Tanis (fossil site)

File:Tanis fossil site, fish with ejecta clustered in the gill region.jpg

Fossil fish from Tanis. The fossil shows microtektites (molten splattered glass droplets) which are a chemical match for ejecta from the Chicxulub meteor crater. The microtektites are clustered in large numbers in the fish's gill rakers, and show that the fish was alive at the time that the impact occurred.

Tanis is the name given to a paleontology site in southwestern North Dakota, USA. Tanis is part of the heavily-studied Hell Creek Formation, a well known site for dinosaur fossils from the Upper Cretaceous and lower Paleocene. It was discovered and its significance identified by Robert DePalma, and the published papers describing it are co-authored by several luminaries famous in their respective fields, including Walter Alvarez, the original proponent of the KPg impact extinction theory. Summary descriptions of the site and some of its findings were presented in two papers by dePalma and co-author Jan Smit in October 2017, and the full pre-publication paper describing Tanis was widely covered in the worldwide media on 29 March 2019 prior to release 3 days later.

Tanis is described as an extraordinary and unique site, because it appears to capture in extreme detail the events from just minutes or hours after the impact of the giant Chicxulub meteor which struck the Gulf of Mexico about 66 million years ago, wiping out all non-avian dinosaurs and many other species, and ultimately paving the way for mammals - including human beings - to dominate the earth at the present time.

The Cretaceous–Paleogene extinction event (the "KPg extinction" or "KT extinction") is marked around the earth by a layer of Iridium, an element rare on earth but common in meteors, and the event is widely accepted as being due to the impact of a meteor in Mexico. At Tanis, unlike any other known site, it appears that freak circumstances preserved exquisite details from the actual impact event itself, and the minutes and hours after it. It is believed that early seismic waves from the impact's massive earthquakes caused seiche waves (mass water movement) in the water at Tanis. These seiche waves exposed and covered the riverbed at least twice, at almost exactly the same time that debris from the impact was raining down, and almost immediately covered them again. Animals and plant material are preserved in 3 dimensional detail and at times upright, rather than pressed flat as usual, their remains thrown together by the massive wave movements, salt and freshwater fish and marine reptiles are found together miles inland, with microtektites (molten debris splattered high into the atmosphere from the impact) embedded in their gills as they tried to breath, millions of "near perfect" primary (not reworked) microtektites are found buried contemporaneous to the fossils in their own impact holes in the soft riverbed mud and also preserved in amber on tree-trunks, large primitive feathers 30-40cm long with 3.5mm quills are believed to come from large dinosaurs, and tiny inhabited burrows are found from some of the first mammals in the area after the impact.

The exceptional nature of the findings and conclusions have led some scientists to await further scrutiny by the scientific community before agreeing that the discoveries at Tanis have been correctly understood, and the site continues to be explored at the present time.

Background

Main articles: Cretaceous–Paleogene extinction event, Chicxulub impactor, Chicxulub crater, and Hell Creek Formation

The KPg extinction event

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Location of Chicxulub crater, Mexico

KPg boundary sample from Wyoming. The intermediate claystone layer contains 1000 times more iridium than the upper and lower layers (San Diego Natural History Museum).

Around 66 million years ago, a mass extinction event took place, known as the Cretaceous–Paleogene ("KPg" or "KT") extinction event. The event wiped out all non-avian dinosaurs and many other species, and paved the way for mammals and eventually human beings to dominate the earth at the present time. It is now widely accepted that the cause of the extinction was a huge meteor, which impacted the earth in the shallow seas of the Gulf of Mexico, giving rise to the Chicxulub crater. The impactor is believed to have been between 11 to 81 kilometres (7 to 50 mi) in diameter and having a mass between 1.0 x 10¹⁵ and 4.6 x 10¹⁷ kilograms (between 1.0 and 460 trillion tons - the mass of the earth is about 6 x 10²⁴kg, or between 13 million and 6 billion times as large). It tore through the earth's crust, creating huge earthquakes and giant waves and a crater 180 kilometers (112 mi) wide. It also sent trillions of tons of dust, debris and climate-changing sulphates (from the gypsum seabed) into the atmosphere, and may have created firestorms worldwide. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.

The meteor impact theory was proposed by father and son team Luis and Walter Alvarez in 1980. Today, a large body of evidence ties the Chibilux impact crater to the extinction event. The impact left a layer of iridium-rich deposit around the world, in the geological record - an element rare on earth but often found in meteors. The crater's peak ring was drilled beneath the sea in 2016, and the results showed that the rock comprising the peak ring had been shocked by immense pressure and melted in just minutes from its usual state into its present form. Unlike nearby sea-floor deposits, the peak ring was made of granite originating much deeper in the earth, which had been ejected to the surface by the impact. Gypsum is a sulfate-containing rock usually present in the shallow seabed of the region; it had been almost entirely removed, vaporized into the atmosphere. Further, the event was immediately followed by a megatsunami (a massive surge of water due to landslide or impact), which had caused sufficiently immense waves to lay down the largest discovered graduated sand layers (separated by grain size) directly above the peak ring.

