The Method of the Multiple Working Hypotheses: Why Disagreement Between Scientists is a Good and Necessary Thing.

Young Earth Creationists don't understand how science works - and they do their best to communicate that misunderstanding to their audience.

The Great American Biotic Interchange

The latest issue of Journal of Creation arrived today. In it is an article by Michael J. Oard that immediately grabbed my attention: "The Great American Biotic Interchange pushed back over 10 million years". The GABI, as it is called for short, is the period of time when large numbers of species went from North America into South America, while other species came from South America into North America. This took place once the Panamanian land bridge was established, some time between 3 and 5 million years ago. We have long known that a very few species made the trip prior to the bridge being established, notably two lineages of giant ground sloths coming from south to north, and one carnivore, a relative of the raccoon, going from north to south.

The claim that the GABI has been pushed back 10 million years is based on an extensive fossil fauna from the Rio Acre region of western Amazonia State, in Brazil. Of the thousands of fossils collected, representing 41 species of mammals, only one single species, represented by a partial skeleton of an elephant, was discovered in 1991, and named Amahuacatherium peruvium by Pittman-Romero in 1996. Amahuacatherium was until recently, the only mammal with North American affinities from the Rio Acre fauna.  Campbell and his colleagues determined its age to be late Miocene, between 9 and 10 million years ago (See Figure 1).

Figure 1, adapted from Campbell, K. E., Jr., Frailey, C. D., Romero-Pittman, L. (2009): In defense of Amahuacatherium (Proboscidea:Gomphotheridae. N. Jb. Geol. Palaont. Abh. Vol.252(1): Figure 4.

The close resemblance between Amahuacatherium (A) and Haplomastodon (C) is readily apparent. 

Subsequently, most paleontologists have disagreed with this on two bases: first, that the fossil is identical to Pleistocene specimens of the well known gomphothere Haplomastodon, and second, that the fossil was recovered from deposits which have not been tied to the dated stratigraphy of the region, which contains many small areas of Pleistocene deposits in addition to the Miocene deposits. 

Recently, these same authors, perhaps influenced by their desire to support a Late Miocene date for a "first pulse" of the GABI, were led to describe what I and other paleontologists believe to be a Pleistocene cervid as the first known South American dromomerycid, a horned ruminant well known from North America. They had at first claimed an associated fragmentary horn, which I and others pointed out was actually a tortoise scapula.

Figure 2.  Mandible of Sudameryx acrensis (type) from Prothero, D. R., Campbell, K.E. Jr., Beatty, B. L and Frailey, C. D., (2014):New late Miocene dromomerycine artiodactyl from the Amazon Basin: Implications for interchange dynamics, Journal of Paleontology: Figure 2.

A number of paleontologists, including me, believe this to be a modern cervid of at most Pleistocene age.  Some pretty sharp paleontologists believe it to be a dromomerycid.  The collecting of further material representing this taxon, and better dating of the sediments, will help resolve this question.

So it is on somewhat shaky grounds, contested by many paleontologists, that this claim rests, and on which Oard bases his comments.

Of course, Oard's conclusion is the predictable Creationist accusation that if there is this sort of controversy among evolutionists, then none of their claims can be relied upon. Oard throws in, at the very end, that recently zircons have been described from basins and rivers in the northern Andes, some of which may have had their origin in Panama about 13 -15 million years ago.

What Oard misses, of course, is that the overall concept of the GABI is still valid - even if such early dates for some Interchange animals were confirmed. The majority of the migrants from South America show up in central Mexico around 3.5 million years ago, and in the southern United States around 2.5 million years ago. Those going into South America show up mostly in the very latest Pliocene and earliest Pleistocene at about the same time. That some made it across earlier does not invalidate that scenario.

Note also that Oard does not quote the scientific paper on the zircons, but rather the teaser from the Prospectives section of that issue of Science. The actual article is worded rather less certainly than Oard would like:

"The Central American Seaway, which once separated the Panama Arc from South America, may have closed 10 million years earlier than is believed. Montes et al. report that certain minerals of Panamanian provenance began to appear in South America during the Middle Miocene, 15 to 13 million years ago (see the Perspective by Hoorn and Flantua). The presence of the minerals indicates that rivers were flowing from the Panama Arc into the shallow marine basins of northern South America. One interpretation of this finding is that large-scale ocean flow between the Atlantic and Pacific had ended by then. If this is true, then many models of paleo-ocean circulation and biotic exchange between the Americas need to be reconsidered."

