be from different groups of calcareous sponges.
The remaining animals (i.e., non-sponge animals) are the Eumetazoa, or "true animals." They share the following specializations:
- Muscles: they can indeed move, either their entire body or just some parts (like tentacles)
- Digestive systems: ancestrally a sac opened at one end, where food goes in, gets digested by the lining of the sac, then "spit" (or a rhyme thereof) out the same opening it came in
- Other tissues and organs: far more specialization of cell types than sponges, with these cells arranged into complex interacting tissues and systems.
- A regular body shape: as opposed to sponges (which are more like plants in terms of having highly variable body forms based on some basic rules), eumetazoans have highly distinctive body structures. It turns out these are regulated by HOX genes.
Most eumetazoans are bilaterians. But the two basal branches (Ctenophora ("comb jellies") and Cnidaria) have radial symmetry: a top and a bottom, but no front/back or right/left. Both groups are very soft bodies, but at least some cnidarians have a good fossil record.
Cnidarians (Cnidaria) (Ediacaran-Quaternary): includes jellyfish, corals, sea anemones, hydras, and their relatives. Have a gut with a single opening, fringed by stinging tentacles. Suspension feeders and/or passive predators. Some live entire life attached to surface as a polyp; others float around with tentacles underneath them as medusa; some alternate between polyp and medusa. Cndarians are soft bodied, so typically are only preserved by impressions. However, the corals produce calcareous skeletons, and so have an excellent fossil record:
- Horn corals (also called rugose corals or tetracorals, technically Rugosa) (Ordovician [maybe Cambrian?]-Permian; most common Silurian-Devonian): mostly solitary, with very large polyps.
- Tabulate corals (Tabulata) (Cambrian-Permian; most common Silurian-Devonian): exclusively colonial, with very small polyps. Major reef formers (along with stromatoporoid sponges) in middle Paleozoic.
- Scleractinian corals (Scleractinia or Hexacorallia, also called hexacorals) (Triassic-Quaternary): modern corals, mostly but not exclusively colonial. Major reef formers of Jurassic, Early Cretaceous, and Cenozoic
Conqueror Worm: Bilateria
he majority of advanced animals are bilaterians ("worms" in the broadest sense): animals with a front end, a back end, a left-to-right symmetry, and a top-to-bottom symmetry. Additionally, bilaterians typically have a mouth at one end, a gut running through the body, and an anus at the other end.
There are a great number of worm-shaped bilateral taxa (nematodes, nematomorphs, annelids, etc.) with no significant fossil record. (One group, the priapulids, show up in many Cambrian sites, and were probably a major group of early predators.) But the vast majority of bilaterians take the basic "worm" body plan and modify it into something very different. As it turns out, nearly all the good fossilizers are such non-wormy "worms."
Two groups of bilaterians whose fossil record is far better than than present one (and for whom there are more paleontologists studying them than modern biologist):
- Bryozoans (Bryozoa) (?Cambrian, definitely Ordovician-Quaternary): colonial suspension feeders; use a tentacled structure called lophophore to capture particles of food; live in small chambers. Exclusively aquatic, mainly marine. Major fossilizing bryozoans include:
- Stony bryozoans (technically Stenolaemata) (Ordovician-Quaternary; most abundant Ordovician-Triassic): form calcareous skeletons. Grow in a wide variety of forms. Minor components of middle Paleozoic reefs, and important components of Permian reefs. One notable group within the stony bryozoans are:
- Lacy bryozoans (technically Fenestrata): (Ordovician-Permian): formed lacy fronds through which water passed. Often found on soft muddy surfaces.
- Cheilostomes (Cheilostomata) (Jurassic-Quaternary; abundant Cretaceous-Quaternary): major modern group; forms encrusting sheets or mats.
- Brachiopods (Brachiopoda) (Cambrian-Quaternary): solitary suspension feeders; have two shells protecting a lophophore which captures particles of food. Once considered close relatives of bryozoans; while still a possibility, is not strongly supported by the evidence. Far more common in the Paleozoic than today. Strictly marine or estuarine. Among the major groups are:
- Lingulates (Lingulata or Linguliformes) (Cambrian-Quaternary): have paired calcium phosphatic shells and long tail-like pedicle; motile infaunal forms. Nearly unchanged throughout their history.
