Early Jurassic
Encyclopedia
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
(in chronostratigraphy
Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of...
corresponding to the Lower Jurassic series
Series (stratigraphy)
Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...
) is the earliest of three epochs of the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event
Triassic-Jurassic extinction event
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, , and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas a whole class and twenty percent of all marine families...
, 199.6 Ma (million years ago), and ends at the start of the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
(175.6 Ma).
Rocks of this age in Europe are called "Lias
Lias
Lias may refer to:*In geology:**The Lias Group, a group in the stratigraphy of Great Britain, formed during the Late Triassic to Early Jurassic epochs. It includes the Blue Lias and White Lias...
" and that name was used for the period, as well, in 19th century geology.
Origin of the name Lias
There are two possible origins for the name Lias: the first reason is it was taken by a geologistGeologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
from an English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
quarryman's dialect
Dialect
The term dialect is used in two distinct ways, even by linguists. One usage refers to a variety of a language that is a characteristic of a particular group of the language's speakers. The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors,...
pronunciation of the word "layers"; secondly, sloops from North Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
ports such as Bude
Bude
Bude is a small seaside resort town in North Cornwall, England, at the mouth of the River Neet . It lies just south of Flexbury, north of Widemouth Bay and west of Stratton and is located along the A3073 road off the A39. Bude is twinned with Ergué-Gabéric in Brittany, France...
would sail to the Vale of Glamorgan
Vale of Glamorgan
The Vale of Glamorgan is a county borough in Wales; an exceptionally rich agricultural area, it lies in the southern part of Glamorgan, South Wales...
heritage coast to load up on lias limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
(lias limestone from South Wales was used throughout North Devon/North Cornwall as it contains calcium carbonate to fertilise the poor quality Devonian soils of the West Country); the Cornish would pronounce the layers of limestone as 'laiyers' or 'lias'.
Geology
There are extensive Liassic outcrops around the coast of the UKUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, in particular in the Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
Jurassic coast
Jurassic Coast
The Jurassic Coast is a World Heritage Site on the English Channel coast of southern England. The site stretches from Orcombe Point near Exmouth in East Devon to Old Harry Rocks near Swanage in East Dorset, a distance of ....
, often associated with the pioneering work of Mary Anning
Mary Anning
Mary Anning was a British fossil collector, dealer and palaeontologist who became known around the world for a number of important finds she made in the Jurassic age marine fossil beds at Lyme Regis where she lived...
of Lyme Regis
Lyme Regis
Lyme Regis is a coastal town in West Dorset, England, situated 25 miles west of Dorchester and east of Exeter. The town lies in Lyme Bay, on the English Channel coast at the Dorset-Devon border...
. The facies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
of the Lower Jurassic in this area are predominantly of clays, thin limestones and siltstones, deposited under fully marine conditions.
Vale of Glamorgan
The Vale of Glamorgan is a county borough in Wales; an exceptionally rich agricultural area, it lies in the southern part of Glamorgan, South Wales...
, in southern Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
. Stretching for around 14 miles (22.5 km) just outside Cardiff
Cardiff
Cardiff is the capital, largest city and most populous county of Wales and the 10th largest city in the United Kingdom. The city is Wales' chief commercial centre, the base for most national cultural and sporting institutions, the Welsh national media, and the seat of the National Assembly for...
, the remarkable strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
of the cliffs, situated on the Bristol Channel
Bristol Channel
The Bristol Channel is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Severn to the North Atlantic Ocean...
are a mixture of Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
/limestone, shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
and liassic limestone, created during a geological upheaval known as the Variscan orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
.
Stratigraphy
There has been some debate over the actual base of the HettangianHettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
stage, and so of the Jurassic system itself. Biostratigraphically
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
, the first appearance of psiloceratid ammonites has been used; but this depends on relatively complete ammonite faunas being present, a problem that makes correlation between sections in different parts of the world difficult. If this biostratigraphical indicator is used, then technically the Lias Group
Lias Group
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...
