Sharks

Shark off the waters of Belize.

The earliest shark ancestor so far discovered can be traced to the Ordovician Period over 450 million years ago. During this time, there was a vast marine diversity, but little diversity on land. While different from modern sharks, the ancestor was still a high-speed predator with sharp teeth.

Fossilized Shark Tooth

As one of the fiercest marine predators, sharks also harbor a disproportionate amount of fear. Of the number of total confirmed shark attacks recorded for centuries, less than a fifth have been fatal. There are greater dangers in the seas such as rip currents and jellyfish, and while jellyfish are deadly, the number of deaths they cause have likely been seriously underestimated due to lack of confirmed deaths. Still, it is far easier to fear a large, sharp-toothed predator rather than a tiny insect no matter the fatality rate.


This post is in response to the recent culling of sharks off the Western Australia coast. The policy states that it is to reduce the risk of shark bites and fatalities. Unfortunately, all this will create are unstable populations in species, which could easily led to a sudden collapse and extinction as was seen in passenger pigeons a century ago. All have their place in their world including large carnivores such as sharks. They help keep populations in check, and if removed, the effects ripple down the food chain until the whole system becomes unbalanced. As with everything else, they have a place and purpose in our environment.

The Google+ post I did mentioning sharks, but with different wording is here.

Western Interior Seaway

Scallop, Kingena wacoensis and Brachiopod, Neithea texana
[Grayson Formation, Lake Arlington, Texas]

The Western Interior Seaway was an extensive epeiric sea formed from the high sea levels between the middle and late Cretaceous Periods over 75 million years ago. It once covered most of the Midwest of North America with many present day states once completely submerged. A vast number of marine fossils, from vertebrates to molluscs, have been unearthed in these regions.

Devil's Toenail, Exogyra ponderosa
[Anacacho, Uvalde County, Texas]

The widespread and well-preserved fossils of marine fauna has allowed for the environment of the Western Interior Seaway to be determined. For the majority of its existence, water column stratification gave way to dysoxic to anoxic bottom-water environments. These conditions led to a number of opportunistic and low oxygen adapted taxa to emerge. There was also a predominance of brackish-water conditions on the surface. As the inland sea stretched from the far north down to the tropics, there was a mixing of cooler, less saline waters with warm tropic waters resulting in a limited presence of typical marine organisms.

Lobsters

A lobster is an invertebrate with a hard, protective exoskeleton. They need to molt in order to grow, a process that may change the color of the animal in some species. Their unequal claws can be categorized as the smaller ripper claw to tear soft flesh and the larger crusher claw to pulverize shells. While the claw types can be either left or right, males generally have larger crusher claws than females.

Clawed lobsters belong to the family Nephropidae. They have existed at least since the Cretaceous period over 140 million years ago; however, the ancestor of lobsters and scorpions, Kooteninchela deppi, has fossil records spanning at least 550 million years. During the Cretaceous period, at least 53 species existed whereas during the Tertiary period, only 18 species have been identified. Currently, at least 29 species exist and have been recorded worldwide.

Tomorrow, October 16th, 2013, is National Fossil Day. As I only post twice a week, and not on Wednesdays, I declare this fossil week where I'll post my final fossil pictures - until the next batch :)

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Hyaenodon

Hyaenodon [Brule Formation, Pennington County, South Dakota]

The genus Hyaenodon contained carnivorous mammals that lived from the Eocene Epoch 42 million years ago until extinction during the Oligocene Epoch 25 million years ago. There so far are records of at least 30 species with fossils found in Asia, Africa, Europe, and North America. Hyaenodon means "hyena-toothed" as these animal had large, sharp teeth for their carnivorous diet.

