mammal evolution

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Sure that long neck is helpful getting food…but water…

Finally, it’s (sort of) done. Very, very simplified synapsid evolution. I started with basic eukaryotic cell, I didn’t even try to imagine what the LUCA was like. Probably some weird, virus-like thingy. I’m not sure I won’t tweak it a bit more, but for now, I consider it finished. I’m happy I managed to get it done now, as tomorrow I’m moving to a new address, and will be busy with cleaning, painting walls, more cleaning, and generally making the place hospitable, and won’t have time to paint or draw, so I’m glad I can at least upload this before disappearing for a while. I’ll also add this to my redbubble at some point.

So, the creatures are:

some generic cells, that weirdo that is Saccorhytus coronarius, a tunicate, Oikopleura dioica, because I was lazy, Pikaia, Haikouella, Haikouichthys, Pteraspis, Entelognathus, Guiyu oneiros, Tungsenia paradoxa, Tiniaru, Panderichthys, Tikataalik roseae, Acanthostega, Ichthyostega, Pederpes, Westlothiana, Echinerpeton, Pantelosaurus, Tetraceratops, Charassognathus, Dvinia, Prozostrodon, Adelobasileus, Hadrocodium, Teinolophos trusleri, Sinodelphys, Juramaia.

Now, Teinolophos (the monotreme) is known, of course, only form a jaw. It’s the oldest monotreme we have in the fossil record and can be a platypus relative, but can also be more basal than that. All we know for certain is: it had teeth as adult and didn’t have a beak. I had no idea how to restore it at first. All living monotremes are specialised weirdos. None have whiskers, for example. But, considering we don’t have anything that could be considered a generic monotreme, that begs the question: are whiskers therian thing, or mammalian thing, and extant monotreme lost them secondarily, because they just had to be wierd? Considering Teinolophos’s teeth, and the fact that it apparently had a rather strong bite (though how we know this is a mystery to me) it’s rather certain that it had a different lifestyle than that of any living monotremes. So, with that in mind, I decided to make it unlike any extant monotreme. And to give it whiskers, because I’m adventurous like that…

Though honestly, anything between Pantelosaurus and Sinodelphys/ Juramaia is known mostly from skulls (or fragments of skulls), so they’re all speculative to some degree. Also, I don’t think I need to say this, but none of them are drawn to scale.

And, while we’re on topic of I don’t think I need to mention it, but I will anyway:

The creatures I chose to paint here aren’t necessarily ancestors of anything that is alive today (and hell, the fish part of this painting definitely shows some non-ancestors (look at me, inventing words…), because we have the Zachełmie tracks that were left by something very much tetrapod-like, with four walking limbs, and tail and body held off the ground, and they predate Tiktaalik for about 12 million years, and Panderichthys by 10 million. I wonder if we’ll ever discover what left those tracks. That would be awesome! If only the fossil record wasn’t so patchy…

Switching Dinosaurs and Mammals

The Triassic was a battleground, in which dinosaurs and mammals warred to see who would inherit the niches left empty after the Permian extinction. At first, both sides seemed equally matched, with dinosaurs like Eoraptor (1) competing more less directly with mammals like Cynognathus (2). The two groups rapidly diverged, however.

Mammals grew every larger and more diverse over the course of the Mesozoic, evolving into towering tree-browsers (10), low-grazing giants armed with plates (11), spikes (12), and tusks (13) as well as predators large and ferocious enough to conquer these defenses (6).

Small, nimble dinosaurs were better suited for life in the shadows. They dug under the ground (3) and climbed trees (4) to escape from mammals, only venturing onto the ground at night, aided by dark-adapted vision, smell, and hearing keener than any mammal’s (5, 6). Some even became modest hunters themselves (7). 

Where dinosaurs excelled was reproduction. Mammals took care of their young after hatching, but one group of dinosaurs carried their eggs and chicks with them in a mobile nest or pouch evolved from the forelimbs (8,14). It was this lineage that would go on to rule the Earth after the next extinction.

WHERE DO MAMMALS COME FROM?

