Lurdusaurus

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Lurdusaurus
Temporal range: Early Cretaceous, 112  Ma
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Lurdusaurus arenatus.jpg
Cast of Lurdusaurus forelimb at the Muséum des sciences naturelles de Belgique, Brussels
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Ornithopoda
Clade: Styracosterna
Clade: Hadrosauriformes
Genus: Lurdusaurus
Taquet and Russell, 1999
Species:
L. arenatus
Binomial name
Lurdusaurus arenatus
Taquet and Russell, 1999

Lurdusaurus ("heavy lizard") is a genus of massive and unusually shaped iguanodont dinosaur from the Elrhaz Formation in Niger. It contains one species, L. arenatus. The formation dates to the Early Cretaceous, roughly 112 million years ago. Lurdusaurus has a highly atypical body plan for an iguanodont, with a small skull, long neck, rotund torso, and powerful forelimbs and claws, somewhat reminiscent of a ground sloth. Its metacarpals (wrist bones) are fused and reinforced into a large block, and the thumb spike is remarkably enormous. These would have allowed the hand to have functioned almost like a ball-and-chain flail. Lurdusaurus is estimated to have been 7–9 m (23–30 ft) long and 2 m (6 ft 7 in) high when on all-fours, but its stomach would have been only 70 cm (2 ft 4 in) off the ground. It may have weighed 2.5–5.5 t (2.8–6.1 short tons), conspicuously heavy for an iguanodontid this size.

Contents

Paleontologist Thomas R. Holtz Jr. speculated Lurdusaurus may have behaved much like a hippo. It lived in a forested, riverine environment alongside the iguanodonts Elrhazosaurus and Ouranosaurus , the sauropod Nigersaurus , an undescribed titanosaurid, the spinosaurid Suchomimus , the carcharodontosaurid Eocarcharia , the abelisaurid Kryptops , and an undescribed noasaurid. The site also yielded several crocodylomorph species and a pterosaur.

Discovery

In 1965, Philippe Taquet discovered the holotype specimen at the Gadoufaoua site of the Elrhaz Formation, in the Tenere desert of Niger. It consists of a nearly complete adult iguanodont skeleton with a fragmentary skull belonging to single individual, which was given the catalogue number MNHN GDF 1700. He noted it had rather massive proportions, and in 1976 noted it should probably be classified into a new genus while briefly describing the material. [1] Paleontologist Souad Chabli described the remains in 1988 for her PhD thesis, under the direction of Taquet. She named it "Gravisaurus tenerensis". [2] However, her dissertation was never published. In 1999, Turquet and American paleontologist Dale Russell published the first formal description, naming it Lurdusaurus arenatus. The generic name comes from Latin lurdus "heavy" and Ancient Greek sauros "lizard", in reference to the enormous weight of the fossils. The specific name arenatus is Latin for "sandy" because it was found in a desert. They also referred a dentary fragment, MNHN GDF 43G, and a right coracoid, GDF 381, to the species. [1]

Description

The tip of the snout may have been about 20 cm (7.9 in) wide, and expanded back to 30 cm (1 ft). That is, like other iguanodonts, it did not have a duck-like bill. No teeth were preserved, but MNHN GDF 43G preserves the tooth sockets for 10 tooth rows within 19.5 cm (7.7 in). The quadrate bone at the base of the skull has an exceptionally low stature at 28.2 cm (11.1 in), in contrast to 489 mm (1 ft 7 in) in Mantellisaurus and 37.6 cm (1 ft 3 in) in Iguanodon . Based on the ratio between the length of the snout and the length of the rest of the skull in iguanodonts, the total length of the holotype's skull may have been 83.3 cm (2 ft 9 in) in life. [1]

Life restoration Lurdusaurus1 flipped.jpg
Life restoration

Lurdusaurus may have had 12 to 14 neck vertebrae. Therefore, the maximum length of the neck is 1.6 m (5 ft 3 in). The neck vertebrae are about the same size as the dorsal vertebrae (the torso, before the sacrum and pelvis), whereas those of European iguanodonts 85–90% the size of the dorsals. Because Iguanodon has 28 presacral vertebrae, Lurdusaurus potentially had at least 14 dorsals. This would make the neck proportionally quite long, as long as the dorsal series. Compared to European iguanodonts, the dorsal centra are proportionally larger and have shorter neural spines (which project straight up from the centrum) and less steep transverse processes (which project up obliquely). [1] Like all derived iguanodonts, the sternum is hatchet-shaped, with a rod-shaped projection caudolaterally (tailwards towards the side). [3] The sacrum, based on the scars on the ilium begotten from sacral ribs, may have measured 60 cm (2 ft). Lurdusaurus could have had 15 proximal caudal vertebra (tail vertebrae which bear transverse processes), which would have represented a third of the entire tail series. [1]

