Alexander von Humboldt and the Hand-Beast

The German naturalist F. W. H. Alexander von Humboldt (1769-1859) is today remembered as great geographer and explorer (maybe one of the most common names found on topographic maps is even Humboldt), but his education focused on mining engineering (and economy, as wished by his mother) and he made some important contributions to geology (for example the coined the term "formation") - however despite his interests in earth sciences, his contributions to palaeontology are rare and almost forgotten...

His geological education made him aware of the controversy surrounding the origin of fossil molluscs (still considered more as curiosities than valuable stratigraphic tools) and large vertebrates found in the Permafrost soils of Siberia. In 1789 he had the opportunity to have a look on the first fossil pterosaur skeleton.
During his famous expedition to America (visited from 1799 to 1804) he collected fossil bones and sent them to palaeontologist Cuvier. He also collected fossil molluscs for fellow German geologist Von Buch, and he even directed paleontological excavations near Bogotá.

In 1833 the school director and amateur archaeologist F. Sickler noted some strange depressions in a slab used in the laying of the foundation wall of a small garden house in the village of Hildburghausen (Germany). The slab was badly damaged and Sickler was not sure what this strange fossil may be. Sickler promised to the workers in the local sandstone quarries a reward if they could provide a better specimen - and so one year later Sickler was able to publish a short account on a new slab with three distinct types of footprints, maybe from some ancient amphibious animal. He "invited" the greatest geological minds of the time (including Humboldt) to study this strange fossil. The discovery excited a larger public, as some imprints resembled a human hand - today these ichnofossils are known as Chirotherium ("the hand-beast"). 

Fig.1. A mid-nineteenth century fanciful view of the unknown Triassic trackmakers: a labyrinthodont amphibian leaves a Chirotherium trackway watched by some primitive reptiles (from the Benjamin Waterhouse Hawkins archive, Natural History Museum, London).

Fig.5. The mid-nineteenth century fanciful view of the trackmakers: a labyrinthodont amphibian (centre) leaves a Chirotherium trackway watched by dicynodonts (left) and rhynchosaurs (right).
(B.W. Hawkins archive,The NaturalHistory Museum, London), - See more at: http://historyofgeology.fieldofscience.com/2011/01/ichnofacies-associations-of-bletterbach.html#sthash.l4qakhYF.dpuf

In a note read to the Academy of Sciences of the Institute of France in the year 1835 Humboldt made public his opinion on the mysterious fossils of Hildburghausen. He considered the imprints as real fossil trackways (some geologist, like Von Buch doubted at first this interpretation) and he considered the ancient trackmaker more similar to a mammal than an amphibian. Based on the toe configuration, Humboldt imagined at first a marsupial, possibly an arboreal possum-like creature (this idea was based on the imprint of - what Humboldt tough - an opposable toe in the Chirotherium tracks). Despite an expert in reptilian anatomy (he had observed caimans along the shores of the Orinoco and studied a Nile crocodile in an Italian collection) he didn´t recognize any similarities between Chirotherium and modern reptilian footprints. The identification of Chirotherium as fossil mammal tracks was at the time a scientific sensation, at it would have significantly pushed mammals into deep time (from the Tertiary to the Triassic). 

However Humboldt´s analysis attracted little interest by contemporary naturalists and the opinion of British palaeontologist Richard Owen - Chirotherium made by a larger reptile - prevailed. In fact even Humboldt in his later work "Cosmos" (published in various volumes between1845-1862) doesn´t mention his research on ichnofossils and even notes that the earliest mammals are found only in Jurassic sediments.
 

It´s not entirely clear why Humboldt, famous for his general interest in all earth sciences, showed so little interest in this subject. Maybe he considered his knowledge too limited, as his preliminary analysis was based only on a specimen displayed in the mineralogical cabinet of the Natural History Museum of Berlin, to engage in a scientific discussion. Maybe he was also more interested in presenting this puzzle to the scientific community, awaiting that others should solve this ancient mystery.

Bibliography:

KNOLL, F. (2009): Alexander von Humboldt and the hand-beast: A contribution to paleontology from the last universal scholar. C.R. Palevol Vol.8: 427-436

Chicxulub Catastrophism, or: Did Alvarez kill Lyell?

Charles Lyell was a great theorist. His Principles of Geology (12 editions between 1830 and 1875) offers his readers a world in equilibrium, where organic and inorganic processes interact and balance; where things move slowly and steadily and naturally within a long timescale.

During the Ordinary General Meeting of the British Geological Society in February 1831 Adam Sedgwick, as president, criticize harshly the geological model of Lyell. Sedgwick made it clear that he accepted the unchanging nature of the fundamental physical laws, but could not believe that 'those secondary combinations' that we call geological processes had remained constant throughout time".

