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''Ptychodus'' (from el, πτυχή 'fold' and el, ὀδούς 'tooth') is a genus of extinct
accessed on 8/23/09 There are many species among the ''Ptychodus'' that have been uncovered on all the continents around the globe. Such species are ''Ptychodus mortoni'', ''P. decurrens'', ''P. marginalis'', ''P. mammillaris'', ''P. rugosus'' and ''P. latissimus'' to name a few. They died out approximately 85
Due to a global distribution ''Ptychodus'' is well represented in the fossil record; many fossils have been uncovered such as isolated teeth, fragments of dentition, calcified vertebral centra, denticles, and associated fragments of calcified cartilage. The very first remains of ''Ptychodus'' were found in England and Germany in the first half of the 18th century. ''Ptychodus'' teeth have long been identified as palates of diodon, or porcupinefish (Osteichthyes, Diodontidae), well-known for their ability to inflate their bodies in defense. At the beginning of the 19th century, several authors including Swiss paleontologist Louis Agassiz eventually demonstrated the affinities of ''Ptychodus'' teeth with those of elasmobranchs (rays and sharks). The first discovery of ''Ptychodus'' teeth in Kansas came in 1868 when Leidy reported and described a damaged tooth near Fort Hays, Kansas. After, many more teeth were uncovered in almost perfect conditions and other species within the genus were identified. Fossils of species within this genus have been found in the marine strata of United States, Brazil, Canada, the Czech Republic, France, Germany, India, Israel, Japan, Jordan, Mexico, Sweden, and the United Kingdom. The fact that so many fossils of ''Ptychodus'' have been found in different regions of the world provides evidence of a distribution of species during the Albian-Turonian time.
The generic name ''Ptychodus'' comes from the Greek words (fold/layer) and (tooth), so "fold teeth" describing the shape of their crushing and grinding teeth that were recovered in deposits around the
''Ptychodus'' was a large shark, previously estimated at long based on extrapolation from tooth. The subadult specimen with the largest vertebra showed that it could reach lengths of , so a length is possible, but more analysis is required for verification. Unlike the colossal nektonic planktivores '' Rhincodon'' (whale sharks) and '' Cetorhinus'' (basking sharks) which relied upon gill rakers to acquire their food, the ''Ptychodus'' had a massive arrangement of crushing plate teeth. A ''Ptychodus'' jaw contains many teeth, up to 550 teeth, 220 of which are on the lower jaw and 260 in the upper jaw. These teeth were very large as well—Paleontologists believe that the largest tooth plate measured 55 centimeters in length and 45 centimeters in width. There are two distinct formations of tooth plates between the genus; one being juxtaposed, non-overlapping tooth rows, and another being imbricated tooth rows. It is believed that the shape coincides with the diet of the species and their geographic locations, but the time it lived has a big part as well. ''Ptychodus marginalis'' teeth differ from ''Ptychodus polygyrus''. ''P marginalis'' was in the Middle Cenomanian to Middle Turonian deposits in the English Chalk, while ''P. polygyrus'' was in the Late Santonian-Early Campanian deposits.
Ptychodus and species 2011 - SYSTEMATIC, STRATIGRAPHIC, GEOGRAPHIC AND PALEOECOLOGICAL DISTRIBUTION OF THE LATE CRETACEOUS SHARK GENUS PTYCHODUS WITHIN THE WESTERN INTERIOR SEAWAY
/ref>
/ref> The ''Ptychodus'' diet in each species slightly differed based on the region they came from. The ''Paraptychodus washitaensis'' species (found in north-central Texas, USA.) has a dental structure similar to that of its ancestors (''Ptychodus''), however, its posterior teeth have a sharply raised and pointed tooth crown- a feature not predominantly present in its ancestors. The presence of the sharply raised and pointed tooth crown compared to the flat, wide crowns designed to crush prey also indicates a shift from eating mostly hard-shelled organisms to other types of organisms that have tough skeletons or exoskeletons.
File:Ptychodus mammillaris.JPG, ''Ptychodus mammillaris'' teeth
File:Ptychodontidae - Ptychodus decurrens.JPG, Teeth of ''Ptychodus decurrens'' from Cretaceous of United States
File:Ptychodontidae - Ptychodus anonymus.JPG, Teeth of ''Ptychodus sp.'' from Cretaceous of United States
File:Ptychodus latissimus 1550.JPG, Teeth attributed to ''Ptychodus decurrens''
BBC page on ''Ptychodus mortoni'': "Giant predatory shark fossil unearthed in Kansas"
{{Taxonbar, from=Q648806 Prehistoric shark genera Cretaceous sharks * Taxa named by Charles Lucien Bonaparte Mooreville Chalk Taxa named by Louis Agassiz
durophagous
Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil tu ...
(shell-crushing) shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s from the Late Cretaceous. Fossils of ''Ptychodus'' teeth are found in many Late Cretaceous marine sediments.The paleobioloy Database Ptychodus entryaccessed on 8/23/09 There are many species among the ''Ptychodus'' that have been uncovered on all the continents around the globe. Such species are ''Ptychodus mortoni'', ''P. decurrens'', ''P. marginalis'', ''P. mammillaris'', ''P. rugosus'' and ''P. latissimus'' to name a few. They died out approximately 85
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...
. A large number of remains have been found in the former Western Interior Seaway
The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...
. A 2016 publication found that ''Ptychodus'' are likely true sharks belonging to Selachimorpha, rather than hybodonts
Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like chondrichthyans, which existed from the late Devonian to the Late Cretaceous. They form the group of Elasmobranchii closest to neoselachians, the clade of modern sh ...
or batoids as previously thought. Their life history coincides with the typical life of many other large sharks: they lived relatively long lives and were slow growing and produced large offspring and small litters.
