What were the gondwanatheres?

Right mandible of Sudamerica ameghinoi a gondwanathere
From Koenigswald W. Acta palaeontologica polonica 1999; 44: 263-300

Gondwanatheria is a clade of mammal-like forms once widely distributed on the southern continents that once were part of Gondwana. Until now they were known only from teeth and jaw fragments such as the one shown above. It therefore was a major breakthrough when a complete skull was found in Cretaceous deposits on Madagascar. It is described in the current issue of Nature (here) as a new genus and species Vintana sertichi.

The most exciting part of the paper is the phylogenetic analysis. Firstly, it reveals a sister group relationship between gondwanatheres (from southern continents) and multituberculates (from the northern continent Laurasia). Secondly, it shows both can be accommodated with another enigmatic group, the haramiyids, in a monophylectic clade Allotheria, i.e. all these fossil species shared a common ancestor.

Finally, Allotheria fits within Mammalia so all these mammal-like species were true mammals. The lineage that led to present day monotremes (duck-billed platypus and echidnas) is basal to Allotheria whereas that of marsupials and placentals came later.

My recent post on Extinct Madagascar concerned more recent mammals, all descendants of individuals that reached the island by rafting. But Madagascar has a more distant past, starting as part of the supercontinent Gondwana. Vintana derives from a lineage that existed on Gondwana before the breakup, evolved in isolation and went extinct, leaving Madagascar without mammals for millions of years.

Origins of the laboratory guinea pig

Newborn guinea pigs (Cavia porcellus)
(c) Per Svendsen

The domestication of guinea pigs dates back hundreds of years. Animals raised for food or the laboratory are of a species (Cavia porcellus) that is not found in the wild. Its closest relatives are the Brazilian guinea pig (C. aperea) and the montane guinea pig (C. tschudii) from western South America including Peru.

Analysis of mitochondrial DNA (here and here) clearly shows that the domestic guinea pig groups with the montane species. Furthermore, analysis of the skeletons of mummified guinea pigs from archaeological sites in Southern Peru and Northern Chile (here) indicates that domestication started in the Andes, the natural habitat of C. tschudii.

Karyotypes of Cavia tschudii male (left) and C. porcellus female (right)
From Walker et al. 2014 (here) (c) Laura I. Walker et al.

A recent paper (here) compared the chromosomes of the wild and domestic species and confirmed that differences arose in the course of this first phase of domestication.

Guinea pigs were imported by European traders in the 16th Century and underwent a second phase of domestication that resulted in the laboratory guinea pig. There was even a further phase of domestication in South America with two lineages of guinea pigs selected for improved meat quality.

Plesiorycteropus was a giant tenrec

Innomate (pelvic bone) of Plesiorycteropus an extinct mammal
from Madagascar (Drawing by Forsyth Major 1908)

The recent fauna of Madagascar included species that were much larger than those found today an example being the gorilla-sized lemur Megaladapis. One of these fossils Plesiorycteropus has defied interpretation. It has been compared to the aardvark and other myrmecophagous (termite-eating) mammals such as pangolins and anteaters.

The most thorough study of the subfossil material, by McPhee (here), defined two species, P.  madagascariensis and P. germainepetterae, and erected a new Order Bibymalagasia to accomodate them. More recently Asher (here) assigned Plesiorycteropus to the superordinal clade Afrotheria.

Phylogenetic analysis based on collagen sequencing has
Plesiorycteropus as sister to the tenrecs from Buckley 2013 (here)

A recent study (here) relied on molecular sequencing of collagen from a fossil Plesiorycteropus and a range of living mammals. The technique, which uses soft-ionization mass spectroscopy, is a promising alternative to sequencing of ancient DNA. The resultant tree confirmed that Plesiorycteropus belonged to Afrotheria but related to tenrecs rather than the aardvark. Therefore it is part of the radiation from a single colonisation event (Sweepstakes Distribution).

Tailless tenrec (Tenrec ecaudatus) the largest Malagasy tenrec
weighs about 1 kg. Photo by Markus Fink (GNU Free Documentation Licence)

Estimated size of Plesiorycteropus was 6-18 kg so it certainly was a giant compared with living Malagasy tenrecs and the giant otter shrew which weigh about 1 kg.

Picturing Madagascar's past

Cover features elephant birds Aepyornis hildebrandti 
and the giant lemur Archaeoindris fontoynontii

Extinct Madagascar by Steven M. Goodman and William L. Jungers has just been published by  The University of Chicago Press (ISBN-13 978-0-226-14397-2). As implied by the subtitle Picturing the Island's Past the text centres around 20 superb colour plates by the Bulgarian artist Velizar Simeonovski each depicting the fauna found at a particular fossil site.

The emphasis is on the larger species of reptiles, birds and mammals that became extinct and the authors explore possible causes ranging from climate change to hunting. This bias means that smaller mammals, such as tenrecs and endemic rodents, are scarcely mentioned except in the synoptic tables.