It is clear from such statements that Lyell's Uniformatism was not strictly applied to geology during the 19th century, the "Ice Age" hypothesis was considered an extraordinary event, but finally accepted in a brief period of time.

Surprisingly there was much more aversions against catastrophic theories in the 20th century: the explanation of the Channeled Scablands in Northamerica as result of a cataclysmic flooding was rejected until the 1960s and 1970s, the role of impacts of extraterrestrial bodies for creating craters on the Moon was underestimated until 1960, even more their impact on Earth.

Until 50 years ago it was believed that a characteristic of the Cretaceous-Palaeogene (C/Pg) transition is the apparent lack of a complete stratigraphic record, and until the decade between 1960 and 1970, with the discovery by Alvarez in the gorge of Gubbio, it was believed that the upper limit of the Cretaceous had gone eroded and lost forever.
Alvarez tried to date the sediments of the "Scaglia rossa" formation outcropping in the gorge by the accumulation of rare elements, which in a constant rate reach the earth through micrometeorites and become incorporated in the turbidite deposits. During this research he discovered the today well-known iridium anomaly.

Fig.1. The famous transition between Cretaceous (lower part) and Paleocene (upper part) Scaglia Rossa, in the gorge of Gubbio, foto rotated by 90 degrees.

The origin of this anomalous concentration of element at first remained unknown, a possible explanation, apart from a slow sedimentation resulting in an apparent concentration of micrometeorites, was the impact of a large extraterrestrial mass with a high concentration of these elements.
But there was no further evidence to confirm this hypothesis.

In 1981 Antonio Camargo-Zanoguera and Glen Penfield during a geophysical conference presented their research on a geological mystery discovered 30 years earlier during surveys on the Yucatan peninsula. The two researchers proposed a new interpretation of a circular structure revealed by seismic investigations and buried under 300 to 1.000 meters of sediment, considered of volcanic origin. But their hypothesis - that it was an impact structure - aroused little interest.

Only 10 years later, researchers from the University of Arizona began to study the crater and obtained the first absolute dates, with an age of 65 millions of years. Further research in 1993 revealed that the structure was in fact an impact crater displaying a complex structure with a central bulb surrounded by concentric circles, reaching a total diameter of 180 km.
The crater was called Chicxulub - "the devil's tail".

Alvarez, who had continued his research on the impact hypothesis, noted the temporal coincidence of the iridium anomaly and the Chicxulub-impact, and proposed that it was the searched culprit of the C-Pg event.
Based on these geological evidences, the limit between the Cretaceous and the Palaeogene in 1995 was defined at the stratotype (GSSP) of El Kef (Tunisia), coinciding with the peak of iridium and the mass extinction of foraminifera at the base of a clay layer (C / Pg boundary clay) deposited after the impact as result of decreased organic productivity in the oceans.
With the alleged importance of the impact as a time marker and the solution to the mystery of the extinction of dinosaurs, an extensive research on the Chicxulub site began. The Yaxcopoil -1 core was recuperated in Mexico during the Chicxulub Scientific Drilling Project, to study the stratigraphy of the crater and its sediment infill.
Sediments were recovered from an intervall between 400 to 1.511m depth. Up to 795m carbonatic silt- and sandstone prevail, followed by 100m of breccias, interpreted as by the impact fractured rock.
Fig.2. Yaxcopoil-1 stratigraphy with the impact breccias between the 795-895m interval (black bar on the left), after TUCHSCHERER et al. 2004.

The melt enclosed in the impact breccia has been dated by the argon method to an age of 65 million years, also zircon crystals and glass ejected from the crater and deposited on the surface of earth have been dated to an age of 65, 07 + -0.1 Ma. But the recovered core also showed two prominent stratigraphic gaps between the Upper Cretaceous (Maastrichtian) and the lower Paleocene (Danian).

More than 350 sites are today known recording the C/Pg transition, and displaying a typical sedimentary succession: a layer that varies in thickness and composition according to the distance from the point of impact.
To a distance of 500km this ejecta layer is very thick, around the crater it reaches a thickness of 100 to 80m! (Proximal facies 1).
Between 500 to 1.000km the sediments are typical for tsunami deposits - thick layers of several centimetres containing lens with clasts and spherules, transported by the waves from the impact point (proximal facies 2).
With increasing distance, the layer thins out to form the known iridium rich clay overlying a layer with small spherules (intermediate facies).
Over a distance of 5.000km the event is represented by a layer of red clay (distal facies) that still contains traces of the material ejected from the crater (at the basis of this layer the C/Pg limit of the El Kef section is defined).

