Chapter 7: Other Life Explosions
The life explosion following the
K/T boundary is the most recent and the most documented one. The
Cambrian explosion is the most dramatic one. But they are not two isolated cases. Virtually
all mass extinctions were followed by life explosions marked by the emergence a new and more complex lifeforms displaying physiological features never observed before.
- The mid-Ordovician extinction, also known as the
Ordovician Meteor Event happened ca. 467 Mya. It was followed by the
Ordovician radiation which took place about 40 My
[1] after the Cambrian explosion described in the previous chapter. While the
Cambrian explosion produced most modern
phyla, the
Ordovician radiation filled these
phyla with numerous new classes and lower-level
taxa[2]. This was a diversity explosion with a
tripling of the total number of marine families and a
doubling of the number of marine orders
[3].
In addition these new life forms revealed a marked increase complexity
[4], particularly among brachiopods, gastropods and bivalves
[5]. Interspecies organization complexity also increased dramatically with the apparition of the reef ecosystem
[6].
- The Ordovician–Silurian extinction ca.450–440 Mya was followed by the apparition of water-conducting cells along with
tracheophytes[7], also known as
vascular plants. The aftermath of the
Ordovician–Silurian extinction also marks the advent of the oldest land animal, a millipede species called
Pneumodesmus [8] along the first land plant, known as
Eohostimella heathana [9]. Until then fauna and flora were exclusively aquatic. Soon after the extinction, appeared the
gnathostoma[10], a
subphylum, containing all the jawed vertebrates and comprising about 60,000 species, which accounts for 99% of all living vertebrates
[11].
The end-Silurian extinction ca. 430 Mya was followed by the
Devonian explosion which marked dramatic evolutions in flora with the apparition of leaves
[12], roots
[13] and meristems
[14] (a type of tissue made of undifferentiated cells capable of cell division). It marks as well the apparition of lungs - indistinguishable from modern lungs
[15] and legs
[16] along with the apparition of the first (wingless) insects on land
[17] and the first amphibians
[18]. The aftermath of this mass extinction also marked the apparition of bones and the first bony fishes amongst which the first shark fossil
[19] (
doliodus) and the first representatives of
osteichthyes, a large taxonomic group of fishes containing about 28,000 species
[20].
- The late Devonian extinction ca. 375–360 Ma saw, soon after its aftermath, major evolutions in plants with the apparition of
Archaeopteris who developed a secondary vascular tissue that produced wood
[21] while
Elkinsia, an early seed fern (not a true fern), had evolved
seeds[22]. The late
Devonian extinction was also followed by the apparition of the first
tetrapods[23].
Around the time of this extinction appeared two species that don’t belong to any
phylum, therefore these two species have no identified ascendants, not even remote ones:
- A small animal called
Gluteus minimus, colloquially known as
horse collar[24].
-
Libodiscus ascites, an organism that doesn’t belong to any
phylum since its morphology is so singular:
[
Libodiscus ascites] consists of a flask-like body bearing a flange of plates or flattened tentacles. At one end a pair of arm-like extensions connects with a disc with concentric markings. The flask has transverse structures with prominent relief.
[25]
Lauret Savoy
Reconstruction of Libodiscus ascites
-
The Carboniferous-Permian extinction ca. 305 Mya witnessed the apparition of a whole animal class of animal, the
conodont, an eel-like creature which features the first appearance of teeth
[26] in the fossil records. Around the time of this extinction also appeared the conifers.
Coniferae is a large group of plants containing 8 families, 68 genera and more than 600 species
[27].
This time marks as well the apparition of the
Tullimonstrum, colloquially known as the Tully Monster. The peculiarity
[28] of this life form is that it doesn’t belong to any
phylum[29]. It shows some similarities with mollusks, arthropods, conodonts and vertebrates but it’s too dissimilar to belong to any of these categories
[30].
- The late Middle Permian extinction ca. 270 Mya, saw the rise of a major group of animals,
therapsida, which featured a posture similar to mammals
[31] and traits, including fur
[32], suggesting endothermy
[33] (maintenance of body heat at a favorable temperature).
The late
Middle Permian extinction marked also the apparition of the
octopus, a taxonomic order containing about 300 species
[34]. Octopuses are dramatically different and more complex than the earlier molluscs, with a brain made of half a billion neurons, six times more than a mouse brain
[35], an elaborate camouflage apparatus
[36] and more gene than humans
[37]. In fact, octopuses are so different from other molluscs that they have no identified ancestors
[38].
