Baryonyx


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Baryonyx
Baryonyx skeletal reconstruction

Baryonyx skeletal reconstruction

Temporal occurrence
Lower Cretaceous ( Barremium )
130.7 to 126.3 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Theropoda
Spinosauroidea
Spinosauridae
Baryonychinae
Baryonyx
Scientific name
Baryonyx
Charig & Milner , 1986
Art
  • Baryonyx walkeri

Baryonyx is a two-legged dinosaur from the Spinosauridae family that lived in the Lower Cretaceous ( Barremium ). A nearly complete skeleton was found in England, it is considered to be one of the best preserved theropod (carnivorous dinosaur) fossils in Europe.

It reached a length of about 8.5 meters; distinctive features include a crocodile-like skull and an unusually large claw on both thumbs of the forelimbs. It fed on fish and other dinosaurs, and according to chemical analyzes of teeth it was possibly partly aquatic. The well-preserved skeleton from England is one of the most important finds of spinosaurids. Stomach contents preserved in fossil form for the first time enabled the now generally accepted assumption that this group fed on fish.

anatomy

Size comparison between baryonyx and humans

Baryonyx is stated to be 8.2 to 8.5 meters in length, depending on the source, and its weight is estimated at 1700 to 2000 kilograms. Since the most complete skeleton likely came from an animal not yet fully grown, an adult baryonyx could have been larger.

The 91 centimeter long skull is proportionally long, narrow and crocodile-like flat, like other spinosaurids. It had 32 teeth in the upper jaw and 64 teeth in the lower jaw - about twice as many as in non-spinosaurid theropods. The tooth crowns were conical in shape and had very fine serrations on the cutting edges, about seven per millimeter. This distinguishes them markedly from the typical teeth of non-spinosaurid theropods, which were designed as laterally flattened, blade-like fangs with coarse serrations. At the tip of the snout, the teeth interlocked strongly ( terminal rosette ). As characteristic of Baryonyx within the spinosauridae the fused apply nasal bones , significant transverse narrowings of the sacrum and the caudal vertebrae, a specially designed hinge joint between the shoulder blade and - Raven leg (coracoid), the projecting distal edge of the pubic bone shovel ( pubic blade ) and very shallow indentation of the fibula .

Its cervical vertebrae were comparatively long and had short appendages. Baryonyx had three fingers; the thumb had an elongated claw, 31 centimeters long in the holotype . In addition to its non-preserved keratin coating , it would have been significantly larger. His humerus was very strongly built and very broad and very flattened at both ends. In contrast to other spinosaurids, no back sail has been proven for him.

Since there was a large difference in size between the front and rear legs, one suspects a bipedal (two-legged) mode of locomotion. The very strong development of the forelegs, especially the humerus, compared to other theropods, could also indicate that he occasionally moved or rested on four legs ( quadruped ).

Find history

The amateur paleontologist William J. Walker discovered one of the 30 centimeter long claws, the first known fossil of Baryonyx, in a clay pit in Surrey (England) in January 1983 . He notified the British Museum of Natural History ; In May and June 1983, near the original site, this hid an almost complete skeleton of Baryonyx (specimen number BMNH 9951), only missing most of the tail. Most of the bones lay in the natural anatomical context; Displacements and damage to bones can largely be traced back to the use of a bulldozer in the recovery process. The find quickly attracted a lot of media interest, which made it known to a wide public. BMNH 9951 is one of the most important fossils in England, until 1983 a partially preserved Eustreptospondylus was the only noteworthy find of a theropod from England.

About three years later it was first described as Baryonyx walkeri by the British paleontologists Alan Charig and Angela Milner . Baryonyx means "heavy claw" (from ancient Greek , βαρύς ( barys ) = heavy, ὄνυξ ( onyx ) = claw), the epithet walkeri honors William J. Walker. Teeth and vertebrae found in isolation also come from England, but they cannot be definitely assigned to Baryonyx . All previous English finds come from the Wealden Group , an important fossil deposit in southern England, and are dated from the Hauterivian to Aptian period.

