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April 6, 2017
by Jonathan Tweet
Comments Off on Chelicerata: Claw-Horns of the Deep

Chelicerata: Claw-Horns of the Deep

Two eurypterids and an early horseshoe crab

The extinct arthropods of the water are chelicerates: a eurypterid, Hughmilleria; a Stylonurid eurypterid; and an early horseshoe crab, Lunataspis. Eurypterids walked on legs and swam with paddles. They also had chelicerae (“claw horns”), which were claws by their mouths that helped them catch and eat prey. This adaptation helped them dominate the seas. Some, such as Hughmilleria, adapted to habitats with brackish or fresh water. Others, such as most of the Stylonurids, lost their swimming legs and only crawled. Like Eurypterids, horseshoe crabs are descended from the original chelicerate ancestors, along with scorpions, spiders, and other arachnids. These arthropods all arose during the Paleozoic Era, which ended in a great extinction event 252 Mya. Many sorts of arthropods survived, but not the eurypterids.

April 3, 2017
by Jonathan Tweet
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Pantestudines: Long Necks, Big Teeth, and Hard Shells

Pliosaurus, Plesiosaurus, and Odontochelys

The sauropsids of the water are a Plesiosaurus, a Pliosaurus, and an Odontochelys, an early turtle relative. Early in the Mesozoic Era, several sorts of lizard-like sauropsids swam and hunted in the water. While some lines of sauropsids led to land-loving lizards, pterosaurs, and dinosaurs, other lines evolved into ichthyosaurs, plesiosaurs, turtles, and crocodiles. Plesiosaurus and its close relatives hunted by sight, but scientists aren’t sure what their long, stiff necks were for. Pliosaurus is also part of the clade of plesiosaurs, and they were top predators, guided by sight to ambush or pursue prey. No one is sure where the turtle line originated, but one popular idea is that they arose from the same clade that led to plesiosaurs, called Pantestudines. Ondontochelys had a shell only on its belly. The turtle line later diverged into some lines that live exclusively in the water, some only on land, and many that both swim in the water and crawl on land.

April 3, 2017
by Jonathan Tweet
Comments Off on Prehistoric Insects: Crawlers, Flitters, and Hunters

Prehistoric Insects: Crawlers, Flitters, and Hunters

Cockroach (300 million years ago), butterfly (35 Mya), and giant dragonfly relative (300 Mya)

The arthropods of the air are flying insects, a cockroach, Aphthoroblattina; a butterfly, Prodryas; and a dragonfly relative, Meganeura. Over 300 million years ago, insects appeared that could lay their eggs on land they could fold their wings behind them, allowing them to crawl easily. These lines evolved into cockroaches, such as Aphthoroblattina, and later into termites, grasshoppers, walking sticks, and their relatives. The butterfly Prodryas represents the clade of insects that develop first as larvas, then as pupas, and finally as adults. These insects, including ants, bees, and flies, have been even more successful than the roaches and their relatives. Among these insects, butterflies are relatively recent. You can think of butterflies as daytime moths, and they evolved from nighttime moths about 50 million years ago. Scientists know about Prodryas from a single, 35 million year old fossil, but it is one of the best butterfly fossils ever found. Meganeura was a predator living 300 million years ago. With a wingspan of 60 centimeters (2 feet), it was one of the biggest flying insects ever. Their clade died out, but the closely related dragonflies have survived for over 300 million years.

March 20, 2017
by Jonathan Tweet
Comments Off on Dinosaurs: From Little Runners to Ponderous Plodders

Dinosaurs: From Little Runners to Ponderous Plodders

Theropod, sauropod, ornithischian

In Clades: Prehistoric, the sauropsids of the land are dinosaurs, specifically a feathered Utahraptor (a theropod), an Apatosaurus (a sauropod), and a Stegosaurus (an ornithischian). The earliest dinosaur precursors were two-legged relatives of crocodiles, as were the first theropods, sauropods, and ornithischians. Walking efficiently on two legs gave them an advantage over crocodiles, lizards, and early mammal relatives. Dinosaurs first appeared about 230 million years ago (Mya), after the Permian–Triassic extinction event of 250 Mya. The plant-eating ”bird-hipped” dinosaurs (Ornithischia) evolved greater size, and several lines evolved a four-legged gait, especially the frilled and armored dinosaurs. The “lizard-hipped” dinosaurs (Saurischia) developed into two major clades. The sauropods evolved long necks to eat tree foliage and large size to protect themselves against theropod predators. Their large size necessitated a four-legged gait. Theropods ate meat, and they, too, became larger over time. Theropods evolved feathers, and some developed flight. Some of these flying dinosaurs were the only dinosaurs to survive the Cretaceous-Paleogene extinction event of 66 million years ago. We call them birds (Aves).

