Dinosauromorpha

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Dinosauromorphs
Temporal range: early Triassic – Present, 249–0  Ma
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(possible Early Triassic record)
Dracohors.jpg
From top to bottom and left to right, different type of dinosauromorphs: Asilisaurus , Borealopelta , Triceratops and Giganotosaurus .
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Ornithodira
Clade: Dinosauromorpha
Benton, 1985 [1]
Subgroups

Dinosauromorpha is a clade of avemetatarsalians (archosaurs closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lagerpetids, [3] with later formulations specifically excluding pterosaurs from the group. [4] Birds are the only dinosauromorphs which survive to the present day.

Contents

Classification

Pelvis of Marasuchus (=Lagosuchus?) specimen PVL 3870 Marasuchus hip photo.png
Pelvis of Marasuchus (=Lagosuchus?) specimen PVL 3870

The name "Dinosauromorpha" was briefly coined by Michael J. Benton in 1985. [1] It was considered an alternative name for the group "Ornithosuchia", which was named by Jacques Gauthier to correspond to archosaurs closer to dinosaurs than to crocodilians. [5] Although "Ornithosuchia" was later recognized as a misnomer (since ornithosuchids are now considered closer to crocodilians than to dinosaurs), it was still a more popular term than Dinosauromorpha in the 1980s. [3] The group encompassed by Gauthier's "Ornithosuchia" and Benton's "Dinosauromorpha" is now given the name Avemetatarsalia. [4]

In 1991, Paul Sereno redefined Dinosauromorpha as a node-based clade, defined by a last common ancestor and its descendants. In his definition, Dinosauromorpha included the last common ancestor of Lagerpeton (a lagerpetid), Marasuchus (a possible junior synonym of Lagosuchus), Pseudolagosuchus (now considered a synonym of the silesaurid Lewisuchus ), Dinosauria (including Aves), and all its descendants. This definition was intended to correspond to a clade including lagerpetids and crownward bird-line archosaurs, but not pterosaurs or other archosaurs. [3] [6]

In 2011, Dinosauromorpha was redefined by Sterling Nesbitt to be a branch-based clade, defined by including reptiles closer to one group than to another. Under this definition, Dinosauromorpha included all reptiles closer to dinosaurs (represented by Passer domesticus , the house sparrow), rather than pterosaurs (represented by Pterodactylus ), ornithosuchids (represented by Ornithosuchus ), or other pseudosuchians (represented by Crocodylus niloticus , the Nile crocodile). Nesbitt's study supported the hypothesis that Pterosauromorpha (pterosaurs and their potential relatives) was the sister group of Dinosauromorpha. Pterosauromorphs and dinosauromorphs together formed the group Ornithodira, which encompasses almost all avemetatarsalians. [4]

Dinosauriformes was coined in 1992 by F.E. Novas, who used it to encompass dinosaurs, Lagosuchus, "Pseudolagosuchus" (=Lewisuchus), and the herrerasaurids, which he did not consider to be "eudinosaurs" (true dinosaurs like ornithischians and saurischians). [7] Contrary to Novas, most paleontologists since 1992 have considered herrerasaurids to be true dinosaurs, though many other dinosaur-like reptiles still fall within his definition of Dinosauriformes. Novas (1992) defined Dinosauriformes as a node-based clade containing the most recent common ancestor of Lagosuchus and Dinosauria, and all its descendants. [7] Nesbitt (2011) provided a roughly equivalent definition, using Marasuchus and Passer domesticus (the house sparrow, a representative of dinosaurs). In his analysis, Dinosauriformes included dinosaurs, silesaurids, and Marasuchus, but not lagerpetids, which were considered to be an earlier-branching family of dinosauromorphs. [4]

