Placodus: Difference between revisions

Placodus; Temporal range: Middle Triassic, 245–235 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Placodus gigas
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Placodontia
Family:	†Placodontidae; Cope, 1871
Genus:	†Placodus; Agassiz, 1833
Species
	†P. gigas Agassiz, 1833 (type); †P. inexpectatus Jiang et al., 2008;

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Placodus (from Greek: plax, plakos, "a plate" and Greek: odous, "tooth")^[1] is an extinct genus of marine reptiles belonging to the order Placodontia, which swam in the shallow seas of the middle Triassic period (c. 240 million years ago). Fossils of Placodus have been found in Central Europe (Germany, France, Poland) and China.

Palaeobiology

Placodus had a stocky body with a long tail, and reached a total length of 2.5–3 m (8.2–9.8 ft).^[2] It had a short neck, and a heavy skull. They were specialized for a durophagous diet of shellfish, such as bivalves. Chisel-like incisors protruded from the anterior margin of the snout, and were probably used to pluck hard-shelled benthic prey from the substrate. The back teeth were broad and flattened, and would have helped to crush the prey.^[3] Before the animals' anatomy was known, they were regarded as fishes' teeth. Similar smaller teeth were present on the palatine bones.

Placodus and its relatives were not as well-adapted to aquatic life as some later reptile groups, like the closely related plesiosaurs. Their flattened tails and short legs, which probably ended in webbed feet, would have been their main means of propulsion in the water.^[3]

The parietal eye on top of the head assisted the animal with orientation, rather than its vision, and its presence is regarded as a primitive characteristic.^{[citation needed]}

The vertebral processes of Placodus dove-tailed into each other and were firmly connected, so that the trunk was rigid. The abdomen was covered with a special armor formed of the bent, right-angled abdominal ribs. Equipped with dense bones, heavy belly ribs, and a row of bony knobs above the backbone, Placodus was a heavily built and negatively buoyant creature that would have had no trouble staying on the seafloor to feed.

This body armour would have offered protection from predators as well, but would have also hampered mobility on land, making Placodus slow and clumsy out of water. It was therefore most likely a terrestrial animal that ventured into the sea in search of food. Molluscs, brachiopods, crustaceans, and other inhabitants of the seabed would have formed its staple diet.

References

^ Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill. p. 153.
^ Diedrich, C.G. (2010). "Palaeoecology of Placodus gigas (Reptilia) and other placodontids — Middle Triassic macroalgae feeders in the Germanic Basin of central Europe — and evidence for convergent evolution with Sirenia". Palaeogeography, Palaeoclimatology, Palaeoecology. 285: 287–306.
^ ^a ^b Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 70. ISBN 1-84028-152-9.

[1] Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill. p. 153.

[2] Diedrich, C.G. (2010). "Palaeoecology of Placodus gigas (Reptilia) and other placodontids — Middle Triassic macroalgae feeders in the Germanic Basin of central Europe — and evidence for convergent evolution with Sirenia". Palaeogeography, Palaeoclimatology, Palaeoecology. 285: 287–306.

[EoDP-3] Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 70. ISBN 1-84028-152-9.

