Tuesday, January 15, 2019

The Tasmanian Tiger, Extinct, or Not?

The uncertain state of affairs

The question of exinction of the Tasmanian tiger (the thylacine) was raised in an interesting article, "Paper Tiger" (Brooke Jarvis, The New Yorker, July 2, 2018, pp. 44-54).  According to Jarvis, the last one in captivity died in a Hobart, Tasmania, zoo in 1936.  That was twenty years before I arrived and was mentored by Dr. Eric Guiler, an expert on many Tasmanian zoological topics, during my year as a Fulbright scholar at the University of Tasmania.

On several field trips with Dr. Guiler (see endnote), and others by myself, many other animals or their sign, such as tracks or droppings were seen.  But such lack of evidence is not very convincing because- such rarities as the Tasmanian devil and the platypus I only saw in zoos, Michigan mammals known to exist but seldom seen outside of zoos include badgers, bobcats, cougars, flying squirrels, mink, and otters.

It seems reasonable that with the bounty put on tigers, to reduce their predation on farm animals, their numbers may have been reduced beyond their ability to survive.  But Tasmania has much uninhabited potential tiger habitat where few would have chances to observe them.  Some suspect that some may still survive in wild country along the north coast of the Australian mainland.  Both are plausible, but seem to require better documented evidence than is presently known.

A few potential factors

In favor of their non-extinction is the possibility those most adapted to avoiding humans may have left some survivors.  Anecdotal reports would seem to support this view.  But the ease for humans to see what they want to see has caused the shooting death of numerous hunters and a few cattle during the hunting season in Michigan; eye-witness testimony is of questionable reliability.

Extinction is perhaps more likely when numbers are greatly reduced.  Habitat reduction is one cause.  But small numbers may increase inbreeding and thus increase the likely of mortality due to deleterious genes.  Small numbers can also interfere with opportunities for mating and consequent reproduction.  Other factors may also operate if social learning is involved, although I have not heard of Tasmanian tigers forming packs.

Extinct or not, it is still an open question.  Negative facts and hypotheses such as extinction are very difficult, if not impossible, for a scientist to prove.

endnote: Dr. Guiler is the one standing to the left in the picture in post number 51 -
https://evolutioninsights.blogspot.com/2014/06/the-baleen-whale-tooth.html

Joseph G. Engemann      Emeritus Professor of Biology    Western Michigan  University, Kalamazoo, Michigan       January 15, 2019

Monday, January 7, 2019

THE EARLY CAMBRIAN SPECIES EXPLOSION

There seems to be a burst of energy put into discovering new species that add to knowledge of the diversity of life in the Cambrian and earlier fossil fauna described in Gould's book about the Burgess Shale deposits in the Rocky Mountains of Canada.  A recent issue of Science summarizes the results of the summer fossil collecting season of an additional site not far from the Burgess Shale site.  Additional sites, especially in China, are major locations of fossils from the same general time over 540 million years ago,

The discoveries are largely more of the same - arthropod groups, some now extinct, and some ancestors of relatively rare living groups such as horseshoe crabs and onychophorans that have not greatly changed.  Ancestral trees show relationships of major arthropod groups appearing rapidly during a few million years of time.

I do not have much hope of researchers finding fossils that clearly show the origins of annelids and mollusks more than indicated in earlier posts of this blog.  It is a little bit like me, not much is new since I turned ninety.

Joe Engemannn     Kalamazoo, Michigan     November 30, 2018

The issue from the mid-November Science issue had a bit about discovery of a method providing information about epithelial layers formerly thought to be unable to present fossil evidence.  It seems unlikely to provide reliable evidence leading to wholesale understanding of gross aspects of fossil structure, although interesting information seems to be revealed.

Arthropods ancestral to known groups may have not provided fossil evidence for a number of reasons such as - inaccessible ancient rock strata, lack of structures that fossilize,  Isolation of one or more small sub-populations of a species provides opportunities for more rapid development of new species.

My shutdown of blogging for the past month had nothing to do with the current government shutdown other than my wasting my time thinking about the ridiculous current events.

Joe Engemann    Kalamazoo, Michigan    January 7, 2019