Insights on the oldest Phorusrhacidae from the Eocene of Argentina (1 Viewer)

[Fred Ruhe]

Carolina Acosta Hospitaleche & Washington Jones, 2024

Insights on the oldest terror bird (Aves, Phorusrhacidae) from the Eocene of Argentina

Historical Biology: An International Journal of Paleobiology.
doi:10.1080/08912963.2024.2304592

Abstract:

Phorusrhacidae, commonly known as terror birds, constitutes a group of Cariamiformes that lived mainly in South America during the Cenozoic. The oldest record is represented by an isolated distal end of tibiotarsus (MLP-PV 75-II-3-22) discovered in the Lutetian (middle Eocene) levels of the Sarmiento Formation exposed in the Cañadón Vaca locality (Chubut Province, Argentina). Despite being frequently cited as the oldest specimen of Phorusrhacidae, this specimen has never been figured or comprehensively described. Motivated by this gap and recognising the significance of this finding, we conducted a detailed comparison of the tibiotarsus MLP-PV 75-II-3-22 with those of other species, assigning it to an indeterminate species of Psilopterinae with an estimated body mass of approximately 5 kg. Furthermore, following the identification of numerous tooth marks on the distal surface, we hypothesised that this small phorusrhacid may have been subjected to an attack or scavenging event by a small-to-medium predator, such as Nemolestes spalacotherinus, a hypercarnivorous marsupial previously recorded in the Cañadón Vaca assemblage.:

Enjoy,

Fred

 

[Fred Ruhe]

Systematic Paleontology

Clase Aves Linnaeus, 1758
Neornithes Gadow, 1893
Order Cariamiformes Fürbringer, 1888
Family Phorusrhacidae Ameghino, 1889
Subfamily Psilopterinae Dolgopol de Saez, 1927
Gen. et sp. indet.

Material

MLP-PV 75-II-3-22 distal end of left tibiotarsus

Locality and age

Cañadón Vaca locality, Chubut Province, central Patagonia
(Argentina). Sarmiento Formation, collected in levels bearing
Vacan ‘subage’ of the Casamayoran SALMA (South American
Mammal Age), dated in 43 Ma (Dunna etal. 2015) Lutetian (middle Eocene).

Measurements (in mm)

maximum distal width 25.9, height of the condylus medialis (in
cranial view) 19.2, height of the condylus lateralis (in cranial
view) 17.5

Estimated measurements (in mm)

Estimated total length of tibiotarsus 265.3, estimated mínimum
diaphyseal cranio-caudal width 10.3 estimated mínimum lateromedial diaphyseal width 13.4, estimated perimeter 37.6.

Fred


Figure 1. Location map. The red star indicates the fossiliferous locality Cañadón Vaca (Chubut Province, Argentina), where Lutetian (Eocene) levels of the Sarmiento Formation are exposed


Figure 2. Psilopterinae MLP-PV 75-II-3-22 gen. et sp. indeterminate from the middle Eocene Sarmiento Formation at Cañadón Vaca (Chubut Province, Argentina). A, Reconstruction of the complete tibiotarsus in cranial view (the lines indicate the level of the least circumference); specimen in B, cranial; C,
medial; D, distal; E, lateral; F, caudal; and G, proximal views. Scale bars: 10 mm.