Baryonyx
Baryonyx is a theropod dinosaur genus which lived about 130-125 million years ago in the Barremian stage of the Early Cretaceous period. The genus has been named after its unique the 31 centimeters long claw on the first finger of the three fingered hands, and the genus name means "heavy claw". The first skeleton, which became the holotype, has been found by William J. Walker, amateur fossil collector, in the Weald Clay Formation (England), in 1983. Because of the low fossilization potential of the keratin, the absolute length of the claw is unknown, but it was probably longer by the keratin cover in it. The two other fingers and claws were much smaller.[1][2] Fossils are known from South England and Iberian Penninsula.[1][3]
Depiction of Baryonyx walkeri. By Lineart by Robinson Kunz (https://teratophoneus.deviantart.com/)Color by Rebecca Slater (https://paleocolour.deviantart.com/) - https://paleocolour.deviantart.com/art/Baryonyx-walkeri-737728903, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=67950886
Known occurrences of Baryonyx fossils.
Classification and valid species
At the time of the discovery of the holotype, a separate family was created for Baryonyx by Charig and Milner, named Baryonychidae, due to its unique features, especially the third finger's claw, of the specimen. Nevertheless, they pointed out that some characteristics of the snout are similar to thecodonts and Dilophosaurus. Moreover, two earlier described fragmentary snouts from Niger may more likely belong to this family than to the Spinosauridae.[1]
Over almost two decades of debate and discovery of new spinosaurid materials made clearer the taxonomic position of the Baryonyx. Nowadays, the type species, Baryonyx walkeri is the only currently known and accepted species of the genus Baryonyx, and it is also a member of the clade Baryonychinae with several other spinosaurid genera, like Suchomimus, Riparovenator and Ceratosuchops. This clade, together with the clade Spinosaurinae, is positioned within the family Spinosauridae which is sister-group of the family Megalosauridae.[3][4]
Mounted skeleton of Baryonyx walkeri. By Kumiko - https://www.flickr.com/photos/kmkmks/38452744530/in/album-72157714091543872/, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=90727034
Description and anatomy
The Baryonyx was a large theropod, its total body length was estimated to 8.0-8-5 meters and weight 1.7 - 1.9 tonnes [2][5]. Some morphological traits of this dinosaur are considered to be related to auqatic or semi-aquatic lifestyle. The jaw morphology of Baryonyx and other spinosaurids is similar to gharials, with their long, ventrodorsally low and particularly narrow built. Although only fragmentary materials are known of the Baryonyx skull, based on close relatives of the genus Suchomimus, the length of the Baryonyx skull can be estimated to 91-95 cm.[2][6][7]
Spinosaurids developed convergently a rudimentary secondary palate similar to crown group crocodilians' bony secondary palate. Its purpose is to separate the oral and nasal cavities, allowing the animal to swallow food underwater without the risk of suffocation.[8] On the outside of the snout, there are extensive foramina, similar to those found on Spinosaurus. These were likely filled with numerous integumentary mechanoreceptors, which receptors enhanced tactile sensitivity, aided in the detection and localization of aquatic prey.[2][9][10][11]
Estimated size of the holotype specimen of Baryonyx walkeri. By DaCaTaraptor - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=65514786
Even though there have not been found any complete Baryonyx skull yet, scientist assume that there were probably 6-7 teeth in each premaxilla, and 64 teeth in the lower jaw of the Baryonyx based on the well-preserved left dentary of the holotype specimen. This number is greater than in most other theropods. These teeth were supported by a bony wall on the lingual side of each tooth row. The first four upper teeth were large, and from the fourth teeth their size progressively decreased while their tighter compaction increased. Their shape was curved, conical, slightly flattened from sideways and finely serrated and their roots were exceptionally long and slender. This morphology made it possible to impale and hold slippery prey.