- Articulate brachiopods (Rhynchonelliformes) (Cambrian-Quaternary): have paired calcitic shells; one has an opening for a short pedicle and is called the pedicle valve; the other has an internal brachidium (lophophore support) and is called the brachial valve. Sessile: some attached to surfaces by short pedicle, others sat in soft sediment. Phenomenally abundant in Ordovician-Permian seas (major reef formers in Permian); common in Triassic and Jurassic seas; rare in Cretaceous and Cenozoic seas.
Shell Games: Mollusca
Mollusks (Mollusca) (?Ediacaran-Quaternary) are "shellfish" in the strictest sense. Ancestrally have a belly-foot for "squidging" over the seafloor, a radula for rasping algae, and gills around the body to breath. Kimberella of the Ediacaran may be an early stem-mollusk whose radula was not mineralized; Cambrian forms include non-shelled mollusks with mineralized radula. Starting in the Early Cambrian are mollusks with small chitinous, and later calcareous sclerites (tiny armor plates). However, most Phanerozoic mollusks either have large calcareous shells or are the descendants of shelled mollusks. The shells (and presumably the sclerites) are formed by the mantle: a specialized tissue on the body surface surrounding the gills. Two minor groups of mollusks are:
but molluscan diversity has long been dominated by the "Big Three" of gastropods, cephalopods, and bivalves:
- Chitons (Polyplacophora) (Cambrian-Quaternary): retain the ancestral habit of algae-scraping squidgers. Have a series of eight plates down the back. Strictly marine.
- "Monoplacophorans" (Cambrian-Quaternary): not a single group, but a grade of primitive mollusks in which there is a single shell. Includes the ancestors to all more advanced mollusks. Marine.
- Gastropods (Gastropoda) (Cambrian-Quaternary): snails, sea slugs, slugs, and their allies. Primitive forms retain the ancestral algae-scraping habit, but include swimming sea slugs, predatory sea snails (Cretaceous-Quaternary), and terrestrial snails and slugs (Devonian-Quaternary).
- Cephalopods (Cephalopoda) (Cambrian-Quaternary): predatory mollusks with chambered shells. Basal form benthic squidger, but all later forms nektonic. Strictly marine. Largest brains among invertebrates. Major fossilizers include:
- "Nautiloids" (Cambrian-Quaternary): paraphyletic grade of predatory shelled non-ammonoid cephalopods. Top predators of Ordovocian (perhaps 10 m long!)
- Ammonoids (Ammonoidea) (Devonian-Cretaceous): planktonivorous shelled cephalopds with complex sutures. Phenomenally abundant in Permian-Cretaceous, major index fossils.
- Coleoids (Coleoidea) (Devonian-Quaternary): predatory cephalopods with internalized shells. Includes modern cuttlefish, squid, and octopi. Major extinct group:
- Bivalves (Bivalvia or Pelecypoda) (also called "pelecyopods") (Cambrian-Quaternary): clams in the broad sense. Epifaunal or infaunal suspension feeders; mainly marine, but a few freshwater. Have left and right valves. Use gills to capture food particles. Important fossilizing clam groups include:
- Rudists (Hippuritoida) (Jurassic-Cretaceous; abundant Late Cretaceous): giant reef-forming clams; major reef formers of the Late Cretaceous.
- Inoceramids (Inoceramida) (Cretaceous): giant scallop-like epifaunal clams.
- Scallops (Pectinidae) (Devonian-Quaternary; abundant Cretaceous-Quaternary): epifaunal, capable of swimming short distances
- Oysters (Ostreidae) (Triassic-Quaternary): epifaunal, often attached, heavily mineralized. Important fossil subgroup was coiled oysters (Gryphaeidae) (Jurassic-Cretaceous), which typically lived on soft sediment
An Inordinate Fondness: Arthropoda
Arthropods (Arthropoda) (Cambrian-Quaternary) are a great clade of bilaterians with an exoskeleton of chitin which is molted and eyes. Many have some form of leg, sometime modified into a mouth part. Panarthropods include a wide variety of extinct early Paleozoic forms, some surviving soft-bodied animals, and the great crown group clade of Euarthropoda.
