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SUNDAY SCIENCE: A NEWLY IDENTIFIED ‘HELL CHICKEN’ SPECIES
SUGGESTS DINOSAURS WEREN’T SLIDING TOWARD EXTINCTION BEFORE THE
FATEFUL ASTEROID HIT  
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Kyle Atkins-Weltman, Eric Snively
January 25, 2024
The Conversation
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_ Did large dinosaurs go extinct the way a Hemingway character
quipped he went broke: “gradually, then suddenly”? Eoneophron adds
evidence that caenagnathids were doing quite well for themselves
before the asteroid ruined everything. _

Birdlike dinosaur Eoneophron infernalis was about the size of an
adult human. , Zubin Erik Dutta

 

Were dinosaurs already on their way out when an asteroid hit Earth 66
million years ago, ending the Cretaceous
[[link removed]], the geologic
period that started about 145 million years ago? It’s a question
that has vexed paleontologists
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like us
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for more than 40 years.

In the late 1970s, debate began about whether dinosaurs were at their
peak or in decline before their big extinction. Scientists at that
time noted that while dinosaur diversity seemed to have increased in
the geologic stage that spanned 83.6 million to 71.2 million years
ago, the number of species on the scene
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during the last few million years of the Cretaceous. Some researchers
have interpreted this pattern to mean that the asteroid that struck
the Gulf of Mexico
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was simply the final blow [[link removed]]
for an already vulnerable group of animals
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However, others have argued that what looks like a decrease in the
diversity of dinosaurs [[link removed]] may be an
artifact of how hard it is to accurately count them
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preserve different dinosaurs more or less often
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favored environment and how easily their bodies fossilized there. The
accessibility of various outcrops could influence what kinds of
fossils researchers have so far found. These biases are a problem
because fossils are what paleontologists must rely on to conclusively
answer how healthy dinosaur populations were when the asteroid hit.

At that crucial moment, what was really happening to dinosaur
diversity? Discovery, identification and description of new dinosaurs
provide vital clues. This is where our work
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comes in. Close examination of what we’d thought was a juvenile
specimen of an already known species of dinosaur from this time period
revealed that it was actually part of an adult from a completely new
species.

Our work focusing on the life stage of our specimen demonstrates that
dinosaur diversity may not have been declining before the asteroid
hit, but rather that there are more species from this time period yet
to be discovered – potentially even through reclassification of
fossils already in museum collections.

[hand on one of three long fossil bones with a ruler]
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Kyle Atkins-Weltman holds the femur of the new dinosaur as it was
received, with the other fossils in the background. Kyle
Atkins-Weltman

Clues inside the bones of a birdlike dinosaur

Our new study focused on four hindlimb bones – a femur
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in South Dakota, in rocks of the Hell Creek Formation
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the final 2 million years of the Cretaceous.

When we first examined the bones, we identified them as belonging to a
family of dinosaurs known as the caenagnathids – a group of birdlike
dinosaurs that had toothless beaks, long legs and short tails. Direct
[[link removed]] fossil
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evidence [[link removed]] indicates
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these dinosaurs
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were covered in complex feathers [[link removed]], much
like modern birds [[link removed]].

The only known species of caenagnathid from this time and region
[[link removed]] was _Anzu_, sometimes
called the “chicken from Hell
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Covered in feathers and sporting wings and a toothless beak, _Anzu_
was between roughly 450 and 750 pounds (200 and 340 kilograms).
Despite its fearsome nickname, though, its diet is a matter of debate.
It was likely an omnivore, eating both plant material and small
animals.

Because our specimen was significantly smaller than _Anzu_, we simply
assumed it was a juvenile. We chalked up the anatomical differences we
noticed to its juvenile status and smaller size – and figured the
animal would have changed had it continued to grow. _Anzu_ specimens
are rare, and no definite juveniles have been published in the
scientific literature, so we were excited to potentially learn more
about how it grew and changed throughout its lifetime by looking
inside its bones
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Just like with a tree’s rings, bone records rings called lines of
arrested growth [[link removed]]. Each annual
line represents part of a year when the animal’s growth slowed. They
would tell us how old this animal was, and how fast or slow it was
growing.

