You’ll know about coelacanth, a lobe-finned fish that is closely related to the ancestor of tetrapods (four-legged vertebrates). The first pre-amphibian that crawled ashore might have looked much like this fish. Lobe-fins originated about 400 million years ago, and until fairly recently all but the lungfish were thought to have gone extinct about 80 million years ago. No fossils were found between then and the present, but then a live specimen was dredged up off South Africa in 1938, astounding biologists (read the whole story at the link!):
On December 23rd, 1938, the Nerine entered port after a stint trawling off the mouth of the nearby Chalumna River. The dockman called Marjorie [Courtenay, curator of a Museum in South Africa], who was busy mounting a reptile collection, but felt she ought at least go down to the docks to wish the crew of the Nerine a merry Christmas. She took a taxi, delivered her greetings, and was about to leave when, according to her account, she noticed a blue fin protruding beneath a pile of rays and sharks on the deck. Pushing the overlaying fish aside revealed, as she would later write, “the most beautiful fish I had ever seen, five feet long, and a pale mauve blue with iridescent silver markings.” Marjorie had no idea what the fish was, but knew it must go back to the museum at once. At first the taxi driver refused to have the reeking, five-foot fish in his cab, but after a heated discussion, he drove Marjorie and her specimen back to the museum.
It’s called a “Lazarus species,” because it came back from the dead. (Of course, there’s no guarantee that modern coelacanths would be reproductively compatible with their fossil relatives.) The next specimen wasn’t found until 1952, but now they’re caught by fishermen (accidentally) fairly regularly. Two species are recognized, with widely divergent habitats: Latimeria chalumnae, living in a few localities off East Africa, and the congener L menadoensis, known from two specimens off Indonesia, the second captured alive (but dying in a few hours). Their status as different species was first based on differences in skin color (a terrible way to diagnose two species as different), but their status is fully confirmed from differences later found in their mitochondrial DNA, which put the divergence between L. chalumnae and L. menadoensis at around 40 million years ago. (I’d bet there are other populations in between these areas!)
Here’s the African species photographed underwater:
The behavior of both species was largely unknown, but we now know a lot more about L. chalumnae from a new paper in Marine Biology by Fricke et al., based on 23 years of study around the Comoro Islands, including many hours of underwater observation by unmanned submersibles. I’ll just hit the high points:
- The population in the study area was stable about about 300-400 individuals.
- (This is known from earlier studies): the embryos aren’t expelled into the sea until three years after zygotes are formed: the longest period of embryonic development of any vertebrate.
- The submersibles watched 115 individuals over the period and were able to recognize individuals. Several were marked by the submersible with acoustic tags, allowing them to be tracked. One fish in 1987 was seen again in 2008, confirming that some can live at least 21 years as adults. But it takes them years to become adults, so the life span is undoubtedly much longer.
- The rate of natural mortality is estimated at about 0.04, or 4% of individuals dying per year. The authors note that there are no known predators on adults except fishermen.
- Based on this low rate of natural mortality, the authors estimate that the mean adult life expectancy is about 23 years, but that some individuals can live over 100 years. This is a long time, but in line with longevities of some other deep-water fish. Females are estimated to give birth only about 7 times during their lives, producing about 140 offspring.
- There is a strong size dimorphism, with males being larger (range 1.6-1.8 meters) than females (range 1.2-1.3 m). How do they know this? Because they measured live individuals with lasers, like this one (figure from Fricke et al.):
- Coelocanths hunt in the depths at night (they’re piscivores, or fish eaters), often at 500 m, and rest during the day (sometimes in small groups) in underwater volcanic caves at lesser depths (180-206 meters). It’s dark 500 m down, and I wonder how these fish hunt. Some individuals use the same “home caves” over and over again.
- Curiously, the authors did not observe a single subadult or juvenile coelacanth during the entire study. (One has been seen elsewhere). The authors hypothesize that the young stay down deep to avoid cannibalism by adults.
- The good news: the population off the Comoros is not declining, due mainly to the use of motorized fishing canoes that take fisherman further offshore, away from where the coelacanths live. The bad news is that coelacanth populations in Tanzania are far more endangered, since they’ve started using deep-water gill nets. More than 80 coelacanths have been killed in this way since 2003. The IUCN status of the African species is “critically endangered” and the Indonesian species as “vulnerable.”
Here’s a wonderful video of L. chalumnae photographed at depth. Note its curious “head-standing” behavior toward the end, which I think is a mystery to biologists.
