Tuesday, November 15, 2016

Top Ten (and more!) discoveries since the last time the Cubs won the World Series

As a Chicagoan, you can bet I was quite proud of the Cubs winning the baseball World Series after 108 years. 108 years can be quite significant, especially in the 20th century’s many, many, events. The 20th century has seen atrocities, wars, tragedies, and hate, but it’s seen technological and social progress, scientific revolutions, and discoveries about ourselves and our world.

One of the early discoveries of the 20th century became significant much later, but is still significant today. In 1909, Charles D Walcott of the Smithsonian Institution was already an established Cambrian expert. For years all that was known from that period were jellyfish, as if life would not flower until the Ordovician. There seemed to be no basal forms of the rest of the Paleozoic marine life. It was in 1909 that Walcott, prospecting in British Columbia, in Burgess Pass between Mt. Burgess and Mt. Stephen, discovered odd invertebrate remains. The following year he brought his family to help him collect. For the remaining 15 years of his life, he would continually visit the site with whatever help he could find, gathering thousands of fossils.

In the 1960s, Canadian and American scientists returned to the site, discovering more fossils, and realizing what they had found. The Burgess shale contains the earliest known members of modern groups-arthropods, echinoderms, chordates, mollusks, etc. These animals were the first with specialized organs, hard bodies, and distinct ecological niches. The largest were only a few feet long, but these animals showed a burst of evolution that Stephen Jay Gould would call “punctuated equilibrium”. Punctuated equilibrium is a caveat to Darwinian gradualism-when conditions change quickly, so does natural selection and so does evolution itself. 

The next discovery, in 1924, is geologically much closer to present-by over 500 million years.  Limestone quarries, emerging as part of South Africa’s still-booming mineral industry, turned up a small primate skull with a preserved brain cast. The company director, E. H. Izod, was given the skull by his workers and he in turn gave it to son Pat, who in turn gave it to his friend Josephine Salmons, who in turn gave it to her teacher Raymond Dart. 

Dart realized it was transitional between humans and other African apes, as it had features of both humans and extant apes.  He called it Australopithecus africanus. However, two things dismissed him-one was the human skull features are neotenies, meaning that most primate infants look alike, especially like human infants. The second was the racism in the scientific communities. European scientists refused to believe that they were descendants of Africans, going as far as to defend the already disputed Piltdown skull. For example, Henry Fairfield Osborn argued that humans diverged from other apes very early on in Asia, and went as far as to send an expedition to Mongolia to find human ancestors (his man in the field, Roy Chapman Andrews, found everything BUT hominid remains)

One of Dart’s colleges, however, was Robert Broom. Despite being a spiritualist he still was interested in evolution. He refused to accept the mechanics of it, but worked hard on proto-mammals in South Africa and saw them as distant ancestors of modern mammals.  Hoping to reignite his fading career, he followed Dart’s lead and prospected in South Africa. There, in 1938 and 1947 he found two skulls which he called Plesianthropus and Paranthropus.  Sir Wilfred Le Gros Clark, another British scientist who would later debunk the Piltdown skull, examined Plesianthropus, and realized it was the adult of Dart’s Australopithecus africanus. The old name is still remembered as Broom’s students dubbed the specimen “Mrs. Ples”. 

A third hominid fossil is notable in this discussion, this one from Tanzania. In the early 1960s, Louis and Mary Leakey found primitive human teeth, a jaw, and a partial skull, next to extremely crude tools. They named it Homo habilis, the earliest species of human. The problem was that Tanzania and South Africa were considered to be too distant from each other to connect the South African Australopithecus and Paranthropus with the Leakey’s Homo habilis and Zinjanthropus (later determined to be another species of Paranthropus), and the East and South African schools of hominin paleontology have been bitter rivals ever since. 