This sequence is consistent with the location of the Chicxulub crater on the Yucatan Peninsula as the source of the sediments.

Fig.3. Distribution of the global offshore drilling sites that have returned sedimentological structures related to the impact of Chicxulub (asterisk).
Magenta: proximal facies 1 (distance of 500km)
Red: proximal facies 2 (distance of 1.000km)
Orange: intermediate facies (distance of 5.000km)
Yellow: distal facies (distance more than 5.000km)
Below the schematic sequence of facies associations (from SCHULTE et al. 2010).

The geological evidence supports the hypothesis that large extraterrestrial bodies can impact on earth, but it's a whole other problem how Chicxulub is related to the extinction of the Mesozoic fauna.
One of the most intriguing aspects of the impact model is the apparent explanation of the Mass Extinction at the Cretaceous-Palaeogene Boundary.
According to this model the selective extinction was caused mainly by the consequences of the impact: the release of large quantities of gas from the vaporized rocks, rich in carbonates and sulphates, changed the global climate, causing a "nuclear winter" with fire storms, followed by low temperatures, diminished solar irradiation and acid rain. Depending on the locality and the ecological niche that a species occupied, and a good dose of luck, these changes decided the specie's fate - to adapt or become extinct. Most of this scenario however is speculative - despite the strong media presence of the crater of doom explanation, the biotic effects of impacts and the response of organisms and ecosystems to such an event are still unknown or at best controversial.

As for Alvarez, the "father" of the C / Pg event, he certainly does not show modesty, so in 2009 he writes:

"Geologists could no longer doubt the reality of catastrophic impact events. The KT impact, first recognized at Gubbio, was a truly catastrophic event in Earth history, whose history is written in detail in the rock record. It correlates with, and probably caused, the great mass extinction 65 Ma. After a century and a half, the uncompromising uniformitarian gradualism of Lyell was dead."

Fig.4. "Cretaceous diary" in the little inn in the gorge of Gubbio.

Bibliography:

ALVAREZ, W., ALVAREZ, L.W., ASARO, F. & MICHELl, H.V. (1979): Anomalous iridium levels at the Cretaceous/Tertiary boundary at Gubbio, Italy: Negative results of tests for a supernova origin. In: Cretaceous-Tertiary Boundary Events Symposium; II. Proceedings (Eds W.K. Christensen and T. Birkelund), pp. 69. University of Copenhagen
ALVAREZ, L.W., ALVAREZ, W., ASARO, F. & MICHEL, H.V. (1980): Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208: 1095-1108
ALVAREZ, W. (2009): The historical record in the Scaglia limestone at Gubbio: magnetic reversals and the Cretaceous-Tertiary mass extinction. Sedimentology 56: 137-148; doi: 10.1111/j.1365-3091.2008.01010.x
ARENILLAS, I.; ARZ, J.A.; GRAJALES-NISHIMURA, J.M.; MURILLO-MUNETON, G.; ALVAREZ, W.; CAMARGO-ZANOGUERA, A.; MOLINA, E. & ROSALES-DOMINGUEZ, C. (2006): Chicxulub impact event is Cretaceous/Paleogene boundary in age: New micropaleontological evidence. Earth and Planetary Science Letters 249: 241-257 doi:10.1016/j.epsl.2006.07.020
BAKER, V.R. (1998): Catastrophism and uniformitarianism" logical roots and current relevance in geology. In: BLUNDELL, D. J. & ScoTt, A. C. (eds) Lvell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143: 171-182
FRENCH, B.M. (2003): Traces of Catastrophes: A handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. Lunar and planetary Institute
KELLER, G.; ADATTE, T.; STINNESBECK, W.; REBOLLEDO-VIEYRA, M.; FUCUGAUCHI, J.U.; KRAMAR, U. & STÜBEN, D. (2004): Chicxulub impact predates the K-T boundary mass extinction. PNAS 101(11): 3753-3758 doi/10.1073/pnas.0400396101
KELLER, G.; ABRAMOVICH, S.; BERNER, Z. & ADATTE, T. (2009): Biotic effects of the Chicxulub impact, K-T catastrophe and sea level change in Texas. Paleogeography, Paleoclimatology, Paleoecology 271:52-68
SCHULTE et al. (2010): The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary. Science 327(5970): 1214 - 1218
THACKRAY, J.C. (1998): Charles Lyell and the Geological Society. In: BLUNDELL, D. J. & SCOTT, A. C. (eds) Lyell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143: 17-20
TUCHSCHERER, M.G.; REIMOLD, W.U.; KOEBERL, C. & GIBSON, R.L. (2004): Major and trace element characteristics of impactites from the Yaxcopoil-1 borehole, Chicxulub structure, Mexico. Meteoritics & Planetary Science 39(6): 955-978

History of Paleomammology: Ex Africa Semper Aliquid Novum

To celebrate the soccer world championship in a geological manner, the story of an extraordinary naturalists on the tracks of mammal ancestors in an extraordinary land: South Africa:

Robert Broom was born in 1866 in the town of Paisley, Scotland, and after graduating in medicine in 1887 undertook several "world"-trips to satisfy his passion: the search for fossils. Doctor by profession, he devoted himself to several paleontological problems in his long career.

