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The first attempt to lay out evolutionary history as a progression based on anatomy  was Ernst Haeckel's Biogenetic Law (1866). His tree "Pedigree of Man" had the correct sequence of  Primitive - Invertebrate - Vertebrate - Mammals. 

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A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.

Time should run past to present from left to right. Most commonly genetic sophistication runs low to high from top to bottom. In a classic tree of life  it is often shown in reverse with high at the top of the tree. 

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A simplified summary of Life on earth can be grouped by architecture and function into; Plants, Fungi, Cnideria (eg. Corals), Molluscs, Arthropoda (eg. Insects), Fish, Amphibians, Reptiles, Dinosaurs, Birds,  Mammals. These evolved by many small mutations selected by "Survival of the Fittest" into a series of steps. The transformation in functionality only results in many diverse new species when an extinction event kills off the current dominants which allows the new species to flourish. On the average there is roughly 75 M years between steps and 75 M years between the branch in DNA and the explosion of new species - its a slow process.

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In the case of mammals, the branch separating the genetic line of mammals from reptiles occurred 320 Mya, long before the dinosaurs. It was not until 170 Mya that the functionality of placental mammals had developed, and 66 Mya that the K/T extinction killed off the dinosaurs which  allowed mammals to flourish and diversify. 

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We now have much more fossil history, biochemical information and DNA. A tree based on Mitochondrial DNA was recently compiled giving a more detailed view of relationships. The family tree drawing was inspired by a linear diagram of species differentiation in cytochrome C from  a biochemistry textbook, Lehninger. Cytochrome C is a genetic protein common in all living things. The organic curved branches is humans centered but not at the top of the tree. Canines evolved with better smell, whales with bigger brains, and eagles with better vision.

https://scitechconnect.elsevier.com/africa-retracing-human-evolution-migration-dna

https://rsscience.com/the-biological-classification-of-paramecium-name-history-and-evolution/

Personal communication from Mark Hom MD

 

I annotated the evolution tree with the key functions of  structure, energy distribution, and reproduction, that distinguished the different branches. The evolutionary path differed in water and land and can be traced by the different skeletons. 

 

Life started in water with cyanobacteria and algae  (phyto-plankton) that used photosynthesis for energy and generated the oxygen that enabled the cycle of life. On land, life needed structure for support against gravity, and calcium was not readily available.  Plants evolved from algae with Cellulose as exoskeleton, they used glucose to produce a  polyester "polysaccharide".   Like phyto-plankton, they used photosynthesis  to absorb CO2 and fix carbon and produce oxygen. Another algae evolved  that  that digested cellulose for energy, and converted it to Chitin, an amino-glucose polyester, for support and became fungi. 

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In water, the first multicellular Animals were Cnidaria that became corals, jelly fish etc. Next the  "Bilateria"  evolved that were symmetric rudimentary worm-like animals. The first Bilateria had nerves bundled through their thorax, and became Mollusks many with Calcium Carbonate exo-skeletons for protection. A branch of Molluscs evolved into Arthropods with Chitin exo- skeleton in diverse architectures  which led to cephalopods and crustaceans in water and insects on land.

 

A branch of  Bilateria  evolved with nerve bundles running along their back, that evolved into Vertebrates with  endo- skeletons. The first evolved with Calcium Carbonate endo-skeletons leading to starfish. Another branch with a CaPO4 endo-skeleton became the first vertebrate fish with eyes, and a basic skeleton architecture that evolved into reptiles, birds and mammals.  ​​​​​​

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Fish evolved with 4 weight bearing  legs "Tetrapods" that were well adapted for life on land with lungs pumped by mouth, and in water through their skin, and became amphibians. The amphibians lead dual lives; starting life with eggs in water, and then developing the land leving features as they mature. Then Tetrapods with lungs and active  (diaphramatic) breathing emerged as the proto-reptiles, the Sauropsids, who laid their eggs on land.  Around 320 Mya, a seeming innocuous branch evolved the proto-mammals (Synapsids), with an opening low in the skull roof behind each eye socket, leaving a bony arch beneath each eye, which eventually closed off in early mammals. Around 250 Mya, there was a second branch in the Sauropsids that led to remarkably large, fast moving bipedal dinosaurs. 

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During the recovery from the extinction event at the end of Permian (250 Mya), a small pig-like proto-mammal herbivore was the dominant species. The large fast dinosaurs quickly dominated the proto-mammals limiting them to underground shrew-like animals until the K/T meteor extinction cleared out the dinosaurs. Eggs and newly hatch have to be kept warm which is very difficult underground. Keeping babies warm inside their bodies was a competitive advantage when living underground. By 170 Mya placental mammals evolved and the first birds evolved from dinosaurs. The Birds and Mammals exploded in diversity after the K/T extinction. Tree climbing for fruit led to the Primates with upper body strength and manual dexterity.