Euarthropods (eurthropoda) (Cambrian-Quaternary) are by far the most numerous group of animals in Earth history! In addition to the above traits, euarthropods have jointed limbs which are modified into many different uses (gills, legs, mouth parts, antennae, etc.). Their segmented bodies often show considerable tagmosis (tendency to form distinct specialized body units, like heads, thoraces, abdomens, etc.). Additionally, euarthropods take advantage of their molting to produce different growth stages with sometimes radically different body forms and ecologies. Major fossilizing arthropods are:
- Trilobites (Trilobita) (Cambrian-Permian): exoskeleton of calcite makes them wonderful fossilizers. Wide variety of life habits: suspension feeders, predators, scavengers, swimmers, burrowers, etc.
- Myriapods (Myriapoda) (?Ordovician, definitely Silurian-Quaternary): centipedes, millipedes, and relatives. First major group of terrestrial animals. During Devonian and Mississippian 2 m long arthropleurids ("godzillipedes") were the largest terrestrial herbivores the world had seen up to that point
- Eurypterids (Eurypterida, "water scorpions") (Cambrian-Permian, most important Silurian-Devonian): large predatory arthropods (including 2.5 m forms: largest arthropods ever). Most lived in water, but some were adapted to life on land. Close relatives of, and possibly ancestral to, the arachnids (true scorpions, spiders, etc.) (Silurian-Quaternary)
- Crustaceans (Crustacea or Pancrustacea) (Cambrian-Quaternary): mostly marine (where they are the most common of all animal groups), some freshwater, a few branches terrestrial. Important fossilizers among the crustaceans are:
- Hexapods (Hexapoda) (Devonian-Quaternary): terrestrial crustaceous with six walking legs. The most important group of hexapods are the insects (Insecta) (Devonian-Quaternary; abundant Carboniferous-Quaternary), or winged hexapods. Insects are the most common group of animals on land. Recent studies show insects are specialized terrestrial crustaceans.
- Vericrustaceans (Vericrustacea) (Cambrian-Quaternary): this clade includes what most of us think about when we hear "crustacean" (prawns, crabs, lobsters, crayfish), but also barnacles, copepods, and branchiopods. Some of these have more heavily mineralized carapace than most non-trilobite arthropods.
Stars Below: Echinodermata and Cousins
Graptolites (Graptolithina) (Cambrian-Carboniferous) are an odd, entirely extinct group. Long known from fossils as carbonized remains on rocks, they look like writing on rock (which is essentially what "graptolithina" means). They were exclusively colonial animals, living either as plankton or attached benthos. They lived by suspension feeders. Their colonies had organic-walled chambers. Because of their rapid evolutionary change, distinctive forms, and widespread dispersal makes them excellent index fossils (especially in Ordovician). Recent studies show that they were related to a group with a much more extensive fossil and living record, the echinoderms.
Echinoderms (Echinodermata) (Cambrian-Quaternary): lose their bilateral symmetry after larvae; early forms have three-fold spiral symmetry but most advanced forms have pentameral (five-fold) symmetry. Body uses a water vascular system as a combination hydraulic power/skeleton system. Skeleton is formed of plates of calcite. Ancestrally ate by using tube-feet to suspension feed, but advanced groups show wide variety of life styles. Ancestrally benthic and relatively sessile. A wide variety of bizarre Cambrian-Ordovician groups, and many important groups from throughout the Phanerozoic:
- Blastoids (Blastoidea) (Ordovician-Permian; most abundant in Mississippian): stalked; compact bodies with tiny tentacles
- Crinoids (Crinoidea, "sea lilies") (Ordovician-Quaternary): stalked; bodies branch out into five (or multiple of five) arms lined with tentacles and tube-feet. Major suspension-feeders in middle Paleozoic, middle Mesozoic, and the deep sea today. Suffered devastation at end of Permian, which nearly wiped out group. Feather stars (Triassic-Quaternary) are stalkless crinoids.
- Eleutherozoans (Eleutherozoa) (Cambrian-Quaternary): non-stalked, free-living echinoderms, including:
- Ophiuroids (Ophiuroidea) ("brittle stars") (Ordovician-Quaternary): relatively fast suspension feeders with five long arms and a compact central body
- Asteroids (Asteroidea) ("star fish" or "sea stars") (Ordovician-Quaternary): predatory echinoderms; entire body divided into (normally) five arms
- Echnioids (Echinoidea) ("sea urchins", "sea biscuits", and "sand dollars") (Ordovician-Quaternary): encased in hard shell (test), and often covered with spines. Ancestrally are symmetrical (regular) epifaunal algae scrapers. Starting in the Jurassic, several groups of irregular infaunal sediment feeders evolve: these include the heart urchins, the sea biscuits, and the sand dollars (Paleogene-Quaternary)
- Holothuroids (Holothuroidea, "sea cucumbers"): worm-like benthic sediment feeders.