In the first years after completing his degree he became interested in the origin of mammals, and so in 1892 he travelled to Australia, where he studied the fossils and the anatomy of modern marsupials, on which he published important contributions. Broom returned to Scotland in 1896, after some problems with the Australian bureaucracy caused by his passion.
After seeing the fossils of the Karoo region exposed in the British Museum, he decided to visit this region. In 1897 he emigrated to South Africa to study the sediments of the Karoo - a semi-arid highland region in South Africa.

Fig.1. Scheme of the Strata in South Africa, from SCHWARTZ 1912.
The Karoo Supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern Gondwana. The strata record 100 million years of almost continuous sediment accumulation from the Permo-Carboniferous (300 Ma) through to the Early Jurassic (190 Ma) under a range of climatic regimes and within several tectonically controlled sub-basins.
Alluvial sediments dominate the succession from the Late Permian onwards. Fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten-fold biostratigraphic subdivision of these strata. The Permian/ Triassic boundary in the Karoo succession is marked by a major extinction of the herbivorous dicynodonts which co-incides with a rapid change in fluvial facies, evidence of environmental changes that may have caused the tetrapod extinctions in the main Karoo Basin (SMITH 1995).

Broom opened a private ambulatory in a small town, not to far from Cape Town, the capital of South Africa. Always looking for new discoveries, he repeatedly changed his place of residence, and in his spare time went to look for fossils, so in 1903 he discovered the remains of the sauropod Algosaurus.
In the Karoo sequence, ranging in age from the Carboniferous to the Jurassic, he discovered and described various species of therapsids. This important work will result in a nomination as zoology and geology professor at the University of Stellenbosch in Cape Town. He remained there until 1909, when a change of government, and new problems with the management of the University, convinced him to return to London.
For a certain period, he shuttled between New York and South Africa. Only from 1916 onwards Broom devoted himself again mainly to the fossils of Karoo, on which he continued to publish extensively.

Fig.2. Fossils of the stratigraphic succession of the Karoo, from a print of 1909.

In the later years of his life, from 1936 onwards, he will discover the human evolution as a prolific field of interest; his most important discoveries in this phase are the remains of hominids in the karst caves of South Africa, including Mrs. Ples - Plesianthropus transvaalensis (today Australopithecus africanus).

Fig.3. Dr. Robert Broom, along with "Mrs. Ples" (image from KOHRING & SCHLÜTER 2004).

Broom has been described as a difficult personality with many "strange" habits.
When searching for fossils, he always went in suit and with tie, but ongoing discovering fossils, he wrapped them in his clothes, and it could happen that he came back home only in his underwear and shoes .
The ladies of the library of the University did follow a strict rule not to accompany him alone, because he had a bad reputation as a "womanizer."
In his life he wrote at least 450 publications, but this productivity had also its drawbacks, he was very hasty in his work, and many species described by Broom are defined very superficially. The figures in his publications are very typical, hastily drawn lines "thrown" on paper very quickly.

Fig.4. Bauria cynops, species described by Broom in 1937, the drawing shows the typical style used by Broom with his sketches, figure from here.

Broom died on 16. Aprile 1951, after a remarkable career - including five honorary degrees, medals, and the myth has it that his last words refer to his great monograph on the hominids (The South African Fossil Ape-Men - the Australopithecinae) "Now that's finished ... and so am I."

References:

KOHRING, R. & SCHLÜTER, T. (2004): Große Paläontologen: Robert Broom (1866-1951). Fossilien - Zeitschrift für Hobbpaläontologen. Heft 1 Jän./Feb.2004: 26-29
ROGERS, A,W, & DU TOIT, A.L. (1909): An Introduction to the Geology of Cape Colony. With a chapter on the fossil reptiles of the Karroo Formation by R. Broom. With Illustrations and coloured Map. Longmans Green, and Co.; London.
SCHWARZ, E.H.L. (1912): South African Geology. Blackie & Son Limited; London.
SMITH, R.M.H. (1995): Changing fluvial environments across the Permian-Triassic boundary in the Karoo Basin, South Africa and possible causes of tetrapod extinctions. Palaeogeography, Palaeoclimatology, Palaeoecology 117: 81-104