"Abstract

Uranium-lead geochronology in detrital zircons and provenance analyses in eight boreholes and two surface stratigraphic sections in the northern Andes provide insight into the time of closure of the Central American Seaway. The timing of this closure has been correlated with Plio-Pleistocene global oceanographic, atmospheric, and biotic events. We found that a uniquely Panamanian Eocene detrital zircon fingerprint is pronounced in middle Miocene fluvial and shallow marine strata cropping out in the northern Andes but is absent in underlying lower Miocene and Oligocene strata. We contend that this fingerprint demonstrates a fluvial connection, and therefore the absence of an intervening seaway, between the Panama arc and South America in middle Miocene times; the Central American Seaway had vanished by that time.

Oard asks (following Hoorn and Flantua), if a land bridge existed 13-15 million years ago, "...why did many organisms wait until migrating around 3 million years ago?" Aside from the distances involved, and the very different ecological zones which had to be crossed, I suppose the real answer is that the GABI critters did not have the convenience of the Noachian Ark to ferry them up along the coast in less than a year.

Now, what is it that so upsets Creationist Michael J. Oard?  Even a cursory reading of his short article quickly reveals the source of his discomfort:  Uncertainty.  For someone used to the absolute certainty he invests in the Biblical account of Genesis (and, indeed, all of the Bible) at least according to his interpretation of the texts, and their infallibility, the uncertainty that is an integral part of science seems to make Oard very uneasy, indeed.  His comments reveal this:  "Since a presumed 'factual' tie point has been challenged......" and "The controversy over this date is at least showing how arbitrary this tie point is and how delicate is uniformitarian chronology."   His conclusion:  "It is best that creation scientists not take these 'events'....seriously, even in a relative timescale."

And don't forget - if science can't agree on a date, and it keeps changing, then nothing science says is true, and Young Earth Creationism wins by default. According to them, of course.

Oard, and other Creationists would do well to re-read an old but very appropriate description of how science works written by T. C. Chamberlain in Science in 1890, entitled "The Method of the Multiple Working Hypotheses".  Chamberlain tells us that the method of the multiple working hypotheses differs from the simple working hypothesis in that it distributes the effort and divides the affections [for any one particular explanation]...... The effort is to bring up into review every rational explanation of the phenomenon in hand and to develop every tenable hypothesis relative to its nature..."

Thus, we have several levels of this at work in therms of the GABI.  We have differing ideas on the identity of the gomphothere from the Rio Acre deposits; we have differing ideas concerning its age. These will gradually be decided when further collecting and dating gives us sufficient information to favor one interpretation over the other.  That the Great American Biotic Interchange was a process that took place over several million years is really not in question. The date when the Panamanian Land Bridge became established remains to be decided.

References:

Campbell, K. E., Jr., Frailey, C. D. & Romero-Pittman,
L. (2000): The late Miocene gomphothere Amahuacatherium
peruvium (Proboscidea: Gomphotheriidae) from
Amazonian Peru: Implications for the Great American
Faunal Interchange. – Instituto Geológico Minero y
Metalúrgico, Serie D: Estudios Regionales, Boletín, 23:
1-152.

Campbell, K. E., Jr., Heizler, M., Frailey C. D., Romero-Pittman,L.
& Prothero, D. R. (2001): Upper Cenozoic
chronostratigraphy of the southwestern Amazon
Basin. – Geology, 29: 595-598

Campbell, K. E., Jr., Frailey, C. D., Romero-Pittman, L. (2009): In defense of Amahuacatherium (Proboscidea:Gomphotheridae. N. Jb. Geol. Palaont. Abh. Vol.252(1):113-128.

Hoorn, C and Flatuna, S. (2015): An early start for the Panamanian land bridge. Science 348:186-187.

Montes, C et al (2015): Middle Miocene closure of the Central American Seaway, Science:Vol 348, Issue 6231:226-229.

Ord, Michael J. 2016, The Great American Biotic Interchange pushed back over 10 million years, Journal of Creation, Volume 30(3): 14-15.

Prothero, D. R., Campbell, K.E. Jr., Beatty, B. L and Frailey, C. D., (2014):New late Miocene dromomerycine artiodactyl from the Amazon Basin: Implications for interchange dynamics, Journal of Paleontology.

Romero-Pittman L. (1996): Paleontología de Vertebrados.
– Instituto Geológico Minero y Metalúrgico, Carta
Geológica Nacional, Boletín, Serie A, No. 81, 171-178

The March of Perfidy: Collapse of a Creationist Trope

I would be most surprised indeed if any of my readers has never seen the famous "March of Progress" illustration from Time-Life Books volume Early Man (1965).  Drawn by master scientific illustrator Rudolph Zallinger, it depicts, in an unfortunately misleading linear fashion, 15 species of primates beginning with Pliopithecus on the left and ending with Homo sapiens on the right.

Yes, we know evolution isn't linear, and yes this illustration has been misunderstood - unfairly so, since the authors of the book clearly understood the nature of evolutionary process and commented in the text that it was not a linear progression, and that several of the species were evolutionary dead ends rather than direct human ancestors.  But that isn't what this essay is about.

