diapsids

Longisquama!

Since it’s April Fool’s Day, and Tumblr is sending images of lizards screaming across all our dashboards at hyper-light speeds, I thought it would be a good time to talk about a lizard who April Fooled the entire paleontological community, long before the Mop/Wretched Tooth divide threatened to send our sociopolitical infrastructure crumbling to the ground.

Is it a tenuous connection?  Yeah, but I was gonna make this post anyway, so live with it!

Longisquama lived during the Triassic Period, 235 million years ago, in modern-day Kyrgyzstan.  It might have been a lizard, as I asserted above, but its place within Reptilia is actually quite uncertain; the only thing known for certain is that Longisquama is a “diapsid reptile”, meaning it could be a squamate, a rhynchocephalian, a crocodilian, or a pre-dinosaur.

Longisquama is distinguished by the row of strange appendanges growing from its back.  The purpose of these appendages is uncertain, and has long been the subject of much paleontological debate.

The most iconic version of Longisquama depicts it with twin rows of appendages, rather than the single row preserved in the only known fossil specimen, and shows it using these twin wing-like structures to glide.  While this is almost certainly not the case, numerous supposedly serious paleontologists - including Dougal Dixon, speculative evolution writer and long-time peddler of insane made-up garbage - have espoused the theory that Longisquama is the true ancestor of birds.

This makes absolutely zero sense from an anatomical perspective, and was essentially nothing more than a very convenient way for a bunch of die-hard dinosaur traditionalists to deny that birds were the descendants of dinosaurs.  Even so, this debate raged on until the shockingly recent year of 2006.

At that time, new studies of the single Longisquama fossil found that the appendages weren’t part of the animal’s body at all.

It was fossilized in front of a plant.

An excerpt from the zoological text The Hunter’s Encyclopedia of Animals (First Edition).
Glossary

A

acuomotor reflex The inflation of the gobul’s spines by taking in water and air into its elastic stomach, in order to expand its body.

aestivation (L. aestivare, from aestās, summer) A state of dormancy or torpor induced by high temperatures and arid conditions. Characterized by inactivity and a lowered metabolic rate.

agonism (Gr. agōnistēs, combatant) An offensive action or threat directed toward another organism.

ailuromorphic (Gr. aílouros, cat, + morphḗ, form) A pseudowyvern with features superficially reminiscent of felids. This includes (but is not limited to) a feathery integument analogous to a pelt, rictal bristles functionally similar to vibrissae, and obligate carnivory.

allogenic engineer Organisms that modify their biophysical environment by changing living or nonliving material.

alpenstock The barioth’s epidermal protrusions on the leading edge of the wings, knees, and lateral sides of the tail. Used for traction atop ice. Synonyms include “spine” and “spike.”

anapsid (Gr. an-, without, + apsis, arch) Amniotes in which the skull lacks temporal fenestrae, with turtles the only living representatives.

anautogeny A condition found in insects where a gravid female must feed on blood before oviposition in order for the eggs to mature.

angiosperm Seed-producing, fruit-bearing, flowering plants.

anisodactyl The arrangement of digits wherein three toes face forward and are accompanied by a single back-facing toe.

anthrax A lethal disease caused by the bacterium Bacillus anthracis. Anthrax can occur in three forms: epidermal, respiratory, and intestinal.

apex predator Carnivorous animals that occupy the highest trophic levels and have a disproportionate influence on the health of their ecosystem.

aratrum (L. arātrum, plough) The cranial bone of the barroth, comprised of trabecular tissue and enlarged sinuses. This structure houses the nasal cavities and supports five dorsally-located nares. The namesake for the eponymous genus Aratrum.

B

benthos (Gr. depth of the sea) Organisms that live along the bottom of seas and lakes; adj., benthic.

biological species concept A reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.

biome (Gr. bíos, life, + -ōma, body) Communities of plants and animals characterized by climatic and soil conditions; the largest ecological unit.

C

caelincolid (L. caelum, sky, + incola, inhabitant) Any species belonging to the family Caelincolidae.

capillaturid (L. capillātūra, false hair) Any species belonging to the superfamily Capillaturoidea. Named for their plumage, which is often compared to fur on mammals. Also known as “wig wyverns.”

cathemeral An organism that demonstrates sporadic intervals of activity during the day or night.

