Sea Spiders

Sea spiders.

I can already hear the exasperated groans coming from the readership of this entry. Sea spiders? Seriously? Why, arachnophobes the world over sigh, are spiders not content to just stay where they belong; many miles away from any potential interaction with my relatively exposed, swimming body? Need they go out of their way to ruin my summer vacation at the beach too? Why do there have to be marine versions of our creepy, spindly-legged friends, especially when we already have sea snakes, saltwater crocodiles, and what are the equivalent of massive “sea wolves” patrolling the briny depths? Perhaps, given the unsettling, lanky body shape of the sea spider, reminiscent of the daddy longlegs clustered in the dark, dusty recesses of our garages, it provides little comfort to say that these animals are not what their common name suggests.

In the same way that “sea cows” are not actually cattle equipped with flippers, and “sea wasps” aren’t really our delightfully sting-happy, land-lubbing acquaintances finding a new home beneath the waves (a nightmarish scenario if there ever was one), sea “spiders” are not simply spiders with water-proof webs and an appetite for calamari. They are something altogether different, belonging the taxonomic class Pycnogonida (meaning “thick knees”, perhaps referring to the shape of the joints in their segmented legs, or a cruel high school nickname for the group). This class is currently allied within the arthropod group known as Chelicerata, which does include arachnids; but, these “sea spiders” are, as previously mentioned, not arachnids themselves. However, even this classification may not provide enough recognition of the pycnogonid’s unique pedigree. There have been some recent studies (from both molecular genetics and evolutionary development angles) that suggest that sea spiders are not nested alongside arachnids at all, but instead are a part of a much older offshoot of the arthropod line…and are potentially the only surviving, highly-derived representatives of some of the first groups of arthropods to evolve (perhaps more closely related to enigmatic, extinct animals from more than half a billion years ago like Anomalocaris). If this is the case, then the pycnogonid lineage is effectively among the oldest animal groups on the planet.

Yes, no matter which classification assignment is correct, these critters occupy a unique branch on the great tree of life, and once someone takes a look at these pycnogonids up close, it becomes abundantly clear that these animals definitely deserve severely distinct classification, and have a tangibly alien quality to them. Seriously, pycnogonids are about as weird as it gets.

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Evolutionary Anachronisms

The avocado.

You may think you have a good relationship with the avocado. The buttery fruit of this plant may regularly accompany your turkey sandwich, sliced and fanned out across the bread. Or, it may serve as a hearty dip in the form of guacamole. More recently, avocado is seemingly being utilized in a greater variety of ways, being deep-fried, thrown in macaroni and cheese, and finding its way onto burgers, Subway sandwiches, and even into ice cream. You’d expect that with all this attention, our green-fleshed, knobby-skinned friend, the avocado, would be content with its current role in human culinary efforts.

However, the avocado may very well be lonely.

Despite all our affection, this loneliness stems from the avocado potentially having eyes for another. I mean this, of course, in the sense of the concept of co-evolution (which I examined in a previous post), which is directly tied to the reproductive role of the fruit itself. The main function of a fruit (a botanical fruit, typically meaning the structure derived from the reproductive tissues of the flower housing the seed(s)), is to move seeds away from the parent plant and into areas that promote growth and survival. Many types of adaptations in fruits exist to help achieve this goal of seed dispersal; from the wind-catching dual blades of maple tree fruits (known as samara), to exploiting the appetites of the ubiquitous (and notably mobile) animals in the neighborhood. This latter evolutionary strategy involves the development of fruits that enrapture animal taste buds and provide irresistible caloric value, allowing consumed seeds to travel safely inside the gut of an unwitting, far-traveling chauffeur until being excreted away from the crippling shade of the parent plant. This is called “endozoochory.”

Most endozoochorous fruits have evolved to be eaten by fairly specific animals. Predictably, fruits adapted to be taken by songbirds are going to have different physical attributes than those associated with insects or elephants. You can try and fit a peach pit through the body of a sparrow, but you aren’t going to get very far. Similarly, expecting tiny, thin-walled seeds to withstand an elephant’s battery of grinding teeth isn’t realistic either. The suite of fruit traits evolved for dispersal by a given group of animals roughly categorize into “seed dispersal syndromes.” By interpreting these syndromes, we can often get a good idea of what the primary dispersing animal, the other partner in a co-evolved relationship, is likely to be.

In light of this, it becomes obvious that despite our love of the avocado (specifically, domesticated cultivars with lots of flesh; wild avocado fruits have a thinner layer of green deliciousness surrounding that pit), it is not “meant” for human consumption and seed dispersal. Any attempt to chew up the whole fruit and swallow the massive pit is bound to land your asphyxiating ass in the cemetery. However, the situation for avocado’s seed dispersal isn’t much better in its wild Neotropical range. Many smaller animals (like monkeys) that partake in avocado consumption are “pulp thieves”, ingesting the oily layer and tossing the seed at the base of the parent tree. In fact, no native animal is known to consistently and effectively disperse wild avocado. Why then does the avocado make a big, energetically expensive fruit that doesn’t cut the mustard on dispersal? Also, who is the true “buyer” of avocado’s product?

The answer to both those questions may be that the avocado’s chief dispersal agent is extinct. Kaput. Gone. Effectively an “ex-animal.” This would mean that the avocado fruit is an evolutionary anachronism, equipped with traits fine-tuned by evolution for interaction with a species that has quite suddenly disappeared, leaving the once perfectly capable seed vessel under-appreciated and inadequately used.

