Stingray (Modern Animal) ->
The Ancient Guitarfish Rhinobatos Productus (rhine meaning shark, batis meaning ray, in reference to their body being the intermediate form between sharks and rays), is approximately 200 million years old and although similar to the Modern Guitarfish which has been around for 100 million years virtually unchanged, it is a much more primitive form. It is the evolutionary ancestor of the modern Stingray, and is said to be the evolutionary link from when certain species of sharks began to evolve in to rays, having characteristics of both. They had a long pointed snout, and guitar shaped body. Being compressed from belly to back, its body is attuned for the sandy ocean floor. For the purpose of this assignment the Ancient species which is similar to the modern Guitarfish will be called the guitarfish or ancient guitarfish, where as the Guitarfish of today will be called the modern guitarfish.
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Guitarfish Fossil - Found in lebanon, believed to be from the Cenomanian Age http://www.fossilmuseum.net/fishfossils/Rhinobatos-hakelensis/L073b.jpg

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Labelled Ancient Guitarfish, Original Image from http://media.photobucket.com/image/guitarfish%20fossil/SilversharkFossils/Shark%2520images/Atlantic_guitarfish.jpg

Kingdom:
Animalia
Phylum:
Chordata
Class:
Chondrichthyes
Subclass:
Elasmobranchii
Order:
Rajiformes
Family:
Rhinobatidae
Genus:
Rhinobatos
Species:
R. productus
Habitat -
200 Million Years ago the earth was a very different place than it is today, the continents were all joined in the super continent Pangaea, before they spilt apart into the configuration we know today. Pangaea was caused by continental drift, in which all the continents are slowly moving around the earth and they came together. South America was joined with Africa, and india was also attached to africa, with the rest of the world fitting together like pieces of a puzzle. Pangaea began to break apart around 150 Million Years ago, and slowly form the earth we know today.

Ancient Guitarfish fossils have been found along the coast of North America in the Eastern Pacific Ocean, from the gulf of California to San francisco and also further south in Mexico. They have been found in the Mediterranean as well. It is believed that they lived in a tropical climate, abundant with reefs, coral and sea grass, as this would have had the food which they required, as well as the warmth and was highly populated at the time with animals.
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ReRed Circles indicate where fossils have been found of the Ancient Guitarfish. Original map from - http://www.webresourcesdepot.com/wp-content/uploads/image/free-vector-world-map.gif

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Guitarfish Habitat: Sandy ocean floors which surround reefs etc. Source: http://fc08.deviantart.net/fs14/f/2007/047/2/6/Underwater_Ocean_Floor_Light_by_Della_Stock.jpg


They lived in sa
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Artists Impression of Pangaea 200 Million years ago, Red Circles indicate where the Ancient Guitarfish is believed to have inhabited. Source - http://www.roslynoxley9.com.au/images/galleries/SHARK_LEWITT_Misc_2007/005.jpg
ndy sea floors, in bays, reefs, seagrass and estuaries, usually at around 15m, but this can range up to 50m. Ancient Guitarfish were known to lie partially buried in sand or mud on the ocean floor, with only their eyes visible, ready to ambush their prey, crabs, worms, clams and small fishes. The presence of soft sand and mud was essential for the Guitarfish as it allowed them to camouflage themselves, and also protect themselves from becoming potential prey to larger predators.

The Ancient Guitarfish were nomadic, moving around and not living in a certain place. They would hide buried in the sand during the day and at night, would venture away from their hiding spot to find food. During the colder months they would migrate to shallower waters to ensure the warmth they required. It is believed that during Spring females would move away from the male partner and stay away until early summer to give birth to the pups. Males would then migrate to the same area to mate, and then females, pups and males would all leave the area once the process was complete.

Although Very similar guitarfish are around today, the bodies on the modern guitar fish are flatter and more disk like than that of the ancient Guitarfish, and they are found in a more restricted area, which extends from San Francisco to Mexico.

Structural Adaptation 1 - Bodies became attuned for ocean floor
The guitarfishes body has evolved from the first sharks were round, and shaped as sharks are today, but overtime the bottom of the belly area has become flatter to assist them with swimming along the ocean floor, and hiding in the sand. The tail has also become slightly longer and thinner, and the dorsal fin has become smaller. The thinner tail disturbs the sand less, and it does not need to be as wide as the body is no longer as heavy to push through the water. The compression which has occured from belly to back has allowed them to hide more easily in the sand, and also hunt more easily, as their mouths are on the bottom of their bodies which comes in contact with the ocean floor. The crustaceans , crabs, worms and small fish which they eat inhabit the ocean floor and this body shape allows them to be more inconspicuous in the hunt and camouflage themselves more effectively.

Environmental Pressures which may have given rise to this adaptation may be the fact that the food which the guitarfish fed on lived on the ocean floor. If the body had not compressed from belly to back then it would be very hard for them to hunt effectively as they could not camouflage and bury themselves in the sand as they were known to do. Also as the mouth is on the bottom of the guitarfish, the body being flat means that it is closer to the ocean floor and therefore closer to their prey, being able to simply graze along at the same level, not having to make sudden movements down to reach their prey.

Structural Adaptation 2 - Sharklike Tail
The ancient guitarfish did not swim using their pectoral fins to swim as most rays do, but use their shark like tail instead. This is because they had not yet evolved to become the rays of today and their pectoral fins were not yet large enough or strong enough to be used for swimming. The tails which they had were still very similar to the tails which sharks today have, being very strong and able to move from side to side very fast to propel them through the water. One of the main advantages of having the 'sharks' tail is that they could move through the water faster, and control their movements better, as the tail, which has a small dorsal fin on top of it, could be used as a rudder for changing direction, and also had a larger range of movement than the pectoral fins.

