Kaedan O'Brien, Ph.D.

A side profile of a Dull-mantled Antbird perched on a moss-covered root. The small, dark bird has a striking bright red eye, a black head and throat, a dark brown body, and small white spots on its wing. The background is a blurred, deep green forest floor.

The Dull-mantled Antbird is a fun one. These birds are fiercely territorial and loud. If you happen across their territory, they'll let you know about it. They like steep, wet ravines with thick vegetation and don't like coming out in the open.

At Cataratas Bijagua #CostaRica this morning. #birds

Peanut Butter Man likes medicine time

Hickory milk (kanuchi) using a Tsalagi recipe

art depicting a pair of chromeornis in a forested environment

the unfortunate holotype of chromeornis, who died in a rather embarrassing way

a warm welcome to chromeornis funkyi, a new enantiornithean described from the early cretaceous jiufotang formation in liaoning province, china. o'connor et al. found that the unfortunate holotype choked to death while swallowing gastroliths
(art by sunny dor)
palaeo-electronica.org/content/2025...

Traveling through South America, I've seen many fossils big and small - so many that I should start my own #FossilFriday posts!
Macrauchenia, one of the last and largest of the litopterns, a South American lineage that is totally extinct. Apparently, Macrauchenia had a remarkable nose ->

a painting of an nature scene with a jaguar chasing small boar-like animals in the foreground and further out on the savannah are deer, elephants and other large animals, and a numbered key to the illustration positioned below it reflecting the list in the linked post

Exhibit #SciArt 🎨 Florida Pleistocene
Paleontologists have found Pleistocene fossils in almost every county in Florida, speaking to our state’s rich biodiversity during this period.

🗝️ Check out the exhibit art + key, and fossils from our collections:
www.floridamuseum.ufl.edu/exhibits/blo...

Awesome work!

44 bison released into Coahuila reserve as part of 25-year grasslands conservation initiative Absent from the central Coahuila desert for 160 years, the American bison has returned to the region as part of a 25-year biodiversity conservation effort in northern Mexico.

One of the best news of the year. mexiconewsdaily.com/news/44-biso...

"The new arrivals were welcomed [..] with a ceremony directed by the indigenous Ndé... The return reconnects the Ndé Nation with a brother that is part of our identity, our spirituality and our collective memory,”

an adult hesperotherium meets an etruscan bear cub in the snow

happy #fossilfriday! this is hesperotherium, a chalicothere from early-middle pleistocene china. hesperotherium was among the last of the chalicotheres, and overlapped in range with the huge ape gigantopithecus
(art by @haiderjaffri.bsky.social)

8 point Whitetail buck

8 point whitetail buck

King of the Northern Hardwoods

Great, balanced article!

On the Absence of Hominins and the Tragedy of Gigantopithecus A 'Prehistoric Planet: Ice Age' Critique

first substack article is up! cascoclauda.substack.com/p/on-the-abs...

'An extreme end of human genetic variation': Ancient humans were isolated in southern Africa for nearly 100,000 years, and their genetics are stunningly different Ancient genomes from southern Africa show that people evolved in isolation for upward of 100,000 years.

Researchers studied 28 new genomes from Africa and found that southern Africans were basically isolated for a long period of time. 🧪🏺

Figure 3 of the paper. Two phylogenetic trees, tree A of different hartebeest subspecies, and tree B including other alcelaphines.

In our phylogenetic analysis the Levantine hartebeest is nested deep within the Bubal+western Hartebeest clade. In other words, we have genetic evidence confirming the hitherto null hypothesis, and no support for East African affinities. 7/13

Figure 1 of the paper, a map of Africa and the Middle East with colour indexed historical ranges of different hartebeest subspecies.

It used to range all across the continent - and even ventured into the Levant, becoming the only alcelaphine to set foot out of Africa!
The Levant is also the earliest known local extinction of the species, with last confirmed records dating to the middle ages. 2/13

Red hartebeest (Alcelaphus buselaphus caama), photographed at Mokala National Park, South Africa. Red hartebeest are the most numerous population of the species in the 21st century. Very different from the Levantine hartebeest. ©️ Uri Wolkowski

Title of new publication, Wolkowski et al. 2025.

