Presentation on theme: "Chapter 15 – Mesozoic Life Major aspects of Mesozoic Life: “Refilling” of niches & habitats “emptied” by the end-of-Permian Mass Extinction Climate was."— Presentation transcript:
Chapter 15 – Mesozoic Life Major aspects of Mesozoic Life: “Refilling” of niches & habitats “emptied” by the end-of-Permian Mass Extinction Climate was generally moderate Appearance of flowering plants Reptile diversification continued Appearance of first dinosaurs Appearance of first birds Appearance of first mammals Diversification of mollusks Diversification of echinoids (sea urchins, etc.) Re-appearance of corals & reefs Mass extinctions at end of Triassic Period & end of the Cretaceous Period
Early Triassic marine survivors included bivalves, gastropods, cephalopods, echinoids (and other echinoderms), and a few brachiopods. The re-establishment of phytoplankton (primary producers) in the oceans helped re-establish the food webs. During the Jurassic Period, this included Coccolithophores which produce minute pieces of calcareous debris which accumulates as chalk. Coccolithophores more common in Cretaceous Period.
North American chalks include the Selma Chalk (AL), the Niobrara Chalk (KS) & the Austin Chalk (TX). The other major Mesozoic phytoplankton was dinoflagellates White cliffs of Dover, England - 15 meters/m.y. Diatoms – Cretaceous to Recent (Fig. 15.4b, p. 281)
Marine Environmental Concepts & Changes Planktonic foraminifera represent the primary consumers of the marine food web. The niche occupied by most brachiopods – benthonic, sessile, filter-feeders (secondary consumers) was largely “taken over” by bivalves (clams). Brachiopods still exist (about 260 living species vs. 30,000 fossil species). Early Triassic = low diversity, short food chains Late Cretaceous = high diversity, longer food chains. Cephalopods (Ammonoidea) (tertiary consumers) – nektonic, carnivores, became the largest carnivorous invertebrates. Nektonic habit and rapid evolution = good guide fossils, esp. during Jurassic & Cretaceous.
Other changes in marine fauna: Some Paleozoic benthonic, epifaunal organisms, including bivalves & echinoids, became infaunal (burrowing into the sea floor), perhaps to escape predation. Regular echinoids appeared during Ordovician Period – examples – pencil urchins. True sea urchins & Irregular echinoids appeared during the Mesozoic Era – examples – heart urchins Re-establishment of reef-building organisms. In Middle Triassic time, Scleractinid corals appeared, re-occupying the niches and habitats of the Paleozoic rugose and tabulate corals.
Middle Jurassic Lithiotids – stick-shaped bivalves that grew to heights of 30 to 40 cm., acted as reef-builders prior to appearance of rudists, Late Jurassic – Cretaceous bivalves in the same niche. Nicole Fraser research on Lithiotids ser.htm ser.htm Rudists Brain coral (Scleractinid)
Echinoids True urchins – Late Triassic - Recent Sand dollars – Early Tertiary - Recent Heart urchins – Cretaceous - Recent - urchins for salt water aquariums See display of Late Eocene echinoids from Georgia Coastal Plain in Science Dept. office. Pencil urchins – Ordovician - Recent
Changes in terrestrial flora During Triassic & Jurassic Periods, seedless vascular plants and gymnosperms dominated land-plant communities, examples of both groups are still common now. Large seed ferns became extinct by the end of the Triassic Period, gingkos survived, conifers spread & now occupy cooler/higher altitude ecosystems not favorable to broadleaf plants. Cycads (palm-like trees) appeared during the Triassic Period (see next slide).
Modern sub-tropical to tropical cycads.
Angiosperms (flowering seed plants) appeared during Late Jurassic/Early Cretaceous Period. Angiosperm ad- vantages: 1) En- closed seed; 2) More seeds, easily scattered; 3) Flowers attract pollinators (bees, etc.). All “hardwoods”, flowering plants included in Angio- sperms.
