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Eurwentala's avatar

Diversity of the Crurotarsi

Some examples of the diversity of the crocodile-line archosaurs or Crurotarsi. This group was very common and diverse in the Triassic, and only a bit less so in the Jurassic and Cretaceous. Many of them were highly specialized and seem to have been active, possibly even warm-blooded animals. The group has many interesting examples of convergent evolution with dinosaurs and other groups. Now only the modern crocodiles remain.

In this picture, from top to bottom:
Saltwater Crocodile, Crocodylus porosus. The largest modern species of crocodile. An opportunistic predator that can eat anything from water buffalo to sharks.
Yacarerari. Belongs to the Cretaceous group Notosuchia. It was a cat-sized animal with very unusual mammal-like teeth.
Metriorhynchus. Member of the completely aquatic group Thalattosuchia. It had a tail fin and it's limbs were modified into flippers. It might have been viviparous, since it's body plan sure doesn't look suitable for laying eggs on dry land. Thalattosuchians are strongly convergent with ichthyosaurs and dolphins.
Terrestrisuchus. A small, obviously cursorian Sphenosuchian that could have weighed around 15 kg. It might be a juvenile specimen of Saltoposuchus.
Postosuchus. A member of Rauisuchia. It might have been partly or completely bipedal, since it's front limbs are small and weak. It was a large predator that had very similar head and teeth as the tyrannosaurid dinosaurs.
Effigia. Another dinosaur-like rauisuchian. It was a fast-running, bipedal animal very similar to ornithomimosaurs (the ostrich-mimic dinosaurs). It even had a toothless beak.
Desmatosuchus. A triassic aetosaur with very impressive armour. It was a herbivore with a surprisingly pig-like head.
Rutiodon. A crocodile-like phytosaur. Despite their appearance, phytosaurs were not closely related to the modern crocodiles. They seem to be another example of convergent evolution.
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CartoonBen's avatar
Magnifying Glass I just love how unique and diverse the animals of the group, Crurotarsi have been since they first evolved. :study: They are so fascinating and LOTS OF FUN to learn about (as are other animals and other living organisms that have existed on our planet, both living and extinct).
Crurotarsi deserves more respect.
Between theropods and crutotarsans, synapsids never reclaimed earth after the Great Dying.
KyuremBlack646's avatar

And some crutotarsans became land-living predators once again.

joeabuy1000's avatar
This is discounting the purported abundance of Lystrosaurus in the early Triassic (which might or might not count because they're, like, one genus) or the takeover of the mammals as the predominant group of large land animals during the Cenozoic, aight?
KyuremBlack646's avatar

Lystrosaurus's abundance only lasted for about 1 million years in the Early Triassic, and only 5 as a whole.

Mammals had to share in the Cenozoic with avian theropods and other diapsids. 
joeabuy1000's avatar
The crutotarsans had to share the ocean with the ichthyosaurs, plesiosaurs, mosasaurs, and sharks. When the mammals came to the sea, they only ever had to deal with the sharks.

Though to be fair, when the synapsids had Earth to themselves in the late permian, they did have to share with the Temnospondyls for some time before that, and well into that, the oceans still belonged to the trilobites.

If you think about it, though, can we really say any of those groups were truly dominant in terms of diversity? Insects still outnumber us today, and there's little reason to assume that they didn't outnumber those guys in the past.
Yeah my sheer diversity and biomass arthropods crush everything.
Postosuchus and Desmatosuchus are basically just Godzilla and Angilas, really. Or the other way around, I suppose.
grisador's avatar
Crocodylmorpha is The best & most successfull group of animals.
They even rivaling The sharks & cockroach'es at evolution, survival and Life
HUBLERDON's avatar
No prisitichampsus?
Crurotarsi are fascinating. It's a shame the stem-crocodile branch of the Archosaur family tree is so obscure in pop culture, compared to the stem-bird lineage - imagine how much little kids would love to play with toy versions of these creatures! Or the way crurotarsan forms could be added into the potpourri of fantasy dragon designs.
And add the stomatosuchines......
FejesValentin's avatar
How about Simosuchus?
Helixdude's avatar
I remember watching "Walking with Dinosaurs(The original series, not that abomination with the Pachyrhinosaurus) and how they portrayed Postosuchus as completely quadrupedal, good thing science marches on as i prefer it being at least partially bipedal. 
Eurwentala's avatar
I still haven't quite figured out how they make sense as bipeds, but apparently they have to. :)
Jdailey1991's avatar
I don't get where they got the idea of someone as heavy as Postosuchus to be bipedal in the first place.
Eurwentala's avatar
Well, things like Tyrannosaurus or Allosaurus are quite a bit heavier and obviously bipedal. It's not the size, but the proportions that make it look odd and unlikely. But if you take an actual look at the forelimbs, they are ridiculously tiny and slender, and fairly easily give the idea of a biped (see the discussion here: phenomena.nationalgeographic.c… ).

Postosuchus doesn't really make much sense on any number of legs, but personally I'd favour the facultative biped hypothesis. On all fours when standing or moving slowly, on hind legs when running, or something like that.

Besides, it wouldn't be the only oddly unbalanced biped. Have you seen videos of pangolins walking?… They're not exactly small animals either, with the giant pangolin weighing at least 33 kg.
The-Episiarch's avatar
Nice! The Crurotarsi certainly get overlooked by most and end up in the shadow of the dinosaurs (even though they are very interesting in their own right). Ironically enough, some of those bipedal rauisuchians rather resemble the scaly theropods many people (who haven't come to terms with feathered dinosaurs) still think of when they think "dinosaurs". My fondness for these reptiles can be seen this piece here…
Which features a few of the genera you have illustrated above (though my piece is a rather off-beat take on those reptiles).
Heytomemeimhome's avatar
Ah if only anatosuchus and other notosuchians were here
Eurwentala's avatar
Yeah, I should make an updated version about this. :)
FancyKarp's avatar
Yacarerani, I feel so proud about one of the national languages of my country gave a name to a prehistoric creature! :D
HellraptorStudios's avatar
Hard to belive that some of them are classed as crocodiles even though they didnt look like that. Very nice comparison pictue.
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