Teeth of the Hyaenodon

During their existence, Hyaenodon was a dominant predator. The species ranged in size from small and fox-like to others as large as rhinos. It is believed the smaller species hunted in packs, likely at night, whereas the larger species likely hunted alone. Extinction of the order Creodonta, of which Hyaenodon belongs, possibly came from competition with Carnivora, the order most carnivores belong to in modern times.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Merycoidodon

Merycoidodon cuibertsoni [White River, Dawes County, Nebraska]

Related to camels, sheep, and pigs, Merycoidodontidae were mammals that once roamed North America 34 million years ago until their extinction 5 million years ago during the Tertiary Period. Their teeth contained long-lasting grinding surfaces well adapted for effective side to side chewing. They were about 1.2 m (4 ft) in length with a heavy build similar to modern day pigs. Fossils of Merycoidodon have most often been found in large numbers in small areas pointing towards the likelihood of these creatures having lived in herds.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Mastodon

Molars of Mammut americanum, Oklahoma.

Related to elephants and extinct for close to 11,000 years, mastodons were one of the megafauna that once inhabited North America. They were similar to modern elephants with large, curved tusks and corrugated grinding surfaces of the teeth, but they were also similar to mammoths with their shaggy hair. Remains of mastodons were first discovered in 1705 when a tenant farmer discovered a five-pound tooth. More teeth were discovered in other parts of North America until a French anatomist finally gave mastodons a name. The common name was based on the teeth as the conical cusps resembled breasts: mastos (Greek for breast) and odont (for tooth). Although the shape of the tooth first gave thought to flesh-eating beasts, it has since been concluded that the shape of the teeth provided best for browsing and grazing.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Sharks

Fossilized Shark Tooth

Sharks have been in existence since at least the Ordovician Period over 450 million years ago. This was during the time of vast marine diversity, and little diversity present on land. One of the earliest representations of sharks discovered was Cladoselache, which differs in form from modern sharks, but was still a high-speed predator. The most common discovery related to ancient sharks are their fossilized teeth. As sharks shed thousands of teeth throughout their lifespan, there is a higher chance for one of these teeth to find the right conditions for fossilization; however this often presents a problem of identification. In addition to scattered and mixed teeth findings, many sharks exhibit dignathic heterodonty, or a difference in the upper and lower teeth in addition to parasymphyseal, or a difference in teeth in relation to jaw position. Gender difference are also often translated to the teeth making it hard to identify the species a shark tooth originated from.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Sea Urchins

Extinct Sea Urchin, Sinaecidaris tauozensis [Taouz, Morocco]

Sea Urchins, of the class Echinoidea, are a type of echinoderm, much like brittle stars and jimbacrinus. Echinoderms, of the phylum Echinodermata, existed Precambrian over 600 million years ago. They have only been found in marine waters with 6,000 species still in existence. They are characterized by a well-developed water vascular system and by their mesodermal skeleton.

Extinct Pencil Urchin, Acrocidaris nobilis [Jurassic Period/LaRochelle, France]

Of the thousands of species of echinoderms, only about 700 species are sea urchins. As with most within the phylum Echinodermata, adult sea urchins have a fivefold symmetry called pentameral. They have characteristic long spines and a spherical shape. These spines serve not only as protection, but also as a way to move and a habitat for other creatures such as fish. Sea urchins feed on organic matter with one of their primary food sources being seaweed.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Brittle Star

Brittle Star, Ophiura graysonensis [Del Rio Formation/Lake Waco Spillway/McLennan County, TX]

The class Ophiuroids is a large group of echinoderms which include the basket stars, Euryalida, and the more familiar brittle stars, Ophiurida. Although similar in appearance, they are not related to starfish which belong to the class Asteroidea. The brittle star has a central, disk-shaped body with long, flexible arms. In order to move, the brittle star wriggles its arms resulting in gliding movement reminiscent of snakes. As the common name implies, brittle stars are fragile, but can replace lost limbs. Although early members of Ophiuroids appeared during the Ordovician Period 500 million years ago, the still extant genus Ophiura is of the more recent Cretaceous Period 145 million years ago. Whole fossils of brittle stars are rare as they rapid fall to pieces after death due to their fragile nature.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Jimbacrinus