Reproductive cycle of a conifer gymnosperm Conifers have advantage in high latitude/high alti- tude environments. 1) Retention of needles = they are ready for short growing seasons; 2) Needles = less heat & moisture loss.
Reptile diversification began during the Mississippian Period with the evolution of the protorothyrids, apparently the first animals to lay amniotic eggs. From this basic stock of so-called stem reptiles (next slide), all other reptiles, as well as birds and mammals evolved. Late Paleozoic reptiles were dominated by pelycosaurs (sail backs). Triassic archosaurs are thought to be common ancestors for dinosaurs, crocodiles, & birds (slide 12).
Development of Reptiles – Late Paleozoic to Cenozoic
Dinosaurs are first observed in the fossil record during the Triassic Period. All dinosaurs possess a number of shared characteristics, but differing hip/ pelvic structures divide the dinosaurs into two orders, Saurischia (lizard-hipped) and Ornithischia (bird-hipped). Theropods were the only Saurischian carnivores. All the rest & the Ornithischians were herbivores. Earliest dinosaurs were bipedal (walked on hind legs). Dinosaurs existed for 140 million years and ranged in size from 10s of metric tons to the size of a chicken. Some may have been endothermic (warm-blooded), some may have dwelt in herds and nurtured their nested young in a manner similar to mammals and birds.
Dinosaur Cladogram Archosaur common ancestor Herbivores Carnivores
Maiasaura, a Late Cretaceous ornithopod, nested in colonies in northern Montana –In this scene a female leads her young to a feeding area
Saurischian Dinosaurs (lizard-hipped dinosaurs) include two distinct groups known as theropods and sauropods All theropods were carnivorous bipeds from the tiny Compsognathus to giants such as Tyrannosaurus (and larger – up to 7 or 8 metric tons). – 123 feet long, 100+ tons - sauropod Giganotosaurus - 47 feet long, 8 tons - theropod Argentinosaurus
Compsognathus weighed only 2 or 3 kg - Bones found within its ribcage indicate it ate lizards
A 1-meter-long theropod known as Eoraptor, dis- covered in Argentina in Late Triassic rocks, is too specialized to be the ancestor of all dinosaurs, but it is likely close to that ancestry. Theropods with feathers – since 1996, Chinese scientists have been studying small theropods with preserved traces of feathers, similar to bird feathers. Archaeopteryx – oldest known bird, with feather impressions & a “wishbone” in the Jurassic Solnhofen Limestone, Germany (next slide) has distinctive theropod features, hip structure, teeth, claws on the wings, & a long tail.
Most theropods are Cretaceous in age, but recent Chinese finds include Jurassic theropods. Older fossils with bird-like features, Protoavis, were not preserved with evi- dence of feathers. Fragile skeletons = poor fossil record.
Sauropods Included among the sauropods are the truly giant, quadrupedal, herbivorous dinosaurs such as Apatosaurus, Diplodocus, and Argenti- nosaurus, the largest known land-animals of any kind. Most common in Jurassic Period, less common in Cretaceous Period. Sauropods were preceded in the fossil record by considerably smaller dinosaurs, prosauropods These Late Triassic and Early Jurassic dinosaurs were certainly closely related to sauropods but probably were not their ancestors.
Ornithischian Dinosaurs Scientists recognize five distinct groups of ornithischians: 1) ornithopods, 2) pachy- cephalosaurs, 3) ankylosaurs, 4) stego-saurs, and 5) ceratopsians Duck-billed dinosaurs
Ornithopods (duck-billed dinosaurs) - All were herbivores, primarily bipedal with well-deve- loped forelimbs that allowed them to walk in a quadrupedal fashion, too (see slide 15). Pachycephalosaurs – thick-boned, dome-shaped skull. Ceratopsians or horned dinosaurs have a good fossil record = small Early Cretaceous forms were ancestors to large Late Cretaceous genera such as Triceratops, a very common dinosaur in North America. Evidence suggests ceratop- sians lived in herds. Stegosaurs – spiked tails (defense), vertical plates on back (temperature control?).