CDIHG The Conservation Division of the International Hunters’ Guild. A group that assesses a species’ susceptibility to extinction, by monitoring populations and establishing criteria for Red List placement. Established forty years ago in response to loss of biodiversity, due to overhunting and anthropogenic ecosystem destruction.

cephalovelos (Gr. kephalé, head, + vélos, arrow) The ribbed hood structure found on the lagiacrus’ head, studded with electroreceptors on its ventral surface.

chitinase (Gr. khitṓn, tunic) Hydrolytic enzymes that break down glycosidic bonds in chitin, most commonly found in bacteria and fungi, and to a lesser extent, plants and some animals.

cloaca (L. cloāca, sewer) The posterior orifice that houses the openings for the digestive, reproductive, and urinary tracts.

conflagrant tube A mucus-lined tubular organ that connects the flame sac to an opening in the oral cavity, where the byproduct waste gas can be expelled through the mouth.

conspecific A member of the same species.

coprophagy The consumption of fecal matter.

convergent evolution See homoplasy.

crepuscular An organism that is active at twilight (dawn and dusk).

crypsis The ability of an animal to avoid detection through methods such as camouflage, nocturnality, subterranean lifestyle, and mimicry. Involves visual, olfactory, and auditory concealment.

D

dagger [†] A typographical symbol that, when used next to a name, indicates death or extinction. Also called an obelisk.

desiccation The state of extreme dryness, or the state of drying.

diapsid (Gr. di-, two, + apsis, arch) Amniotes in which the skull bears two pairs of temporal fenestrae, including birds and reptiles (barring turtles).

dog wyvern Any theropod species belonging to the family Vipracanidae. Includes the genera Magnaraptor (the greats) and Dromos (the dromes).

E

ectoparasite Parasites that live on the outside of the host.

ectothermic (Gr. ektós, outside, + thermē, heat) An organism that cannot internally maintain its body temperature and must rely on external sources of heat to moderate metabolic rates. “Cold-blooded.”

elaiopteral gland (Gr. élaio, oil, + pterón, wing) An oil-secreting gland found on the inner forearm (antebrachial) of pseudowyverns in Capillaturoidea. The gland secretion is conveyed to the surface in hollow ducts, terminating at a modified spur. Used for maintenance of feather integrity, pheromone production, and waterproofing.

elder dragon A catch-all term applied to unrelated species with similar cultural and religious significance, capable of posing high-level threats to human populations. The term elder dragon is often a misnomer, used to describe very specific organisms from groups such as the squamates, cephalopods, and perissodactyls.

electrocyte Flat disc-shaped cells stacked in thousands that function by pumping sodium and potassium ions.

electrogenesis The biological generation of electricity by living organisms.

electroreception The ability to perceive ambient electrical stimuli.

electroreceptor Sense organs located in the skin used for electrolocation.

endothermic (Gr. endon, within, + thermē, heat) An organism that can internally maintain its body temperature by balancing metabolic heat production by heat loss. “Warm-blooded.”

epibiont An organism that lives on the surface of an organism, typically in a commensalistic relationship.

euryhaline A species that has a tolerance to a wide range of salinities.

exsanguination Sufficient blood loss, normally to the point of death.

extant When a species is still existing.

extinct When a species is no longer in existence. Extinction is typically decided by the death of the last individual of a species.

F

Fatalis Trinity An occult religion practiced the world over. Its chief deities are the Fatalis Brethren (species of the genus Fatum), whose worshippers believe that they are living gods reincarnated in the form of six-limbed dragons. Their Temple maxim is “Damus nostra fāta tibi.”

fire gurgling An agonistic display seen in raths and espinas. The animal will release small concentrations of methane that ignites on contact with a hypergolic chemical secreted by modified venom glands, causing tendrils of fire to ooze from its jaws.

fire regime The pattern, frequency, and intensity of wildfires prevailing within an area. Fire regimes are an integral component of fire ecology, and the interactions between fire and biotic/abiotic components of an ecosystem.

flame sac An organ connected to the stomach of raths and espinas, used for storing methane produced by microbial bacteria during the breakdown of roughage.

formic acid A carboxylic acid synthesized by ants in the family Formicidae, transmitted by sting from a modified ovipositor, spray ejected from the abdomen, or autothysis.

formicary An ants’ nest.

frenzy virus A viral disease that causes heightened aggression and acute inflammation of the brain after a period of incubation. The pathogen modifies its host’s mortality and behavior long enough to facilitate its transmission to other hosts. The shagaru magara is its primary vector.

frost sac An organ derived from a heavily-modified foregut, found in the mountain barioth. The stomach oil stored within can be ejected in a forceful spray, which then rapidly cools once exposed to frigid temperatures.