Discovery
Due to a global distribution ''Ptychodus'' is well represented in the fossil record; many fossils have been uncovered such as isolated teeth, fragments of dentition, calcified vertebral centra, denticles, and associated fragments of calcified cartilage. The very first remains of ''Ptychodus'' were found in England and Germany in the first half of the 18th century. ''Ptychodus'' teeth have long been identified as palates of diodon, or porcupinefish (Osteichthyes, Diodontidae), well-known for their ability to inflate their bodies in defense. At the beginning of the 19th century, several authors including Swiss paleontologist Louis Agassiz eventually demonstrated the affinities of ''Ptychodus'' teeth with those of elasmobranchs (rays and sharks). The first discovery of ''Ptychodus'' teeth in Kansas came in 1868 when Leidy reported and described a damaged tooth near Fort Hays, Kansas. After, many more teeth were uncovered in almost perfect conditions and other species within the genus were identified. Fossils of species within this genus have been found in the marine strata of United States, Brazil, Canada, the Czech Republic, France, Germany, India, Israel, Japan, Jordan, Mexico, Sweden, and the United Kingdom. The fact that so many fossils of ''Ptychodus'' have been found in different regions of the world provides evidence of a distribution of species during the Albian-Turonian time.
The generic name ''Ptychodus'' comes from the Greek words (fold/layer) and (tooth), so "fold teeth" describing the shape of their crushing and grinding teeth that were recovered in deposits around the Niobrara Formation
The Niobrara Formation , also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous. It is com ...
.
Description
''Ptychodus'' was a large shark, previously estimated at long based on extrapolation from tooth. The subadult specimen with the largest vertebra showed that it could reach lengths of , so a length is possible, but more analysis is required for verification. Unlike the colossal nektonic planktivores '' Rhincodon'' (whale sharks) and '' Cetorhinus'' (basking sharks) which relied upon gill rakers to acquire their food, the ''Ptychodus'' had a massive arrangement of crushing plate teeth. A ''Ptychodus'' jaw contains many teeth, up to 550 teeth, 220 of which are on the lower jaw and 260 in the upper jaw. These teeth were very large as well—Paleontologists believe that the largest tooth plate measured 55 centimeters in length and 45 centimeters in width. There are two distinct formations of tooth plates between the genus; one being juxtaposed, non-overlapping tooth rows, and another being imbricated tooth rows. It is believed that the shape coincides with the diet of the species and their geographic locations, but the time it lived has a big part as well. ''Ptychodus marginalis'' teeth differ from ''Ptychodus polygyrus''. ''P marginalis'' was in the Middle Cenomanian to Middle Turonian deposits in the English Chalk, while ''P. polygyrus'' was in the Late Santonian-Early Campanian deposits.
Paleobiology
While there is no solid evidence of members of the ''Ptychodus'' species living among otherdurophagous
Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil tu ...
sharks like members of Heterodontidae (bullhead sharks), it is believed that this Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
macropredator was the precursor to crushing plate teeth seen in many similar sharks and rays. ''Ptychodus'' would have predated benthic shelled invertebrates, however ''Ptychodus'' itself was probably not benthic but more likely to be pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
. It is believed that ''Ptychodus'' species not only preferred this area because of the subtropical environment but due to the higher concentration of their prey source ''Cremnoceramus
''Cremnoceramus'' ("cremno-" = ''kremnos'' reek precipice or over hanging wall or bank; "ceramus" = ''keramos'' reek clay pot) is an extinct genus of fossil marine pteriomorphian bivalves that superficially resembled the related winged pearly ...
'', '' Volviceramus'' and other members of the inoceramids.Shawn HamPtychodus and species 2011 - SYSTEMATIC, STRATIGRAPHIC, GEOGRAPHIC AND PALEOECOLOGICAL DISTRIBUTION OF THE LATE CRETACEOUS SHARK GENUS PTYCHODUS WITHIN THE WESTERN INTERIOR SEAWAY
/ref>
Diet
Diets of ''Ptychodus'', for example ''P. decurrens'' (found in southern India) were probably animals with hard shells. Bivalves andammonites
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttl ...
are example of shelled invertebrates that are probably main food source of ''Ptychodus''. '' Platyceramus'', genus that includes one of the largest bivalves at the time, is able to be a part of the diet of ''Ptychodus''.A Field Guide to Fossils of the Smoky Hill Chalk/ref> The ''Ptychodus'' diet in each species slightly differed based on the region they came from. The ''Paraptychodus washitaensis'' species (found in north-central Texas, USA.) has a dental structure similar to that of its ancestors (''Ptychodus''), however, its posterior teeth have a sharply raised and pointed tooth crown- a feature not predominantly present in its ancestors. The presence of the sharply raised and pointed tooth crown compared to the flat, wide crowns designed to crush prey also indicates a shift from eating mostly hard-shelled organisms to other types of organisms that have tough skeletons or exoskeletons.
Gallery
References
* Williston, Samuel (1900) ''University Geological Survey of Kansas, Volume VI: Paleontology part II, (Carboniferous invertebrates and Cretaceous fish)''External links
*BBC page on ''Ptychodus mortoni'': "Giant predatory shark fossil unearthed in Kansas"
{{Taxonbar, from=Q648806 Prehistoric shark genera Cretaceous sharks * Taxa named by Charles Lucien Bonaparte Mooreville Chalk Taxa named by Louis Agassiz