The ankylosaur Euoplocephalus - Note the heavy armor and bony club at the end of the tail The ankylosaur Sauropelta Anklyosaurs were most heavily- armored dinosaurs.
Some evidence exists suggesting that some dinosaurs were endothermic (warm-blooded), see text pp Flying reptiles – Pterosaurs – Late Triassic – Late Cretaceous. Adaptations for flight included: 1) Wing membrane supported by elongated 4 th finger; 2) Light, hollow bones; and 3) Greater development of brain areas controlling muscle coordination and sight. One pterosaur species had a coat of hair or hair- like feathers, this suggests it (and all pterosaurs) may have been endothermic. Birds – 2 nd and 3 rd fingers fused to support wing. Bats – 2 nd through 5 th fingers support wing. Largest pterosaur (in Texas) – 12 meter wingspan.
Wing-bone structures suggest large pterosaurs were unable to sustain prolonged flapping, rather were adapted to soaring on updrafts, with wing movements for maneuvering. Smaller pterosaurs may have been able to flap their wings on a more sustained basis, like small birds today. Marine Reptiles – turtles, crocodiles, placodonts – adapted to aquatic life. Ichthyosaurs, plesio- saurs, and mosasaurs were truly aquatic, but other than all being reptiles, they are not particularly closely related to other reptiles. Dinosaurs in the Southeastern United States Oceans of Kansas – Mosasaurs
Restoration showing ichthyosaurs, fully aquatic animals, that evolved from land-dwelling ancestors Size range -.7 meters to 18.2 meters
The fate of the un- collected dinosaur bone… Arrow shows direction of erosion transport. Mary Anning ( ), at about 11 years old discovered & directed the excavation of a nearly complete ichthyosaur in southern England. This and subsequent discoveries made her a well-known fossil collector. Many scientists of her time could not accept an untutored girl as the source of these discoveries. Professional vs. Amateur.
Although the plesio- saurs were aquat- ic animals, their flipperlike fore- limbs probably allowed them to come out onto land, to lay eggs. Short-necked “plesies” may have been bottom feeders, while long-necked may have been fish eaters. Is this “Nessie”?
Therapsids, (advanced mammal-like reptiles) diversified into numerous species of herbivores and carnivores, most diverse and numerous during the Permian Period. Cynodonts (carnivorous) were the most mammal- like of all and by the Late Triassic gave rise to mammals. Distinctions between mammal-like cynodonts and mammals is based on are based largely on details of the middle ear, the lower jaw, and the teeth. Transitions make some distinctions hard to define, i.e., which is a reptile and which is a mammal.
Proximity of Mesozoic landmasses and moderate temperatures facilitated widespread movement and colonization by plants & animals. By the Late Cretaceous, the North Atlantic had opened further, and Africa and South America were completely separated. South America remained an island continent until late in the Cenozoic, and its fauna became increasingly different from faunas of the other continents. Marsupial mammals reached Australia from South America via Antarctica, but the South American connection was eventually severed.
End of Cretaceous Mass Extinction casualties were dinosaurs, flying reptiles, and marine reptiles Several kinds of marine invertebrates also went extinct, including ammonites, rudistid bivalves, and some planktonic organisms Current paradigm – based on discovery of iridium- rich clay layer at K/T boundary (Cretaceous/ Tertiary) in Italy, in 1980, has been correlated an other worldwide sites. Iridium is rare in crustal rocks, more common in meteorites. Debris from impact blocked sunlight for months, plant communities crashed as did food webs. Nitrogen & sulfur gases = acid rainfall. Cooler temps = stress. Volcanics – India more gases.
Iridium contents – boundary clay, Italy Boundary clay layer, Raton Basin, NE New Mexico
Iridium source is Proposed meteor- ite impact crater centered on Chix- ulub on the Yuca- tán Peninsula, Mexico. Some K/T sites have soot & shock-quartz = more evidence. Crater measures approx. 180 km in diameter.