The Earth plays host to a remarkable variety of creatures all of which diverged from a single, unknown common ancestor. In the 540 million year history of complex life there have been repeated turnovers in dominant life forms, from The Age of Fishes during the Devonian to The Age of Reptiles during the Mesozoic which gave way to our current era in time, the Cenozoic, or otherwise known as The Age of Mammals. But where do mammals come from…?

Pelycosaurs…
The Pelycosaurs first appeared 306Ma and are the most basal synapsids. Synapsids are mammal-like reptiles; a distinguishable feature is their skull with only one post orbital fenestra, reptiles have two. The mammal-like reptiles show the earliest signs of evolution towards more mammal characteristics, Dimetrodon is a classic example. Dimetrodon had only a single temporal fenestra, this feature allowed for jaw muscle attachment to be further back providing a stronger bite force over a wider range of jaw movements, subsequently making Dimetrodon one of the most successful predators of its age.
Dimetrodon quite literally means “two sets of teeth” and this refers to its elongated incisors, this is the beginnings of the mammal feature known as heterodonty (differentiated teeth). Dimetrodon also exhibits deep ridges of the inner nasal cavity providing a larger surface area for the attachment of olfactory epithelium indicating a larger reliance of the sense of smell (something that will become more important in future mammal evolution).

Therapsids…
Therapsids appear around 275Ma and likely evolved from pelycosaurs or a similar sort of ancestor. They are still classed as synapsids but they even more mammal-like features than their ancestors. Therapsids have less of a sprawling gait than the pelycosaurs and other reptiles (although the herbivorous kind still retain a rather sprawling gait, this is a feature that is slow to disappear). Therapsids have an even larger temporal fenestra and more elongated incisors as the teeth continue to differentiate. The skull of therapsids is also beginning to change; mammals have a single jaw bone called the dentary, this is present in synapsids along with many other jaw bones such as the quadrate and articular, but as mammal evolution gets underway the dentary expands and the quadrate and articular reduce in size and become part of the middle ear bones. Some Therapsids were apex predators throughout the permian such as Gorgonops.

Cynodonts…
Cynodont fossils are some of the most important fossils in the mammals evolutionary record and we are classed as part of Cynodontia. They are dog-like creatures and appear around 260Ma, they were hugely successful and diversified rapidly. One of the best examples of cynodonts in mammal evolution is Thrinaxodon. The cynodonts exhibit even greater tooth differentiation and tooth occlusion (precise tooth contact of the upper and lower teeth, a feature unique to mammals). Tooth occlusion also suggests the cynodonts had controlled tooth replacement like mammals (mammals exhibit diphyodonty meaning two sets of teeth, the milk teeth and the adult teeth).
More importantly, cynodonts also show partial or complete secondary palates meaning they are able to swallow food and breathe at the same time, something reptiles cannot do. Many taxa also show absence of abdominal ribs allowing for the presence of a diaphragm which increased lung capacity. A diaphragm paired with the secondary palate and tooth occlusion suggests that cynodonts had a higher metabolism than other extant animals of the time. The cynodonts dentary continues to expand further back of the skull.
Some cynodont skulls have small indentations around the nasal region which may be indicative of nerve passages towards sensitive hairs, possibly whiskers, if so, cynodonts had hair. Thrinaxodon and others also have a larger brain size in comparison to the rest of the body than other animals as well as enlarged auditory and olfactory regions suggesting they were nocturnal.

The Permian extinction struck 250Ma due to extensive volcanism of the Siberian Traps leading to a runaway greenhouse effect. Between 80% and 96% of living species died out, including most of the cynodonts and the therapsids. Reasons why the reptiles battled through this extinction and rose to dominate is still debated but it may be due to the fact that reptiles can secrete nitrogenous waste as a uric paste whereas mammals must secrete is as a liquid. This allowed the reptiles to conserve water and see the extinction through.
Whilst most cynodont species perished, a few individuals made it through, they were mostly small, nocturnal burrowers capable of getting water from underground root nodules and tubers. However, the cynodonts would not rise to dominance again but their descendants would, although not for another 200 million years. They would spend the Mesozoic Era in the dinosaurs shadows, their evolution driven by a nocturnal lifestyle and the need for endothermy. The evolution of our ancestors was shaped by the dominance of the dinosaurs, when their reign ended 65 million years ago our true mammalian ancestors would quickly take over the niches left behind and become some of the most spectacular creatures the world has ever seen.