Phylogeny

A phylogenetic analysis by Andrea Cau in 2018 resolved two different topologies for dinosaur origins, depending on whether it was run using parsimony or bayesian inference. Cau coined the term Dracohors for the clade uniting all taxa closer to the theropod Megalosaurus bucklandi than the basal form Marasuchus lilloensis . The name is derived from the Latin words for "dragon" and "cohort", draco and cohors. Under parsimony results, Dracohors included only Silesauridae and Dinosauria, the latter including the groups Herrerasauria, Sauropodomorpha, Theropoda and Ornithischia, along with the basal form Eodromaeus . However, under bayesian results, Herrerasauria placed outside Dinosauria within Dracohors, and Dinosauriformes, Dinosauromorpha, and Pan-Aves were synonyms, with Marasuchus in a clade with lagerpetids. Pisanosaurus was resolved within Silesauridae. Cau identified the synapomorphies of Dracohors as: [8]

The anterior tympanic recess, the axial epipophyses, the centrodiapophyseal laminae in the presacral vertebrae, the relative size enlargement of the postacetabular process of ilium, the elongation of the pubis, the proximal sulcus and the reduction of the ligament tuber in the femoral head, and the further reduction in length of the fourth metatarsal and toe compared to the third.

Skeletal diagram of Ixalerpeton Ixalerpeton skeletal.png
Skeletal diagram of Ixalerpeton

Following the discovery and description of more cranial and postcranial material of the genera Kongonaphon , Ixalerpeton and Lagerpeton , it was found that lagerpetids shared many features with the basal taxa of Pterosauria. Features of the maxillary bone, teeth, braincase and forelimb meant that the 2020 phylogenetic analysis of Ezcurra and colleagues placed Lagerpetidae next to pterosaurs within Pterosauromorpha, removing the family from Dinosauromorpha. The contents of Dinosauromorpha was thus restricted to only Silesauridae, Dinosauria, and individual genera like Lagosuchus . [9]

Simultaneously, Rodrigo Müller and Maurício Garcia published novel results that reduced the family Silesauridae to a grade of basal dinosaurs in Ornithischia. Pisanosaurus , considered by various authors to be either a silesaurid or basal ornithischian, was found to be intermediate between the grade of silesaurids and true ornithischians, explaining its peculiar combination of silesaurid and ornithischian features that has resulted in its phylogenetic inconsistency. Lewisuchus , a carnivorous form, was found to be the most primitive form of ornithischian, which was almost universally considered to be an only-herbivorous clade before. Dinosauromorpha was reduced to only including Lagerpetidae and Lagosuchus as a result of the reclassification of silesaurids. [10]

Below are the results of:

A variety of individual species and taxa have at times been found to place within Dinosauromorpha and its subgroups, but outside Dinosauria. The taxon Marasuchus has been consistently recovered as a dinosauromorph between lagerpetids and silesaurids, but may also be a junior synonym of the coexisting form Lagosuchus , another dinosauromorph. [11] Pisanosaurus, traditionally considered an ornithischian, was recovered in an unpublished analysis as a dinosauriform outside other clades, [12] but has since been recovered only as a member of Silesauridae or Ornithischia. [10] [13] [14] [15] Saltopus , an enigmatic taxon from the Late Triassic of Scotland, has been placed closer to dinosaurs than Marasuchus, in a polytomy with Silesauridae and Dinosauria, [13] as a sister taxon to Marasuchus, [14] [15] or within Dinosauria as a basal saurischian. [10] The British taxon Agnosphitys was originally described as a dinosauriform closer to Dinosauria than Herrerasaurus , [16] but has also been classified as a dinosauriform more derived than silesaurids but basal to Herrerasauridae and Dinosauria, [15] a silesaurid, [13] or a basal saurischian. [10] [14] The genus Nyasasaurus from the early Late Triassic of Tanzania is known from multiple incomplete specimens, making it difficult to classify. It has been found as the direct sister taxon of Dinosauria, the basalmost ornithischian, a basal theropod, [17] or a deeply-nested sauropodomorph. [13] [14] [15]

