u/Technical_Valuable2

Art by literally miguel,connor ashbridge,gabriel ugueto,dibgd and dinosaur a day

the vaca muerta is a formation in argentina dated to 150-140 million years ago and it is noted for a diverse marine fauna.

the largest predator is a pliosaur referred to as Liopleurodon sp. It was big, a 2026 paper estimated it as 11 m long with a 2.1 m skull.

pliosaurus lived here but the patagonian species was notably smaller.

dakosaurus was a 5m croc relative with steak knife like teeth and one of the top predators of the formation.

cricosaurus was a smaller croc relative at only 2m in length and likely a piscivore.

the giant filter feeding leedsicthys is reported from vaca muerta.

various icthyosaurs like caypullisaurus and catutosaurus have been reported from vaca muerta.

art by cesar diaz

ive seen estimates for them vary all over the place and i just wanted clarity? this picture alone had a previous version where its size was only 9m,now its been updated and its nearly 11 m,

Art by gabriel ugueto,pedro andrade,corallianasa,dan folkes

when it comes to giants of the late jurassic, the morrison formation is indisputedly the king. So many giant dinosaurs come from there. Often understimated in the capacity to provide giants is the lourinha formation of portugal.

this formation has many overlapping dinosaurs with morrison but their often not held in the same idea of size as those from the morrison.

although definitely more fragmentary,there is still evidence of giants from portugal.

torvosaurus from portugal is already estimated at 10 meters in length and 4 tonnes. The north american torvosaurus is 11m plus if the edmarka remains are included.

in 2010 octavio mateus described a footprint 80 cm long by 60 cm wide. He referred it to torvosaurus because its the only theropod large enough to have left it. a torvosaurus that left this track might have been around 11-12m in length.

from the same site that produced the cf.torvosaurus track, a giant sauropod foot print 105 cm long has been found. Only diplodocids and brachiosaurids were big enough to have left that print. Its morphology is more consistent with diplodocids because the track is longer than it is long. Brachiosaur pes were much more broad and circular as to support their greater weight. Dinheirosaurus was found at the same site and if this footprint belongs to it could indicate a size similar to its supersaurus relative back in the states. Other large diplodocid remains include a partial femur according to pedro andrade and according to the SHN of torres vedra (whove given me permission to share this info) A 30 m animal is known from the blue beach locality,with 2.2 m long ribs.

new remains from pombal are belived to come from lusotitan and indicate an animal of 25 meters in length. first described in a 2023 abstract and in another in 2025. The authors have stated in outside sources that the remains come from lusotitan.

A giant footprint 70cm in length belonged to a camptosaurus like animal,but huge. It was possibly 9m in length.

Dacentrurus is 9m long and is known from the lourinha formation.

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https://observador.pt/2014/05/20/sociedade-de-historia-natural-tenta-salvar-sauropode-ameacado-pelo-mar/

https://www.scup.com/doi/10.1111/j.1502-3931.2009.00190.x

https://doi.org/10.3390%2Fd17010029

https://www.researchgate.net/publication/373273025_The_giant_sauropod_dinosaurs_of_Pombal_new_discoveries

https://www.youtube.com/watch?v=s6QNyQVKu7Y

https://vertpaleo.org/wp-content/uploads/2025/12/2025_SVP_Program_Final_Final.pdf

art by literally migeul and the byu

i mean razana is the oldest known notosuchian and utahraptor is the oldest dromaeosaur known from definitive remains. Despite this they are already derived.

Mastodonsaurus

prionosuchus

beast of lesotho

art by smokeybjb and slate weaserl

this is the fauna of the phosphoria sea,based off the meade peak member of the phosphoria formation.

helicoprion is one of the most iconic permian fish. A bizarre shark like fish with a buzzsaw for teeth.

the meade peak of the phosphoria formation is the richest source of their fossils. this is about the animals of this member.

helicoprion is the apex predator. Its at least the size of a great white but possibly much bigger. We only have the whorls and partial bits of the jaw cartilage. It had several hundred pounds of force concentrated along the saw. it likely sawed through cephalopods and smaller cartilaginous fish.

