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Information about Synapsid1

Published on January 2, 2008

Author: Elliott


The Carboniferous Period - SYNAPSIDS RULE :  The Carboniferous Period - SYNAPSIDS RULE Slide2:  Continents are in collision course... Slide3:  Marine Life of the Carboniferous See a recovery after the Late Devonian extinction of tabulate-stromatoporoid reefs, extinctions of many fish, floating and swimming animals, and many freshwater forms. Ammonoids rediversified quickly. Reefs remained poorly developed after the demise of the tabulate-stromatoporoid reefs near the end of the Devonian. Brachiopods continued to thrive. Bryozoans were prominent. Crinoids and blastoids were common in the sea. Large foraminifera (fusulinids) appeared. First occur in Upper Mississippian; most abundant in Pennsylvanian and Permian. Ammonoids :  Ammonoids Ammonoids are relatives of the modern squid, as well as the octopus and chambered Nautilus, all of which belong to the group of animals called cephalopods. Ammonoids were important predators in the ancient oceans, eating fish, crabs, and other shellfish. Ammonoids appeared in the fossil record during the early part of the Devonian Period, about 400 million years ago. They died out about 65 million years ago, during the mass extinction at the end of the Cretaceous Period that killed the dinosaurs and many other kinds of land and sea animals. The top specimen belongs to the genus Goniatites. The lower specimen is Schistoceras missouriense. Brachiopod:  Brachiopod Bryozoans Fusulinid foraminifera Crinoid Slide6:  A Golden Age of Sharks Sharks and ray-finned fishes persisted as a diverse group of predators. Heavily-armored fish were replaced by more mobile forms. Sharks have undergone two major adaptive radiations and survived at least five mass extinctions, with the first major shark radiation occurred during the Carboniferous Period Indeed, with the exception of acanthodians (a type of placoderm), few fishes swam in early Carboniferous seas. The fossil record indicates that more than 75% of fish groups alive during the late Devonian died out before the beginning of the Carboniferous. The placoderms - a once dominant group of armored fishes - survived the devonian extinction event, but at greatly reduced diversity and abundance. Slide7:  Stethacanthids The misfortune of the placoderms presented a splendid opportunity for sharks in general and one group in particular: the stethacanthids. Perhaps in response to the ecological niches vacated by the placoderms, the stethacanthids exploded into a riot of bizarre forms and lifestyles. It was a kind of stethacanthid Mardi Gras - complete with outrageously unwieldy headgear and strange but fascinating rituals. Stethacanthus:  Stethacanthus Stethacanthus was an odd, dogfish-sized shark of the Carboniferous Period, about 320 million years ago. The brush-like dorsal fin with enlarged denticles on its flattened top and corresponding denticled patch on top of its head have generated much speculation about their possible function. Slide9:  Stethacanthus cont. It looked like a fish with a brush sticking out of its back. In addition, male Stethacanthus had similar enlarged scales on top of the head, making the whole contraption resemble a set of large, bristle-toothed jaws. It seems likely that the dorsal brush and cranial bristles of Stethacanthus played some role in their courtship rituals. Perhaps the brush and bristles were used during male-to-male pushing matches, enabling the combatants to grapple together as they tested each other's strength in competition for access to mating grounds or sexually receptive females. Falcatus:  Falcatus Asmall stethacanthid inhabiting the warm, shallow seas that invaded the American mainland during the early Carboniferous A female Falcatus falcatus biting the shoulder spine of a male, possibly as a prelude to mating. Paleoichthyologist Richard Lund actually found a pair of Falcatus preserved together in this position. Slide11:  Additional Comments on Sharks Shark diversity during the Carboniferous Period was nothing less than astonishing - Carboniferous boasted about 45 families of sharks (compared with about 40 families of modern sharks). But at the close of the Permian Period (~250 mya), there occurred what has been called the "Mother of All Mass Extinctions". In a geological instant, fully 99% of marine species were wiped out - including the extravagant stethacanthids. But some shark lineages squeaked through this catastrophe, one of which gave rise to modern sharks. Although modern sharks are remarkably diverse in form and lifestyle, no shark