Kurzgesagt – In a Nutshell
Sources – The Mysteries of the Past that are Lost forever
We would like to thank the following experts for their support:
Prof. Thomas Holtz
Dept. of Geology, University of Maryland
Albert Chen
Department of Earth Sciences, University of Cambridge
– We now recognize about 1.5 million eukaryotic species but there may be as many as 10 million alive today. And although we are adding some 15,000 new species to our collective knowledge each year, the vast majority of life on earth is still undiscovered.
Following study predicts the number of eukaryotic species as 8.7 million with an error bar of 1.3 million, so the more inclusive estimate is 8.7 + 1.3 = 10 million.
#Number of species on Earth tagged at 8.7 million, Nature, 2011
https://www.nature.com/articles/news.2011.498
Quote: “There are 8.7 million eukaryotic species on our planet — give or take 1.3 million. The latest biodiversity estimate, based on a new method of prediction, dramatically narrows the range of 'best guesses', which was previously between 3 million and 100 million. It means that a staggering 86% of land species and 91% of marine species remain undiscovered.”
#Mora C, Tittensor DP, Adl S, Simpson AGB, Worm B. How Many Species Are There on Earth and in the Ocean?, 2011
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127
Quote: “This approach was validated against well-known taxa, and when applied to all domains of life, it predicts ∼8.7 million (±1.3 million SE) eukaryotic species globally, of which ∼2.2 million (±0.18 million SE) are marine. In spite of 250 years of taxonomic classification and over 1.2 million species already catalogued in a central database, our results suggest that some 86% of existing species on Earth and 91% of species in the ocean still await description.”
#Robert M. May, Why Worry about How Many Species and Their Loss?, 2011
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001130
Quote: “Currently, diligent field taxonomists are adding newly discovered species at the rate of very roughly 15,000 each year (when discounted for synonyms) [2]. Given that we currently recognize something like 1.5 million distinct eukaryotic species, Mora et al.'s estimated species number suggests 480 years to finish the job. It is, however, reasonable to expect that in the near future, molecular methods—“barcode taxonomy”—will greatly speed up the task of keying-out collected material, as well as resolving synonymies”
– This is just what is around today. An estimated four billion species emerged on our planet in the past eons. But at least 99% of them have died out, way before humans spoke the first words.
#Barnosky, A., Matzke, N., Tomiya, S. et al. Has the Earth’s sixth mass extinction already arrived?, 2011
https://www.nature.com/articles/nature09678
Quote: “Of the four billion species estimated to have evolved on the Earth over the last 3.5 billion years, some 99% are gone”
– For a dead animal to fossilize a number of things must go just right: The right environment, timing and conditions. And then the fossil needs to survive for millions or hundreds of millions of years and then get back to the surface – and then be discovered within the short time before natural processes dissolve it. So it is kind of a wonder that we have what we have and know what we know.
There are several features contributing our likelihood of finding fossils and introducing biases:
1. Size of the organism: Bigger species generally have larger bones that are more likely to mineralise, harder to erode over time and easier to find than the smaller organisms.
2. Habitat of the organism: Organisms that lived (or died) closed to a body of water have higher chances to turn into fossils. Hot and moist environments speed up the decay of carcasses so remaining won't have time to be buried. Therefore, rainforests are not the best places to die to make it into the fossil record whereas floodplains, stagnant lakes or coastal lagoons are great.
3. Period: The older a fossil is, the more time it has to be eroded, or destroyed.
4. Age of the organism: Adults generally have better ossified bones than younger members of the same species. Therefore, they accumulate more materials to mineralise and are better preserved.
5. Population: If there are more individuals of the species then we would be more likely to stumble upon their fossils compared to species with smaller population sizes or restricted to smaller environmental niches.
6. Geography: Some countries are not open for fossil excavations (political reasons) or difficult to excavate (thick vegetation).
7. Number of body parts contributing to fossil record: Theropods shed teeth constantly over their lifespan so there would be a few hundred teeth that could be found for an individual. However, a toothless animal would only have a single skeleton to be buried.
8. Large body parts other than skeleton: Sizable bits of ossified body parts other than the main skeleton such as armour, tail clubs, scutes and plates increase the chances of entering the fossil record. For example, an aetosaur with its armoured plates would have double the number of ossified parts than a same sized prosauropod.
9. Likelihood of loss of bones before turning into fossils: Theropods probably never preyed on Ankylosaur tail clubs, but juveniles were far easier to destroy entirely.
10. Current research interest on the organism: Theropods get far more research attention than do stegosaurus, it may be that many stegosaurus remains have been skipped attention when excavating in the field or misidentified when found?
11. Invertebrate vs. vertebrates: Invertebrates are of course typically far more common than vertebrates since they don't have a skeleton to get ossified. We find shells from them of course but insects and worms are much less likely to come across than bones. For example, it is not even possible to talk about an octopus fossil record.
12. Other special cases: Predators can dominate a fossil bed or large groups of herbivores could have been destroyed by natural disasters and appear to be the only thing in a fossil bed as a result.
Following sources were used to put the above list together:
#David Hone, Bias in the fossil record, 2008
https://archosaurmusings.wordpress.com/2008/10/15/bias-in-the-fossil-record/
#Dinosaur Bones, AMNH,
https://www.amnh.org/dinosaurs/dinosaur-bones
– Take the dinosaurs since they were one of the largest and most successful groups of animals for some 165 million years – also a lot of fun to animate.
#When did dinosaurs become extinct?, USGS
Quote: “Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for about 165 million years. If all of Earth time from the very beginning of the dinosaurs to today were compressed into 365 days (one calendar year), the dinosaurs appeared January 1 and became extinct the third week of September. (Using this same time scale, the Earth would have formed approximately 18.5 years earlier.) Using the same scale, people (Homo sapiens) have been on earth only since December 31 (New Year's eve). The dinosaurs' long period of dominance certainly makes them unqualified successes in the history of life on Earth.”