It’s easy to get the names sauropsid and sauropod mixed up. A sauropod (“lizard foot”) is one type of sauropsid (“lizard face”).

March 20, 2017
by Jonathan Tweet
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Aves: Dinosaurs that Survived

Robin, eagle, and ostrich

In Clades, sauropsids of the air are represented by birds. Today’s birds all descend from a species of flying theropod dinosaur that lived before the Cretaceous-Tertiary extinction event of 70 million years ago. Unlike today’s common birds, these early birds did not perch in trees. Four bird lineages survived the extinction event that wiped out the other dinosaurs. One surviving lineage led to today’s ostriches and their close relatives (Paleognatha, or “old jaws”). The other lineage, the Neognatha or “new jaws”, survived in three separate lines, one leading to ducks and fowl, another to sea gulls and their relatives, and the third to “earth birds” (Telluraves). Telluraves predominate today, and they mostly perch and nest in trees. Telluraves split into Afroaves (or “African birds”) and Australaves (or “southern birds”), represented in Clades by a bald eagle and an American robin, respectively. The common ancestor of all eagles and robins was evidently a carnivorous bird that perched on tree branches. “Old-jaw” birds and “new-jaw” birds together form the clade Aves, or birds. If one includes the many birdlike dinosaurs that didn’t survive the last extinction event, this larger clade is called Avialae (“bird wings”). Archaeopteryx are in the clade Avialae, but they are a separate branch from Aves.

March 20, 2017
by Jonathan Tweet
Comments Off on Pterygota: Insects with Wings or Winged Ancestors

Pterygota: Insects with Wings or Winged Ancestors

Bees, mantises, and dragonflies

The arthropods of the air are the clade Pterygota (“winged”), known as “winged insects” and represented here by a bee, a praying mantis, and a dragonfly. The bee represents Endopterygota (“inner winged”), the massively successful clade of insects that undergo complete metamorphosis (larva, pupa, and imago or adult). They first evolved around 300 million years ago, and they have since evolved into flies, fleas, beetles, ants, wasps, and moths. Around a 100 million years ago, moths co-evolved with flowering plants as their pollinators. One sort of wasp also co-evolved with flowering plants as a pollinator; we call them bees. The praying mantis represents Exopterygota (“outer winged”), a quite successful clade of insects whose young resemble the adult form. The young develop through multiple stages called instars (“forms”), and their wings develop on the outsides of their bodies, not within a pupa shell, as with Endopterygota. This clade, which preceded Endopterygota, includes cockroaches, termites, grasshoppers, lice, and more. The bee and mantis together represent Neoptera (“new wings”), the clade comprising all insects that can fold their wings back over their abdomens. The most successful neopterans are those that have evolved eusocial lifestyles with non-reproducing workers, such as bees, ants, and termites. The dragonfly represents the few species within Pterygota that are not neopterans. Dragonflies begin life as water breathing predators, and they develop toward the adult form one molt at a time until they finally climb out of the water, converting to adults that breathe air and fly. Nearly all insects are winged insects, although silverfish and some other forms are not. Fleas are winged insects (pterygotes) even though their ancestors lost their wings over 100 million years ago.

When I first chose three winged insects, the second was a butterfly because butterflies are highly recognizable. The bee and the butterfly, however, are both endopterygotes, so there was no insect to represent the important clade of cockroaches and grasshoppers. My plan was to swap in a cockroach for the butterfly because the cockroach has an ancient form perhaps similar to the earliest exopterygotes. A prominent backer, however, requested a praying mantis, and the mantis is a fine representative of Exopterygota. Karen drew the mantis face on to bring out all its character, but we might yet switch it to back view, like the others.