today matches those of the Carboniferous for sheer weirdness. Slide12:  Freshwater Habitats Ray-finned Fishes The modern bony fishes (class Osteichthyes) appeared in the late Silurian or early Devonian (about 395 million years ago). The early forms were freshwater fishes, for no fossil remains of modern bony fishes have been found in marine deposits older than Triassic time, about 230 million years ago. Recall that the Osteichthyes may have arisen from the acanthodians. A subclass of the Osteichthyes, the ray-finned fishes (subclass Actinopterygii), became and have remained the dominant group of fishes throughout the world – they were certainly common in the Carbonifierous Slide13:  Freshwater Habitats cont. However, it was not the ray-finned fishes that led to the evolution of the land vertebrates. Ancestors of the land vertebrates are found among another group of bony fishes called the Choanichthyes or Sarcopterygii. Choanate fishes are characterized by internal nostrils, fleshy fins called lobe fins, and cosmoid scales. The choanate fishes appeared in the late Silurian or early Devonian, (390 mya) and possibly arose from the acanthodians. Choanate fishes include a group known as the Crossopterygii, which has one living representative, the coelacanth Latimeria. During the Devonian Period some crossopterygian fishes of the order Rhipidistia crawled out of the water to become the first amphibians. Slide14:  Freshwater Habitats cont. Sharks Also in freshwater lakes swam lungfishes and xenacanth sharks (descendants of Antarctilamna that persisted in freshwater environments until the early Triassic Period, about 220 million years ago). Xenacanths were almost exclusively freshwater inhabitants, and had a long, rearward-pointing fin spine just behind the cranium (the name xenacanth means "strange spine"), diplodont teeth, a slender, eel-like body, an elongate dorsal fin extending along most of the back, and a symmetrical, tapering tail. Freshwater Xenacanth Sharks:  Freshwater Xenacanth Sharks Reconstruction of Xenacanthus, an eel-shaped shark that haunted freshwater habitats in what is now Europe during the early Permian (about 280 million years ago). Carboniferous Coal Forest:  Carboniferous Coal Forest Large trees with straight trunks are lychophytes; tree to the left is a horestail The Carboniferous is famed for extensive coal beds, which were formed in swamps. That is, coal deposits formed from plant remains in lowland swamps. Coal represents an enormous biomass of plants. Common coal swamp plants include: lycophytes, ferns, sphenopsids, cordaites Lycopod trees or club mosses :  Lycopod trees or club mosses Lepidodendron Note leaf scars on the trunk. (Trees grew to 30 m tall; 90 ft). The club-moss tree Lepidodendron This tree, in size up to 40 meters, grew in the coal-swamps of the Carboniferous.  Lycopods are spore-bearing plants, and were confined to swamps. Some grew to about 100 ft tall and were 3 feet across at the base Spore-bearing ferns and seed ferns:  Spore-bearing ferns and seed ferns Spore fern Seed fern Sphenopsids:  Sphenopsids Sphenopsids (like Calamites) were spore-bearing and similar to living horsetails or scouring rushes. They are often interpreted as living in moist areas, even perhaps standing water Calamites leaves Calamites trunk Slide20:  A Reconstruction of Calamites Cordaites:  Cordaites Note the horizontal ridges on this cast of the pith cavity stem of Cordaites, together with a leaf attached obliquely on the left side. The small foliage on the right is likely a variety of rhodea. A common seed plant of drier areas was Cordaites, a tall gymnosperms up to 100 ft in height Slide22:  Cordaites cont. Reproductive structures of Cordaites. (A) Foliage with fertile shoots. (B) Portion of the ovule-bearing Cordaianthus including part of the primary axis with ovulate secondary shoots bearing pendant ovules. (C) Pollen-bearing Cordaianthus Tree growth-form of Cordaites. Slide23:  Carboniferous Terrestrial Invertebrates Detritivores - land snail, millipedes, mites, and insects (roaches, earwigs) Wings appeared by the Late Carboniferous. Note: Insects first appeared in Devonian as wingless. Types of wings: Fixed wings (ex.: dragonflies, damselflies, mayflies) Folding wings - many specializations develop Predators - scorpions, arachnids (spiders, mites, etc.), centipedes, insects Many kinds of spiders lived on the ground and from the late Carboniferous a millepede with a length of more than 1.8 metres is known. Gigantic dragonflies, with a wingspan of over 60 centimetres, flew among the tree tops. Herbivores - insects with piercing, sucking, tearing - no clear leaf-eaters, however. Fossil Insects:  Fossil Insects Paleodictyoptera: Dunbaria fasciipennis Tillyard in Dunbar & Tillyard 1924.  