Further finds , unequivocally from Baryonyx , were found mainly in Spain: in 1995 paleontologists described skull remains of Baryonyx from the Barremium of the Encisco group in the Spanish province of La Rioja , in 2001 a partially preserved skull from the Hauterivium of the province of Burgos was reported. Portuguese finds from the 19th century, originally interpreted as the remains of a crocodile named Suchosaurus , were attributed to Baryonyx in 2007 . They come from barremium layers in the vicinity of Lisbon .

Paleobiology

nutrition

Live reconstruction of baryonyx

The skull of baryonyx and other spinosaurids shows a number of features that suggest piscivorie (diet of fish). The crocodile-like snout was long, flat and narrow, so it would have had less resistance when diving into the water. The narrow snout and a bony roof of the palate reduced the torsional stress caused by wriggling fish. The general cranial mechanics of Baryonyx are more similar to that of the piscivorous Gavial crocodile than that of normal theropods. A bone crest of the spinosaurids, which stretches dorsally over the entire skull, is also an indication of pronounced neck muscles, which are necessary to pull the snout through the water against the water resistance and to pull the head back quickly. The elongated conical teeth, which only have very fine sawed edges, are particularly suitable for grabbing and holding on to the entire prey and thus differ from the teeth of carnivores, which have to tear off or cut parts of the prey after grabbing. The notion of a baryonyx , which, like a heron, would lie in wait for fish on the bank or in shallow water , is widespread . It may also have grabbed fish with its 30 centimeter long claws. The unusually large front extremities also had bone ridges as a starting point for muscles; Baryonyx arms were probably very strong. Perhaps their power in conjunction with the claw was used in hunting larger, land-dwelling animals. They may also be used to tear open the prey.

In the almost complete skeleton from England, fossil stomach contents were preserved in the abdomen: the scales and teeth of a fish ( lepidotes ) attacked by stomach acid and the bones of a young iguanodon (a herbivorous dinosaur that is often found in Europe). The find confirms the assumption that Baryonyx piscivor ate - but the thesis of pure piscivory is refuted by the finding of Iguanodon as stomach contents. Pterosaurs (Pterosauria) are also considered prey by Spinosauriden, this one concludes from bite marks in pterosaur bones. Most often, paleontologists suspect a mixed, opportunistic diet that includes fish and terrestrial vertebrates, similar to today's crocodiles. A number of Spanish paleontologists speculate about a far less fish-heavy food spectrum; They refer to finds of teeth from baryonychin theropods from the Spanish province of Teruel : Fossil water fleas in a stage to survive dry seasons from this region show that there were no larger, permanent bodies of water. This also explains the absence of larger fish. Thus, Baryonyx or a close relative in the Lower Cretaceous of Teruel did not feed on fish.

In the abdomen of Baryonyx were Gastrolithen found (swallowed stones in the stomach). In some animal groups they fulfill various purposes, in the case of Baryonyx it is assumed that they have been accidentally swallowed.

Semi-aquatic way of life

According to a more recent study, spinosaurids were semi-aquatic, that is, partially aquatic. Researchers led by Romain Amiot examined the mineral apatite from the teeth of spinosaurids for the ratio between two isotopes of oxygen , oxygen-16 and oxygen-18. The analysis shows a ratio of the two isotopes, as is typically found in animals living in water. The isotope ratio is different in terrestrial and aquatic animals because the body of land animals loses water through evaporation, with the heavier oxygen-18 isotope building up in the body. A semi-aquatic way of life appeared to the researchers as the most plausible explanation for the ratio of the isotopes. Traces of a theropod from La Rioja provide evidence of swimming locomotion: They show that a bipedal theropod swam in about three meters high water; scratch marks on the hind legs were left in the sediment.

However, the physique of Baryonyx shows no adaptation to a semi-aquatic behavior, therefore paleontologists mostly deny a way of life that is too strongly bound to water. His physique corresponds to that of a rural runner. More research is needed to substantiate the theses of Romain Amiot and colleagues.

