#effigia

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Pseudosuchians, or "croc-line archosaurs", are one of the two major lineages of archosaur reptiles, alongside the avemetatarsalians (pterosaurs and dinosaurs). Although today they're represented only by crocodilians, they were especially successful and diverse back in the Triassic – and it was only after a mass extinction took out most of them that the dinosaurs were able to rise to prominence for the rest of the Mesozoic Era.

A grouping of pseudosuchians traditionally known as "rauisuchians" had upright limbs in a distinctive "pillar-erect" hip arrangement. Many of these croc-relatives were large quadrupedal predators, but others developed bipedal theropod-like postures, with some so remarkably convergent that they were initially misidentified as ornithomimosaurs.

The first rauisuchians were discovered in the 1930s, represented only by fragmentary remains, and while they were initially recognized as being pseudosuchians their exact evolutionary relationships within that group were poorly understood for a long time. Over the next several decades they were classified with aetosaurs (early armored pseudosuchians), then ornithosuchids (even earlier pseudosuchians), and then erythrosuchids (not even pseudosuchians but an earlier type of archosauriform).

More complete fossil discoveries and better cladistic analysis methods in the 1980s led to them being classified as being very closely related to crocodylomorphs, with three main lineages recognized: the prestosuchids, the rauisuchids, and the poposauroids.

The "prestosuchid" Prestosuchus chiniquensis, the rauisuchid Postosuchus kirkpatricki, & the poposauroid Effigia okeeffeae (not to scale)

But even by the end of the 20th century "Rauisuchia" had never actually gotten a formal definition, and it had very much become a wastebasket taxon for a variety of paracrocodylomorph pseudosuchians that didn't easily fit into any other major lineages.

In the 2000s renewed interest in rauisuchians' anatomy and evolutionary relationships led to increasing recognition that they weren't even a single defined group, with various species instead falling into different points along an "evolutionary grade". The poposauroids and rauisuchids still seem to be distinct lineages, but the "prestosuchids" were found to be polyphyletic, with some forming a grade between the other two "rauisuchid" groups and others turning out to not even be paracrocodylomorphs.

And although the taxonomic concept of "Rauisuchia" as a distinct group has now been abandoned, the term "rauisuchians" does still remain in common use as an informal name for these animals – probably because it's much more concise than saying "non-crocodylomorph paracrocodylomorphs".

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By Stolpergeist 

Etymology: Ghost

First Described By: Nesbitt and Norell, 2006

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Disapsida, Neodiapsida, Sauria, Archosauromorpha, Crocopoda, Archosauriformes, Eucrocopoda, Archosauria, Pseudosuchia, Suchia, Paracrocodylomorpha, Poposauroidea, Shuvosauridae

Referred Species: E. okeeffeae

Status: Extinct

Time and Place: Around 205 million years ago, in the Rhaetian of the Late Triassic 

Effigia was found at Ghost Ranch in the Chinle Formation in New Mexico 

Physical Description: Effigia was a small, bipedal animal that remarkably resembled dinosaurs it lived with at the time. In total, from head to tail, it would have been about two meters long. It walked on two legs that were held directly underneath the body, and it had small arms that weren’t used in supporting its weight. It had a long body, with a decently sized tail and long neck. The head of Effigia was small and narrow, ending in a beak and having no teeth whatsoever. So, in short, it looked like the later Limusaurus, except it wasn’t feathered - and it wasn’t a dinosaur! This is the first known example of the lightly-built bipedal animal with a beak body plan, aka, the “ostrich” body plan, even though this iteration - the first iteration - had nothing resembling feathers or efficient breathing or hollow bones. In fact, it probably would have breathed primarily based on abdominal muscles, based on its close relatives. And it did have hollow bone walls, much like dinosaurs. Effigia also had a somewhat endothermic body temp - ie, it was closer to warm-bloodedness than modern crocodilians, and may have even been warm-blooded outright. It had five fingers on each hand, though only three of each would have claws; it had four main toes on each foot, unlike the three in theropods, and a little toe raised up (kind of like the fourth toe in theropods). It was rather front heavy, unlike theropods that lean more towards the hip, giving it a forward-leaning appearance.

Diet: Probably herbivorous. While the exact diet of Effigia is murky, the beak of this species indicates it probably would have fed on a variety of plant material, like the later mimics such as Limusaurus and Ornithomimus. However, omnivory was certainly not out of the question.

Behavior: Because Effigia was front-titled, it’s actually not clear whether or not it would have behaved similarly to the animals it resembles. In fact, it doesn’t seem very well adapted for fast movement at all - it looks exactly like the sort of creature that may have tripped over itself on a regular basis. That said, it is entirely possible that it would have balanced itself differently, or adjusted its position in such a way to make up for this oddity in posture. That said, it also had fairly short legs compared to its overall body length, so it’s doubtful that it would have been a fast mover in any position. As such, it probably would have moved slowly throughout its ecosystem, grazing on plants and following fresh vegetation where it came up and utilizing its long neck to reach into areas where food was less accessible, and grabbing on to it for feeding. It may not have been a particularly social animal though, like living archosaurs, it probably would have taken care of its young in some fashion.

Ecosystem: Ghost Ranch was a large floodplain, not quite as forested as the environment had been in earlier times (when they were literally called the “petrified forest”), however, there were still extensive dry forests that experienced dramatic dry and wet seasons each year. These seasons were interspersed with regular flooding, which lead to rapid preservation of a very diverse Late Triassic ecosystem. This was an extremely diverse habitat, with a variety of other reptiles that lived alongside Effigia. There was the slender dinosaur Coelophysis, the weirdly-toothed dinosaur Daemonosaurus, the Silesaurids Kawanasaurus and Eucoelophysis, the Lagerpetid Dromomeron, the early Crocodylomorph Hesperosuchus, the Aetosaur Stenomyti, the phytosaur Redondasaurus, the Drepanosaurs Avicranium and Drepanosaurus, the aquatic archosauriform Vancleavea, the sphenodont Whitakersaurus; coelocanths, ray-finned fish, mystery fish, and even invertebrates such as branchiopods and ostracods. It’s possible that Effigia lived alongside other animals as well, but more research is needed into the exact environment of the Chinle Formation where Effigia was found before that can be confirmed. It is entirely possible that Effigia would have been preyed upon by Coelophysis.

Other: Effigia is so freaking weird, you guys. Like, the Triassic may as well be called the Period in Which Reptiles Tried Out All The Things Dinosaurs Would Later Do (But Only Dinosaurs Would Get Paid For It). It is so similar to later Ornithomimosaurs that at least a few paleontologists used to think that the remains later called Effigia were actually dinosaurs, before their proper reassignment into the Pseudosuchians. This just emphasizes how much different reptiles were trying out new designs and new ideas in the Triassic Period, some of which superficially resembled later dinosaurs - but with surprise twists. It also demonstrates exactly how much crocodile-relatives were diversifying extensively in the Triassic, and how hard they would be hit by the end-Triassic extinction.

~ By Meig Dickson

Sources Under the Cut