Dyrosaurus

Dyrosaurus is a genus of extinct crocodylomorph that lived from the upper Cretaceous to the Eocene period, surviving the K-Pg extinction event.[1] Dyrosaurus are linked to pholidosaurids as a clade and are defined as slender-snouted, fish-eating specialists adapted to near-shore marine habitats.[2]

The Dyrosauridae are a group of mostly marine, long jawed, crocodile-like quadrupeds up to 6 metres (20 ft) long.[3] Based on bone tissue evidence, it has been hypothesized that they were slow-growing[4] near-shore marine animals with interlocking closed jaws,[4] able to swim as well as walk on land. External nostrils at the posterior end of its snout and an internal naris in its pterygoid indicated a habit of hunting while swimming with the top of the head above the water, enabling it to breathe while stalking prey.[3]

Fossils from this genus have been found in Africa, Europe, North and South America, Southern Asia and India.[5] Although the family Dyrosauridae is quite diverse with many forms of crocodyliforms, the genus Dyrosaurus has only two described species: D. phosphaticus and D. maghribensis. D. phosphaticus was first discovered in Algeria and Tunsinia whereas D. maghribensis has only been found in Morocco.[6] D. maghribensis differs from D. phosphaticus by several synapomorphies, most notably: a smooth dorsal margin of the parietal and widely opened choanae, interfenestral bar wide and strongly T shaped instead of moderately T shaped.

Dyrosaurus
Temporal range: Late Cretaceous to Eocene, 90–40 Ma
Dyrosaurus mount
Restored skeleton
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Family: Dyrosauridae
Genus: Dyrosaurus
Pomel, 1894
Species
  • D. phosphaticus (Thomas, 1893) (type)
  • D. maghribensis Jouve et al., 2006

Description

Dyrosaurus BW
Restoration

Dyrosaurids are known to have a very characteristic skull shape with a long and thin snout that is approximately 68% of the total skull length. The most anterior part of the skull and snout is the external naris followed posteriorly by two premaxillae bones until they reach two maxillae bones separated by a single nasal bone.[3]

Typical in dyrosaurids is a single nasal element with a characteristic collection of small pits and a constant width until it widens to contact the lacrimal bones, then tapering off for a short distance until it meets the boundary of the frontals and prefrontals.[3]

Dyrosaurus tooth
Tooth

Dyrosaurs have a premaxilla with shallow pits that extend posterior to the third maxillary alveoli. There are two premaxillae that are narrow as compared to the maxillary bones and extend in the two long maxilla bones which separated by the single nasal bone. The last premaxilla and first maxilla are widely separated by a fourth dentary tooth. Alveoli are widely spaced anteriorly and the space between them decreases posteriorly from the fifteenth alveolus with the diameter remaining constant.[3]

The maxilla is long (approx. two and a half times the length of jugal) and forms most of the lateral margin of the skull.[7] According to Jouve and Barbosa and perhaps depending on the age of the animal, each maxilla bears 13-19 teeth.[7]

An important feature of the dyrosaurid dentition are deep occlusal pits, present particularly in the posterior region of the maxillae that get less pronounced anteriorly. The pits are indicative of an interlocking closed jaw for dyrosaurids because the pits give a way for the upper and lower jaws to alternate. Although they are still present in dyrosaurus phosphaticus, this feature of deep occlusal pits become less developed and broad.[7] Dyrosaurus teeth are homodont, conical, long, and slender, with asymmetrically labial and lingual surfaces. Posterior teeth are shorter and more compressed than anterior tooth indicating that the tooth size decreased anterior to posterior.

Dyrosaurus jaw
Jaw fragment

Dyrosaurs have a snout to skull length of about 68% and the genus Rhabdognathus and Atlantosuchus, Dyrosaurus and Arambourgisuchus have the largest snout proportions of all dyrosaurids. Snout length was previously used it to establish dyrosaurid relationships, while considering the lengthening of the snout to be a ‘more evolved’ character. This was not congruent with Jouve's conclusion which was that the longest snout is actually the primitive condition so the shorter or longer snout appears independently at least four times in dyrosaurid evolution.[8]

While both are species in the Dyrosaurus clade, D. maghribensis and D. phosphaticus have some difference, one of them being the shape and style of their osteoderm. D. maghribensis have lateral and medial dorsal osteoderms that are not sutured and have no serration.The anterolateral margin of medial row of the dorsal osteoderms have a rounded lateral lobe and the lateral row of dorsal osteoderms are square in shape with rounded corners. D. phosphaticus has four longitudinal rows of square osteoderms that are thin and have shallow and wide pits. The osteoderms are square and the anterolateral margin of the medial dorsal osteoderms have an acute rounded process directed laterally.[6]