- The Permian–Triassic extinction ca. 252 Mya was followed by the
Mesozoic marine revolution which heralded the apparition of numerous new predators in particular shell-crushing species
[39] and new taxonomic groups of sea snails like neritaceans,
mesogastropods and
neogastropods, who developed shells with external sculptures and asymmetric shapes to defend against this new mode of predation
[40].
Also the
Permian–Triassic extinction was soon followed by the apparition of the earliest frog:
Triadobatrachus massinoti[41].
The earliest
teleost fossil dates back to the early
Triassic[42].
Teleosts constitute a broad and successful infraclass of fish, which displays numerous innovations like protruding mouth, elongated neural arches and unpaired basibranchial toothplates
[43]. With more than 23,500 species, the teleost subclass contains 95%
[44] of all extant fish species.
Around the time of the advent of the first
teleost fish, also appeared the first flying vertebrate, the
pterosaur
[45] whose innovative features are stunning even for today’s standards:
“Pterosaurs were just the coolest things that were ever in the air," says Padian. "They were the first vertebrates to fly. They did it long before birds and bats. And it terms of size, they pushed the envelope as far as it could go for a flying animal."
[46]
Besides the apparition of the new and more complex lifeforms described above, the aftermath of the
Permian-Triassic extinction was marked by a generalized increase in complexity among lifeforms and ecosystems:
Likelihood analyses of 1176 fossil assemblages of marine organisms from Phanerozoic (i.e., Cambrian to Recent) assemblages indicate a shift in typical relative-abundance distributions after the Paleozoic. Ecological theory associated with these abundance distributions implies that complex ecosystems are far more common among Meso-Cenozoic assemblages than among the Paleozoic assemblages that preceded them. This transition coincides not with any major change in the way fossils are preserved or collected but with a shift from communities dominated by sessile epifaunal suspension feeders to communities with elevated diversities of mobile and infaunal taxa. This suggests that the end-Permian extinction permanently altered prevailing marine ecosystem structure and precipitated high levels of ecological complexity and alpha diversity in the Meso-Cenozoic.
[47]
- The Triassic–Jurassic extinction, ca. 201 Mya marked the disappearance of 70% of all species. There was no recovery interval, a life explosion happened right after the mass extinction:
The
end-Triassic mass extinction is one of the most significant during the
Phanerozoic for both marine and terrestrial groups, but the recovery has been poorly documented.
Bivalves, ammonites, brachiopods, crinoids, foraminifera, and
ostracodes in Europe show no survival interval but simply a steady diversification over several myr
[48]
The first armored dinosaurs
[49] appeared right after the
Triassic–Jurassic extinction. The aftermath of this extinction also marked the sudden and dramatic transformation of crocodylomorphs
[50]:
The TJ [Triassic-Jurassic] extinction was followed by a geologically rapid adaptive radiation of crocodylomorphs. This radiation marks the beginning of the spectacular evolutionary history of crocodylomorphs in post-Triassic Mesozoic ecosystems, which saw the clade evolve an astonishing range of body sizes, habitats and niches
[51]
- The Jurassic-Cretaceous extinction, ca. 145 Mya was followed by the apparition of
angiosperms[52] (flower plants). This sudden apparition was so problematic for the theory of gradual evolution that
Charles Darwin called it an "abominable mystery”
[53]. Soon after this extinction event also appeared the
graminaea family[54] with includes rice, maize, wheat, bamboos or grasses.
- The end-Eocene extinction[55], ca. 34 Mya was soon followed by the apparition of the C4 carbon fixation pathway in plants enabling higher temperature tolerance, water use efficiency
[56] and nitrogen use efficiency
[57]. The
late-Eocene extinction was also followed by the apparition
[58] of
Thalassocnus, a kind of giant sea sloth
[59] who doesn’t belong to any
phylum. Its morphology is so odd that it’s been euphemistically called an “iconic example of transcendent evolutionary change”
[60].
The aftermath of The
late-Eocene extinction was marked by the apparition of new complex mammals:
- The
cricetidae[61], a family of rodents that includes about 600
[62] species like hamsters or lemmings.
- The
castoridae[63], another family of rodents that included dozen of species including the two extant species of beavers.
- The
erinaceidae[64], a family of small mammals including the hedgehog and the moonrats.
- The
felidae[65], colloquially known as cats, a taxonomic family that contains 34 species.
