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For a homework assignment I received the following question:
Which statement best explains the evolution of fins in whales and fish?
a. The common ancestor of whales and fish possessed genes for fins.
b. Whales and fish possess the same mutations in their genomes.
c. Fins evolved in whales and fish because they both use them to swim in water.
d. Fins evolved in whales and fish because of different mutations that occurred in their genomes.
e. Fins evolved in whales and fish because their most recent common ancestor swam in water.
My answer is (c). Of the given options, it seems most accurate. I feel that the language is unclear as many organisms who do not have fins swim in water. That can be a logic against the option. But, the given answer is (d). That seems too bizarre as even humans and fishes have different mutations in their genomes. (c) seems more appropriate as it can exemplify convergent evolution.
d) is definitely correct.
The crucial element is that whales returned from land to the sea and re-evolved fins.
- a) is incorrect, as the common ancestor may not have had fins. In fact, it is thought it was a sea squirt, a sedentary species without fins, that was the most recent ancestor of fish.
- b) is incorrect, as they may share some mutations but overall they have very different mutations and very different genomes altogether, being fish and mammals;
- c) is incorrect as they have to develop fins first before they can use them;
- d) is correct, as the emphasis in the answer is on
Fins evolved in whales and fish because of different mutations that occurred in their genomes.
Fins in whales have developed from arms and feet. Hence there are different mutations going on, as fish don't have arms and feet.
- e) The common ancestor from fish and whales may have been in the water, but may not have had fins.
I agree with you that the question is ambiguous, and also that the most sensible answer would be C. However, one could make a more or less reasonable argument in favor of several other answers, too.
a. The common ancestor of whales and fish possessed genes for fins.
Technically, this statement is true. At least some of the fins of whales and fish are even distantly homologous, even though the lineages leading to tetrapods (including whales) and to ray-finned fishes diverged quite early in their evolutionary history.
(Specifically, the flippers of whales are modified tetrapod forelimbs, which are homologous to the pectoral fins of ray-finned fishes. Whether one should also consider the tails fins of whales and fish to be homologous is a bit more debatable: the actual fin structures are very different, and presumably share few if any developmental pathways, but the tail and the spinal column which they attach to and are powered by is clearly a shared feature of both groups.)
However, while shared evolutionary history may explain why fish and whales have similarly placed flippers / pectoral fins, and why they both have a flexible spine that supports undulatory swimming with the help of a tail fin, it does not explain the convergent evolution of whales' forelimbs (which were formerly adapted for walking on land) into fin-like flippers. So in that sense, while perhaps partially correct, this answer is also quite incomplete.
b. Whales and fish possess the same mutations in their genomes.
It's hard to even tell what this statement means. Insofar as it's a restatement of the fact that whales and fish share some of their evolutionary history (up to the divergence of the bone-finned and ray-finned fishes), it's no more or less correct than statement A above.
However, I suspect that the intended meaning of this statement is that whales and (ray-finned) fish would've separately evolved the same "fin-making" mutations after their lineages diverges, which is both clearly incorrect and also, even prima facie, statistically very unlikely. So I would rule this one out.
c. Fins evolved in whales and fish because they both use them to swim in water.
This statement is written using teleological language, which some may consider misleading, as it could be misinterpreted as implying that evolution was a directed process: it could be interpreted as saying that whales needed to be able to swim, so they chose to evolve fins (or that some guiding consciousness granted them fins). This is, of course, incorrect - or, at least, we have no scientific evidence of there being any such conscious force guiding evolution, or of any organism (with the arguable exception of humans) being able to deliberately direct their own evolution.
However, it's quite possible to interpret this statement in a way that makes it perfectly correct: as both whales and fish move around by swimming, possessing fins (or something similar to fins) is an advantageous trait for them, and has thus been favored by natural selection. If pressed, I would thus choose this one as the most correct answer out of the given options.
In particular, note that the argument made by AliceD that "they have to develop fins first before they can use them" is not really true: the ancestors of both whales and fish were swimming long before they evolved fins, and thus the selection pressure in favor of having fins (or fin-like structures) was already present before the fins themselves evolved.
In particular, the first aquatic ancestors of whales are believed to have swum much like modern-day otters and seals, using their flipper-like limbs as makeshift fins. While there's no discrete transition point where one could definitely say that whale limbs turned into proper fins, it is clear that the fins, and their direct evolutionary predecessors, were being actively used for swimming, and that this fact directly drove their evolution into the actual fins that modern whales have.
d. Fins evolved in whales and fish because of different mutations that occurred in their genomes.
While technically correct, this statement is so vague that it's all but meaningless. All evolution is driven by mutations, and those mutations, being basically random, are rarely if ever the same in any two lineages.
Certainly, it would be silly to claim that "different mutations occurring in their genomes" is an explanation of why whales and fish evolved fins: humans also constantly have different mutations occurring in our genomes, but we clearly don't seem to be evolving fins. Neither are pigs or bumblebees or sunflowers, even though all of those species (and, of course, all others too) are also constantly experiencing different mutations in their genomes.
