Pliosauroidea
From Wikipedia, the free encyclopedia
Pliosauroidea is an
extinct clade of
marine reptiles.
Pliosauroids, also commonly known as
pliosaurs, are known from the
Jurassic and
Cretaceous Periods. The pliosauroids were short-necked
plesiosaurs with large heads and massive toothed jaws. These swimming reptiles were not
dinosaurs, but distant cousins of modern
lizards. They originally included only members of the family
Pliosauridae, of the order
Plesiosauria,
but several other genera and families are now also included, the number
and details of which vary according to the classification used.
The distinguishing characteristics are a short neck and an elongated head, with larger hind
flippers compared to the fore flippers, vice-versa of the plesiosaurs. They were
carnivorous
and their long and powerful jaws carried many sharp, conical teeth.
Pliosaurs range from 13 to 49 feet (4 to 15 metres) and more in length.
[1][2] Their prey may have included
fish,
sharks,
ichthyosaurs,
dinosaurs and other plesiosaurs.
The largest known genera are
Kronosaurus and
Pliosaurus; other well known genera include
Rhomaleosaurus,
Peloneustes, and
Macroplata.
[3] Fossil specimens have been found in
Africa,
Australia,
China,
Europe,
North America and
South America.
Many very early (from the
Early Jurassic and possibly
Rhaetian (Latest
Triassic)) primitive pliosauroids were very like
plesiosauroids in appearance and, indeed, used to be included in the family
Plesiosauridae.
Name
Pliosauroidea was named by
Welles in 1943. It is adapted from the name of the genus
Pliosaurus, which is derived from
Greek,
πλειων meaning "more/closely" and
σαυρος meaning "lizard"; it therefore means "more saurian". The name
Pliosaurus was coined in 1841 by
Richard Owen, who believed that it represented a link between plesiosauroids and
crocodilians (considered a type of "saurian"), particularly due to their crocodile-like teeth.
Classification
Taxonomy
The taxonomy presented here is mainly based on the plesiosaur
cladistic analysis proposed by Hilary F. Ketchum and Roger B. J. Benson,
2011 unless otherwise noted.
[4]
Phylogeny
Pliosauroidea is a
stem-based taxon that was defined by
Welles as "all taxa more closely related to
Pliosaurus brachydeirus than to
Plesiosaurus dolichodeirus". Pliosauridae and Rhomaleosauridae are
stem-based taxons too. Pliosauridae is defined as "all taxa more closely related to
Pliosaurus brachydeirus than to
Leptocleidus superstes,
Polycotylus latipinnis or
Meyerasaurus victor". Rhomaleosauridae is defined as "all taxa more closely related to
Meyerasaurus victor than to
Leptocleidus superstes,
Pliosaurus brachydeirus or
Polycotylus latipinnis".
[8] The
cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.
[4]
Large pliosauroids
In 2002, the discovery of a very large pliosauroid was announced in
Mexico. This pliosauroid came to be known as the "
Monster of Aramberri".
The size of this specimen has been estimated to be about 49 feet (15
meters) long and it had a 10 foot (3 meter) long skull. Consequently,
although widely reported as such, it does not belong to the genus
Liopleurodon.
[9] The remains of this animal, consisting of a partial vertebral column, were dated to the
Kimmeridgian of the La Caja Formation.
[10] The fossils were found much earlier, in 1985, by a geology student and were at first erroneously attributed to a
theropod dinosaur by Hahnel.
[11] The remains originally contained part of a rostrum with teeth (now lost).
In August 2006, palaeontologists of the
University of Oslo
discovered the first remains of a pliosaur on Norwegian soil. The
remains were described as "very well preserved, as well as being unique
in their completeness". The large animal was determined to be a new
species of
Pliosaurus.
[3] In the summer of 2008, the fossil remains of the huge pliosaur were dug up from the permafrost on
Svalbard, a Norwegian island close to the
North Pole.
[12] The excavation of the find is documented in the 2009
History television special
Predator X.
On 26 October 2009, palaeontologists reported the discovery of
potentially the largest pliosauroid yet found. Found in cliffs near
Weymouth,
Dorset, on Britain's
Jurassic coast,
the fossil had a skull length of 7 feet 10 1/2 inches (2.4 meters) and a
body length of 52 feet 6 inches (16 meters). Palaeontologist Richard
Forrest told the BBC: "I had heard rumours that something big was
turning up. But seeing this thing in the flesh, so to speak, is just jaw
dropping. It is simply enormous."
[13]
Brachauchenius lucasi (Williston
1903, 1907) Turonian, early Late Cretaceous ~92 mya, ~10 m in length
represents the last known pliosaur in North America. Derived from a
sister to
Trinacromerum,
Brachauchenius was a sister to its contemporary,
Kronosaurus.
Overall larger and distinct from
Trinacromerum, the skull of
Brachauchenius
was relatively longer, wider and flatter. The orbits (eye sockets) were
angled anteriorly and so appear to provide binocular vision. A notch
appeared between the premaxilla and maxilla.
The cervicals were relatively more gracile. The dorsal ribs were longer.
The femur was much longer than the humerus.
Pliosaurs were a type of short-necked
plesiosaur: marine reptiles built for speed compared to their
long-necked cousins. One study estimated that certain Pliosaurs could
swim at a little under 10 km/h. They were predators that hunted fish,
cephalopod molluscs and other marine reptiles. Pliosaur skeletons have
even been found with dinosaur remains in their stomachs, suggesting
perhaps that they were not averse to scavenging carcasses that floated
out to sea. Eventually the mosasaurs took over the Pliosaur niche in the
prehistoric seas