This would equate to a 4 m (13 ft) tail, and a total body length of 9 m (30 ft). It may have been 2 m (6.6 ft) tall at the hips. Based on the length of the ribs, the stomach may have been less than 70 cm (2 ft 4 in) off the ground when standing quadrupedally (on all-fours). Based on the circumferences of the limbs – 29.5 cm (1 ft) for the humerus and 45.7 cm (1 ft 6 in) for the femur – Taquet and Russell estimated that the holotype weighed approximately 5.5 t (6.1 short tons), conspicuously heavy for an ornithopod this size. [1] In 2016, however, Gregory S. Paul proposed a significantly lower size estimate of 7 m (23 ft) in length and 2.5 t (2.8 short tons) in body mass. [4] The headward dorsal ribs are preserved in their original positions, and show the torso was rather rotund. The diverging wings of the ilia and horizontally-orientated tailward dorsal ribs indicate a flat back about 1 m (3 ft 3 in) across. [1]

Cast of Lurdusaurus thumb spike at the Museum National d'Histoire Naturelle, Paris Lurdusaurus.JPG
Cast of Lurdusaurus thumb spike at the Muséum National d'Histoire Naturelle, Paris

The limbs are exceptionally massive and proportionally stout. The forelimbs are 60% the size of the hindlimbs. [5] The metacarpals in the wrist were fused together into a massive block, [1] which is also exhibited in Iguanodon, Ouranosaurus, and Camptosaurus . Like Camptosaurus but unlike derived iguanodonts, the metacarpals (except for the thumb) were short and dumbbell-like as opposed to long and narrow. Compared to Camptosaurus, the unguals (claws) are flatter. [3] The hand features a massive thumb spike. The pelvis is proportionally short but powerful, somewhat reminiscent of a ceratopsian pelvis. The femur slightly recurves toward the midline like in ceratopsians, and is flattened anteroposteriorly (from front to back) like in sauropods. The heavily built fourth trochanter is located on the bottom half of the femur, like Iguanodon but unlike Mantellisaurus and Ouranosaurus . The tibia is incredibly short relative to the femur, respectively 77.7 cm (2 ft 7 in) vs. 91 cm (3 ft 0 in). The metatarsals were too short to make contact with each other, and there was likely a fleshy pad to support the weight. [1]

Classification

In 1999, Taquet and Russell classified Lurdusaurus as a derived iguanodont or an intermediate between the iguanodonts and the more derived hadrosaurs, based on the presence of a posterolaterally orientated (towards the back and side) process on the sternum, slight tailward expansion of the pubis, a reduced posterior process of the pubis, and opisthocoelus (concave posterior ends) neck vertebrae and front dorsal vertebrae. They preliminarily placed it into the family Iguanodontidae, though conceded there is poor resolution on its higher classification, because the fourth trochanter is almost suspended off the femur like basal iguanodonts, but the neck vertebrae series is long like hadrosaurs. They were unable to satisfactorily explain the evolution of such an unusual body plan. [1]

In 2004, British paleontologist David B. Norman placed it outside of Iguanodontidae but still within the clade Styracosterna, which he defined as containing all iguanodonts with a hatchet-like sternum and flattened hand claws. He agreed Lurdusaurus is a more derived iguanodont. [3] In 2005, Chinese paleontologist You Hai-Lu and colleagues suggested that the newly discovered and massively built Lanzhousaurus from China was closely related to Lurdusaurus, and the former was basal to the latter. He classified both of them as basal styracosterns. [6]

In 2008, American freelance researcher Gregory S. Paul argued that because Lanzhousaurus has a much deeper prepubic process, the two genera are probably not closely allied, though such hypotheses are wholly unverifiable without more complete remains. Paul agreed that Lurdusaurus is more basal to Iguanodontidae based on its short, broad hands and massive thumb spike, but he noted that the contemporary and more derived hadrosauriform Ouranosaurus has similar hand morphology. Therefore, Lurdusaurus could be a basal hadrosauriform, but Paul could not resolve the matter any further until more complete remains are discovered. [7] In 2009, American paleontologist Peter Galton placed Lurdusaurus at the base of Styracosterna and closely allied it with the Chinese Equijubus . He classified more derived iguanodonts into the new clade Iguanodontea. [8] In 2012, Taquet agreed with Paul that it falls outside Iguanodontidae, but was also unsure how exactly Lurdusaurus relates with other iguanodonts. [5]