Another morphological feature that supports the hypothesys of semi-aquatic lifestyle is the position of the external nares, which were long, low, and placed far back from the snout tip. It could help the Baryonyx breath while its mechanoreceptor-rich snout was in the water during fishing.[2][12] On mid-line of the nasals, there is the triangular, narrow bony sagittal crest, which anterior part is narrow and sharp, and raised in a cross-shaped posterior part between the eyes.[2]
Despite the early misconception based on that the centra of the neck vertebrae are not at an angle to each other, the neck was not straight. The results of an analysis show that the neck has a sigmoidal curvature, though less intense than in other theropods.[2][13]
Depiction of Baryonyx walkeri. By PaleoGeekSquared - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=114762232
Paleobiology and paleoecology
Ecological role, diet and feeding method of Baryonyx have been the subject of several debates. Some researchers suggested a piscivorous diet but with two different feeding method. Because of the huge claws on its powerful forelimbs, it was thought to gaff fish out of the water, like grizzly bears do today. While, due to its long narrow snout, others proposed that Baryonyx could behave and catch fish like a heron or stork.[1][2] The other theory is that Baryonyx was a specialized scavenger similar to vultures. Its strong forelegs and long claws are ideal for breaking into the carcass as well as holding it, while the posterior nares allowed breath at the same time when the narrow jaws entered into the body cavity and have access to the viscera. However, carcasses of large dinosaurs would be already broken up by predators, so the theory about the specialized carcass-opening claws is doubtful and the large size of Baryonyx would not necessarily mean it was slow to catch fish.[14][15]
A Finite Element analysis showed similar resistance to bending and torsional feeding loads between the gharial and Baryonyx jaw models, with good resistance to ventrodorsal bending but weak resistance to lateromedial and torsional loads, unlike alligator and generalized theropod jaws. These results support the hypothesis that Baryonyx pursued piscivorous lifestyle.[7]
Furthermore, a study published in 2022, presented that Baryonyx and Spinosaurus, but not Suchumimus, were subaqueous foragers. These two taxa showed increased bone density, similar to known aquatic animals such as penguins, crocodiles and marine mammals.[16] Fortunately, there are direct evidences what Baryonyx ate, which may shed light on its behaviour. In the gut region of the holotype specimen there were acid etched Lepidotes scales and partly abraded or etched juvenile iguanodontid bones. From the fossil remains, it can not be determined whether Baryonyx was actively hunting for large herbivores or just fed from a carcass.[2]
Submerged Baryonyx. By Andrey Belov - https://www.deviantart.com/abelov2014/art/Spinosauridae-773270478, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=74712043
The Baryonyx most likely lived in wetlands, rivers and lakes. The Weald Clay Formation, where the Baryonyx was first found, has preserved a humid, subtropical environment and ecosystem. Common plants were the tree-fern Weichselia reticulata and the aquatic or marsh-dwelling herbaceous early angiosperm Bevhalstia pebja.
Also, there were presented ferns, horsetails, club mosses and conifers in this ecosystem. On the other hand, the Wessex Formation's floodplain was covered with chaparral-like vegetation and likely experienced seasonal dry periods. The conifer Pseudofrenelopsis parceramosa and pteridophytes were the dominant element of the flora of this area. Water bodies were populated with aquatic and wetland plants.[2][17][18] When these waters have dried up, the terrestrial mobility of Baryonyx would have allowed it to move from lake to lake.[19]
Baryonyx catching a shark. Author: Peter Montgomery. Source link: https://www.flickr.com/photos/paleopeter/18206577079.
