Geosaurus
Encyclopedia
Geosaurus is an extinct genus
of marine crocodyliform within the family
Metriorhynchidae
that lived during the Late Jurassic
to the Early Cretaceous
. Geosaurus was a carnivore
that spent much, if not all, its life out at sea. No Geosaurus eggs or nests have been discovered, so little is known of the reptile's lifecycle, unlike other large marine reptiles of the Mesozoic
, such as plesiosaur
s or ichthyosaurs which are known to give birth to live young out at sea. Where Geosaurus mated, whether on land or at sea, is currently unknown. The name Geosaurus means "Earth
lizard", and is derived from the Greek
Ge- ("Earth") and -sauros ("lizard"). The name Geosaurus was established by the French
naturalist
Georges Cuvier
in 1824.
The modern Chinese term for Geosaurus is Dilong
地龍 "earth dragon" (地龙 in simplified Chinese). This contrasts to the dinosaur
genus Dilong
which was named from Chinese dilong 帝龍 "emperor dragon".
, the line leading to modern crocodilia
ns. Specifically, it was a "marine crocodile", or thalattosuchia
n. Geosaurus was similar in appearance to the related Dakosaurus
with a relatively short skull and curved teeth designed for slashing, which it likely used to attack large prey.
Many early depictions of Geosaurus were based on a nearly complete specimen described by Eberhard Fraas
, which Fraas classified as a distinct species of Geosaurus, G. suevicus. This specimen was found in Germany and dated to the late Jurassic (Late Kimmeridgian
) period. G. suevicus had a distinctively long, narrow snout filled with small, pointed teeth very different from skulls belonging to the type species. Further study and a re-description of Geosaurus published in 2009 showed that these long-snouted form actually represent individuals of Cricosaurus
.
of Geosaurus. Although some traditional species, such as G. suevicus and G. araucanensis formed a natural group
, Enaliosuchus is also within that group. This, as well as further study showing that traditional metriorhynchid genera were not grouped based on actual relationships, necessitated almost all traditional species being removed from Geosaurus and reclassified elsewhere, as well as several species previously placed in other genera to be reclassified as species of Geosaurus.
The species included below follow this revised classification, presented by Young and Andrade in 2009.
A new, previously unknown large species of Geosaurus known only from a single tooth from the Nusplingen Plattenkalk of Germany
.
Cladogram
after Cau & Fanti (2010).
. Rhacheosaurus gracilis
, another long-snouted species, was also at one time considered a species of Geosaurus (as G. gracilis).
Geosaurus carpenteri, also formerly referred to Dakosaurus, is known from a partial skull. Teeth identical to the known teeth of this species are also known from Yorkshire
, UK. It was assigned to its own genus, Torvoneustes
by Andrade et al., 2010.
An unnamed specimen classified as Geosaurus was found in Oxfordian
age rocks of Cuba, though further study has shown this species to be more closely related to Cricosaurus as well.
, early Tithonian) of Bavaria
, Germany. Alongside Dakosaurus maximus
, three species of Geosaurus are known, including G. giganteus, G. suevicus and G. gracilis. It has been hypothesised that niche partitioning
enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be Dakosaurus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted G. suevicus and G. gracilis would have feed mostly on fish, although the more lightly built G. gracilis may have specialised towards feeding on small prey. In addition to four species of metriorhynchids, a moderate-sized species of Steneosaurus
was also contemporaneous.
From the slightly older Nusplingen
Plattenkalk (late Kimmeridgian) of southern Germany, both G. suevicus and Dakosaurus maximus are contemporaneous. As with Solnhofen, G. suevicus feed upon fish, while Dakosaurus was the top predator.
