From an ecological perspective - particularly focusing on interspecies interactions - explain how the structural development of this type of head may have aided the survival and reproduction of this type of organism, explaining the functional value of this structural development.
- Vincent Fiorentini
(vincent@panatechcomputer.com)
Tiktaalik differs from its aquatic counterparts because of its shoulder bones which would eventually lead to an independent head in amphibians. This shoulder bone gave Tiktaalik several selective advantages. Most notably, however, are the advantages Tiktaalik had in predator-prey relationships.
ReplyDeleteTiktaalik literally lived in fish-eat-fish world. In fact, the most common fossilized species near Tiktaalik is “seven feet long and has a head as wide as a basketball” (41). This is certainly an intimidating creature for which a prospective prey would need defense mechanisms as protection in order to avoid being eaten (Campbell 1201). One of Tiktaalik’s mechanisms was the shoulder bone and beginning of an independently moving head. Especially when hunted by predators lacking a shoulder bone and independent head, Tiktaalik would be better able to maneuver around his attacker, using his head to quickly duck out of harms way. The shoulder bone, which allowed Tiktaalik to perform push ups, may also indicate that Tiktaalik was able better maneuver on all fours than were his predators (http://blogs.discovermagazine.com/loom/2008/10/15/the-shoulder-bones-connected-to-the-ear-bone/). These defense mechanisms undoubtedly disrupted a predators hopes in acquiring a Tiktaalik dinner, directly affecting interdependence in nature.
Yet, not only did Tiktaalik have an advantage against predators, he also had an advantage when hunting prey. Similar to when he himself was hunted, Tiktaalik was probably able to use his more flexible head to dive and grab prey before they were able to escape. This gave Tiktaalik a selective advantage allowing him to prevail before other species.
On a more long term scale, Tiktaalik’s shoulder bones allowed him to do push- ups which may have allowed Tiktaalik to bob above shallow waters and breathe air which contains a higher concentration of oxygen than water. The development of mechanisms that would allow animals to breathe air would be a major contributor to their land invasion. This in turn gave terrestrial animals, whom evolved from Tiktaalik, a selectice advantage for they gained access to new food resources while escaping aquatic predators.
Ultimately, Tiktaalik’s shoulder bone, over hundreds of millions of years, would give way to the flexible neck exhibited by humans and many other animals. This shoulder bone allowed Tiktaalik to escape predators, capture prey, and eventually pave the way for many of the land animals seen today.
Sami mentions that Tiktaalik’s head-shoulder joint relationship allowed it to move its head, as opposed to its entire body, in order to catch its prey. But, in order to get close enough to its prey, Tiktaalik had to be ninja-like and evade being seen by its dinner. Shubin describes Tiktaalik’s head to be shaped like the heads found on an alligator or crocodile (26). An alligator or crocodile’s head is shaped the way it is because it allows them to become almost completely immersed with water and still be able to see and breathe. Tiktaalik’s head structure must have served the same exact function: to allow it to sneak around its prey and strike when it was within biting distance. Sami also mentions that Tiktaalik’s flexible head could have been advantageous because it allowed it to escape from its predators with ease, compared to fish with no neck. In order to react to a predator’s presence, Tiktaalik would have needed to spot its predator in the first place.
ReplyDeleteTiktaalik’s shoulder and elbow joints allowed it to do “pushups”. Sami did mention Tiktaalik’s advantage over other “non-shoulder-elbow” fish in terms of its escape in water, but what about on land? Tiktaalik’s shoulders and elbows allowed it to be one of the first, if not the first, animals to ever set feet, in this case fins, on land. If Tiktaalik truly is the first transitional animal between water and land, then there wouldn’t be any other animal inhabiting the land. It was probably one of the first animals that was able to successfully escape predation without the use of physical defense mechanisms, like hard shells etc. “The strategies to succeed…were pretty obvious: get big, get armor, or get out of the water. It looks as if our distant ancestors avoided the fight” (Shubin 41).
Tiktaalik’s flexible head allowed it to look at a much broader angle than a fish’s viewing angle. Looking out for a predator at different angles is very inefficient for an animal that doesn’t have a neck. It would be like trying to watch a ping pong ball zip across the table while keeping your neck rigid! A human would probably barf by the time the game was over! However, for Tiktaalik being on the lookout was a much easier task because its neck allowed it to search for predators without having the shift the position of the rest of its body. This feature could have made migrating over large distances a lot easier in terms of energy conservation. If Tiktaalik wasn’t able to swivel its head horizontally, it would swim in a zigzag-like pattern, but with a relatively flexible neck, Tiktaalik could swim in a straight line while keeping its guard up for predators, which at a mathematical standpoint, is a shorter path than a bunch of zigzags.
Mikey Ling (mikeyling@ymail.com)