What was needed to solve this was either Homo habilis in South Africa or an Australopithecus in East Africa. To this end, Mary Leakey joined forces with Yves Coppens and Donald Johanson in 1971 to search the north end of the Rift Valley in Ethiopia. Their success was mixed-limb bones and jaws were uncovered, but nothing determinate. In 1974, however, Johanson and his team discovered a single specimen-hundreds of fragments of a single skeleton. It was crushed and took months to reassemble, but what they found was amazing. All the previous hominin material was cranial-teeth and skulls and jaws. This time, however, the head was found with a body, a body with a pelvis and femurs and feet. All these pieces showed that this ape, named Lucy after the Beatles song, was a biped. Walking upright evolved before the brain, contradicting Osborn one last time.  

Hominin fossils are fragile, meaning they’re rare. Of course, tell a paleoentomologist that and they’ll laugh at your face. Insects, being tiny and fragile, seldom ever fossilize. The good part of that is that when they do fossilize, said fossils are incredibly detailed and preserved. In this case, it came from the urbanization of Scotland. In 1910, a beautifully complete fauna of Devonian land planets was discovered near Rhyne, in what’s called the Rhynie Chert. In addition to these first land plants, are the oldest known insects.

Insects today rule almost every ecological niche, making up most of earth’s biomass. Where did they start? With the first land plants, animals spread from the water to breathe this new oxygen and feed on the plants. So, it follows that with these first land plants come the first land herbivores. In this case, it’s the tiny insect Rhyniognatha, identified in 1928. Slightly younger is the springtail Rhyniella, found in the same year. These insects are only about a millimeter long, but already adapted for eating decaying plant matter, being predigested by cellular rot. These tiny animals are the ancestors to herbivorous insects armed with sophisticated jaws and digestive systems that can break down almost all natural fibers, and the deadly predators that prey on them. With the first land herbivores, carnivores in turn evolve to take advantage of this new food source, and this will continue through present day. Long after our own species falls extinct, herbivorous insects will continue to chew their way through time.

Following the early insects were the first tetrapods. By 1908 lobe finned fish like Eusthenopteron and amphibians like Philoderpeton and Dendrepeton seemed to be the links to life on land. However, for decades there was a missing link in this intuitive fish-to-amphibian transition, no aquatic amphibian that was “fishy” enough. 
In the lull between the World Wars, before Europe fell under the feet of dictators, the Scandinavian countries explored Danish-held Greenland. In 1931, the Danish explorer and scientist Lauge Koch led a pan-Scandinavian expedition to Greenland. Among the scientists was paleontologist Gunnar Säve-Söderbergh, who recovered amphibian bones from the eastern region of the island. Said bones were a half- complete skeleton of the oldest amphibian.

Säve-Söderbergh dubbed the animal Icthyostega. The ribs, chest, and hips were strong enough to support the animal on land, and the skull resembled other amphibians, but the skull also contained gills, the feet were seven-toed paddles and the tail was tall and long for swimming.  Säve-Söderbergh identified four different species, but all were hailed as the greatest link between fish and amphibians.
In the next 20 years, two more of these “fishapods” were found in Devonian rocks of Northern Europe-the fishlike amphibian Acanthostega (far more aquatically adapted than Icthyostega) and Pandericthys (a lobe finned fish with a head just like that of an amphibian). But it would take until the 21st century for the greatest of these missing links to be found. 

An expedition to Ellesmere Island, Nunavut in 2004 revealed an extraordinary fossil. Like the previous finds, it was only half complete, but enough was found (and the rest of the skeleton later) to establish a transition between amphibians and fish. Ted Daeschler of the Academy of Natural Sciences of Philadelphia, Neil Shubin of the University of Chicago, and the late great Farish Jenkins of Harvard University discovered and described this new species, dubbing it Tiktaalik.
Tiktaalik has an amazing mixture of traits from both fish and amphibians, barely qualifying as a fish instead of a tetrapod. While having fish scales, gills, and fins, it also had Icthyostega’s strong ribs, necks, pectoral girdle and lungs. The limb joints and ears fit in between fish and amphibian forms, qualifying it as the transitional fossil. Extinct amphibians are often fishlike, and extinct lobefin fish had strong muscular fins like limbs, but this specimen has the perfect mix of characteristics, and in such a way that it makes complete biological sense.