These findings strongly support the impact's role in the extinction event. The impactor was large enough to create a 190-kilometer-wide (120 mi) peak ring, to melt, shock, and eject deep granite, to create colossal water movements, and to eject trillions of tons of vaporized rock and sulfates into the atmosphere, where they would have persisted for a long time. This worldwide dispersal of dust and sulfates would have affected climate catastrophically, led to large temperature drops, and devastated the food chain.

However, because it is rare in any case for animals and plants to be fossilized, the fossil record leaves some major questions unanswered. One of these is whether dinosaurs were already declining at the time of the event (due to other ongoing climate change), and the exact details of how the event affected Earth and its biosphere. No fossil beds were yet known, which could clearly show the details that might resolve these questions. There is considerable detail for times greater than hundreds of thousands of years either side of the event, and for certain kinds of change either side of the KPg boundary layer. But relatively little fine detail is available from times nearer to the event itself, and very little detail indeed is available in the fossil record, from the time of the impact itself and immediately afterwards. This is known as the "Three metre problem" - the fossil record is frustratingly incomplete at that time, in fine detail.

Hell Creek Formation

The Hell Creek Formation is a well-known and heavily studied fossil-bearing formation (geological region) of mostly Upper Cretaceous and some lower Paleocene rock, that stretches across portions of Montana, North Dakota, South Dakota, and Wyoming in North America. It is named for exposures studied along Hell Creek, near Jordan, Montana. It was designated as a National Natural Landmark in 1966.

The formation contains a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian and Danian (respectively, the end of the Cretaceous and the beginning of the Paleogene periods) by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The iridium-enriched Cretaceous–Paleogene boundary, which separates the Cretaceous from the Cenozoic, is distinctly visible as a discontinuous thin marker above and occasionally within the formation. Numerous famous fossils of plants and animals, including many types of dinosaur fossils, have been discovered there.

At the time of the Chicxulub impact, the present-day North American continent was still forming. Most of central North America had recently been a large shallow seaway, called the Western Interior Seaway (also known as the North American Sea or the Western Interior Sea), and parts were still submerged. This had initially been a seaway between separate continents, but the seaway had narrowed in the late Cretaceous to become, in effect, a large inland extension to the Gulf of Mexico. The Hell Creek Formation was a region which was partly very low-lying land not far from the shore, and partly still submerged or partly submerged, at the northern end of this area, and the Chicxulub impact occurred in the shallow seas at the southern end.

Although Tanis and Chixculub were closely related by the Inland Seaway, the massive water waves from the impact area were probably not responsible for the deposits at Tanis. They would have arrived hours later, long after the microtektites had already fallen fell back to earth, and far too late to leave the geological record found at the site. Instead much faster earthquake waves, travelling through the earth itself, are believed to have caused surging water movements known as seiches in the shallow waters close to Tanis within minutes to less than an hour from impact.^{Exact time needed from paper}

Robert DePalma

Skeletal replica of a Dakotaraptor compared in size with a human. The description of this species by DePalma drew criticism due to the interpretation of turtle bones as being a furculum of the dinosaur

Robert DePalma is a lifelong paleontologist, described in media articles as a "graduate student in paleontology at the University of Kansas", and described by The New Yorker as the "unpaid curator of vertebrate paleontology at the Palm Beach Museum of Natural History" (a nascent museum), and as having no especial standing in the world of paleontology. A 2013 paper he published gained wide coverage when he presented a tyrannosaur tooth embedded in a hadrosaur tail, showing that tyrannosaurs were indeed hunters rather than pure scavengers - a controversy at the time. On the other hand a second paper was criticized in 2015 and corrected in 2016, after other scientists noticed that in his reconstruction of a new species he called Dakotaraptor, he had accidentally also included turtle entoplastron (armour) fragments in error, taking them to be part of the fossilised furculum. As a result, among the few who knew of him, some felt he might be prone to "overinterpret".

DePalma curates his museum, the Palm Beach Museum of Natural History, through which he does his research. The museum lacks public exhibition space, and Rudy Pascucci is the director. His practices in managing the institution are considered non-standard. These include his direct control over the specimens he discovers, as opposed to the usual practice of ceding specimen ownership to the institution itself. Federally unfunded, he pays costs himself and helps this funding through the selling of specimen replicas to owners of private collections. Private collections are largely considered a bad influence on palaeontology, and curators of larger museums are not allowed to possess any. DePalma's treatment of his finds has therefore been controversial, but he defends his methods. Discoveries from Tanis have been kept in a lab at the Palm Beach Museum of Natural History.

