Dinosaurs Rediscovered

by Michael J Benton

  Dinosaur neuroscientists used to look for natural rock casts from inside the braincase. Then they found that they could gain some understanding of the brain shape and size by filling up the braincase region of a cleaned-up fossil skull with casting medium. Now they use CT scanning, and the resulting brain models (see pl. xi) can be spectacular, showing the so-called ‘optic lobe’, responsible for processing images from the eyes, on two stalks sticking well forward, and then the mid- and hindbrain portions within the braincase. At the sides, the cranial nerves sprout out, those key nerves that make the organs of the face function. The semi-circular canals of the middle ear are even visible (see pl. xii) – these are the key organs of balance.

  This is all very well, but were dinosaurs intelligent or not? Intelligence has always been a topic of great importance for humans because we define ourselves based on our intelligence – we called our species Homo sapiens, meaning ‘wise person’. Indeed, our brains are large, but a whale’s brain is larger. Is it more intelligent? Not necessarily, because of course brains are scaled in proportion to body size. So, brain biologist Harry Jerison proposed a measure of the ratio of brain size to body size, which he called the encephalization quotient (EQ) in 1973, and he argued it was a pretty useful way to measure animal intelligence. As expected, mammals have relatively large brains, whereas reptiles have relatively small brains. Birds fall somewhere in between, closer to mammals than to reptiles, and dinosaurs fall between modern reptiles and birds in their EQ.

  So, dinosaurs on the whole weren’t very brainy at all, even though some of them might have shown complex behaviour around mate choice. We can probably say that some dinosaurs at least, perhaps the small theropods, were as brainy as birds, and more intelligent than lizards or crocodiles. Here we are pushing the limits in trying to retrieve information about unfossilizable soft tissues, but could we find more? What about unusual conditions of preservation?

  Can dinosaurs be preserved in amber?

  Who could dream of a better headline than ‘dinosaur preserved in amber’? And yet that’s what happened in 2016, when we announced one of the most spectacularly perfect dinosaur fossils ever discovered. I had the good fortune to be invited by Lida Xing, palaeontologist at the China University of Geosciences in Beijing, to be part of a team to describe an amazing fossil he had acquired in 2016 – a tiny dinosaur tail preserved in amber (see pl. vi). Under the microscope, you could clearly see the bones of the tail skeleton, the fluff of feathers around the tail, and even the withered remains of tail muscles and skin inside the amber.

  This was the most reported fossil discovery of 2016, with thousands of headlines around the world. In fact, it was rated as the eighth most reported scientific discovery that year, based on the number of reports, Tweets, and Facebook mentions. Look at the photographs – this is a truly astonishing fossil!

  The specimen came from Myanmar (Burma), from famous mid-Cretaceous amber deposits that had been known for their fossils since the 1890s. In a review published in 2002, palaeoentomologist David Grimaldi reported beautiful specimens of angiosperm flowers and other plant remains, as well as examples of thirty families of insects and spiders, and some isolated feathers. By 2010, the number of insect families represented had risen to nearly 100. The amber is dated at 98.8 million years ago, placing it squarely in the early phase of the Cretaceous Terrestrial Revolution, the key event mentioned in Chapter 2, when flowering plants and all their buzzing accompaniment of insects exploded onto the Mesozoic scene.

  Amber is a yellowish or orange-brown substance, partly transparent, and quite light in weight. It has been collected for centuries and used in jewelry and decoration. Many amber pieces contain insects and leaves, and these are often sold as unusual and attractive pendants and brooches. Amber is the fossilized resin of ancient trees, especially conifers such as pines and cypresses, which leak a sticky resin-like sap from their bark. Close study of the trapped organisms inside the amber shows all the fine details – for example, a tiny insect trapped in amber might show microscopic hairs over its back, and every lens in its compound eye. Some of the specimens even show colour patterns and perhaps the original colours. In the amber collections around the world, as well as insects and bits of plants, people have also found very rare examples of mushrooms, feathers, mammal hair, and even whole lizards and frogs.