Really, this answer reminds me of the story about a person in a car who gets lost and stops to ask a passerby where they are; the passerby, after a moment's thought, replies "you're in your car." While technically correct, that answer is absolutely useless - and so is this one, too.
e. Fins evolved in whales and fish because their most recent common ancestor swam in water.
Again, this answer could be interpreted as basically a restatement of answer A, and thus as being partially correct. However, it completely ignores the convergent selection pressure described in answer C, which is responsible for the more recent evolution of whale flippers into something resembling fish fins more than, say, human hands or the feet of hippopotamuses (currently believed to be the closest living relatives of whales and other cetaceans). Thus, I would not pick this answer, for the same reason that I wouldn't pick answer A.
This was a question on the 2016 Toronto Biology Exam, precisely question 42.
Though the question was asked vaguely, d is the best answer. It's quite obvious that if animals are in water, fins will eventually evolve to improve fitness, that's pretty obvious.
However, if they are both in water, why are their fins different? This touches on the more complex concept of analogous structures; structures that perform similar functions but are anatomically different.
Well, why are they anatomically different? Different mutations in their genomes resulted in those differences.
Therefore, d is the better answer. It does ask which "best" explains.
The making of differences between fins and limbs
'Evo-devo', an interdisciplinary field based on developmental biology, includes studies on the evolutionary processes leading to organ morphologies and functions. One fascinating theme in evo-devo is how fish fins evolved into tetrapod limbs. Studies by many scientists, including geneticists, mathematical biologists, and paleontologists, have led to the idea that fins and limbs are homologous organs now it is the job of developmental biologists to integrate these data into a reliable scenario for the mechanism of fin-to-limb evolution. Here, we describe the fin-to-limb transition based on key recent developmental studies from various research fields that describe mechanisms that may underlie the development of fins, limb-like fins, and limbs.
© 2012 The Authors. Journal of Anatomy © 2012 Anatomical Society.
Skeletal domains (patterns) in fins…
Skeletal domains (patterns) in fins and limbs. The proximal end of the appendages…
Model for diversification of the…
Model for diversification of the appendage skeleton: relationship between the AP width of…
Proportion, location, and orientation of…
Proportion, location, and orientation of the pectoral fin bud in zebrafish. (A–D) Developmental…
The repression mode of the…
The repression mode of the AF. Morphological differences among fins, limb-like fins, and…
What are Agnathans?
Agnathans refer to jawless fish or craniates. They are vertebrates. But, unlike other types of fish, they lack paired lateral appendages or fins in their anatomical structure. Most agnathans are extinct however, two main groups still exist. They are hagfish and lampreys. The very early agnathans are ostracoderm. They also do not consist of bones in their scales.
Figure 01: Agnathans
Hagfish, in general, belongs to a clade known as Myxini. There are about 20 identified species of hagfish. They are eel-like fish that live in the deep seabed. Also, these are mostly found in polar regions. Moreover, these species show special adaptations, such as the ability to move in a twisting fashion and escape from the grip of predators. They also possess a cartilaginous skull and are also called the clade craniate.
Meanwhile, the lampreys belong to the clade Petromyzontidae. There are approximately 30 – 40 species of lampreys. They also lack paired appendages. However, they possess a preliminary vertebral column in comparison to that of hagfishes.
The waters surrounding Victoria are an exciting place to go whale watching because there are so many different types of wildlife that call this region home. People from around the world flock to this area, excited to have an opportunity to see the greatest predator in the world’s oceans- the killer whale!
Photo Credit: Rachael Merrett (Orca Spirit Adventures)
It often comes as a surprise to many people that there are actually different types of killer whales that inhabit the world’s oceans and two types frequently spend time in the Salish Sea around Victoria. These different kinds of killer whales are called ecotypes and they differ in many aspects including the types of foods they eat, their social structures, languages, behaviors, home ranges and even in the way that they look. Around Victoria, the two different ecotypes of killer whales that you may see on a whale watching tour are known as the Southern Residents and the Transients or Bigg’s killer whales.
Each population is genetically unique and they do not mate with one another. In fact, genetic evidence has revealed that the Transient and Resident orca populations have not shared a common ancestor for at least 750,000 years! Killer whales are the only known species to have genetically segregated populations due to social and cultural differences and not because they are separated by a geographical barrier. In fact, Resident and Transient orcas can be seen in relative close proximity but they will never engage in social interactions.
Figure 1: (a) Southern Resident killer whale population range and identified critical habitat areas (b) Transient killer whale population range. Graphics Credit: Vancouver Aquarium Marine Mammal Research Program
Different diets are a major distinguishing characteristic between the two types of orcas found off the southwest coast of Vancouver Island. Southern Residents eat fish and a small amount of squid. They are selective however with salmon and in particular Chinook, making up about 90% of their diet. Specializing on Chinook makes sense when one considers that they are the largest and fattiest of the salmon species- the orcas get the best “bang for their buck” by eating Chinook.