Origins

Dinosauromorphs appeared putatively around 242 to 244 million years ago by the Anisian stage of the Middle Triassic, splitting from other ornithodires. Early Triassic footprints reported in October 2010 from the Świętokrzyskie (Holy Cross) Mountains of Poland may belong to a dinosauromorph. If so, the origin of dinosauromorphs would be pushed back into the Early Olenekian, around 249 Ma. The oldest Polish footprints are from a small quadrupedal animal named Prorotodactylus , but footprints belonging to the ichnogenus Sphingopus that have been found from Early Anisian strata show that moderately large bipedal dinosauromorphs had appeared by 246 Ma. The tracks show that the dinosaur lineage appeared soon after the Permian-Triassic extinction event. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic. [18] The oldest known dinosauromorph is Asilisaurus , a silesaurid which may have lived as early as the Anisian age of the middle Triassic period, about 245 million years ago, [19] although it is possible that Nyasasaurus is a dinosaur of the same age, pushing the origins of the groups back further. [13]

Putative basal dinosauromorphs include Saltopus , [20] [21] Marasuchus , the perhaps identical Lagosuchus , the lagerpetid Lagerpeton from the Ladinian of Argentina and Dromomeron from the Norian of Arizona, New Mexico, and Texas (all in the United States), Ixalerpeton polesinensis and an unnamed form from the Carnian (Santa Maria Formation) of Brazil, [22] [23] and the silesaurids, which include Silesaurus from the Carnian of Poland, Eucoelophysis from the Carnian-Norian of New Mexico, Lewisuchus and the perhaps identical Pseudolagosuchus from the Ladinian of Argentina, [24] [25] Sacisaurus from the Norian of Brazil, [26] Technosaurus from the Carnian of Texas, [27] Asilisaurus from the Anisian of Tanzania, [28] and Diodorus from the Carnian(?) to Norian of Morocco. [29]

Related Research Articles

<i>Lagosuchus</i> Genus of fossil bipedal reptile closely related to dinosaurs

Lagosuchus is an extinct genus of avemetatarsalian archosaur from the Late Triassic of Argentina. The type species of Lagosuchus, Lagosuchus talampayensis, is based on a small partial skeleton recovered from the early Carnian-age Chañares Formation. The holotype skeleton of L. talampayensis is fairly fragmentary, but it does possess some traits suggesting that Lagosuchus was a probable dinosauriform, closely related to dinosaurs.

<i>Agnosphitys</i> Extinct genus of dinosaurs

Agnosphitys is a genus of dinosauriform that lived during the Late Triassic. It contains only one species, the type species A. cromhallensis. Its remains include an ilium, maxilla, astragalus and humerus, which date variously from the Norian and Rhaetian stages of the Late Triassic, or possibly as late as the Hettangian stage of the Early Jurassic. The fissure fill at Avon, of which Agnosphitys was probably recovered from, was a sinkhole formed by the dissolution of Lower Carboniferous limestones.

<i>Marasuchus</i> Extinct genus of reptiles

Marasuchus is a genus of basal dinosauriform archosaur which is possibly synonymous with Lagosuchus. Both genera lived during the Late Triassic in what is now La Rioja Province, Argentina. Marasuchus contains a single species, Marasuchus lilloensis.

Technosaurus is an extinct genus of Late Triassic silesaurid dinosauriform, from the Late Triassic Cooper Canyon Formation of Texas, United States.

<i>Pisanosaurus</i> Extinct genus of dinosauriforms

Pisanosaurus is an extinct genus of early dinosauriform, likely an ornithischian or silesaurid, from the Late Triassic of Argentina. It was a small, lightly built, ground-dwelling herbivore, that could grow up to an estimated 1 m (3.3 ft) long. Only one species, the type, Pisanosaurus mertii, is known, based on a single partial skeleton discovered in the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. This part of the formation has been dated to the late Carnian, approximately 229 million years ago.