Crinoid, Jimbacrinus bostocki

Jimbacrinus, nicknamed feather star, belong to the order Cladida, long since extinct. These marine creatures were a type of crinoid, a class that is characterized by a fivefold symmetry and often confused for plants. While few crinoids exist in the present-day, they were once found found in larger numbers during the Paleozoic Era, particularly during the Permian Period. An abundance of fossils of Jimbacrinus are found in Western Australia where some species once grew up to 25 cm (10 in) tall. This specific genus lived solely in what is now Australia, but other fossils from the extinct family Calceolispongiidae have also been found in the United States and India in addition to Australia.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Trilobites

Trilobite, Asaphiscus wheeleri [Wheeler Shale/Middle Cambrian]

Trilobites are an extinct class of arthropods defined by distinctive three-lobed, three-segmented forms. Evidence of their existence dates back to the beginning of the Cambrian Period 542 million years ago. They dominated the seas until their extinction during the Great Dying, the most severe extinction event which occurred between the Triassic and Permian Period 251.4 million years ago. Fossils of these creatures have been found on every continent, with areas such as the Wheeler Shale in Utah, the Emu Bay Shale in Australia, the Burgess Shale in British Columbia, and the Chengjaing Formation in China as being notable locations to find trilobites. They ranged in size from 1 cm to 70 cm (28 in), had a flower-like eye, and a thick chitinous exoskeleton which was shed often. There are currently over 20,000 recognized species of trilobites organized into 10 different orders.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Ammonites

Pervinquieria trinodosa, Duck Creek, Bryan, Oklahoma

Ammonites are of the extinct marine invertebrates of the subclass Ammonoidea within the class Cephalopoda. The name ammonite arose in 79 AD from Pliny the Elder. It is derived from the Egyptian god Ammon and the symbolic rams horns in his depictions. As seen in all fossils, ammonites are recognized for their spiral shape shells although there is variation between species.

Ammonite, Unknown

These predatory creatures lived in a shell that were constantly built as they grew. The size varied with fossils of many found to be over 1 m (3 ft) in diameter. Their tentacles extended from the shell to snare prey. A sharp, beak-like jaw awaited in the middle of the tentacles. Although not closely related, they moved like modern-day nautilus. Chambers within the shell were full of either fluid or gas and allowed movement within the water column. They also had a method of jet propulsion through a funnel opening within the shell for more precise horizontal movement.

Unknown, Arcadia Park Shale, West Dallas, Texas

Ammonites first appeared and evolved during the Devonian Period of the Paleozoic Era 419.2 million years ago, and they existed until the end of the Cretaceous Period of the Mesozoic Era 66.0 million years ago, disappearing with the dinosaurs. Fossils of these creatures play an important role as size, shape, and shells of ammonites can be used to date geological layers. The septa, or dividing walls of the shell, can be used to classify order, and therefore time period, of the specimen.

From the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary.

Fossils

Fossil of a "bony fish" of the infraclass Teleostei

The word paleontology refers to the study of ancient life from the Greek words palaios (ancient) and logos (study). The word fossil comes from the Latin word fossilis (obtained by digging). Fossilisation occurs with the right circumstances: protection from scavengers and elements, and death in an optimal substrate such as sand, soil, mud, a river bed, or seabed. A sub-fossil is where decay, although slowed down, is still occurring and bone is still evident. A fossil is when chemicals and minerals percolate through the remains and recrystallizes it, or else erodes it leaving a hollow space. These remains that are dug up, from bones to teeth to skin, can be categorized by types. Trace fossils are evidence of animal behavior such as tracks, burrows, or coprolites. Mineralized fossils are when organic matter is replaced with minerals such as with bones, shells becoming pyrite or opal, or wood replaced with silica. An impression is when the creature decays but leaves an imprint in the sediment.

I was recently given a wonderful opportunity to photography, in detail, the newest fossil collection at the Heard Natural Science Museum and Wildlife Sanctuary. While the next number of post will be looking at some of these unique fossils, I will additionally be doing more detailed posts on Google+ if you'd like to see fossils that may or may not appear on this blog.