March 18, 2017
by Jonathan Tweet
Comments Off on Clades & Clades: Prehistoric Ready for Preorder

Clades & Clades: Prehistoric Ready for Preorder

Now you can preorder our two evolution games, Clades and Clades: Prehistoric. In 2016, Karen and I raised funds on Kickstarter to create two create them, and we have reached a deal with Atlas Games, which will publish the games when they release in December.

Preorder Clades & Clades: Prehistoric

Atlas Games have been publishing fine tabletop games since 1990. To check out their catalog of games, click here.

—Jonathan

March 14, 2017
by Jonathan Tweet
Comments Off on Tetrapulmonata: Fangs, Silk, and Feelers

Tetrapulmonata: Fangs, Silk, and Feelers

Tetrapulmonata: ob-weaver, tarantula, and amblypygid

In the Clades game, the arthropods of the land are represented by tetrapulmonates (“four-lungs”), specifically an orb-weaver spider, a tarantula, and an amblypygid. Tetrapulmonates evolved from one line of trigonotarbids, the first arachnids adapted to air-breathing (about 400 million years ago). Orb-weaver spiders and their relatives compose most of Earth’s spiders. They have fangs that point toward each other like pincers, and their ability to capture winged insects in their webs has helped them spread across the globe. Tarantulas and their relatives have fangs that point down, which makes for a weaker “bite”. These spiders create silk but don’t weave webs. Also descended from trigonotarbids are the spider-like amblypygids, whose front legs have evolved into long feelers. These feelers are similar to the antennae that pancrustaceans have, including insects, but obviously they evolved separately. Many types of animals have evolved new uses for their front legs other than walking. What other animals can you think of that have limbs that used to be legs but that aren’t any more?

Spiders and scorpions are descended from water-breathing ancestors, not air-breathers.

When I first chose animals for the “land arthropod” card, they were a spider, a scorpion, and a tick—all land animals. Then I learned that the most recent common ancestor of these three groups lived in the water. The lines that led to today’s land-loving spiders and scorpions evolved air-breathing independently. I switched from the arachnid clade to the tetrapulmonate clade because in Clades it’s the most recent common ancestor that determines a card’s environment (water, land, or air).

US preorders are now available from the game’s future publisher, Atlas Games, for both Clades and Clades: Prehistoric. Preorder here.

December 2, 2016
by Jonathan Tweet
Comments Off on Malacostraca: From the Sea Floor to Under a Log

Malacostraca: From the Sea Floor to Under a Log

water arthropodsThe arthropods of the water are a crab, a lobster, and a woodlouse, together representing the most recognizable branch of crustaceans, the malacostracans. Lobsters and their relatives are distinct from other crustaceans in that mothers incubate their eggs, which are attached to the mother’s swimming legs. Many other clades are successful because of adaptations that help them take better care of their offspring, mammals included. While lobsters live in crevices or burrows on the sea floor, crabs often live in shallower waters. Many sorts of crabs have evolved some degree of air-breathing, allowing them to take advantage of air’s higher oxygen content suisse acheter cialis. Woodlice still breathe through gills like their water-breathing ancestors, but their gills are adapted for life on land. A woodlouse’s gills stop working if they dry out, and that’s also true for your lungs. Like other crustaceans, malacostracans eat with side-by-side mandibles, quite different from arachnids’ fangs. Other crustaceans tend to be tiny, such as copepods, which often resemble shrimp but are smaller than a grain of rice. Another successful branch of the crustacean clade is the insects. They were originally classified as a sister group to crustaceans when in fact they’re a daughter. The clade of all crustaceans and insects is Pancrustacea (“all shelled ones”).

November 29, 2016
by Jonathan Tweet
Comments Off on Clades and Clades: Prehistoric Both Funded!

Clades and Clades: Prehistoric Both Funded!

Karen and I have raised enough money on Kickstarter to fund not only Clades but a second version of the game with all prehistoric animals—Clades: Prehistoric. For the real dinosaur lover, we’ve added a pledge level that lets you tell us which dinosaur to include in the game. The Kickstarter continues until December 6th.

http://bit.ly/Clades

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