Those of us engaged in the debate with Young Earth Creationists have come to be familiar with a similar, but radically different version of the March of Progress created by by Jack Chick for his infamous 1972 Creationist tract, Big Daddy, which can be seen by clicking here.

Presented as a linear illustration in the original Chick Tract, it depicts nine primate species supposedly relied upon by paleontologists and paleoanthropologists to bolster their claim that humans evolved from primate ancestors.  I call this the March of Perifidy in recognition of the deception and inaccuracy it represents.

It most often is seen today stacked as the illustration at left, to better fit into the ubiquitous meme format and in website layouts.

We cringe when we see it, for each and every one of the images is a misrepresentation.  What is of considerable interest is trying to trace where Creationists got the misinformation that fills this graphic.  In most cases, we can trace it back - to earlier Creationist claims, and ultimately to the kernel of truth which lies at the beginning.

Left to right (or perhaps left to wrong would be more appropriate here) they are listed below in Table 1, showing the commentary under each picture, and the status  of that species or subspecies as understood today.

Name in Chart	Claim by Creationists	Modern Disposition
Lucy	Nearly all experts agree Lucy was just a 3-foot tall chimpanzee.	Australopithecus afarensis
Heidelberg Man	Built from a jaw bone that was conceded by many to be quite human	Homo heidelbergensis
Nebraska Man	Scientifically built up from one tooth, later found to be the tooth of an extinct pig.	Misidentification of a fossil peccary tooth of Prosthennops crassigenus
Piltdown Man	The jaw bone turned out to belong to a modern ape.	Hoax
Peking Man	Supposedly 500,000 years old, but all evidence has disappeared.	Homo erectus
Neanderthal Man	At the Int'l. Congress of Zoology (1958), Dr. A.J.E. Carr said his examination showed that this famous skeleton found in France over 50 years ago is that of an old man who suffered from arthritis	Homo neanderthalensis
New Guinea Man	Dates way back to 1970.  This species has been found in a region just north of Australia.	Archaic Homo sapiens
Cro-Magnon Man	One of the earliest and best established fossils is at least equal in physique and brain capacity to modern man...so what's the difference?	Anatomically modern Homo sapiens
Modern Man	This genius thinks we came from a monkey.	Homo sapiens

 Let's look at the accurate story for each of these.

Lucy

"Lucy is the common name of AL 288-1, several hundred pieces of bone fossils representing 40 percent of the skeleton of a female of the hominin species Australopithecus afarensis. In Ethiopia, the assembly is also known as Dinkinesh, which means "you are marvelous" in the Amharic language. Lucy was discovered in 1974 near the village Hadar in the Awash Valley of the Afar Triangle in Ethiopia by paleoanthropologist Donald Johanson.^" (Source)

Lucy is not the only specimen known of her species or of her genus.  Abundant remains have been recovered.

Now, as to claims that Lucy is just a chimp, I have been unable to find any such claims by a paleontologist or paleoanthropologist. The claim appears frequently on the Internet, but only on Creationist websites, and never with any referenced quotation.  Until Creationists can supply such a reference, their claim is empty gesturing and nothing more.

Just to anticipate a "But what about..." response from Creationists, if you are interested in Lucy's knee, click here.

Heidelberg Man

Based initially on a lower jaw from a gravel pit at Mauer, Germany, near Heidelberg, it was initially described as close to modern humans, but with a few differences, especially in the robustness of the body of the mandible compared to the relatively small size of the teeth.  Otto Schoetensack placed the fossil in the same genus as modern humans, when he described the species in 1907 as Homo heidelbergensis.  Although there is still lively debate about its exact phylogenetic relationships, it is consistently placed somewhere between Homo erectus and Anatomically Modern Humans.  The discovery of Sima de los Huesos in Spain, with more than 5,000 bones from at least 32 individuals has added greatly to our knowledge of Heidelberg Man.  Is it really surprising that Heidelberg Man is "conceded by many to be quite human"?

Nebraska Man

 Hesperopithecus haroldcookii was described by Henry Fairfield Osborn from a single worn molar found in northwest Nebraska on the ranch of geologist Harold Cook.  Cook sent the tooth to Osborn in March of 1922. In April of 1922, Osborn named the species and announced it as the first anthropoid ape from America.  Far from being accepted by the scientific community, many leading scholars expressed their doubts.  within 5 years, further collecting at the locality where the tooth was found revealed that it was in fact a worn molar of the peccary Prosthennops crassigenus.  A correction was published in Science in 1927 by William K. Gregory, Osborn's colleague. 

The famous reconstruction of Nebraska Man was done by artist Amedee Forestier for the Illustrated London News; it was not done under Osborn's direction.  Osborn and his colleagues in fact called it "a drawing or 'reconstruction' .... doubtless... only a figment of the imagination of no scientific value, and undoubtedly inaccurate."