– In the last 200 years tens of thousands of fossils from over 1000 dinosaur species have been found.
It is not easy to put an exact number on the individual fossils. However, we can have a good estimate based on the new dinosaur species discovered each year since the early 19th century. The chart below for instance shows Mesozoic dinosaur species named each year (Courtesy of Albert Chen). Even though the exact numbers would depend on the preferred taxonomy, the chart could still give us an idea about the increase in the number of discoveries in recent years. From the 90s onwards, the number of new Mesozoic dinosaurs named per year hit 40 compared to the rate of 10 species per year in the earlier portion of dinosaur paleontology. The chart below gives a grand total of 1700 known Mesozoic dinosaurs.
Data Courtesy of John D'Angelo and Justin Tweet
#Katie Peek, Dinosaur Discoveries Are Booming, 2021
https://www.scientificamerican.com/article/dinosaur-discoveries-are-booming/
Quote: “In the two centuries since the first dinosaur bones were identified in England, nearly 11,000 dinosaur fossils have been unearthed worldwide, two thirds of them in North America and Europe. [...] Widening the scope depends on building local expertise—a tricky task for a fairly niche (and not particularly lucrative) field. Investment could be fruitful: paleontologists have identified about 1,000 dinosaur species and estimate that at least that many more have yet to be found.”
Following database helps to visualize the distribution of some of the fossil record across the globe.
#The Paleobiology Database
– Lately we entered a golden era of discovery and about 50 new dinosaur species are discovered each year, expanding what we know and what we know that we don’t know about them, which is amazing. But it also makes us aware of all the things lost in the past forever.
#DINOSAURS, National Geographic, October 2020
Quote: “For several years scientists have unveiled an average of about 50 new dinosaur species a year, a pace unthinkable decades ago. The updated menagerie ranges from pint-size fliers with bat wings to long-necked herbivores that were Earth’s biggest ever land animals. Medical scanners, particle accelerators, and chemical analyses are letting researchers virtually separate rock from bone and see fossils’ tiniest hidden features. From the colors of dinosaurs’ eggs and feathers to the shapes of their brains, our dino encyclopedia now includes unprecedented details on how these animals were born, grew up, and lived.”
Even though there is a lot more unknown about dinos now compared to the last decades, there are still gaps in the knowledge regarding some of the basic behaviors of dinosaurs such as mating rituals, parenting or hunting behavior.
Most dinosaur fossils, for example, do not retain the reproductive organs. To gain insights as to how these giant animals reproduce, scientists turn to their relatives, birds and crocodilians. A common trait in both groups is cloaca, the single end point for the reproductive, urinary and intestinal functions in males and females of birds and crocodilians, so probably of dinosaurs as well. Therefore, genitals of dinos would not be visible but concealed in cloaca. Recently, scientists found remains of such an opening in an exceptionally well-preserved Psittacosaurus –an ornithischian dinosaur that lived about 110 million years ago in today’s China. The researchers note that the structure is highly pigmented which might function in display and signalling, similar to living baboons and some breeding salamanders.
#Jakob Vinther, Robert Nicholls, Diane A. Kelly. A cloacal opening in a non-avian dinosaur, 2021.
Quote: “We show here that the fine anatomy of the vent is remarkably well preserved and can be retrodeformed to illustrate its three-dimensional nature. The vent’s scale anatomy and pigmentation are distinct from adjacent body regions, and although its anatomy does not reveal much information about the ecology, or sex, of this dinosaur, it suggests possible roles for visual and olfactory signalling.”
Similarly, parenting behaviors are also not straightforward to read out directly from the fossils,since dinosaur nests are rare in the fossil record. Rather scientists have to infer a great deal from the available evidence. The following study, for instance, found a partial skeleton of a medium-sized oviraptorid with some cervical bones on a clutch of at 24 eggs. The researchers also found that the eggs were incubated at similar temperatures to the body temperature of the parent, suggesting that it might have been sitting on the nest to keep the eggs warm.
#Bi et al., An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avian theropod dinosaurs, 2021.
https://www.sciencedirect.com/science/article/abs/pii/S2095927320307635?via%3Dihub
Quote: “Recent studies demonstrate that many avialan features evolved incrementally prior to the origin of the group, but the presence of some of these features, such as bird-like brooding behaviours, remains contentious, in non-avialan dinosaurs. Here we report the first non-avialan dinosaur fossil known to preserve an adult skeleton atop an egg clutch that contains embryonic remains. The preserved positional relationship of the adult to the clutch, coupled with the advanced growth stages of the embryos and their high estimated incubation temperatures, provides strong support for the brooding hypothesis.”
Another area that is still vague is whether dinosaurs were hunting in packs or they were scouting alone. Even though researchers found evidence of dinos walking together, they still do not know for sure what was the underlying social reason.
#Titus et al, Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousness, 2021.
https://peerj.com/articles/11013/
Quote: “Tyrannosaurids are hypothesized to be gregarious, possibly parasocial carnivores engaging in cooperative hunting and extended parental care. A tyrannosaurid (cf. Teratophoneus curriei) bonebed in the late Campanian age Kaiparowits Formation of southern Utah, nicknamed the Rainbows and Unicorns Quarry (RUQ), provides the first opportunity to investigate possible tyrannosaurid gregariousness in a taxon unique to southern Laramidia.”
– Imagine if we took all the animals that lived in the last 50 million years and randomly chose 10,000 individuals from 1000 species to fossilize.
