The Baryonyx. Taylor Franks. Florida State University

Transcription

1 1 The Baryonyx Taylor Franks Florida State University

2 2 Abstract Baryonyx is interesting due to it s rare diet and skull shape. Found in various places like England, Portugal and Spain- there were several studies on this dinosaur. It s long narrow skull and it s curious arms possibly being used as legs set it apart. It s huge claws were most likely used to trap fish when walking through rivers. Due to this fact, it s habitat was almost always near the water, by a stream or river. Many specimens that were not initially identified were found in Portugal and then compared to the Baryonyx walkeri. Introduction The Baryonyx lived in the Barrremian stage of the early Cretaceous Period, million years ago. (Atkinson) Baryonyx was named by Angela C. Milner and Alan J Charig (1987). It s fossil was discovered in 1983 in Surrey, England by an amateur fossil hunter named William Walker. (Charig 1987) The Baryonyx skeleton was about 70% complete and contained fossilized stomach contents, specifically fish scales, fish bones and partial bones of a baby Iguanodon. The fish was identified as a Lepidote and had an average length of 1 meter. The Baryonyx s length is reported to be 32 feet long and 8 feet tall with a weight between tons. The Baryonyx s Classification is Kingdom- Animalia, Phylum- Chordata, Class- Chordata, Order-Saurischia, Suborder-Theropoda, Family- Spinosauria, Genus-Baryonyx, Species- b. walkeri. The anatomy of the Baryonyx consisted of 1 foot claws on each hand and very long, narrow jaws with 96 small saw-like teeth. The Baryonyx had a long neck and more teeth compared to other theropods. It has a long tail and two legs with two arms and it may have walked on all fours because of lack of difference in size of its arms and legs. The Baryonyx is a close relative to Suchomimus, Carcharodontosaurus, and the Spinoasaurus. They all have narrow snouts like a crocodile but the Spinosaurus has a sail on it s back.

3 3 Discussion After the Baryonyx was discovered, details of the Baryonyx were published by Milner and Croucher (1987). They discovered how William Walker found an incomplete haemapophyisis, a less complete ungual phalanx, a much bigger ungual phalanx and the Claw which originally was missing it s tip on January 7 th, 1983 at Ockley s Brick Company s claypit in Surrey, England. Charig and Milner visited the site on February 7 th and found the pelvis and hind-limb bones. However, were not able to collect the skeleton until the 25 th of May in The skeleton was greatly disarticulated and the elements gently scattered although some were in the appropriate place. Since there was a great amount of siltstone matrix, it was hard to separate the material. Some were used for chemical treatment with thioglycollic acid. The acid had no effect on the bones so they all had to be removed mechanically. Each part of the skeleton was thoroughly examined and described by Charig and Milner (1987). There was several interesting things discovered about the skull despite not having much to look at. The skull seemed to have been long, the anterior 170 mm of the conjoined premacillae form a long low rostrum with round dorsal surface. The maxilla seems to belong in the hind part of the ventral margin of the premaxilla. The skull has 6 premaxillary teeth on the left side and 7 on the right which is more than a usual theropod. There s a lack of co-osssification between each part of the skull except in the midline and in the braincase. Premaxillae are preserved by being sutured together. The pre maxillae are not fused with any other elements but each has an advanced articulation with the maxilla. The long and low snout ascends from the front of the conjoined premaxillae. The snout is seen laterally to bifurcate posteriorly into two rami. One rami short and the other long. In the dorsal view the snout seems narrow when looking from side to side. The upper ramus goes down to a thin like spike meeting at the nasals. It s smooth but has two longitudinal ridges

4 4 on each side, one low and one a strong later ridge. They supported the internal septum and soft tissues. When looking at the premaxilla in palatal view between each row of teeth on both sides are narrow, transversely rounded features. They are sown together in the midline and are cut off short behind the last premaxillary tooth. Figure 1 shows the anterior portion of the paired vomers which are formed to be a vertical lamina in the midline and clasped between the vertical phalanges of the premaxilla. The middle of the lamina is connected to the roof of the premaxillary trough. The nasal part of a skull is one single element. Three pieces were found and preserved with one resembling an arrow head with it s apex forwards. The lateral extremities have a wing like flat surface which is underneath the arrowhead pieces. On the back of the arrowhead and its shaft there was a small significant fenestra between the nasal, prefrontal, frontal and the lacrimal. This is a rare find since the only other known theropod anyone knows that has a fenestra in this area is the Syntarsus. When looking at the lacrimal, only the left was able to be preserved. The jugul ramus of the lacrimal extends anteroventrally. There is a complete anterodorsal margin and a second ridge is on the posterodorsal half only. It encloses a narrow groove by going under and parallel the first ridge. In the lower jaw the only parts preserved are the left side dentary, splenial, and angular, the right side dentary, splenial, angular and coronoid. The angular central parts are preserved in both left and right side. The angular is large and thick laterally. The posterior end is broken at a ninety degree angle to each margin, thus suggesting that it was thickening towards the backside. The coronoid is a triangle bone with the dorsal being the longest and the posteroventral edge being shorter. The lateral and medial surfaces are flat and two similar facets go along the posterior of the dorsals edge.