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The first species that had a transport system for oxygen were the mollusks that had copper based blood that flowed through their body cavity. Octopus evolved a  closed blood distribution that  enabled oxygen to be delivered to key organs.  Iron based blood (hemoglobin) in a closed circulation system then became universal in vertebrates from lampreys and fish onwards. Warm blood evolved in dinosaurs on, enabling much faster metabolism. Water based species extracted oxygen by diffusion using gills. Land based species evolved lungs to absorb oxygen from the air.

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The final evolutionary step increases the development of their young. Eggs provide a finite amount of energy to the developing fetus. Reptiles have fully developed, small, independent young when they break out of their eggs. Birds hide their underdeveloped young in nests while they feed them.  Octopus' actively protect their eggs, sharks let them develop in their bodies for protection, and monotremes suckle their young after hatching. The placental mammals provide unlimited time and access to energy to maximize fetal development.

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This evolution of species has progressed in bursts. The earth has  changed over time; through continental drift, volcanism, orbit changes, meteor impacts etc. Each change affects climate, sea levels, and hence the vegetation, and all the life that feeds on the vegetation. A change that disrupts the local balance of between predators and prey, creates a new niche that provides an opportunity for new species to thrive.

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Extinction drivers:

​Volcanism cooling  versus microbes heating by removing CO2. 

 

There are 8 great extinction/explosion of species;

1. Oxygen explosion (2.3 Bya) - Oxygen atmosphere leading to Eukaryotes explosion,                                                      enabled by extinction from the Vredefort asteroid.

2. Pre Cambrian (538 Mya) - Baikanur glaciation leading to Marine explosion

3. End Ordovician (444 Mya)  - Gonwanda at S Pole  glaciation leading to Vertebrate                                                        fish  explosion

4. Late Devonian (360 Mya) - Volcanism lowers sea O2 leading to Insect & Reptile                                                          explosion,

5. End Permian (250 Mya) - Siberian trap volcanism leading to  Proto mammal                                                             explosion

6. End Triassic (200 Mya) –  CAMP volcanism leading to Jurassic dinosaur explosion

7. End Cretaceous (65 Mya) –    K/T asteroid  wipes out everything >50 lbs. Mammal &                                                     bird explosion

8. Quaternary extinction (0.012 Mya) -  probably human predation, kills off the                                                                               Megafauna and enables domestic agriculture

https://ourworldindata.org/mass-extinctions

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There were 2 cycles of thriving shelled live - the Cambrian explosion 500 Mya of invertebrates and Limestone deposits in the Jurassic 200 Mya. Alkaline oceans from decreasing CO2 and mineral erosion are the likely enablers. 

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The most immediate source of competitive advantage when food is plentiful is size - the bigger wins ! Predation in forest favors large size because prey cannot run away, and large prey are difficult to bring down. However in open grasslands small size and agility becomes essential. Life in trees is another good way to avoid predators exploited by primates. Small size that can hide underground is another avoidance strategy. Diet driven adaptations also happen quickly, by natural variations and/or hybridization.  Mutations are the engines of new capabilities such as placentals, whereas environmental changes that create new unfilled niches are the engines of species diversification. For example, mammals evolved underground as a minority while dinosaurs ruled. Underground mammals could not grow much larger or faster, but keeping babies warm inside their bodies was a real advantage. In addition, longer gestation and parental support encourages brain development. These advantages were not enough to challenge the dinosaurs dominance. Then the K/T meteor cleared the dinosaurs out and    mammals and birds exploded and diversified.  Whereas, when all the niches are filled, such as either side of the Wallace line, new species have great difficulty migrating across the line and getting established. 

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Intelligence as competitive advantage probably starts with the Octopus, essentially a defenseless animal, that relied on subterfuge and camouflage to avoid predation. Mammals such as Primates, Squirrels, Bears and Elephants are known to use detailed location and season memories to locate food. Carnivores such as Lions memorize migration patterns of prey. Birds are navigators capable of migration across the planet  for optimal food and child rearing locations. Tool use is being discovered in more and more species including; octopus, primates, ravens, hawks etc. 

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Evolution sequence

The ancestors of bacteria were unicellular microorganisms "Prokaryotic" either bacteria or archea,  that were the first forms of life to appear on Earth about 4 billion years ago. There are 2 groups of bacteria; photosynthetic cyanobacteria, and anerobic proteobacteria. The archea are often called "extremophiles". Asgard  archea are aerobic. 

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Eukaryotes with a cell containing a  DNA nucleus and both aerobic and anerobic digestion,  evolved from a combination of protobacteria and asgard archea and led to animals. An additional  combination with cyanobacteria led to plants capable of photosynthesis and digestion of nutrients through roots. 

 

Bacteria flourish  3,500 Mya

Water living life started with a simple single and multicell structures such as bacteria, archaea or bacteria with genes, algae with photosynthesis, protozoa or scavenger cells, microscopic fungi that secrete digestive enzymes. It starts  with a bacteria  lipid walled, single cell with a ring of DNA.  