kaibabvenator is a large 6 m ctenacanth. It had serrated teeth and was likely designed to hunt big game. Originally known from the kaibab formation, in 2025 teeth from across phosphoria were realized to be similar to kaibabvenator and thus considered potential material. Kaibab formation is also chronologically correlated with phosphoria based off conodonts. Thus these teeth indicate that this apex predator lived in the same seas as helicoprion.

glikmanius is a smaller ctenacanth. At just 2-3 m in length, it was likely a mid level predator. its teeth were pointed,likely used to grasp prey.

cochliodontiforms are known phosphoria and would likely have been durophagous and of decent size.

janassa was a 1m long fish that vaguely resembled rays.

deltodus is a 1m cartilaginous fish thought to have been durophagous.

im starting a series called old chalk chronicles. Here i will travel to various ecosystems across the early cretaceous and talk about them.

the first one is the himes member of the cloverly formation. This is such a nostalgic formation for me, i have such fond memories of it.

It took place in montana and wyoming around 109 million years ago.

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Theropods

Acrocanthosaurus is the most distinct, at 12 m long and 7 tonnes in weight it is one of the largest theropods ever. It killed with a flesh tearing bite. it had a 1.3 metre long head and knife like teeth. it would have been the apex predator of the formation.

deinonychus is the eponymous terrible claw. 3m long,1m tall and 75kg it was mesopredator. it primarily hunted small plant eating dinosaurs in its enviroment. its sickle claw is the origin of its name.

microvenator is caenagnathid,distant relatives of oviraptor. it was likely a beaked herbivore possibly possessing a crest. it would have been 3m as an adult.

ostrom described ornithomimids in the 1970s as coming from the cloverly formation. However they more likely represent basal ornithomimosaurs,a la arkansaurus.

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Ornithschians

tenontosaurus was the most common herbivore. at 6m and 1 tonne it would have been the zebra of its enviroment so to speak. it likely lived in herds and had distinctive broad,tall and stiffened tail.

zephyrosaurus was relative of thescelosaurus. it was 2m,herbivorous and possibly lived in burrows.

sauropelta was 6m long and 2 tonnes. this ankylosaurian had huge shoulder spikes, a formidable defence. the name literally means shield lizard.

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Sauropods

sauroposeidon is the king of kings amongst early cretaceous north american sauropods. At 30m and 40-50 tonnes it was one of the largest dinosaurs to roam the north american continent. its thought to be a close relative of titanosaurs.

rugocaudia is small titanosauriform. It was only 10m long and is considered potentially dubious due to poor material.

Moderators, I deleted and reposted in order to provide a post body with better sources and because someone in the comments spread hella misinformation.

This is my ranked list of the largest extinct cats in prehistory

The minimum benchmark of size is they have to be consistently estimated at above 300kg. That is the maximum weight of the largest living cat, the Siberian tiger, so that is our benchmark. So cats whose max estimates are either just at or below 300 kg are not to be included. Animals whose mass is based on more fragmentary remains will have points deducted for that. The ngandong tiger and natodemri lion are extinct examples of extant cats,so that would add confusion. Complete skulls and longbones provide good mass estimates.

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#1: 3-way tie between panthera atrox, Panthera spelaea fossilis and smilodon populator

These 3 are tied for number one spot. All 3 are consistently estimated at between 400-500kg in weight. Scientists havent exactly coalesced around a single given weight in that range in all 3 taxa,they are all consistently estimated at being within that range however. They are also known from complete remains to provide certainty. 

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Link <provides longbone analysis to justify 400-500kg estimate for p atrox

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#2:Adeilosmilus kabir

2nd place goes to Adeilosmilus kabir. This is a large homotherine from the late miocene of Africa.

It's estimated at 350-490kg. With that range you might argue it belongs in the top spot. Unfortunately its estimates are based off fragments of longbones instead of complete ones. For this reason i had to deduct points. So it could only be put in second place

  
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#3: Nimravides catocopsis

Originally the material was assigned to machairodus but it was reassigned to Nimravides.

The largest estimate is 427kg and it comes from a complete long bone. I put it behind the kabir because the upper range of the kabir outsized it. But it was almost tempting to put it above kabir since it had better material to justify that massive size.