Another first would be one of the first mammals. Protomammals had been known for a while, but Mesozoic mammals were poorly known, especially those from the brief but dramatic Triassic.  German paleontology had reached a dramatic stop in the 1930s and 40s as evolution was forced to apply to a nationalistic purpose when it was even discussed. The Origin of Species was considered atheist and therefore communist by Hitler and his departments-evolution undermined German claims to be masters of the earth.  Almost all the finest scientists in Germany fled for their lives, including Walter Georg Kühne.  As the story goes, he walked into Cambridge in 1939, and went directly to the office of the great Francis Rex Parrington, an expert on the early archosaurs and synapsids of British Africa.  Kühne gave Parrington a carefully wrapped jaw of an animal transitional between mammals and their ancestors and said “I know where to discover early mammals”.
With Parrington, Kühne investigated the origin of mammals. With travel limited, Kühne decided to prospect the Vale of Glamorgan, a known Triassic site on British soil. It took him until 1949 to find what he was looking for, but what he found was amazing. The animal was small, only 4 inches long, and had to be studied under a microscope. However, it was huge in terms of significance-a mammal that was more primitive than a Platypus. 

This creature, Morganucodon was unique. The teeth are deciduous like those of mammals, but only two types of teeth existed rather than the standard mammalian three. The jaw had the same shape as a mammal with great mechanical strength, but the ear bones were still attached to the jaw. Most significantly, the jaw was double articulated-with two joints, one in the reptilian fashion and another high one like that of a mammal. The jaw is the exact middle between the mammal shape and the reptile shape, a key feature of the transition. 

Between these two milestones are the first reptiles.  The great British geologist Sir Charles Lyell and his protégé John W Dawson discovered Hylonomus in Nova Scotia, an ancient, primitive reptile. However, there remained the question of transitional animals between amphibians and reptiles. Animals like Limnoscelis, Seymouria and Diadectes had reptile-like anatomy, but coexisted with amniotes. This meant that the first amniotes came earlier in the Carboniferous. 

One of the greatest sites of Carboniferous life is the East Kirkton Quarry in West Lothian Scotland. Ancient amphibians had been found there since the 1840s, before Darwin put his ideas down on paper. It took until 1984, however, that the quarry revealed an amazing find. Fossil collector Stan Wood discovered this 6-inch animal, and named it 'Lizzy the Lizard’. It remained in the private collection until 1990, when Tim R Smithson of Cambridge College and William D Rolfe of the National Museum of Scotland analyzed it and gave it the name Westlothiana. 

Lizzie’s head and body resembled that of other ancient amphibians like Icthyostega,  but it had reptilian ankles and skull morphology. It’s still considered a temnospondyl amphibian, but only just. The long body and short limbs suggest a life for burrowing or swimming rather than climbing or fast movement on the floor.

The Museum of Scotland received another fossil in 1992 collected in Cheese Bay, this skeleton with reptilelike claws but lacking a skull. This animal, Casineria, also examined by Smithson, resembles Westlothiana albeit with much longer limbs and digits, suggesting a tree-climbing lifestyle instead of a burrower or swimmer like Lizzie.  Together, these tiny Scottish animals represent a point in time when animals can finally be born outside of water and conquer the land.

When it comes to firsts, macroscopic life in general has a first, or at least an oldest. In earth’s 4.5 billion years of existence, there are two eons: the eon of large life or Phanerozoic, and the longer Precambrian eon. For 4 billion years, life was small when it even did exist.  The Burgess fauna showed a clear transition to the Cambrian-there were no Precambrian animals, and life exploded rather swiftly. 

Or so it was thought in 1958. It was in 1958, in the ancient crags of Charnwood in Leiscestershire, England, what looks like a fossilized leaf was discovered. A teenage girl, Tina Negus, first discovered them, but when she told her teacher, the possibility of a Precambrian animal was dismissed. It was only that Roger Mason, a teenage boy later to become a geology professor in China, took this fossil to Trevor Ford of the University of Leicester, that the fossil was revealed.  Shocking facts came in-first, that it was an animal, not a plant. It was Precambrian, not Cambrian, and it was a deep water organism.  Ford dubbed it Charnia.