<i>Lagerpeton</i> Extinct genus of reptiles

Lagerpeton is a genus of lagerpetid avemetatarsalian, comprising a single species, L. chanarensis. First described from the Chañares Formation of Argentina by A. S. Romer in 1971, Lagerpeton's anatomy is somewhat incompletely known, with fossil specimens accounting for the pelvic girdle, hindlimbs, posterior presacral, sacral and anterior caudal vertebrae. Skull and shoulder material has also been described.

<i>Lewisuchus</i> Extinct genus of reptiles

Lewisuchus is a genus of archosaur that lived during the Late Triassic. As a silesaurid dinosauriform, it was a member of the group of reptiles most commonly considered to be the closest relatives of dinosaurs. Lewisuchus was about 1 metre (3.3 ft) long. Fossils have been found in the Chañares Formation of Argentina. It exhibited osteoderms along its back.

<i>Nyasasaurus</i> Extinct genus of reptiles

Nyasasaurus is an extinct genus of avemetatarsalian archosaur from the putatively Middle Triassic Manda Formation of Tanzania that may be the earliest known dinosaur. The type species Nyasasaurus parringtoni was first described in 1956 in the doctoral thesis of English paleontologist Alan J. Charig, but it was not formally described until 2013.

<i>Teleocrater</i> Extinct genus of reptiles

Teleocrater is a genus of avemetatarsalian archosaur from the Middle Triassic Manda Formation of Tanzania. The name was coined by English paleontologist Alan Charig in his 1956 doctoral dissertation, but was only formally published in 2017 by Sterling Nesbitt and colleagues. The genus contains the type and only species T. rhadinus. Uncertainty over the affinities of Teleocrater have persisted since Charig's initial publication; they were not resolved until Nesbitt et al. performed a phylogenetic analysis. They found that Teleocrater is most closely related to the similarly enigmatic Yarasuchus, Dongusuchus, and Spondylosoma in a group that was named the Aphanosauria. Aphanosauria was found to be the sister group of the Ornithodira, the group containing dinosaurs and pterosaurs.

<i>Silesaurus</i> Extinct genus of reptiles

Silesaurus is a genus of silesaurid dinosauriform from the Late Triassic, of what is now Poland.

<span class="mw-page-title-main">Avemetatarsalia</span> Clade of archosaur reptiles

Avemetatarsalia is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinosaurs were the largest terrestrial animals for much of the Mesozoic Era, and one group of small feathered dinosaurs has survived up to the present day. Pterosaurs were the first flying vertebrates and persisted through the Mesozoic before dying out at the Cretaceous-Paleogene (K-Pg) extinction event. Both dinosaurs and pterosaurs appeared in the Triassic Period, shortly after avemetatarsalians as a whole. The name Avemetatarsalia was first established by British palaeontologist Michael Benton in 1999. An alternate name is Pan-Aves, or "all birds", in reference to its definition containing all animals, living or extinct, which are more closely related to birds than to crocodilians.

<span class="mw-page-title-main">Pterosauromorpha</span> Extinct clade of reptiles

Pterosauromorpha is one of the two basic divisions of Ornithodira that includes pterosaurs and all taxa that are closer to them than to dinosaurs and their close relatives. In addition to pterosaurs, Pterosauromorpha also includes the basal clade Lagerpetidae and some other Late Triassic ornithodirans.

<i>Dromomeron</i> Extinct genus of reptiles

Dromomeron is a genus of lagerpetid avemetatarsalian which lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the Southwestern United States and northwestern Argentina. It is described as most closely related to the earlier Lagerpeton of Argentina, but was found among remains of true dinosaurs like Chindesaurus, indicating that the first dinosaurs did not immediately replace related groups.

<span class="mw-page-title-main">Santa Maria Formation</span> Geologic formation in Brazil

The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age, and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and other dinosauromorphs, including the herrerasaurid Staurikosaurus, the basal sauropodomorphs Buriolestes and Saturnalia, and the lagerpetid Ixalerpeton. The formation is named after the city of Santa Maria in the central region of Rio Grande do Sul, where outcrops were first studied.