G

gaster The bulbous posterior portion of the metasoma found in hymenopterans.

Gause’s law An ecological principle which states that species competing for the same resource cannot coexist if all ecological factors are constant. If one species has an advantage over the other, then the less fit species will either undergo extinction or an evolutionary or behavioral shift toward a different niche.

H

haemal arch A bony arch on the underside of tail vertebra.

heterodont (Gr. heteros, different, + odous, tooth) Having teeth differentiated into incisors, canines, and molars for different purposes.

heterogeneity A property ascribed to environments with a mix of uneven concentrations of multiple species (biological), terrain formations (geological), or environmental characteristics (meteorological).

homoplasy The emergence of a characteristic or adaptation shared by a set of species but not present in their ancestors, acquired independently by unrelated groups.

hydrophyte Plants with specific adaptations for living in aquatic or marine environments, submerged, on the surface, or in proximity to water.

hyperphagia (Gr. hupér, over, + -phágos, eater) A preliminary stage to heterothermy, in which an organism will gorge in order to increase its body weight. It will then subsist off of the accumulated fat reserves during its seasonal metabolic depression.

I

immunohistochemistry The process of detecting antigens in cells by observing the principle of antibodies binding to target antigens in tissue segments.

insectivory A diet of a carnivorous organism consisting chiefly of arthropods.

International Hunters’ Guild An organization whose jurisdiction supersedes that of any government. Its foremost goal is to act as a support network for hunters, while providing education, medical attention, and economic opportunity to people. Abbreviated as IHG.

J

K

keystone species A species (typically a predator) whose removal leads to reduced species diversity within the community, and the cessation of the entire ecosystem.

kinsect Any number of domesticated neopteron species trained by hunters for insectry (Fr. insecterie, from insecte + -erie).

L

leviathan Any species belonging to the order Arcacollum, defined by the characteristic arched neck. The term has also been inaccurately applied to suchians such as the nibelsnarf.

lynian A member of the species Felis comes. The term is not exclusively used with actual lynians, and can refer to bipedal organisms with humanoid characteristics such as the urukis and shakalakas (relatives of the human and wyverian).

M

Mandibulaformia (L. mandibula, jaw, + fōrma, shape) A genus of flying wyverns characterized by an ossified protrusion of the jaw. While they serve no function in prey-capture or mechanical digestion, the sickle-shaped appendages are thought to be used in intraspecific communication.

membranalan (L. membrāna, skin, + āla, wing) An organism from a clade of nonavian theropods. Characterized by membraned wings (with or without feathers), bipedalism, and endothermy.

motion parallax A monocular depth cue discerned through the proximity of objects, and how fast they appear to move relative to the viewer.

N

necrosis The death of cells and/or tissues within an organism due to disease, injury, or failure of the circulatory system.

necrotoxin Toxins that cause necrosis (death) in all cells they encounter and destroy all tissue types. Transmitted through the bloodstream.

nictitating membrane A transparent or translucent third eyelid. Protects the eye from UV exposure, debris, water, snow, and impact damage.

O

olfaction The sense of smell.

ovoviviparity A mode of reproduction in which the embryos that develop inside eggs are hatched and retained within the body without a placental connection to the mother.