A number of geologic periods (
Cambrian, Jurassic, Cretaceous,…) has been mentioned in the life explosions described above. Since the Cambrian, each geologic period lasts on average 50 million years.
One fundamental factor upon which the time boundaries of these geologic periods are established are the fossils they contain:
Fossils are fundamental to the geologic time scale. The names of most of the eons and eras end in zoic, because these time intervals are often recognized on the basis of animal life.
[66]
Each geologic period is
characterized by a stable and specific set of fossilized life forms, which is markedly different from the set of the geologic period that precedes it and from the set that follows it. This fact is recognized even by Darwinists:
It remains an indisputable fact that in the most thoroughly explored regions, those where the fauna is best known. As for instance, the Tertiary of the Paris basin,
the species of one bed often differ widely from those of the preceding, even where no stratigraphic gap appears between them. [67]
The picture below illustrates how each geologic period is characterized by specific life forms,
showing a marked increase complexity compared to the previous period:
© Brittanica
Each geologic period since the Cambrian with its characteristic life forms
The above listed mass extinctions and subsequent evolutionary leaps show that each geological period reveals the same pattern:
- It starts with a mass extinction that removes most life forms that characterized the previous period.
- It is followed by the sudden apparition of new fully developed life forms appearing seemingly out of thin air:
Look at the
Ordovician, when jawless fish with no known ancestors suddenly appeared; or the
Silurian, when algae crawled out of the sea and onto the barren ground; or the
Devonian, when coniferous trees suddenly appeared, as did ferns, seemingly out of thin air […] So many new kinds of fish appeared in the
Devonian that it's called the "Age of the Fishes." Sharks appeared suddenly, and the first amphibian, Ichthyostega, crawled out of the water and onto the land.
[68]
-
It lasts for tens of millions of years without any dramatic changes in the life forms of this period, until the next mass extinction that ends the geologic period.
The correlation between the aftermath of mass extinctions and the apparition of new lifeforms is striking, in fact almost all major living branches of life appeared right or soon after a mass extinction, as shown in the illustration below:
© Eisenberg
Mass extinctions and new forms of life.
From the new life forms around cometary events like
Tunguska or the
Carolina Bays to the
Cambrian life explosion, the
K/T cometary induced mass extinction with its subsequent life explosion and virtually all other mass extinctions. All these events reveal the same thing:
major cometary impacts are not only destructive acts through the removal of obsolete life forms during mass extinctions but also creative acts through the introduction of more elaborate life-forms.
But what is the mechanism beyond these sudden life explosions? This question will be addressed in the next part of this book
[69]; but before that we’ll dedicate one chapter to recap what we have learnt about mass extinctions and evolutionary leaps and how these observations fit with the two main kinds of evolution theories.
[1] Servais, T. et al. (2008) "The Ordovician Biodiversification: revolution in the oceanic trophic chain". Lethaia. 41 (2): 99–109.
[2] Servais, T. et al. (2010) "The Great Ordovician Biodiversification Event (GOBE): the palaeoecological dimension" Palaeogeography, Palaeoclimatology, Palaeoecology. 294 (3–4): 99–119
[3] Droser, M. et al. (2003) "The Ordovician Radiation: A Follow-up to the Cambrian Explosion?" Integrative and Comparative Biology. 43: 178–184
[4] Munnecke, A. et al. (2010) "Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis" Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 389–413
[5] Stigall, A.L et al. (2016) "Biotic immigration events, speciation, and the accumulation of biodiversity in the fossil record". Global and Planetary Change. 148: 242–257
[6] Douglas H. Erwin. (2001). “Lessons from the past: Biotic recoveries from mass extinctions”. PNAS 98 (10) 5399-5403
[7] Jennifer L. Morris et al. (2018) ‘’Timescale of early land plant evolution”. PNAS 115 (10) E2274-E2283
[8] Paul Selden & Helen Read (2008). "The oldest land animals: Silurian millipedes from Scotland". Bulletin of the British Myriapod & Isopod Group. 23: 36–37
[9] Niklas, Karl J. (1976) "Chemical Examinations of Some Non-Vascular Paleozoic Plants". Brittonia 28 (1): 113–137.