I'm glad to share my M.Sc thesis about the extinct Levantine #hartebeest , now published and #openaccess ! Link following 🧵

The hartebeest is a staple antelope of eastern and southern African savannahs. However, the species had a far wider past distribution 1/13

Photo montage of Tinamus resonans sp. nov., a new species of tinamou from the montane forests of the Serra do Divisor, western Amazonia, Brazil. The species is distinguished by a unique combination of plumage pattern, vocal repertoire, and ecological characteristics, including a conspicuous dark slate facial mask, vivid rufous-cinnamon underparts, and a uniform brownish-gray back. Its vocalizations are remarkable, consisting of long and powerful songs that echo strikingly across the steep montane slopes, producing a characteristic resonant effect. The species was documented exclusively at higher elevations within a transitional zone between submontane and stunted forests, where the understory is densely structured by root mats. A preliminary population estimate, based on field detections and spatial extrapolation, suggests approximately 2,106 individuals restricted to the Serra do Divisor massif. Although no immediate anthropogenic pressures were observed within its range, the species may be highly vulnerable to climate change and to proposed infrastructure projects that threaten the integrity of this federally protected region. The discovery of T. resonans highlights the biological uniqueness of the Serra do Divisor, reinforces its status as a center of montane endemism, and underscores the critical importance of maintaining its long-term conservation.

Huge News from the Western Amazon: it's the year 2025 and we are still describing entirely new, strikingly-distinctive large-bodied bird species! Behold Tinamus resonans sp. nov. the Slaty-masked Tinamou mapress.com/zt/article/v... #Ornithology @tetzoo.bsky.social 🪶

Can't wait to read it!

Yes, no problem!

Extinction pulses around 30 ka in Australia, 13 ka in the Americas, and 10 ka in Africa (though the last is very spread out), followed by thousands of years of apparently sustainable living and nearly zero extinctions outside islands until the 1500s and European colonization.

Humans (Homo) evolve in Africa by 2.8 Ma, and Homo sapiens emerged by 300 ka. By 60 ka, humans have spread across Eurasia, by 50 ka, to Australia, by 21 ka, through the Americas (probably earlier in every case). Extinctions only seem to occur once humans have reached high populations in each (1/2)

Of course! My own research looks into this extensively, and does find mixed results of human impacts.

The StW 573 Little Foot Fossil Should Not Be Attributed to Australopithecus prometheus Objectives To test the hypothesis that the StW 573 (Little Foot) fossil specimen should be attributed taxonomically to Australopithecus prometheus. Materials and Methods We adopt the methods of cl...

Challenging the name!
Jesse Martin & colleagues argue Little Foot (StW 573) can’t be called Australopithecus prometheus…
…dissent in the fossil world 🦴😅😁

onlinelibrary.wiley.com/doi/10.1002/...

Depictions of evolution where a phylogeny often has humans on the far right or top can give an impression of evolution being progressive of leading to ‘increased complexity’ when it does not. Top figure shows such a phylogeny which can look the same as ‘the March of progress’ depiction most commonly used to depict evolution (showing monkey to man erroneous march of evolution) - instead swiveling some nodes on a phylogeny where humans are shown closer to the center (which doesn’t change relationships) can lead to better ‘tree thinking’

New post by me on #MITPressReader @mitpress.bsky.social

On the 100th anniversary of the #ScopesMonkeyTrial
the ways we depict #evolution can still give an erroneous progressive view (that evolution leads to humans or ‘increased complexity’).

thereader.mitpress.mit.edu/is-our-pictu...

The declines in large herbivores are constant since about 6.5 Ma. They're driven by decreasing CO2 and grasslands expansion, not humans. And those turnover pulses didn't actually exist--They're artifacts of sampling bias.

Concept sketch of three Rusingoryx walking on an African grassland

Concept sketch on this weird bovid Rusingoryx atopocranion from Pleistocene Africa.

As you can see, this taxon was closely related to modern wildebeest. Also, like wildebeest, Rusingoryx was a migratory species.

🐡 🎨 🧪 #paleontology

The term "dude" was a deliberate choice here.

The whole "but Jurassic World is inspiring future paleontologists!" argument fails to mention that those are going to be the most insufferable dudes imaginable at conferences in about 15 years.

Hobbes*