P

paradraconian (Gr. rapá, para, beside, + drákōn, dragon) See pseudowyvern.

patagium A membranous structure that assists an animal in gliding or flight. It is found in bats, birds, some dromaeosaurs, pterosaurs, gliding animals, true wyverns, pseudowyverns, bird wyverns, and dragons.

pentadactyl (Gr. pénte, five, + dáktulos, finger) The condition of having five digits on each limb.

phalange Digital long bones found in the hands and feet of most vertebrates.

photophore A light-emitting organ found of various marine animals that appear as luminous areas on the skin.

phylogeny (Gr. phylon, tribe, race, + geneia, origin) The origin and diversification of any taxon, or the evolutionary history of its origin and diversification, usually presented in the form of a dendrogram.

piscivory A diet of a carnivorous organism consisting chiefly of fish.

pneumatization The formation of air-filled cavities in hard tissues such as bone.

praesidiosaur (L. praesidium, fortress, + Gr. sauros, lizard) Any species belonging to the clade Praesidiosauria.

prenuptial hunt A behavioral assessment demonstrated by raths, in which a courting pair will hunt a prey item together. The success of the outcome determines whether or not the rathian will form a monogamous pair with the suitor rathalos.

proventriculus The narrow, glandular region of the stomach located between the crop and gizzard that uses enzymes to commence digestion, and/or stores food. Also called the foregut.

pseudowyvern (Gr. pseudḗs, lying) An organism from a clade of nonavian theropods. Characterized by membraned wings (with or without feathers), pronograde posture (quadrupedalism), and endothermy.

Q

R

receding rhampotheca A keratinized epidermal sheath found in many non-avian theropod lineages, thought to have once formed a full or semi-complete beak in ancestral species.

riparian zone The interface between land and rivers/streams, characterized by a high biodiversity of hydrophilic plants along the banks and river margin.

ruminant (L. ruminare, to chew the cud) Cud-chewing artiodactyl mammals with a complex four-chambered stomach.

S

satellite colony In hymenopterans: Small, outlying colonies staffed with soldier-caste ants that encircle the larger, central colony.

scutum (L. scūtum, shield) A chitinous extension of the pronotum, found on altaroths. Acts as an esophageal blockage when swallowed by barroths, and protects the head region when the altaroth sprays formic acid toward its anterior end.

shellshocker An electric organ derived from modified nerve tissue, located on the medial region of the lagiacrus’ spine.

symbiosis (Gr. sún, with, + bíos, life) The living together of two different species in an intimate relationship. Symbiont always benefits; host may benefit, be unaffected, or be harmed (mutualism, commensalism, and parasitism).

synapsid (G. synapsis, contact, union) An amniote lineage comprising the mammals and the ancestral mammal-like reptiles, having a skull with a single pair of temporal openings.

T

tapetum lucidum (L. tapetum, tapestry, + lūcidum, bright) A layer of tissue behind the retina in most vertebrates that reflects visible light, increasing the availability of light to photoreceptors. Increases night vision in nocturnal and deep sea organisms.

thagomizer The distinctive arrangement of four to ten horizontal spines on the tail of reptiles. Coined by cartoonist Gary Larson and perpetuated by paleontologist Ken Carpenter.

torpor A state of decreased physical activity indicated by decreased metabolic rates and internal temperature.

U

ungulate (L. ungula, hoof) Any hooved mammal.

V

vipracanid (L. vīpera, snake, + canis, dog) See dog wyvern.

vivernan (It. viverna, wyvern, from L. vīpera, snake) An organism from a clade of nonavian theropods, colloquially known as “true wyverns.” Characterized by featherless membraned wings, bipedalism, and ectothermy.

W

X

xerophyte (Gr. xērós, dry) Plants with specific adaptations for living in dry environments with little moisture, such as deserts or snow- and ice-covered biomes.

xyrafitperid (Gr. xyráfi, razor, + pterón, wing) Any species belonging to the family Xyrafipteridae.

Y

Z



Definitions written and compiled by the author, with some wordings borrowed from Integrated Principles of Zoology (14 ed.). Etymologies sourced from various websites, books, and online databases, including wiktionary.org.

Daily Paleo Art Month #19: Odontochelys

Living around 220 million years ago in the Late Triassic of China, Odontochelys was the oldest known of all chelonians. About 40cm long (~16in), it lacked the beak and full armored carapace of its modern relatives, instead possessing a mouth full of teeth and only the plastron on its underside – this was quite literally a “turtle in a half shell”!

