Placenta Atlas Tool (PAT)

NICHD have just launched this tool to aid pregnancy research. It promises to be of great value (found here).

Those interested in comparative placentation should go to Explore Images and use the Species filter. This brings up a list that may include your favourite mammal. Click on that and you will get a menu of large icons, although only after a further click can you be sure what they represent (room for improvement here).

The images are fully annotated with original figure legends plus additional context from the source paper.

Open Access appears to be a prerequisite for images to be selected as they link to the Open-i resource of the U. S. National Library of Medicine. 

Pregnant tenrecs run hot and cold

Tailless tenrec (Tenrec ecaudatus)
Photo by Markus Fink (Wikimedia Commons CC)

Tenrecs do not maintain a constant body temperature. It waxes and wanes throughout the day. A recent study found this applies even to pregnant tenrecs. Yet after they give birth their body temperature becomes stable and warm.

As mentioned in a recent post, this tenrec (Tenrec ecaudatus) has large litters. In the present study up to 19 young. They grow quickly from 12 g at birth to 400 g at 5 weeks (weaning). Perhaps thermoregulation becomes more important when the mother is lactating.

In the closely related species Echinops telfairi, gestation length varies in the range 50-79 days (here). Just speculating, but if body temperature varies could this affect fetal growth rate and thereby the timing of delivery?

Reproduction in tenrecs is quite interesting as we discuss for the ovary here and placenta here.

Congratulations Hiroaki Soma

Professor Hiroaki Soma (at left) recipient of the 2018
IFPA Senior Award

It is a pleasure to record that my good friend and colleague Hiroaki Soma received the Senior Award of the International Federation of Placenta Associations at their recent meeting in Tokyo.

In his address, Professor Soma looked back over 60 years of research including important clinical work on gestational trophoblastic disease in Japan and placental lesions associated with pregnancy at high altitude in Nepal.

In addition, he gave valuable insights about comparative placentation. The range of mammals included chinchilla, giant panda. Japanese serow, sloth, chimpanzee, elephant, manatee and hyrax. As if this were not enough, Professor Soma also presented his research on pregnancy in sharks and rays conducted at the Churaumi Aquarium in Okinawa. 

Kurt Benirschke (1924 - 2018)

Kurt Benirschke (right) with Oliver Ryder

Sad to record the death of Kurt Benirschke at age 94. Among many achievements is his web site Comparative Placentation (previous post). This invaluable resource is particularly strong on primates and even-toed ungulates such as antelopes.

The placentas came mainly from San Diego Zoo where Kurt Benirschke also took the initiative to create a biobank of cryopreserved tissues (The Frozen Zoo) and laid the foundation for what became San Diego Global's Institute for Conservation Research. 

To many he is best known for his textbook Placental Pathology. The second  (1990) and subsequent editions were written with Peter Kaufmann. It is now in a sixth edition edited by Kurt Benirschke, Graham Burton and Rebecca Baergen.

The Annual Kurt Benirschke Lecture at UC San Diego 2018

Five years ago Kurt Benirschke suffered a stroke but he remained active and alert. According to today's obituary in San Diego Union Tribune, he and his wife visited San Diego Zoo as recently as last week. 

To learn about Kurt Benirschke's life in his own words see the short version here or his interview with Rebecca Baergen here.

Why Luzia was important

Cast of the skull known as Luzia as displayed at
National Museum of Natural History Washington DC
Photo by Ryan Somma CC BY-SA 2.0

Luzia was excavated from Lapa Vermelha, Minas Gerais, Brazil and was the oldest human fossil from South America. She was found in strata dated to 11,000 years ago. Whilst casts of the skull exist elsewhere the original was lost (at best severely damaged) in the catastrophic fire that destroyed the National Museum in Rio de Janeiro. 

Luzia Woman belonged to an ancient population formerly known as Lagõa Santa Man or Paleoamerind. The first to excavate such skulls was the Danish Naturalist Peter Lund, who found them as far back as 1840. Based on the classical craniometric criteria used by anthropologists until well into the twentieth century, this population clearly diverged from all others in North and South America.

Lagõa Santa skull excavated 1840 by Peter Wilhelm Lund

There is an interesting correlate in modern genomic data. David Reich and colleagues postulate an ancient Population Y corresponding to a genetic signal borne by the Surui people of the Amazon region (discussed here - see previous post for Reich's book where this is further discussed). The interesting thing about this signal is that it is shared with the faraway Andaman Islanders and natives of New Guinea and Australia.