Paleoecology

The fossils from Great Britain were found in the deposits of the Wealden Group, which in the Cretaceous period was largely an extensive wetland area with rivers and a large freshwater lake, Wealden Lake. The climate was subtropical by today's standards. The Spanish finds were in areas that were covered by lakes in the Cretaceous period, the Portuguese fossils probably come from the area of ​​a lagoon. Piscivorie would have been possible in such an environment. One of the most common European dinosaurs at that time was Iguanodon , which has been shown to be part of the food spectrum of Baryonyx . He also lived with a number of other theropods of about the same size, such as Neovenator and Eotyrannus . It can be assumed that it avoided competition with these typical theropods due to its possibly semi-aquatic way of life and piscivorous diet and occupied a special ecological niche . An example of this from today's time is the coexistence of mainly piscivorous Australia crocodile and more specialized to mammals and birds strips crocodile in Australian rivers.

Systematics

Live reconstruction of Suchomimus , a close relative of Baryonyx
Skeletal reconstruction of Megaraptor
Some Spinosauridae in size comparison: Spinosaurus , Suchomimus , Baryonyx , Ichthyovenator , Irritator

When it was first described, a separate family (Baryonychidae) was suggested for the genus Baryonyx , today it is part of the Spinosauridae family. The Spinosauridae are defined by synapomorphies (similarities) in the structure of the skull as well as in the number and size of the teeth. Baryonyx has been assigned to the subfamily Baryonychinae since 1998, which faces the Spinosaurinae with Irritator and Spinosaurus . The Baryonychinae probably split from the Spinosaurinae more than 130 million years ago. Their synapomorphies are a large number of teeth and strongly keeled vertebrae. Suchomimus was first described from Africa in 1998 ; it is very similar to Baryonyx and is classified together with it within the Baryonychinae. Some paleontologists consider Baryonyx and Suchomimus to be one and the same genus, the majority of them use the separation of Suchomimus and Baryonyx within the Baryonychinae , which has also been confirmed by other scientists . Recent studies also see the Megaraptora very close as a baryonyx : Megaraptora fossils were found in Australia and South America and show a number of characteristics that suggest a relationship with Baryonyx and Suchomimus ; among other things, the Megaraptora also had a greatly elongated claw on the thumb of the fore limb.

A possible cladogram :

 Spinosauridae 
 Spinosaurinae 

Spinosaurus


   

Irritator



 Baryonychinae 

Baryonyx


   

Suchomimus




The only recognized species of the genus Baryonyx is Baryonyx walkeri , but numerous finds of isolated teeth indicate different species. They are very similar to the teeth of BMNH 9951, but show slight differences. It is not clear whether these differences are due to different species or individual differences, so up to now, ambiguous findings have been classified as Baryonyx sp. (unspecified species of baryonyx ) or baryonychine remains are preferred.

After the paleontologist Eric Buffetaut recognized the species Suchosaurus girardi, described in 1841, as a synonym for Baryonyx in 2007 , the genus Baryonyx should henceforth be called Suchosaurus according to the rules of the ICZN ( priority rule ). However, since the holotype of Suchosaurus is only an isolated tooth, whereas Baryonyx is a nearly complete skeleton, the generic name Baryonyx is still used. The assignment of the second Suchosaurus species remains dubious ; the English Suchosaurus cultridens is probably also a spinosaurid, but cannot be clearly assigned to Baryonyx .

Paleobiogeography

The evolution of Baryonyx is often explained by allopatric speciation . At the time of the Lower Cretaceous, the then northern continent Laurasia (Europe, Asia, North America) and the southern continent Gondwana (Africa, South America, India, Australia, Antarctica) were separated by the Tethys Ocean . It seems certain that the Baryonychinae and its oldest known representative, the Baryonyx, developed in Europe. Basal (primeval) spinosaurids from Africa emigrated to Europe before the separation of the two continents and developed into Baryonychinae due to geographical isolation . This is supported by finds of baryonychin teeth from the Hauterivium of Spain and England, which are older than any African remains of baryonychin. The basal spinosaurids that remained in Gondwana developed into Spinosaurinae with irritator and Spinosaurus . The geologically younger Suchomimus seems to descend from Baryonyx due to some synapomorphies or to share a common ancestor with this, but lived in Gondwana. It is believed that an unspecified occurrence led ancestors of Suchomimus to Gondwana, or that the Iberian Peninsula (Spain & Portugal) formed a land bridge through the Tethys. Due to insufficient fossil evidence, the evolution of the Spinosauridae remains unclear.