The evolutionary history of turtles is rather murky, with little early fossil evidence to work with. They were traditionally classified as the last surviving group of anapsids based on the lack of temporal openings in their skulls, but more recent morphological and molecular studies have placed them firmly within the diapsids. Their exact relationships are still debated, with some scientists considering them to be related to the lepidosaurs (modern lizards, snakes, and tuataras), and others suggesting them to be very closely related to the archosaurs.

anonymous asked:

Could you maybe clarify all the terms on your cladogram? I mean I know that they're all defined by evolutionary relationship and stuff but maybe both define them AND provide an example animal? I'm just a little confused by some of the names...

Oh yeah, sure! 

Chordata (Brick Red): Tunicata + Craniata + Cephalochordata; their most recent common ancestor, and all its descendants. Typically characterized by having a notochord, a dorsal neural tube, pharyngeal slits, a post-anal tail, and an endostyle at some stage of their lives. Examples include hagfish, sea squirts, sharks, sea bass, lungfish, frogs, humans, birds, and lizards (all vertebrates are chordates). 

Vertebrata (Red): Myllokunmingia + Gnathostomata (+ MRCA and all descendants); typically all chordates that have a backbone. Includes: sharks, sea bass, lungfish, frogs, humans, birds, lizards, and lampreys. 

Gnathostomata (Brown): Chondrichthyes + Placodermi + Teleostomi (MRCA & des.; jawed vertebrates. Includes: Sharks, sea bass, lungfish, frogs, humans, birds, and lizards. 

Placodermi (Beige): All gnathostomes more closely related to Dunkleosteus than to any living “fish”; these are the “armoured fish” that had huge armor plating on their heads. All non-placoderm Gnathostomes are in Eugnathostomata. Includes Dunkleosteus; all are now extinct. 

Chondricthyes (Orange): All Eugnathostomatans more closely related to Carcharodon than to humans; is all cartilaginous fish. Originally it was thought that bony fish evolved from cartilaginous fish, however, it has since been found that both diverged from a common Placoderm ancestor. Includes sharks and rays. 

Teleostomi (Yellow): All Eugnathostomatans more closely related to humans than to Carcharodon; “bony fish”. Includes sea bass, lungfish, frogs, humans, birds, and lizards. It is subdivided into Acanthodii & Euteleostomi. 

Actinopterygii (Olive Green): All Euteleostomis more closely related to sea bass than to humans. “Ray-finned fish”. Includes sea bass, clownfish, tuna, and goldfish. 

Sarcopterygii (Lime Green): All Euteleostomis more closely related to humans than to sea bass. “Lobe-finned fish”. Includes lungfish, coelacanth, frogs, humans, birds, and lizards. 

Tetrapoda (Light Green): Frogs + Humans, MRCA & all its descendants. Essentially, all land vertebrates - there are many forms of lobe-finned fish that were able to crawl onto land that form Tetrapoda’s most recent ancestors, but tetropoda proper is just all the descendants of the MRCA for all modern land animals (amphibians, sauropsids, and mammals). Includes frogs, humans, birds, and lizards.

Lissamphibia (Green): Caecilians + Frogs, MRCA & all its descendants. Essentially amphibians, though it excludes many extinct amphibians (when you use the term amphibian to mean all non-amniote tetrapods). This might not actually be a proper cladistic group, but I included it as it definitely does not contain any amniotes. Includes caecilians, frogs, and salamanders. 

Amniota (Dark Green): Humans + Birds, MRCA & all its descendants. All hard-shelled-egg laying land animals (specifically, they produce an egg with an amnios, allowing the animal to lay the egg on land, rather than water). Even though many mammals (and some reptiles!) have secondarily lost this ability, their ancestors did have it, making them a part of this group. Includes humans, birds, and lizards. 

Synapsida (Seafoam): A group of amniotes that includes mammals and all amniotes more closely related to mammals than other living amniotes. Synapsids are not reptiles; though many non-mammalian synapsids resemble them heavily. They are easily characterized by their skulls: many amniotes have temporal fenestra (a hole behind their eye socket); synapsids only have one of these. Most reptiles have two. Includes Dimetrodon, humans, and whales. 

Mammalia (Teal): Platypus + Humans, MRCA & all its descendants. All mammals, essentially. Mammals are typically characterized by the ability to produce milk from mammary glands. Most don’t lay eggs, but either give birth to their young in a pouch (marsupials) or grow the young inside of a placenta (placentals, aka us). Includes echidnas, humans, whales, and kangaroos. 