History of discovery

Dyrosaurus fossils
Jaw and other fragments

French paleontologist Auguste Pomel named the genus Dyrosaurus in 1894 for Djebel Dyr, a mountain near Tebessa in Algeria where its fossilized vertebrae were found in a phosphate mine.[9][10] Thévenin (1911a, 1911b), with some better preserved material, was the first to confirm indisputably that Dyrosaurus phosphaticus was a Lower Eocene crocodyliform. Many dyrosaurid remains are known, but unfortunately they are often poorly preserved which makes it difficult for paleontologists to get a strong understanding of the family.[1]

The genus Dyrosaurus was created by A. Pomel (1894a) after M. Philippe Thomas discovered teeth and bone fragments from the Lower Eocene of Tunisia as Crocodilus Phosphaticus.[3] In 1903, the family Dyrosauridae was named by Giuseppe de Stefano referring to the locality for the holotype was found in Djebel Dyr, Algeria.[5] Stephanie Jouve found and published her results on the study of Dyrosaurus maghiribensis a species of the genus Dyrosaurus in 2005.

Paleobiology

Dyrosaurus skull
Skull

Evidence for the semi-aquatic life of dyrosaurids comes from careful analysis of bone structure. There are two types of structural bone organization that can occur in aquatic tetrapods: osteoporotic or pachyostotic. Osteoporotic bone is spongy and porous whereas pachyostotic involves an increase in skeletal mass. Spongy/porous bone such as osteoporotic is associated with faster swimming and better maneuverability in water because of the reduction in bone tissue, many extant cetaceans and marine turtles have osteoporotic bone which enables them to be good swimmers. Pachyostotic bone is a general/local increase in skeletal mass which can be caused by osteosclerosis (inner compaction of bone), pachyostosis (hyperplasy of compact cortices) or pachyeosclerosis (combination of the two). Research on dyrosaur bone performed by Rafael César Lima Pedroso de Andrade, Juliana Manso Sayao revealed that this family had osteoporotic bone tissue indicative of a fast-swimming ecology as well as some osteosclerosis which is a component of pachyostotic bone tissue. Osteoporosis is associated with a fully aquatic lifestyle whereas pachyostotic is not fully aquatic but is associated with fast swimming ecology. Therefore dyrosaurs are semi-aquatic fast swimmers as indicated by their bone structure. Other evidence for near shore, semi-aquatic lifestyle is where the fossils are found, often in transitional marine sediments.[4] -using axial frequency swimming (that used primarily by extant crocodylians) with a greater undulatory motion and frequency of the tail due to highly developed musculature allowing a more powerful forward thrust.[4]

Dyrosaurids have a tissue pattern that is indicative of a slow-growth animal that was determined by careful analysis of a right femur and left tibia. In the left tibia, the cortex had a lamellar zonal bone with five lines of arrested growth (LAGs) which were spaced 300 mm apart, well as a clear vascular networks of primary osteons that decreased in density towards the membrane (periostially). The right femur had double LAGs and an EFS later as well as secondary osteons occurring in the deep cortex and the spongiosa. This tissue growth pattern is a common characteristic of slow growing animals.[4]

Palaeoecology

Dyrosaurus vertebra
Vertebra

Dyrosaurids are found in transitional marine sediments from the Late Cretaceous to Lower Eocene.[4] This family is known mainly from Maastrichthian deposits in New Jersey and the late Cretaceous to early Paleogene rock from the Tethys Sea in northern and western Africa.[4] Fossils have also been found from the Paleocene and Eocene strata of Pakistan, as well as South America, Brazil, India, Southern Asia as well as coastal. Generally dyrosaurids are recovered from coastal and estuarine deposits through North Africa and the Middle East confirming their existence as semi-aquatic animals.[11] A newer specimen was found in the deposits of the Maria Farinha Formation, the Poty Quarry appears to be an important area because it contains the most complete exposed marine section of the Cretaceous-Paleogene transition in South America.[4]

Dyrosauridae had its greatest taxonomic diversity during the Early Paleogene but it appears as though the clade was able to obtain a greater and more widespread geographic distribution during the Late Cretaceous. The earliest records of dyrosaurids are either in or close to Africa with fragmentary occurrences from the Cenomanian of Sudan and Portugal and several other pre-Maastrichtian, Late Cretaceous discoveries in Egypt. Later, by the Maastrichtian of North America, the record of dyrosaurids became more complete by establishing a widespread distribution that appears to be maintained through the Paleocene and Eocene.[5]

