Robert A. DePalma1, 2; Florentin
Maurrasse3; Anton Oleinik2; David A. Burnham4; Loren Gurche4;
Jeremy Klingler5; Peter L. Larson6; Thomas Beasley7; Tina
Geraki8; Konstantin Ignatyev8; David M. Unwin9; Uwe
Bergmann10, 11; Nicholas Edwards11; Roy A. Wogelius1; Victoria
Egerton1; Phillip L. Manning1
1. Department of Earth and Environmental Sciences, University
of Manchester, UK; 2. Florida Atlantic University Department
of Geosciences, Boca Raton, FL; 3. Department of Geology,
Florida International University, Miami, Fl; 4. University of
Kansas Biodiversity Institute, Lawrence, KS; 5. Department of
Biological Sciences, Southwestern Oklahoma University,
Weatherford, OK; 6. Black Hills Institute of Geological
Research, Hill City, SD; 7. Florida Center for Analytical
Electron Microscopy, Florida International University, Miami,
Fl; 8. Diamond Lightsource, Oxfordshire, UK; 9. University of
Leicester, Leicester, UK; 10. Department of Physics,
University of Wisconsin, Madison, WI; 11. Stanford Synchrotron
Radiation Lightsource (SSRL), Menlo Park, CA;
The Chicxulub impact, demarking the end of
the Mesozoic, is widely regarded as the main driver of the
Cretaceous-Paleogene (KPg) mass extinction event. Some long-
and short-term detrimental effects attributed to the impact
have also been clearly identified, however our understanding
of immediate effects on an hour-to-day scale is incredibly
limited due to a lack of well-preserved coeval sediment
packages with high temporal fidelity. In addition, the
identity of the Chicxulub impactor, which was obliterated on
contact during the cratering process, has never been
conclusively identified.
Here we provide new data from a terminal-Cretaceous locality
in the Hell Creek Formation, North Dakota, containing a
uniquely preserved sediment package with unusually high
temporal fidelity. At the locality, known at Tanis, a massive
onshore surge of water, triggered by the impact, deposited an
ejecta-bearing drape of sediment that provides one of the most
highly constrained (hour-scale) temporal records of the KPg
impact in terrestrial strata. The deposit, which contains a
unique concentrated death-assemblage of organisms directly
attributed to the Chicxulub impact, reveals new aspects of the
impact' first damaging effects in unprecedented detail. Biota
entombed in the strata also offer new insight into the latest
Cretaceous faunas in the Western Interior, resolving a more
accurate ecological baseline immediately preceding the KPg
mass-extinction. While the extinction itself is
well-documented worldwide, much less is known about the
immediate fate of specific animal groups from the thriving
biomes that immediately preceded the Chicxulub impact. For
example, dinosaurs and pterosaurs, both ubiquitous in Mesozoic
terrestrial biomes, have thus far never been reported in-situ
from deposits immediately below the KPg boundary.
Here we report the first known in-situ pterosaur and dinosaur
fossils coincident with the Chicxulub impact event, providing
a unique window to examine the only known terminal-Cretaceous
examples of these clades in the fossil record, and providing
the first direct evidence that these groups existed up to the
terminal-Cretaceous extinction event. The pterosaur,
consisting of a well-developed semi-articulated prenatal
skeleton in ovum, and the dinosaur, a subadult ornithischian
(Thescelosauridae), were examined via synchrotron rapid
scanning X-ray fluorescence (SRS-XRF), scanning electron
microscopy (SEM), and traditional light microscopy, which
revealed extensive preservation of soft tissue consisting of
distinct signatures of organic residues as well as
three-dimensional microstructure. Because the pterosaur embryo
comprises the first known specimen from the Late Cretaceous
and the only example thus far from North America, it
contributes vital information about the prenatal development
and early ontogeny of these animals from a time interval for
which no such data exists. The ornithischian dinosaur, on the
other hand (c.f. Thescelosaurus), is characterized by
extensive skeletal articulation within preserved portions of
the three-dimensional lithified tubercular skin envelope,
providing hitherto unknown details about the integument,
appearance, and osseous anatomy of the Thescelosauridae.
