Land bridges to Madagascar

 

Sweepstakes distribution as envisaged by G. G.Simpson

One of the first posts on this blog (here) was about sweepstakes distribution as proposed by George Gaylord Simpson. Simply put it envisaged that animals endemic to Madagascar, such as lemurs and tenrecs, as well as now extinct hippopotami, crossed the Mozambique Channel on rafts of vegetation. 

This has been widely accepted and bolstered by evidence that ocean currents in the Cenozoic might have been more favourable to rafting than they would be today (here).

Now a cross-disciplinary group has taken a fresh look at the question and reached quite a different conclusion (here). They begin by questioning whether small primates or tenrecs could survive on the crossing which they estimate could take several months. Further they dismiss the idea that a hippo could swim to Madagascar; their arguments on this point are convincing. Could a raft be strong enough to support a hippo during the crossing (as pictured in the cartoon above)?

Verreaux's Sifaka (Propithecus verreauxi)

They suggest that there has been too much focus on the width of the Mozambique Channel and not enough on its depth. They present a mass of data, bewildering to me, but supporting the possibility of land bridges from Africa to Madagascar. The first of these at the Cretaceous-Palaeocene boundary might have been used by the ancestors of lemurs and tenrecs (their African cousins are lorises and otter shrews).

A land bridge at the Eocene-Oligocene boundary could have been used by the ancestors of Malagasy rodents and Malagasy carnivores such as the fossa. Finally there was an incomplete land bridge at the Miocene-Pliocene boundary that might be a more plausible route for a hippopotamus to cross.

The obvious question is why the Malagasy fauna is so depauperate. Why are there no monkeys, large cats or ungulates? The authors suggest they may have made it to Madagascar but gone extinct. Fortunately for this argument, the fossil record on Madagascar is very poor.

And what about that other discussion of land bridges versus rafting - how did hystricognath rodents and the ancestors of Neotropical primates reach South America (see previous post)?

The Sediments of Time - Book Review

 

This account of Meave Leakey’s search for human ancestors in the Turkana region of Kenya is at once intensely personal and scientifically sound.

Born Meave Epps in 1942 she read marine biology at Bangor but found herself without a job because research ships lacked facilities for women. On a whim she answered an advertisement by Louis Leakey who was recruiting for a primate research centre in Kenya. Once there she soon found herself looking for hominin fossils with Louis’s son Richard whom she later married. Their life together was full of drama as Richard suffered both kidney failure and the loss of his legs in a plane crash.

Reconstruction of Homo rudolfensis
(KNM-ER 1470) discoved by Meave Leakey 
Photo byy Don Hitchcock CC BY-SA 4.0

Meave soldiered on and discovered or co-discovered significant specimens of several hominins ranging from australopithecines through early members of our genus (above) to Homo erectus. The first part of the book details this story and gives a fascinating account of work in the field (with no facilities for men or women!) and the ever present need to find fossils attractive enough to ensure continued funding. In the second part the emphasis shifts towards putting individual fossils in the context of work by others (including mother-in-law Mary Leakey) and painting a broader view of human evolution. The final part continues the story of exploration while explaining the changes in biology that led to evolution of our species.

Meave and Richard had two daughters. Louise followed in the Leakey family business of finding fossils while Samira co-authored this book. One chapter considers the importance of grandmothers for human reproduction and indeed there are grandchildren. Who knows if a fourth generation of Leakeys will search for clues to our past?

There are excellent photos from life in the field and some very useful line drawings. But surprisingly few photos of the fossils themselves. That is really my only criticism of an excellent book. I found it useful to have the well illustrated book Our Human Story to hand as a complement to the text (reviewed here).

Arsenic and old lakes

Microbial Mats (purple) at Laguna La Brava Chile
From Visscher et al. 2020 CC BY 4.0

Atmospheric oxygen was not plentiful until the Great Oxidation Event yet life appeared much earlier during the Archean Eon (more than 3 gigayears ago). One suggestion has been that  arsenic acted as an electron donor to drive photosynthesis in early life forms.

A new paper by Visscher et al. shows how this might have worked. They investigated microbial mats from Laguna La Brava in northern Chile. These survive under hypersalinic and anoxic conditions by using arsenic and sulphur as electron donors.

A parallel is drawn with the Archean lakes of the Tumbiana Formation where lithified microbial mats are found. 

Kindred or cavemen

 

Neanderthals gained prominence in the Eemian interglacial some 130 thousand years ago and survived several cold and warm periods before disappearing 40 thousand years ago. So they have a much longer history than modern humans. What were they like? Becky Wragg Sykes gives some answers and where answers are missing supplies well argued speculation. Often speculation is backed up by comparison with recent human hunter-gatherers.