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#4:Amphimachairodus horriblis

Number 4 spot goes to amphimachairodus horriblis. Its estimated at 405 kg in weight and is extrapolated from a complete skull.

Because it had good extrapolative material and still came out below nimravides it only gets 4 th place.

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#5: the uruguayan xenosmilus?

Number 5 spot goes to the possible specimen of xenosmilus from uruguay. Its size is estimated at 350-410kg. Unfortunately its based off a small dentary fragment so its kind of crap.

Link

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#6: xenosmilus hodsonae

Number 6 spot goes to xenosmilus from north america. Actually known from good material,its estimated at 300-350 kg in weight. 

It was similar in height and length dimensions to smilodon fatalis and homotherium at 1 m tall and nearly 2m long, but was much more robust,even more so than smilodon. Thus much heavier,

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gabriel ugueto

https://www.sciencedirect.com/science/article/abs/pii/S0277379122001482

so ive seen people mention this article and state its phylogenetics indicate xenosmilus is a synonym of homotherium.

however ive read the paper and looked at the cladogram and it appears to show xenosmilus as branching off of homotherium and nowhere in the paper does it state that xenosmilus is a synonym of homotherium. by the working it still appears to consider it distinct.

so im confused.

this is a list of the largest prehistoric cats ever.

in order to count on the list,the prehistoric cat must be consistently estimated at greater than 300 kg in weight. the Siberian tiger is the largest living cat and 300 kg is its largest weight. thus that is the benchmark ive set. it has to be consitently estimated to exceed 300 kg in weight, so contenders like smilodon fatalis and amphimachairodus giganteus are excluded,they either max out at 300 kg or tickle it.

animals like the ngandong tiger,natodemri lion are exlcuded since im focusing on extinct cats and extinct subspecies of extant cats add extra confusion,plus some studies estimate them as being too small. the panthera spelaea is exlcuded because the largest specimens are possibly confused with p fossilis and it showed massive size reduction as the ice age went on.

estimates derived from complete skull and longbones will be ranked higher than estimates from more incomplete material,since they are good extrapolative material.

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Number 1

its a 3 way tie between Panthera atrox,smilodon populator and panthera fossilis

all 3 are consitently estimated to be between 400-500 kg. Smilodon populator and Panthera atrox are known from abundant material and so their estimates are relatively sound. Panthera fossilis's estimates are from skulls so its less certain but still decent.

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Number 2

number is amphimachairodus kabir.

its estimated at 350-490 kg. however this is based off fragmentary longbone material.

i was tempted to put catocopsis in its place because its maximum specimen comes from a more complete longbone. but the average range of kabirs size estimates are greater than of catocopsis so i put it before catocopsis.

however although its range of size strongly overlaps with the big 3,its fragmentary nature costs it points,thus it gets second place.

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Number 3

nimravides catocopsis

it was originally referred to machairodus layahishpup,but was reassigned to nimravides.

the maximum estimate of 427 kg comes from a complete humerus and im more confident in that size than i am with kabir. However its material is only marginally less sloppy.

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Number 4

amphimachairodus horriblis

the size comes from a complete 16 inch skull,providing a mass estimate of 405 kg.

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number 5

the uruguayan xenosmilus,the raigon formation homotherine

just like kabir has a wide ranging estimate based off sloppy material,in this case however the material is fragmentary lower jaw and the estimates are based off teeth.

this is costs its point on the ranking. horriblis has better material and number 5 only exceeds by 5 kg at max. but because of the crap material i can only put it at number 5.

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number 6

proper north american xenosmilus hodsonae

FINALLY! an animal known from decent material! hodsonaes 2 type specimens cover most of the body.

its estimated to be similar to smilodon fatalis and homotherium in height and length,1m at the shoulder and nearly 2m in length. An s fatalis at those dimensions is 300 kg in weight and homotherium would 250 kg in weight

however it was more robustly built,even than smilodon,according to its description paper.

a 2019 study estimated it at 300-350 kg and the 2024 of the uruguayan xeno provided a long bone estimate of 330 kg for X hodsonae.

because of its complete nature and the fact the largest estimates come from long bone analysis, i think it can be confidently estimated at this weight.