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+{{Short description|Extinct genus of reptiles}}
-{{italictitle}}{{Taxobox
+{{Automatic taxobox
-| name = ''Placodus''
 | fossil_range = [[Middle Triassic]], {{Fossil range|245|235}}
 | image = Placodus gigas 2.JPG
-| image_width = 250px
+| image_upright = 1.1
 | image_caption = ''Placodus gigas''
+| parent_authority = [[Edward Drinker Cope|Cope]], 1871
-| regnum = [[Animal]]ia
+| taxon = Placodus
-| phylum = [[Chordate|Chordata]]
-| classis = [[Reptile|Sauropsida]]
+| authority = [[Louis Agassiz|Agassiz]], 1833
-| superordo = [[Sauropterygia]]
-| ordo = [[Placodont]]ia
-| familia = [[Placodontidae]]
-| familia_authority = [[Edward Drinker Cope|Cope]], 1871
-| genus = '''''Placodus'''''
-| genus_authority = [[Louis Agassiz|Agassiz]], 1833
 | subdivision_ranks = Species
 | subdivision =
-* ''P. gigas'' ([[type species|type]])
+* {{extinct}}''P. gigas'' <small>Agassiz, 1833 ([[type species|type]])</small>
-* ''P. inexpectatus''
+* {{extinct}}''P. inexpectatus'' <small>Jiang ''et al.'', 2008</small>
 }}
-'''''Placodus''''' (meaning 'flat tooth') was a genus of marine [[reptile]]s, belonging to the order [[Placodont]]ia, which swam in the shallow seas of the middle [[Triassic]] period (c. 240 million years ago). Fossils of ''Placodus'' have been found in [[Central Europe]] ([[Germany]], [[France]], [[Poland]]) and [[China]].
+'''''Placodus''''' (from {{lang-el|plax, plakos}}, "a plate" and {{lang-el|odous}}, "tooth")<ref>{{cite book |last1=Colbert |first1=Edwin H. (Edwin Harris) |last2=Knight |first2=Charles Robert |title=The dinosaur book: the ruling reptiles and their relatives |date=1951 |publisher=McGraw-Hill |location=New York |page=153 |url=https://archive.org/details/bookruli00colb/page/152/mode/2up}}</ref> is an extinct genus of [[marine reptile]]s belonging to the order [[Placodont]]ia, which swam in the shallow seas of the middle [[Triassic]] period (c. 240 million years ago). Fossils of ''Placodus'' have been found in [[Central Europe]] ([[Germany]], [[France]], [[Poland]]) and [[China]].
+==Palaeobiology==
-History
+[[File:Placodus_BW.jpg|thumb|left|Restoration]]
-The first recorded placodont reptile remains of the world are from Placodus which were discovered in 1809 near Bayreuth (Bavaria, south Germany) at the northern Lainecker Höhenzug (Middle Triassic mountain chain) mainly due to the activities of Graf zu Münster, in more then six, today only partly remained quarries at Hegnabrunn, Bindlach and Laineck. Placodus remains were first identified as a “large Triassic fish”, but subsequently named and recognized after first skull finds as a marine reptile.
+[[File:Placodus gigas AMNH 4985 cast skull.jpg|thumb|right|Skull ([[AMNH]] 4985)]]
+[[File:Placodus_gigas_3.jpg|thumb|left|upright|Under surface of the upper jaw and palate of ''Placodus gigas'']]
+''Placodus'' had a stocky body with a long tail, and reached a total length of {{cvt|2.5|-|3|m|ft}}.<ref>{{cite journal|last=Diedrich|first=C.G.|year=2010|title=Palaeoecology of ''Placodus gigas'' (Reptilia) and other placodontids — Middle Triassic macroalgae feeders in the Germanic Basin of central Europe — and evidence for convergent evolution with Sirenia|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=285|pages=287—306}}</ref> It had a short neck, and a heavy skull. They were specialized for a [[durophagy|durophagous]] diet of shellfish, such as [[bivalve]]s. [[Chisel]]-like [[incisors]] protruded from the [[anterior]] margin of the snout, and were probably used to pluck hard-shelled [[benthic]] prey from the substrate. The back teeth were broad and flattened, and would have helped to crush the prey.<ref name=EoDP>{{cite book |editor=Palmer, D.|year=1999 |title= The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals|publisher= Marshall Editions|location=London|page= 70|isbn= 1-84028-152-9}}</ref> Before the animals' anatomy was known, they were regarded as fishes' teeth. Similar smaller teeth were present on the [[palatine bone]]s.
-Single teeth, bones and skulls of Placodus from the Middle Triassic were recorded mainly from Bindlach near Bayreuth in southern Germany with descriptions of many different today non-valid “species”but also more recently from many other German and even Dutch localities .
+''Placodus'' and its relatives were not as well-adapted to [[aquatic ecosystem|aquatic life]] as some later reptile groups, like the closely related [[plesiosaur]]s. Their flattened tails and short legs, which probably ended in webbed feet, would have been their main means of propulsion in the water.<ref name=EoDP/>
-The first and only European placodont skeleton of the world was discovered then much later with a skeleton of Placodus gigas Agassiz, 1839 at Steinsfurt (South Germany).
+The [[parietal eye]] on top of the head assisted the animal with orientation, rather than its vision, and its presence is regarded as a primitive characteristic.{{citation needed|date=April 2009}}
-Time range and biogeography