This insect, with its beautifully-patterned wings and long cerci (the "tails"), had a wingspan of about 37 mm.  It flew some 260 million years or so ago over what are today the prairies of central Kansas.  Dragonfly reconstruction, Pennsylvanian coal swamp Slide25:  Carboniferous Tetrapods During the Carboniferous and the Permian the basic groups of tetrapods (amphibian-like animals) evolved that would populate the post-paleozoic world. The early tetrapods were, like early land plants, tied to the water by their reproductive mechanisms. Like most "fish" they had external fertilization in water and laid eggs in water which developed into aquatic larvae. The larvae metamorphosed into land-living adults. Living "amphibians" have inherited this primitive mode of reproduction. Revisiting the Devonian Tetrapods:  Revisiting the Devonian Tetrapods Neoceratodus Lepidosiren Protopterus Tetrapod Phylogeny:  Tetrapod Phylogeny Amphibians-like tetrapods diversified dramatically during the Carboniferous, and came to dominate terrestrial and aquatic habitats Slide28:  Amphibian-like Tetrapods Temnospondyls - had a rounded, crocodile-like snout.  They were diverse fish eaters in both water and on land.  They gave rise to the modern amphibians (frogs, toads, etc.). Slide29:  An Aistopod or lepospondyls skull Amphibian-like Tetrapods cont. Aistopods - Legless, snake-like animals with large eyes and light skulls.  They ate insects and fish.  Probably aquatic. Slide30:  Amphibian-like Tetrapods cont. Nectridians - Newt-like, aquatic, medium-sized animals.  Many had bizarre horns on the back of their heads.  They probably ate fish. Microsaurs - Lizard-like bodies, short teeth perhaps for puncturing arthropod cuticles.  Both aquatic and terrestrial forms Reptile-like amphibians Seymoriamorphs - Large (>2m) reptile-like animals with long snouts.  The Carboniferous forms were aquatic, fish eaters.  In the Permian, they became more fully terrestrial. Diadectomorphs: Large (>2m) reptile-like animals with short, deep skulls, massive limbs, and peg-like teeth. Fully terrestrial. These animals were the first tetrapod herbivores Slide31:  The Amniotic Egg Sometime during the Carboniferous, one group of tetrapods developed the amniotic egg. Primitively, the amniotic egg has a shell hardened by calcium carbonate which is impermeable to water but allows gases to be transpired. The embryo lies floating in the amniotic fluid, which is formed by the embryo. The shell is formed by the mother. Amniotic Egg cont.:  Amniotic Egg cont. The amniotic egg is a major shared derived character for the taxa in the Amniota, which includes us as well as the dinosaurs. Soon after the amniotes appeared, two distinct group are recognizable - these are the Synapsida (which includes us) and the Sauropsida (which includes the dinosaurs). Slide33:  What is an amniotic egg, and why do we care? Amphibian females (like their fishy ancestors) lay a large number of eggs in water, which the male then fertilizes externally.  The larval amphibian emerges from the egg, and develops as a largely aquatic organism.  Some metamorphose into a more terrestrial form, and move onto land.  Others spend their entire life in water. Animals with an amniotic egg have similar stages, but they all take place inside a well-protected egg.  They emerge from the egg into air with an adult-like form. Slide34:  Key Innovations in the Amniotic Egg Semipermable shell: allowsO2 in and CO2 out, but retains water.  Extra-embryonic membranes: Amnion: encloses the embryo with a fluid very similar to environmental water. Chorion: coats the inside of shell and the yolk (nutrient source). Allantois: encloses a cavity for solid wastes. The amniotic egg allowed tetrapods to breed away from water.  It opened up a vast new landscape that they could invade. Slide35:  The boundary between Amniotes and Amphibians is hard to define because: Eggs don't fossilize well.  "Amphibians" aren't a clade (not a natural group). There are no novelties that are shared only by the animals we call Amphibians. This is because we have, rather arbitrarily, decided to call some descendents of amphibians something else.  As a consequence, the Amphibian-Amniote boudary is "fuzzy". Westlothiana lizziae - the first amniote, is known from the early Carboniferous. Despite this early appearance, Amniotes don't diversify until end Carboniferous. Slide36:  What are the main groups of amniotes? The primary subdivisions of amniotes are based on "holes in the head". Early tetrapods had a braincase enclosed by bone, as well as outer skull armor that was separated from this braincase.  