This one was taken in a submarine canyon; you can see its distinctive lobe fins very well:
____________________
Fricke, H., Hans Fricke, K. Hissmann, R. Froese, J. Schauer, R. Plante and S. Fricke. 2011. The population biology of the living coelacanth studied over 21 years. Marine Biology 158: 1511-1522, DOI: 10.1007/s00227-011-1667-x.
They weren’t really measuring them, they were actually trying to attach the lasers to their heads.
Win.
Not “lasers”, “LASERs”!
/@
Really wonderful post!
Just so interesting to read about, I’m sure there is so much left for us to know of what’s on in deep waters…
I hope the discovery of these new species won’t bring them to extintion…
well not so “new” of course.. 😀
Such marvelous, intriguing creatures. About the headstand – (I bet its not that simple), but are they just orienting away from the light?
I haz a quibble with the first paragraph. Given the series of fossils represented by Eusthenopteron, Tiktaalik, Acanthostega, Icthyostega, etc., it seems misleading to say that the first pre-amphibian to crawl ashore might have looked like a coelocanth. All of those speces had much more developed tetrapod limbs (Acanthostega had all three elements of the limb already developed) and yet were still mainly aquatic (walking in shallow waters). In my experience, this fish “crawling ashore” metaphor does more harm than good – it seems quite implausible to creationists.
Second, since lobe-finned fishes are not tetrapods, the common ancestor of all modern tetrapods was more similar at the sequence level (and more closely related) to modern tetrapods than to coelocanths, lungfishes, etc.
I heartily recommend Samantha Weinberg’s A Fish Caught in Time: The Search for the Coelacanth, a wonderful little book in which the author chronicles in great detail the happenings surrounding the discovery and description of the two species.
The history of the fish revolves around improbable characters such as the famous South African ichthyologist J.L.B. Smith who was obsessed with the coelacanth, as well as the above-mentioned Hans Fricke who built his own submarine specifically to study the fish.
In addition, an interesting ethical question emerged when the Indonesian species was first described. The man who found a single specimen in a fish market wasn’t quick enough to publish his description and was beaten to it by a French scientist.
Ouch! And it was an accidental discovery on his honeymoon too…
Three years? Wow.
As the Marine Biology article mentions, this is actually the length of the “pregnancy” since coelacanths are ovoviviparous and give live birth. The embryos remain inside the mother for some time after hatching, until the yolk sacs are consumed.
Yes, I fixed this, thanks. It’s still pretty amazing.
or even MORE amazing!
Nice overview! A bunch of things in there I didn’t know.
One correction, though. It was not thought that lobe-finned fish were extinct. Lungfish are lobe-finned fish and their existence has been known for a long time, being relatively common in fresh water on multiple continents. What was thought to be extinct were the coelacanths, a specific order within the lobe-finned fish class.
Fixed this, too, thanks!
Don’t forget the Paris coelacanth, posted about earlier this year:
http://whyevolutionistrue.wordpress.com/2011/02/20/paris-peregrinations/
How could we! 😉
As to your comment on skin color, take a look at Rachovia hummelincki and R. pyropunctata in the link below. DNA says they are sister species. Their ranges come close but they are alloptric and live in waters of different water chemistry. Incidentally, when I first collected R. pyropunctata, I misidentified it as R. hummelincki.
http://www.itrainsfishes.net/content/
As a little girl I actually got to see this exhibition as I spent a few of my childhood years in East London.
As a result I learned about evolution for the very first time at the age of five.
See link for the letter from Dr Smith to Marjorie.
http://www.eastlondon.org.za/coelacanth.html
Whoops, I mean: to Dr Smith from Marjorie.
Oh well, you know what I mean.
Cool fish; interesting ref with cool new observations; kind of a sloppy post. Quibbles:
no it’s not. See #4.
no it didn’t. See #4.
What? Are you suggesting that there are fossils referred to the extant species?? Citation needed!
Yeah? where/
Yeah? where/
Good point… on seamounts, maybe, but I wouldn’t bet on it.
I apologize for not meeting your exacting scientific standards; I do the best I can when writing these posts early in the morning.
But is it necessary for you to repeat criticisms that have already been made? What’s that about?
