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Jurassic Period


Abstract

This page describes the Jurassic Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.

Keywords: Jurassic, Jurassic biota, fossil record, evolution

Introduction

 
 

Related Topics


Further Reading

  • Ogg et al. 2008: The Concise Geologic Time Scale. Cambridge.
       
       

      Stratigraphy

      Type Section

      Lower (Triassic–Jurassic) Boundary

      “The end-Triassic mass extinction terminated many groups of marine life, including the conodonts, whose distinctive phosphatic jaw elements constitute a primary zonation for much of the Paleozoic and Triassic, and the majority of ammonoids. Indeed, in the few regions with continuous deposition there is an interval devoid of either typical latest-Triassic taxa (e.g., conodonts or Choristoceras ammonoids) or earliest-Jurassic forms (e.g., Psiloceras ammonites). A sea-level fall produced extended gaps in many shallow-marine sections; therefore, the boundary between upper Triassic and the overlying lower Jurassic was commonly a sequence boundary and hiatus” (Gradstein et al. 2012, p. 733, and references therein).

      The GSSP for the base of the Jurassic is set at 5.80 m above the base of the Tiefengraben Member of the Kendelbach Formation, corresponding to the local lowest occurrence of the ammonite Psiloceras spelae subsp. tirolicum, in the Kuhjoch section, Northern Calcareous Alps, Austria. Other useful markers include the FAD of Cerebropollenites thiergartii (a pollen grain), Praegubkinella turgescens (a foraminifer), and Cytherelloidea buisensis (an ostracod) (see Gradstein et al. 2012).

      Upper (Jurassic–Cretaceous) Boundary

      As yet there is no ratified GSSP for the base of the Berriasian Stage (= the base of the Cretaceous System) although, by common usage, it lies near the first appearance datum (FAD) of the ammonite, Berriasella jacobi. Unfortunately, this ammonite is largely confined to the Mediterranean realm, so the datum is not much use internationally.

      Chronology

      Paleogeography

      Major Tectonic Events

      Land and Sea

      Ron Blakey (Northern Arizona University) paleogeographic reconstruction)

      Climate

      Paleontology

      General Characteristics

      Major Taxa

      Mammals

      “The Jurassic period is an important stage in early mammalian evolution, as it saw the first diversification of this group, leading to the stem lineages of monotremes and modern therian mammals. However, the fossil record of Jurassic mammals is extremely poor, particularly in the southern continents. Jurassic mammals from Gondwanaland are so far only known from Tanzania and Madagascar, and from trackway evidence from Argentina” (Rauhut et al. 2002, p. 165).

      Throughout the early Mesozoic they remained small, becoming more abundant, larger, and more diverse in the Cretaceous, which may have been a time of explosive radiation of Tribosphenida – early relatives of marsupials and placentals (Rougier 2002).

      Major Evolutionary Events

      Evolution of Birds

      Three possibilities for the origins of birds are still being credibly debated: The first is that they evolved from some unknown group of basal archosaurs, probably in the Triassic Period. Second, that they are a sister group to the Crocodylians, perhaps arising from within the sphenosuchian crocodylomorphs in the Early Jurassic. Certainly the most widely held view – though unfortunately misrepresented as the only credible modern view by the popular media – is for an ancestry among the theropod dinosaurs, specifically the Maniraptora, in the Middle to early Late Jurassic.

      Despite intensive searching, the earliest known bird is still the famous Archaeopteryx, known from only seven skeletons and an isolated feather, all recovered from the Late Jurassic (Tithonian, ~152 to 145 Ma) Solnhofen Limestone of Germany. The small theropod dinosaur, Compsognathus, has also been recovered from the Solnhofen. This fossil record represents a difficult problem for advocates of the theropod hypothesis: birds (specifically Archaeopteryx) are supposed to be most closely related to the dromaeosaurids, which do not appear in the fossil record until Albian times (mid Cretaceous, about 110 Ma) yet Compsognathus, which is believed to have diverged from the theropod lineage long before the evolution of the dromaeosaurids, occurs alongside Archaeopteryx 40 million years earlier. At present, only the vagaries of the fossil reord can be invoked to ‘explain’ the stratigraphic disjunction; our present understanding is unsatisfactory.

      The first known beak and pygostyle (the “parsons-nose” which is all that remains in birds of the reptilian tail) occur in a Chinese fossil dated at 130 Ma. Feathers and bird bones have also been recovered from 110 Ma sediments in Victoria and Queensland.

      Rahonavis is a primitive bird from 80 million-year-old rocks of Madagascar. Despite being more bird-like than Archaeopteryx, raven-sized Rahonavis retains some very distinctive theropod-like features. Other small primitive birds have been found elsewhere around the world. From Mongolia comes a large flightless bird, Mononykus, with wings replaced by a pair of single-digit hands that projected forwards. Another flightless bird is known from Patagonia. A sparrow-sized bird from Spain had a more modern shoulder joint than Archaeopteryx and a perching foot but it still had teeth.