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Ancient algae have left Stromatolites, mounds of sand glued together by bacteria residues,

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Microfossils in Western Australia from 3,500 Mya appear to be Archaea consistent with the rRNA “tree of life,” confirms the earlier disputed biogenicity of the Apex fossils, and suggests that methane-cycling methanogen−methanotroph communities were a significant component of Earth’s early biosphere. Archaeal cells have unique properties separating them from Bacteria and Eukaryota, including: cell membranes made of ether-linked lipids; metabolisms such as methanogenesis; and a unique motility structure known as an archaellum.

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The most recent common ancestor (MRCA) of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billion–3.2 billion years ago.

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Great oxygen event 2.4-2.0 B years ago

There was a great extinction  from Arcaic to Protozic eras "Great Oxygen Event"  initiated by increasing oxygen levels. Before the extinction, there are cycles of increasing microbe levels  followed by die offs. The cycles are signaled by alternating black and red iron oxide deposits in rocks. Eventually, the photosynthesizers evolved resistance and iron gets depleted resulting in much higher oxygen levels even in the deepest oceans, killing of any non-photosynthetic life such as deep ocean vent species.  ​

For the first time life affected the planet increasing  oxygen levels to 10% of todays level. This would have enabled oxygen consuming life to get going. It would seem likely that the extinction that followed the rise in oxygen was triggered by the Vredefort asteroid, similar in size to the K/T asteroid. Probably enhanced alkalinity in oceans.

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First Eukaryotes 2,200 Mya

​Eukaryotes first appeared as a cell with a nucleus and basic genetic processes . Around 2000 Mya the principle genetic threads  spit into Bikonts with 2 flagella that led plants and  Amorphae with 1 flagella which in turn evolved around 1,300 Mya  into threads for Holomycota such as Fungi, and Holozoa such as Animals.

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Around 1Bya, Bangiomorpha pubescens, the first sexually reproducing Eukaryotes appeared. 

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First Proto-plants  1,300 Mya

Algae  cells possess a true nucleus enclosed within a membrane, along with other membrane-bound organelles like chloroplasts and mitochondria.   They can be unicellular, like diatoms, or multicellular, such as giant kelp, and are found in aquatic or moist environments.  Bikonts developed into Charophytes or  freshwater green algae,  The terrestrial plants evolved possibly from terrestrial unicellular charophytes. 

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Seaweed are collections of  macroscopic, multicellular, marine algae that have been found as early as 1 billion years ago, and are further precursors of plants. ​​​

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First Proto-Fungi 1000 Mya

The genetic line leading to Fungi developed from eukayotes that could decompose protiens for energy. Fungi, are the clean up crew as decomposers of protein and cellulose. 

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Algae Animal precursor 950 Mya

Holozoa evolved into Choanozoa, the first choanoflagellates.  They have  the characteristic funnel-shaped "collar" of interconnected microvilli (microscopic cellular membrane protrusions) and the presence of a flagellum (whip-like appendage). More recent genomic work has suggested that choanoflagellates possess some of the important genetic machinery necessary for the multicellularity found in animals.

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First Animals 850 Mya

Animalia are the first multicellular, eukaryotic organisms. With few exceptions, animals consume organic material, breathe oxygen, have muscles (mycotytes) to move,   can reproduce sexually, and grow from a hollow sphere of cells,  during embryonic development.​ The earliest widely accepted animal fossils are rather modern-looking cnidarians, possibly from around 580 million years ago,  fossils from these rocks strongly resemble tubes and other mineralized structures made by corals. 

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First Cinderia 580 Mya

Cindaria  are predatory marine invertebrates including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are an uncentralized nervous system distributed throughout a gelatinous body and the presence   specialized cells  stinging   and capturing prey. Their bodies consist of  a non-living, jelly-like substance, sandwiched between two layers of epithelium . The Blue button (Porpita porpita) is an example of a modern species that was an early Cniderian fossil.

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Corals are the most spectacular subgroup with Calcium carbonate superstructure. Although some corals are able to catch plankton and small fish using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic algae that live within their tissues.  Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.  The shapes of the skeleton is thought to have evolved to trap nutrients and colonizers depending on the local flow patterns. A coral "group" is a colony of very many genetically identical polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in height. A set of tentacles surround a central mouth opening. Each polyp excretes an exoskeleton near the base. Over many generations, the colony thus creates a skeleton characteristic of the species which can measure up to several meters in size. Individual colonies grow by asexual reproduction of polyps. Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously overnight, often around a full moon. Fertilized eggs form planulae, a mobile early form of the coral polyp which, when mature, settles to form a new colony.  The different shapes result from combinations of 3 different calcium carbonate crystal structures, with different symmetries. ​

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First Bilateral body 570 Mya

The Animalia genetic threads branched into the  Bilatria. The first Bilatria  is hypothesized to be a bottom dwelling worm with a single body opening. Bilateria are characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly (ventral) and back (dorsal) surface.  It is easy to see that a 2 sided symmetric body is crucial for locomotion. 