In the public eye

Live model of Baryonyx in the British Museum of Natural History, London

Baryonyx caused a great deal of public attention after its discovery in 1983; Initially, it was assumed that the elongated claw was a normal claw of the foot, and a press release assumed it was a gigantic tyrannosaurid . The news first came to the public on July 19, 1983, and the dinosaur was subsequently given nicknames like "Claws", "Big Claws" or "Superclaws". The newspaper The Guardian about headlined with "Dinosaur find of the century" ( "Dinosaur find of the century"), which The Times published on July 20, 1983 article "fossil hunter unearths Surrey dinosaur" ( "fossil hunter discovered Surrey -Dinosaur "), the following day the headline " New chapter for Dinosaur "appeared . Baryonyx also appeared later in the British press: on November 27, 1986, The Guardian headlined following the first description " Claypit dinosaur claws takes on plumber's name ", alluding to the epithet walkeri and the profession of William J. Walker).

Similarly, Baryonyx a popular dinosaurs in exhibitions; Skeleton replicas and living reconstructions can be found in numerous museums and dinosaur parks.

Individual evidence

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  2. a b c d e f g h i j k l Alan J. Charig , Angela C. Milner : Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. In: Bulletin of the Natural History Museum. Geology Series. Vol. 53, No. 1, 1997, ISSN 0968-0462 , pp. 11-70, digitized .  
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  8. ^ A bone to pick with science. In: The Guardian , July 21, 1983, p. 15.
  9. Angela Milner, Ron Groucher: Claws. The story (so far) of a Great British dinosaur, Baryonyx walkeri. British Museum (Natural History), London 1987, ISBN 0-565-01033-6 .
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  16. ^ A b c Emily J. Rayfield, Angela C. Milner, Viet Bui Xuan, Philippe G. Young: Functional morphology of spinosaur "crocodile-mimics" dinosaurs. In: Journal of Vertebrate Paleontology. Vol. 27, No. 4, 2007, pp. 892-901, doi : 10.1671 / 0272-4634 (2007) 27 [892: FMOSCD] 2.0.CO; 2 .
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  22. a b c Romain Amiot, Eric Buffetaut, Christophe Lécuyer, Xu Wang, Larbi Boudad, Zongli Ding, François Fourel, Steven Hutt, François Martineau, Manuel Alfredo Medeiros, Jinyou Mo, Laurent Simon, Varavudh Suteethorn, Steven Sweetman, Haiyan Tong, Fusong Zhang, Zhonghe Zhou : Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods. In: Geology. Vol. 38, No. 2, 2010, ISSN  0091-7613 , pp. 139-142, doi : 10.1130 / G30402.1 .
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  26. Jump up ↑ Roger BJ Benson, Stephen L. Brusatte, Stephen Hutt, Darren Naish: A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle Of Wight, England. In: Journal of Vertebrate Paleontology. Vol. 29, No. 2, 2009, pp. 612-615, doi : 10.1671 / 039.029.0202 .
  27. Oliver WM Rauhut: The Interrelationships and Evolution of Basal Theropod Dinosaurs (= Special Papers in Palaeontology. Vol. 69). The Palaeontological Association, London 2003, ISBN 0-901702-79-X .
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  29. Nathan D. Smith, Peter J. Makovicky , Federico L. Agnolin, Martín D. Ezcurra, Diego F. Pais, Steven W. Salisbury: A Megaraptor-like theropod (Dinosauria: Tetanurae) in Australia: support for faunal exchange across eastern and western Gondwana in the Mid-Cretaceous. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 275, No. 16947, 2008, ISSN  0080-4649 , pp. 2085-2093, doi : 10.1098 / rspb.2008.0504 , digital version (PDF; 454.18 kB) .
  30. ^ Dinosauria Translation and Pronunciation Guide B ( Memento of November 6, 2011 in the Internet Archive )
  31. ^ Dinosaur find of the century . In: The Guardian July 20, 1983
  32. Fossil-hunter unearths Surrey dinosaur . In: The Times July 20, 1983
  33. ^ New chapter for Dinosaur . In: The Times , July 21, 1983
  34. Claypit dinosaur Claws takes on plumbers name . In: The Guardian November 27, 1986

Web links

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This version was added to the list of articles worth reading on November 27, 2010 .