Many similarly sized adults but very few juvenile dyrosaurids have been found in the Oulad Abdoun Basin and Lower Eocene beds. This is indicative of juvenile Dyrosaurids living in freshwater environments whereas large adults live in marine environments. Marine environments are known to have been highly affected by the K-T mass extinction whereas freshwater environments were less affected. Therefore, under the assumption the juveniles lived in freshwater environments and adults lived in marine environments juveniles were able to survive better and the genus could avoid total extinction.[12]

References

  1. ^ a b Jouve, S., Iarochène, M., Bouya, B., and Amaghzaz. M. 2005. A new dyrosaurid crocodyliform from the Palaeocene of Morocco and a phylogenetic analysis of Dyrosauridae. Acta Palaeontologica Polonica 50 (3): 581–594.
  2. ^ Sereno C., Paul; Larsson E. C., Hans; Sidor, Christian A.; Gado, Boubé. The Giant Crocodyliform Sarcosuchus from the Cretaceous of Africa. 2001. Science. Vol 294. 1516-1519. Downloaded from http://www.sciencemag.org on March 2, 2015
  3. ^ a b c d e f Jouve, Stephanie. A new description of the skull of Dyrosaurus phosphaticus (Thomas, 1893) (Mesoeucrocodylia: Dyrosauridae) from the Lower Eocene of North Africa. 2005. Retrieved March 2, 2015 from http://cjes.nrc.ca.
  4. ^ a b c d e f g h Andrade RCLPd, Saya ̃o JM (2014) Paleohistology and Lifestyle Inferences of a Dyrosaurid (Archosauria: Crocodylomorpha) from Paraíba Basin (Northeastern Brazil). PLoS ONE 9(7): e102189. doi:10.1371/journal.pone.0102189
  5. ^ a b c Ashu Khosla, Joseph J. W. Sertich, Guntupalli V. R. Prasad and Omkar Verma Source: Journal of Vertebrate Paleontology, Vol. 29, No. 4 (Dec. 12, 2009), pp. 1321-1326 Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate Paleontology Stable URL: https://www.jstor.org/stable/20627142. Accessed: 03-03-2015 07:01 UTC
  6. ^ a b Jouve, Stephanie; Larochène, Mohamed; Bouya, Baâdi; Amaghzaz, Mbarek. A new species of Dyrosaurus (Crocodylomorpha, Dyrosauridae) from the early Eocene of Morocco: phylogenetic implications. 2005. Published in Zoological Journal of the Linnean Society. pg 603-656.
  7. ^ a b c Antonio Barbosa, José; Wilhelm Armin Kellner, Alexander. Somália Sales Viana, Maria. New dyrosaurid crocodylomorph and evidences for faunal turnover at the K–P transition in Brazil. 2008. Proceedings of the Royal Society. Downloaded from http://rspb.royalsocietypublishing.org/
  8. ^ Jouve, Stephanie; Bouya, Baadi; Amaghzaz, Mbarek. A LONG-SNOUTED DYROSAURID (CROCODYLIFORMES, MESOEUCROCODYLIA) FROM THE PALEOCENE OF MOROCCO: PHYLOGENETIC AND PALAEOBIOGEOGRAPHIC IMPLICATIONS. 2008. Paleontology, vol. 51, part 2. pp 281-294.
  9. ^ Buffetaut E. 1985. L'évolution des crocodiliens. Les animaux disparus-Pour la science, Paris, p. 109
  10. ^ Pomel, A. N. 1894. Découverte de Champsosauriens dans les gisements de phosphorite du suessonien de l'Algérie. Comptes Rendus de l'Académie des Sciences, 118 : 1309-1310.
  11. ^ Matthew C. Lamanna, Joshua B. Smith, Yousry S. Attia and Peter Dodson Source: Journal of Vertebrate Paleontology, Vol. 24, No. 3 (Sep. 10, 2004), pp. 764-768 Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate Paleontology Stable URL: https://www.jstor.org/stable/4524765 Accessed: 04-03-2015 17:11 UTC.
  12. ^ Jouve, Stephanie; Bardet, Nathalie; Jalil, Nour-Eddine; Superbiola, Xabier Pereda; Bouya, Baâdi and Amagzaz, Mbarek. 2008. The oldest African crocodylian: phylogeny, paleobiogeography, and differential survivorship of marine reptiles through the Cretaceous-Tertiary boundary. Journal of Vertebrate Paleontology 28(2):409–421, June 2008
Acherontisuchus

Acherontisuchus is an extinct genus of dyrosaurid neosuchian from Middle to Late Paleocene deposits of Colombia. The only known species is A. guajiraensis, whose name means "Acheron crocodile of the Guajira Peninsula".