Nebraska Man was based on a mistaken identification of a peccary tooth.  It was neither a hoax nor a fraud.  It was corrected in print within 5 years, and never referred to again as a valid human ancestor.  In spite of frequent Creationist claims that it is still featured in textbooks today as a human ancestor, no such textbook has ever been produced by the Creationists in evidence of that claim.

The full story of Nebraska Man can be read here.  

Piltdown Man

Perhaps the most famous hoax in all of 20th Century science was the discovery of Piltdown Man, a partial skull found in a gravel pit near East Sussex, England.  Found by a local amateur archaeologist, Charles Dawson, Arthur Smith Woodward, of the Natural History Museum in London, helped Dawson excavate addition parts of the same skull and the lower jaw, and published the find as Eoanthropus dawsoni in 1912.  Almost immediately Piltdown Man was heavily criticized, by, among others, Sir Arthur Keith, David Waterson, American mammalogist Gerrit S. Miller and Franz Weidenreich.  Many others, particularly European scientists, accepted Piltdown Man uncritically.  It took more than 40 years for a definitive statement to be published, based largely on the new fluorine absorption dating developed by Kenneth Oakley.    The fossil was confirmed to be a modern human skull, a 500 year-old orangutan lower jaw, and some chimpanzee teeth, all modified by various methods including filing with a steel file and chemical staining.  A study released in 2016 which took 8 years to conduct, confirmed that Dawson was the forger, and that neither Teilhard de Chardin nor Sir Arthur Conan Doyle were involved, as had been previously proposed. (Reference here)

Piltdown was a hoax.  It was accepted, at least by some parts of the scientific community, for an unfortunately long period of time.  It is one of the few hoaxes or forgeries so often quoted by Creationists that actually was a fraud.  It was, as is the case for the few other hoaxes or mistakes, revealed to be such by other researchers questioning and investigating the evidence.

Peking Man

Peking Man, now known as Homo erectus pekinensis, was discovered at Choukoutien Cave between 1929 and 1937.  15 partial skulls, 11 mandibles, many teeth and a few postcranial bones were found.  Good photographs and casts of most of the material were made and shared around the world; the American Museum of Natural History has a complete set of the casts in their collection.  All the material but a few teeth was lost when the bones were removed from Peking prior to the outbreak of hostilities at the beginning of World War II.  Despite intensive efforts to find them, including monetary inducement, they were never seen again.  Rumors and not a few conspiracy theories have swirled around ever since.

We now know that the deposits at Choukoutien Cave in which the hominid fossils were found date to somewhere between 680,000 and 780,000 years old.

Even with the loss of the original fossils, Homo erectus is well known from numerous other finds from northern, eastern and southern Africa, western Asia, and Indonesia.  It rightfully has a place on the hominid family tree.

Neanderthal Man

This particular bit of nonsense is completely fabricated.  Rudolf Virchow first made the claim that the original Neanderthal skull represented a pathological modern human in 1872.  It was later repeated by Rush K. Acton in an article for the Institute for Creation Research's Impact Series. In his paper  Creationists and Neanderthals, Ernest Conrad (Creation Evolution Journal, Volume 6(3):24-33) notes that he asked British anatomist A. J. E. Cave about claims that the original specimen was pathological, specifically evidencing syphilis, and Cave wrote to him, probably in 1984, that "No competent morphologist could confuse the frontal bossing of the congenitally syphilitic cranium with the distinctive configuration of the Neandertal skull.  Neandertal was a morpholgically distinct type of rational human being, which appeared and disappeared when and why, we know not."  Other comments traceable to Cave indicate that he accepted Neanderthal Man as a valid species of hominid.

I was not been able to find any reference to Cave's supposed presentation at the 1958 Congress of Zoology.  In fact, there doesn't appear to be any "Congress of Zoology" anywhere, in any year. Checking Evan Shute's book Flaws in the Theory of Evolution, from which it appears that Jack Chick cribbed much of his information,  I found this mention of Cave's work: "Cave (155) told the International Congress of Zoology in 1958 that Neaderthal man did not stoop."  Footnote 155 says "Cave, A.J. E. -- Quoted in Time, July 28, 1958 p. 46".  Chick apparently just omitted the "International" as unimportant.  Checking that issue of Time, the following short article was found:

"A missing link got demoted at last week's London meeting of the International Congress of Zoology. The chimp-size fossil primate Proconsul africanus, which lived in east Africa 30 million years ago, had been described as sitting in the family tree of both ape and man. Its skull, though primitive, is not conclusively apelike, so there seemed to be a good possibility that its descendants could be humans or apes or both.