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Diver Keri WIlk has been one of the few people to observe a strange sperm whale trait, described as a “poonado”.

This is thought to be a rarely used defence mechanism, which is different to when the whales defecate before their descent into deeper waters. The whale released an unusual amount of faeces, turned on its side and used its flipper to propel the excrement in a huge 30 metre arc.

This could be the first time this mechanism has been photographically documented, but has been observed in the wild previously.

(Via Daily Mail)

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I’ve finally uploaded synapsid evolution to my redbubble (link to my shop is in my blog description, apparently tumblr now hides posts with outgoing links from search. Not cool.)

As always with things without background, I wasn’t sure what background color to add, and finally ended up going with the default white. It’d be great if there was option for customers to choose  background colors on all sorts of things, like they can do with t-shirts now.

I was tempted to make the background black on things where you the buyer can’t choose  background color themselves, but then I’m aware of the fact that not everyone shares my obsession with black.

Now I’m thinking about uploading this again, so I’ll have to listings for it: one with white background, and one with black.

And as an aside, adding artwork to redbubble is a pain. It literally took well over an hour to get this done.

I recently read about a nice example of quantitative evolutionary changes leading to qualitative ones. It’s such an important and well-studied piece of evolutionary history that it has its own Wikipedia article: the evolution of mammalian auditory ossicles.

Very early in the evolution of mammals - probably at least as far back as 200Mya - the articular and quadrate bones of the jaw (both present in most tetrapods) came free from the jaw and became the malleus and incus of the inner ear, connecting to the existing stapes.

Together, these three bones act as an acoustic impedance matcher, improving the quality of vibration transfer from the air to the cochlea, especially at high frequencies. That’s why many mammals can hear sounds up to 10^5 Hz, while amphibians, reptiles, and birds tend to max out around 10^4 Hz or lower.

Being able to hear higher-pitched sounds may have paid off in the short term for mammals, many of whom were nocturnal insectivores, by helping them hear the sounds made by insects. But in the long run, it enabled the evolution of the characteristic distress call of mammalian infants - all infant mammals, when lost, cry out in order to attract the attention of their mothers, which doesn’t attract non-mammalian predators because they can’t hear it.

So this quantitative increase in the hearing range of early mammals was a key part of the evolution of parental care behavior, a crucial part of our eventual success.

What if elves were just big weird ants

Basically what i want to do with worldbuilding Elves is experiment with the implications of what a sentient eusocial clade of mammals would be like? There’s been authors who’ve flirted with similar ideas, like Terry Pratchett, but that aspect of fairy society has mostly been underdeveloped.  

To me it makes so much sense with Fairies. The lack of any recognizable social structure or hierarchy, despite the presence of “Queens.” The androgyny and morphological diversity (reproductive castes, hello!). The weird alien psychology and the propensity to “take” members of other species, a behavior found in various forms within many insect colonies. And of course they’re already aesthetically associated with insects, as well as with plants, implying a deep symbiosis. 

The setting I have in mind is one of those stock worlds that is turning so slowly on its access that one side is always in light and the other always in shadow. Hence their association with living either underground or in a “twilight zone” where time is permanently screwy (ie the meridian between the day and night zones). The harsh, constantly changing environment created a group highly adaptable social animals able to solve complex problems and “magically” parasitize genes from host species. Hence why Elves, whose “natural” form we typically call goblins, orcs, etc., produce human-like offspring with just a few external signifiers of their species. 

The lore is that, in an effort to fight overpopulation in an environment with dwindling resources, Elves, instead of wasting their time with interstellar travel, tunnel through space itself into other versions of their planet across different universal instances. Their colonial efforts bleed into worlds like our own, where they find mixed success and failure, often being unable to maintain human-level populations due to pathogens and other threats. Hence why the assimilation with humans, giving us the unearthly beauties as well as the older “monstrosities.” Human-elf relations are aided by both the subtle bending of brainwaves and attractive pheromones. 

angelicuscadere  asked:

For a sentient specie of omnivorous raptors (think feathered dino) with social complexity, technology and population density similar to humans ~300 years ago, what would be the most prominent health issues for the common folk?