Transient or Bigg’s killer whales, on the other hand, are the mammal hunters. They have evolved to be excellent predators of seals, porpoises, sea lions, dolphins and even other species of whales. Different killer whale populations have evolved to be expert predators on different types of prey, which reduces competition between the populations and allows them to utilize the various species of prey that their environment provides.
Fish-eating Resident Orcas Mammal-eating Transient (Bigg’s) Orcas
Southern Residents are a small population divided into three pods known as J,K and L. These pods are made up of multiple related matrilines that are more closely related to each other than they are to matrilines of the other pods. All the pods socialize with each other and mating occurs between the pods. When you are born into a Resident pod, you will remain with your mother and extended family for the rest of your life whether you are male or female. This creates large family units and very tight bonds between members.
Figure 2: An example of matrilines within the Southern Resident population’s K-pod. Photo credit: Center for Whale Research Southern Resident Killer Whale ID Guide 2014.
The social structure of transient orcas is a bit looser than that of their fish-eating cousins. Because Transients hunt mammals who have keen senses to detect their predators, they can’t travel around in huge groups because their prey would easily detect them. Instead, they travel in matrilines- a female and her offspring. If the family unit becomes too big and their hunting success starts to decrease, adult daughters and any offspring they may have to tend to split off first. If there are no adult daughters, then the oldest son in the group will part ways from the family unit, but males tend to try to remain close to their mothers for life.
Figure 3: An example of matrilines within the Transient killer whale population. Source: Photo-identification Catalogue of Bigg’s (Transient) Killer Whales From Coastal Waters of British Columbia, Northern Washington, and Southern Alaska. 2012.
Resident and transient killer whales do look slightly different from each other, but it takes a trained eye to pick out the differences quickly. Marine naturalists and scientists are often able to identify which ecotype they are watching within a few minutes of spotting the orcas. Transient killer whales are slightly longer and heavier than Resident killer whales, but this is hard to identify on the water. What is more obvious is the tendency for Transient orcas to have a sharply pointed tip to their dorsal fin whereas Residents have a more rounded tip to theirs.
All killer whales have what is called a saddle patch on their back, which is a greyish-white area just behind and extending below their dorsal fin. The saddle patches of Transient orcas are always solid or closed whereas the Residents can have either a closed saddle patch or one that has some sort of black shape in it, which is called an open saddle patch. The unique shapes of their dorsal fins and saddle patches are the characteristics used to identify individual orcas all over the world. Making identification more challenging is the fact that the saddle patch is not necessarily a mirror image of itself on either side of an orca’s back and can actually be quite different from one side to the other. You need to memorize two saddle patches per whale to become an expert at identifying the whales!
Figure 3: (a) Female Transient orca T11 with a pointed tip to her dorsal fin, large nicks from battles with prey, and a solid or closed saddle patch. (b) Female Resident orca K-20 or Spock, showing a rounded tip to her dorsal fin and a large opening in her saddle patch. Photo Credit: Rachael Merrett (Orca Spirit Adventures)
Another very important distinction between the mammal hunters and the fish eaters is their vocalizations. Every population of killer whales has its own distinct set of calls that are not used or understood by other populations of orcas. The three pods of the of the Southern Resident community all speak the same language, but each pod has its own unique dialect of that language. Some calls are unique to each pod and even to each matriline. Calls are learned and passed down from one generation to the next.
Transient orcas along the entire coast of British Columbia all use a distinctive set of calls, with some additional calls that can be specific to a region. The vocalizations of the different populations of killer whales are very distinct and can be used to identify which orcas and even which matrilines are present in a given area. Have a listen!
Southern Resident Orca Vocalizations
Transient (Bigg’s) Orca Vocalizations
As we spend more and more time with the different ecotypes of killer whales, we expand our knowledge and understanding of their differences. Orcas are dynamic, intelligent creatures who have evolved over millennia, developing socially and ecologically diverse populations. We continue to learn from them and our fascination with their lives and families grows every day.
Unit 2: Cetaceans
Whales and dolphins are members of the kingdom Animalia, phylum Chordata, and class Mammalia. That means that whales and dolphins are mammals, not fish. They give birth to their young rather than lay eggs. They nurse their young through mammary glands, and they give extensive parental care to their offspring. Collectively, we place all of the 80-90 whales and dolphins in the order cetacean. Cetus from the Latin meaning whale. Cetaceans are generally placed into two distinct sub-orders the Mysticeti (whales with baleen) and Odontoceti (toothed whales.)
The Evolution of Whales
The fossil record of Whales and dolphins shows us that they are decedents of land based mammals. Although they have been extremely successful, whales have a lot of features that are not ideally suited for life in the ocean. To start with, whales and dolphins breathe air, limiting them to life at the surface. They are warm blooded and most species struggle to maintain high body temperatures. They have a spine and pelvis that moves up and down like other mammals, rather than the side to side movement of fish. The bone structure of their fins matches that of hoofed land mammals rather than fish. They nurse their young with milk and most species have hair or fur. Additionally, many whales have residual leg bones that are no longer attached to their pelvis.