  Amber is known from many localities, including the Baltic and Dominica, and it is mainly mid-Cretaceous to Cenozoic in age, so only known from the past 125 million years. New papers about fossils from the Burmese amber are coming out at the rate of 100 or more per year, so eventually this one assemblage will probably number hundreds of species.

  Understanding that birds are dinosaurs opened a new field of research, and the huge number of astonishing new fossils of feathered dinosaurs from China were perfect vindication of the great endeavours and insights of leading Victorian scientists such as Huxley and Darwin. New fossil finds fuel the field of palaeobiology, and the fossils from the Burmese amber in particular are providing access to specimens and soft tissues that would previously have been believed long destroyed.

  Yet, as we have seen, it is not just new finds, but also new technologies, that increase our knowledge. In delving deep into the structure of dinosaur bones and feathers, using CT scanning and high-powered microscopy, we have learned more in the past decade about thermoregulation, colour, and behaviour than in the previous century.

  Often, as we have found, the knowledge about modern organisms and tissues just isn’t there, and so the dinosaur studies stimulate a new investigation of their living relatives. For example, when Vinther and we began our studies of feather colour, there was no compendium of the distributions of melanin and melanosomes among the differently coloured feathers of modern birds. This stimulated ornithologists to gather together stray natural history observations and construct a detailed data frame that links colour to structure and chemistry, and so enables the palaeontologists to interpret their fossils reliably.

  The future will see more exceptional fossils, and closer attention to detail in exploring their microscopic structures. I still can’t imagine a better fossil than our dinosaur tail in amber…unless it was a whole baby dinosaur?

  Chapter 5

  Jurassic Park? (Or Not…)

  Traditionally, dinosaurs have been famed only for their extinction, but that’s quite negative – certainly from the dinosaur’s own point of view. Surely their lives were amazing, and we explore their astonishing palaeobiologies as living, breathing, eating, running, growing, and mating creatures in this book. How much fun it would be, then, to have a living dinosaur!

  The idea has been posited many times in science fiction. In his 1912 novel The Lost World, Sir Arthur Conan Doyle describes how the zoologist Professor George Edward Challenger and his team explore remote regions of South America. They have heard rumours of a high plateau in the mountains, far from any civilization, that remains frozen in time from the days when dinosaurs roamed the Earth. After many adventures, the explorers reach the plateau, and they find a strange ancient world, populated with fiendish ape-men and terrifying prehistoric creatures. Challenger’s team are chased by dinosaurs, and great leathery-winged pterodactyls dive-bomb them from the air. Eventually they get back to safety, and they bring a baby pterodactyl back to London to show to an amazed and disbelieving world.

  Sir Arthur Conan Doyle’s The Lost World (1912) was first made into a film in 1925.

  Towards the end of the First World War, Edgar Rice Burroughs imagined a world of living dinosaurs and mammoths on the island Caprona, mysteriously located somewhere in the South Pacific, in his novel The Land that Time Forgot (1918), another classic in the genre. His story involves German and British troops, U-boats, and a world at war.

  There were many more such adventure tales through the twentieth century, but the most convincing and scientific account was by Michael Crichton, in his novel Jurassic Park, published in 1990, and made into a film by Steven Spielberg in 1993. The s
tory is well known, and founded in Crichton’s knowledge of major advances in genomics around that time. He suggested that minute fragments of dinosaur DNA recovered from the gut of a blood-sucking mosquito preserved in 100-million-year-old amber could be amplified, inserted into the ovum of a modern amphibian as the host, genetically engineered, and then a baby dinosaur would hatch from the egg.

  The focus on DNA (short for ‘deoxyribonucleic acid’) was justified, because DNA famously carries the genetic code – it is the stuff of the chromosomes inside the nucleus of every cell in your body. In a human, there are some 3 billion base pairs (bits of genetic code), distributed through 46 chromosomes (2 × 23 unique chromosomes), and these base pairs are arranged into 30,000 genes which, together, provide all the instructions to make a human being, and to maintain the cells by repair. So, Michael Crichton could describe the laboratory work in convincing detail in his book, and it was an equally believable part of the film. But could it really work?