The recently found bones of Proconsul's forearm and hand spoiled this theory. According to Anatomists John Napier and Peter Davis of the University of London, they clearly belonged to a brachiator, a creature that swung by its hands from bough to bough. So Proconsul must have been an ape, perhaps an ancestor of modern apes but not of non-brachiating man. The true missing link is still to be found.

Another long-established notion got its comeuppance at the same congress. Dr. A. J. E. Cave of London's St. Bartholomew's Hospital told the zoologists that the stooping, bent-kneed, apelike stance of Neanderthal man was a libelous misconstruction. About 1911, said Dr. Cave, French Paleontologist Pierre Marcelin Boule fitted together a Neanderthal skeleton found in France. He did not allow for the fact that the bones belonged to an old Neanderthaler who suffered from arthritis. Recently Dr. Cave himself examined those same bones. With age and arthritis properly allowed for, the Neanderthaler looked better. His face may have been brutish, and his body a trifle too hairy for modern tastes, but he probably walked like modern men and stood as straight."  (Time, July 28, 1958: online archive)

So, while Chick has portrayed Cave as saying that Neanderthal was a modern man, he said nothing of the sort.  While Jack Chick tried to make it appear that Cave said Nedanderthal Man is simply an old, arthritic modern human, that is not what he said.  In fact, his latter comment quoted above shows that he considered it a valid species similar to modern man in some aspects, but distinct.

While there is still some controversy as to if Neanderthal man should be considered a separate species, H. neanderthalensis, or a subspecies of Homo sapiens, H. s. neanderthalensis, the phylogenetic hypothesis best supported by the data, including the most recent DNA analyses, places H. neaderthalensis as a separate species not directly ancestral to modern man.  Its position on the hominid tree is secure.  

New Guinea Man

In an analysis of the Chick tract which appears in the TalkOrigins archive, New Guinea Man is mentioned:

"The real oddity in Chick's list is "New Guinea Man". As far as I know, no one has ever proposed this as any sort of transitional form. It presumably refers to fragments of a fossil modern human skull thought to be about 5000 years old found at Aitape (now Eitape) about 60 years ago. This is the only human fossil ever found in New Guinea, and is very obscure; I have never seen it even mentioned in any mainstream scientific or popular literature on human origins. The only place (other than Big Daddy) I have ever seen it referred to is a 1961 book by Canadian creationist Evan Shute, Flaws in the Theory of Evolution. Shute merely mentions the existence of this fossil in a list of many other fossils and does not discuss it individually, so Chick may have found out about this fossil from another unknown source." (Source)

Checking Shute's book, the only further information given is that the "sponsor" of the fossil was the Australian Geological Survey.  Fortunately, I have been able to find additional information concerning the identity of New Guinea Man. The find was published in the Records of the South Australian Museum, Volume 6, Number 4, in 1941.  Frank J. Fenner authored the article entitled "Fossil  Human Skull Fragments of Probable Pleistocene Age from Aitape, New Guinea."

The Aitape fossils were discovered in 1929 by a petroleum prospecting operation in the Barida Range in northern New Guinea.

The fossil, which consists of some con-joined fragments of a human skull (nearly complete frontal bone, the anterior portion of both parietal bones) as well as a separate fragment of the frontal joined to the sphenoid.  The original describer of the fossil, Frank. J. Fenner, determined it to be from a female about 45 years of age and found "no evidence that it belonged to an individual differing greatly from the modern Australian aboriginal (southern type)" (Fenner, 1941).  A later study (Durband and Creel, 2011) with larger samples for comparison (13 Late Pleistocene or Early Holocene Australian fossils, 101 modern Australian and 126 modern New Guinea skulls) found that the Aitape skull shared some traits (a longer, flatter frontal bone) with ancient Australian skeletal material which are not shared with modern Australian and New Guinea samples.

The Aitape bones were at first allocated to the Late Pleistocene, presumably because of their stained, dark brown coloration, slight mineralization, and geological context in a deposit of blue clay.  Later radiocarbon dating provided an age of about 5,000 years BP.  A date on coconut shell fragments recovered in a 1962 re-examination of the site gave a date of 4,555 + 80 PB, while carbonized wood gave dates of 4915 + 65 and 5070

 So, New Guinea Woman, as we now know her to be, was an anatomically modern Homo sapiens who lived about 5,000 years ago, and who shared a few primitive characteristics with much older Australian Late Pleistocene and Early Holocene populations.

New Guinea Man has never  figured in any review of the evolution of man except in Creationist writings.

Cro-Magnon Man

Cro-Manon Man is a name given to a group of European skeletal fossils of Homo sapiens.  It is a term that has no taxonomic equivalence or standing. The preferred term today is European early modern humans (EEMH).  Since they are the same species as modern humans, they differ very little - being a bit more robust and with slightly larger cranial capacity.  DNA analysis indicates that some Cro-Magnons had blue eyes, dark hair and an olive complexion.  So Cro-Magnon Man is not different from modern man - his and her remains are separated out on the basis of their age, being the earliest Anatomically Modern Humans found in Europe.