One can actually project this thought experiment back onto the existing fossil record to come up with a quantification of how much we might be missing today from the biological abundance of the past. Although scientists can learn a great deal from the fossil record about the individual species, it is still difficult to infer population-level information such as population density and abundance, mainly due to the incompleteness of the fossil record. Following study estimated that among the 2.5 billion T-rexes that ever lived, 1 in ~80 million individuals has been recovered by humans as fossils so far.
#Marshall et al., Absolute abundance and preservation rate of Tyrannosaurus rex, 2021.
https://science.sciencemag.org/content/372/6539/284
Quote: “We estimate that its abundance at any one time was ~20,000 individuals, that it persisted for ~127,000 generations, and that the total number of T. rex that ever lived was ~2.5 billion individuals, with a fossil recovery rate of 1 per ~80 million individuals or 1 per 16,000 individuals where its fossils are most abundant. The uncertainties in these values span more than two orders of magnitude, largely because of the variance in the density–body mass relationship rather than variance in the paleobiological input variables.”
Another study accounted for extant species and estimated that of the modern species considered threatened, only about 9 percent have a known fossil record – which means that the future fossil record would be highly biased and underwhelmed compared to the actual diversity.
#Roy E. Plotnick, Felisa A. Smith, S. Kathleen Lyons, The fossil record of the sixth extinction, 2016.
https://www.researchgate.net/publication/296693662_The_fossil_record_of_the_sixth_extinction
Quote: “Comparing the magnitude of the current biodiversity crisis with those in the fossil record is difficult without an understanding of differential preservation. Integrating data from palaeontological databases with information on IUCN status, ecology and life history characteristics of contemporary mammals, we demonstrate that only a small and biased fraction of threatened species (< 9%) have a fossil record, compared with 20% of non-threatened species. We find strong taphonomic biases related to body size and geographic range. Modern species with a fossil record tend to be large and widespread and were described in the 19th century.”
– Animals so weird and selected for ecological niches so specific that evolution molded their bodies so absurd that they’d seem made up to us today.
One example of this from the fossil record is Shuvuuia deserti of Late Cretaceous. In the following study, researchers looked into inner ears and scleral eye rings of Shuvuuia and estimated that these dinos would have amazing hearing, comparable to that of barn owls today who hunt at night relying on hearing only. They also assessed the size of the bones around the pupil which predicts a great night vision for this dino and altogether making it a great fit for nocturnal lifestyle.
#Choiniere et al., Evolution of vision and hearing modalities in theropod dinosaurs, 2021.
https://science.sciencemag.org/content/372/6542/610
Quote: “Combined visual and auditory specializations for nocturnality evolved independently in mammals, birds, and, as reported in this study, nonavialan dinosaurs, providing an example of convergent sensory evolution in vertebrates. The sensory paleoecology of dinosaurs remains poorly understood in general. Nevertheless, our findings provide information on deep evolutionary divergences of activity patterns among nonavialan theropods and strong evidence for nocturnal specialization through 95 million years of alvarezsauroid evolution. Many living animals are active at night, but nocturnal communities remain poorly studied both today (28) and in the past. Identifying specialized night foragers such as Shuvuuia highlights the occurrence of diel partitioning among predators in Mesozoic terrestrial ecosystems. It indicates that richly sampled paleoecosystems such as the Djadokhta Formation hosted previously unrecognized nocturnal and diurnal subcommunities, and expands our understanding of the structure of past ecosystems and of the ecological traits of theropod dinosaurs.”
Following image shows a skeletal reconstruction of the animal:
#Hendrickx et al., An overview of non-avian theropod discoveries and classification, 2015.
– We know a lot of species are lost forever just because of the environment they lived in. For example, lush jungles are basically bound to prevent fossilization as the chance for an animal to get buried here is minimal. Countless scavengers of all sizes break freshly deceased animals extremely quickly and the soil is often so acidic that bones get dissolved. And so fossils of dinosaurs from jungles are practically nonexistent.
#What are the odds of a dead dinosaur becoming fossilized?, Scientific American, 2016
https://www.scientificamerican.com/article/what-are-the-odds-of-a-de/
Quote: ”Studies by taphonomists (paleontologists who study the transition of animals from the biosphere to the lithosphere; taphonomy literally means "burial laws") have shown that organisms that die on land in lush jungle locales are rarely fossilized. In these settings, there is little chance of being buried, scavenging vertebrates and insects are prevalent, bacteria that break down flesh and bones are abundant, and the soils are extremely acidic and tend to dissolve bones. As a result, remains of dinosaurs from such former surroundings are practically nonexistent. ”
Some of the species used as an inspiration in the video:
Sinomacrops bondei (Middle-Late Jurassic, China):
Pterosaurs are the first vertebrates known to develop active flight (other two are birds and bats). Images below show the fossil evidence and the reconstruction made based on it. However, reconstructions are generally not set in stone, they change as new fossil evidence comes. So we do not know how our understanding of Sinomacrops, and therefore its reconstructed image, is going to evolve in time.
#Wei, Xuefang et al. Sinomacrops bondei, a new anurognathid pterosaur from the Jurassic of China and comments on the group. 2021.
Deinocheirus mirificus (Mongolia, Late Cretaceous):
The following dino is one of the weirdest found so far. It had unusually large forelimbs (~ 2.4 m) which were probably used for defense against the abundant predators around. Scientists found fossils of fish cartilages in its stomach. It was probably living on floodplains/swamps with grassland so it might be using its horrible hands to dig up around the aquatic vegetation to find food.
#Lee et al., Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus, 2014.
– Today half of all known species live in the few remaining rainforests that only cover 2% of earth's landmass.