My comment about the “Lazarus species” was not meant to imply “Linnaean” conspecificity with fossil species, but to dispel the COMMON NOTION that the extant species are identical to the fossil ones. I’m perfectly aware that the fossil fish are similar but not identical to exant ones. And I can’t look at your map, but I was simply guessing that there are places in the Indian Ocean, in between Indonesia and Africa, that also harbor coelacanths. Do you have a problem with that speculation?
Really, if you’re going to post on this website, which I consider my online home, I’d ask you to tone down your dickishness when you want to criticize the science. Check comment 4 if you want to see how to offer criticism in a civil way.
Actually, “Lazarus taxon” is used for groups at any level of systematic resolution that disappear and then reappear in the fossil record, or vanish in the fossil record but have living representatives show up today. So your usage is perfectly good – my palaeo friends use it in this sense, and they’d know.
Does the low pressure of the upper ocean Kill them when they are caught I wonder? I mean, do they decompress too quickly & die or can they be caught alive?
They are really gorgeous creatures.
They’ve been brought up alive – the Comoros fishermen who fished the population that the second specimen came from brought that one in alive, as I recall, and kept it alive in a flooded canoe for a day or so, but it didn’t do very well – possibly kept too warm. No doubt further efforts have been made, this was almost 70 years ago.
As I recall (also – pertinent books are out of reach behind a huge barrier of office talus), the lung is largely filled with fat and wouldn’t likely be greatly affected by pressure changes.
“…office talus.”
LOL.
ta!
Thanks for the beautiful videos and great story. I read a book about the discovery when I was a child, and it left a deep impression. I never imagined we could now sit around and watch videos of live coelacanths, and see with our own eyes those big, muscular articulated fins in action….amazing.
Lou
I think I read that same book as a kid. It was about the Latimeria species and the woman it was named after, right?
That rings a bell…
That’s right! I think “Latimeria” may have been the first scientific name I ever learned.
Great post! I got much elsewhere but this still added points.
Also nitpicks. I will add one more which I believe is wrong, whether we use biology (?) or common definition:
“The authors note that there are no known predators on adults except fishermen.”
There doesn’t seem to be feeding involved, since the fish tastes terrible. (Hence the absence of known predators, likely.)
I think most of the fishermen put it back, it seemed to have a something of a taboo status here and there if I understood correctly.
But deaths did happen, especially if fishermen went out for night-fishing, mostly oilfish I take it: one of the proposed remedies was to offer – medication! Oilfish can be used as laxative, apparently.
[Wax esters. Wow, what will nature come up with next?]
“…there are no known predators on adults except scientists.”
There, fixed it. 😀
There doesn’t seem to be feeding involved, since the fish tastes terrible. (Hence the absence of known predators, likely.)
Maybe you’re kidding, but if not, it’s a bit subjective to assume that something “tastes terrible” for all predators. The real issue seems to be that wax esters are indigestible (at least for us). There are suggestions that large sharks may feed on coelacanths if they get the chance (they don’t generally occur in the same habitats).
But deaths did happen, especially if fishermen went out for night-fishing, mostly oilfish I take it: one of the proposed remedies was to offer – medication! Oilfish can be used as laxative, apparently.
Sorry, but it’s very unclear what you are saying here. Deaths from what? Remedies for what?
No kidding, but poorly written. The first sentence is what was said on human tastes. (IIRC; maybe I can find it again.)
The other was an inference from this one example to predict the general absence of predation (and presumably why they the species still exist).
Nothing subjective in the latter hypothesis, unless you put it there by some addition.
Poorly written indeed. 🙂
Deaths from fishing. Remedies for whatever ailments laxatives are used for.
[In this context, I take it laxatives and other visibly working “medication” are overused outside of medicine, since they offer placebo and “proof” of function in the purported remedy.]
Nothing subjective in the latter hypothesis, unless you put it there by some addition.
I meant that our tastes are subjective, so it’s a bit risky to infer generally applicable biological hypotheses from them. A billion flies can’t be wrong, and so on…
Also, hypothesis fail: putative shark predation.
Intersting how the fins move like limbs of a lumbering tetrapod.
Interesting observation, and perspicacious of you to pick up on it – apparently this is true of all living sarcopterygians, and functional morphologists think that it’s significant.
‘Note its curious “head-standing” behavior toward the end, which I think is a mystery to biologists.’
Not at all. Coelacanths are known to moon creationists (who think the coelacanth is an anomaly which refutes evolution, of course). Clearly this was merely a case of the coelacanth misidentifying the photographer….
Measuring fish with Fricke lasers?