[10] Zhao, Wenjin & Zhu, Min (2010) “Siluro-Devonian vertebrate biostratigraphy and biogeography of China” Palaeoworld 19. 4-26. 10.1016
[11] Brazeau, M. D., & Friedman, M. (2015) “The origin and early phylogenetic history of jawed vertebrates” Nature, 520(7548), 490–497
[12] Boyce, C. (2005) “The Evolutionary History of Roots and Leaves”. Vascular Transport in Plants. 479-499
[13] Meyer-Berthaud, B. et al. (2010) "The land plant cover in the Devonian: a reassessment of the evolution of the tree habit". Geological Society, London, Special Publications 339 (1): 59–70
[14] Boyce ; Knoll, C. A. (2002). "Evolution of developmental potential and the multiple independent origins of leaves in Paleozoic vascular plants" Paleobiology 28 (1): 70–100
[15] Kamenz, C. et al. (2008). “Microanatomy of Early Devonian book lungs”. Biology letters, 4(2), 212–215
[16] Grzegorz Niedźwiedzki et al. (2010) "Tetrapod trackways from the early Middle Devonian period of Poland" Nature 463 (7277): 43–8
[17] B. Misof et al. (2014) "Landmark study on the evolution of insects". Sciencedaily.com
[18] Michael Melford (2021) “Devonian Period” National Geographic
[19] John G. Maisey et al. (2017) "Pectoral Morphology in Doliodus: Bridging the ‘Acanthodian’-Chondrichthyan Divide" American Museum Novitates 2017(3875), 1-15
[20] The Editors of Encyclopaedia Britannica (2021) ‘’Bony fish’’ Encyclopaedia Britannica
[21] Retallack, G.J et al. (1985) "Fossil Soils as Grounds for Interpreting the Advent of Large Plants and Animals on Land [and Discussion]" Philosophical Transactions of the Royal Society B. 309 (1138): 105–142
[22] Rothwell, G. W. et al. (1989) "Elkinsia gen. nov., a Late Devonian gymnosperm with cupulate ovules" Botanical Gazette 150 (2): 170–189
[23] Alexander, Pyron R. (2011) "Divergence Time Estimation Using Fossils as Tematic Biology". Systematic Biology. 60 (4): 466–481
[24] Richard Arnold Davis et al. (1975) "Fossils of uncertain affinity from the Upper Devonian of Iowa". Science 187 (4173): 251–254.
[25] Morris, S.C., Savoy, L.E. And Harris, A.G. (1991). “An enigmatic organism from the ‘Exshaw’ Formation (Devonian-Carboniferous), Alberta, Canada”. Lethaia, 24: 139-152
[26] Shubin, Neil (2009). Your Inner Fish: A Journey into the 3.5 Billion Year History of the Human Body (reprint ed.). Pantheon Books. pp. 85–86.
[27] Lott, John N. A; et al. (2002). "Iron-rich particles and globoids in embryos of seeds from phyla Coniferophyta, Cycadophyta, Gnetophyta, and Ginkgophyta: characteristics of early seed plants". Canadian Journal of Botany. 80 (9): 954–961
[28] Greshko, Michael (2016). "Scientists Finally Know What Kind of Monster a Tully Monster Was". National Geographic.
[29] A level of classification or taxonomic rank below kingdom and above class. See taxonomic table in chapter 1.
[30] Brian Switek (2017). “Tully Monster Still a Mystery”. Scientific American.
[31] Romer, A. S. (1966). “Vertebrate Paleontology” (3rd ed.). University of Chicago Press.
[32] Bajdek, Piotr et al. (2016). "Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia". Lethaia. 49 (4): 455–477.
[33] Kévin, Rey et al. (2017). "Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades". eLife. 6
[34] Wikipedia contributors (2021) “Octopus”. Wikipedia
[35] Herculano-Houzel, S. et al. (2006) ‘’Cellular scaling rules for rodent brains”. PNAS 103, 12138–12143
[36] Kröger, B., et al. (2011). “Cephalopod origin and evolution”. Bioessays 33, 602–613
[37] Albertin, C., et al. (2015) The octopus genome and the evolution of cephalopod neural and morphological novelties. Nature 524, 220–224.
[38] Mark Carnall. (2016). ‘’ I, for one, welcome our new cephalopod overlords ... but what are they?”. The Guardian
[39] Vermeij, G. J. (1977). "The Mesozoic Marine Revolution: Evidence from Snails, Predators and Grazers". Paleobiology. 3 (3): 245–258.
[40] Vermeij, G. J. (1977). "The Mesozoic Marine Revolution: Evidence from Snails, Predators and Grazers". Paleobiology. 3 (3): 245–258.