5 5 In the Dentition most teeth are not intact but the ones that remain are premaxilla and maxilla. They are recurved cones with a serrated mesial and distal carinae. They have extremely fine denticles, 7 to the millimeter. The enamel has a granular appearance. The main difference between the teeth that have been found are size and amount of recurvature. In the vertebral column, five cervical vertebrae were preserved and ordered based on their morphological trends. Other Baryonyx remains were found in the Papo Seco Formation of Portugal. Includes a partial dentary, isolated teeth, pedal ungual, two calcanea, presacral and caudal vertebrae, fragmentary pubis, scapula, and rib fragments. The specimen named ML1190 from Portugal shared similar characteristics to Baryonyx walkeri like dental enamel surface with small wrinkles, varying denticle size along the carinae, 6 7 denticles per mm, wrinkles that form a 45 degree angle near the carinae. In 1995, skull fragments of the Baryonyx were found in Spanish province of La Rioja. Later in 2001 another parital preserved skull was recorded from province of Burgos. Some Portuguese artifacts that were originally thought to be crocodile skulls in the 19 th century were actually discovered to be the head of a Baryonyx skull. The proposed evolution of the Baryonyx introduces allopatric speciation. When both major continents were separated between Laurasia and Gondwana, the Baryonyx came from the Spinosauriden when migrated from Africa. Geographic isolation in Europe caused the Baryonyx to form. Similar from Spain and England support this theory.

6 6 Jaw fragments were found in Boca Do Chapin in Portugal in The most important was a part of a right dentary with four incomplete teeth. The lingual part of the bone had disintegrated. The nicest looking tooth, the third from the front, has the apex broken off but reveals an almost round cross section. The crown has ridges on both the lingual and labial faces and the surface of the enamel is very wrinkled looking. The surface wasn t taken care of properly but it has a rugose dorsoventral ridge in its anterior part. The associated bones were so badly preserved, that everything has to be based on the teeth. All the teeth share similar traits with the Baryonyx found in England which I previously described but some parts of it was different. They both have a few ribs on the lingual face of the crown. Some of the teeth from England though showed ribs on both the lingual and labial surfaces. The teeth from Boca do Chapin are similar to Siamosaurus tooth from Japan because of the tooth s overall shape. Due to some difference with Baryonyx walkeri the dinosaur from Boca do Chapin in Portugal is considered Baryonyx sp. (Buffetaut 2007) When referring to the Baryonyx s claw, there were some theories as to why it s claw was so much larger than other theropods. Due to finding fish scales in it s stomach, there was speculation that the huge claws were made to hook into fish swimming past as the Baryonyx stood in the water. With having a very narrow snout, they probably could not handle eating large prey so eating fish and dead Iguanodons would have been ideal for them to survive. The Baryonyx family starts at the Megalosauroidea which is the classification for a group of theropods. Then it branches to three different dinosaurs- the Megalosauridae, Spinosauridae and Xuanbanosaurus. From the Spinosauridae it branches to Spinosaurus and Irritator in our group

7 7 and Suchomimus and Baryonyx in another. Even though the Suchomimus and Baryonyx are in the same group, there are some differences. For example, Suchomimus is estimated to have a weight of 10,000 lbs. while the Baryonyx has an estimates 4,000 lbs. Even though there s been a weight estimated for the Baryonyx, bone studies have proved that all of the known specimens are not fully grown. One study at the University Of Bristol, UK illustrated the Baryonyx skull when eating a fish, similar to the Indian fish eating gharial- crocodile instead of a dinosaur or an alligator. In the diagram of the computer image it shows the teeth had extremely elongated roots and the Baryoyx had independently evolved a bony palate. Conclusion Even though the Baryonyx is classified as Bipedal, it could have walked on all fours in the water to find fish like a bear. It s snout is of resemblance to a crocodile which makes sense to have eaten mainly fish during it s life. Instead of having sharp long teeth like a Tyrannosaurus, it had small serrated teeth that were not meant to bite into the necks of other dinosaurs. It s claws were mainly used to injure the animal or instantly kill fish by hooking in to them. There is a rare small hole between the nasal, frontal, prefrontal and lacrimal. The Baryonyx s teeth is studied more so than other body parts because of how well preserved they are. The Baryonyx is the only known theropod that eats fish. None of the Baryonyx s that have been found were fully grown so therefore it is easy to think that their legs could have grown longer which then would cause a more significant difference between the arms and legs which would cause it to stand on two legs instead of all fours. I think this could be a significant argument and may be concluded with more research and evaluation. I think the Baryonyx did not have feathers due to the fact that it lived mostly near water and was in the water to hunt. Feathers in this case may not have

8 8 been needed. It s skin might have been a dark color in order to blend in so it wouldn t scare away fish or hide from bigger predators. The Baryonyx could have very well hid underwater like a crocodile only showing it s snout in order to breathe. In Portugal, the teeth findings might have been a Baryonyx that adapted to its conditions due to some differences that were displayed in comparison to the Baryonyx found in England.

9 Figure 2 C- Premaxillae in palatal view, showing vomers. 9

10 10 References Atkinson, Lee. "BARYONYX : From DinoChecker's Dinosaur Archive." Dinochecker RSS. N.p., n.d. Web. 04 Dec "Baryonyx Dinosaur, Facts Pictures - Baryonyx Habitat." Baryonyx Dinosaur, Facts Pictures - Baryonyx Habitat. N.p., n.d. Web. 03 Nov "Baryonyx vs Suchomimus." - Dinosaurs Comparison. N.p., n.d. Web. 03 Nov Buffetaut, Eric. "The Spinosaurid Dinosaur Baryonyx in the Early Cretaceous Of Portugal." Cambridge Univeristy Press. N.p., 11 Sept Web. 3 Nov Charig, A.J., and A.C. Milner. "Biodiversity Heritage Library." V ( ). N.p., n.d. Web. 28 Oct Strauss, Bob. "Baryonyx Facts." About.com Education. N.p., n.d. Web. 28 Oct "New Scientist." Google Books. N.p., 27 Nov Web. 28 Oct. 2015