Phylogeny of Iguanodontia according to Galton, 2009 (left) [8] and You and colleagues, 2005 (right) [6]

Paleoecology

Reconstruction of the Elrhaz Formation with Nigersaurus and Suchomimus Erlhaz Formation.jpg
Reconstruction of the Elrhaz Formation with Nigersaurus and Suchomimus

In 2007, paleontologist Thomas R. Holtz Jr. speculated that "Lurdusaurus may have been the dinosaur equivalent to a hippo" as they both share a heavy, stocky body plan. He suggested Lurdusaurus, like the hippo, was a generally slow-moving animal on both land and water, but could reach high speeds when necessary. [9] Generally, iguanodonts are thought to have been predominantly bipedal or facultatively bipedal, and Lurdusaurus, judging by the marked robustness of the limbs, was likely capable of quadrupedal locomotion for an extended period of time. [3] Overall, with its unusual and massive body plan including a small skull, circular chest, powerful and clawed forearms, and flattened femora, Lurdusaurus may have been reminiscent of a ground sloth. In squatting position, it may have resembled an ankylosaur. [1]

Taquet and Russell compared the fortified hand with its massive thumb spike to a ball-and-chain flail, and believed it was primarily used for defense. [1]

Lurdusaurus was recovered from the Elrhaz Formation, and lived alongside the iguanodonts Ouranosaurus and Elrhazosaurus , the sauropod Nigersaurus , an undescribed titanosaurid, the spinosaurid Suchomimus, the carcharodontosaurid Eocarcharia , the abelisaurid Kryptops , and an undescribed noasaurid. The Gadoufaoua site has also yielded an ornithocheirid pterosaur, and the crocodylomorphs Anatosuchus , Araripesuchus , Stolokrosuchus , and the giant Sarcosuchus . It dates to roughly 112 million years ago during the Early Cretaceous at the AptianAlbian boundary. Geologically, it is composed of almost entirely cross-bedded fluvial sandstone (the sediments were deposited by rivers), intermittently interrupted by migrating sand dunes. [10] The presence of Nigersaurus suggests widespread forests with soft understory vegetation, such as immature ferns or horsetails. [11]

See also

Related Research Articles

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Iguanodon, named in 1825, is a genus of iguanodontian dinosaur. While many species found worldwide have been classified in the genus Iguanodon, dating from the Late Jurassic to Early Cretaceous, taxonomic revision in the early 21st century has defined Iguanodon to be based on one well-substantiated species: I. bernissartensis, which lived during the Barremian to early Aptian ages of the Early Cretaceous in Belgium, Germany, England, and Spain, between about 126 and 122 million years ago. Iguanodon was a large, bulky herbivore, measuring up to 9–11 metres (30–36 ft) in length and 4.5 metric tons in body mass. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food.

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

Hypsilophodon is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put this into question.

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

Sarcosuchus is an extinct genus of crocodyliform and distant relative of living crocodilians that lived during the Early Cretaceous, from the late Hauterivian to the late Cenomanian, 133 to 93 million years ago of what are now North Africa and South America. The genus name comes from the Greek σάρξ (sarx) meaning flesh and σοῦχος (souchus) meaning crocodile. It was one of the largest pseudosuchians, with the largest specimen of S. imperator reaching approximately 9–9.5 metres (29.5–31.2 ft) long and weighing up to 3.45–4.3 metric tons. It is known from two species; S. imperator from the early Albian Elrhaz Formation of Niger, and S. hartti from the Late Hauterivian of northeastern Brazil. Other material is known from Morocco and Tunisia and possibly Libya and Mali.

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

Suchomimus is a genus of spinosaur dinosaur that lived between 125 and 112 million years ago in what is now Niger, north Africa, during the Aptian to early Albian stages of the Early Cretaceous period. It was named and described by paleontologist Paul Sereno and colleagues in 1998, based on a partial skeleton from the Elrhaz Formation. Suchomimus's long and shallow skull, similar to that of a crocodile, earns it its generic name, while the specific name Suchomimus tenerensis alludes to the locality of its first remains, the Ténéré Dese.

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

Ouranosaurus is a genus of herbivorous basal hadrosauriform dinosaur that lived during the Aptian stage of the Early Cretaceous of modern-day Niger and Cameroon. Ouranosaurus measured about 7–8.3 metres (23–27 ft) long and weighed 2.2 metric tons. Two rather complete fossils were found in the Elrhaz Formation, Gadoufaoua deposits, Agadez, Niger, in 1965 and 1970, with a third indeterminate specimen known from the Koum Formation of Cameroon. The animal was named in 1976 by French paleontologist Philippe Taquet; the type species being Ouranosaurus nigeriensis. The generic name is a combination of ourane, a word with multiple meanings, and sauros, the Greek word for lizard. The specific epithet nigeriensis alludes to Niger, its country of discovery. And so, Ouranosaurus nigeriensis could be interpreted as "brave lizard originating from Niger".