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The first Bilteria  were   Protostomes appeared first and  have ventral nervous systems – nerves concentrated in their bellies. Many evolved an CaCO3 exo-skeleton presumably for protection against predators, and essential for mechanical support out of water. Many of the creatures we would think of as invertebrates, from cuttlefish, orthocones and octopuses to crabs, lobsters, worms and insects are all protostomes.

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A branch of Bilteria were Deuterostomes evolved from a common ancestor that had pharyngeal gill slits, a hollow nerve cord, circular and longitudinal muscles and a segmented body.    Deuterostomes that became Echinodermata, such as Starfish, and Chordata, Vertibrates, such as Fish.​

 

Cambrian explosion 538 Mya

No accepted explanation for the Cambrian explosion, one possibility is that he Baykonurian glaciation that  affected both paleohemispheres was responsible for an extinction that then enabled the explosion of life in water. Mineral rich alkaline oceans would have encouraged shells in shellfish.  Molluscs and Arthropods were the dominant groups, however there were many other bizarre body forms mostly found in the Burgess Shale deposits in Canadian Rockies. Stephen Gould argued that these oddities were evidence that random chance rather then survival of the fittest was responsible for success. His argument has lost out to evidence that many oddities have surviving descendants. A better argument is probably that the successful body forms were those that provided a format that could adapt easily to different niches after an extinction event. 

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Molluscs thrive 535 Mya

Protostomes also  branched into Spiralia, such as  Lophotrochozoa an early Mollusk. It has two distinct characteristics; the lophophore, a feeding structure consisting of a ciliated crown of tentacles surrounding a mouth, and the developmental stage of the trochophore larva.There was evolution of gastropods (e.g., Aldanella such as snails), cephalopods (e.g., squids and octopus such as Plectronoceras) and bivalves (Pojetaia, Fordilla such as clams)  Around 450 Mya, Cameroceras evolved with a 2m shell is an early giant  cephalopod. Around 230M Nautilus cephalopod had evolved. Around 170 Mya Octopus evolved with no protective shell in a world filled with fish predators. 

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The  Mollusks appeared with an shell and a whole body circulation of oxygen using "Hemolymph" and copper based blood. The snails evolved into squids and octopus with closed circulation of a copper containing blood, which enables oxygen to be delivered to key organs. Early Cephalods, are remarkable as the first examples of a species with pinhole camera eyes. 

 

Without a skeleton, octopus has very limited evolutionary options as a predator or for defense, Becoming a smarter is the option leading to camo and clever hiding. 

Octopus blood is copper-based (hemocyanin), which turns it blue and helps it bind oxygen efficiently in cold, low-oxygen water. But it’s thicker than human blood, making it hard to pump. To manage this, octopuses evolved three hearts. Two branchial hearts oxygenate the blood at the gills, while a third circulates it through the body. When the octopus swims, it shuts off the branchial hearts to reduce workload — making swimming tiring. This is why they prefer crawling. 

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The octopus only have one cycle of reproduction in their lives. The female protects their eggs as they develop, one of the hallmarks of higher intelligence.  Octopuses, like other coleoid cephalopods but unlike more basal cephalopods or other molluscs, are capable of greater RNA editing, changing the nucleic acid sequence of the primary transcript of RNA molecules, than any other organisms. Editing is concentrated in the nervous system, and affects proteins involved in neural excitability and neuronal morphology. More than 60% of RNA transcripts for coleoid brains are recoded by editing, compared to less than 1% for a human or fruit fly. Coleoids rely mostly on ADAR enzymes for RNA editing, which requires large double-stranded RNA structures to flank the editing sites. Both the structures and editing sites are conserved in the coleoid genome and the mutation rates for the sites are severely hampered. Hence, greater transcriptome plasticity has come at the cost of slower genome evolution.  In addition, the octopus  evolved a genome as complex as humans with "jumping genes". In these, the DNA is  45% transposed (reorganized within the animal) a feature that has been linked to  intelligence in humans.  The octopus has demonstrated remarkable intelligence in problem solving  and ability to self camouflage in color and texture. The octopus seems be a real "alien" intelligence on this planet with completely different design, and biochemistry. What they found was a brain more complex than that of a rat or a mouse. In fact, its complexity was similar to that of a dog’s brain. Some cephalopods have more than 500 million neurons. In comparison, the resourceful rat has 200 million, and the ordinary mollusk has 20,000.   Their brain-to-body-mass ratio falls between that of cold and warm blooded vertebrates. They demonstrate tool use, recognition of humans, the ability to solve abstract problems for instance;  captive cephalopods have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on captive crabs, and return to their own aquarium. They can unscrew the lids of bottles from the inside. These suggest an intelligence superior to dogs, on a par with primates.