We already know of two branches to the population that crossed the Bering Strait and peopled North and South America - thanks to work by Eske Willerslev's group (here). Was there a third branch that gave rise to the Paleoamerinds or even a separate and earlier migration?

To piece this together it would have been useful to extract ancient DNA from the Luzia skull. That had not been done prior to the fire. There are other skulls around including those excavated by Peter Lund and now housed in Copenhagen. They may yet yield new pieces to complete the puzzle.

Litter size in the tailless tenrec and a Jurassic tritylodont

Tailless tenrec (Tenrec ecaudatus) with litter
Photo (C) by H. Schütz. From Goodman, Benstead and Schütz
The Natural History of Madagascar

The record for litter size in mammals - 32 viable fetuses - is held by the tailless tenrec. The source for this is Bluntschli (Revue Suisse de Zoologie 1937; 44: 271-282). The tailless tenrec polyovulates and an even larger number of unimplanted blastocysts has been observed (Nicoll & Racey).

Small litter size is nonetheless typical for mammals and is currently in focus because of a remarkable fossil from the Early Jurassic (Hoffman & Rowe). This comprised a clutch of at least 38 perinates and the presumed mother in the genus Kayentatherium. 

The mammals derive from the synapsids and Kayentatherium is on a non-mammalian side branch called tritylodontids. The trees in Prothero (previous post) suggest they diverged from the branch leading to mammals way back in the Triassic. So the finding does not exactly pinpoint when a reduction in litter size started to happen. 

The abstract claims that 38 is "well outside the range of litter sizes documented in recent mammals." Except one might add in the tailless tenrec.

Aye-aye captain of its own raft

An aye-aye (Daubentonia madagascariensis) foraging
Joseph Wolf c. 1863 Wikipedia Commons (public domain)

We are used to molecular data shaping our view of evolution, so it is all the more delightful when a morphological study shakes the mammalian tree.  The pleasure is no less for it involving that strange Malagasy primate the aye-aye (Daubentonia madagascariensis).

It is widely accepted that Madagascar was colonized by mammals rafting across the Mozambique Strait (see previous post). The lemurs (Lemuriformes) and the aye-aye (within its own Infraorder Chiromyiformes) have hitherto been thought to be descended from a single founder.

New tree for strepsirrhine primates from Gunnel et al. 
Nature Communications 2018 (here) CC

Now a study in Nature Communications paves the way to a new scenario. The historical background is interesting. George Gaylord Simpson (a proponent of the rafting hypothesis) once proposed a new fossil species of strepsirrhine primate Propotto leakeyi from the early Miocene of Kenya. Subsequently this was reinterpreted as a fruit bat. Now Gunnell and co-authors have unearthed the specimens from the National Museums of Kenya and compared the morphology (especially the dentition) both to the aye-aye and to Plesiopithecus teras from a late Eocene site in Egypt.

Firstly, they show Simpson was right about Propotto. Secondly, they construct a tree (combining morphological and molecular data) showing the split between Lemuriformes and Chiromyiformes occurred in the Eocene. Thirdly, it is most parsimonious to assume two separate rafting events with the ancestor of the aye-aye drifting to Madagascar on its own raft. Finally, both rafting events are likely to have occurred in the Miocene, which explains the lack of fossils of earlier date.

Placentation in the aye-aye

Allantochorion of the aye-aye. From Hill & Burne 1922 (here)

Milne-Edwards briefly described the placenta of the aye-aye (C R Acad Sci 1884), but the first complete account is by Hill and Burne (here). They described the villous nature of the allantochorion and the presence of chorionic vesicles. This contributed to Hill's later characterisation of the "lemuroid stage" of placentation where the placenta is diffuse, non-deciduate and epitheliochorial (reviewed here).

Who We Are and How We Got Here

Oxford University Press 2018
ISBN 978-0-19-882125-0

In little more than a decade, studies of ancient DNA have transformed our knowledge of human history. A recurrent theme is the migration of people over long distances to mingle with and often to replace existing populations. Often the immigrants brought with them new technologies and languages. Although there are also examples of skills dispersing without migration (spread of the Beaker culture from Iberia) and succesive waves of migrants adopting local languages (southwest Pacific islands).

All this and much more is related in David Reich's new book. Although his prose is stilted at times, that is more than compensated by the breadth of material presented and by excellent diagrams. These include maps showing the probable origin, direction and timing of human migrations. 