#Rainforest Alliance, Rainforest Facts Everyone Should Know, 2019.
https://www.rainforest-alliance.org/everyday-actions/9-rainforest-facts-everyone-should-know
Quote: “Although rainforests cover only 2 percent of the Earth’s surface, these ecological powerhouses are critical to nearly every aspect of the planet’s health—including our very ability to breathe. [...] Tropical rainforests cover less than 3% of Earth’s area, yet they are home to more than half our planet’s terrestrial animal species”
#Britannica, The loss of populations
https://www.britannica.com/science/conservation-ecology/The-loss-of-populations
– Millions of years ago when dinosaurs roamed earth, jungles covered much more of the planet.
The Cretaceous Period (144–66 million years ago) was the latest one of the three periods of the Mesozoic, the time of dinosaurs. It was one of the warmest intervals in Earth’s history. The sea levels were higher and atmospheric carbon dioxide concentrations were around 1,000 parts per million by volume. This caused a strong greenhouse effect which shaped the flora. Even the Antarctic was covered with a temperate rainforest whereas the polar ice caps were minimal. Through Mesozoic, in general, conifer and cycads were abundant which were later accompanied by flowering plants in the Cretaceous.
#Britannica, Cretaceous Period
https://www.britannica.com/science/Cretaceous-Period
Quote: “The climate was generally warmer and more humid than today, probably because of very active volcanism associated with unusually high rates of seafloor spreading. The polar regions were free of continental ice sheets, their land instead covered by forest. Dinosaurs roamed Antarctica, even with its long winter night.”
#Peralta-Medina, Emiliano & Falcon-Lang, Howard. Cretaceous forest composition and productivity inferred from a global fossil wood database, 2012. https://www.researchgate.net/publication/220013324_Cretaceous_forest_composition_and_productivity_inferred_from_a_global_fossil_wood_database
Quote: “Our global patterns of forest composition and productivity are mostly consistent with Cretaceous climate models (Beerling et al., 1999; Sellwood and Valdes, 2006), indicating expansion of the tropical belt and poleward extension of forests. Tree-ring data also support the hypothesis that extreme greenhouse warmth and/or CO2 fertilization significantly influenced terrestrial biomes, more than doubling global forest productivity (Beerling et al., 1999).”
#Klages, J.P., Salzmann, U., Bickert, T. et al. Temperate rainforests near the South Pole during peak Cretaceous warmth, 2020.
https://www.nature.com/articles/s41586-020-2148-5
Quote: “The assemblage is dominated by pollen of the conifer tree families Podocarpaceae and Araucariaceae with abundant ferns, including the tree ferns Cyathea, documenting the initial stages of an austral temperate rainforest (Fig. 2; Extended Data Fig. 2; Extended Data Table 2). The presence of the heterocyst glycolipids HG30 triol and keto-diol (Extended Data Fig. 4; see Methods) also indicates that benthic cyanobacterial mats colonized fresh water bodies within this temperate rainforest, providing additional evidence for the development of a highly complex ecosystem in the ASE during the Turonian–Santonian. In combination with published palaeo-topographic and palaeo-tectonic information22,24,31,32, the different taxa and their bioclimatic importance (see Methods) were combined and visualized to create Fig. 3. Members of the Proteaceae family presumably formed a flowering shrub understorey in the tall Late Cretaceous conifer rainforest of the ASE depicted in Fig. 3. The lignite layer is rich in spores of Stereisporites antiquasporites (NLR: Bryophyte, Sphagnum), which further suggest the temporary existence of a peat swamp in the diverse temperate lowland rainforest.”
– This means that almost all boneless or shell-less animals are practically wiped from the fossil record. If we take a look at the stunning diversity of weird animals like worms, jellyfish and slugs alive today we can just speculate what we are missing.
#Fossils, Earth Science
https://courses.lumenlearning.com/earthscience/chapter/fossils/
Quote: “For animals that lack hard shells or bones, fossilization is even more rare. As a result, the fossil record contains many animals with shells, bones, or other hard parts, and few softbodied organisms. There is virtually no fossil record of jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils. Because mammal teeth are much more resistant than other bones, a large portion of the mammal fossil record consists of teeth. This means the fossil record will show many organisms that had shells, bones or other hard parts and will almost always miss the many soft-bodied organisms that lived at the same time.”
– Although kindly many mostly soft and gooey species also left us an incredible diversity of shells that tell us an incredible lot about our past, so at least we have that. Still when we think about all the boneless species that may have existed in the last half billion years even our best attempt at imagining them falls short.
The shells of cephalopods, clams, snails and mostly all soft and squishy animals with a hard outer cover fossilize quite well. In fact, the fossil record of molluscs is even better than that of vertebrates. Shells of these animals are made of calcium carbonate which is the main ingredient of limestone that makes these fossils technically rocks.
#The mollusca, UCMP, 2007
https://ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php
Quote: “They also have a very long and rich fossil record going back more than 550 million years, making them one of the most common types of organism used by paleontologists to study the history of life. [...] The Mollusca include some of the oldest metazoans known. Late Precambrian rocks of southern Australia and the White Sea region in northern Russia contain bilaterally symmetrical, benthic animals with a univalved shell (Kimberella) that resembles those of molluscs. The earliest unequivocal molluscs are helcionelloid molluscs that date from Late Ediacaran (Vendian) rocks. In the Early Cambrian the Coeloscleritophora are also present. Most of the familiar groups, including gastropods, bivalves, monoplacophorans, and rostroconchs, all date from the Early Cambrian, whereas cephalopods are first found in the Middle Cambrian, polyplacophorans in the Late Cambrian, and the Scaphopoda in the Middle Ordovician. Most of these early taxa tend to be small (‹10 mm in length). The Late Vendian-Early Cambrian taxa bear little resemblance to the Cambrian-Ordovician taxa (most of which remain extant today).”