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https://www.sciencedirect.com/science/article/abs/pii/S089598112400453X

https://www.researchgate.net/publication/309409331

https://doi.org/10.1016%2Fj.crpv.2004.10.002

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

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

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

https://link.springer.com/article/10.1007/s10914-021-09540-1

art by literally miguel,armin reindl,artbyjrc,and nix illustrations.

my definition of supercroc is as follows: a crocodylomorph whos size estimates approach or exceed 6 meters in length. approaching 6 meters i define as being a croc estimated at 5.5 - 6 m. If it is estimated to that size then i will include it in this category.

I will being doing a series called cenozoic super crocs. As i stated,any crocs whos size approaches the benchmark i set will be counted as a supercroc and included.

the first continent i am covering will be south america,others are upcoming.

south america appears to have been an absolute hotspot of giant crocodylomorphs in the cenozoic,miocene in particular.

lets get into it.

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Anthracosuchus

this is a dyrosaur from the cerrejon formation,a coexistent to titanoboa.

Its description paper estimated its length at 5m based off the largest skull a 68 cm long one. However they used the simplified head to body length ratios of sereno et al instead of more rigorous estimates to estimate its length.

its skull is extremely broad and short for its body length. Its skull length and width (68 cm long by 40-45 cm long) is similar to or exceeds large crocodilians alive today, so it seems reasonable it approached the super croc benchmark.

it was a durophagous predator,likely using its broad strong skull to crack open turtle shells.

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Acherontisuchus

this is a dyrosaur from the cerrejon formation as well. its skull is 86 cm long and it to was estimated at 6.5 m long.

however since it was estimated to that size based off serenos equations,it should be treated with caution.

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Barinasuchus

a giant sebecid that lived in northern south america from 17-12 million years ago, this would have been the apex predator of its ecosystem.

it would have been a terrestrial predator,using its serrated to butcher big game animals. its size is best estimated at up to 5-6m in length.

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purussaurus

this giant caiman comes from across northern south america and live in the miocene from 16-5 million years ago. every species reaches super croc threshold.

p neivensis was 6.5-9 meters in length based off multiple studies.

p braziliensis,based off supplementary material from that 2025 study about deinosuchus, was 10-12 m in length.

p mirandai based off the same aforementioned sup data would be 8-12 meters in length.

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Mourasuchus

a big flatheaded caiman that lived in northern south america around the same time as purussaurus.

based off the 2025 study on deinosuchus, the largest species m amazonensis approaches 8m in length.

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Gryposuchus

this is a giant relative of gharials. It lived alongside purussaurus and mourasuchus.

g colombianus is estimated at 8m in length while g croatzi is estimated at 10m in length.

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Piscogavialis

is large relative of gharials,known from the pisco formation of peru. interestingly it coexisted alongside megalodon.

its been estimated at 6.5-8m in length.

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Paranacaiman

it was described from the late miocene ituzaingo formation of argentina.

based off a 70cm skull according to armin reindl,it was likely around 6m in length.

WARNING-post is a long read,dont read if you dont like a word mountain.

This is a comprehensive list of large animals lliving in Florida during the late blancan land mammal age,more specifically the late Late blancan which is styled as the bl3 substage. The specific time would be 2 million years ago,medianed from a span of 2.2 - 1.8 Million years ago. This is simplified and will include simplified stats. This is meant to provide a comprehensive list of animals living in Florida 2 million years ago.

Art by thalassoatrox and hodari nundu

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Titanis Walleri- 2 m tall and 200 kg in weight

Giant flightless Bird 

Carnivore,apex predator. macrophage = prefers large prey. Has a large hooked beak and sickle clawed feet. Killing through blood loss inflicted by meat tearing bite. Sociality is likely solitary

Preferred habitat is woodland.

Bl3 localities are Inglis 1a.

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Xenosmilus hodsonae- 1m tall and 300 kg in

Large sabre toothed cat of the homotherine tribe,sociality uncertain

Carnivore, apex predator. Macrophage

Of robust build. Possesses thumb like dew claws and all teeth in mouth are serrated. Thought to have killed with a shearing bite. Likely preferred forested habitat

Bl3 localities are inglis 1a and haile 7g.