Skull from Lapa Vermelha, Lagōa Santa, Brazil
Photo by Ryan Somma CC BY-SA 2.0

Although Reich delights in disproving established concepts, it is interesting to find that some long-standing ideas receive support. For example, there is a clear genomic evidence of two waves of migration into Central and Southern America. The first wave of migrants designated "Population Y" left a genetic signature that is strongest in some isolated Brazilian communities (Tupí). This finding lends support to the concept of an ancient people called Palaeoamericans by Neves (here) and named a century ago as Palaeo-Amerind by Haddon (previous post). These ideas were fostered by excavations at Lagõa Santa, Brazil, started 175 years ago by the Danish scientist Peter Lund and continued until this day.

Similarly, present day peoples of India derive much of their genetic makeup from two previous populations. One of these described as "Ancestral South Asians" bears a striking resemblance to the "Pre-Dravidians" postulated by Haddon.

There has been some animus engendered by Reich's book - exacerbated by an opinion piece he wrote for The New York Times. Part II of the book has chapters on the origins of Europeans, South Asians, Native Americans, East Asians and Africans. Inevitably this division reflects the broad racial categories of the past. The flight from racial stereotyping in the last 50 years is laudable, but a mist of political correctness can make recent studies hard to decipher. Reich's book disperses the mist and inevitably invites controversy. 

IFPA now on Twitter

The International Federation of Placenta Associations (IFPA) now has a Twitter account: ＠IFPA_Official 

Abstract deadline for the upcoming meeting i Tokyo is 2 April 2018.

Parturition and placentophagy in baboons

Yellow Baboon (Papio cynocephalus) female with young
Wikimedia Commons

Two important papers just appeared on reproduction in baboons (Papio spp.). Natalia Schlabritz-Loutsevitch and co-authors (OA here) describe normal birth and pregnancy complications as observed in the laboratory. Their study was based on imaging (MRI, X-ray, ultrasound) and video recording of deliveries. 

I found it particularly fascinating to see the delivery process. When the baby's head emerges it is face upwards so looking directly at the mother (unlike in humans and chimpanzees where the head emerges face down). After cleaning the baby, the mother ignores it for several minutes and devotes all her attention to eating the placenta. Some of this can be seen in the delivery video (supplementary material here). 

Gesquiere and co-authors (here) summarize no less than 36 years of observations in free-ranging baboons, mainly yellow baboons (P. cynocephalus) from Amboseli in southern Kenya. Their focus is on what determines the interval between births. The main determinant was lactational amenorrhoea due to suppression of the ovarian cycle while the infant was breastfeeding. Once the baby was weaned, most females became pregnant again within 6-8 cycles.

There is an interesting parallel with human hunter-gatherers (previous post). Based on data from the !Kung people of South Africa, Roger Short (here) calculated that a woman in a hunter-gatherer society was pregnant for nearly four years of her life and spent 15 years in lactational amenorrhoea. As a consequence she endured menstrual cycles for rather less than four years. Short contrasted this with present day society where a woman might expect to have menstrual cycles for 35 years of her reproductive life.

Przewalski's horse an also-ran

Przewalski's horse Photo by Claudia Feh

CC BY-SA 4.0 

Przewalski's horse has long been seen as the last population of wild horses. No more. A new attempt to find the origins of domestication using ancient DNA is full of surprises (here). 

The Botai Culture of Central Asia has been tied to domestication of horses some 5500 years ago. Ancient DNA was extracted from the bones of Botai horses and the genomes compared with those of other ancient and modern horses.

Cord at term of Przewalski's horse

From Benirschke Comparative Placentation

The first surprise was that Przewalski's horse clustered with the Botai horses. The inescapable conclusion is that Przewalski's is a feral population descended from those domesticated at Botai.

The second finding was that all other horses descend from a separate branch. This was foreshadowed in a previous study (previous post). The most parsimonious explanation is that there was a second centre of domestication yet to be identified.

Benirschke has several images of the placenta of Przewalski's horse (see also previous post).

Mammal Diversity Database



Zebu cattle (Bos taurus indicus)
Agricultural Research Service (USDA) Public Domain

How many species of mammals are there? That is the appropriate title of an article (OA here) accompanying the launch of the American Society of Mammalogy's new Mammal Diversity Database (here).


The answer is 6495 species and counting. Compared to Wilson & Reeder Mammal Species of the World (MSW3), which has its own database (here), that is an increase of 1250 in 13 years.