Fossilized bones from the Valley of the Whales in Egypt. Image from Wikipedia Commons
A great diversity of whale and whale ancestor fossils tell a compelling evolutionary story of the movement from land to water. Ancient whale ancestors most likely moved into the water to take advantage of abundant food resources and gradually over time evolved into highly successful modern whales. Watch a video clip from PBS Evolution to learn more about whale evolution.
The embryological development of whales living in the present also tells a story of their evolutionary history. In many embryonic whales, external hind limb buds are visible for a time but then disappear as the whale grows larger. Some whale embryos will develop hair and rudimentary ear pinnae, which disappear before birth. In some whale species developing embryos start off with nostrils in the front of their head like land mammals, only to have these migrate backwards to the blow hole position as the embryonic whale continues to develop.
Mysticeti (Baleen Whales)
Description: Mysticeti are the largest living animals that have ever existed on Earth. They are larger than elephants, and some even larger than the largest of the dinosaurs. Blue Whales, the largest whale species on Earth, have an average adult length of 80 feet (24 meters) and have been measured to 98 feet (30 meters). It is impossible to weigh such an animal, but estimates have put the large ones near 190 metric tons. What gets lost in that size is how long and sleek these animals are. Blue whales are also some of the fastest swimming animals in the ocean, reaching 50 kilometers per hour for short distances. All baleen whales have large convex skulls with attached baleen plates hanging down from the maxilla of their skull. Baleen whales also have a large double nostril blow hole on the top of their head through which they breath.
Gray whales use about 300 baleen plates attached to the roof of their mouth to strain food from water and sediment. Compared to other baleen whales, gray whale baleen is quite short, ranging from about five to 25 centimeters in length. Image from: Haikai Magazine, Photo by Christopher Swann/Minden Pictures
Feeding: Aside from their size, the mysticeti’s most distinctive feature is the baleen plates that hang down from their top jawbone. Whales use these baleen plates to filter out food items such as small fish, krill, and plankton from immense quantities of water. It may seem strange that the largest animals on earth would feed on organisms that are frequently less than an inch long, but from an ecological perspective it makes perfect sense. Krill, copepods, and other types of plankton are some of the most abundant (by weight) forms of life on Earth.
All baleen whales are filter feeders, but different whales use a variety of different strategies for capturing food. Some whales, such as bowhead whales and right whales, have exceptionally long baleen. They will skim the surface of the water with mouths agape, gathering small phytoplankton in their mouths. (YouTube Clip) Some whales, such as blue and fin whales, will swim quickly into schools of prey, gulping up huge schools of prey at a time and filtering out the water as they close their very large mouths. (YouTube Clip) Gray whales, who have very short and stiff baleen, feed by scraping the side of their heads along the bottom, sucking up mouthfuls of sediment and filtering out the crustaceans living in the mud. Humpback whales have some of the most interesting feeding style of all. They will often feed in small groups producing nets of bubbles to entrap schools of fish. (YouTube Clip)
Unlike other baleen whales, gray whales feed on bottom-dwelling organisms by suctioning sediments and filtering out worms and crustaceans. Picture by Flip Nicklin, image found at The Smithsonian Insider.
Life Cycles: The life cycle of most baleen whales includes late reproductive maturity, long gestational periods, and calves every 3-4 years. Baleen whale mothers will nurse their calves for up to two years. Most species of baleen whales make great migrations with calving often taking place in calm shallow and protected waters. Most baleen whales feed in the colder and more nutrient rich waters of the higher latitudes. Baleen whales are generally considered less social than their gregarious cousins the tooth whales, but they will form small feeding or mating groups. Baleen whales have a variety of courtship styles they are can be highly competitive, often elaborate, and sometimes aggressive. Male humpbacks, the most unique in this regard, participate in an annual “sing off” to attract potential female mates.
Behavior: Observing whales can be an exciting experience. This is despite the fact that they spend much of their time underwater. Several obvious behaviors can be observed when whale watching. Whales will often stick their heads out of the water to look around in a move called spy hopping. Sometimes they throw themselves completely out of the water in a move called breaching. Whales may also slap their fins or flukes (tails) to make sounds that can be heard for great distances.
Odonticeti (Toothed Whales)
Pacific White Sided Dolphin, Image from wikipedia
Description: With the noted exception of the sperm whale, the toothed whales are smaller than the baleen whales. They have highly developed brains and are aggressive predators. Toothed whales have concave skulls with a large bulbous organ called a melon, which they use to focus sound.
Behavior: Toothed whales are defined by their social groups that are typically large extended families led by a matriarchal head. Males, especially male sperm whales, are more likely to be isolated into bachelor groups.” Smaller groups will often come together to form larger “super pods” for the purpose of mate selection. Dolphins and toothed whales give the appearance of being highly playful, putting on frequent aerial and acrobatic displays. Dolphins are often observed riding the waves, pushed by the front of boats in a behavior called bow riding or even surfing.