      Mammals

      Early mammals had a Pangean distribution, including Europe, Asia, Africa, Australia and the Americas. Mammals were presumeably abundant in the Mesozoic, though their fossil record is poor, probably due to their small size which makes the fossils fragile and difficult to find.

      “The Jurassic period is an important stage in early mammalian evolution, as it saw the first diversification of this group, leading to the stem lineages of monotremes and modern therian mammals. However, the fossil record of Jurassic mammals is extremely poor, particularly in the southern continents. Jurassic mammals from Gondwanaland are so far only known from Tanzania and Madagascar, and from trackway evidence from Argentina” (Rauhut et al. 2002, p. 165).

      Throughout the early Mesozoic they remained small, becoming more abundant, larger, and more diverse in the Cretaceous, which may have been a time of explosive radiation of Tribosphenida – early relatives of marsupials and placentals (Rougier 2002).

      Lagerstätten

      Posidonia/Holzmaden Shale: Early Jurassic; Holzmaden, approx. 30 km east of Stuttgart, Germany; fossil reptiles – noteably ichthyosaurs, crustaceans, cephalopods; Selden & Nudds 2012, Hauff & Hauff 1981

      Stonefield Slates: Middle Jurassic; Stonefield, Oxfordshire, England; bed of sandy slate 30-45 cm thick; surface occurrences exhausted and the underground mine is now closed; most important for a large number of small mammal jaws and teeth representing three orders: Multituberculata, Triconodonta and Pantotheria; also pterosaurs, crocodilians, invertebrates and a possible dicotyledonous angiosperm

      Christian Malford: Middle Jurassic; England; soft-body preservation of squids; Allison 1988

      Solnhofen Limestone: Late Jurassic (Lower Titonian); Altmuhl Valley, Bavaria, Germany; fine-grained lagoonal sediments; most famous for the Archeopteryx and Compsognathus fossils found there, though these two together amount to only nine out the many thousands of specimens known from the Solnhofen; Barthel et al. 1990, Viohl 1985.

      Morrison Formation: Late Jurassic; North American states of Wyoming and Colorado

      Purbeck Beds: Late Jurassic; England, esp. near Drulston Bay; essentially modern, temperate insect fauna including dragonflies, locusts, grasshoppers, butterflies, ants and aphids; elsewhere (”Beckel’s Mammal Pit”) numerous mammal species representing five orders and having similarities with those of the contemporaneous Morrison Formation of Wyoming and Colorado

      Extinctions

      New Zealand Occurrences

      For most of the Paleozoic and Mesozoic, the rocks which would become the basement rocks of the Zealandia continent formed part of the Pacific margin of Gondwana, flanking Australia and Antarctica (Edbrooke 2017; Strogen et al. 2017). During this time, the Zealandia basement developed mainly by subduction-driven, episodic accretion.

      “In an initial period of growth, from Cambrian to Carboniferous time, the oldest sedimentary rocks known in mainland New Zealand were deposited and acreted…. Intrusion of granitic rocks occurred intermittently but mainly during Late Devonian and Early Carboniferous time” (Edbrooke 2017, p. 31).

      References

      Allison, P.A. 1988: Phosphatised soft bodied squid from the Jurassic Oxford Clay. Lethaia 21: 403-410.

      Barthel, W.; Morris, S.C.; Swinburne, N.C. 1990: Solnhofen, 2nd ed. Cambridge University Press.

      Edbrooke, S.W. 2017: The geological map of New Zealand. GNS Science Geological Map 2: 1-183.

      Gradstein, F.M.; Ogg, J.G.; Schmitz, M.D.; Ogg, G.M. 2012: The Geologic Time Scale 2012. Elsevier 1-2.

      Hauff, B.; Hauff, R.B. 1981: Das Holzmadenbuch. Self published: 1-136.

      Ogg, J.G.; Ogg, G.; Gradstein, F.M. 2008: The Concise Geologic Time Scale. Cambridge: 1-177.

      Rauhut, O.W.M.; Martin, T.; Ortiz-Jaureguizar, E.; Puerta, P. 2002: A Jurassic mammal from South America. Nature 416: 165-168. Nature.

      Rougier, G.W. 2002: Mesozoic Mammals. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001571].

      Selden, P.; Nudds, J. 2012: Evolution of Fossil Ecosystems (2nd Edition). Academic Press: 1-288.

      Strogen, D.P.; Seebeck, H.; Nicol, A.; King, P.R. 2017: Two-phase Cretaceous–Paleocene rifting in the Taranaki Basin region, New Zealand; implications for Gondwana breakup. Journal of the Geological Society, London 174: 929-946.

      Viohl, G. 1985: Geology of the Solnhofen Lithographic Limestone and the habitat of Archeopteryx. In Hecht, M.K.; Ostrom, J.H.; Viohl, G.; Wellnhofer, P. (eds.) 1985: The beginnings of birds. Eichstatt. Freude des Jura-Museums Eichstätt, Willibaldsburg. : 31-44.


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