We also describe two well-preserved meteoric fragments from
the same deposit, directly associated with Chicxulub impact
ejecta adjacent to the Tanis biota. The fragments are
preserved as inclusions within unaltered glassy ejecta
spherules, encapsulated immediately after impact while the
glass was still malleable. The ejecta spherules, themselves,
were preserved in amber coeval with the impact event, which
likely increased their preservation potential and inhibited
their usual breakdown to smectitic clay. Geochemical
examination using energy dispersive X-ray analysis,
laser-ablation inductively-coupled-plasma-mass-spectroscopy,
and synchrotron X-ray techniques, provided multiple lines of
evidence that support a cosmic origin and chemistry indicative
of a CM subtype carbonaceous chondrite. Constraining the
identity of the Chicxulub impactor using data from this work,
which supports prior hypotheses, helps to fill a critical gap
hitherto missing from the Chicxulub story. The findings of
this study also help to greatly augment our understanding of
the Chicxulub impact event, its effect on ancient biota, and
more broadly, provides valuable insight into the dynamic
interplay between cosmic bodies and life on Earth.
About Robert DePalma:
Robert DePalma is a vertebrate paleontologist, based out of
Florida Atlantic University (FAU), whose focus on terrestrial
life of the late Cretaceous, the Chicxulub asteroid impact,
and the evolution of theropod dinosaurs, was sparked by a
passionate fascination with the past. Robert completed his
Bachelor's degree in geology at FAU, earned his Master's
degree from the University of Kansas (summa cum laude), and is
completing his PhD at the University of Manchester UK.
Robert's interest in fossils, osteology, and exploration began
at a very young age, and formally kicked off when he started
working in the Florida Museum of Natural History prep lab at
the age of 14. Robert's fascination with the natural world and
artistic media led him to build his skills in drawing,
painting, sculpting, fossil preparation, scientific
investigation, fleshed reconstructions, museum exhibit design,
and visual effects, guided by paleo artist John Gurche,
Hollywood visual effects guru Stan Winston, and various
professional scientists including Robert Bakker, Larry Martin,
Mark Norell, and Walter Alvarez. As a professional scientist,
Robert has collaborated with museums and institutions across
the globe, including the Florida Museum of Natural History,
the University of Kansas Natural History Museum, University of
Manchester, American Museum of Natural History, and others.
Since 1996 Robert has led over 25 expeditions in the US and
abroad in an effort to expand our knowledge of natural history
and provide educational opportunity to students from diverse
backgrounds. Robert's research work has included the discovery
of the first known dinosaur-aged amber insects from the Hell
Creek Formation, discovery and description of the giant
dromaeosaurid dinosaur Dakotaraptor steini, documentation of
the first known fossil of healed dinosaur skin, and
research/excavation of dozens of dinosaur skeletons. Robert
has appeared in a number of different dinosaur related
episodes for the National Geographic Channel, Discovery, PBS,
and others, and his scientific work has been published in
high-impact journals such as the Proceedings of the National
Academy of Sciences, Nature: Scientific Reports, and others.
Most recently, Robert has focused on a unique research site,
known as Tanis, that preserves evidence of a devastating
inundation wave and mass-death assemblage triggered by the
Chicxulub impact, a geologic snapshot of the first hours after
the impact. Joined by Walter Alvarez, Jan Smit, Florentin
Maurrasse, Phillip Manning, and other top scientists, Robert's
team is painstakingly documenting the biota that experienced
the last moments of the Cretaceous, in an effort to
more-precisely decode Earth's last mass extinction. This
research adds valuable dimension to our knowledge of the
Chicxulub event that killed 75% of species on Earth including
non-avian dinosaurs, but is also critical to understanding how
life as a whole responds to global-scale hazards. It can
therefore play a critical role in helping us to navigate the
current global ecological crisis. Robert has been an Adjunct
Professor in the Geosciences Department of Florida Atlantic
University for over 5 years, where the research continues to
this day.