Sauropsida (Aqua): All amniotes more closely related to birds than to mammals. Essentially reptiles. Since birds and dinosaurs are included in this group, there aren’t a whole heck of a lot of good unifying characteristics. Many sauropsids are endothermic (warm-blooded); many have feathers in addition to scales; and some even give birth to live young. Includes turtles, plesiosaurs, lizards, tuatara, snakes, mosasaurs, icthyosaurs, crocodiles, pterosaurs, dinosaurs, and because it includes dinosaurs, birds. 

Lepidosauria (Dark Purple): Lizards + Tuatara, MRCA & all its descendants. Characterized by having overlapping scales. A part of the larger group Lepidosauromorpha within Sauropsida. Includes lizards, tuatara, snakes, and mosasaurs. 

Squamata (Purple): Lizards + Snakes; MRCA & all its descendants. Characterized by skins with horny scales and shields, and can move the upper jaw as well as the lower jaw (not something most jawed vertebrates can do). Includes lizards, snakes, and mosasaurs. 

Mosasauridae (Lavender): Mosasaurus + Plioplatecarpus, MRCA & all its descendants. The mosasaurs - large marine reptiles, similar to monitor lizards, but elongated and streamlined for swimming. Extinct now. Includes - you guessed it - Mosasaurus, as well as Tylosaurus and many others. 

Serpentes (Fuchsia): Blind snakes + Vipers, MRCA & all its descendants. Essentially all snakes. They’re distinct from lizards due to lack of eyelids and external ears - there are many legless lizards, but snakes are a specific group of “lizards” (given that squamates on the whole can be called lizards). Includes the garter snake, blind snakes, and cobras.  

Ichthyosauria (Hot Pink): All animals more closely related to Icthyosaurus than to Grippia; essentially, a group of sauropsids not a part of Lepidosauromorpha or Archosauromorpha. They were adapted for completely aquatic life and are now completely extinct; they sort of looked like dolphins. Includes Icthyosaurus, Opthalmasaurus, and Mixosaurus. 

Archosauromorpha (Azure): Birds + Crocodiles + Turtles, MRCA & all its descendants. Essentially all modern sauroposids more closely related to birds than to lizards, though of course it includes many extinct groups as well that are descended from their most recent common ancestor. This is a very diverse group with a wide variety of characteristics. Includes turtles, plesiosaurs, crocodiles, pterosaurs, dinosaurs and therefore birds. 

Pantestudines (Dark Violet): All sauropsids more closely related to turtles than any other animal. A group of archosaurimorphs. Genetic analyses have shown strong evidence that they are more closely related to archosaurs than to lepidosaurs; these genetic analyses that include fossils also reveal that animals such as plesiosaurs and placodonts are in this group. Includes turtles, plesiosaurs, Liopleurodon, and Placodus.   

Plesiosauria (Plum): Plesiosaurus + Peloneustes, MRCA & all its descendants. The plesiosaurs - the long-necked (though many lost this) marine reptiles from the Mesozoic. This group also includes the pliosaurs, which on the whole lost the long necks characterizing the group. Includes Plesiosaurus, Elasmosaurus, Kronosaurus, and Liopleurodon. 

Testudines (Violet): Xinjianchelys + Trionyx, MRCA & all its descendants. Essentially, all modern turtles - characterized by having a shell developed from the ribs that acts as a shield. The classification of turtles has been a struggle, given that they are anapsids - meaning, they have no temporal fenestra. The earliest amniotes were anapsids and it was assumed from fossil evidence that turtles, therefore, were descended directly from them, and were not part of any more derived amniote groups (such as synapsids or archosaurs). Most sauropsids are diapsids - meaning, they have two temporal fenestrae. It has since been theorized, however, that turtle ancestors were diapsids; turtles actually lost their temporal fenestrae during their evolution. This is not a completely ridiculous idea, of course; many traits are secondarily lost in groups, making classification by traits a nightmare and unfeasible. Genetic analyses have revealed that the closest living relatives for turtles are crocodiles and birds, making them a part of Archosauromorpha. Includes Green sea turtles, the African spurred tortoise, and terrapins such as the Red-eared turtle. 

