c. 2011.
Re-reading it: February 21, 2022.
Original Post
Other links:
Horseshoe Crabs and Velvet Worms
The other problem with the book is the title: I'm not sure if the author even really likes the title. A better title would have alluded to the fact that horseshoe crabs and velvet worms, still both living, are "survivors." Humans love stories about survivors. Most of the book is spent on organisms that did not survive. They were certainly left behind, as the title suggests, but it just doesn't sound right, and it's cumbersome, to boot.
Be that as it may, a book like this requires one to re-read specific chapters of interest.
Here are the highlights by chapter.
Old Horseshoes
From Dawkin's The Ancestor's Tale: "Everyone agrees that spiders and scorpions, together with the terrifying eurypterids [giant sea scorpions], belong together in the group called chelicerates. Limulus, the living fossil known, unfortunately, as the horseshoe crap, is also placed in the chelicerates, despite its superficial resemblance to the extinct trilobites, which are separated off in their own group." -- p. 382, softcover edition. [In Evolution, Parker and Roberts, c. 2015, page 98, Limulus, horseshoe crabs are classified as "Xiphosura," -- alone by themselves and not chelicerates!]
- horseshoe crabs; not crabs at all (see phylum: arthropoda)
- blue blood (copper, not iron, as the oxygen-carrying element)
- Delaware Bay
- I don't know if the author mentions the red knot migrates from the tip of South America to the Arctic; stops over in Delaware Bay to feed on horseshoe crab eggs to double their weight in two to three weeks, to enable them to finish their 3,000-mile flight
- blue blood of the horseshoe crab clots very, very quickly; has medicinal importance
- in past the horseshoe crabs were harvested for their blood, left to die; never returned to nature
- now, the crabs can be captured; donate their blood, and return to the beach/sea
- traceable back to the Ordovician (first confirmed), early paleozoic; shortly after/during the Cambrian explosion
Chelicerates: head appendages situated in front of the mouth; spiders have "fangs" that inject venom into prey; from wiki: chelicerae arise from segment two, ahead of the mouth, and pedipalps from segment three, behind the mouth.
Eurypterids: extinct sea scorpions
The Search for the Velvet Worm
- to New Zealand
- the story of Gondwana, and Pangaea
- Gondwana: peninsular India; Africa; South America, Australia; Arabia; Antarctica
- named for the central region of India; Sanskrit, forest of the Gonds;
- Gondwana: think Paleozoic, first era of the Phanerozoic
- came together in the neoproterozoic (just before the Cambrian) and joined with Euramerica in the Carboniferous period, only to break apart again in the Mesozoic Era
- the swamp: Carboniferous -- one large continent; one large swamp
- Triassic: breaks apart; dry, dry desert
- have to confirm, but trilobites almost the very same time span -- Cambrian to Permian
More:
- finding the velvet worm
- Burgess Shale
- Hallucigenia
- Conway Morris misinterpretation later corrected
- where does the velvet worm fit?
- check evolution / family trees / vertebrates evolve from Hallucigenia -- two big groups: spiders and scorpions in one group; insects and crustacea in the other group; true worms probably not in the Hallucigenia family; true worms led to chordates and vertebrates;
- I'll have to check the book again, but I don't recall any discussion of protostomes and/or deuterostomes;
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Ediacaran, p. 48: above the Precambrian, below the Cambrian, before the time of abundance and variety of marine life and before the appearance of shells. Before the Cambrian explosion.
- The Ediacaran (635 - 542 million years ago) is the latest geological period to have been named, only added to the official list of geological periods in 2004.
- I should note that a small number of skeletal fossils are now known in strata earlier than the base of the Cambrian, such as the enigmatic little shell Cloudina.
- "... the appearance of shells.'' This appears to be a big deal, that he mentions "shells" in this context and we will come to "shells" in a later chapter (Chapter 5: An Inveterate Bunch).
Shells: a huge, huge deal. Paleontologists use shells to identify geologic strata; continues into the age of oil;
Slimy Moulds
Chapter 5: An Inveterate Bunch
Sponges and Jellies, p 144
After sponges, came Bilateria. Sponges were not Bilateria; they can come in almost any shape.
Sponges were first to branch off the evolutionary tree from the common ancestor of all animals, making them the sister group of all other animals.
5,000 to 10,000 known species
First animal: Ediacaran
- split in two
- sponges (no organized tissues)
- everything else (eumetazoa) (organized tissues
- from sponges, page 148, Fortey moves seamlessly to jellyfish
- Jellies: comb jellies, jellyfish
- nice overview;
- comb jellies: streamlined; not poisonous, Phylum Ctenophora
- jellyfish: poisonous tentacles, Phylum Cnidaria (includes corals)
Corals and jellyfish are still evolving. Yet medusae and comb jellies are also messengers from deep geological time. They have moved with the ages, but only along their distinctive and fundamental tracks. They insert on the tree of life above sponges, but below the bilaterally symmetrical animals that been the subject of much of this chapter. That they are only one step up from the sponges is proved by their internal organization; unlike their goblet precursors (the sponges), they are blessed with a stomach and a rudimentary nervous system.There are no corals in the same Cambrian rocks where we first find sponges and medusae. The trick of building limy skeletons was not acquired for another 50 million years. During the Ordovician Period, the first reefs grew, constructed by the new marine builders. Trilobites scuttled among the branched corals; brachiopods were tucked into cavities inside the reef front; early relatives of Nautilus cruised the surface, looking for prey. Interestingly, these new corals are NOT related to the similar-looking structures we see today. The early cnidarian monumental masons disappeared during the end of the Permian Period.