Sterling Nesbitt is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Department of Geosciences.

<i>Asilisaurus</i> Genus of reptiles (fossil)

Asilisaurus ; from Swahili, asili, and Greek, σαυρος is an extinct genus of silesaurid archosaur. The type species is Asilisaurus kongwe.Asilisaurus fossils were uncovered in the Manda Beds of Tanzania and date back to the early Carnian, making it one of the oldest known members of the Avemetatarsalia. It was the first non-dinosaurian dinosauriform recovered from Africa. The discovery of Asilisaurus has provided evidence for a rapid diversification of avemetatarsalians during the Middle Triassic, with the diversification of archosaurs during this time previously only documented in pseudosuchians.

<span class="mw-page-title-main">Silesauridae</span> Extinct family of dinosaur-like reptiles

Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids comprised an early diverging clade or a paraphyletic grade within ornithischian dinosaurs. Silesaurids have a consistent general body plan, with a fairly long neck and legs and possibly quadrupedal habits, but most silesaurids are heavily fragmentary nonetheless. Furthermore, they occupied a variety of ecological niches, with early silesaurids being carnivorous and later taxa having adaptations for specialized herbivory. As indicated by the contents of referred coprolites, Silesaurus may have been insectivorous, feeding selectively on small beetles and other arthropods.

<span class="mw-page-title-main">Lagerpetidae</span> Extinct family of reptiles

Lagerpetidae is a family of basal avemetatarsalians. Though traditionally considered the earliest-diverging dinosauromorphs, fossils described in 2020 suggest that lagerpetids may instead be pterosauromorphs. Lagerpetid fossils are known from the Late Triassic of Argentina, Arizona, Brazil, Madagascar, New Mexico, and Texas. They were typically small, although some lagerpetids, like Dromomeron gigas and a specimen from the Santa Rosa Formation attributed to Dromomeron sp., were able to get quite large. Lagerpetid fossils are rare; the most common finds are bones of the hindlimbs, which possessed a number of unique features.

<i>Diodorus scytobrachion</i> Extinct species of reptile

Diodorus is a genus of silesaurid dinosauromorph that lived during the Late Triassic in what is now Morocco. Fossils were discovered in the Timezgadiouine Formation of the Argana Basin, and were used to name the new genus and species Diodorus scytobrachion. The genus name honors the mythological king Diodorus and the ancient historian Diodorus Siculus; the specific name is ancient Greek for 'leathery arm' and also honors the mythographer Dionysius Scytobrachion. The holotype specimen is a partial dentary bone (front of the lower jaw), and assigned specimens include isolated teeth, two humeri (upper arm bones), a metatarsal (foot bone), and femur (thigh bone).

<i>Lutungutali</i> Extinct genus of reptiles

Lutungutali is an extinct genus of silesaurid dinosauriform from the Middle Triassic of Zambia. The single type species of the genus is Lutungutali sitwensis. Lutungutali was named in 2013 and described from a fossil specimen, holotype NHCC LB32, including hip bones and tail vertebrae. The specimen was collected in 2009 from the upper Ntawere Formation, which dates to the Anisian stage of the Middle Triassic. Lutungutali is the first known silesaurid from Zambia and, along with the Tanzanian silesaurid Asilisaurus and dinosauriform Nyasasaurus, the oldest bird-line archosaur known from body fossils.