https://www.medicalnewstoday.com/articles/are-squids-as-smart-as-dogs#Squids-have-more-complex-brains-than-rats

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First Arthropods​​​​ 535 Mya,

Protostomes branched into  Ecdysozoa that led to the Arthropods.  Around 508 Mya, Burgess Shale sandstone on Mt Burgess near to Lake Louise in the Canadian Rockies, were deposited with Arthropod fossils on display at The Smithsonian's National Museum of Natural History. Amazing collection of early soft shelled fossils including Trilobites and  many others that appear to be from bizarre lineages that have become extinct. Around 500 Mya, a subset of the Arthropods, the Pancrustacea branched into Crustaceons in the sea and Hexapods such as flies. 

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First Proto-vertibrates  520 Mya  

The dorsal nerve cord is an anatomical feature found in all chordates, that distinguishes them from Molluscs. Lancelets are an example still alive today. Around 518 Mya,  Deuterostomes evolved Haikouichthys, the earliest known vertebrates. They had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail, but lacked jaws and were 1" long.​

 

Ordovician extinction  444 Mya 

The Ordovician extinction is thought to be triggered by rapid drop in CO2, and extreme glaciation over Gondwana that was centered around the South Pole. Around 445 M years ago,  in the Devonian or the  "age of fishes"  ray finned fish (bony vertebrates) became easily the largest class of fish.   This extinction event coincides with the recovery from ice age associated with the Appalachian uplift  and falling CO2 levels . Mass extinction events cause an explosion of new species. Numerous ecological niches are suddenly empty of both competition and predators. New herbivores and insectivores can flourish, eventually leading to new predators, and new balanced ecosystems. 

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First Fish 444 Mya

Coelacanth is the best known ancient lobe finned fish from 410 Mya that is still being found today. 

 

Cartilaginous include sharks and rays. The sharks  evolved keeping their eggs inside their bodies until they hatched to protect their young. Fish have a 2 chamber (atrium & ventricle)  heart. 

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Mudskippers, are a recently evolved species of fish that can absorb oxygen in air through its skin, and look like a proto-amphibian. 

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The vertebrate genetic thread led to amphibians, reptiles, dinosaurs, birds and mammals. ​

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First Plants  450 Mya

Algae evolved into the first land plants, with Chlorophyll for trapping light and Cellulose (a polysaccharide or natural polyester) for superstructure.

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Around 420 Mya  Prototaxites, cone-like some standing over 8 meters tall, formed the first "forests" on Earth.  Its internal structure consisted of interwoven, tube-like filaments, unlike any modern plant. As the tallest organism on land in its time, it would have towered over the primitive, knee-high plants, creating a bizarre and alien skyline. 

 

Club mosses, ferns then appear. By the end of the 363 My ago, most of the basic features of plants today were present, including roots, leaves and secondary wood in trees.  

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Around 358-298 Mya, saw the development of forests in swampy environments dominated by clubmosses and horsetails, including some as large as trees, and the appearance of early gymnosperms, the first seed plants. In the time of the dinosaurs the world was covered by a hardy conifer forest, providing accessible food for very large herbivores. By the end of the Cretaceous 66 million years ago, over 50% of today's flowering plants "angiosperm"  had evolved,  accounting for 70% of global species. It was around this time that flowering trees became dominant over conifers, providing a new high calorie niche ready and waiting for the primates. 20 million years ago, grasslands took over from trees as the climate cooled and dried out providing a new niche for ruminants, the grass digesting herbivores, and their predators. 

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Around 460 Mya, fungi evolved  that  includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.

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Increasing Oxygen levels from thriving vegetation would have enabled Oxygen consuming life to also thrive. 

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First Amphibians 375 Mya

Tiktaalik appeared as a fish with "tetrapod' features.​ Around 370 Mya The amphibians  appeared as the  original tetrapod vertebrates with  lungs pumped by the floor of the mouth, and under water through their skin.  The Late Devonian extinction event 370 M years ago enabled the species diversification  of the amphibian era coincides with the recovery from an ice age  thought to triggered by  the explosion of plant life and falling CO2. The amphibians, such as frogs, marked the transition onto land, while needing water for reproduction and their young.

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Devonian extinction 370 Mya

Extinction caused by sudden drop in oxygen levels in the ocean, probably caused by loss of oxygen generating microbes. Underlying cause probably volcanism from the Vitik traps also in Siberia.