– But it's not like reimagining something from its bones is straightforward and so how we imagined dinosaurs has changed a lot in the last few years. In the past many illustrations had a bony, minimalistic look, with a toothy grin for fierceness and danger.
The change of Spinosaurus would be a good example to demonstrate this point. Below is a 1985 reconstruction by artist John Sibbick, in which it is depicted as a pretty average meat-eating dinosaur with a sail on its back.
https://4.bp.blogspot.com/-gk_IzhlV41o/T940MTo5uVI/AAAAAAAAA80/5EWoJDw266I/s400/Spinosaurus.jpg
However, as more complete specimens are found, reconstructions also get more refined. Scientists now know that Spinosaurus had curious features like a tall, paddle-like tail but shorter legs, and a longer snout resembling more of crocodiles’. It was probably spending most of its day in the water. A recent reconstruction from 2020 pulls together these features:
https://pbs.twimg.com/media/EYkieDMXsAAu5VR?format=jpg&name=large
– But if we draw today's animals in a similar way, based on their skeletons, just for the fun of it, we get the most bizarre creatures. Elephants, swans and baboons look like monsters right out of nightmares.
Many characteristic anatomical features of animals are primarily defined by soft tissue. Lack of fossil evidence from soft tissue might lead future paleontologists to depict todays elephants, rhinoceros and horses in fundamentally different ways and also might give us a clue about all the misconceptions we have of the animals of the distant past.
We got a lot of inspiration and based our illustrations for this scene on the ones from the book:
#Darren Naish, C.M. Kosemen, John Conway, Scott Hartman, All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals, 2012
https://cmkosemenillustrated.tumblr.com/post/117679426290/an-elephant-a-rhinoceros-and-a-horse
– So similar to animals today, we should imagine dinosaurs with much more soft tissue, fat bellies or chests, weird soft parts like skin flaps, lips and gums and just more pronounced features that would make them seem much more pleasant fellows.
Traditionally, the fleshy nostril of dinosaurs has been placed in the back of the bony opening, but studies of extant dinosaur relatives suggest that it is located far forward. This would not only help them to better sample the odoronts immediately in front of them, but also would give them a softer face compared to the fierce demonstrations of T-rex, for instance, with wide nostrils and bony face.
#Witmer, Nostril Position in Dinosaurs and Other Vertebrates and Its Significance for Nasal Function, 2001
– Some soft features actually leave distinctive traces on bones that we can look for in the skeletons of extinct animals, which is where today’s animals with similar features are really helpful.
Large scales and keratin sheaths would give dinosaurs a distinct look for sure. But they also often leave distinctive textures on the bones, so that the scientists can infer and reconstruct some of that marked expression.
The figure from the following study demonstrates how some of the facial skin structures were inferred based on the marks they left on the facial bones of Pachyrhinosaurus.
#Hieronymus et al., The Facial Integument of Centrosa, 2009
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.20985
Another piece of clue that scientists use is the bumps on the arm bones of birds. These are generally where the feathers would attach for instance. Therefore, when scientists find the same structures on dinosaurs, they can have a good estimate of whether they had feathers or not. This is, for instance, the piece of fossil evidence that earned Velociraptor its feathers.
#Alan H. Turner, Peter J. Makovicky, Mark A. Norell. Feather Quill Knobs in the Dinosaur Velociraptor, 2007.
– A similar story applies to colors. Because we know how living birds color their feathers, modern technology combined with the exceedingly rare fossils with preserved remains of fuzzy feathers give us a peek at the real colors of extinct dinosaurs.
Some pigments are preserved in fossils. This is how scientists can predict and reconstruct their color palettes.
In the following study, scientists discovered of small theropod Caihong juji (Jurassic, China)
#Hu, D., Clarke, J.A., Eliason, C.M. et al. A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution, 2018.
https://www.nature.com/articles/s41467-017-02515-y
Quote: “Based on the assumption that these structures are melanosomes, most of the plumage of Caihong is predicted by discriminant function analysis as black, with iridescence primarily on the head, chest and, to a lesser extent, the base of the tail
(Supplementary Table 4, Supplementary Fig. 6). The morphospace of the platelet-shaped structures overlaps that associated with iridescent colours of vivid, highly variable hues in
hummingbirds and swifts (Figs. 5e–g, 6b)42–44, but also with grey and black colours in penguins45. However, unlike melanosomes in those penguin grey or black feathers, the structures in the 21 samples from the fossil appear aligned in sheets and dorsoventrally compressed (Fig. 5; Supplementary Fig. 7). This organization was further confirmed in SEM images taken on a rotating stage at three different angles to the preserved structures
(Supplementary Fig. 8).”
https://natureecoevocommunity.nature.com/posts/29859-a-bizarre-dinosaur-informs-feather-evolution
– We know that tiny Sinosauropteryx had a striped tail and its tiny dino buddy Anchiornis huxleyi was white and black with gorgeous red feathers around its head.
Pigments found in Sinosauropteryx ~130 million year old fossils in China indicated that it used a camouflage strategy called countershading: the back of the animal is lighter than the belly making it look less 3d. Based on this info, scientists can also infer the habitat of these animals: Animals that live in open habitats with direct sunlight and less-dense vegetation, have the dark-light transition sharper and higher up in their bodies (closer to back of the animal), and animals that live in closer habitats (like forests), have more gradual transitions and lower down (closer to underside of the animal). So they predicted that these guys were living in an open environment.
