Cladoselache

Cladoselache species

Today's Shark is the largest one that we have talked about so far, and it is also the oldest. Cladoselache is the name of a genus containing eight different Shark species, all of which lived during the Devonian Period, around 370 million years ago.

Sharks have been around for hundreds of millions of years, and the Cladoselache Sharks are some of the best known of the ancient species. This is because many of their fossils were very well preserved in a formation near Lake Erie. Some of these fossils are so detailed that we know their stomach contents!

These extinct sea creatures are interesting not only because they lived a very, very long time ago, but also because they had some interesting anatomical features. For one, they almost completely lacked scales. The only scales it had were found on the tips of the fins, and around the mouth and eyes. Secondly, these Sharks lacked "claspers"-- the reproductive organs that are found not only in modern sharks, but in many other ancient species as well. Scientists are still unsure how they specifically reproduced. Finally, the Cladoselache Sharks had smooth, blunt teeth. Rather than tear apart their prey, they grasped it and swallowed it whole.

Cladoselache Sharks were probably very fast and agile, based on their body shape, dorsal fins, and large tail fin. They were high speed predators who also needed to be quick in order to avoid becoming prey themselves. Sharks weren't the only large predators swimming the seas-- this was the time of the 30ft Dunkleosteus as well!

There are no close relatives of the Cladoselache Sharks left today. All other genera within the family are extinct, and that family was the only one within the entire order.

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Status : Extinct for around 370 million years
Location : North America
Size : Length up to 6ft (1.8m)

Classification : Phylum : Chordata -- Class : Chondrichthyes -- Order : †Cladoselachiformes
Family : †Cladoselachidae -- Genus : †Cladoselache

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Horn Shark

Heterodontus francisci

Today's Shark is a very interesting looking species-- it has a very blunt head, prominent ridges over its eyes, two tall dorsal fins with spines, and a sandy colored body covered in dark spots. It also happens to be on the smaller side, though not as small as yesterday's Shark. Horn Sharks can reach lengths of around 3ft.

You can find Horn Sharks swimming off of the western coast of North America, in a range that extends from Monterey to Baja. As juveniles they live in deeper sandy flats, and as adults they move closer to shore, swimming near reefs as shallow as 2m!

The adult Horn Sharks have small ranges, and actually return to the same shelter after each night of hunting (they are nocturnal). They feed in small fish and a large variety of benthic invertebrates, including squid, crabs, and sea urchins. Interestingly, Horn Sharks aren't the greatest swimmers, and are quite slow and clumsy. They often use their large pectoral fins to pull themselves along.

Horn Sharks are one of those cool Shark species that shows some sort of care towards their offspring. After mating takes place in December or January, the female will spend 2-3 months laying her eggs two at a time (layings are spaced 11-14 days apart). Each egg measures 4-5in long, is conical in shape and has spiraled flanges around it. The females will take the eggs and wedge them into crevices so that they are protected from predators (other sharks will often just lay their eggs and leave). The eggs take 6-9 months to hatch.

Horns Sharks are not normally dangerous to humans, though bites have happened due to harassment. The Sharks are kept and bred in captivity, and are sometimes hunted for their spines (which are made into jewelry).

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IUCN Status : Data Deficient
Location : Western North America
Size : Length up to 3.3ft (1m)

Classification : Phylum : Chordata -- Class : Chondrichthyes -- Order : Heterodontiformes
Family : Heterodontidae -- Genus : Heterodontus -- Species : H. francisci

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Dwarf Lanternshark

Etmopterus perryi

The 25th Annual Shark Week starts today, so obviously we need to learn about a Shark! Sharks have been very popular on Animal A Day, and we've learned about loads of them in the past (a full list can be found here). But we haven't yet talked about the smallest of all the sharks-- the Dwarf Lanternshark.

Dwarf Lantersharks reach mature lengths of around 7in, and pregnant females can grow a small bit larger, topping out around 8in. They are an ovoviviparous species, and give birth to 2-3 pups at a time.

Not only are these Sharks very small, but they are also quite mysterious. They have only been found in a small section of the Caribbean, off the coat of Colombia and Venezuela. They swim at depths of between 900-1,400ft (274-426m), and are rarely caught or observed.

So little is known about the biology and population size of these tiny sharks that they are listed as "Data Deficient." They have no economic value in the fishing industry and there are no conservation measures being taken.

So unfortunately there isn't a whole plethora of information out there regarding this particular shark, but that's isn't all that surprising considering its small size and tiny range. Stay tuned for a few more sharks during the rest of the week!

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IUCN Status : Data Deficient
Location : Caribbean
Size : Length up to 7in (18cm)

Classification : Phylum : Chordata -- Class : Chondrichthyes -- Order : Squaliformes
Family : Etmopteridae -- Genus : Etmopterus -- Species : E. perryi

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Eastern Tiger Salamander

Ambystoma tigrinum

The Eastern Tiger Salamandar is the largest land-dwelling Salamander is all of North America, and it also has the distinction of being the most widespread. You'll find these guys just about everywhere on the continent except in the coldest northern reaches-- they live throughout the United States, Mexico, and in most of Canada.

You can identify Eastern Tiger Salamanders by their large size and their blotchy green and black markings. As adults they are almost completely terrestrial, and live in burrows that can be as far as two feet underground. They live in a huge range of habitats, including forests, grasslands, and developed areas.

Adults are very loyal to their birthplace, and will return to that spot to breed int eh Spring. Larges numbers will congregate on a single spots, and males will have to isolate the females from the group in order to breed. Males will deposit spermatophores that are picked up by the females to fertilize the eggs. Sometimes other males will actually interrupt this process, deposing the first male on the scene and then placing his own spermatophores. Once the eggs are fertilized, they are laid in masses that number up to 100. The young Salamanders are completely aquatic, but grow very fast-- by the end of summer they have already become adults.

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IUCN Status : Least Concern
Location : North America
Size : Length up to 14in (36cm)

Classification : Phylum : Chordata --Class : Amphibia -- Order : Caudata
Family : Ambystomatidae -- Genus : Ambystoma -- Species : A. tigrinum

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Pumpkinseed

Lepomis gibbosus

The Pumpkinseed is a species of small freshwater fish that belongs to the same genus as the Bluegill. They once had a range that spread only through eastern North America, but they can now be found all the way west to the Pacific Coast. Pumpkinseeds have also been introduced in Europe, where they are considered an invasive species (due to their competing with other fish for food).

Pumpkinseeds have body shapes similar to their namesake, and have scales that range from brown to olive green. They also have small speckles across their bodies, and faint vertical lines. The coloration is more vibrant and pronounced during the breeding season. The Pumpkinseeds' scales are used for protection-- they are able to reflect back their surroundings and serve as camouflage.

The species is most commonly calm, clear waters. They are active during the day, feeding on insects and small aquatic creatures both at the surface and near the bottom. At night they hide out in submerged plants and other covered areas.

During the breeding season males will actually build little nests in the lake floor, sweeping away rocks and debris and making an indent. These nests are often built in small colonies, and are sometimes intermingled with Bluegill nests (Bluegills and Pumpkinseeds sometimes school together, and will even interbreed). Females can lay up to 1,700 eggs, and will sometimes lay them in multiple nests. They leave after the laying is done. Males hang around until the eggs hatch (around 3 days) and will actually guard their new offspring for up to two weeks. If they wander off the dads will even return them back to the nests in their mouth!

Pumpkinseeds are often fished up by anglers, due to the fact that they swim close to shore and will take worms very easily. They are sometimes a source of some frustration though, as they'll often bite when fishermen are going after larger fare.

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IUCN Status : Least Concern
Location : North America
Size : Length up to 8in (20cm)

Classification : Phylum : Chordata -- Class : Actinopterygii -- Order : Perciformes
Family : Centrarchidae -- Genus : Lepomis -- Species : L. gibbosus

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Bohaskaia monodontoides

Bohaskaia monodontoides

The animal that we're going to learn about today has been extinct for around 3 million years-- but it bears a very striking similarity to some of the creatures that are still swimming around in the Earth's oceans, and also gives scientists some insight into where those modern animals came from.

Bohaskaia monodontoides is known from just a single skull that was unearthed in Virginia is 1969. It wasn't until very recently that it was studied using modern methods, and the species was only just named in spring 2012. The skull looked similar to that of a Beluga or Narwhal, yet was still different enough to be recognized as a different genus and species entirely.

Belugas and Narwhals, as you may know, live in cold waters. B. monodontoides swam in warmers seas, yet shared many of the same physical traits. Interestingly, another extinct whale Denebola brachycephala also hailed from warmer parts (the fossils were found in Baja, Mexico). It now appears that this particular group of whales evolved in the more temperate waters, but were eventually driven north were they adapted to the climate and survived. How this happened, and when it happened is not yet known, but it is pretty amazing to think that the warm-water origin discovery was due in part to a single fossil found over 40 years ago!

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Status : Extinct for 3 million years
Location : North America

Classification : Phylum : Chordata -- Class : Mammalia -- Order : Cetacea
Family : Monodontidae -- Genus : †Bohaskaia -- Species : †B. monodontoides

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Dunlin

Calidris alpina (breeding plumage)

Meet the Dunlin, a small wading bird that can be found all over the Northern Hemisphere (depending on the time of year). Populations breed in the northern reaches of Europe, Asia, and North America, and migrate south as far as Africa, Southeast Asia, and Central America during the winter. The species is highly gregarious, especially in winter, and can be found in massive flocks that number into the thousands. The worldwide population as a whole is estimated to be around 4 million birds.

Dunlins are easy to identify in their breeding plumage. They have bright reddish-brown feathers on their backs and a large black patch on their underside. During the winter their backs turn a duller grey and the underside is pale. Dunlins are also easy to tell apart from other Shorebirds in that their long black bills curve downwards. They use those bills to probe into mud and shallow water for insects, crustaceans, and other small creatures.

When the breeding season rolls around, males are the first ones on the scene. Females get to the nesting ground after, and the birds pair up. They are monogamous during the season, and some pairs will continue to couple up year after year. Males start out the nest building process, scraping a few possible locations into the ground. The female will pick the location she likes the best, finishing the construction at the site.

Young Dunlins are precocial, and are flying after only 3 weeks. Interestingly, the mother usually abandons her family within the first week of hatching, and it is the father who cares for the offspring until they are fully fledged.

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IUCN Status : Least Concern
Location : Europe, Asia, North America
Size : Length up to 8in (20cm), Wingspan up to 14in (35cm)

Classification : Phylum : Chordata -- Class : Aves -- Order : Charadriiformes
Family : Scolopacidae -- Genus : Calidris -- Species : C. alpina

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