Feeding: As in all things, toothed whales feed in groups. Often, working collectively as unit, they are highly adapted hunters. Dolphins have been observed to successfully corral fish into shallow areas where they are easy to eat. Even more remarkably, killer whales will sometimes beach themselves onto shallow beaches when going after pinnipeds or penguins. Toothed whales make extensive use of echolocation to locate, and in some cases can use sound to disable or “stun” their prey. Sperm whales, in particular, have a large arsenal of sounds to locate and disable their prey. Their skills at hunting are so well adapted that large schools of tuna will often follow below pods of dolphins, taking advantage of the dolphins ability to locate prey through echolocation. Some groups of toothed whales are migratory, and others prefer to stay in local habitats. Toothed whales will often dive to great depths in the search for prey (particularly squid). Most notably, sperm whales can dive to depths of three kilometers and stay down for over an hour.
Questions to Research
Use the reading above and slide deck for this unit to help you answer these questions.
What is the difference between the evolution of fins in whales and fish? - Biology
Isn't it strange that there is a group of air-breathing mammals that lives in an environment that may result in them suffocating? Other than humans in space, the only other creatures that chose to leave their comfort zones are cetaceans (whales and porpoises).
The explanation for humans is simple: adventure and/or stupidity. But what about whales?
Comparative Anatomy is the study of the similarities and differences in the anatomy of difference species. It has long served as one of the main evidences for evolution, due to the fact that it is very concrete, and does not require extensive technology.
Scientists will go more in depth than just looking at the outer appearences of organisms. Many times, scientists use bones to determine similarities and differences in comparative anatomy. There are two types of structures you will now research. These have both been used to determine whale evolution.
The first are Homologous Structures. These are parts of the body in organisms that have similar structure to other organsisms' comparative parts. One example of this is the bone structure in limbs of different mammals, shown below.
How often do creatures evolve to leave one environment for another? Are there other examples?
How and why did the pelvic bone and hind legs of whales detached itself from its spine? What are the evolutionary advantages of it?
Why did cetaceans adapt for a fully aquatic environment, while ancient semi-aquatic animals such as crocodiles and alligators remain unchanged?
Paleoanthropology and Comparative Anatomy , from the University College London's Anthropology department.
Why did whales evolve horizontal tailfins instead of vertical like fish?
Iɽ like to know the purported nuances behind this question, whether it was pure chance or if there was an initial seeded cost reduction for them to evolve into an aquatic niche by doing it this way. Or if there was a real advantage to having horizontal tail fins for exceedingly large marine animals.
Because mammal spines are built to flex horizontally, unlike fish spines, which flex laterally. This allows mammals more mobility, because a horizontally bending spine assists with running on 4 legs. When the ancestors of whales returned to the water, they used horizontal movements because those generated greater amounts of force, since the muscles and skeletal structure were already arranged that way. And thats why tailflukes are horizontal: the fluke is arranged orthogonally to the main force propelling the body because that gives it the most resistance. If you look at other marine mammals like seals and manatees it's a similar story.
Came here to post this. Watch the way a dog or a cheetah runs!
Precisely. If you look at ichthyosaurs, they are arranged like fish because early reptiles still bend the body side to side like fish. On the whales, simply bend your own back to see which way you are stronger side to side or front to back. We are definitely stronger bending forwards.
So now that that is cleared up: are there any other benefits to either orientation that we know of?
So when did mammal spines go from horizontal to lateral?
On the otherside seals turtles frogs and penguin don’t have tall or flat tailfins because they use a more oar-like propulsion to swim
So whales' locomotion is more like twerking than Milk shaking.
I guess because they evolved from creatures with hind legs. If you put your legs together, you can only move them up and down, so a horizontal fin added to the end would boost your movement more.
Fish, on the other hand, don't really have that problem and move by moving their spine side to side, hence a vertical tailfin.
I'm trying to figure out if you think the whales tail is due to their legs being fused. Their tail is an extension of their spine like every tail. Whales have remnants of their leg bones in their bodies, but it is not in their tail.
Mammals vertebrae are more rigid than fish to stabilize better while walking (also we have a box like rib cage and are the only one that have diaphragm) Despite being an marine animal, whales inherited this trait and ondulate vertically while locomoting like a horse galloping rather than laterally like a fish swimming ir a lizard crawling. We can observe that while salamanders, snakes, crocs and lizards are swimming they kind of imitate fish, some extinct marine reptile like ictiosaurs also evolved vertical fishlike fins by swimming this way. But aquatic mammals, descendants of upright legs animais, moves more simillary to it’s terrestrial counterparts. Not only this happens to whales but also to manatees, otters and beavers with their flat rather than tall tails.
I figured the undulation seeded the fitness that would force adaptive developement in that direction to begin with.
I read somewhere that for equal body size with other aquatic vertebra, whales are in fact worse swimmers (take Dolphin vs Swordfish/shark/Tuna) apples-to apples-to their vertical tailbone counterparts, perhaps having something to do with their suboptimal motility. But also offset this disadvantage by the fact that their warm blooded metabolism helps them keep up for burst and sustain.