Modern Man

The comment under Modern Man in the Chick Tract echos the common Creationist challenge "If we evolved from monkeys, why are there still monkeys?"  Evolutionary biologists do not claim that humans evolved from monkeys.  Humans and the other great apes had a common ancestor, and if you go back far enough, the apes, including us, had a common ancestor with the monkeys.

Incidentally, the type specimen of Homo sapiens is Carolus Linnaeus (1701-1778), the famous classifier of living plants and animals, and not Edward Drinker Cope as wrongly claimed and unethically paraded by Psihoyos (1994).See Spamer 1999 for details Here).

I certainly would like to think this will put an end to the parading of the March of Perfidy on Creationist websites, and its uncritical use by Creationist crusaders on Facebook and other internet forums, but I am realistic enough to suspect that it won't.  They'll continue to use it, knowing that it is wrong.

Purgatorius may be from Hell Creek, but it's currently in Limbo:  Why it is so difficult to place early members of a group on the Tree of Life?

Recent discussions on a Facebook Group, Creationism, has centered around a series of yellow memes produced by Creationist and retired pastor Luke Lefebvre.  I've reproduced the latest with his permission, which summarizes Luke's point that since scientists can't exactly agree on whether Purgatorius is a primate, a near-primate or even a true (eutherian) mammal, we can't trust anything those scientists have to say about evolution.

So is this true? And if it is true, why should there be such confusion among paleontologists and paleoanthropologists over the nature of this little critter?  As is so often the case, the Young Earth Creationists like Luke seize upon the usual, healthy give and take of the scientific method as a sign of weakness, and use it to bolster their fear and loathing of science.

Background

First, a little background.  Purgatorius was first described by Leigh Van Valen and Robert E. Sloan in 1965 on the basis of teeth from Purgatory Hill, and placed in two species, Purgatorius unio and Purgatorius ceratops.  P. unio was assigned to the early Paleocene, while P ceratops, because it was a single eroded and weathered tooth, to the underlying Cretaceous part of the Hell Creek Formation.  Both teeth were from a small channel deposit which has a mixture of earliest Paleocene and latest Cretaceous fossils in what is known as a "time-averaged" assemblage. Most of the fossils represent animals that lived at the time the channel was formed, but a few, like the Purgatorius tooth, were eroded out of the older deposit into which the channel was cut.  Most securely dated occurrences of Purgatorius are limited to the second and third phase of the Puercan North American Land Mammal Age (Puercan 2 and Puercan 3), dating between about 64.75 and 64.11 MYA (million years ago), with only a few known from the Puercan 1 phase.

Purgatorius was thought by Van Valen and Sloan to be an early Paramomyid primate, but discussions between 1965 up to today have called Purgatorius a stem primate, or placed it outside the primates; one study has even suggested that it may not be a placental mammal (Eutherian) at all, but should be placed with the Metatheria, which includes the living marsupials as well as a host of extinct groups like the multituberculates.  But why should there be such confusion?  We don't need to get into all the details of dental morphology, although that is where the problem arises.  The answer is really much simpler than that.

The Facebook Meme

Above is Luke Lefebvre's meme entitled Lucy vs. Purgatorius: Who to Believe?  He quotes Don Johanson, then goes on to say "Purgatorius is thought to be an early form of primate (That means that's where you come from) although its exact place in the evolutionary history of primates is much debated.  This is mostly due to the fact that the only fossils we have of this animal are its teeth and jaws. Lefebvre concludes "Ask any evolutionist and wait to get different answers."

Luke is correct in these points:  Purgatorius is thought (by most paleontologists) to be an early primate.  Its exact place on the mammal tree is debated on the basis of different analyses of different data sets. A few paleontologists think it is a proto-primate, or even outside the placental mammals altogether, but the general consensus, using the total evidence available, is that it is a primate.  It is true that the fossil remains of Purgatorius are mostly teeth and jaws, but in 2015 7 astragali and 9 calcanea (both ankle bones) were described by Chester et al.  These were important in being the first postcranial bones attributable to Purgatorius, and in indicating the first Paleocene mammals which were at least partially arboreal.  Note that the tarsal bones were not directly associated in skeletons, but were isolated bones in faunas which had many teeth and jaws of Purgatorius.  How Chester et al. identified each of the particular species of Paleocene mammals is another story, but it is well supported by the evidence.

So why is there any uncertainty?

