Aucasaurus

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Aucasaurus
Temporal range:
Ma
↓
Mounted skeleton reconstruction
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Abelisauridae
Tribe: †Carnotaurini
Genus: †Aucasaurus
Coria et al., 2002
Type species
†Aucasaurus garridoi
Coria et al., 2002
Synonyms

Aucasaurus is a

stage) of the Anacleto Formation.[1] It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers.[2]
The type skeleton is complete to the thirteenth
paleontologists to speculate that it was involved in a fight prior to death.[3]

In 2009, Novas suggested that Aucasaurus garridoi might be a

junior synonym of Abelisaurus comahuensis.[4] In 2010, Gregory S. Paul renamed Aucasaurus garridoi into Abelisaurus garridoi.[5] Despite their similarities, other researchers have placed both genera as separate taxa.[6]

Discovery

Aucasaurus is known from finds in the

sauropod eggs are also known from this deposit.[7]

Description

Reconstruction
Size compared to a human

Aucasaurus was a medium-sized abelisaur, measuring 5.5–6.2 m (18–20 ft) long and weighing approximately 700 kg (1,500 lb).[5][8][9] Its skull was not as short or as deep-snouted as that of Carnotaurus. Also, instead of horns, it had a pair of low ridges above each eye.[7]

Forelimbs and hands

The small arms of Aucasaurus were also like that of its horned relative, but were proportionally longer due to its small size, and the bones lacked the bony processes and some unusual proportions present in Carnotaurus. The

metacarpals were present, but the first and fourth lacked fingers. The second and third had fingers, but they were quite short and had no claws.[7]

Braincase

3D scan of the braincase

A study was done on the braincase of Aucasaurus in 2015 by Ariana Paulina-Carabajal and Cecilia Succar, in which the skull material was scanned using a medical CT machine. Virtual three-dimensional inner ear and cranial endocasts were obtained and visualized using the imagine software at the

flocculus is enclosed in an 8-shaped floccular recess, similar in shape and size to that observed in Abelisaurus, suggesting that the two Patagonian taxa were capable of a slightly wider range of movements of the head. The labyrinth of the inner ear is similar in shape and size to the semicircular canals of Majungasaurus, although the lateral semicircular canal is shorter in Aucasaurus.[10]

Pathology

Pathologic fused tail vertebrae

The 5th and 6th holotype tail vertebrae of Aucasaurus provide evidence of failed developmental vertebral segmentation, so two of the vertebrae are fused. Baiano et al. (2024) interpret this as a

congenital disorder (birth defect) called block vertebrae. This represents the earliest known occurrence of this pathology in the non-avian theropod fossil record.[11]

Classification

Aucasaurus was closely related to Carnotaurus and they are united in the Carnotaurini.[7]

Below is a cladogram by Canalle et al. in 2009.[6]

Carnotaurinae

See also

References

  1. ^ The Theropod Database on Aucasaurus
  2. S2CID 131148538
    .
  3. ISBN 978-0822567912
    .
  4. ISBN 9780253352897
    .
  5. ^
    ISBN 9781400836154
    .
  6. ^
    S2CID 23619863
    .
  7. ^
    ISBN 978-0-7566-9910-9
    .
  8. doi:10.1016/j.cretres.2016.09.001
    .
  9. PMID 32983636
    .
  10. doi:10.4202/app.2013.0037
    .
  11. PMID 38291378
    .
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