What kind of animal it was is still hotly debated. Ford thought it was algae before realizing it was an animal. Glaessner in turn suggested a sea pen before 2000’s studies showed it to be an animal of an unknown order. These animals were also found in the Edicaran Hills; as before, Elkanah Billings’ proposal of Precambrian life was dismissed until 1959.  Austrian scientist (who narrowly escaped the Holocaust) Martin Glaessnar put two and two together in 1959 and the Edicara fauna of jellyfish, sponges, and Charnia and its kin emerged as life before the Burgess shale.

Charnia is not really a transitional form, having no real ties to extant life, being more a colonial organism without bilateral symmetry.  Our next big find was a sophisticated animal, but with a similar paleontological history. When the legendary Barnum Brown, the discoverer of Tyrannosaurus, discovered the successful ornithopod Tenontosaurus in Montana’s Cloverly Formation, he also discovered a small theropod dinosaur. However, he could not publish a paper on the limestone-encased specimen, as it was too hard to extract without damaging the fragile fossil. He simply called it Daptosaurus and hoped to uncover it later, but it was lost in the collections as Barnum was too preoccupied with other fossils. He did also find a small headless theropod associated with large teeth on the expedition, calling it Megadontosaurus. 

In 1964, a year after Brown died, the late great John Ostrom of the Yale Peabody Museum went to a nearby site in Montana. He found more Tenontosaurus and theropod teeth, and was packing up to go when he noticed a fossil nearby. Digging with his fingers , he managed to scrape out a large talon. He decided to take the rest of the block with him and return the next year. Over the next two years, he returned again and again to the site, finding thousands of fossil bones of anything from three to fifty individuals.  

Ostrom, armed with this wealth of fossils, finally reconstructed the animal-a lightly build, agile predator armed with long claws. The shape of the body was unlike any other theropod-despite the powerful claws and jaws that fit traditional theropod morphology, it was slender, nimble and extremely birdlike. The forelimbs, though armed with giant claws, had the exact same shape as a bird’s hand and wrist. The hips had the pubis pointing backward. The inner toe of each foot was tipped with a huge sickle-shaped claw, which Ostrom identified as a powerful weapon for carving into flesh.  The eyes were huge and equipped with sclerotic rings to aid vision. This animal was shaped for leaping, kicking, and fast movement. 

This was unlike any dinosaur discovered before. In Ostrom’s own Peabody Museum at Yale University, the dinosaur hall of Marsh’s discoveries was accompanied by a giant mural from 1947 by Rudolph Zallinger, showing dinosaurs in mostly static poses living sedate, reptilian lives. Ostrom’s student Robert Bakker saw the contrast between the mural and the new dinosaur, and began to dig not only for fossils, but through the papers of Marsh and Cope themselves. 

Ostrom and his student Bakker began the Dinosaur Renaissance, when the scientific community realized that dinosaurs were far more akin to birds.  While Thomas Henry Huxley certainly proposed it a century earlier, an idea that both Charles Darwin and Richard Owen agreed on (although they argued over the implication of this-Darwin and Huxley saw a direct link, while Owen instead saw it as evidence that dinosaurs, birds, and modern reptiles were all distant kin of each other), the ancestry of birds from dinosaurs was now in debate again.  Dinosaurs entered the popular consciousness once again, culminating in the hit book Jurassic Park by the late Michael Crichton and the incredible film adaptation of it by Stephen Spielberg.

The link was secured by the 2000’s amazing discovery of Deinonychus’ tiny, winged relative Microraptor from Liaoning. The great paleontology Xu Xing described it as an animal that lived in the trees, gliding from tree to tree in search of small prey. In the same site, other dromaeosaurs and other dinosaurs were found with perfectly preserved feathers and quills. Even a relative of Tyrannosaurus rex itself was found covered in feathers. It was finally confirmed: birds are a lineage of dinosaurs. 

