IB's terror bird thread

[Supercommunist]

Thought I would include paleoart if that's okay.

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[Infinity Blade]

Yeah, that's fine, considering most of the posts in this thread so far contain publications anyway.

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I usually avoid double-posting, but I feel like I kind of killed Supercommunist's thunder here with my most recent post in "Recommended literature". So I'll bump this thread a bit so his paleoart post can be seen, and to post this recent image here.

Also posted in the Size comparisons thread (image source given in that post).


Really interesting to see how the largest terror birds compare with some of the Cenozoic's largest and most famous terrestrial predators.

[Supercommunist]

I wouldn't worry to much about double posting given that this is a small forum:

[Supercommunist]

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[Supercommunist]

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Something I learned just now from an old book by Greg Paul (link->). Back in 1998, scientists found evidence of an impact event just off the coast of South America 3.3 million years ago. It's been suggested that this could have caused (Schultz et al., 1998). A later paper in 2004 seems to think that this is still a plausible cause for the local faunal turnover event at the time (an alternative suggested by a 2001 study was a tectonic event) (Vizcaíno et al., 2004).

I have noticed before that Titanis seems to have been the only large-bodied terror bird that went up to North America, and that large phorusrhacids seem to have gone extinct in South America before Titanis did up north. it could be either this impact event or tectonic event was the reason why.

EDIT: It's been estimated that terror birds migrated to North America ~9-7 million years ago (Prevosti & Forasiepi, 2018). This makes sense, considering Titanis is known from North America as early as 5 million years ago, so either it or one of its ancestors must have migrated up north some time before.

Migrations from South to North America occurring in the interval ~9–7 Ma (late Miocene) include ground sloths and terror birds (Fig. 2.8), followed by other groups of ground sloths and giant armadillos in the early Pliocene (~5 Ma), hydrochoerids (capybaras), megatherids, and porcupines in the late Pliocene (~2.7 Ma), and anteaters, toxodonts, and opossums in the Pleistocene (Woodburne 2010; Cione et al. 2015).

[Supercommunist]

Paper discussing terror bird toes claws. Sadly, it's not English so I can't read it.

www.colibri.udelar.edu.uy/jspui/bitstream/20.500.12008/4112/1/uy24-14537.pdf

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Oh yeah, I have this thread! Would be fitting to post the recent info on phorusrhacid footprints, confirming that these animals were functionally didactyl with their digit II raised off the ground (like a dromaeosaurid or seriema) (Melchor, 2023).

Terror birds (Aves, Phorusrhacidae) comprise the most outstanding group of South American Cenozoic avifauna, and have been considered dominant predators. Terrestrial habits were inferred using the reduction of their forelimbs and high body mass. Phorusrhacids were considered functionally tridactyl with three relatively short digits II–IV and a small, elevated digit I. The function of the ungual phalanges of digit II have been debated, including the utility of the ungual for retention or stabbing of prey. Incomplete or lack of preservation of foot bones have hampered understanding of the evolution and diversification of Phorusrhacidae. Here we show the first known and well-preserved footprints of Phorusrhacidae with a didactyl posture, which are named Rionegrina pozosaladensis igen. et isp. nov. These footprints yield unprecedented information on the locomotor habits of the group. The finding implies that medium-sized, Late Miocene (~ 8 Ma) phorusrhacids developed strong cursorial adaptations; achieved through reduction of digit II, raised metatarso-phalangeal pad, main body support in a large and thick digit III, and digit IV as outrigger. Raised and long claw of digit II was probably used in pining of prey. Phorusrhacid footprints differ from the Early Cretaceous didactyl footprints of deinonychosaurian dinosaur affinity by its larger size and strong mesaxony.

The marked reduction in digit II, large and deep impression of digit III with deep and large claw trace, and shallower digit IV in R. pozosaladensis can be interpreted as a noticeable adaptation to cursoriality and running. Comparison with a biomechanical study of the foot of the ostrich (Struthio camelus) is particularly enlightening, because this extant bird is didactyl as result of adaptation towards fast and sustained bipedal locomotion. Ostriches have lost digit II and display a raised metatarso-phalangeal pad. The very shallow digit II impression in R. pozosaladensis suggest a reduced role in body weight support, especially considering the moderate speed inferred for the producer. By comparison with didactyl ostriches, the functional advantage of this relative shortening probably lies in the lightening of the distal limb, with the consequent optimization of swing dynamics and potential higher stride frequencies. A shallowing of digit II impression in running when compared to walking locomotion was also observed in the emu (Dromaius novaehollandiae), which is a large cursorial ratite species with tridactyl foot. The deep impressions of digit III in R. pozosaladensis indicate its function as main load-bearing digit, whereas the shallower and smaller lateral digit impression (IV) probably reflect its secondary role in body support and stabilizing the animal during rapid locomotion. As in didactyl ostriches, large and deep claw imprint in digit III probably reflect an essential traction function during push-off, whereas reduced claw imprint in digit IV agrees with its function as outrigger. The shallow impression of the metatarso-phalangeal pad in R. pozosaladensis is indicative of a secondary role as weight-bearing. Alternatively, this pad was potentially used during prey immobilization along with digit II claw as was observed in seriemas and has been also proposed for deinonychosaurs. This inference is compatible with consumption of small prey or application of multi-targeted strikes on larger prey as suggested for the medium-sized Neogene phorusrhacid Andalgalornis steulleti.

Rionegrina pozosaladensis reveals the presence of a phorusrhacid of moderate size, probably comparable to M. milneedwardsi, with noticeable adaptations for running and predation. The latter features include functionally didactyl posture, with stabilization during running facilitated by digit IV, and a combination of a large curved claw in digit II with an adjoining metatarso-phalangeal pad that assisted in the pinning and grasping of prey.

[Supercommunist]

[Supercommunist]

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

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.

www.tandfonline.com/doi/full/10.1080/08912963.2024.2304592

[Supercommunist]

Artist's instagram page.

www.instagram.com/pantydraco/?hl=en

[Supercommunist]

[Supercommunist]

Thoughts on terror birds being able to retract their necks?







The artist apparently had an example of a seriema doing this but the link broke.

alphynix.tumblr.com/post/116314700171/the-newly-named-terror-bird-llallawavis-terror