The authors of ASM MDD have erred in favour of the splitters. In particular, acceptance of the taxonomy of Groves & Grubb for Artiodactyla and Perissodactyla (previous post) will raise eyebrows. In anticipation they write, "inclusion of the taxonomy of Groves and Grubb (2011) in the MDD ensures that these taxa are vetted by the greater mammalogical community."


I note, however, that unlike Castello (previous post), they list the zebu as a subspecies of Bos taurus. Important because this species is a focus in research on bovine placentation and reproduction in places like Brazil.


I found the new MDD more difficult to navigate than MSW3. For example, if you enter a higher taxon than genus you get all the entries in that taxon rather than any definition of the Family or Order itself.


As far as I can see there is no possibility to search for synonyms as on MSW3. I have found this search function of MSW3 enormously valuable when delving into the older literature on placentation. Similarly there is little information about subspecies names.


Some choices of terminology meet my approval. They drop Cetartiodactyla in favour of Artiodactyla (whales and their kin are nested within even toed ungulates). Inevitably they retain Afrosoricida for the order that includes tenrecs, otter shrews and golden moles (a really unfortunate name as African shrews are numerous and belong to an entirely different clade).


Most regrettaby, however, they retain Infraclass Placentalia for eutherians. This unfortunate term was introduced by McKenna & Bell and I have ranted about it before (previous post). It has caused countless confusion and the vernacular "placentals" or even "placental mammals" can mislead the unwary to believe marsupials are without placentation. Prothero among them (previous post).

Placentation in the wildebeest

Blue Wildebeest (Connochaetes taurinus)

Photo by Muhammad Mahdi Karim (Wikimedia Commons)

In ruminants binucleate trophoblast cells (BNCs) migrate to and fuse with uterine epithelial cells to form a fetomaternal hybrid - either a syncytium or trinucleate cells. This remarkable mechanism was described some 40 years ago by Peter Wooding. The fusion is aided by a syncytin, the product of an endogenous retroviral gene (previous post).

Almost all the ruminants studied hitherto have trinucleate cells. A fetomaternal syncytium is formed in the basal tragulids (chevrotains), which have a diffuse placenta without cotyledons. The other exception hitherto is syncytium formation in sheep and goats.

Binucleate trophoblast cell of bovine placenta from Benirschke

Now Wooding et al. (here) have undertaken to survey a wide range of ruminants including a chevrotain (Tragulidae), 8 bovids (Bovidae), 8 deer(Cervidae), the pronghorn (Antilocapridae) and a giraffe (Giraffidae). Only the musk deer (Moschidae) are missing.

Almost all the pecoran ruminants studied had trinucleate cells. Exceptions were the sheep and the wildebeest (Connochaetes taurinus). This is a new and highly interesting observation.

Three groups of bovids, classified as Tribes by Groves and Grubb (previous post) and Subfamilies by Wilson and Reeder share a common ancester (here and here). These are Alcelaphini, Hippotragini and Caprini. The first includes the wildebeest and the last sheep and goat. So it is likely that the most recent common ancestor (MRCA) of sheep and goats and the wildebeest had a fetomaternal syncytrium.  

To summarize. The basal Tragulidae have fusion of BNCs and maternal epithelium to form a syncytium. The trinucleate cell replaced this in the MRCA of pecoran ruminants (those with cotyledons). Then a fetomaternal syncytium reappeared in the MRCA of wildebeest and sheep and goats. 

To test this hypothesis it would be useful to have studies of the third tribe Hippotragini, i.e. an oryx, the roan and sable antelopes or the bluebuck.

Our Human Story - Book Review



ISBN 978 0 565 09391 4 Cover Price £14.99

This short book (160 pages) can be highly recommended to anyone who, like me, often loses the plot when reading papers on human evolution. It covers all phases in hominin evolution during the past 7 million years. The most important fossils are named (and the names explained), illustrated, and placed in geographical context by some excellent maps.



There is a good index so next time you are unsure what is referred to by KNM-ER 1470 you can quickly look it up!


I had anticipated that the book might lack the very latest info such as the redating of the early humans from Jebel Irhoud or the early dispersals to Arabia and India. But Louise Humphrey and Chris Springer have it all. Only the 120,000 year-old human fossil from Misliya, Israel (here) was published too late to make it into their book.


Chris Stringer is a strong proponent of the Out of Africa hypothesis that has all modern populations deriving from a single dispersal 45-55,000 years ago. But in this book alternative scenarios are given a fair treatment.


Near the end there is a neat diagram summarizing human evolution during the last million years.