“Fruit’s almost ripe, guys. Come and get it! Hello? ….Guys?!”

It’s a very serious case of being all dressed up with nowhere to go.

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Metatherians (Part 2 of 2): Odd Living Representatives

…so, some more about those metatherians/marsupials.

In the previous part to this two part series, I went over some of the now-extinct metatherian megafauna that once graced Australia and South America. These animals were fantastic and marvelous pinnacles of metatherian specialization, yes, but there are plenty of surviving metatherians, all of them of the ‘marsupial’ clade, that are also largely ignored and their lives obscured. There are some truly bizarre and amazing marsupials outside of the traditional koala/kangaroo/wombat/possum group that essentially everyone on the planet associates with the marsupial infraclass, and all of them somehow survived invading hoardes of humans and other placental species (although, in most cases, just barely).

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Metatherians (Part 1 of 2): Extinct Megafauna

Marsupials.

The immediate association most people have with the term ‘marsupial’ is that of fantastical, adorable, fluffy beasts in the far-away magical land of Oz, equipped with built-in fanny packs for storing their tiny, even more adorable, offspring. Bounding, big-eared kangaroos, sleepy koalas, and perhaps a hyperactive sugar glider or a waddling opossum might cross their minds. Not too far beyond this is where the train of thought pulls into its final stop, and suddenly they’re caught up in the romanticism of Australia itself; the sun-baked, tawny Outback scabland, didgeridoo droning in their mind’s ear, impossibly colorful fish flitting about the Great Barrier Reef, and perhaps Hugh Jackman or Nicole Kidman (whatever their fancy) driving cattle across the Northern Territory during The Dry.

While this idealization is all well and good, there is actually a lot more to these pouched animals than what fits on the in-fold of a Qantas brochure.
Marsupials are really bizarre by mammalian standards, and have a rich and relatively unrecognized evolutionary history that spans back 125 million years. This entry is one of two that will be devoted to these weird little creatures, focusing first on their unrealized illustrious past, and then on lesser known representatives of their clan in the present.

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Keas

The kea.

New Zealand is a place with many faces. A quaint, rural country of farms and adorable accents. Or a rugged and untamed playground for adrenaline-seeking white trust-fund kids. Or that place with the sheep and Flight of the Concords. Or Middle Earth.

But New Zealand, from a biological and geological standpoint, is an incredibly special place. The islands were once part of Australia and Antarctica nearly 100 million years ago. The chunk of land that made up New Zealand split off and traveled along the intersection of two giant tectonic plates, causing the uplift of the snowy Southern Alps and various volcanoes. It’s isolation from major landmasses (Australia is more the 900 miles to the west, nearest Polynesian islands are about 600 miles away) has given New Zealand a set of flora and fauna unlike anywhere else on Earth. It was so isolated, that it is likely one of the last places on Earth (with the exception of Antarctica) to be colonized by humans; potentially as late as 1300 A.D. by Polynesian sailors. Its location in temperate latitudes (roughly between 30 and 50 degrees south) gives it a climate more akin to the Pacific Northwest than to its Australian or Oceanic neighbors. With the exception of some parts of southern Chile, New Zealand is the only appreciable bit of land in the Southern Hemisphere to experience this type of climate, and the completely unique set of biological players give New Zealand an aire of alieness, clouded by the familiarity put forth by convergent evolution.

One such unique biological player is the kea (Nestor notabilis), one member of a small family of New Zealand parrots (Strigopidae) that diverged from their closest parrot cousins around 80 million years ago, when New Zealand separated from the southern supercontinent of Gondwanaland. Keas are found in patches all over the uplands of the South Island, and are the only alpine parrots in the world. Adapting to the harsh-as-hell conditions in the jagged peaks of the Southern Alps, and surviving repeated Ice Age glaciations, has resulted in the evolution of some intriguing behaviors.

Keas are among the brainiest birds around. They are incredibly social, living in tight-knit groups of about thirteen birds. They are capable of working together to solve problems of acquiring food and surviving the harsh winter season. They will even frolick and play with each other in snowbanks (as shown above) in a disgustingly cute display of ridiculous birdy intelligence. Look at that. You can almost hear the giggles and “tee hees.”

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Flightlessness

Flight.

Powered flight (in the biological world, flight that comes from the mechanical flapping of wings as opposed to passive drifting or gliding) can be found in a wide range of animals on our planet. It is has evolved independently in insects multiple times, leading to a biologically diverse menagerie of colorful blotches on our windshields. While insects are far and away the first creatures to master the air (by a solid 200 million years), and the only invertebrates to do so, they share the skies with the much larger vertebrate fliers like birds, bats, and at one time, the reptilian pterosaurs. Aerial locomotion provides an animal with obvious advantages; ease in avoiding predators, access to new habitats and food sources, and the nullification of the game of Monkey in the Middle. There definitely are interesting correlations concerning the success of flying; it appears as though once evolved, flight is an incredibly successful strategy. Bats account for a fifth of all mammal species, birds have the most species of any land-lubbing vertebrate class, and the class containing insects is more speciose than all other animal groups combined. So it obviously pays to take to the skies, on a numbers and diversity level. That, and flying is quite clearly the most badass way to get around.

And yet, some representatives of these flying lineages drop the practice altogether. One explanation is that they are ungrateful, arrogant pricks who wouldn’t know the value of an honest day’s wingbeat if it bit them in the ass.

“Soaring elegantly through the heavens is sooooo mainstream.”

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