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Edwards wolf(classification disputed between aenocyon and canis)- 30-50 kg in weight, 50 cm shoulder height minimum

apex predator,macrophage. Pack hunter

Stated to be similar in size to a modern day red wolf. Isotope analysis and carnassial characteristics indicate it is a pack hunter.

Bl3 localities include inglis 1a

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Smilodon gracilis- 100 kg in weight,<1m height at shoulder

Carnivore, apex predator,macrophage. Sociality is uncertain

Smallest species of smilodon. Thought to be ancestral to the larger later species s. Populator and s. Fatalis. Isotopic analysis indicates llamas,peccaries and deer make up its diet. Dietary overlap with the Edwards wolf is indicated by isotopes.

Bl3 localities include inglis 1a and waccasa river 9a

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Chasmaporthetes ossifragus- ~~50-75 kg~~ in weight,~1m~ at shoulder. 

Carnivore,apex predator,macrophage. Likely a social hunter in clans.

A moderately large species of hyena,the only known american hyena. Stated to be social by Anton et al 2006. Likely lived in open habitat.

Bl3 occurrences include inglis 1a.

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Miracinonyx inexpectatus- 75 kg in weight,~1m in height~

Carnivore,apex predator,solitary.

Often erroneously called a cheetah,closely related to pumas. Likely lived in an open habitat.

Bl3 occurence includes inglis 1a.

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Arctodus pristinus- 500kg,1m> in height

Opportunistic omnivore

A large bear,similar in size to a grizzly. Smaller ancestor of the larger arctodus simus.

Bl3 occurrences include inglis 1a.

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**Alligator hailensis-**4.5-6m in length(based off extrapolated skull length of 70 cm),500-1000kg

Carnivore,apex predator,semi aquatic ambush hunter

Considered ancestral to the modern day american alligator. Largest reptile in florida at the time.

Bl3 occurrences are haile 7g and 7c

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Equus leidyi- 130-160cm in height ( metapodials roughly 27 cm in length  source ,   height extrapolated using kiesewalters method),300-600kg in weight

Herbivore,likely grazer

Enigmatic equine horse. Known primarily from teeth and metapodial elements. 

Bl3 occurrence includes inglis 1a

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Nannipus peninsulatus- 1m tall,100 kg in weight

Herbivore,browser as indicated by teeth and isotopes

Last of the 3 hoove hipparion-esque horses. Thought to be a forest dwelling browser.

Bl3 occurrence is FLORIDA SHELL AND FILL in the callosahatchie river.

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Eremotherium eomigrans- 5 tonnes in weight,6m long

Herbivore, high browser

Gigantic ground sloth,ranked as among the largest of all time. Possibly hairless due to heat issues and size.

Bl3 occurrences include haile 7c and 7g,inglis 1a

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Megalonyx leptostomus- 500 kg? Stated to be half the size of the later species m.jeffersoni

Herbivore,mid browser

Decently large ground sloth,smaller relative and ancestor of later species.

Bl3 occurrences include inglis 1a and caloosahatchie river

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Paramylodon harlani- 1000kg in weight

Herbivore,grazer

A large grazing ground sloth. Specimens from later in the pleistocene show a size increase.

Bl3 occurrences include inglis 1a

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Holmesina floridanus- 100 kg in weight

Herbivore,generalist

Large armadillo. Possessed segmented armor.

Bl3 occurrences include inglis 1a, haile 7g and 7c

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Glyptotherium texanum- 500 kg in weight

Herbivore,grazer

A large glyptodont armadillo. Possessed inflexible shell.

Bl3 occurrences include inglis 1a and haile 7c and 7g

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Tapirus lundeliusi- 200 kg in weight

Herbivore,preference uncertain

Mid sized tapir species.likely preferred forest.

Bl3 occurrences include inglis 1a and haile 7g

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**Hemiauchenia gracilis-**100-200kg in weight

Herbivore,mixed browser and grazer

Mid sized species of hemiauchenia, an american llama.