For the same reason you flap your legs up and down not side to side when doing butterfly stroke.
There’s a section in Jerry Coyne’s book, Why Evolution is True, that talks about Whale evolution. Quite interesting.
because they hadvlegs at one point. Try moving your hips any legs together up and down and then side to side and see what feels better.
Whales are mammals evolved from previously land dwelling mammals. Dinosaurs and mammals have a more upright posture with their legs beneath them so as they walk they flex in the forward and backward direction instead of side to side. The ancestral state was a side to side motion still seen in lizards, amphibians, and fish.
Because whale ancestors flexed in an up and down or forward and backward direction already they retained it when they lost their legs and their tail followed the same motion as the rest of their body.
The short answer is that whales are mammals, fish are not. They move differently because of that. Both methods work so there’s no reason to change this because they stopped having legs. Snakes still move side to side without legs because that’s how lizards move never developing the more upright posture. With legs a more upright posture helps with speed.
I don’t have a clue about an actual answer, but I wanna guess. I’m hoping some whale biologist will come along and tell how wrong our right I am.
I bet there probably isn’t too big a difference efficiency while completely submerged. Where I think the difference comes in is that whales, like dolphins, sea lions, seals all have horizontal tails because they all need to break surface to breathe. In addition, I’m pretty sure all water mammal ancestors were land walkers. Mammals have their rear appendages arranged horizontal to one another, so it would make sense that as the legs shortened and became more fin like that the fins would be horizontal. I think the fact that they breathe air also encouraged the fins to remain horizontal because it would be easier for the water mammal ancestors to angle the fins to go up. I’m sure their incredible ability to hold their breaths took some time to evolve and in that time their ancestors would need every advantage to stay under longer and break the surface faster and cheaper.
Here’s to Hoping an expert will come sort me out.
It may come as a surprise to learn that the toothed whales include all species of dolphins and porpoises. In fact, 32 species of dolphins and 6 species of porpoises are toothed whales. Orcas, sometimes called killer whales, are actually the world's largest dolphins. While whales are larger than dolphins, dolphins are large (and more talkative) than porpoises.
Some toothed whales are freshwater animals these include six species of river dolphins. River dolphins are freshwater mammals with long snouts and small eyes, which live in rivers in Asia and South America. Like baleen whales, many species of toothed whales are endangered.
- Are generally smaller than baleen whales, although there are some exceptions (e.g., the sperm whale and Baird's beaked whale).
- Are active predators and have teeth that they use to catch their prey and swallow it whole. The prey varies depending on species but can include fish, seals, sea lions or even other whales.
- Have a much stronger social structure than baleen whales, often gathering in pods with a stable social structure.
- Have one blowhole on top of their head.
- Unlike baleen whales, males of toothed whales species are usually larger than females.
Examples of toothed whales include the beluga whale, bottlenose dolphin, and common dolphin.
The evolution of whales
In Moby Dick, Herman Melville has his protagonist enumerate the reasons why scientists believe that whales are mammals, but then, with bold eloquence, he exclaims: “Be it known that, waving all argument, I take the good old fashioned ground that the whale is a fish, and call upon holy Jonah to back me.”
That American classic was written in 1851, eight years before the publication of another classic that shook the intellectual world of its time: The Origin of Species. In it, Charles Darwin proposed that all species were descended from other species and eventually had one common ancestor. With whales being mammals, and mammalian ancestors being land animals, whale ancestors must have lived on land too. Even Darwin struggled with that concept, he proposed, in the first edition of his book, that whales might have evolved from ancestors that waded in rivers catching insects. This brought ridicule from his readers, and the statement was shortened in subsequent editions until whale origins was banished altogether in the last edition published during his life.
Indeed, the land ancestry of whales remained a thorny issue for the scientists, as all fossil whales, throughout the 19th and much of the 20th century showed the fully aquatic features of animals that could not survive on land. Where were those land ancestors, or the intermediates to life in water, creationists demanded and they made fun of the idea that whales were somehow related to cows and their even-toed relatives, calling the idea an "udder" failure.
That all changed in the 1990s and 2000s, when a remarkable series of fossils was discovered: intermediate animals showing a mix of land and water features water ancestral to all modern cetaceans (whales, dolphins, porpoises). The relevant fossil record went from non-existent to excellent, and confirmed the molecular biologists’ finding that the closest relatives of cetaceans were indeed the artiodactyls (even-toed ungulates including cattle, deer, pigs, hippos, camels, and giraffe).