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 marine crocodyliform within the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Metriorhynchidae
Metriorhynchidae
Metriorhynchidae is an extinct family of metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period of Europe, North America and South America. Metriorhynchids are fully aquatic crocodyliforms. Their forelimbs were small and paddle-like, and unlike living crocodilians,...
that lived during the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
to the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
. Geosaurus was a carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
that spent much, if not all, its life out at sea. No Geosaurus eggs or nests have been discovered, so little is known of the reptile's lifecycle, unlike other large marine reptiles of the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
, such as plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s or ichthyosaurs which are known to give birth to live young out at sea. Where Geosaurus mated, whether on land or at sea, is currently unknown. The name Geosaurus means "Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
lizard", and is derived from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
Ge- ("Earth") and -sauros ("lizard"). The name Geosaurus was established by the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
naturalist
Natural History
Natural history is the scientific study of plants or animals.Natural History may also refer to:In science and medicine:* Natural History , Naturalis Historia, a 1st-century work by Pliny the Elder...
Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
in 1824.
The modern Chinese term for Geosaurus is Dilong
Dilong
Dilong Ward is one of the sixteen wards of Mokokchung town. It is located in the lower slope of the town and forms the Northern part of Mokokchung....
地龍 "earth dragon" (地龙 in simplified Chinese). This contrasts to the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
genus Dilong
Dilong (dinosaur)
Dilong is a genus of small tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 130 million years ago...
which was named from Chinese dilong 帝龍 "emperor dragon".
Description
Geosaurus was a large, marine reptile of the group CrurotarsiCrurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
, the line leading to modern crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns. Specifically, it was a "marine crocodile", or 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...
n. Geosaurus was similar in appearance to the related Dakosaurus
Dakosaurus
Dakosaurus is an extinct genus within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially . The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named...
with a relatively short skull and curved teeth designed for slashing, which it likely used to attack large prey.
Many early depictions of Geosaurus were based on a nearly complete specimen described by Eberhard Fraas
Eberhard Fraas
Eberhard Fraas was a German geologist and paleontologist. He worked as a curator at the Stuttgarter Naturaliensammlung and discovered the dinosaurs of the Tendaguru formation in then German East Africa ....
, which Fraas classified as a distinct species of Geosaurus, G. suevicus. This specimen was found in Germany and dated to the late Jurassic (Late Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
) period. G. suevicus had a distinctively long, narrow snout filled with small, pointed teeth very different from skulls belonging to the type species. Further study and a re-description of Geosaurus published in 2009 showed that these long-snouted form actually represent individuals of Cricosaurus
Cricosaurus
Cricosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian of Germany...
.
Classification and species
Genera considered junior synonyms of Geosaurus include Brachytaenius and Halilimnosaurus . Numerous species had been assigned to this genus since the 19th Century. However, phylogenetic analyses begun in 2005 did not support the monophylyMonophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
of Geosaurus. Although some traditional species, such as G. suevicus and G. araucanensis formed a natural group
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
, Enaliosuchus is also within that group. This, as well as further study showing that traditional metriorhynchid genera were not grouped based on actual relationships, necessitated almost all traditional species being removed from Geosaurus and reclassified elsewhere, as well as several species previously placed in other genera to be reclassified as species of Geosaurus.
The species included below follow this revised classification, presented by Young and Andrade in 2009.
Valid species
- The type speciesType speciesIn biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
Geosaurus giganteus, meaning "giant Earth lizard", is known from Western Europe (Germany) of the Late Jurassic (Early TithonianTithonianIn the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
). It was originally named Lacerta gigantea by von Sömmerring. - Geosaurus grandis, first described by Wagner in 1858, was formerly considered a species of CricosaurusCricosaurusCricosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian of Germany...
. It is known from a complete skull. - Geosaurus lapparenti is known from south-east France and dates to the early Cretaceous period (ValanginianValanginianIn the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 140.2 ± 3.0 Ma and 136.4 ± 2.0 Ma...
). It was named in honour of FrenchFranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
palaeontologist Albert-Félix de LapparentAlbert-Félix de LapparentAlbert-Félix de Lapparent was a French palaeontologist. He was also a Sulpician priest. He undertook a number of fossil-hunting explorations in the Sahara desert. He contributed greatly to our knowledge of dinosaurs and other prehistoric creatures...