References

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  2. ↑ Matthew G. Baron; Megan E. Williams (2018). "A re-evaluation of the enigmatic dinosauriform Caseosaurus crosbyensis from the Late Triassic of Texas, USA and its implications for early dinosaur evolution". Acta Palaeontologica Polonica. 63. doi:10.4202/app.00372.2017.
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  11. ↑ Agnolin, Federico L.; Ezcurra, Martin D. (2019). "The Validity of Lagosuchus Talampayensis Romer, 1971 (Archosauria, Dinosauriformes), from the Late Triassic of Argentina" (PDF). Breviora . 565 (1): 1–21. doi:10.3099/0006-9698-565.1.1. ISSN   0006-9698. S2CID   201949710.
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  19. ↑ Nesbitt, S.J.; Sidor, C.A.; Irmis, R.B.; Angielczyk, K.D.; Smith, R.M.H.; Tsuji, L.M.A. (2010). "Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira". Nature. 464 (7285): 95–98. Bibcode:2010Natur.464...95N. doi:10.1038/nature08718. PMID   20203608. S2CID   4344048.
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  21. ↑ Baron, M.G.; Norman, D.B.; Barrett, P.M. (2017). "A new hypothesis of dinosaur relationships and early dinosaur evolution". Nature. 543 (7646): 501–506. Bibcode:2017Natur.543..501B. doi:10.1038/nature21700. PMID   28332513. S2CID   205254710.
  22. ↑ Cabreira, Sergio Furtado; Kellner, Alexander Wilhelm Armin; Dias-da-Silva, Sérgio; Roberto da Silva, Lúcio; Bronzati, Mario; Marsola, Júlio Cesar de Almeida; Müller, Rodrigo Temp; Bittencourt, Jonathas de Souza; Batista, Brunna Jul’Armando; Raugust, Tiago; Carrilho, Rodrigo (November 2016). "A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet". Current Biology. 26 (22): 3090–3095. doi: 10.1016/j.cub.2016.09.040 . PMID   27839975.
  23. ↑ Garcia, Maurício S.; Müller, Rodrigo T.; Da-Rosa, Átila A.S.; Dias-da-Silva, Sérgio (April 2019). "The oldest known co-occurrence of dinosaurs and their closest relatives: A new lagerpetid from a Carnian (Upper Triassic) bed of Brazil with implications for dinosauromorph biostratigraphy, early diversification and biogeography". Journal of South American Earth Sciences. 91: 302–319. Bibcode:2019JSAES..91..302G. doi:10.1016/j.jsames.2019.02.005. S2CID   133873065.
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  25. ↑ Nesbitt, Sterling J.; Irmis, Randall B.; Parker, William G.; Smith, Nathan D.; Turner, Alan H.; Rowe, Timothy (2009). "Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America". Journal of Vertebrate Paleontology. 29 (2): 498–516. Bibcode:2009JVPal..29..498N. doi:10.1671/039.029.0218. S2CID   34205449.
  26. ↑ Ferigolo, J.; Langer, M.C. (2006). "A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone". Historical Biology. 19 (1): 1–11. doi:10.1080/08912960600845767. S2CID   85819339. Archived from the original on 2009-06-22. Retrieved 2007-07-23.
  27. ↑ Nesbitt, Sterling J.; Irmis, Randall B.; Parker, William G. (2007). "A critical re-evaluation of the Late Triassic dinosaur taxa of North America". Journal of Systematic Palaeontology. 5 (2): 209–243. doi:10.1017/S1477201907002040. S2CID   28782207.
  28. ↑ Nesbitt, S.J.; Sidor, C.A.; Irmis, R.B.; Angielczyk, K.D.; Smith, R.M.H.; Tsuji, L.M.A. (2010). "Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira". Nature. 464 (7285): 95–98. Bibcode:2010Natur.464...95N. doi:10.1038/nature08718. PMID   20203608. S2CID   4344048.
  29. ↑ Kammerer, Christian F.; Nesbitt, Sterling J.; Shubin, Neil H. (2011). "The first basal dinosauriform (Silesauridae) from the Late Triassic of Morocco" (PDF). Acta Palaeontologica Polonica. 57: 277–284. doi: 10.4202/app.2011.0015 . S2CID   55015883. Archived from the original (PDF) on 2012-03-14. Retrieved 2011-07-16.
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