Now, so many fossils have been found that it became possible to study evolutionary changes in great detail, allowing an unprecedented understanding of land adaptations evolving into water adaptations. Such evolutionary changes occurred throughout the body. The limbs lost their function in body support, but now had to work as locomotor organs in the new, dense medium. The ears had to change, since sound in water is very different from sound in air. The nose shifted back onto the forehead, to make breathing while submerged easier. The kidneys also changed, since freshwater is not available to drink in ocean living mammals. And all of those changes, and many others, accumulated in short succession. In eight million years, cetacean ancestors went from land mammals to obligate marine swimmers. This early phase in cetacean evolution was characterized by great experimentation. There were crocodile-like whales, otter-like whales, and seal-like whales, and all these body plans were tested and then went extinct, until, in the end, only one body type was left. This is the same body type present in all roughly 90 modern species of cetaceans: a streamlined body with no neck, ending in a horizontally placed triangular fluke, lacking external hind limbs and with paddle shaped forelimbs, with a skin that is mostly devoid of hair, and a nose opening that forms the blowhole on the forehead. However, the traces of the ancestral land mammal ancestors are still retained in cetacean embryos, which have a distinct neck, with a long and narrow tail instead of a fluke, and with hind limbs that protrude from the body. Hairs are common on the faces of small fetuses, and the nasal opening is at the tip of the nose.
With the new fossils and DNA data, molecular biologists were also able to solve Darwin’s vexing problem of what whales are related to. The DNA evidence points to one particular artiodactyl as the closest relative to whales: the hippopotamus. However, the last common ancestor of hippos and whales goes back some 50 million years, and it did not look at all like a hippo or a whale. Fossil evidence indicates that a nimble, deer-like mammal called Indohyus is even more closely related to whales. It is possible that both cetaceans and hippos are derived from Indohyus or a similar species. Indohyus lived near the northern edge of the Indian subcontinent at a time when the Himalayas were just forming, and the Tethys Sea separated the Indian and Asian land masses. It is here that cetaceans originated.
Indoyus was the size of a cat, but proportionally more similar to a deer without antlers. In looks, Indohyus may have been similar to the modern mouse deer of Africa and Southeast Asia. Mouse deer eat fruits and leaves on the forest floor, and like to live near small streams. When they perceive danger, they jump into the water, hiding fully submerged. It is possible that Indohyus lived similarly, and that predator avoidance was the first aquatic behavior displayed by the ancestors of cetaceans. From the chemistry of the teeth, it is clear that Indohyus was a plant eater, and its dense bones suggest that they functioned as ballast, allowing the animal to stay submerged. Aged individuals have teeth that are worn down with use, and that tooth wear is different from that of related plant-eaters. In fact, the tooth wear looks more similar to that of the meat-eating early whales. This is a puzzle that is not solved and maybe Indohyus ate a kind of plant food that required processing by teeth similar to meat. That feature may have helped it as its descendants became meat-eating whales.
The next step on the evolutionary ladder are the first cetaceans, pakicetids. Like Indohyus, pakicetids are only known from Pakistan and India. Even though they are the first whales, they looked nothing like modern whales. Instead, they were more similar to a large dog or wolf. Their fossils are only ever found in rocks that formed in shallow streams, never in the ocean, and it is likely that pakicetids were waders or bottom walkers in these streams. Their dentition indicates that they are meat eaters, and their eyes and ears are located high on the skull, a feature often associated with animals that have a submerged body, but are interested in things that happen out of the water, such as crocodiles spying for terrestrial prey. It is indeed thought that pakicetids were ambush predators, preying on land animals coming to the water to drink, or maybe catching fish trapped in shallow water.
Around 48 million years ago, cetaceans moved toward the ocean. The first known species to do this is Ambulocetus natans. Ambulocetus is known from Pakistan, and only one complete skeleton has ever been discovered. It resembles crocodiles even more than pakicetids, while pakicetids had long limbs that could raise it up on land, Ambulocetus was more sprawling. Ambulocetus’ limbs are short, the tail powerful and the snout long. In spite of the short limbs, the feet are large, and they were probably the organ that these animals swam with. Even though there is an abundance of marine shells associated with the rocks that Ambulocetus is found in, it is also clear that there was freshwater nearby. Ambulocetus was possibly coastal, still taking advantage of thirsty prey coming to drink, but also venturing out in lagoons and the surf.
Following pakicetids and Ambulocetus in time as well as on the evolutionary branches leading to modern cetaceans are remingtonocetids, again a family known only from Pakistan and India. The trend toward more aquatic life continues, the limbs are shorter than in the earlier whales, and the tail is long and powerful. The shape of the vertebrae indicates that remingtonocetids do not have a fluke, but the tail vertebrae are somewhat flattened, suggesting that the tail was flat in the horizontal plane. It is likely that they swung this tail through the water in an up-down movement, which is of course the movement that the modern cetaceans make to propel themselves with their triangular fluke. Some other features are also indicative of more aquatic life. The eyes of remingtonocetids are small, suggesting that they were less important in catching prey, and indeed, the rocks that these fossils are found in indicate that many remingtonocetids lived in swamps with muddy water. The placement of the eyes is also unusual. Instead of being located on the top of the head, to see outside the water, remingtonocetid eyes are placed on the side of the head, consistent with hunting aquatic prey. The part of the skull that houses the remingtonocetid ear is large, suggesting that they had excellent hearing. It is likely that remingtonocetids used their ears in prey detection, a feature in common with modern toothed whales.