Bl3 occurrences include inglis 1a.

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**Platygonus bicalcaratus-**30 kg

Herbivore,grazer

A grazing peccarie,a pig like animal.

Bl3 occurrences include inglis 1a

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Phugatherium or neochoerus dichroplax or aesopi? Species uncertain- 50-100kg

Herbivore,mixed browser and grazer

A large capybara,a herbivorous rodents. Likely would have lived near water.

Occurrences in bl3 include inglis 1a and haile 7g and c.

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Mammut americanum- 3m tall,8 tonnes

Herbivore,browser

A large mastodon. A forest dweller or denizen of woodland.

Bl3 occurrences include inglis 1a

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Additionally modern day white tailed deer have been found in localities like inglis 1a or haile 7g or 7c.

SOURCES

VP collection database

PBDB navigator

 florida museum website 

wikipedia pages of respective creatures

sources are comprehensive databases and further sources were obtained by searching those databases.

Credit to the florida museum of natural history for the skeleton picture

Xenosmilus is one of the most unique saber tooth cats ever found. It lived in a dangerous and competitive early ice age world. 

Originally found in Florida,other potential remains have since been found in Arizona,Venezuela and Uruguay;Spanning a period of time from 2.5 million to 1 million years ago.

When it was first described it shook up the orthodoxy of sabertooth cat morphology. Originally homotherine cats were thought to be long legged and lightly built while smilodonts were thought to be heavily built and short legged. Xenosmilus was a homotherine but robustly built,showing a greater diversity amongst the scimitar tooth cat morphology.

It had 4 inch long canines and all the teeth in its mouth were serrated. It was 300kg in weight and 1m tall at the shoulder. It also lacked a gap between incisors and canines,which formed a continuous cutting edge in its mouth. It had an aforementioned robust build and its dewclaws were fashioned almost like thumbs,giving it an excellent grip. Based on its robust build,it likely preferred closed habitats like forest.

It would have eaten whatever megafauna it could have hunted,with peccaries having been found in the holotype site. Its method of dispatching prey would have been some kind of flesh tearing bite. It coexisted with many other animals. One of its most interesting neighbours was Titanis the terror bird. How they coexisted and partitioned would be an interesting subject.

Additional remains from Arizona,Uruguay and Venezuela have been referred to the genus of xenosmilus.  The arizona material is tentatively referred to as ‘’xenosmilus sp.’’. The uruguayan materials classification has gone back and forth in classification,the most recent analysis by manzuetti and colleagues support its attribution to xenosmilus. The venezuelan material was originally referred to as homotherium but more analysis suggests it is a smaller venezuelan species of xenosmilus.

There's been a lot of misconceptions and misinformation in regards to xenosmilus size. 

The first is some overestimates. Some sources have suggested the original floridian material is similar in size to Smilodon populator or amphimachairodus kabir,both some of the largest cats ever. This isn't right because the skull of the original floridian xenosmilus is only about 13 inches in length,compared to the15-16 inch skulls of S.populator or the similarly giant 16 inch skull of M. Horriblis. This is more similar in size to Amphimachairodus giganteus which has a 14 inch skull ( the 1 inch difference is because Xenosmilus has a proportionately shorter snout while conversely A.giganteus is more elongated in snout proportions). The most recent 400 kg estimates come from Manzuetti et al analyzing the Uruguayan material. But the uncertain referral of the material to xenosmilus combined with its fragmentary nature,means this estimate needs to be cautioned. There was also an estimate giving the holotype material a weight of only 120 kg. This is ludicrous because the type material of Xenosmilus is similar in dimension to A. giganteus,such as possessing 4 inch long canine teeth,similar in size to homotheriums sabers. The study in question wasnt a detailed analysis of xenosmilus specifically but it was talking about nasal apertures of cats,the size estimate was only a fleeting mention.