The strength of this book lies in covering so much ground. For example I have followed the ancient DNA closely, know a bit about fossil finds, but have steered clear of lithics (e.g. bifaces formerly known as stone axes). Yet there are so many more of these remains and new methods to get the most out of them. They are key to understanding the Neanderthals skills and way of life.

Importantly Neanderthals did not just huddle in caves between hunting woolly mammoths. They also lived through warmer periods and hunted horses and other prey. They were geographically diverse too living in the warmer climes of Iberia and across Asia to the Altai mountains in Mongolia.

It is common knowledge that Neanderthals mated with humans and with the enigmatic hominins called Denisovans about whom we know very little. Sykes thinks they may have been so like us that sex could have been consensual. She is a great fan of Jean Auel (whose books I too have read).

My enthusiasm waxed and waned with every chapter. I could not quite get accustomed to the author's style of writing. Apart from lithics I did not learn an awful lot. But perhaps the book was not written for me.

This one was more my style.

Embryologists meet 1913 in Rio de Janeiro

From left: J. P. Hill, E. Bresslau and G. S. Sansom 1913

Instituto Oswaldo Cruz

J. P. Hill had made his name studying placentation in Australian marsupials. He returned to England in 1907 as Professor of Zoology at University College London. In October 1913, accompanied by G. S. Sansom he went to Brazil to obtain material from South American marsupials in particular the Brazilian common opossum (Didelphys aurita) (see biography here).

Whilst in Rio de Janeiro he met up with the eminent German zoologist Ernst Bresslau who was there from 1913 until the outbreak of war in the following year (see biography here). Bresslau was interested in the evolutionary origins of the mammary gland. Thus like Hill his research spanned monotremes, marsupials and eutherians. 

Bresslau was then at the University of Strasbourg. Later he was recruited to Cologne where he built up the zoology department. He was dismissed from this post by the Nazi regime in 1934 but went to start up zoology at the newly established University of Sao Paulo. Sadly he died there in the following year.

G. S. Sansom did interesting work on germ layer inversion in the water vole (Arvicola amphibius) and later with Hill on the guinea pig (Cavia porcellus). Sansom was a renowned climber. During World War I he served in the Royal Flying Corps and RAF and was awarded the Military Cross and Distinguished Flying Cross. 

Note on the photo: I have identified Hill and Bresslau by comparison with other photos. The printed text reads, "Prof. Ernest Bresslau - Strasborgo; Prof. J. P. Hill - Londres; Mr G. S. Sansom - Londres"

Kees Naaktgeboren 1934-2020

Birth in Domestic and Wild Dogs

Cornelis (Kees) Naaktgeboren was a pioneer in research on the biology of birth. His preferred method was to observe, photograph and film animals before, during and after birth. He kept several wild animals in his home to gain their trust.

This 1970 photo shows Kees (left) when I visited him at Zaandam

I was privileged to work with Kees in 1967 when we filmed the birth process in the rabbit. He incorporated our work in a film (one of many) for Institut für den Wissenschaftligen Film in Göttingen.

Title page of Kees' most important publication
The Biology of Birth ISBN 3 490 04518 1

Most of Kees' publications were in German and his important book, co-authored with E. J. Slijper, is relatively unknown to anglophones. In addition to summarizing his own work it is an exceedingly valuable source for the older literature.

Kees was born 7 November 1934 and died 25 February 2020.

Congratulations to Sofie Lykke Møller

Sofie Lykke Møller's Ph.D. Thesis

Sofie Lykke Møller successfully defended her Ph.D. thesis last week. It was my privilege to be one of her examiners. This is part of an ambitious project conducted in rural Tanzania by researchers from the University of Copenhagen (here). Sofie examined the vasculature of placenta at term and related her findings to a history of anaemia (here) or malaria (here) at various stages of pregnancy.

After the oral exam: Anthony Carter, Sofie Lykke Møller,
Annetine Staff and Peter Damm

This involved a sophisticated stereological analysis with random sampling of the placenta in the field and random orientation of the tissue blocks for sectioning in the laboratory.

Anaemia or malaria in the second half of pregnancy led to adaptive responses that included increases in the length and surface area of the capillaries in the terminal villi. 

Malaria infection before 14 weeks of gestation was reflected in changes at term including a reduction in the volume of intermediate villi and thickening of the endothelial component of the interhaemal barrier. Thus even though entry to the intervillous space is limited at this time, the surface proteins on infected erythrocytes seem able to hinder normal placental development.