 

Amphibians flourish ​​​​​​ 360 Mya

​Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish

 

By 323 Mya, amphibians were everywhere on land. They evolved primitive lungs, which were helpful in adapting to dry land. Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes.   In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. They have lungs and a heart that consists of a single ventricle and two atria. ​Around 250Mya, lissamphibia or modern amphibians such as frogs and salamanders appeared. ​

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First Reptiles 350Mya,

Amniota are the original tetrapod vertebrates with coastal breathing using a rib cage and  hard shelled eggs that no longer needed water emersion to develop. This lead them to spread all over Pangea. After the Carboniferous rainforest collapse 305M years ago, amphibian dominance gave way to reptiles, and amphibians.  Fauna moving to the land was the second great species explosion. Hylonomous is the one of the first Amniota.

 

Around 310-330 Mya,  the genetic thread split; the first branch are called the Sauropsids, "pelycosaurs" led to Archosaurs, todays reptiles . The reptiles today include; Lizards, Snakes, Iguanas, and lastly Turtles, and Crocodiles. Along with lungs, the first 4 chamber heart appears in the crocodile reptile line, separating blood supply to the lungs and everything else.  The earliest reptile is Eyrthrosuchus.

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Reptiles are distinguished by two holes in the their skulls "fenestra", used as anchors for jaw muscles and consistent with the fact that most reptiles are carnivores 

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Insects thrive  320 Mya

The Arthropods made to land in the form of insects as the reptiles took over on land. 

Today, they probably represent 90% of the species on earth. They show some amazing collective capabilities. Butterfly's evolved around 50 M years ago post KT extinction. Butterflies have the unique migration from Mexico to Alaska, travelling north over 4-5 generations each lasting 2 months using the sun as a guide, following the flowering of milkweed.  They then fly south in a single 8 month generation. Bees have developed signals to show each other the direction to food. Ants are herbivores that  demonstrate large scale communication and cooperative action. 

https://www.nationalgeographic.com/animals/article/monarch-butterfly-migration

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First Proto-Mammal 318 Mya

 Synapsida branched from the Sauropsids and are distinguished by only 1 hole in their  skull structure. This hole disappeared over time, these holes were anchors for jaw muscles and suggest that these proto-mammals were herbivores. By 279 Mya, Therapsids evolved from earlier synapsids commonly called "pelycosaurs".  

 

Permian extinction 251 Mya

The Permo-Triassic extinction events radically changed the structures of communities with a 60% marine extinction. A large volcanic event centered on the Siberian Traps is thought to be the triggering event.  Ocean acidification decimated any species with calcium carbonate shells. This may have set the scene for the evolution of flowering plants in the Triassic (~200 million years ago),  Conifers diversified from the Late Triassic onwards, and became a dominant part of floras in the Jurassic as a niche food source for huge herbivores.  On land, there was the largest known mass extinction of insects. Aridification induced by global warming was the chief culprit behind terrestrial vertebrate extinctions. There is enough evidence to indicate that over two thirds of terrestrial labyrinthodont amphibians, sauropsid ("reptile") and Synapsida ("proto-mammal") taxa became extinct. Large herbivores suffered the heaviest losses. Burrows containing early mammal fossils from just after the P-T extinction  have been found in South Africa, presumably they were hiding from from the impact of the extinction.  The species diversification that followed the extinction enabled the rise of the dinosaurs. 

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First Dinosaurs 245 Mya

In the steaming swamps of the late Carboniferous period, the Sauropsids  branched to  the dinosaurs.   The common ancestor of all dinosaurs were probably small, bipedal predators similar to Eoraptor.

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The dinosaurs rapidly dominated the landscape, primarily due to size and mobility, enabled by a number of factors. The dinosaurs continued to grow throughout their lives, like reptiles. The warm wet earth of the time ensured plenty of food,. A single connected land mass on the planet ensured that there was no where for other species to hide. The dinosaurs had hollow bones, to minimize body weight, and naturally enabled birds in due course. Upright gate enabled high speed and  access to tree tops. 

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By 231 to 228 Mya, the first dinosaur predator Eoraptor had evolved as a 10 Kg carnivore.​ 

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Proto-mammals thrive 230 Mya

After the Permian extinction,  Lystrosaurus, a warm blooded, pig sized, herbivore thrived probably because the carnivores had not yet recovered. They were replaced probably by early  dinosaurs predators such as Eoraptor or simply grew into larger herbivores that competed for food. Lystrosaurus  had a "semi sprawling" gate evolving towards an erect gate. It is notable for dominating southern Pangaea for millions of years during the Early Triassic. At least one unidentified species of this genus survived the end-Permian mass extinction and, in the absence of predators and herbivorous competitors, went on to thrive and re-radiate into a number of species  becoming the most common group of terrestrial vertebrates during the Early Triassic; for a while, 95% of land vertebrates were Lystrosaurus. Of the survivors, only the 1.5 m (5 ft)–long carnivore therapsid Moschorhinus and the large proto-reptile 252-250 Mya Proterosuchus appear to be large enough to have preyed on the Triassic Lystrosaurus species, and this shortage of predators may have been responsible for a Lystrosaurus population boom in the Early Triassic.  By 228 Mya, Lystrosaurus lost out, probably to carnivores recovering from the Permian extinction.