Protocetid cetaceans lived at the same time as remingtonocetids, but in somewhat different habitats. In addition to South Asia, protocetids also conquered the oceans, and have been found in continents from Africa to South and North America. Unlike the earlier families, this implies that protocetids were able to cross large stretches of water and were thus good swimmers. They are a diverse group, with much morphological diversity. It is clear that some protocetids had a tail similar to that of ambulocetids and remingtonocetids, and it is also possible that some already had a fluke.
Unlike remingtonocetids, protocetids are found in localities that indicate open, clear water, and they had big eyes. Protocetids are also the first whales in which the nasal opening is not near the tip of the snout, it has shifted higher up on the skull, although it is not a blowhole like it is in modern cetaceans. They still had powerful fore- and hind limbs allowing them to come ashore and get around on land, and possibly hauled out for functions related to reproduction, similar to modern sea lions. They may have been the first cetacean pursuit predators in open water.
The first fully aquatic cetaceans, and the group from which all modern cetaceans are derived, are the basilosaurids. Just like protocetids, basilosaurids are distributed widely across the world. Basilosaurids have the familiar attributes of modern cetaceans, they are streamlined, they have a fluke, and their forelimb is a paddle. Unlike modern whales, basilosaurids did have external hind limbs, but these were so small that they could not bear the animal’s weight, and their function, if any, is unclear. Some basilosaurids looked like a dolphin, and it is likely that their lifestyle resembled that of dolphins.
The entire evolutionary sequence, from little Indohyus diving into streams, to modern cetacean-like basilosaurids took about 8 million years. Evolution designed new forms, tried them out, and discarded most of them, until at the end only the modern cetacean body plan remained. It is mind-boggling to think that all the different organs – limbs, ears, nose – had to change all at the same time, and one wonders how the genome changes needed to enable the morphological changes accumulated.
With such a complete fossil record, a rich diversity of modern whales and their embryos, and the powerful new molecular techniques, it may be possible to approach that question. Could it be that some changes in the genome affected several disparate organ systems simultaneously, in fact creating an evolutionary shortcut that created novel morphologies at a high rate? This is an exciting concept. If we are able to identify some genes that are engaged in the development of multiple organ systems and that show consistent differences between cetaceans and other mammals, we may have identified the fingerprints of the process of cetacean origins.
J. G. M. ‘Hans’ Thewissen is the Ingalls Brown Professor of Anatomy at Northeast Ohio Medical University. He is the author of The Walking Whales: From Land to Water in Eight Million Years.
Whale, dolphin blowholes developed differently, research reveals
April 28 (UPI) -- All whales have blowholes, but not all of them evolved them the same way -- according to a new study, the two major forms of cetaceans turned their noses into blowholes in different ways.
Cetaceans, the group of marine mammals that includes whales and dolphins, evolved from land mammals. The earliest cetaceans had noses a lot like their land-based relatives, but at some point, the forward-pointing nose became an upward-facing blowhole.
Often, scientists trying to understand the evolutionary origins of a distinct anatomical feature focus on fossils. For the latest study, presented this week in the Experimental Biology meeting, scientists observed the development of spotted dolphin and fin whale embryos and fetuses.
During embryonic and fetal development, researchers watched as the nasal passage initially formed like a nose before migrating back to its position atop the body, where blowholes are found.
"The main difference is in which other parts of the skull change orientation in relation to the nasal passage," study lead author Rachel Roston told UPI in an email.
Scientists were surprised to find the development of the blowhole during embryonic and fetal development followed two distinct patterns.
"In dolphins, which are toothed whales, odontocetes, those changes occur in the middle of the skull. But, in fin whales, which are baleen whales, mysticetes, we did not see the same changes the middle of the skull as the dolphins," said Roston, a postdoctoral fellow at the University of Washington.
Instead, the anatomical transformation in fin whales involves the rear of the skull, at the nexus of the neck and vertebral column.
"Other closely-related species seem to follow each pattern," Roston said. "So, it seems there are at least two ways to reorient the nasal passage into a blowhole during development, one in toothed whales and another in baleen whales."
Because most previous studies have focused on the shapes and structures of whale blowholes, Roston and her colleagues wanted to look at how the nasal passage relates to the other parts of the head and body.
The differences in the way the nasal passage reorients itself during prenatal development may help explain the functional difference in the blowholes of toothed and baleen whales.
"Baleen whales use their nasal passages for breathing, and toothed whales use their nasal passages for both breathing and echolocation," Roston said.
"So, the differences in development that we've identified are accompanied by many other interesting functional and anatomical differences in the two groups," Roston said.
As so often happens, researchers said their findings have raised more new questions about blowhole evolution than they have answered.
"It will be interesting to see how these developmental differences relate to other differences in blowhole and head anatomy among fossil and living cetaceans," Roston said.
"Likewise, it will be interesting to see how these discoveries in cetacean development reshape how we think about skull and head development and evolution in other mammals," she said.