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

Camptosaurus is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic period of western North America and possibly also Europe. The name means 'flexible lizard'.

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

Altirhinus is a genus of hadrosauroid ornithopod dinosaur from the Early Cretaceous period of Mongolia.

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

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

Cristatusaurus is a genus of theropod dinosaur that lived during the Early Cretaceous Period of what is now Niger, 112 million years ago. It was a baryonychine member of the Spinosauridae, a group of large bipedal carnivores with well-built forelimbs and elongated, crocodile-like skulls. The type species Cristatusaurus lapparenti was named in 1998 by scientists Philippe Taquet and Dale Russell, on the basis of jaw bones and some vertebrae. Two claw fossils were also later assigned to Cristatusaurus. The animal's generic name, which means "crested reptile", alludes to a sagittal crest on top of its snout; while the specific name is in honor of the French paleontologist Albert-Félix de Lapparent. Cristatusaurus is known from the Albian to Aptian Elrhaz Formation, where it would have coexisted with sauropod and iguanodontian dinosaurs, other theropods, and various crocodylomorphs.

<i>Ekrixinatosaurus</i> Extinct genus of dinosaur

Ekrixinatosaurus is a genus of abelisaurid theropod which lived approximately 100 to 97 million years ago during the Late Cretaceous period. Its fossils have been found in Argentina. Only one species is currently recognized, Ekrixinatosaurus novasi, from which the specific name honors of Dr. Fernando Novas for his contributions to the study of abelisaurid theropods, while the genus name refers to the dynamiting of the holotype specimen. It was a large abelisaur, measuring between 6.5 and 8 m in length and weighing 800 kg (1,800 lb).

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

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

Eocarcharia is a genus of carcharodontosaurid theropod dinosaur from the Early Cretaceous Elrhaz Formation that lived in the Sahara 112 million years ago, in what today is the country of Niger. It was discovered in 2000 on an expedition led by University of Chicago paleontologist Paul Sereno. The type and only species is Eocarcharia dinops. Its teeth were shaped like blades and were used for disabling live prey and ripping apart body parts. Eocarcharia’s brow is swollen into a massive band of bone, giving it a menacing glare. It may have reached lengths of 6–8 m (19.7–26.2 ft).

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

Nigersaurus is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of this dinosaur were first described in 1976, but it was only named Nigersaurus taqueti in 1999, after further and more complete remains were found and described. The genus name means "Niger reptile", and the specific name honours the palaeontologist Philippe Taquet, who discovered the first remains.

<span class="mw-page-title-main">Elrhaz Formation</span>

The Elrhaz Formation is a geological formation in Niger, West Africa.

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

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

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

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<span class="mw-page-title-main">Ankylopollexia</span> Extinct clade of dinosaurs

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<span class="mw-page-title-main">Baryonychinae</span> Subfamily of dinosaurs (fossil)

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References

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  2. Chabli, S., 1988, Étude anatomique et systématique de Gravisaurus tenerensis n. g., n. sp. (Dinosaurien, Ornithischien) du gisement de Gadoufauoua (Aptien du Niger). Ph.D. dissertation, Université de Paris VII. UFR de Biologie et des Sciences de la nature 164 pp
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  6. 1 2 You, H.-L.; Li, D.-Q.; Ji, Q. (2005). "Lanzhousaurus magnidens gen. et sp. nov. from Gansu Province, China: The largest-toothed herbivorous dinosaur in the world". Geological Bulletin of China. 24 (9): 788.
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  8. 1 2 Galton, P. M. (2009). "Notes on Neocomian (Lower Cretaceous) ornithopod dinosaurs from England - Hypsilophodon, Valdosaurus, "Camptosaurus", "Iguanodon" - and referred specimens from Romania and elsewhere". Revue de Paléobiologie, Genève. 28 (1): 214. CiteSeerX   10.1.1.610.8299 .
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  10. Sereno, P. C.; Brusatte, S. L. (2008). "Basal abelisaurid and carcharodontosaurid theropods from the Lower Cretaceous Elrhaz Formation of Niger". Acta Palaeontologica Polonica. 53 (1): 15–46. doi: 10.4202/app.2008.0102 . hdl: 20.500.11820/5d55ed2e-52f2-4e4a-9ca1-fd1732f2f964 .
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