Another paleontological mystery for most of paleontological history was the origin of ichthyosaurs. When first discovered by Mary Anning and her brother Joseph in the early 19th century, these fishlike animals seemed perfectly adapted for marine life. There were no vestiges other than general reptilian anatomy to suggest the ancestry of the ichthyosaurs. They seemed to have just popped out of nowhere to conquer the Mesozoic seas. Owen even used them as proof of a special creation event in earth’s prehistory. 

This changed in 1978, when the great Japanese scientist Tokio Shikama discovered a small, primitive ichthyosaur in Miyagi prefecture. It had a small skull and broad tail, unlike its dolphinlike successors.  Shikama named it after the nearby town of Utatsu, but died before he could examine it in depth.  It was only in 1998 that, armed with imaging software, a team led by Ryosuke Motani took a close look.

 The teeth are small and slightly blunted, it turned out, and the humerus and femur were of equal length. In terrestrial reptiles, the femur is longer, and in ichthyosaurs the humerus is longer. The pelvic girdle was still attached to the spine, but not strong enough to support the weight of the animal on land. Finally, the morphology was compared overall to other reptiles, and phylogenic analyses were applied. The conclusion: ichthyosaurs fit in diapsids, like most Triassic reptiles including dinosaurs, crocodiles, and lizards. 

Since then, Utatsaurus has been joined by even more basal and primitive ichthyosaurs-the short snouted Sclerocormus from Anhui, China, the mysterious Omphalosaurus from Spitzbergen Norway, the small-beaked oddball Parvinatator from British Colombia, and, most important of all the tiny, amphibious Cartorhynchus.  This foot-long animal had strong flexible wrists and a short generalized skull, the long-sought after missing link to Icthyosaurs and their terrestrial ancestors.

Speaking of aquatic animals, our next big find is about an evolutionary step even Charles Darwin was stumped about. Since the days of Aristotle people had known about whales being mammals (to the confusion and argument of many Christian and Muslim scholars in the middle ages), but how mammals came to live in the sea was still confusing. All Darwin could offer was some wild speculation about amphibious animals like bears, but it was half-hearted and he deleted it from later editions.

Sir Richard Owen himself described an early whale, Basilosaurus, a giant from Egypt and Southeast USA. Basilosaurus had hind limbs, but said limbs were not a connection to any particular mammal. Ungulates, carnivorans, elephants, etc were all speculated to be the relations, but there were no transitional fossils for a century. The animal was fully aquatic, and while unlike any living whale, it was still strictly a whale. 

The mudstones of Pakistan were only rarely prospected for fossils, but in 1981 they yielded an amazing find. The great mammal paleontologist Daniel E Russell of the Institut de Paleontologie and Phillip D Gingerich from the University of Michigan discovered a strange transitional mammal. The legs were long, heavy, and strong, tipped with long, wide-spread fingers and toes. The neck is short but flexible. The tail is long and strong but unspecialized.  Oddest of all is the skull: while it has three distinct tooth shapes like a land animal and has its nostrils at the tip of its snout, the skull is smooth, long, and large, the eyes point upwards, and the auditory bulla is identical to that of a whale. 
This animal had adaptations both for hunting on water and land-the front teeth are long and pointed for catching fish, but the back teeth are broader for cutting through meat. It could hear prey through both air and water. The limbs and tail were shaped like that of an otter or a capybara or beaver-this animal could movie efficiently through both land and water.  In the salt marshes of Eocene Pakistan, Pakicetus could easily switch between terrestrial and aquatic prey. 

The link was strengthened in 1994 when Gingerich’s student Johannes G.M. Thewissen and Pakistani Paleontologist Sayed Taseer Hussain found the complete skeleton of an aquatic successor to Pakicetus. This animal was more specialized than Pakicetus but still had traces of terrestrial ancestry. It retained the long hindlimbs and digits of Pakicetus, but the forelimbs were shortened. The tail is shorter but well-muscled; this animal swam with vertical undulation like an otter.
The skull was different-it was longer than Pakicetus’, with the eyes moved sideways to give a sweeping point of view, the teeth are all the same shape and size-long and sharp and strong, acting like spears to capture fish and larger prey. Both the head and body are larger, suggesting than it was eating larger prey both in the water and on land. It might have hunting like a crocodile-ambushing reptiles, fish and land animals in quick bursts and dispatching them with its powerful jaws. The limbs could still support its weight, but only barely. This animal spent very little time on land, unlike Pakicetus. 