Think about evolution as the branching pattern often depicted as a phylogentetic tree.  The further back in time you go, the closer you get to the common ancestor, in this case the common ancestor shared by all eutherian mammals.  But remember, evolution isn't a single line from the past to the present. "Decent with modification', Darwin's wonderful phrase, predicts that all the diversity we see in  eutherian mammals traces back to the common ancestor, each modern mammal (as well as all the extinct ones) traces its ancestry back to that same spot on the tree, each by a different route.  Carnivores, proboscideans (elephants), rodents, perissodactyls (horses, rhinos and tapirs), artiodactyls (deer, sheep, cows, giraffes, etc.) all can trace their ancestry back to that same point.  While all those animals are wildly diverse today. as we trace the lines backward toward the common ancestor, they get more and more alike, less different and would be much harder to tell apart if we could see them as living creatures.  Their morphology - teeth, bone structure and all the details that are the basis for understanding the fossil record, also get more and more alike as you move backwards in time and down the tree.  In fact, when you get to the early Paleocene, 61-65 million years ago, all these eutherian mammals, just beginning their evolutionary radiation, are nearly impossible to tell apart.  If we didn't have their descendants identified in some detail, we'd lump them into one group as most closely related to each other.  It is only because we know what they would become later in time, that we can separate them from the other early "primitive" mammals and place them in the proper group known from their descendants.

So, most of the confusion - all of the confusion! - comes from disagreements between researchers as to the legitimate place of Purgatorius on the tree.  It isn't resolved now, and likely won't be until better evidence is available, such as a complete skull and skeleton of Purgatorius and some of the other Paleocene mammals.

In order to illustrate better what I'm talking about, I've taken a slide from a PowerPoint presentation by the Joint Experimental Molecular Unit and the Royal Museum for Central Africa entitled "Introductory seminar on the use of molecular tools in natural history collections" dated November 6-7, 2007.  On a part of this slide I have added more information, as follows:

Each red dot in a red circle indicates a possible positions that Purgatorius could be placed in, with the present hypothesis most favored by the evidence being a stem or near-stem primate.  Another possible position is at the base of the unresolved archontan trichotomy - which just means that the three groups, primates, tree shrews (Scandentia) and the colugo (Dermoptera) are closely related, but the evidence doesn't clearly tell us which two of the three are more closely related to each other than either one is to the third.  Yet another possibility is that Purgatorius represents a common ancestor of all the Euarchontoglires - a group composed of the colugo, tree shrews, primates, rabbits and rodents.  A final possibility which no one has suggested and which has no evidence is that Purgatorius could stand at or near the common ancestry of the rodents and rabbits.

The diagram also has some dashed green lines between the living taxa (blue dot to blue dot) which show that the distance between those dots indicates roughly the morphological "distance" or divergence between the evolving lineage leading up to those dots.  Remembering that each of those blue lines represents a long series of ancestor / descendant species, genera and families, we can also draw those dashed lines between the blue lineages at any time point along the line, demonstrating that as we move back in time - towards any of the common ancestors, the morphological difference between them gets to be less and less as shown by the green dashed lines between the blue Primate line and the blue Dermoptera line.  By the time we reach the early Paleocene - the time of Purgatorius - an early tree shrew is going to be morphologically quite close to an early relative of the colugo, and both will be very similar to an early primate.

The final figure provides yet a different illustration of the problem.  In this diagram, the three living orders, Primates, The Colugo and the Tree Shrews, are shown across the top.  The blue line under each one represents the evolutionary history of that group, called a "clade".  The red oval includes a cloud of fossil species - some are on the direct line back to the earliest member of each clade; others are either just a little off that mainline ("first cousins") or aberrant members, dead ends with no surviving descendants.  One such fossil species is represented for each clade in the diagram by a red dot.  

Now, as is often the case for the most primitive members of the major clades, the earliest members look very much like the earliest members of other related clades.  In fact, we often can't tell to which surviving clade they belong because they lack the specialized characters which help us define the clade.  So all these primitive species get lumped together in a group called a "grade"  It's much like a small dense cloud of species which we can't differentiate and connect to their eventual descendants until sufficient material is collected, a careful analysis is done, and unique shared characters are identified which will connect a given "red-cloud" species to a particular clade.

Summary

So Luke Lefebvre is correct - you can get different hypothses when you read different papers.  But you have to read them carefully, mindful of when each was written, and look at what new evidence each brings to bear on the problem.  That's what science is about.  Science would be no fun at all if there weren't new discoveries to be made, new connections to be drawn and new hypotheses to be proposed - and then tested.

References

Chester, Stephen G. B., Jonathan I. Bloch, Doug M. Boyer, William A. Clemens, 2015, "Oldest known euarchontan tarsals and affinities of Paleocene Purgatorius and Primates" Proceedings of the Academy of Science, U.S.A. Volume 112 (5): 1487-1492

Van Valen, Leigh and Robert Sloan, 1965, "The earliest primates". Science. 150 (3697): 743–745. <>

I thank Luke Lefebvre for allowing me to use his "Yellow Meme" for the anchor point of this blog entry.

