Placentation in sloths

Placenta and fetal membranes of Hoffmann's Two-toed
Sloth (Choloepus hoffmanni) from Turner 1872

Two recent papers cast light on the evolution of sloths. Delsuc and colleagues obtained mitochondrial genomes from living and extinct sloths (here) while Presslee and colleagues used proteomics to describe Type I collagen - likewise from extant and extinct species (here). They agree that notions of sloth evolution based on morphology need revision. 

It was confirmed that two-toed and three-toed sloths are not closely related and group with different forms of ground sloths. A third group with a suspensory life style was found to have diverged even earlier. These sloths crossed a land bridge to the Greater Antilles and went extinct just a few thousand years ago.

Interhaemal barrier of the pale-throated three-toed sloth
(Bradypus tridactylus) Courtesy of Allen C. Enders

Together with anteaters and armadillos, sloths belong to the ancient superorder Xenarthra. Armadillo placenta has been studied in some detail. It is villous haemochorial (discussed here). Anteater placentation is rather similar (previous post). Sloths are different. As shown by Turner, the placenta is lobulated in appearance. It is labyrinthinre and endotheliochorial (here).

Given current opinion on the relations between sloths (Folivora), anteaters (Vermilingua) and armadillos (Cingulata), parsimony dictates that their common ancestor would have had a villous haemochorial placenta. Thus the sloth placenta represents a derived state. The most recent common ancestor of two-toed and three-toed sloths lived >25 million years ago whereas sloths diverged from anteaters >50 mya. 

Hermann von Ihering and polyembryony in armadillos

Uterus of the mulita (Dasypus hybridus) with 9 identical
embryos. From Fernandez Morph Jahrb 1909; 39:302-333

In 1886 Hermann von Ihering opened the uteri of two pregnant armadillos. Both contained 9 fetuses of the same sex. Each fetus had its own amnion but all were enclosed in a common chorion (placenta). He was the first to propose that the embryos were derived from a single fertilized egg with splitting into separate embryos occurring early in development.

Arrangement of fetal membranes in the mulita (Dasypus hybridus).
From Fernandez Morph Jahrb 1909; 39:302-333

Ihering had studied the mulita or Southern Long-Nosed Armadillo (Dasypus hybridus). Later Fernández demonstrated that splitting occurred at the embryonic shield stage in the mulita. Newman & Patterson, working with the nine-banded armadillo (D. novemcinctus), came to a similar conclusion. Fernández, however, was the first to obtain early stages before splitting occurred. More recently, the nine-banded armadillo was the object of elegant studies by Allen Enders (summarized here). Specific polyembryony is known only from Dasypodinae and is thought not to occur in the two other subfamilies of armadillo.

Hermann von Ihering (1850-1930)
CC BY-SA 3.0 Wikimedia Commons

Hermann von Ihering was a German zoologist who relocated to Brazil in reaction to his family's disapproval of his marriage to a widow with a child. This was in 1880. His first years were spent as a collector in the southern state of Rio Grande do Sul, based on an Island known as Ilha do Doutor (Doctor's Island). In 1893 he became the first director of Museu Paulista (State Museum of Sao Paulo) and held this post for 23 years.

Hermann von Ihering´s principal area of expertise was mollusks. He also became an expert on the birds of the State of Sao Paulo, of which he observed 695 species and subspecies. For my Brazilian readers there is an excellent recent biography by Hitoshi Nomura (open access here). It lists 338 of his publications.

His son Rodolpho von Ihering (1883-1939) was also a zoologist. He was appointed vice director of Museu Paulista, which led to the accusation of nepotism that was to force Hermann's resignation. Rodolpho was an expert on fish and is credited with founding Brazilian pisciculture with stations at Porto Alegre in Rio Grande do Sul and Pirassununga, S.P.

References: Biol Zentralblatt 1886; 6:532-9 and Arch Physiol 1886; pp. 443-50

A placenta pioneer from Philadelphia

Newborn and afterbirth of six-banded armadillo
(Euphractus sexcinctus) from Chapman 1901

Some of the earliest studies of placenta in the United States were those of Henry C. Chapman published in Proceedings of the Academy of Natural Sciences of Philadelphia (available on JStor). His observations on the placenta of a six-banded armadillo (Euphractus sexcinctus) were published in 1901 and went unsurpassed for over a century. Importantly, Chapman noted that polyembryony, known from the more widely studied nine-banded armadillo (Dasypus novemcinctus), did not occur in Euphractus.

Fetal membranes of a kangaroo (Macropus giganteus).
Note the small allantois. From Chapman 1881

Chapman is notable for an early study of the fetal membranes of the Eastern grey kangaroo (Macropus giganteus). He noted that there was a large yolk sac but a relatively small allantois that did not form a placenta.

Zonary placenta of an African elephant (Loxodonta africana)
From Chapman c. 1880

Chapman got his armadillo and kangaroo specimens from the Philadelphia Zoo, but his African bush elephant (Loxodonta africana) placenta was from Cooper and Bailey’s London Circus. His was one of several early descriptions of elephant placentation, including a paper by Assheton (here), but there was then a hiatus until the classical work by Amoroso and Perry in 1964 (here). Based on the records of the elephant keeper, Chapman was able to estimate gestation to 650-655 days.

Henry Cadwalader Chapman (1845-1910)

Chapman came from a prominent Philadelphia family. His grandmother was a Biddle and her sister had married a Cadwalader, which may explain his middle name. He studied medicine then spent three years in Europe under Richard Owen in London and Alphonse Milne-Edwards in Paris.

Chapman’s work has been cited by Mossman, Amoroso, Wislocki and Enders (here), but is in danger of being forgotten. When the next paper on Euphractus appeared in 2012 (here), Chapman’s earlier contribution was not acknowledged.