I’m using birds and alligators as references for most things anatomy, so what would be avian/crocodilian equivalent to fleas, flu, cholera, measles, or other highly contagious and common ailments? (They have both feathers and scales)  They have had little to no contact with any large mammals over the course of their evolution - upon contact with mammals (including humans), would that make them less or more susceptible to be affected by human illness, or a random mix? I know this is very broad so I’m not expecting a detailed answer - I was just hoping you could give me some pointers as to what kind of diseases to investigate and inspire myself from.   Thank you! I really love your script blog! :)

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Yay raptors! I hope you like info-dumps.

Originally posted by gifovea

If I assume a similar medical scene to the 1700-1800′s, I’d first broadly group the common diseases into parasitic, bacterial, viral and fungal. Most of these species don’t congregate in terribly large numbers, except in farms and fortunately for your writing, both birds and crocodiles are bred on farms in large numbers to give you disease examples that are probably common at high densities with sub-optimal hygiene. I will link to other sites for the most interesting ones.

Parasites are the group that were extremely common before effective medication, and also the most externally obvious. They’re also potential vectors for the other groups, to spread disease from one raptor to another (think about how mosquitoes do this today).

External parasites are your equivalent to fleas. Avians can get fleas, but mites and lice are far more common. Almost all wild birds are harboring some kind of feather lice. Reptiles commonly get ticks. Scaly leg mite might give you inspiration for a suitably interesting looking disease.

Internal parasites get a bit more variable, depending on the internal anatomy of your raptor species. Almost everything can get intestinal worms (because almost everything has intestines). Where exactly in the intestines they live will depend on anatomy, and young won’t get any placental transmission from their mother if they lay eggs. Worms like Heterakis can transmit other diseases to certain species too.

Birds get respiratory parasites, which are quite unique. Air sac mites may be relevant if your raptors have them, and gapeworm is one of my personal favorites. (Yes, I have favorite parasites. I’m not weird.)

Moving onto bacterial diseases, Cholera was a big killer of humans, and poultry have Fowl Cholera of their own. Botulism toxin kills a lot of birds that congregate around waterways, but interestingly birds and reptiles seem very resistant to tetanus.

Gut pathogens like salmonella are common in reptiles and birds, and are not species specific. These things can get into just about anything, but they are often host adapted. This means the usual species they infect doesn’t get as severe pathology as a new species. This may be relevant for your mammals who encounter this species, as it’s commonly spread by poor hygiene practices.

Psittacosis is a bacterial disease that you should definitely look into. It can affect both humans and parrots, and can be lethal in both. It was historically something of a mystery disease for a while, and worth reading about.

Most species (honestly, probably all species but we haven’t bothered to look) have a poxvirus of their own. Some of these poxviruses will cross species (eg goats and sheep) and will vary in how virulent they are (smallpox vs chickenpox). They hang around in the environment for a really long time and are difficult to exterminate. Your species probably has one, but despite the name not all poxviruses present with pox on the skin.

If your species is feathered, then Psittacine Beak and Feather Disease is simply fascinating and visually dramatic. It’s a chronic disease and may fill a similar social role as leprosy

Influenza viruses commonly affect many species of birds and will also potentially cross over to humans or other mammals. Human and mammal influenza can also cross over into birds. When you get an influenza type into a ‘new’ species, death rates are typically higher.

Most concerning, however, is when you have two different influenza strains infect the same individual, recombine by infecting the same cell, and then by chance produce a totally new strain of influenza which may then infect any species that could have been infected by either parent virus. Immunity to on strain of influenza offers little protection against another.  This is why bird flu outbreaks are such a concern.

I noticed you said no contact with large mammals over their evolution. If they’re farming, what’s eating their stored food? Rats are common and disease vectors to boot, if they have no rats, what do they have instead? Something will be taking advantage of food stores, and will be relevant to the diseases in the population.