#Fiann M. Smithwick, Robert Nicholls, Innes C. Cuthill, Jakob Vinther, Countershading and Stripes in the Theropod Dinosaur Sinosauropteryx Reveal Heterogeneous Habitats in the Early Cretaceous Jehol Biota, 2017.
https://www.sciencedirect.com/science/article/pii/S0960982217311971
Quote: “Countershading is common across a variety of lineages and ecological time [1, 2, 3, 4]. A dark dorsum and lighter ventrum helps to mask the three-dimensional shape of the body by reducing self-shadowing and decreasing conspicuousness, thus helping to avoid detection by predators and prey [1, 2, 4, 5]. The optimal countershading pattern is dictated by the lighting environment, which is in turn dependent upon habitat [1, 3, 5, 6]. With the discovery of fossil melanin [7, 8], it is possible to infer original color patterns from fossils, including countershading [3, 9, 10]. Applying these principles, we describe the pattern of countershading in the diminutive theropod dinosaur Sinosauropteryx from the Early Cretaceous Jehol Biota of Liaoning, China.”
Anchiornis huxleyi lived during the Late Jurassic as per the fossil evidence found in China. In the image below, scientists reconstructed its color palette based on one complete specimen and another one with the tail only. Scientists study the morphology of specific organelles in the fossils: melanosomes which are melanin-containing organelles that determine key aspects of color. By analyzing melanosome size, shape, density, and distribution, plumage color patterns can be reconstructed. They also found that all the melanosome morphologies they found were within the range of those observed in birds living today.
#Quanguo Li et al., Plumage Color Patterns of an Extinct Dinosaur, 2010.
https://science.sciencemag.org/content/327/5971/1369
Quote: “The plumage color pattern elements of the Late Jurassic A. huxleyi are strikingly similar to various living birds, including domesticated fowl, providing insights into the evolution of feather-pigment pattern development (SOM text). [...] Complex within- and among-feather plumage coloration, such as that in A. huxleyi, is used in display and communication in living birds. Such communication, however, may function in different ways: commonly in intersexual communication (15), and less so in interspecific and intraspecific competition for restricted foraging [for example, multiple species of antbirds forage on army ant swarms (16)]. ”
– Still, for the vast majority of really any ancient extinct species we have no real clue what color they were. But we know what modern dinosaurs, birds, look like and here we find the most amazing variety.
Color patterns of Anchiornis huxleyi were revealed through comparison of its pigments to modern birds. Authors of the study report their complicated pattern of reddish brown, black, gray, and white feathers was perhaps used for attracting mates or some form of visual communication, similar to living birds.
Another example is the iridescent feathers of a Microraptor from middle Jurassic:
#Li et al., Reconstruction of Microraptor and the Evolution of Iridescent Plumage, 2012
https://science.sciencemag.org/content/335/6073/1215
Quote: “Quantitative comparison of these data with melanosome imprints densely sampled from a previously unknown specimen of the Early Cretaceous feathered Microraptor predicts that its plumage was predominantly iridescent. The capacity for simple iridescent arrays is thus minimally inferred in paravian dinosaurs. This finding and estimation of Microraptor feathering consistent with an ornamental function for the tail suggest a centrality for signaling in early evolution of plumage and feather color.”
Following image shows the fossil found in China (top) and the color coded image showing bones (blue) and feathers (orange). Researchers investigated the relations between the properties of melanosome and iridescent arrays in living birds with iridescent feathers, like Amazonetta brasiliensis, and the ones found in this previously unassigned feathered dinosaur specimen.
Scientists put melanosomes samples from the fossil specimen and extant (currently living) birds under the scope and compare the structures with each other to reconstruct what the old fellows were looking like. Of course, the whole processes was a little more complicated than this but in the end scientists had these scanning electron micrographs to characterize the melanosome morphologies: Melanosomes from matte black, brown, and gray feathers from living birds were significantly shorter (~1160 versus 1000 nm) and wider (~211 versus 279 nm) compared to iridescent feathers. In the following image for example one can compare the rod shape structures both in the iridescent feathers of Brazilian duck (E) and Microraptor (F)
Below is a life reconstruction of the Microraptor with glossy black feathers, to which researchers attributed an ornamental or signaling type of function:
It is not only dinosaurs themselves but also their eggs would come with different colors as well. Eggs of Heyuannia had a blue-green tint to them for instance.
#Wiemann et al., Dinosaur origin of egg color: oviraptors laid blue-green eggs, 2017
https://peerj.com/articles/3706/
Quote: “The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.”
– So some dinosaurs will have tried to blend in the background, while others might have fielded aggressive color schemes to attract mates or to appear dangerous.
Of course there is no way that we could know exactly how these amazing creatures would look back then. We can only use our imagination to speculate based on the current evidence.
A good camouflage, for instance, would get quite handy for the small plant-eating Orodromine to avoid predators.
#Varricchio David J, Martin Anthony J and Katsura Yoshihiro. First trace and body fossil evidence of a burrowing, denning dinosaur. 2007.
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2006.0443
https://twitter.com/studio252mya/status/974575991673638912
Another example of camouflage is Psittacosaurus’s strategy of countershading. Similarly to Sinosauropteryx, Psittacosaurus also had a lighter belly and a darker back with a smooth transition across its body – which would help it to navigate the closed conifer forests of Early Cretaceous China.
#Vinther, Jakob et al. 3D Camouflage in an Ornithischian Dinosaur, 2016.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5049543/
Quote: “This Psittacosaurus was countershaded [16] with a light underbelly and tail, whereas the chest was more pigmented. Other patterns resemble disruptive camouflage, whereas the chin and jugal bosses on the face appear dark. We projected the color patterns onto an anatomically accurate life-size model in order to assess their function experimentally. ”
– Some might have had impressive decorations or colorful beaks. Some may have been striped or patterned.