Show a Little Spine: Chordata
The chordates (Chordata) (Cambrian-Quaternary) are the vertebrates and our kin. Primitive chordates are soft-bodies suspension feeders; the living swimming lancelets and the mobile larvae of the (sessile as adult) tunicates still live this way.
The most important group of chordates, however, are the craniates (Craniata) (Cambrian-Quaternary). Craniates have heads with eyes, brains, nostrils, organs of balance. They are nektonic, and ancestrally were suspension feeders.. Primitive craniates include the living and extinct hagfish.
The conodonts (Euconodonta) (Cambrian-Triassic) are an extinct group of craniates (possibly primitive vertebrates) known mostly from their elements (bony biting mouth parts). Major index fossils for much of Paleozoic and Triassic. They were predators on tiny animals.
Things Seem A Little Fishy: Vertebrata
True vertebrates (Vertebrata) (Cambrian-Quaternary) have internal skeleton of cartilage (ancestrally) or bone, divided into separate vertebrae. Primitive vertebrates lack jaws. Jawless vertebrates include:
- Lampreys (Petromyzontida) (Devonian-Quaternary): lack of bone makes them difficult to fossilize. Include parasitic and suspension feeding forms
- "Ostracoderms" (Ordovician-Devonian): paraphyletic group of jawless fish with bony exoskeleton. Includes ancestors of jawed vertebrates. Most ostracoderms would have been suspension feeders.
The remaining vertebrates are the gnathostomes (Gnathostomata), and are characterized by having jaws (and thus gills no longer had to both breath and feed). The major gnathostome groups are:
- "Placoderms" (Silurian-Devonian): jawed fish generally lacking true teeth (a few newly discovered specimen shows some simple teeth) and heavily armored front parts of the body. Recently shown to be a paraphyletic series relative to toothed gnathostomes.
- "Acanthodians" (Silurian-Permian, most common in Devonian): jawed and toothed fish with spines in each fin. Recently recognized to be a paraphyletic series, including stem-chondrichthyians, stem-actinopterygians, and presumably the outgroups to these two together.
- Chondrichthyians (Chondrichyes, "cartilaginous fish") (Silurian-Quaternary): sharks and their allies. Toothed, but skeleton is cartilage rather than bone.
- Osteichthyians (Osteichthyes, "bony vertebrates") (Silurian-Quaternary): have internal skeleton of bone, and a lung. Two major divisions:
- Actinopterygians (Actinopterygii, "ray fins") (Silurian-Quaternary; abundant Devonian-Quaternary): major group of living fish. In many the lung no longer functions as a respiratory organ, and is lost or evolves into the swim bladder. Major group of ray-finned fish is:
- Teleosts (Teleostei) (Jurassic-Quaternary): fish which can protrude their mouths. Vast majority of living fish are teleosts. Major radiation of freshwater teleosts begins in Paleogene
- Sarcopterygians (Sarcopterygii, "lobe fins") (Devonian-Quaternary): have series of long bones supporting the fins. Ancestrally aquatic (life habit retained in lungfish (Devonian-Quaternary) and coelacanths (Devonian-Quaternary)), but some became adapted to life at land. Series of transitional forms in Devonian freshwater and seawater (Tiktaalik with wrists and ankles; Acanthostega with fingers and toes; etc.) document the rise of the fully terrestrial tetrapods.
Four On The Floor: Tetrapoda
Tetrapods (Tetrapoda, land vertebrates) (Carboniferous-Quaternary): have necks, digits (fingers and toes), and live adult life stage on land (or descend from animals that did). Primitive tetrapods, including ancestors of today's lissamphibians, laid eggs in water and had aquatic larvae.
The "amphibian" grade (with external gills in the larva) is a paraphyletic assemblage relative to the living amphibians and the fully terrestrial amniotes. We'll see more about Paleozoic tetrapods in a few weeks.