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Based on the minuscule tubes of the inner ear, places the evolution of mammalian warm-bloodedness at around 233 million years ago .

https://www.livescience.com/warm-blooded-mammals-evolution

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Triassic extinction 200 Mya

The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic Magmatic Province (CAMP).

 

Dinosaurs dominate 208 Mya

In the Jurassic, the giants of the dinosaur era had evolved.​​ Dinosaurs originated in a part of Pangea that is now South America, diverging into Saurischians which include Therapods (Trex and birds), Sauropods (huge long necked)., and the Ornithischians which include a range of herbivores Back Armored, Duck Billed, Horned (Triceratops)  They dispersed more than 220 million years ago across parts of Pangea that later became separate continents.

https://www.eurekalert.org/news-releases/771395

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Around 143 Mya, at the start of the Cretaceous defined by chalk limestone deposits in Europe there was a partial extinction of the giant  dinosaurs. There is no clear cause, but the fact that the extinction of giants coincided with the appearance of massive Calcium Carbonate deposits, points to acidification by vulcanism, that would cause a loss of vegetation. 

 

By 97 Mya, the middle of the Cretaceous, the diversity of dinosaurs recovered, without  the extreme size of the Jurassic. 

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By 70 My ago (Creataceous), the continents had started to move apart, Africa, S. America, Australia, Antarctica all separate. N America was the home of the widest variety of dinosaurs, with a land bridge to the other continents.  Dominant dinosaur predators blocked any chance for the mammals, birds and reptiles to thrive. ​​​​​

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​The dinosaur era lasted 200M years and was the cradle of most of todays species.

​Some dinosaurs probably raised their young rather than just abandoning. Maiasaura (Late Cretaceous herbivore) individuals were found tangled together, in different stages of development. But further analysis demonstrated that newly hatched Maiasaura possessed immature leg muscles (and thus were probably incapable of walking, much less running), and their teeth had evidence of wear. What this implies is that adult Maiasaura brought food back to the nest and cared for their hatchlings until they were old enough to fend for themselves — the first clear evidence of dinosaur child-rearing behavior.

https://www.thoughtco.com/were-dinosaurs-good-parents-1091906

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Warm bloodedness in dinosaurs is still a subject of debate. There is evidence for warmer blooded physiology, short of fully stable thermoregulation as in mammals. These include simple large size, high activity level generating heat. It seems most likely that dinosaurs had higher metabolism than reptiles, but not full thermo-regulation that was forced on small mammals with underground lifestyle.

https://en.wikipedia.org/wiki/Physiology_of_dinosaurs

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Reptiles also became monsters, Deinosuchus was a 35 ft crocodile with a 4 ft long head that dined on dinosaurs around 75 Mya. 

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The dinosaur era famously ended with the K/T extinction caused by the meteor. 

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Limestone is a geological marker for the dinosaur era  

Around 200 Mya, algae that produce minerals (Coccolithophores) first appeared in the late Triassic. Limestone is the most complete record of early life as deposits at the bottom of oceans, probably associated with alkaline ocean caused by decreasing CO2 from thriving photosynthesis and minerals from rock erosion.  The alkalinity increases the solubility of calcium carbonate in water. About 20% to 25% of sedimentary rock is calcium carbonate, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms such as algae,  radiolarians such as zooplankton, corals). The "White Cliffs of Dover" are Chalk limestone composed of unicellular coccolithophores from the Mezozoic around 170 Mya. The start of Chalk deposits marks the end of the Jurassic and start of the Cretaceous. It also coincides with an extinction of  the Jurassic monster dinosaurs. 

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First birds 160 Mya

The feathered birds evolved from warm blooded dinosaurs around 160 M years ago, the first is Anchiornis with large brains and  a closest relative to  the Velociraptor.  Dinofuzz appeared 125Mya, feathers on microraptors 112Mya, fully functional birds with hollow bones (eg Archiopterix)  90Mya. Small ground welling omnivore birds were the only survivors along with underground mammals of the KT meteor.   “It seems like birds had happened upon a very successful new body plan and new type of ecology—flying at small size—and this led to an evolutionary explosion,” when the niches opened up after the K/T meteor. 

https://www.scientificamerican.com/article/how-dinosaurs-shrank-and-became-birds/

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Structural differences that led to modern birds are seen in "Ichthyornis", as light hollow bones. wing articulation and a large keel sternum to anchor flapping muscles.:

https://royalsocietypublishing.org/doi/10.1098/rsbl.2024.0500

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Mammals survivors 160 Mya​​

The Therapsids lived through the dinosaur era as small herbivores, some living in trees. There is limited fossil record. It appears one of the most common became insect eating burrowers and led to todays mammals. It appears that by living in burrows, just like shrews or meercats, they survived predation by dinosaurs and extinction events for 200M years ! Animals that reproduce using eggs must keep them warm until the hatch and during early stages after birth. This is a challenge when having to live underground to avoid dinosaurs. Also, a nest in a network of underground tunnels would be a easy target for predators. Reproduction when the young is kept inside the body would have many advantages, hence the evolution of placentals. 