An oviraptorid might have presented its precocious feathers and head crest to attract mates. Oviraptors were bipedal dinosaurs with toothless beaks resembling that of parrots. They were smaller with slender but grasping hands and feathers. Some had ostentatious crests on their heads.
#W. Scott Persons, IV, Philip J. Currie, and Mark A. Norell. Oviraptorosaur tail forms and functions, 2014.
http://www.app.pan.pl/article/item/app20120093.html
Quote: “Based on the observed osteological morphology and inferred muscle morphology, along with the recognition that many members of the group probably sported broad tail-feather fans, it is postulated that oviraptorosaur tails were uniquely adapted to serve as dynamic intraspecific display structures.”
Some example species:
– Nomingia (Late Cretaceous, Mongolia):
https://en.wikipedia.org/wiki/Nomingia#/media/File:Nomingia Gobiensis.png
– Conchoraptor (Late Cretaceous, Asia):
https://twitter.com/MarioGBartual/status/836303813808115713/photo/1
– Citipati (Late Cretaceous, Asia):
Some other species had multiple epidermal structures covering their bodies, such as the different types of scales covering the tail, hands and feet of Kulindadromeus.
#Godefroit P., Sinitsa S.M., Cincotta A., McNamara M.E., Reshetova S.A., Dhouailly D. (2020) Integumentary Structures in Kulindadromeus zabaikalicus, a Basal Neornithischian Dinosaur from the Jurassic of Siberia.
https://link.springer.com/chapter/10.1007/978-3-030-27223-4_4
Other examples for bold displays with showy color patterns would be the horned ceratopsids and crested lambeosaurine duckbills. The following images are only glimpses into the great diversity of the head structures of Ceratopsians and Lambeosaurines:
https://commons.wikimedia.org/wiki/File:Lambeosaurus_BW_draft.jpg
Chinese Heterodontosaurid Tianyulong had spike-like body hair:
#Zheng, XT., You, HL., Xu, X. et al. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures, 2009
– Similarly we don’t know that much about dinosaur behaviour, although once again we can draw conclusions from extant animals. For example even apex predators like lions spend a lot of their time lying around and cuddling and licking and playing. Why would dinosaurs be so different?
There are many things that can not be directly read from the fossil record, rather scientists have to infer many things from the seemingly small amount of evidence. Detail of the behaviors such as mating, parenting or hunting can only be deduced upon close investigation and comparison to behaviors of living animals. Digital paleontology let scientists dig more information from the fossil evidence which was not possible before.
Using CT scans of the skull of Parasaurolophus, scientists reconstructed the mesh of air cavities and tubes in the crest of the animal. Modeling the air flow through these structures, scientists reproduced the low-frequency sound Parasaurolophus might have been producing.
#Sandia LabNews, Digital paleontology: Producing the sound of the Parasaurolophus dinosaur, 1997
https://www.sandia.gov/labnews/1997/12/19/dinosaur-story/
Quote: “Since it’s uncertain whether the Parasaurolophus had vocal cords, a variation of sounds with and without vocal cords was simulated.
“The sound may have been somewhat birdlike, and it’s probably not unreasonable to think they did songs of some sort to call one another,” Carl says. “Fossil records of the large bones in the dinosaur’s ears compared to corresponding bones in human ears suggest they were able to hear lower frequencies than humans.”
Williamson speculates that the dinosaur’s ability to make distinctive sounds probably enhanced its tendency to socialize with other Parasaurolophuses.”
#Hanson et al, The early origin of a birdlike inner ear and the evolution of dinosaurian movement and vocalization, 2020
https://science.sciencemag.org/content/372/6542/601.long
Quote: “Our analyses demonstrate that inner ear variation is structured in predictable ways across large evolutionary distances, and that this variation is correlated with locomotor behavior and hearing acuity in those taxa for which such data are available. The markedly avian semicircular canals of troodontids (Figs. 2 and 3 and fig. S1) suggest that these dinosaurs had locomotor control comparable to that of pterosaurs, Archaeopteryx, and early-diverging crown birds (Figs. 1 to 3 and 5). Many neoavian birds have a modified semicircular canal structure associated with high-maneuverability flight, aerial feeding, and predation that suggests these behaviors originated in this clade, but this group also exhibits reversals in vestibular-system structure corresponding to derived losses of these behaviors.”
– When we first found the skull of T. rex with its mighty teeth and probably the strongest bite of any land animal ever, we imagined a fierce and stupid beast.
In the following study, scientists reconstructed the biomechanics of the skull and jaw of T-rex and calculated the force it exerts when it chewed up its prey.
#Bates K. T. and Falkingham P. L., Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics, 2012
https://royalsocietypublishing.org/doi/10.1098/rsbl.2012.0056
Quote: “Bite mechanics and feeding behaviour in Tyrannosaurus rex are controversial. Some contend that a modest bite mechanically limited T. rex to scavenging, while others argue that high bite forces facilitated a predatory mode of life. We use dynamic musculoskeletal models to simulate maximal biting in T. rex. Models predict that adult T. rex generated sustained bite forces of 35 000–57 000 N at a single posterior tooth, by far the highest bite forces estimated for any terrestrial animal. Scaling analyses suggest that adult T. rex had a strong bite for its body size, and that bite performance increased allometrically during ontogeny. Positive allometry in bite performance during growth may have facilitated an ontogenetic change in feeding behaviour in T. rex, associated with an expansion of prey range in adults to include the largest contemporaneous animals.”
– But modern scanning technology revealed that T.rex had a larger brain-to-body ratio than some earlier giant meat-eaters.
Another well-known carnivore, Allosaurus, for instance, would have a smaller brain size relative to its body, compared to T-Rex.