However, one group of tetrapods became fully terrestrial. These are the amniotes (Amniota) (Carboniferous-Quaternary). The fully land vertebrates have amniotic (shelled) eggs and claws. The entire life cycle is on land. Amniotes fall into two main divisions: the Synapsida (mammals and our extinct kin) and Sauropsida (reptiles, including birds).
Wild & Woolly: Mammalia and other Synapsida
Synapsids (Synapsida) (Carboniferous-Quaternary) were the dominant group of Permian terrestrial vertebrates. Among the synapsids were the more specialized therapsids (Therapsida) (Permian-Quaternary), which may have evolved warm-bloodedness and fur even before the rise of their most diverse subdivision, the:
- Mammals (Mammaliformes) (Triassic-Quaternary): furry, warm-blooded, large-brained. Most of mammal history was spent as several lineages of diverse but small-bodied forms in the shadow of the dinosaurs. After K/Pg extinction, four groups of mammals survived and diversified:
- Monotremes (Monotremata) (Cretaceous-Quaternary): egg-laying mammals, minor part of fauna.
- Multituberculates (Multituberculata) (Jurassic-Paleogene): important group of early mammals; includes some early
- Marsupials (Marsupalia) (Paleogene-Quaternary): dominant group in Australasia and Paleogene-Neogene South America. Stem-relatives of the marsupials are present in the Cretaceous and Paleogene, and because Metatheria (marsupials and their closest kin) are the sister taxon to eutherians, they must have been present in the Jurassic.
- Placentals (Placentalia) (Paleogene-Quaternary): the dominant group in rest of world. Includes such diverse groups as rodents, bats, elephants, odd and even-toed hoofed mammals (including whales), carnivorans, and primates. Stem-relatives of the placentals (collectively Eutheria) are present from the Jurassic onward.
"Here There Be Dragons": Sauropsida (Reptilia)
Reptiles (Reptilia or Sauropsida) (Carboniferous-Quaternary) were the dominant group of animals during Mesozoic Era. There are many lineages. Some important fossil reptile groups include:
- Parareptiles (Parareptilia) (Permian-Triassic, or -Quaternary if turtles are parareptiles) were a successful group of early reptiles. Diverse forms of armored herbivores, fast-running insectivores, fish-eating swimmers, and more. Some evidence suggests that Testudinata (Triassic-Quaternary) (turtles) are a parareptile group.
- Lepidosaurs (Lepidosauria) (Triassic-Quaternary) are tuataras and their diverse extinct relatives, and the even more diverse lizards and snakes. A highly successful group were the mosasaurs (Mosasauroidea) (Cretaceous): honest-to-goodness marine lizards
- Euryapsids (Euryapsida, marine reptiles) (Triassic-Cretaceous), aquatic reptiles that could retain the young inside the body. Include the fully-marine ichthyosaurs (Ichthyopterygia) (Triassic-Cretaceous) and plesiosaurs (Plesiosauria) (Triassic-Cretaceous), two very successful groups of swimmers.
- Archosaurs (Archosauria) (Triassic-Quaternary): reptiles with advanced respiration and four-chambered hearts. Archosaurs were dominant land vertebrates of the Mesozoic. Crocodilians (Crocodylomorpha) (Triassic-Quaternary) are a surviving part of the archosaurs. Many archosaur groups may have been warm-blooded. Two major groups of archosaurs are:
- Pterosaurs (Pterosauria) (Triassic-Cretaceous): flying reptiles, including the true pterodactyls (Pterodactyloidea) (Jurassic-Cretaceous)
- Dinosaurs (Dinosauria) (Triassic-Quaternary): including:
- Ornithischians (Ornithischia) ("bird-hipped dinosaurs") (Triassic-Cretaceous; abundant Jurassic-Cretaceous): herbivores including beaked, duckbilled, plated, armored, and horned groups
- Sauropodomorphs (Sauropodomorpha) (Triassic-Cretaceous): long-necked herbivores, including the largest land animals of all time
- Theropods (Theropoda) (Triassic-Quaternary): diverse group of bipedal, mostly carnivorous forms. Includes giant predators, but also specialized small feathered forms. The latter include the birds (Avialae) (Jurassic-Quaternary)
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Last modified: 27 March 2014