Corals that construct reefs today were almost certainly a separate group of chidarians that learned the same constructional skill all over again.
Jellyfish, of both major types -- Ctenophora and Cnidaria -- comb jellies and jellyfish -- apparenlty appeared before all the bilaterian animals.
Some of these Cambrian organisms are still extant.
The question is: can we trace them back to the pre-Cambrian, to the Ediacaran?
Page 152.
Greenery
Of Fishes and Hellbenders
languages, page 196
Lithuanian: ancient -- closest to original Sanskrit as any (Indo-European)
Indo-European
modern Romance languages
Celtic, German, Slavic
many minor languages, living and extinct
Lithuania and lampreys
Heat in the Blood
Islands, Ice
Survivors Against the Odds
*********************************
Mass Extinctions
Link here. The Cambrian explosion begins with a mass extinction, the Ordovician.
The end-Ordovician extinction event was the second largest recorded extinction event, when about 85 percent of marine species (land plants and a few groups of animals lived outside the oceans) became extinct.
Researchers hypothesize the cause was a period of glaciation and then warming in a one-million-year time span.The cooling period caused an initial bout of extinctions, and a second round of extinctions occurred during the subsequent warming.
The cooling and warming climate changes affected not only temperatures but also sea levels. Some researchers have suggested that a gamma-ray burst from a nearby supernova was a possible cause of the Ordovician-Silurian extinction. The gamma-ray burst would have stripped away the Earth’s ozone layer causing intense ultraviolet radiation from the sun and may account for climate changes observed at the time. The hypothesis is speculative, but extraterrestrial influences on Earth’s history are an active line of research. Recovery of biodiversity after the mass extinction took from 5 to 20 million years, depending on the location.
The end-Devonian extinction may have occurred over a relatively long period of time. It appears to have affected primarily marine species and not terrestrial plants and animals. The causes of this extinction are poorly understood.
The end-Permian extinction was the largest in the history of life, with an estimated 96 percent of all marine species and 70 percent of all terrestrial species lost.[New research suggests that the end-Permian extinction was still the biggest, but not as bad as 96 percent; perhaps close to 80%.]
It was at this time, for example, that the trilobites, a group that survived the Ordovician–Silurian extinction, became extinct.
On land, the disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to emerge, the dinosaurs. With respect to biodiversity, the planet looked very different before and after this event.The causes for this mass extinction are not clear, but the leading suspect is extended and widespread volcanic activity that led to a runaway global-warming event. Evidence for this lies in the massive layers of basaltic rock of the Siberian Traps, which indicate the outfall of volcanic eruptions that lasted for approximately two million years. The oceans became largely anoxic, suffocating marine life. Terrestrial tetrapod diversity took 30 million years to recover after the end-Permian extinction. The warm and stable climatic conditions of the ensuing Mesozoic Era promoted an explosive diversification of dinosaurs into every conceivable niche in land, air, and water. Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became very large on the abundant food available.
The causes of the end-Triassic extinction event are not clear and hypotheses of climate change, asteroid impact, and volcanic eruptions have been argued. The extinction event occurred just before the breakup of the supercontinent Pangaea, although recent scholarship suggests that the extinctions may have occurred more gradually throughout the Triassic.
The end-Cretaceous extinction event 65 million years ago saw the loss of the dinosaurs, the dominant vertebrate group for millions of years, with the exception of a theropod clade that gave rise to birds. Indeed, every land animal that weighed more than 25 kg became extinct.
The main cause of the end-Cretaceous extinction event resulted from the cataclysmic impact of a large meteorite, or asteroid, off the coast of what is now the Yucatan Peninsula. Evidence in support of this hypothesis includes a sharp spike in the levels of iridium (which rains down from space in meteors at a fairly constant rate but is otherwise absent on Earth’s surface) at the rock stratum that marks the boundary between the Cretaceous and Paleogene periods and an appropriately aged and sized impact crater. At the time, skies darkened and temperatures fell as the meteor impact and tons of volcanic ash blocked incoming sunlight. Plants died, herbivores and carnivores starved, and the mostly cold-blooded dinosaurs ceded their dominance of the landscape to more warm-blooded mammals. Recovery times for biodiversity after the end-Cretaceous extinction are shorter, in geological time, than for the end-Permian extinction, on the order of 10 million years.
In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs, and birds, the warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists. The appearance and dominance of flowering plants in the Cenozoic Era created new niches for insects, as well as for birds and mammals. Changes in animal species diversity during the late Cretaceous and early Cenozoic were also promoted by a dramatic shift in Earth’s geography, as continental plates slid over the crust into their current positions, leaving some animal groups isolated on islands and continents, or separated by mountain ranges or inland seas from other competitors. Early in the Cenozoic, new ecosystems appeared, with the evolution of grasses and coral reefs. Late in the Cenozoic, further extinctions followed by speciation occurred during ice ages that covered high latitudes with ice and then retreated, leaving new open spaces for colonization.
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