Evolution of brain shape - and why babies are not better developed at birth

Brain shape of present-day human (left) and a Neanderthal (right)

From Neubauer, Hublin and Gunz (OA here) CC BY-NC

The difference between Neanderthals and modern humans lies not so much in brain size as in brain shape. In modern humans, the brain changes from an elongated to a more globular shape. This occurs mainly after birth (OA here). 

Now a remarkable paper in Science Advances (OA here) shows evolution of brain shape was a gradual process in Homo sapiens. The earliest modern humans from North and East Africa (300,000 to 200,000 years ago) had much more elongated brains.

Brain shape comparable witrh modern humans is first seen in fossil skulls that are 35,000 to 10,000 years old. These are associated with the more advanced culture of the Upper Paleolithic, i.e. with behavioural modernity.

Conveniently, there is a group of fossils from 130,000 to 100,000 years ago with intermediate brain shapes. They include some from the Levant mentioned in my last post (here). It has been suggested that they represent an early dispersal from Africa that reached far into Asia and persisted for a long period of time. Perhaps they were supplanted by a second wave of humans with more globular brains and a more advanced culture.

Quite a lot has been written about the constraints on human childbirth consequent on evolution of a larger brain (e.g. OA here and here). Changing the shape of the brain and skull could have complicated matters further. Maybe that is why most of the rounding up of the brain, which includes rapid growth of the cerebellum, occurs in the first months of life. The other region that rounds up is the parietal area. It is thought that this reflects changes in "an important hub of brain organization" called the precuneus.

Most mammals with a long gestation and a single young have newborns that are well developed (previous post). Babies need extensíve parental care leading Portmann to describe humans as "secondarily altricial." Maybe the postnatal growth of critical brain areas, reflected in a more globular brain, is part of the explanation for this conundrum. 

P.S. Right now there is a great deal of buzz about a modern human fossil from Israel dated to 177,000 years ago (OA here). As there is no cranium it cannot yield data on brain size.

Did humans reach Asia earlier than we think?

Map of early human migration

NordNordWest (public domain)

An insightful perspective in Nature Ecology and Evolution (abstract here) questions if there was just one successful dispersal of Homo sapiens from Africa to Asia. The current consensus - the Out of Africa Hypothesis (here) - is that modern humans left Africa some 65-55 thousand years ago and rapidly spread around the globe (see map). 

Stone hand axe from Wadi Dabsa, Saudi Arabia

From Foulds et al. (here)

An earlier migration from Africa to the Levant is supported by fossils and increasingly by archeological evidence, including from recent digs in the Arabian peninsular (here). Hitherto this exodus has been regarded as short lived and restricted in geographical extent.

Leveraging the increasing amount of evidence emerging from Asia, Rabett argues that, on the contrary, this first dispersal reached far beyond the Levant with populations surviving for many thousands of years.

Therefore he questions whether all the sites attributed to Homo sapiens in Southeast Asia and Australia stem from a single dispersal. Some sites from 45-65 thousand years ago might represent late-surviving enclaves of an earlier dispersal. At the very least, much of the archeologcal data conflicts with a rapid dispersal along the Southern coastal route.

Genomic data including ancient DNA support the view that all human populations living outside Africa derive from a single exodus albeit there was subsequent admixture with other hominins (including Neanderthals and Denisovans). The earlier migration did not contribute to the extant human gene pool. But to quote Rabett, "should evolutionary success be measured only by genetic and demographic continuity into the present?"

Temerity of the tenrec

Lesser hedgehog tenrec © Peter J Stephenson

After human and mouse the tenrec was one of the first mammals to be sequenced (link here). When this was still in the works, the popular science magazine ScienceNews put a tenrec on the cover. The caption to the article read, "They're sequencing a what?" (here). 

Sadly the tenrec has had it's 15 minutes of fame. When Nature News and Comment ran a report on a recent study from the Chavan lab., it was headlined, "Armadillo, hedgehog and rabbit genes reveal how pregnancy evolved." Once the editors realized Echinops telfairi was a tenrec, this was shortened to "Armadillo and rabbit genes..."

The irony to this was that a previous paper from the lab. (OA here) wrote that their hypothesis - about implantation evolving from an inflammatory reaction - could be tested by looking at the basal eutherian clades Afrotheria and Xenarthra. The lecture on which Nature News and Comment was reporting showed this had now been addressed in a tenrec (Afrotheria) and an armadillo (Xenarthra).

The temerity of a tenrec dressing up like a hedgehog!