Another is the notion that xenosmilus was somehow much smaller in the earlier blancan stage (when it coexisted with titanis) than the later irvingtonian stage(the quarry that produced the type specimens of xenosmilus is irvingtonian). This notion is problematic. For one, no piece of peer reviewed literature or source from a paleontologist states that it was smaller,it appears to just be observation from paleonerds. Second is the sample size of Irvingtonian xenosmilus is too small to even make the assertion. Based on the VP collection database from the florida museum of natural history,most of the xenosmilus specimens are from the blancan and the xenosmilus thare being compared to the blancan xeno are the 2 type specimens. For one that's only 2 individuals and second both of them are large individuals. Not only is this too small of a sample size to compare the blancan specimens too but both the individuals are large,so the size results would be skewed. Plus other xenosmilus from irvingtonian quarries are just as small as blancan xenosmilus

Using the aforementioned VP collection database,there are large xenosmilus specimens from the blancan. One is a canine from the inglis 1a quarry. It  is partial,its missing part of the top and the tip is worn down. Nonetheless the canine as preserved is 3.5 inches in length. In life without the damage it would have probably been 4 inches in length. This is similar in length to the canine measurements of the type specimens and to homotherium. Sure most blancan specimens aren't as big as the type specimens but that's just nature? Most animals won't reach the maximum size of their genus. 

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i love walking with monsters! one of the retrospective criticisms of their dimetrodon is the sprawling lizard like gait they gave it,even more perplexing because they gave edaphosaurus a proper gait.

in this shot of dimetrodon just before the evolution transition,you can see it has the proper more erected gait.

art by hodari nundu and olmagon

the most popular image of terror birds has to be them using that hooktip of the beak to bludgeon prey to death like a pick ax. its just the popular image of it and has been so for a long time.

however,ive always considered this method of killing fanciful and ridiculous. im sure it could do it effectively on small prey but pickaxing horse or deer sized prey is where i draw the line. let me explain why i think its a dumb theory.

first things first biomechanics of terror birds heads and neck shows their heads and necks were great at downward thrusts and pullbacks,but bad at resisting lateral movements. it wouldnt have shaken its head from side to side. this had been interpeted multiple ways. the ''borden beak hypothesis'' where it killed the prey with axe like strikes. the ''blade beak hypothesis'' where the hooktip is used to slash the prey. and the ''butcher beak hypothesis'' where it thrusted its beak into the flank of prey with its neck muscles,clamped down and then rapidly pulling its neck back, cleaving a huge chunk of flesh off.

lemme tear apart the borden beak hypothesis.

for one, its not a practical implement against larger prey. the hooktip would probably have been a couple inches long,similar in size to the canines of lions or tigers. lions and tiger have several canines in their mouth. a lion can bite a zebra in the hide multilple times and even bite the throat and the zebra can walk away and survive. Large mammals have thick hides and muscles,forming almost like biological gambison. this can temper the damage done by small piercing implements. Point is even a lions canines arent enough to quickly kill or even fatally wound a horse or deer sized animal,so i dont know why terror bird hook tips are any different.

in order to bring prey down quickly,the hooktip would have to be directed at the neck arteries,spinal cord or head. For one these are relatively small targets that are difficult to hit and would have a high margin of error. A horse has thick neck muscles and hide and once again, a lion can bite a zebra neck with hundreds of pounds of force and the zebra can still walk it off because the canines arent enough. The spinal cord and skull protect their respective vulnerable organs and a terror bird risks breaking its hooktip by hitting the bones. in the case of the terror birds the loss of the hooktip could mean starvation. they need the hooktip to help wound and kill prey and process kills. if broken they would be restricted to eating smaller prey they could swallow whole,which wouldnt be efficient for long. and even if bone grows back it often grows back irregularly,which could make the hooktip worthless.

the attacks would rarely have been instantly fatal and all that would happen is youd have a pissed off horse or prey animal that could then fight back.

a more likely mode of attack is using that beak like a meat shearer. the hooktip and curvature of the beak would allow to puncture and clamp down on a large chunk of flesh. the beak would have been covered by keratin that would have formed a protective sheath and additionaly would have made the beak edges sharp like a blade. It would use its excellent vision to lock on to a vulnerable part of the body(flank,caudo fem or rear) drive its beak into the flesh with its neck muscles,clamp down and then pull its head back. this would rip off a huge chunk of flesh and fatally wound the prey.