Thewissen also recently found an animal that brackets Pakicetus on the other side, an animal that was barely aquatic but ancestral nonetheless to whales. In 1971, A. Ranga Rao of India collected many interesting fossils, but died before he could examine them. For 35 his widow held on to the bones, forgotten by paleontology until 2007. Then, Thewissen and his colleges Baipai and Sahni finally discovered these bones and began to work on them. They found out that they were of a new animal ancestral to Pakicetus itself.

This animal, best resembling a cross between a small deer and a pig, with a long tail, is called Indohyus. While small and having a terrestrial physiology, it connects with Pakicetus in two significant ways. First, the ear is shaped exactly like that of Pakicetus and whales, indicating that it spent time underwater. Secondly, like Pakicetus and other amphibious animals, it had solid or osteosclerotic bones to reduce buoyancy.  Other scientist saw a clear connection with the water chevrotain, a nocturnal primitive ungulate living in central Africa. These solitary, tusked animals have very similar skeletons to Indohyus, adapted for plowing through thick bush and swimming through water.  Unlike Pakicetus and like the water chevrotain, the teeth and jaws indicate it was a herbivore.

It was Indohyus, along with DNA analysis, that revealed that the ancestors of whales were distant relatives of hippos and pigs, basal aritodactyls. Something pressured some of these herbivores and omnivores to an aquatic lifestyle in the tropical Eocene, and within 15 million years they evolved into the mighty whales like Basilosaurus. The evolutionary puzzle, the ancestry of whales, is finally solved.

Our final fossil I remember being in the news from 1993, back when dinosaur paleontology was experiencing a renaissance. In this case, Paul Sereno of the University of Chicago and Ricardo Martínez of the University of San Juan were the protagonists. The join university expedition was prospecting in the rich fossil biome of Ischigualasto in San Juan Argentina, and discovered a tiny dinosaur that seemed to enter a new chapter in paleontology. 

Only about 20 lbs and 3 feet long, this dinosaur had more primitive traits than any other. However, it already had the key dinosaur adaptation of long, erect limbs for fast running.  It had three vertebrae attached to the pelvis, unlike other dinosaurs with had two. It had five fingers on each hand, but two of them were tiny and vestigial.  Most importantly, it had heterodont teeth-it had both leaf shaped teeth like that of basal sauropomorphs like Anchisaurus, and serrated recurved teeth like basal theropods like Coelophysis. 

It's this mixture of features that have made paleontologists argue whether it is a basal theropod or a basal sauropodomorph.  This mixup confirms an old classification by Harry Seeley in 1888; Seeley divided dinosaurs into two divisions based on the shape of their hips. In one group were the beaked dinosaurs with birdlike hips: stegosaurs, ankylosaurs, ceratopsians, pachycephalosaurs, and ornithopods. In the other were the giant sauropods and the carnivorous theropods in a collective group called the Saurichians or lizard-hips.  What Eoraptor did was finally present a common ancestral morphology to both lines. Eoraptor and its kin were omnivores, with teeth that could be used for either eating plants or meat.  As the Triassic went on, these dinosaurs split into plant eating sauropods and prosauropods, and meat eating theropods who would only re-evolve herbivory at the end of the Jurassic.   Eoraptor is the link between the robin and the brontosaur. 

What will we discover in the next 108 years? Who knows. There are many questions left unanswered by the fossil record, many lineages with tiny gaps, many fossils yet to be discovered. Evolution is full of surprises even in living animals, and extinct animals spanning millions of years of evolution show an amazing variety of lineages and body shapes.  New amazing fossils are found even today. I’m sure we’ll find plenty of scientific gold by the next time the Cubs win the next World Series.

1 comment:

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