  At one level, Crichton was hugely prescient. He had early on trained as a medical doctor, and so was comfortable with the medical and biological literature. He was quick to appreciate the potential of the new cloning method, the polymerase chain reaction (PCR), which had been developed in 1983 by Kary Mullis, and for which he received the Nobel Prize for Chemistry a decade later. PCR allows medical doctors and biologists to amplify a single copy or a few copies of a segment of DNA to thousands or millions of copies. Before PCR, large, purified samples were needed before any assay could be carried out, and this made molecular biology and genetic engineering hugely costly and time-consuming. After PCR came the genetic revolution, with all its economic consequences for the future of medicine and agriculture.

  Here is a step-by-step outline of how to clone a dinosaur, or at least in the way they did it in Jurassic Park:

  1.Extract blood from a mosquito in amber by inserting a fine-needled syringe.

  2.Concentrate the DNA by spinning the blood sample very fast in a centrifuge.

  3.Take a small sample of the concentrated DNA and clone (= multiply) it.

  4.To clone the DNA, it is cut into sections; these are inserted into bacteria that then copy the segments, and divide many times. So, one copy becomes many copies.

  5.The multiplied DNA sample is then injected into the egg of a modern frog (the frog DNA has already been removed, and the egg is just a single cell at the start).

  6.The dinosaur DNA takes over the working of the frog’s egg and, instead of having the genetic code for a frog, it has the genetic code for a dinosaur.

  7.The scientists then wait for the frog’s egg to develop – into a dinosaur.

  8.The egg does not turn into a tadpole, which would then turn into a frog. The genetic code has been replaced, and the single-celled egg then divides into two, four, eight, sixteen…but each of those cells is being guided by the dinosaur DNA to be a dinosaur cell.

  9.The outside cells form a hard eggshell, and so the egg looks like a dinosaur egg, with a hard shell like a bird’s egg, not a soft and squishy frog’s egg.

  10. Then comes the day of hatching, which is shown in the film. A crack appears in the hard, white shell, a scaly snout pokes out, and then a head, and at last a small dinosaur hops out, ready to snap and bite and looking for food.

  So, this seems quite straightforward. Molecular biology and genetics have advanced so much in the century since Conan Doyle wrote The Lost World that anything seems possible. Can we really hope to use modern molecular techniques to bring ancient animals back to life?

  Has dinosaur DNA ever been identified?

  I remember reading Crichton’s book when it came out in 1990, and palaeontologists were intrigued. Many, I’m sure, read the book hoping to pick holes in it, but mostly they had to admit the scenario was plausible. The technical problem of implanting the DNA and making a dinosaur was surely very tricky, but then it was not universally rejected that we might some day recover real dinosaur DNA. And, indeed, that’s just what happened, even before the film came out in 1993.

  In 1992, Raúl Cano and his West Coast colleagues caused a sensation. They announced that they had extracted DNA from a fossil bee, preserved in amber from the Dominican Republic in the Caribbean, dated at up to 40 million years old. This was not from a dinosaur, but any record of ancient DNA was a start. A year later, Cano and colleagues revealed that they had extracted DNA from a plant in the Dominican amber, and something even more amazing: DNA from a weevil preserved in amber from the Lebanon, dated at 120–135 million years old.

  Extracting organic molecules from fossils in amber was all the rage around 1990, and independent labs announced their extractions of DNA from a termite in the Dominican amber and from a beetle in Lebanese amber, apparently confirming the Cano team’s results. These reports of DNA from an ancient weevil and an ancient termite, insects that lived at the same time as the dinosaurs, could not have been better timed. Admittedly, the teams had not extracted the blood of a dinosaur from a mosquito, but they had apparently proved that DNA could exist for millions of years, from the age of the dinosaurs. So maybe Crichton’s imaginative story could come true.

