Euparkeria

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Euparkeria
Temporal range: late Olenekian – early Anisian?
SAM-PK-5867, the holotype skeleton of Euparkeria capensis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Clade:
Eucrocopoda
Family: †Euparkeriidae
Genus: †Euparkeria
Broom, 1913
Type species
†Euparkeria capensis
Broom, 1913
Synonyms
  • Browniella africana Broom, 1913

Euparkeria (

Archosauria, the reptile group that includes crocodilians, pterosaurs, and dinosaurs (including birds
).

Fossils of Euparkeria, including nearly complete skeletons, have been recovered from the

Karoo Basin. Tentative dating schemes place the CAZ around the latest Early Triassic (late Olenekian stage) or earliest Middle Triassic (early Anisian
stage), approximately 247 million years old.

Euparkeria is among the most heavily described and discussed non-archosaur archosauriforms. It was a small carnivorous reptile with a boxy skull, slender limbs, and two rows of tiny teardrop-shaped

high walk. Biomechanical
analyses suggests that Euparkeria was incapable of even short periods of bipedal activity.

Palaeobiology

Locomotion

Life reconstruction of Euparkeria capensis in a quadrupedal pose with semi-erect limbs

The hind limbs of Euparkeria are somewhat longer than its forelimbs, which has led some researchers to conclude that it could have occasionally walked on its hind legs as a facultative biped. Other possible adaptations to bipedalism in Euparkeria include rows of osteoderms that could stabilize the back and a long tail that could act as a counterbalance to the rest of the body. Paleontologist Rosalie Ewer suggested in 1965 that Euparkeria spent most of its time on four legs but moved on its hind legs whilst running.

However, adaptations to bipedalism in Euparkeria are not as obvious as they are in some other Triassic archosauriforms such as dinosaurs and

calcaneum (an ankle bone) that would have given strong leverage to the ankle during locomotion. A calcaneal projection might have enabled Euparkeria to move with all four limbs in a semi-erect "high walk" similar to the way in which living crocodilians sometimes move about on land.[1]

A 2020 study of range of motion in the hindlimbs of Euparkeria found conflicting evidence for its posture. The structure of the femur (thigh bone) and hip socket suggest that the legs were capable of a very wide range of motion, ranging from a nearly vertical stance to a thigh which projects forwards, backwards, or outwards at a nearly horizontal angle. Rotation of the thigh was more limited, a factor that argues against a sprawling gait reliant on broad outward leg sweeps. Although the hip socket argues in favor of an upright 'pillar-erect' hindlimb stance, the structure of the tibia (inner shin bone) and ankle show that the lower legs and feet would have splayed outwards during normal usage, supporting a semi-erect rather than fully erect stance. The hindlimbs of Euparkeria have been used to argue that the evolution of a fully erect gait in true archosaurs was a stepwise process which first developed in bones closer to the hip.[2]

A 2023 paper analyzed the possibility of facultative bipedalism and came to the conclusion that Euparkeria was quadrupedal at all times. Models of weight distribution found that the

plantarflexor group (the muscles which bend the foot down to maintain stability) would have been overexerted to the point of failure if a bipedal posture was attempted by the animal.[3]

Nocturnality

nocturnal, suggesting that Euparkeria had a lifestyle adapted to low-light conditions. During the Early Triassic the Karoo Basin was at about 65 degrees south latitude, meaning that Euparkeria would have experienced long periods of darkness in winter months.[4]

Classification

Artist's interpretation of a jumping Euparkeria

The family Euparkeriidae is named after Euparkeria. The family name was first proposed by German paleontologist Friedrich von Huene in 1920; Huene classified euparkeriids as members of Pseudosuchia, a traditional name for crocodilian relatives from the Triassic (Pseudosuchia means "false crocodiles"). Early phylogenetic analyses created by Jacques Gauthier in the 1980s provided an alternative hypothesis, that Euparkeria was closer to dinosaurs (including birds) rather than crocodilians.[5] Many genera have been assigned to Euparkeriidae in the past, but only two other valid genera are currently believed to be part of the family, apart from Euparkeria itself: Halazhaisuchus and Osmolskina.[6]

More recent analyses starting with Benton & Clark (1988)[7] place Euparkeria as a member of Archosauriformes in a position outside both crocodilian-line and bird-line (Avemetatarsalian). Although the ancestor to archosaurs likely shared several similarities with Euparkeria, archosaurs are probably not directly descendants of the genus. The precise placement of Euparkeria and other euparkeriids within Archosauriformes is controversial.

Most analyses agree that Euparkeria was a closer relative of archosaurs than the

Ezcurra (2016).[14]

On the other hand, several other notable studies consider Euparkeria to be closer to archosaurs than proterochampsians. Sterling Nesbitt's influential 2011 monograph on archosaurian relationships found a similar result, although he also placed phytosaurs as the sister group to Archosauria, rather than Euparkeria.[15] Roland Sookias, a paleontologist responsible for many studies on euparkeriids in the 2010s, also considers them to be closer archosaur relatives than the proterochampsians.[1][6] Like Nesbitt (2011), he found phytosaurs to be the closest relatives of Archosauria, followed by the Euparkeria-like reptile Dorosuchus, and then by the euparkeriids.[9]

References

  1. ^
    S2CID 219205317
    .
  2. PMID 32958770
    .
  3. PMID 36704253
    .
  4. S2CID 33253407
    .
  5. ISBN 978-0-940228-14-6
    .
  6. ^
    PMID 25469319
    .
  7. ^ Benton, Michael J.; Clark, James M. (1988). "Archosaur phylogeny and the relationships of the Crocodylia" (PDF). In Benton, Michael J. (ed.). Phylogeny and Classification of the Tetrapods. Vol. 1. Oxford: Clarendon Press. pp. 295–338. Archived from the original (PDF) on July 15, 2007.
  8. S2CID 7025069
    .
  9. ^
    PMID 27069658
    .
  10. doi:10.1080/02724634.1991.10011426
    .
  11. JSTOR 4523513
    .
  12. ^ Juul, Lars (1994). "The phylogeny of basal archosaurs" (PDF). Palaeontologia Africana. 31: 1–38.
  13. PMC 1692658
    .
  14. PMID 27162705
    .
  15. S2CID 83493714
    .
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