We cut through the middle of three of the bones so that we could
microscopically examine the internal anatomy of the cross-sections.
What we saw completely uprooted our initial assumptions
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[cross-section 'slice' of yellowish fossilized bone with growth lines
like the rings of a tree]
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Teal markers point to lines of arrested growth on the cross-section of
fossilized bone. Toward the outside of the bone, the lines are much
closer together, reflecting less growth per year. Researchers counted
exactly six lines, meaning this animal was between 6 and 7 years old
when it died. Holly Woodward

In a juvenile, we would expect lines of arrested growth in the bone to
be widely spaced, indicating rapid growth, with even spacing between
the lines from the inside to the outside surface of the bone. Here, we
saw that the later lines were spaced progressively closer together,
indicating that this animal’s growth had slowed and it was nearly at
its adult size.

This was no juvenile. Instead, it was an adult of an entirely new
species, which we dubbed _Eoneophron infernalis_. The name means
“Pharaoh’s dawn chicken from Hell,” referencing the nickname of
its larger cousin _Anzu_. Traits unique to this species include ankle
bones fused to the tibia, and a well-developed ridge on one of its
foot bones. These weren’t features a young _Anzu_ would outgrow, but
rather unique aspects of the smaller _Eoneophron_.

Expanding the caenagnathid family tree

With this new evidence, we started making thorough comparisons with
other members of the family to determine where _Eoneophron infernalis_
fit within the group.

It also inspired us to reexamine other bones previously believed to be
_Anzu_, as we now knew that more caenagnathid dinosaurs lived in
western North America during that time. One specimen, a partial foot
bone smaller than our new specimen, appeared distinct from both _Anzu_
and _Eoneophron_. Where once there was one “chicken from Hell,”
now there were two, and evidence for a third: one large (_Anzu_),
weighing as much as a grizzly bear, one medium (_Eoneophron_),
humanlike in weight, and one small and yet unnamed, close in size to a
German shepherd.

[wooded scene with three different sizes of bird-like dinosaur]
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_Eoneophron infernalis_ and the smaller unnamed species now join the
larger _Anzu_ as late-Cretaceous caenagnathid dinosaurs from the Hell
Creek region. Zubin Erik Dutta

Comparing Hell Creek with older fossil formations such as the famous
Dinosaur Park Formation of Alberta
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dinosaurs that lived between 76.5 million and 74.4 million years ago
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same number of caenagnathid species, but also the same size classes.
There, we have _Caenagnathus_, comparable to _Anzu_, _Chirostenotes_,
comparable to _Eoneophron_, and _Citipes_, comparable to the third
species we found evidence for. These parallels in both species count
and relative sizes offer compelling evidence that caenagnathids
remained stable throughout the last part of the Cretaceous.

Our new discovery suggests that this dinosaur group was not declining
in diversity at the very end of the Cretaceous. These fossils show
that there are still new species to be discovered, and support the
idea that at least part of the pattern of decreasing diversity is the
result of sampling and preservation biases.

Did large dinosaurs go extinct the way a Hemingway character quipped
he went broke: “gradually, then suddenly
[[link removed]]”? While
there are plenty of questions still outstanding in this extinction
debate, _Eoneophron_ adds evidence that caenagnathids were doing quite
well for themselves before the asteroid ruined everything.

_This article has been updated to correct the full name in English of
the new species._[The Conversation]

Kyle Atkins-Weltman
[[link removed]],
Ph.D. Student in Paleoecology, _Oklahoma State University
[[link removed]]_
and Eric Snively
[[link removed]], Associate
Professor of Anatomy and Cell Biology, _Oklahoma State University
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This article is republished from The Conversation
[[link removed]] under a Creative Commons license. Read
the original article
[[link removed]].

The Fallout Never Ended
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By Robert Alvarez
Bulletin of the Atomic Scientists
February 1, 2024

Decades of nuclear weapons tests and other radioactive experiments
injured or killed scientists, soldiers, and innocent bystanders. Many
of them, and their relatives, have never been compensated, but new
efforts may change that. A former Senate staffer and expert on the US
nuclear program looks back at its harmful effects, and how the
government addressed them—or didn't.

* Science
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* paleontology
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* dinosaurs
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* extinction
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