  Then, in 1994, came the bombshell. Dinosaur DNA was announced, in a paper in Science, the leading US science journal. The discovery was reported by New Scientist at the time:

  Dinosaur bones retrieved from a coal mine have given up some of their secrets to scientists at Brigham Young University in Utah. Scott Woodward and his team have extracted short stretches of the dinosaur’s DNA, although they have a long way to go before they can reconstruct a whole creature as in Michael Crichton’s Jurassic Park.

  Woodward and his team extracted DNA from nine samples during a year of experiments, but the success rate was only 1.8 per cent. ‘If we hadn’t gotten one in an early round (of experiments), we probably would have given up,’ he admitted. As New Scientist continued, ‘The DNA came from two unfossilised pieces of bone from deposits 80 million years old in a Utah coal mine. Although the prehistoric owner of the bones has not been identified, their size and location makes Woodward “confident they are dinosaur bones”.’

  A mosquito preserved exquisitely in amber.

  However, within a year, the story had been blown. The ‘dinosaur DNA’ was in fact human. Woodward denied this initially, and promised follow-up work, but his paper was one of several under close scrutiny at the time. In most of these early experiments, the authors had not taken sufficient precautions to avoid the risk of contamination. A key property of PCR is that it clones multiple copies of DNA from very small samples, and indeed all it can take is a drop of sweat or a sneeze by one of the technicians in the lab, and the whole study is spoiled.

  Do organic molecules survive in the fossil record?

  The risk of contamination when measuring ancient molecules in fossils, especially ancient DNA, was highlighted from the 1990s. Critics noted the risk of contamination, not just by human DNA, but also by DNA from modern animals. Indeed, the risk in the early reports of plant and insect DNA was that the fossil samples were being analysed in labs that also processed DNA of modern relatives. So, for example, the DNA extracted from the Cretaceous weevil or termite in amber could easily be mixed up with DNA from modern weevils and termites. Something stricter was needed for all future studies of ancient DNA.

  Since the 1990s, the technology of ancient DNA labs has advanced enormously to exclude all risk of contamination. The strict measures include the following: (1) everyone entering the lab has to remove their outer clothing and change into a cleaned suit, which has a hood to cover the hair, and a face mask to prevent the technicians from breathing or shedding hair onto the samples; (2) all ancient DNA is studied in one lab, and modern DNA is studied elsewhere, to avoid any risk of mixing; (3) every analysis is repeated in another lab, to ensure any contamination is highlighted; and (4) the ancient DNA lab is sterilized every night by bathing everything in ultraviolet rays overnight, so any living organisms, whether flies or bacteria, are killed.

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p; These precautions should ensure that contamination is excluded, but how long can DNA survive? One of the most prominent critics of the reports of ancient DNA was biochemist Tomas Lindahl in London. He noted that DNA degrades in days, months, or years. So, under normal conditions, there wouldn’t be much DNA left after 100 years, let alone 100 million years. Subsequent studies have shown that it is possible to extract DNA from museum skins and skeletons of recently extinct animals, such as 100-year-old specimens of the horse-like quagga from southern Africa, and the dodo, which died out before 1681. Records were pushed back even further to ancient Egyptian mummies from 5,000 years ago, then 10,000-year-old mammoths, and finally, in 2013, DNA was retrieved from a horse dated as 700,000 years old.

  This horse example is much older than all other examples, and the DNA is fragmented into many short sequences. Indeed, even after 100 years, the quagga DNA had broken down substantially, and this makes its interpretation very tricky. Once the fragments consist of fewer than ten base pairs, it might seem impossible to reconstruct anything like an original DNA sequence of any length; the only solution is to use massive computing resources to crunch through every possible combination of answers until something plausible emerges. So, it’s unlikely that any dinosaur DNA, or indeed any DNA older than 1 million years, let alone 100 million years, will ever be retrieved.