Prehistoric Sharks

Falcatus lived in the Carboniferous period, around 325 Million Years Ago ("MYA"). It was probably piscivorous (meaning it ate fish), and lived in deeper waters, which is why it has such large eyes. The most obvious feature of this shark was its long, forward pointed spine. However, specimens of Falcatus can be found without this spine, and it does not appear to have any specific purpose.

So what could it be? Well, since it is found on only some specimens, scientists have concluded that the spine was for mating purposes, most likely as a display. This is a great example of sexual dimorphism, common among many animals today.

Edestus lived in the late Carboniferous. It was related to Helicoprion, and had strange, outward curving tooth whorls that looked like a giant pair of scissors. It probably ate soft bodied animals, and attacked using a vertical thrashing strike.

Hybodus lived throughout the mesozoic era, approximately 260 to 66 MYA. Unlike some of the previous animals, these were generalists. They had two different types of teeth: sharp teeth for grasping prey, and rounded teeth, which could crush hard shells. They most likely ate whatever they could find, and that is probably why they lived for so long. Another adaptation that helped them to survive was long spines on their dorsal fins. These were probably used for defense.

Squalicorax lived during the late Cretaceous period (approximately 105 to 65 MYA). This shark looks a lot likee a modern shark. Its teeth were definately those of a predator, and we also find its teeth in fossils of other animals, includinng turtles, Mosasaurs, and even Hadrosaurs (duck billed dinosaurs)!

And now we get to Megalodon. Megalodon lived from the early Miocene to the late Pliocene (approximately 23 to 2.6 MYA), making it the most recent of these sharks to swim the seas. it was a massive predator, reaching about sixty feet in length. It would have eaten mainly small whales, which were common in the southern oceans at the time. Scientists believe that the whales began to adapt to northern climates and migrated, but megalodon could not adapt to follow their major food source, which likely explains its extinction.

Here is my attempt to estimate Megalodon's size:

And here is my measurement, which shows I was a bit off in my estimate:

I used a 120 inch, or ten foot, tape measure, and marked off each 10 foot distance with chalk.

This is a lifesize 3D model of a megalodon tooth. I created it with Tinkercad software.

It is 18 cm long (approximately 7 inches), which is about as big as they come.

And this is a fossil megalodon tooth that my mom gave me:

Chordate Evolution

My assignment was to "[c]reate a project that shows the evolutionary developments that helped to lead to true vertebrates in the following animals. Begin with the most primitive, and work your way up to the most advanced.

Amphioxus

Hagfish

Hemichordates

Lampreys

Tunicates"

Hemichordates came first, and they had two of the distinguishing features of chordates: gill slits and a dorsal nerve cord. (They also had a ventral nerve cord.)

Next came the Tunicates, or at least their larvae. They have the dorsal nerve cord and pharyngeal gill slits, like their predecessors, but they also have something new: the notochord. Thus, they have three of the four distinguishing chordate characteristics. However, most of these features are lost when they become adults, leaving only the gill slits behind.

Amphioxus was the first organism to have all four chordate features as an adult. The fourth chordate feature is a post-anal tail.

The hagfish was the first agnathan, and just barely scrapes across the boundary to vertebrates. Though more advanced than amphioxus, its spine (derived from the notochord) was a single cartilaginous rod, and it has no jaw.

The next step was the Lamprey. It had all the chordate features, plus fins, and individual vetebrae.( It still no jaw, though.)

Marine Invertebrate Safari

These photos are mostly from a recent family trip to the Georgia Aquarium. My mom took lots more photos of the whale sharks, skates and rays than of marine invertebrates, though, so a couple of pictures are from an earlier trip to the New York Aquarium.

My assignment was to do a photo safari of marine invertebrates, and identify their phylum and what features identify them as belonging to that phylum. I was supposed to identify them down to class or order if I could, and create a cladogram showing their evolutionary relationships.

In this first photo, we have two different creatures. First, there's a Sea Star, of the Phylum Echinodermata, Class Asteroidea. You can tell this by its pentaradial symmetry, its spiny skin, and by the thick attachments of its arms to the central disk. There is also an anemone in this photo, Phylum Cnidaria, Class Anthozoa. It has the radial symmetry and tentacles of a cnidarian, but it is sessile as an adult and has a polyp body form.

This second photo of anemones is of the bubbe tip anemone Entacmaea quadricolor of the phylum Cnidaria, Class Anthozoa.

This is some sort of clam, in the Phylum Mollusca, Class Bivalvia. It has two shells.

Here is a table coral. It is a Cnidarian (phylum), Anthozoan (Class), Sclereactinian (Order) coral. I know this since it is part of a larger reef structure, which are made by scleractinians.

This is a moon jelly, Aurelia aurita. Because it has radial symmetry, and tentacles with stinging cells, it must be a cnidarian. And due to its round bell with tentacles all along the rim, it has to be a member of class Scyphozoa, i.e., a true jellyfish.

Pictured here is a Japanese sea nettle, Chrysaora pacifica. It is also a Cnidarian, and a Scyphozoan, for the same reasons as above.

This is a Japanese Spider Crab, scientific name Macrocheira kaempferi, of the Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, and the Order Crustacea. I can tell that it is an arthropod based off its jointed legs, and that it is a decapod because it has ten legs.

This is a Nautiloid. It is from Phylum Mollusca, Class Cephalopoda. This is evident by its soft body with multiple tentacles, and its siphon for jet propulsion, as well as the fact that it has a shell.

This is a sea fan, a soft coral, from phylum Cnidaria, Class Anthozoa, Subclass Octocorallia.

It has a sessile polyp body form as an adult, lacks tentacles or an osculum, spongeocoel, or ostia, so it isn't an anemone or a poriferan, and must be a coral. It does not have a hard calcium carbonate skeleton, so it is a soft coral.

This is a sea urchin, of the Phylum Echinodermata and the Class Echinoidea. I can tell this because of the spiny skin, and the Aristotle's Lantern that is clearly visible.

This is a white striped cleaner shrimp, Lysmata ambonensis. Phylum Arthropoda, Subphylum Crustacea, Class Decapoda, which I know because of its ten, jointed limbs and hard carapace/exoskeleton.

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This is a sea snail, of Phylum Mollusca, Class Gastropoda. it has a radula, a soft foot, and a helical shell with one opening.

The second part of my assignment was to create a cladogram showing the evolutionary relationships between the animals I chose.

Sea Star Water Vascular System

The water vascular system starts with the Madreporite, where water enters the body. The water is then funneled into the starfish's core through the Stone canal, which then flows into the Ring canal. The ring canal distributes water around the center of the organism, where it then enters one of the radial canals. The radial canals take the water from the center of the creature all the way down the arms, into the ampulla, where it can then be used for locomotion, by hydraulically moving the tube feet, and assist in feeding (also with tube feet).