This interior space between the brain case and outer skull is filled with musculature to open and close the jaws.  Some amnniotes begin to open windows in this outer skull armor and begin to expand jaw muscles onto the outside of the head. It's thought that this expansion of jaw musculature allows greater diversity in chewing and food processing.   Slide37:  Main Groups of Amniotes Anapsids - no holes in head behind the eye.  This is the primitive state for tetrapods.  It occurs in the earliest tetrapods and is also seen in turtles, the most primitive reptiles. Synapsids - one hole in head behind the eye.  This is one of the evolutionary novelties in head holes.  It occurs in pelycosaurs, therapsids, and mammals. Diapsids - two holes in head behind the eye.  This is another evolutionary novelty in head holes.  It occurs in nearly all reptiles except turtles (i.e., lizards, snakes, crocodiles, pterosaurs, dinosaurs and birds). Main Groups of Amniotes:  Main Groups of Amniotes Terrestrial Ecosystems of Permian Period:  Terrestrial Ecosystems of Permian Period The swamps of tropical Europe and America were drying out. Evaporites (salt deposits) and red beds (indicating dry soils) were more common. Early Permian tetrapods are only known from the equatorial zone. All the continents had crashed together to form the supercontinent, Pangea. Slide40:  Permian Plants Drying of the swamps took a long time; spanning from Late Carboniferous through the late Permian. Seed plants came to dominate lowlands. Wet areas with spore-bearing plants persisted, but were increasingly rare. Slide41:  Permian Tetrapods Amphibian diversity drops, but some groups persist and become better adapted for life in the air. The decline is tied to: Drying of swamps. Amphibian reproduction is tied to water. Competition and/or Predation by amniotes. Amniotes were free to breed and feed away from water. Drying wasn't a problem. Synapsid amniotes (one hole) dominate landscapes in the Permian. There were two main synapsid groups in the Permian: Pelycosaurs and Therapsids Permian Pelycosaurs:  Permian Pelycosaurs Dominated in the late Permian. Pelycosaur communities of the early Permian only occur in the tropical zone. Slide43:  Popularly known as the 'finback' because of the large sail on its back supported by elongated spines from the vertebrae . This sail may have helped control temperature by acting as a radiator, or may have been used for display. It was a formidable predator , with huge canine teeth Dimetrodon (carnivorous) Carnivorous pelycosaurs: up to 2 meters and 200 kg, big heads & eyes, long snouts, strong jaws, pointy teeth with some differentiation from front-to-back. They ate fish & amphibians. Some had sails; Sprawling front & hind legs, but vertebral spines prevented lateral undulation during locomotion. Slide44:  Edaphosaurus (herbivorous) This pelycosaur also featured a sail. Like Dimetrodon, this may have been used for heat exchange or display. Unlike Dimetrodon, its teeth show it to have been a herbivore . Herbivorous pelycosaurs: medium to large (3 m, 300 kg), small heads, blunt undifferentiated teeth, large gut cavity, some had sails.  The same sprawling posture as in carnivorous pelycosaurs. Permian Therapsids:  Permian Therapsids This is an artist's representation of the possible appearance of a therapsid. Therapsids, now extinct, were reptilians which were descended from the stem reptiles. They are presumed to be the ancestors of the mammals. "Non-reptilian" characteristics of members of this group were thoracic and pelvic skeletal features which permitted the legs to be positioned directly underneath the body. Slide46:  Herbivory among the Tetrapods Plant eating arose many times in tetrapods. Plant feeding animals use two different strategies for dealing with this problem. Be small and picky - avoid cellulose-rich plant parts; only eat nutrient-rich plant parts (fruits & nuts). There is only enough high-nutrient food to support small animals with this strategy. Be big and indiscriminate - eat everything that you can. Pack your gut with microbes and let them ferment this low quality food. Eat the microbes and the waste products they exude. Must be large to fit the massive, fermenting-chamber gut. Herbivorous pelycosaurs took the big, indiscriminate route.  They were large, and probably evolved from large carnivorous ancestors.  They had small heads, so cellulose digestion must have come from microbes.  They did, in fact, have big guts.

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