— a lithostratigraphical
Lithostratigraphy
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...
division — spans the Jurassic / Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
boundary.
Ammonites
During this period, ammonoids, which had almost died out at the end-of-Triassic extinction, radiated out into a huge diversity of new forms with complex suture patterns (the ammonites proper). Ammonites evolved so rapidly, and their shells are so often preserved, that they serve as important zone fossils. There were several distinct waves of ammonite evolution in Europe alone.Marine reptiles
The Early Jurassic was an important time in the evolution of the marine reptiles. The Hettangian saw the already existing RhaetianRhaetian
The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...
ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s and plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s continuing to flourish, while at the same time a number of new types of these marine reptile
Marine reptile
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semi-aquatic life in a marine environment.The earliest marine reptiles arose in the Permian period during the Paleozoic era...
s appeared, such as Ichthyosaurus
Ichthyosaurus
Ichthyosaurus is an extinct genus of ichthyosaur from the Early Jurassic of Europe . It is among the best known ichthyosaur genera, with the Order Ichthyosauria being named after it...
and Temnodontosaurus
Temnodontosaurus
Temnodontosaurus was an ichthyosaur from the Early Jurassic, some 198 and 185 million years ago , in Europe...
among the ichthyosaurs, and Eurycleidus
Eurycleidus
Eurycleidus is an extinct genus of plesiosaur. The type species is E. arcuatus, which lived during the Hettangian age . Like other plesiosaurs, Eurycleidus probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful...
, Macroplata
Macroplata
Macroplata , meaning, , is an extinct genus of Early Jurassic basal plesiosaur which grew up to in length. Like other plesiosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward...
, and Rhomaleosaurus
Rhomaleosaurus
Rhomaleosaurus is an extinct genus of Early Jurassic rhomaleosaurid pliosauroid known from Northamptonshire and from Yorkshire of the United Kingdom. It was first named by Harry Seeley in 1874 and the type species is Rhomaleosaurus cramptoni...
among the plesiosaurs (all Rhomaleosauridae
Rhomaleosauridae
Rhomaleosauridae is a family of extinct reptiles in the Plesiosauria order. It includes the Macroplata, Maresaurus, Rhomaleosaurus, Yuzhoupliosaurus and Meyerasaurus genera....
, although as currently defined this group is probably paraphyletic). All these plesiosaurs had medium-sized necks and large heads. In the Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
, at the end of the Early Jurassic, the thalattosuchia
Thalattosuchia
Thalattosuchia is the name given to a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are sometimes colloquially referred to as marine crocodiles or sea crocodiles, though they are not actually members of Crocodilia.The term...
ns (marine "crocodiles
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
") appeared, as did new genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of ichthyosaurs (Stenopterygius
Stenopterygius
Stenopterygius is an extinct genus of thunnosaur ichthyosaur known from Europe . Maximum length was 4 meters.-Description:...
, Eurhinosaurus
Eurhinosaurus
Eurhinosaurus is an extinct genus of ichthyosaur from the Early Jurassic of Europe...
, and the persistently primitive Suevoleviathan) and plesiosaurs (the elasmosaurs
Elasmosauridae
Elasmosauridae was the family of plesiosaurs. They had the longest necks of the plesiosaurs and survived from the Late Triassic to the end of the Cretaceous. They had a diet of fish and shelless cephalopods.-Size:...
(long-necked) Microcleidus
Microcleidus
Microcleidus is an extinct genus of sauropterygian reptile belonging to the plesiosaur suborder. It was about the size of a whale.Species include: Microcleidus homalospondylus and Microcleidus macropterus . The species has 40 neck vertebrae and a short tail of 28 vertebrae.-External links:*...
and Occitanosaurus
Occitanosaurus
Occitanosaurus is an extinct genus of plesiosaur from the Early Jurassic of what is now France. The type species is Occitanosaurus tournemirensis , first named by Sciau et al. in 1990...