And I don’t know if you considered it, but crocodillians tend to be cannibalistic. If they are, then you could potentially have a tapeworm species that spends it’s entire life cycle within this species. It matures and drops cysts in the intestine of one individual, those cysts are eaten by a second individual (faecal contamination of food most likely), then forming cysts in muscle or meat tissue, and when the 2nd individual is eaten by a 3rd individual, those cysts mature into the adult tapeworm to live inside their intestine, and the cycle begins again. There may also be a prion disease, though they are rare.

Anisodon grande, a large chalicothere from the Late Miocene of Europe, about 15 million years ago. Standing 1.5m tall at the shoulder (4′11″), it looked somewhat like a cross between a gorilla, a horse, and a giant sloth – or like a mammal trying to mimic a therizinosaur. Its long forelimbs were probably used to pull down high tree branches so it could browse on the leaves, while spending most of its time sitting on its well-padded haunches.

Despite its huge claws, knuckle-walking gait, and distinct lack of hooves, it was actually an odd-toed ungulate related to modern horses, rhinos, and tapirs.

nevertickleasleepinglucy  asked:

I do recall hearing in one of my Animal Science classes that the digestive tract of an animal is indicative of its diet. For example: carnivores having shorter digestive tracts as they lack a rumen or cecum which is used by herbivores to digest plant material. I was wondering if you knew of any other examples, and if there was any journal articles published on the subject.

Yep, the above is very true. Herbivores require long, complex digestive tracts with specialised organs, because breaking down cellulose in plant matter is tough. They need to have specialised gut bacteria, stomachs, teeth and even saliva in order to be herbivorous. 


This figure sums up it up really well. You can tell just from looking that the length between a ruminant herbivore to a carnivore is dramatically different. And the size of the cecum is quite big in herbivores but pretty tiny in carnivores. 

Here’s a few studies (though they may all be behind a pay wall. I’m not sure since I have access to them via my uni): 

Procranioceras skinneri, a palaeomerycid ruminant from the mid-Miocene of North America, living about 15 million years ago. Standing around 1m tall at the shoulder (~3′3″), its most striking feature was its odd headgear: two long straight ‘horns’ over its eyes and a third protrusion at the back of the skull.

But despite its superficially deer-like appearance, these structures weren’t antlers. They were in fact ossicones, like those of its closest modern relatives the giraffids, and were probably covered in skin and fur rather than horn.

Weird prehistoric beast conjures up images of ‘Star Wars’ queen

What does a strange giraffe-like animal with three horns atop its head and a set of fangs that roamed Europe about 15 million years ago have in common with a pretty young queen from the “Star Wars” movies?

Plenty, according to the scientists who on Wednesday announced the discovery in Spain’s Cuenca province of beautifully preserved fossils of this creature.

They gave it the scientific name Xenokeryx amidalae, meaning “strange horn of Amidala,” referring to the “Star Wars” character Queen Amidala, played by actress Natalie Portman.

The peculiar shape of Xenokeryx’s largest horn was “extremely similar to one of the hairstyles that Amidala shows off in 'Star Wars’ Episode 1 when she is the queen of her home planet Naboo,” said paleontologist Israel Sanchez of the National Museum of Natural History in Madrid.

Xenokeryx was a herbivore about as big as an average deer. The males had two small horns like those of a giraffe above the eyes and a larger one shaped a bit like the letter “T” on the back of the head. The males also boasted enlarged sabre-like upper canines that likely were used for display to impress other members of the species, Sanchez said.

Females were hornless and fangless.

Continue Reading.

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My copy of ‘The Wonders of Life on Earth’ just arrived today! Thinking it was just a general book on nature, I was surprised (and very pleased) to find it actually is a detailed look at Charles Darwin’s voyage of the Beagle. Each chapter describes the various places he stopped at, looking at the ecology and evolution of the various creatures of South America, Australia, and Southern Africa. It’s a pretty old book (from 1960) and includes early information on genetics. Of particular interest is the opening introduction featuring a look at Darwin’s early years, including authentic photos of his office and collected specimens. This is one I really recommend!