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They appear to have evolved rapid growth and short lifespan, a life history trait also found in numerous modern small-bodied mammals.[24] They also adapted to a burrowing lifestyle, losing their large tail-based leg muscles which allowed dinosaurs to become bipedal, which may explain why bipedal mammals are so rare. In Namibia multi-chambered burrows have been found, containing as many as 20 skeletons of the Early Triassic cynodont Trirachodon.

 

They slowly evolved into highly developed mammals that provided their growing offspring with unlimited energy through their placenta and milk.  Mammals and birds thrived after the K/T meteor and share about 80% of their DNA, and a similar number of mutations from their common root over the same time span. 

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The lineage leading to today's mammals split up in the  Creataceous. Around 160 Mya, Juramaia evolved as a first mammal. Around 140 Mya  Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes.[1] Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, a small  shrew like animal, the earliest known therian (marsupial and/or placental), lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.

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In the proto-mammal genetic thread, the monotremes were the first mammals who laid eggs but suckled their young extending the time before a fully functioning digestive system needed. The duck billed platypus is the best known. DNA evidence supports a South American origin for marsupials, with Australian marsupials arising from a single Gondwanan migration of marsupials from South America, across Antarctica, to Australia, 100-120 My ago. The Marsupials thrived in Australia, Wallacea and the Americas now  include kangaroos, koalas,  Tasmanian devils, wombats, wallabies, possum and bandicoots. The Opossum is a close relative, a marsupial that originated in S America, and now live in N America.  

 

True placental mammals (the crown group including all modern placentals) arose from stem-group members of the clade Eutheria, which had existed since at least the Middle Jurassic period, about 170 mya. These early eutherians were small, nocturnal insect eaters, with adaptations for life in trees.[5]. Eutheria also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials.

Eutherians (placentals)  are distinguished from marsupials by the absence of bony extension in the pubis "epipubic bones", which are present in  marsupials and monotremes. This allows for expansion of the abdomen during pregnancy and support pouches.  The earliest unambiguous eutherians are known from the Early Cretaceous Yixian Formation of China, dating around 120 million years ago. True placentals may have originated in the Late Cretaceous around 90 Mya

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Genetic evidence suggests that primates diverged from other mammals about 85 Mya.​

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K/T extinction 66 Mya

The KT asteroid impact produced a combination of blast, tsunami, firestorm from re-entering impact debris, dust that blocked the sun for years and acidified the oceans. As a result, there was a  mass extinction of  anything over 50 lbs which included all large herbivore and their predator carnivore dinosaurs, presumably the little guys could hide underground. Marine invertebrates were also decimated. In these new uninhabited niches new species of mammals, reptiles, and birds had a better chance of survival. ​​Over the next 65 M years, plate tectonics created all the young mountain features such as Himalayas, Alps, and Rockies which were eroded back creating new ecological niches filled by new mammal and bird species After the extinction, different species were localized in Africa (Elephants etc), S. America (Sloths etc), Laurasia (Rodents, Ungulates and Primates).

https://www.britannica.com/science/K-T-extinction

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Small size, short lifespan and large litters in birds and mammals, supports more rapid adaptation to environmental changes. This in turn produces species diversity to fill new niches. 

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Bird explosion

After the KT impact, the survivors were warm blooded small mammals, birds and cold blooded reptiles. Once the plant life recovered, all the resource niches occupied by large dinosaurs become available such as grasslands and tree tops accessed from land and air. The flightless birds such as ostrich were first.  Overtime, flight allowed them to hide their young in nests. These young did not have to fend for themselves and were underdeveloped at the point when they used up all the food in the egg.  The parents had to feed them until they could fly, supporting longer development time and greater functionality. The corvids (ravens, crows, jays, magpies, etc.) and psittacine (parrots, macaws, and cockatoos) are often considered the most intelligent. They demonstrate tools use. Cormorants have been shown to count to 7.  Kea's also show malicious destruction including letting air out  of tires. After the extinction, lobe finned fish disappeared and were replaced by ray finned fish. The "perch like" ray finned fish (Percomorpha) and the "perching" song birds (Passeriformes)  thrived into tens of thousands of variants.  Passeriformes feed on insects and in some cases nuts and fruits as well. Apparently they were particularly adapted to exploit the new environment after the KT impact.  A 2017 study in the journal Science reported that a Galapagos finch immigrated to a new island and bred with a native bird, producing a new reproductively isolated lineage within three generations. That lineage may represent the very fast initiation of speciation via hybridization of species, rather than the slower accumulation of adaptations. ​​​​​​​