Aegyptosuchidae

Aegyptosuchidae is an extinct family of eusuchian crocodyliforms from the Cretaceous period of Africa. They are characterized by their large size and flat heads. The family includes two genera, Aegyptosuchus and Aegisuchus.

Arambourgisuchus

Arambourgisuchus ("[Prof. Camille] Arambourg's crocodile") was a dyrosaurid crocodylomorph from the late Palaeocene of Morocco, found in the region of Sidi Chenane in 2000, following collaboration by French and Moroccan institutions, and described in 2005 by a team led by palaeontologist Stéphane Jouve.

Its type and only species is A. khouribgaensis, after the town of Khouribga, near which the holotype was found.

Cerrejonisuchus

Cerrejonisuchus is an extinct genus of dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to Cerrejonisuchus and to several other dyrosaurids have been found from the Cerrejón open-pit coal mine in La Guajira. The length of the rostrum is only 54-59% of the total length of the skull, making the snout of Cerrejonisuchus the shortest of all dyrosaurids.

Coelosuchus

Coelosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the Graneros Shale of the Benton Group in Wyoming, and are of Cenomanian age. It was slightly over 1 meter in length.

Congosaurus

Congosaurus is an extinct genus of dyrosaurid mesoeucrocodylian. Fossils have been found from Lândana, in Angola and date back to the Paleocene epoch. In 1952 and 1964 Congosaurus was proposed to be synonymous with Dyrosaurus. The genus was later thought synonymous with Hyposaurus in 1976 and 1980. It has since been proven a distinct genus of dyrosaurid separate from both Dyrosaurus and Hyposaurus.In 2007, a new species of Congosaurus was constructed after previously being assigned to Rhabdognathus, and named C. compressus, extending the geographic range of the genus into the present-day Sahara. Lateromedially compressed teeth show its close relation to C. bequaerti.

Dyrosauridae

Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. Over a dozen species are currently known, varying greatly in overall size and cranial shape. All were presumably aquatic, with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.

Eusuchia

The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.

Hyposaurus

Hyposaurus is a genus of extinct marine dyrosaurid crocodyliform. Fossils have been found in Paleocene aged rocks of the Maria Farinha Formation in Pernambuco, Brazil, Iullemmeden Basin in West Africa,

?Campanian–Maastrichtian (Late Cretaceous) Shendi Formation of Sudan and Maastrichtian (Late Cretaceous) through Danian (Early Paleocene) strata in New Jersey, Alabama and South Carolina. Isolated teeth comparable to Hyposaurus have also been found in Thanetian (Late Paleocene) strata of Virginia. It was related to Dyrosaurus, and is the only dyrosaurid known from the western hemisphere.

The priority of the species H. rogersii has been debated, however there is no sound basis for the recognition of more than one species from North America. The other North American species (i.e. H. fraterculus, H. ferox and H. natator) are therefore considered nomina vanum (i.e. empty names).

Nannosuchus

Nannosuchus (meaning "dwarf crocodile") is an extinct genus of goniopholidid mesoeucrocodylian from the Berriasian of England.

Neosuchia

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.

Pholidosauridae

Pholidosauridae is an extinct family of aquatic neosuchian mesoeucrocodylian crocodylomorphs. Fossils have been found in Europe (Denmark, England, France, Germany, Spain and Sweden), Africa (Algeria, Niger, Mali, Morocco and Tunisia), North America (Canada and the United States) and South America (Brazil and Uruguay). The pholidosaurids first appeared in the fossil record during the Bathonian stage of the Middle Jurassic and became extinct during the Late Turonian stage of the Late Cretaceous.Sarcosuchus is one of the best known pholidosaurs. It is believed to have attained lengths of up to 12 metres (39 ft 4 in) and weighed up to 8 tonnes (7.9 long tons; 8.8 short tons). One genus, Suchosaurus, once thought to be a pholidosaur, has since been shown to be a spinosaurid theropod dinosaur.

Pholidosaurus

Pholidosaurus is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian stage of the Early Cretaceous. Fossil material found from the Annero and Jydegård Formations in Skåne, Sweden and on the island of Bornholm, Denmark, have been referred to as a mesoeucrocodylian, and possibly represent the genus Pholidosaurus.