, and is based upon isolated skull and post-cranial bones (eck and tail vertebrae and a partial pelvic girdle) from the Early Cretaceous (Valanginian) of France. It was originally classified as a species of DakosaurusDakosaurusDakosaurus is an extinct genus within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially . The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named...
.
A new, previously unknown large species of Geosaurus known only from a single tooth from the Nusplingen Plattenkalk of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
.
Cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
after Cau & Fanti (2010).
Reclassified species
In 2009, Young and de Andrade published a re-description of Geosaurus, examining its relationships and the validity of species lumped into the genus. After performing a phylogenetic analysis of metriorhynchids, they found that many species were grouped in a paraphyletic manner or with the wrong genera. Specifically, they found that several species formerly classified as Geosaurus, including G. suevicus, G. saltillense, G. vignaudi, and G. araucanensis were actually examples of the related CricosaurusCricosaurus
Cricosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian of Germany...
. Rhacheosaurus gracilis
Rhacheosaurus
Rhacheosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by von Meyer in 1831 for skeletal remains from the Tithonian of Germany.-History and classification:...
, another long-snouted species, was also at one time considered a species of Geosaurus (as G. gracilis).
Geosaurus carpenteri, also formerly referred to Dakosaurus, is known from a partial skull. Teeth identical to the known teeth of this species are also known from Yorkshire
Yorkshire
Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...
, UK. It was assigned to its own genus, Torvoneustes
Torvoneustes
Torvoneustes is a genus of extinct metriorhynchid mesoeucrocodylian. It is known from a partial skull and some postcranial remains that have been found from the Kimmeridge Clay of Wiltshire, England. The skull was first to be found, and was first assigned to the species Metriorhynchus superciliosus...
by Andrade et al., 2010.
An unnamed specimen classified as Geosaurus was found in Oxfordian
Oxfordian stage
The Oxfordian is, in the ICS' geologic timescale, the earliest age of the Late Jurassic epoch, or the lowest stage of the Upper Jurassic series. It spans the time between 161.2 ± 4 Ma and 155.7 ± 4 Ma...
age rocks of Cuba, though further study has shown this species to be more closely related to Cricosaurus as well.
Niche partitioning
Several species of metriorhynchids are known from the Mörnsheim Formation (Solnhofen limestoneSolnhofen limestone
The Solnhofen Plattenkalk is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organisms such as sea jellies...
, early Tithonian) of Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...
, Germany. Alongside Dakosaurus maximus
Dakosaurus
Dakosaurus is an extinct genus within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially . The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named...
, three species of Geosaurus are known, including G. giganteus, G. suevicus and G. gracilis. It has been hypothesised that niche partitioning
Niche differentiation
The term niche differentiation , as it applies to the field of ecology, refers to the process by which natural selection drives competing species into different patterns of resource use or different niches...
enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be Dakosaurus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted G. suevicus and G. gracilis would have feed mostly on fish, although the more lightly built G. gracilis may have specialised towards feeding on small prey. In addition to four species of metriorhynchids, a moderate-sized species of Steneosaurus
Steneosaurus
Steneosaurus is an extinct genus of teleosaurid crocodyliform from the Early Jurassic to Early Cretaceous . Fossil specimens have been found in England, France, Germany, Switzerland and Morocco.-Species:...
was also contemporaneous.
From the slightly older Nusplingen
Nusplingen
Nusplingen is a Swabian town in the Zollernalb district, Baden-Württemberg, Germany.The town is located in the valley of the small river Bära, about 12 miles up-river from where it flows in to the Danube. In the Middle Ages Nusplingen gained the rights of a city...
Plattenkalk (late Kimmeridgian) of southern Germany, both G. suevicus and Dakosaurus maximus are contemporaneous. As with Solnhofen, G. suevicus feed upon fish, while Dakosaurus was the top predator.