In 2004, DePalma was studying a small site in the well-known Hell Creek Formation, containing numerous layers of thin sediment, creating a geological record of great detail. His advisor suggested seeking a similar site, closer to the KPg boundary layer. Hells Creek is largely privately owned land, so access for digging is usually on a commercial basis. A site was offered to him by a disappointed fossil collector, which lacked the fine sediment layers he had sought. Instead, the layers had never solidified, and everything appeared to have been laid down in one single large flood.

Discovery and exploration of 'Tanis'

File:Tanis fossil site, locator map and layout.jpg

Tanis location, schematic layout, and photo, showing: (1) Impact event deposits, covering (2) the slope of a prograding point bar of a river meander (bend). (3) Densest accumulations of fossil carcasses. (4) KPg boundary tonstein which directly overlays the impact deposit, and (5) directly overlays the adjacent river overbank. (6) location of Brooke Butte, the closest KPg outcrop to Tanis.

Inset: Tanis at time of impact. The site is some miles from a large inland sea connected to the Gulf of Mexico.

From dePalma et al 2019

Initially disappointed at his new site, DePalma began excavating and quickly found it to contain very unusual and promising features. Everything he found, had been covered so quickly that details were exceptionally well preserved, and the fossils as a whole formed a very unusual collection - fish fins and complete fish, tree trunks with amber, fossils in upright rather than squashed flat positions, skeletons of freshwater paddlefish and saltwater mosasaurs which had ended up on the same mud bank miles inland, fragile body parts such as complete and intact tails, ripped from the seafish's bodies and preserved miles inland in a manner that suggested they were covered almost immediately after death, and everywhere, millions of tiny spheres of glassy material known as microtektites, the result of tiny splatters of molten material reaching the ground. The microtektites were present in the gills of fossilized fish, in amber, and buried in the small pits in the mud which they had made when they contemporaneously impacted.

Later discoveries included large primitive feathers 30-40cm long with 3.5mm quills believed to come from large dinosaurs and burrows of small mammals living at the site immediately after the impact, and analysis of early samples showed that the microtektites at Tanis were almost identical to those found at the impact site, and were likely to be primary deposits (directly from the impact) and not reworked (moved from their original location by later geological processes).

DePalma quickly began to suspect that he had stumbled upon a monumentally important and unique site - not just "near" the KPg boundary, but a unique site and killing field that captured the actual minutes and hours after impact, when the KPg boundary was actually created, along with an unprecedented fossil record of creatures and plants that died on that day, and material directly from the impact itself, in circumstances that allowed exceptional preservation.

When I saw that [microtektites in their own impact craters], I knew this wasn’t just any flood deposit. We weren’t just near the KT boundary. This whole site is the KT boundary ... We have the whole KT event preserved in these sediments. With this deposit, we can chart what happened the day the Cretaceous died.

— Robert dePalma

It is truly a magnificent site ... surely one of the best sites ever found for telling just what happened on the day of the impact.

— Water Alvarez

By 2013, he was still studying the site, which he named 'Tanis' after the ancient Egyptian city of the same name, and had told only 3 close colleagues about it. Tanis' secrecy was maintained until disclosed by dePalma and co-author Jan Smit in two short summary papers presented in October 2017, but records of news media and websites show no reference to any fossil discovery or research by dePalma other than these, prior to widespread media coverage of the full prepublication paper on 29 March 2019.

PNAS Paper published in 2019

Initial papers at GSA Conference, 2017

Eighteen months prior to publication of the peer-reviewed PNAS paper in 2019 dePalma and his colleagues presented two conference papers on fossil finds at Tanis on 23 October 2017 at the annual meeting of the Geological Society of America. Jan Smit first presented a paper describing the Tanis site, its association with the Cretaceous-Paleogene boundary event and associated fossil discoveries, including the presence of glass spherules from the Chicxulub impact clustered in the gill rakers of acipenciform fishes and also found in amber. dePalma then presented a paper describing excavation of a burrow created by a small mammal that had been made "immediately following the KPg impact" at Tanis.

Prepublication and authorship

A paper documenting Tanis was released as a pre-publication on 1 April 2019, with widespread media coverage from 29 March 2019.

dePalma's co-authors include luminaries such as Jan Smit (paleontologist and authority on the KPg impact) and Walter Alvarez (professor and co-developer with his father of the KPg impact theory). Other authors are his advisor David Burnham, Klaudia Kuiper (professor of geochronology focusing on chronology of the late Cretaceous), Phillip Manning (professor of natural sciences, specialist in soft tissue scanning), Anton Oleinik (associate professor geosciences, specializing in Cenozoic periods of change and stratigraphy), Peter Larson (paleontologist and fossil collector), Florentin Maurrasse (professor specializing in stratigraphy and biostratigraphy, and the KPg boundary in the Carribean), Johan Vellekoop (postdoctoral researcher, published on microfossil record of the Chicxulub impactor), Mark Richards (professor earth and planetary sciences, focus on earth crust tectonic and dynamic processes), and Loren Gurche (a colleague at the Palm Beach Museum of Natural History). A wide range of other people are credited with analysis, specific studies, and other contributions