The figure below from the following study compares the relative brain sizes among different dinosaurs and other reptiles:
#Lautenschlager et al., The Endocranial Anatomy of Therizinosauria and Its Implications for Sensory and Cognitive Function, 2012.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052289
– And it probably had very sharp hearing, vision and smelling and was in all likelihood not a stupid animal.
#McKeown et al., Neurosensory and Sinus Evolution as Tyrannosauroid Dinosaurs Developed Giant Size: Insight from the Endocranial Anatomy of Bistahieversor sealeyi
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24374
Quote: “They had large brains compared to many other dino-saurs, sharp senses of smell and hearing, and an expansive network of endocranial sinuses that may have been related to their sensory abilities and/or an adaptation for weight saving.”
#Hughes and Finarelli, Olfactory receptor repertoire size in dinosaurs, 2019.
https://royalsocietypublishing.org/doi/10.1098/rspb.2019.0909
Quote: “The largest reconstructed repertoires were for Tyrannosauroidea, specifically the large-bodied taxa, such as Tyrannosaurus rex (electronic supplementary material, table S1). The substantially smaller Dilong paradoxus has OBs that are both absolutely and relatively much smaller than Tyrannosaurus rex, consistent with the body size scaling relationship. Among tyrannosaurs, the large taxa had larger OR repertoires than any other non-avian dinosaurs, whereas Dilong paradoxus falls within the inner 95th quantiles of the modern bird distribution, even if the outlier taxa (zebra finch, chicken and budgerigar) are excluded. This overall increase in olfactory capability within Tyrannosauroidea may reflect ecological adaptation, allowing the tracking of prey over large distances, as in modern wolves [36], or to effectively scavenge carrion, as in the modern turkey vulture (electronic supplementary material, table S1).”
#Carr, T., Varricchio, D., Sedlmayr, J. et al. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system, 2017.
https://www.nature.com/articles/srep44942#citeas
Quote: ”Daspletosaurus was an important apex predator in the late Campanian dinosaur faunas of Laramidia; its absence from later units indicates it was extinct before Tyrannosaurus rex dispersed into Laramidia from Asia. In addition to its evolutionary implications, the texture of the facial bones of the new taxon, and other derived tyrannosauroids, indicates a scaly integument with high tactile sensitivity. Most significantly, the lower jaw shows evidence for neurovasculature that is also seen in birds.”
– So maybe T.rex was a cuddly fellow that spent a lot of time playing around or impressing potential mates when it was not hungry.
Some scientists hypothesize that closer investigation of fossil evidence may suggest play behavior in T-rex. They thought that the t-rex bite marks on the then-meatless ceratopsid bones might belong to juvenile T-rexes tossing bones around for fun.
#Snively & Samman, Unexpected behavior in the Cretaceous: tooth-marked bones attributable to tyrannosaur play, 2014.
https://www.tandfonline.com/doi/abs/10.1080/03949370.2014.984346
Quote: “Tyrannosaur bite marks on several bones, including ceratopsian (horned dinosaur) occipital condyles scattered in bone beds, have recently been attributed to play behavior. In the cited cases, play was considered a more likely behavior than feeding, because the bones had been isolated and dissociated from other skeletal elements on the surface before final burial, and in this condition there would be little if any remaining meat. Although the hypothesis of play is difficult to falsify or to support specifically, the evidence is reasonable that the tyrannosaurs were engaged in activity without immediate selective consequences (common in their modern relatives).”
– Likewise, while their horns and shields might have made ceratopsids seem like natural born fighters, they were probably much more than that. Deducing from modern animals and the complex dances some have to go through to mate, maybe their shields were amazingly colorful, maybe it danced for its mates like many birds do today.
It is not always bones, teeth or shells that ancient animals left behind. Evidence other than animal parts can also serve inferring details regarding behavior. Authors of the following study, for instance, found large scrapes with similar patterns to the ones generated by courting birds today.
#Lockley et al.,Theropod courtship: large scale physical evidence of display arenas and avian-like scrape ceremony behaviour by Cretaceous dinosaurs, 2016.
https://www.nature.com/articles/srep18952
Quote: “Large scrapes, up to 2 m in diameter, occur abundantly at several Cretaceous sites in Colorado. They constitute a previously unknown category of large dinosaurian trace fossil, inferred to fill gaps in our understanding of early phases in the breeding cycle of theropods. The trace makers were probably lekking species that were seasonally active at large display arena sites. Such scrapes indicate stereotypical avian behaviour hitherto unknown among Cretaceous theropods and most likely associated with terrirorial activity in the breeding season. The scrapes most probably occur near nesting colonies, as yet unknown or no longer preserved in the immediate study areas. Thus, they provide clues to paleoenvironments where such nesting sites occurred.”
Investigating the shapes of the lesions on the shields and head gears of Triceratops, scientists could predict whether the traces were due to fight or not. The following study hypothesized that not all pathologies found in frill bones are due to combat, although the overall evidence suggests intra-specific fight.
#Farke AA, Wolff EDS, Tanke DH, Evidence of Combat in Triceratops, 2009 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004252
Quote: “The horns and frill of Triceratops and other ceratopsids (horned dinosaurs) are interpreted variously as display structures or as weapons against conspecifics and predators. Lesions (in the form of periosteal reactive bone, healing fractures, and alleged punctures) on Triceratops skulls have been used as anecdotal support of intraspecific combat similar to that in modern horned and antlered animals. If ceratopsids with different cranial morphologies used their horns in such combat, this should be reflected in the rates of lesion occurrence across the skull. [...] This pattern is consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure for this taxon. Lower pathology rates in Centrosaurus may indicate visual rather than physical use of cranial ornamentation in this genus, or a form of combat focused on the body rather than the head.”