-Placodus is known over a period of 11 My between 247-236 My. The placodonts were distributed within the late Lower Triassic along the southern coasts of Pangaea and immigrated at the Aegean (lowermost Anisian) time into the marine developing Germanic Basin of Europe. Their distribution was obviously depend on shallow marine carbonate platform environments surrounding the Tethys Ocean, and its marginal basins. Those shallow marine habitats changed drastically within the Triassic time. The main reproduction and Placodus herd areas were in the intracratonic Germanic Basin. This marginal macroalgae-rich basin disappeared within the early Late Triassic, and with this Placodus and other reptiles.
+The [[vertebra]]l processes of ''Placodus'' dove-tailed into each other and were firmly connected, so that the trunk was rigid. The abdomen was covered with a special armor formed of the bent, right-angled abdominal [[rib]]s. Equipped with dense bones, heavy [[gastralia|belly ribs]], and a row of bony knobs above the backbone, ''Placodus'' was a heavily built and negatively buoyant creature that would have had no trouble staying on the seafloor to feed.
-Systematic position
-The systematic position of pPlacodus within the extinct sauropterygian reptiles have been discussed by several authors, mainly on the cranial morphology but not solely and most recently only in an cladistic way  but recently initially in more biostratigraphic, taphonomic and ecological context.
+This body armour would have offered protection from predators as well, but would have also hampered mobility on land, making ''Placodus'' slow and clumsy out of water. It was therefore most likely a terrestrial animal that ventured into the sea in search of food. [[Mollusc]]s, [[brachiopod]]s, [[crustacean]]s, and other inhabitants of the seabed would have formed its staple diet.
-Triassic Sea cows and macroalgae feeders
-Former interpretations described all placodonts as “shell crushing durophagous” reptiles, based solely on their “shell crushing tooth morphology” without taking into account any other considerations. Most recent studies have, however, now identified Placodus as having been a “macroalgae feeder”. Placodus had a special orientation of the teeth in the jaws to facilitate the expulsion of fluids and sand particles during the food-crushing process. The macroalgae sea plants those removed from the seafloor by using the anterior spatula-like procumbent teeth.
+==References==
-Macroalgae meadows as "Triassic sea cow habitats"
+{{Reflist}}
-There are several but only indirect evidences for the existence of macroalgae, and even for macroalgae meadows, in the Gemanic Basin of Central Europe, within the two facies types of the Jena Fm (Lower Muschelkalk) and the Bad Sulza/Bindlach/Hegnabrunn and Meissner Fms (Upper Muschelkalk), and also in the northern Tethys Cassina Fm (Upper Muschelkalk equivalent) of the Alps. In the “Lower Muschelkalk” benthic communities the marine snail genera Wortheniella, Omphaloptycha and Polygyrina indicate the presence of larger macroalgal meadows. Whereas Triassic Placodus lived in macroalage meadow shallow marine carbonate palaeoenvironments in the Germanic Basin and northern Tethys, extinct Tertiary or Modern Sirania such as Halitherium or Dugong fed and feed on seagrass in similar environments.
+{{Portal|Paleontology}}
-Convergence to mammallian Sirenia
+{{Sauropterygia|P.}}
-The main arguments for describing placodont reptiles as "Triassic sea cows" that were herbivorous macroalgae feeders derive from the macroalgae meadow environmets and their anatomical and osteological similarities to the mammalian Sirenia (especially Dugong). A very similar convergence of the body shape in Placodus/Halitherium and the body-weight enhancements of Placodus in general is quite obvious compared to the European Oligocene siren Halitherium schinzii. Whereas dugongs developed pachyostotic ribs to enhance their body weight for better diving, Placodus achieved a similar result with its pachyostotic thick gastral ribs, pchyostotic skull and bones in general and especially the thickened stomach ribs (= gastralia).
+{{Taxonbar|from=Q138066}}
+{{Authority control}}
-References
-Diedrich, C., 2010a. Palaeoecology of Placodus gigas (Reptilia) and other placodonts - Middle Triassic macroalgae feeders in the Germanic Basin of central Europe - and evidence for convergent evolution with Sirenia. Palaegeography Palaeoclimatology Palaeoecology 285, 287-306.
-Diedrich, C., 2011a. Fossil middle Triassic “sea cows” – placodont reptiles as macroalgae feeders along the north-western Tethys coastline with Pangaea and in the Germanic Basin. Natural Science 3(1): 8-26.
-==References==
-{{reflist}}
 [[Category:Placodonts]]
-[[Category:Prehistoric reptiles of Europe]]
+[[Category:Middle Triassic reptiles of Europe]]
+[[Category:Sauropterygian genera]]
+[[Category:Fossil taxa described in 1833]]
-{{paleo-reptile-stub}}
-{{portal|Paleontology}}
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