Environmental pressures which could have led to this adaptation may be that as they were gradually evolving to become attuned to life on the ocean floor (due to the fact that there was an abundance of food there), the presence of the already strong tail allowed them to swim well already, but it adapted slightly, becoming flatter, slightly thinner and longer due to the fact that it would disturb less sand when used to swim, and therefore be more inconspicuous to predators and prey. Therefore the pectoral fins did not need to be used for swimming as they are today in many rays.

Behavioral Adaptation 1 - Migration to Shallower waters
During the colder seasons of the year the Ancient guitarfish were believed to migrate to shallower waters to ensure the warmth that they required. They did this as in the cold season, the deeper water could cool slightly as the suns rays could not reach as far to penetrate it and the water is more still, and also prey is not as common in the deeper water over the winter months for the same reason of water temperature. The movement to the shallower, warmer waters ensures that there will be enough food, and also the warmth which they required to keep them healthy.

Environmental pressures which may have given rise to this adaptation may be that the guitarfish needs to live in an environment which is warm enough to keep them healthy. During winter the deeper water further out cools slightly, and this change was significant to the guitarfish, not only on their health but on their food sources. During winter the food which the Guitarfish fed on was more commonly found in shallower waters, warmer waters. Hence the guitarfish followed the food source, as without food how would they have survived?

Behavior Adaptation 2 - Females leave males during breeding
At the beginning of spring females move into the shallower bay waters and stay until early summer when they give birth to their pups. Males arrive soon after (late summer) the pups are born to mate, and then both males and females leave the area. This is an advantage to the stingrays as it is safer for the pups in shallower waters as there is food, and less predators, and also pups require slightly warmer water, and the shallower water is generally warmer. The males come after the pups have been born in late summer to mate as this ensures that the offspring will not be born in the wrong season and gives them the greatest chance of survival. They all then leave together once the pup has sufficiently grown to head back to the deeper waters which they inhabit.

Environmental Pressures which may have led to this adaptation could be that if the pups were born in deeper water they would be at risk of attack from the many predators, and also the water is cooler, pups require slightly warmer water than the adults do for the first few months of their life as they do not have the stored body fat to keep them warm. An environmental factor which could have led to the males coming after the pups are born to mate may be that for the offspring to survive they need to be born at a certain time during the year when the temperature is right, and there isn't a shortage of food to give them the greatest possible chance of survival.

Physiological Adaptation - Breathing
The Ancient guitarfish pumps water through two small holes called Spiracles , on the top of its head, the water then travels through the gills and out through the gill openings on the bottom of its body. Guitarfish can not take in water to breath through their mouths as this would damage their very delicate gills. The presence of the Spiracles helps the Guitarfish enormously as the water above them is much clearer and has less silt and sand in it, than the water beneath them. Guitarfish always swim with spiracles pointing away from the sea floor which makes it very hard for sand to get in, but if they used their mouths to breath then sand would damage their breathing system, and it would need to be much more complex to ensure that food does not enter their breathing system and their digestive system does not become full with water.

Environmental pressures which could have given rise to this maybe that as they became attuned to life on the ocean floor if their breathing system was taking in water on the underside of their body it would become full of sand and other substances which would damage their gills. The spiracles on the top of the body allow clean water to be taken in, with minimal sand so that the gills remain working and intact.

Extinction Pressure -
Although technically not extinct , this Ancient Guitarfish form has adapted into many modern ancestors such as the Ray Family, and also its very similar relative the Modern Guitarfish. Pressures which could have led to this change could be that they did not have any real defense against predators as many rays do today. They had lost the defense of the Sharks teeth over time, and had not yet attained the venomous tail which we know evolved to become a common feature on many rays. Also they could not camouflage themselves very well as their bodies were not yet flat enough to become completely buried in the sand, and therefore were still visible, and prone to attack. As Pangea gradually drifted apart the oceans were changing and become more acidic the Ancient Guitarfish had insufficient food sources and begun changing to become its modern counterpart which was more suited to the changing oceans. They can tolerate ranging salinity levels, feed on a larger variety of animals, and have been around for the past 100 million years unchanged.

http://www.biodiversityexplorer.org/chondrichthyes/glossary.htm - Glossary of terms on Sharks and Rays, retrieved on 17th July 2010
http://media.photobucket.com/image/guitarfish%20fossil/SilversharkFossils/Shark%2520images/Atlantic_guitarfish.jpg - Guitarfish Drawing Photobucket, Retrieved on 22nd July 2010
http://library.thinkquest.org/17701/high/pangaea/ - The Pangaea Theory, Retrieved on 21 July 2010
http://www.elasmodiver.com/elasmobranch_evolution.htm - Elasmodiver Evolution of Sharks and Rays, retrieved on 29th June 2010
http://evomech1.blogspot.com/2006/09/stingray-fossil-goes-under-hammer-in.html - Stingray Fossil goes under the hammer in Edinburgh - Retrieved 20th July 2010
http://www.fossilmuseum.net/fishfossils/Rhinobatos-hakelensis/Guitar-Fish.htm - Guitarfish Fossil found in lebanon, Retrieved on 18th July 2010
http://inselbergerevolution.blogspot.com/2010/03/fossil-confirmation-of-evolution.html - Fossil Proof of Evolution, Retrieved on 12th of July 2010
http://en.wikipedia.org/wiki/Guitarfish - Wikipedia Guitarfish, 14th July 2010
http://seapics.com/feature-subject/fish/guitarfish-pictures-001.html - Guitarfish which is the link between sharks and rays, Retrieved on 9th July 2010
www.monteryaquarium.com - Montery Aquariam Ancient Guitar Fish Retrieved on 14th July 2010