Modern Bird Species in the Cretaceous?  No!

 Introduction:

Don Batten, a writer associated with Creation Ministries International, has been the most vocal advocate of the claim that modern species of birds have been found in rock layers with dinosaurs.  He usually quotes Dr. Carl Werner.  Two examples of this claim are:

"Dr Carl Werner’s book and DVD, Living Fossils, reveals that fossil researchers have found many modern bird remains with dinosaurs..."

"Most people are surprised to learn that many modern bird species have been discovered buried with dinosaur remains: “parrots, owls, penguins, ducks, loons, albatross, cormorants, sandpipers, avocets, etc.” (Batten, Don, “Living Fossils: a Powerful Argument for Creation,” Creation 33 (2), 2011.) “This symphysis appears to represent the oldest known parrot and is, to my knowledge, the first known fossil of a ‘terrestrial’ modern bird group from the Cretaceous. The existence of this fossil supports the hypothesis, based on molecular divergence data that most or all of the major modern bird groups were present in the Cretaceous.” (Stidham, Thomas A., Nature 396, 29-30, November 5, 1998.)" [quoted from the webside "Genesis Park"]

What is important to notice here is that Dr. Werner never says that modern species of birds are found buried with the dinosaurs.  He says "modern birds" or "modern groups of birds".  Werner is hoping that his audience won't know that there is a difference between a modern group of birds, and a modern species of bird.  A modern species of bird is one which is living today, such as the Red-crowned Amazon Parrot, (Amazona viridigenalis), native to Mexico.  The modern group is the Order Psittaciformes, which has almost 400 species in 92 genera living today, but includes all the fossil relatives of the Order, going back perhaps to the Late Cretaceous 70 million years ago, if Stidham's fossil is confirmed to be a parrot.  Modern species are limited to the present day, or perhaps a few million years into the past.  No modern species is known from the Oligocene, Eocene or Paleocene, and certainly not from the Cretaceous.  But most of the modern orders of birds  are well known back to the beginning of the Paleocene, some 65 million years ago, meaning that they evolved in the Late Cretaceous, or earlier.

Analysis of Werner's claims:

We can take Werner's claims and check the facts.  We have to make some assumptions about what he meant, since the "modern birds" he mentions are not all of equivalent rank in the scientific classification, but I've tried to do so to mirror what I think was Werner's intention.  I've given examples of modern species which would fit within Werner's group name, and indicated the family or order to which they belong.  Next is the age of the earliest known fossil from that family or order, and the fossil species upon which it is based.

Werner's name	Living example common name	Living species name	Order or Family	Age of earliest known fossil	Fossil species
parrot	Amazon Parrot	Amazona viridigenalis	Psittaciformes	Late Cretaceous	Unnamed but described
owl	Great Horned Owl	Bubo virginianus	Strigiformes	Paleocene	Berruornis, Ogygoptynx Supposed Cretaceous owls are non-avialian dinosaurs
penguin	Magellan's Penguin	Spheniscus magellanicus	Sphenisciformes	Early Paleocene	Waimanu manneringi
duck	Mallard	Anas platyrhynchos	Anatidae	Late Eocene	Romanvillia sp.
loon	Common Loon	Gavia immer	Gaviformes	Late Eocene / Early Oligocene	Colymboides minutus
albatross	Wandering Albatross	Diomedia exulans	Diomedeidae	Middle Eocene	Murunkus subitus
cormorant	Double Crested Cormorant	Phalacrocorax auritus	Palacrocoracidae	Late Cretaceous	Unnamed species in Asia and North America
sandpiper	Sandpipers, curlews and snipe	various	Scolopacidae	Early Eocene	Paractitis bardi
avocet	American Avocet	Recurvirostra americana	Recurvirostridae	Late Eocene / Early Oligocene	Recurvirostra sanctaeneboulae

So where does Werner and the Creationists who parrot him go wrong?  They make three mistakes:

1.  The  Cretaceous and early Tertiary fossil birds are not members of any species living today.  They are not members of any living genus.  Recurvirostra is the sole exception, and one suspects that the very fragmentary fossil, a partial coracoid, is insufficient to support such a generic assignment.  They may be members of families which have modern survivors.

2.  They cherry-pick paleontologists who make statements about a fossil species like "This fossil would have looked very similar to a modern duck".  That does not mean it is from a living species of duck, or that it is even in the same family (Anatidae) or order (Anseriformes) as living ducks.

3.  They use common names with vague definitions rather than give the name of the fossil so that anyone can check their claims.

Conclusion:

  

Cretaceous dinosaurs did not co-exist with any modern bird species.