Archosauria (Cerulean): Crocodiles + Birds, MRCA & all its descendants. Characterized by having teeth in sockets, though some archosaurs (such as birds) lost their teeth secondarily. Many members of the group have erect or partially erect gaits, unlike other sauropsids, which have sprawling gaits (such as lizards). Archosaurs were the dominant land vertebrates for the entirety of the Mesozoic Era (though dinosaurs were only really during the Jurassic and Cretaceous; a wide variety of archosaurs were common throughout the Triassic). Given that birds are far more diverse than mammals; it can still be argued that archosaurs continue to be the dominant land vertebrates today. Includes crocodiles, pterosaurs, dinosaurs and therefore birds. 

Pseudosuchia (Aqua): Living crocodilians and all archosaurs more closely related to crocodilians than birds. They have massively built skulls, and many still have the typical reptilian sprawl, though some have an erect gait. They typically also had armored plates. Includes crocodiles, alligators, Deinosuchus, phytosaurs, and aetosaurs. 

Ornithodira (Indigo): A subgroup of Avemetatarsalians, which is all archosaurs more closely related to birds than to crocodiles. Ornithodira is, specifically, Dinosaurs + Pterosaurs, MRCA, and all descendants (Ornithodira was easier to fit into the diagram). This group potentially has protofeathers as a characteristic of the entire clade, though many lost them secondarily (such as hadrosaurs). Includes almost all flying vertebrates. Members include Scleromochlus, all pterosaurs, all dinosaurs and therefore all birds.  

Pterosauria (Blue-Violet): Anurognathus + Preondactylus + Quetzalcoatlus, MRCA & Descendants. The pterosaurs. These are all of the “flying reptiles” that one typically knows about from the Mesozoic Era. They had pycnofibres - small filaments similar to hair, potentially the same as protofeathers; and flew using membraneous wings that stretched across an extended finger. Includes Dimorphodon, Pteranodon, Pterodactylus (”pterodactyl”), and Ornithocheirus. 

Dinosauria (Blue): Megalosaurus + Iguanodon, MRCA & descendants. All dinosaurs. Note that this does not include many of the animals listed above! Dinosaurs are a very specific group of animals that all, typically, were able to walk with the limbs directly beneath the body. Protofeathers were also an ancestral trait for this group, though many dinosaurs secondarily lost them - the same proteins that make protofeathers were turned into scales. Includes Brontosaurus (yes, it’s a thing again, there was a study this year), Stegosaurus, Triceratops, Tyrannosaurus, Allosaurus, Velociraptor, Brachiosaurus, Troodon, Parasaurolophus, Ankylosaurus, Pachycephalosaurus, Archaeopteryx, the Dodo, Bald Eagles, Emus, Cassowaries, Chickens, Ducks, Finches, Parrots, Robins, Crows, Geese, Blue Jays, Penguins, Auks, Seagulls… 

Avialae (Light Blue): All dinosaurs more closely related to modern birds than to Troodon. This is typically the group I mean when I say “birds,” though the clade that includes only modern birds is called Neornithes - all non-Neornithes Avialaens are extinct. Many basal Avialae, furthermore, are almost indistinguishable from their closest dinosaurian relatives, the troodontids. It is uncertain whether the earliest Avialaens (such as Archaeopteryx) could properly fly. Includes Archaeopteryx, Confuciusornis, Hesperornis, the Dodo, Bald eagles Emus, Cassowaries, Chickens, Ducks, Finches, Parrots, Robins, Crows, Geese, Blue Jays, Penguins, Auks, Seagulls… essentially, all birds. 

I hope that was helpful!

coronalthoughtejection  asked:

In response to your recent post about what is a dinosaur and what isn't, how do you tell the difference? This is something that's always perplexed me.

The problem with a word like “dinosaur” is that it’s really not very precise or descriptive. Scientists use much more precise terms when classifying and describing the species and groups under the general term “dinosaur” but most people just point at anything reptilian that lived a long time ago and call it a dinosaur.

Technically, a dinosaur is any land-dwelling diapsid descendant of archosaurs. But those are strange and confusing words that don’t exactly roll off the tongue or mean anything obvious. 

Fear not! I’ve assembled some awesome videos from The Brain Scoop and SciShow to help you learn the difference. Check ‘em out below: