#fuck yeah evolution

[heckyeahpaleozoology]

Velociraptor

No, not the ones from Jurassic Park (these more closely resembled Deinonychus antirrhopus, a related, but different species). That movie implanted false ideas of what velociraptors are in the minds of millions, most of whom will, sadly, never be corrected.

In actuality, velociraptors were small (about 1.5m at the hip - they would come up to about the average man's thigh), feathered dinosaurs. They were apparently fast runners, possibly able to use their feathered, wing-like forelimbs to gain speed; these specialized forelimbs may have also been used along with the long, stiff tail for balance while perched atop prey, and both of these functions may have contributed to the eventual development of flapping flight. They likely began eating prey alive, after having pounced and pinned their victim down with their powerful back limbs, which did possess a long, retractable claw on the second toe. Analysis of this claw, and examination of the "Fighting Dinosaurs" fossil indicates it was probably used to puncture and damage the throat rather than tear open the abdomen, which it was likely not sharp enough for.

Velociraptors were probably also warm-blooded. Their predatory behavior would have required a lot of energy. The presence of feathers supports this idea, as they are useful as insulation, important in species that actively thermoregulate. Mark Norell, of the American Museum of Natural History is of the opinion, and I must agree, that animals such as this are better thought of as "very unusual-looking birds."

Velociraptors roamed the deserts of prehistoric Mongolia for about four million years in the late Cretaceous, when they went extinct at the KT extinction event.

[heckyeahpaleozoology]

Crinoidea

Crinoidea is a class of echinoderms (think starfish) that, while not extinct, qualifies for inclusion in this blog by having first appeared in the fossil record in the Ordovician Period, 488-444 mya. As there are still extant members of Class Crinoidea, they can be directly observed and studied, meaning that our knowledge base regarding them is vastly improved.

Crinoids are generally composed of three major body sections: the stem, which anchors it to a substrate; the calyx, the central portion which contains its vital organs; and the arms, which are used to capture food particles and are lined with structures called cirri that move these particles to the calyx for digestion. While most extant crinoids are free-swimming and have more or less lost their stems, some deep-sea species may have stems of over 1 m in length. Like starfish and other echinoderms, crinoids exhibit pentaradial symmetry. Crinoids have no true brain, instead possessing three distinct sets of nerves, all centered in the calyx.

After the Permian Mass Extinction, crinoids propagated immensely, although most of these new species were unable to survive into the modern era. Other echinoderms that occupy similar ecological niches have been noted as showing greater individual numbers and diversity, but Crinoidea alone remains today.

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Belemnitida

Belemnites were squid-like mollusks that lived from the early Jurassic Period until the late Cretaceous. Unlike squids, they possessed ten arms of equal length with sharp, curved hooks that were used for grasping prey, but no tentacles, and also had a hard internal skeleton, which is absent in modern cephalopods. Belemnite fossils are typically the remains of the rostrum, the large, bullet-shaped portion of this skeleton.

Fossils that preserve the soft parts of belemnite bodies show ink sacs, large and well-developed eyes, and powerfully muscular arms, indicating that they were incredible swimmers, just like squids.

Belemnitida went extinct about 70 mya.

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Eurypterida

Eurypterida, or more commonly, sea scorpions, are ancient relatives of chelicerates (spiders and scorpions) that thrived from the Ordovician to the Permian Periods 460 to 248 mya, predating the earliest fishes. They are named for the wide, wing-shaped lobes on either side of the body, which were used to propel this predator through the waters as it hunted. Eurypterids were incredibly successful, with a near global distribution.

The long spine at the end of the tail of most Eurypterids may have been used to inject venom, but there is no evidence that any members of Eurypterida were venomous. The animals also possessed one pair of compound eyes, and another set of smaller eyes called ocelli between them. The stout walking legs of some species suggest that they may have been amphibious, and may even have been the first animals to colonize land.

The largest known Eurypterid attained a length of 2.5 m (8 ft 2 in), making it the largest arthropod ever discovered. They went extinct in the Permian-Triassic extinction event 251 mya.

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Meganeura

Meganeura is the genus of famously huge dragonfly-like insects from the Carboniferous Period, about 300 mya. These relatives of modern dragonflies could have wingspans of up to 75 cm and were named for the pronounced and well-defined network of veins on their wings (the generic name, Meganeura, means "large-nerved"). These monstrous bugs were predatory, feeding on other, smaller insects (which may still have been enormous by today's standards) and even small amphibians. Interestingly, the larvae of modern dragonflies still hunt tadpoles.

These and other varieties of huge insects are thought to have been able to survive and fly because of the much higher oxygen levels of the Carboniferous Period, as oxygen percentage is known to act as a limiting factor on maximum size of an insect due to the structure of their respiratory system. Falling oxygen levels, competition from other species, and the appearance of new terrestrial predators are all factors that could have contributed to the extinction of Meganeura.

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Discosauriscus

Discosauriscus refers to a genus of reptiliomorphs - reptile-like amphibians - that lived in what is now Central and Western Europe during the Permian period, about 299-271 mya.

Reptiliomorphs in general are known for technically being amphibians, but exhibiting traits of both amphibians and reptiles; forming a series of "missing links" in an evolutionary chain. Such reptilian traits possessed by Discosauriscus include a sharp-toothed jaw, short limbs, and a body covered in scales (which are interestingly arranged in concentric circles). These traits likely developed in response to the drier climate of the Permian Period, which included an expansive desert covering the interior of the supercontinent Pangaea.

All known specimens of Discosauriscus appear to be juvenile, so it is not clear if only larval specimens have yet been discovered, or if the genus was highly neotenic, retaining many juvenile characteristics into adulthood, as is the case with some modern amphibians. This also makes it difficult to ascertain the animal's adult size. Discosauriscus specimens have been described as retaining evidence of a lateral line system which, with the presence of electroreceptive organs, would indicate an ability to sense electric fields, well-known as a sense of sharks and other extant fish. This animal likely went extinct during Olson's Extinction 270 mya.

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Bothriolepis

Bothriolepis is a genus of the heavily armored placoderm fish that flourished in the second half of the Devonian Period, 387-360 mya. Having radiated into over 100 species with a known fossil presence on all of Earth's continents, it is considered one of the most successful placoderms.

With an adult length of roughly 30 cm, these fish would have easily been hunted by others if not for their heavily armored heads, shield-like thoracic plates, and spike-shaped pectoral fins, which were adapted both for covering the fish in sediment to hide as well as launching it off of the ocean floor, where it likely fed on detritus, to swim, as the armored body made it rather heavy.

Bothriolepis species were likely anadromous like Salmon, spending most of their lives in saltwater, but returning to freshwater to breed. A pair of lung-like pouches located on either side of the esophagus, paired with the jointed fins and supportive skeleton, have even led to speculation that these fish were capable of travelling over land.

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Megatherium americanum

Megatherium americanum, as its name suggests, is one of the largest terrestrial mammals on the fossil record. Weighing up to eight tons (about as much as an African Bull Elephant) and reaching a height of 6m (20 ft) when balanced on its hind legs, this relative of the modern tree sloth ruled the grasslands and lightly wooded areas of Central and South America when it appeared 5.3 mya.

These large animals mostly lived in groups, but would have been safe living singly, as their sheer size was an effective deterrent to most predators. Long considered an herbivore, recent analysis of the teeth and forelimb musculature of M. americanum indicates that it may have supplemented its (considerable) dietary needs with meat, possibly taking over kills of Smilodon, the sabre-toothed cat, using the massive, curved claws on its forelimbs, though this claim is still hotly debated.

M. americanum was unfazed by the mass extinction that occurred as a result of the Great American Interchange following the formation of the Central American Isthmus and migrated north, only to be hunted to extinction by humans some 10,000 years ago.