There are many known dinosaurs from the Wealden Formation and the Wessex Formation of the Isle of Wight where Baryonyx may have shared its habitat with sauropods (such as Ornithopsis hulkei, Eucamerotus foxi, and Chondrosteosaurus gigas), ornithopods (Iguanodon bernissartensis, Mantellisaurus atherfieldensis and Brighstoneus simmondsi), ankylosaur (Polacanthus foxii) and small herbivores (Hypsilophodon foxii and Valdosaurus canaliculatus)[20][21][22][23], furthermore, with other large theropods like the carcharodontosaurid Neovenator salerii and the early tyrannosauroid Eotyrannus lengi. Smaller theropods of this ecosystem were the compsognathid Aristosuchus pusillus, and dromaeosaurid Ornithodesmus cluniculus and Vectiraptor greeni.[4][23][25][26][27] The Baryonyx was not the only spinosaurid of this ecosystem - there were two other spinosaurid species, the Riparovenator milnerae and the Ceratosuchops inferodios. They were sligthly smaller than the Baryonyx and probably occupied different niche in the Wessex Formation.[4]
The Iberian Peninsula is also known to gave home for spinosaurid theropods, but the fragmentary fossils, which are mostly teeth, made difficult more distinct identification.[4][3] Further fossils of the genus Baryonyx are most certainly known from the Spanish Salas de los Infantes deposit. The Salas de los Infantes deposit was once an inland wetland and inhabited by iguanodontids, hypsilophodontids, polacanthids, the sauropod Demandasaurus darwini, possibly the carchcarodontosaurid Concavenator corcovatus and the ornithomimosaurid Pelecanimimus polyodon.[28][29] The Papo Seco Formation was a more coastal and lagoon-like environment where juvenile and immature Baryonyx may compete with Anteophthalmosuchus crocodilians for food.
Author: Péter Imre Fábián, Biologist MSc student
Scientific references
[1] Charig, A. J., & Milner, A. C. (1986): Baryonyx, a remarkable new theropod dinosaur. Nature, 324(6095), 359-361.
[2] Charig, A. J., & Milner, A. C. (1997): Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin-Natural History Museum Geology Series, 53, 11-70.
[3] Malafaia, E., Gasulla, J. M., Escaso, F., Narvaéz, I., & Ortega, F. (2020): An update of the spinosaurid (Dinosauria: Theropoda) fossil record from the Lower Cretaceous of the Iberian Peninsula: distribution, diversity, and evolutionary history. Journal of Iberian Geology, 46(4), 431-444. doi: 10.1007/s41513-020-00138-9.
[4] Barker, C. T., Hone, D. W., Naish, D., Cau, A., Lockwood, J. A., Foster, B., Clarki, C.E., Schneider, P. & Gostling, N. J. (2021): New spinosaurids from the Wessex Formation (Early Cretaceous, UK) and the European origins of Spinosauridae. Scientific reports, 11(1), 1-15. doi: 10.1038/s41598-021-97870-8.
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[13] Evers, S. W., Rauhut, O. W., Milner, A. C., McFeeters, B., & Allain, R. (2015): A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the "middle" Cretaceous of Morocco. PeerJ, 3, e1323. doi:10.7717/peerj.1323.
[14] Kitchener, A. (1987): Function of Claws' claws. Nature, 325(6100), 114-114.
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[16] Fabbri M, Navalon G, Benson R, Pol D, O'Connor J, Bhullar BA, Erickson GM, Norell MA, Orkney A, Lamanna MC, Zouhri S. (2022): Subaqueous foraging among carnivorous dinosaurs. Nature. doi: 10.1038/s41586-022-04528-0.
[17] Hill, C. R. (1996): A plant with flower-like organs from the Wealden of the Weald (Lower Cretaceous), southern England. Cretaceous Research, 17(1), 27-38. doi:10.1006/cres.1996.0003.
[18] Batten, D. J. (1998): Palaeonenvironmental implications of plant, insect and other organic-walled microfossils in the Weald Clay Formation (Lower Cretaceous) of southeast England. Cretaceous Research, 19(3-4), 279-315.
[19] Holtz Jr, T. R., Molnar, R. E., & Currie, P. J. (2004): 4. Basal Tetanurae. In The Dinosauria, second edition (pp. 71-110). University of California Press.
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[28] Pereda-Suberbiola, X., Ruiz-Omenaca, J. I., Canudo, J. I., Torcida, F., & Sanz, J. L. (2012): Dinosaur faunas from the Early Cretaceous (Valanginian-Albian) of Spain. Bernissart dinosaurs and early Cretaceous terrestrial ecosystem. Indiana University Press, Bloomington, 379-407.
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