[41] Ascarrunz, Eduardo; et al. (2016). "Triadobatrachus massinoti, the earliest known lissamphibian (Vertebrata: Tetrapoda) re-examined by µCT-Scan, and the evolution of trunk length in batrachians". Contributions to Zoology. 58 (2): 201–234.
[42] Clarke, John T.; Friedman, Matt (2018). "Body-shape diversity in Triassic–Early Cretaceous neopterygian fishes: sustained holostean disparity and predominantly gradual increases in teleost phenotypic variety". Paleobiology. 44 (3): 402–433.
[43] Patterson, C.; Rosen, D. E. (1977) "Review of ichthyodectiform and other Mesozoic teleost fishes, and the theory and practice of classifying fossils". Bulletin of the American Museum of Natural History. 158 (2)
[44] Volff, JN. (2005) “Genome evolution and biodiversity in teleost fish” Heredity 94, 280–294
[45] David W. E. Hone et al. (2008) “Pterosaur distribution in time and space: an atlas”. Zitteliana An International Journal of Palaeontology and Geobiology, 61–107
[46] Richard Monastersky. (2021) “Pterosaurs—Lords of the Ancient Skies” National Geographic
[47] Wagner, Peter J. et al. (2006) “Abundance Distributions Imply Elevated Complexity of Post-Paleozoic Marine Ecosystems”. Science 1289-1292
[48] Douglas H. Erwin (2001) “Lessons from the past: Biotic recoveries from mass extinctions” PNAS 98 (10) 5399-5403
[49] University of Berkeley Editors (2021) “Introduction to Thyreophora - The armored dinosaurs” University of Berkeley
[50] A group of archosaurs that includes the crocodilians and their extinct relatives
[51] Olja Toljagić (2013) “Triassic–Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs” Biology Letters
[52] Feild, T. S et al. (2011) "Fossil evidence for Cretaceous escalation in angiosperm leaf vein evolution" PNAS 108 (20): 8363–8366
[53] Davies TJ. et al. (2004) "Darwin's abominable mystery: Insights from a supertree of the angiosperms" PNAS. 101 (7): 1904–9
[54] Prasad, V. et al. (2011) "Late Cretaceous origin of the rice tribe provides evidence for early diversification in Poaceae". Nature Communications 2: 480
[55] Prothero, D. R. (1994) “The Late Eocene-Oligocene Extinctions”. Annual Review Of Earth And Planetary Sciences, Volume 22, pp. 145-165
[56] Osborne CP. et al. (2012) "Evolution of C4 plants: a new hypothesis for an interaction of CO2 and water relations mediated by plant hydraulics" Philosophical Transactions of the Royal Society 367 (1588): 583–600
[57] Sage, RF et al. (1987). "The Nitrogen Use Efficiency of C(3) and C(4) Plants: I. Leaf Nitrogen, Growth, and Biomass Partitioning in Chenopodium album and Amaranthus retroflexus". Plant Physiology 84 (3): 954–8
[58] Jaime Trosper (2021) "Problematica: The Abominable Species” Futurism
[59] Riley Black. (2019) “Sloths in the Water” Hakai Magazine
[60] Riley Black. (2019) “Sloths in the Water” Hakai Magazine
[61] Freudenthal, M. (1996) "The Early Oligocene rodent fauna of Olalla 4A" Scripta Geologica 112: 1–67
[62] Worls Species Editors (2021) “Cricetidae’’ Worls Species
[63] Rybczynski, N. (2006) "Castorid phylogenetics: implications for the evolution of swimming and tree-exploitation in beavers" Journal of Mammalian Evolution. 14 (1): 1–35
[64] Butler, P.M. (1948) “On the Evolution of the Skull and Teeth in the Erinaceidae, with Special Reference to Fossil Material in the British Museum” Proceedings of the Zoological Society of London, 118: 446-500
[65] Kitchener, A. C.; et al. (2017) "A revised taxonomy of the Felidae: The final report of the Cat Classification Task Force of the IUCN Cat Specialist Group". Cat News. Special Issue 11
[66] Lucy E. Edwards et al. (1997) “Fossils, Rocks, And Time” Chapter “The Relative Time Scale” USGS
[67] Félix Bernard (1895) ‘’Elements de Paléontologie’’ J.-B. Baillière p. 25
[68] Felix, R. (2008) “Magnetic Reversals and Evolutionary Leaps: The True Origin of Species” Sugarhouse Publications
[69] Part III: Virus are the Drivers of Life