Phosphatosaurus

Phosphatosaurus is an extinct genus of dyrosaurid crocodylomorph. It existed during the early Eocene, with fossils having been found from North Africa in Tunisia and Mali. Named in 1955, Phosphatosaurus is a monotypic genus; the type species is P. gavialoides. A specimen has been discovered from Niger, but it cannot be classified at the species level.Phosphatosaurus is closely related to the Cretaceous genus Sokotosuchus, which is known from Niger and Mali. Because Phosphatosaurus is only known from Paleogene localities, the close relationship with Sokotosuchus implies that there is a long ghost lineage extending back into the Maastrichtian that is not known in the fossil record.

Rhabdognathus

Rhabdognathus is an extinct genus of dyrosaurid crocodylomorph. It is known from rocks dating to the Paleocene epoch from western Africa, and specimens dating back to the Maastrichtian era were identified in 2008. It was named by Swinton in 1930 for a lower jaw fragment from Nigeria. The type species is Rhabdognathus rarus. Stéphane Jouve subsequently assessed R. rarus as indeterminate at the species level, but not at the genus level, and thus dubious. Two skulls which were assigned to the genus Rhabdognathus but which could not be shown to be identical to R. rarus were given new species: R. aslerensis and R. keiniensis, both from Mali. The genus formerly contained the species Rhabdognathus compressus, which was reassigned to Congosaurus compressus after analysis of the lower jaw of a specimen found that it was more similar to that of the species Congosaurus bequaerti. Rhabdognathus is believed to be the closest relative to the extinct Atlantosuchus.

Symptosuchus

Symptosuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is known from the Late Cretaceous of Argentina. Argentine paleontologist Florentino Ameghino named the genus in 1899, along with the type species S. contortidens. It was formally described by Carlos Rusconi in 1934.

Tethysuchia

Tethysuchia is an extinct clade of neosuchian mesoeucrocodylian crocodylomorphs from the late Middle Jurassic (Bathonian stage) to the Early Eocene (Ypresian stage) of Asia, Europe, North America and South America. It was named by the French paleontologist Eric Buffetaut in 1982 as a suborder. Tethysuchia was considered to be a synonym of Dyrosauridae or Pholidosauridae for many years. In most phylogenetic analyses the node Dyrosauridae+Pholidosauridae was strongly supported. De Andrade et al. (2011) suggested that Tethysuchia be resurrected for that node. They defined it as a node-based taxon "composed of Pholidosaurus purbeckensis (Mansel-Pleydell, 1888) and Dyrosaurus phosphaticus (Thomas, 1893), their common ancestor and all its descendants". In their analysis they found that the support for Tethysuchia is actually stronger than the support for Thalattosuchia. The following cladogram shows the position of Tethysuchia among the Neosuchia sensu this study.

Vivian de Buffrénil

Vivian de Buffrénil is a French histologist and paleobiologist who has been working at the Muséum National d'Histoire Naturelle in Paris since 1982. His doctorate (1980) and his doctorat d'état (1990), a diploma now replaced by the habilitation, were supervised by Armand de Ricqlès. His main fields of interest include basic histological descriptions, growth dynamics as recorded in bone growth marks, and adaptation (both histological and microanatomical) of the tetrapod skeleton to a secondarily aquatic lifestyle. He is also interested in life history and population dynamics of exploited or threatened reptile taxa, especially among Varanidae and Crocodilia. He has published at least 92 papers, including 76 research papers, 10 reports on exploited or threatened species, and six popular papers.

His first papers dealt with the skeletal growth marks in extant crocodilians, but very soon after that, he also tackled paleobiological issues, such as growth of an Eocene crocodilian then identified as Crocodylus cf. affinis. Other extinct taxa on which he has published include the Ypresian crocodilian Dyrosaurus phosphaticus, thalattosuchian crocodilians, the Triassic presumed ichthyosaur Omphalosaurus nisseri, other ichthyosaurs, the Permian diapsid Claudiosaurus germaini, champsosaurids, the placodont Placodus, Plesiosauria, the early snakes Simoliophis and Eupodophis, and the mosasaur Carentonosaurus mineaui among reptiles, and early cetaceans and sirenians among mammals. While his early papers typically dealt with only one or two taxa each, some of his most recent studies are based on comparative datasets including several taxa.As a recognized leader in bone histology, he evaluates drafts regularly for several journals and serves on the editorial board (as Reviewing Editor) of the Comptes Rendus Palevol of the Académie des sciences (France). So far, his work has been cited more than 1561 times in scholarly works, according to Google Scholar.

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