, and the pliosaur
Pliosauridae
Pliosauridae is a family of pliosauroid plesiosaurs from the Earliest Jurassic to the early Late Cretaceous of Australia, Europe, North America and South America. It was formally named by Harry G...
Hauffiosaurus
Hauffiosaurus
Hauffiosaurus is an extinct genus of Early Jurassic pliosaurid plesiosaur known from Holzmaden of Germany and from Yorkshire of the United Kingdom. It was first named by Frank Robin O’Keefe in 2001 and the type species is Hauffiosaurus zanoni. In 2011, two additional species were assigned to this...
).
Terrestrial animals
On land, a number of new types of dinosaurs - the heterodontosauridsHeterodontosauridae
Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal members of the group...
, scelidosaurs
Scelidosaurus
Scelidosaurus is a genus of quadrupedal, lightly plated, herbivorous dinosaur about long. It lived during the Early Jurassic Period, during the Hettangian to Sinemurian stages around 199.6 to 194 million years ago. Its fossils have been found in both England and in Arizona, in the United...
, stegosaurs, and tetanurae
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
, appeared, and joined those groups like the podokesaurs
Podokesaurus
Podokesaurus was a small carnivorous dinosaur of the Early Jurassic Period , and as such is one of the earliest known dinosaurs to inhabit the eastern United States . The small, bipedal carnivore was about 90 cm long and 0.3 m tall...
, prosauropods and the sauropods that had continued over from the Triassic. Accompanying them as small carnivores were the sphenosuchid
Sphenosuchia
Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, which include all living crocodilians.-Stratigraphic...
and protosuchid
Protosuchus
Protosuchus is an extinct genus of carnivorous crocodylomorph from the Early Jurassic. The name Protosuchus means "first crocodile", and is among the earliest animals that resemble crocodilians...
crocodilians. In the air, new types of pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s replaced those that had died out at the end of the Triassic. While in the undergrowth were various types of early mammals, as well as tritylodont
Tritylodontidae
Tritylodontids were small to medium-sized, highly specialized and extremely mammal-like cynodonts. They were the last family of the non-mammalian synapsids. One of the last cynodont lines to appear, the Tritylodontidae descended from a Cynognathus-like cynodont...
mammal-like reptiles, lizard-like sphenodonts
Sphenodontia
Sphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara , and only two living species...
, and early Lissamphibia
Lissamphibia
The subclass Lissamphibia includes all recent amphibians and means smooth amphibia.Extant amphibians fall into one of three orders — the Anura , the Caudata or Urodela , and the Gymnophiona or Apoda .Although the ancestry of each group is still unclear, all share certain common characteristics,...
ns.
Literature
- Davies, A. M.A. Morley DaviesA. Morley Davies was a British palaeontologist and author or co-author of a number of books on the subject. He was an Honorary Fellow of the Royal Geographical Society, and Reader in Palaeontology at the Imperial College of Science and Technology, University of London....
, An Introduction to Palaeontology, Thomas Murby & Co., London - House, M.R. (1993) Geology of The Dorset Coast, The Geologists' Association.
- Simms, M.J.,Chidlaw, N., Morton, N. and Page, K.N.(2004) British Lower Jurassic Stratigraphy, Geological Conservation Review Series, No.30, Joint Nature Conservation Committee, Peterborough.
External links
- Early Jurassic Period - The Lias epoch - Palaeos - overall presentation.
- Lecture 12 - Early Jurassic - informative lecture notes by Dr. Paul OlsenPaul E. OlsenPaul E. Olsen is an American paleontologist and author and co-author of a large number of technical papers. Growing up as a teenager in Livingston, New Jersey, he was instrumental in Riker Hill Fossil Site being named a National Natural Landmark as a teenager by sending President Richard Nixon a...
.