Aldabra giant tortoises - relatives of the extinct Malagasy species
Muhammad Mahdi Karim (Gnu Free Documentation Licence)

However, I found it fascinating to learn that the extinct giant tortoises (Aldabrachelys spp.) are likely to have been important grazers and that the extant species on the Aldabra Atoll represent a greater biomass per square km than the mammals on the Serengeti grasslands.

Malagasy crowned eagle piercing the shoulder blades of a sloth lemur

The chapter on an extinct raptor, the Malagasy crowned eagle Stephanoaetus mahery, was exciting; by analogy with the extant African species S. coronatus, it likely was a predator of large lemurs including the likewise extinct sloth lemurs (Palaeopropithecus spp.). But the book's plan makes it harder to find a coherent account of, for example, the "Madagascar aardvark" Plesiorycteropus madagascariensis. No reference is made to a study showing that this enigmatic species belongs to the Afrosoricida and thus is related to the tenrecs and golden moles (here).

Apart from the plates, figures are in grey tone. They include historical photos such as Grandidier's 1898-99 expedition. However, even more recent photos lack sharpness and contrast, perhaps due to the quality of paper chosen.

The introductory chapters give useful information on the geology and history of the island including the origins of the Malagasy people from Austronesians and Africans. In general the impact of humans in past centuries may have been overstated. The chapter on elephant birds concludes there is no evidence they were hunted to extinction and some evidence they may have been victims of climate change. The real and frightening aspect is the enormous habitat loss that has occurred in the last 60 years and that is still ongoing.

Reproduction in domestic ruminants

ISBN13: 9781899043637

Every four years there is a conference on reproduction in domestic ruminants. The latest was held this August at Obihiro, which is on Hokkaido, the North Island of Japan. The accompanying book (details here) is a useful collection of reviews covering most aspects of male and female reproductive biology.

The opening chapter Ruminant phylogenetics: a reproductive biological perspective by William J. Silvia is an excellent overview that integrates molecular phylogenetics with morphology including various aspects of placentation.

There are several chapters on placentation including Early placentation and local immune regulation by Kazuhiko Imakawa and colleagues. This deals with transcriptional regulation of IFNT the gene coding for interferon-tau, which is secreted by the trophectoderm at the blastocyst stage and results in maternal regulation of pregnancy. Another topic is syncytins (previous post) in ruminants. In addition, I have contributed a chapter on Evolution of placental structure and function in ruminants.

Previous volumes in this series have appeared under the imprint of the journal Reproduction. Although the current volume conforms to that journal's format, it has been published in book form by Context. As far as I can make out, it is not possible to purchase individual chapters.

Placenta-derived exosomes and the immune response to pregnancy

Placental exosomes at the maternal-fetal interface
Reproduced with permission from Mincheva-Nilsson and Baranov Am J Reprod Immunol 2014
(c) 2014 John Wiley & Sons A/S

Exosomes are tiny vesicles (30-100 nm) released from living cells that facilitate intercellular communication (previous post). Exosomes are assembled by and released from the syncytiotrophoblast of human placenta. They carry molecules that could be of critical importance for suppression of the maternal immune response, which might otherwise cause rejection of the fetal allograft.

A brand new review by Lucia Mincheva-Nilsson and Vladimir Baranov (here) summarizes several mechanisms that might be involved and suggest "the placenta is surrounded by a cloud of exosomes that creates a beneficient and protective mileau for its existence." Among these mechanisms (summarized in the Figure) are reduced NK-cell cytotoxicity (through down regulation of the NKG2D receptor), impaired T-cell signalling, apoptosis of activated lymphocytes and effects mediated by TGF-beta that might include recruitment of regulatory T-cells (previous post).

There is more. The syncytiotrophoblast also releases much larger particles (0.2-2 micrometers) often referred to as STBM (for syncytiotrophoblast-derived microparticles). They are not carefully assembled as are exosomes but resemble a form of cellular debris. Importantly, they are pro-inflammatory with the potential to activate the immune system. Mincheva-Nilsson and Baranov hypothesize that placental exosome production may counterbalance the deleterious effects of STBM. They argue that determination of a normal range for the STBM/exosome ratio should be a research priority as it could lead to development of new diagnostic tools.

The Blakiston line

Thomas Wright Blakiston (1832-91)

Thomas Blakiston spent 23 years in Hakodate, one of the Japanese Treaty Ports opened to foreign trade in 1858. He failed in his original enterprise, to establish a saw mill, but flourished as a merchant. More importantly he made many observations as an ornithologist.

Blakiston was the first to observe that fauna of the northern island of Hokkaido differed from that of Honshu. Thus the Strait of Tsugara formed a zoogeographical barrier of a type similar to the Wallace Line (previous post). It is referred to as the Blakiston Line.

Blakiston's Fish Owl (Bubo blakistoni)

There is a memorial to Thomas Blakiston atop Mount Hakodate. In addition the former British Consulate, now a museum in the historic quarter of Hakodate, commemorates his several contributions. Blakiston's Fish Owl was named in his honour.