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it * Coelacanth Is a Surrlivor frorn Prehistoric Times

by MurraY Eiland

TTto the general public. the coellcanth i:l. arguabll the most widely recognized

fish outside of familiar sport-fished vari-eties. With a shape totally unlike otherfish, a bulky body and a profusion of fins

ending in a massive paddle tail. it looks

every bit like the "living fbssil" it is billedto be. Popular imagery of the evolutionaryprocess almost never lails to depict a hy-pothetical "landing" of a paddle tish upon

some ancient shore, well on its way to be-

coming an amphibian, which in the popu-

lar imagination will later give rise to ani-mals that will become human. At the same

time. this lish demonstrates how little is

really known of oceanic life, as the dis-

covery of such a large animal points to a

future with yet more surplises. It has

served as something of a "flagship" for in-troducing science to a young audience.The story of the first time a living coela-

canth was discovered is no less romantic

than its lineage.On Dec. 22, 1938, Marjorie Courtney-

Latimer. curator of the East London Nat-

ural History Museum in South Afiica,lr ent doil n to lhe docks lo exutnine a

routine haui of lish specimens. She rec-

Murch 2001

ognized that an unusually shaped, steely

blue fish, 54 inches long and weighing127 pounds, was distinctive, and broughtit back for study. It was caught about fivemiles offshore at the mouth of theChalumna River, an area that was not of-ten trawled. The lish was reported to the

only active ichthyologist in South Africa,James Leonard Brierly Smith, who foundthat it was related to fossil specimens.Having determined that the specimenwas new to science, Smith coined thegenus and species names Latimeriachalumnae, rellecting the person whodiscovered the tirst example and the geo-

graphic region. A media blitz followed,prompting a search for further speci-mens. More were found in the ComoroIslands in 1952, after an intense search'

In the initial, heady days of discovery,it was thought that the coelacanth was a

direct descendent of fishlike Devonianancestors that gave rise to tetrapods (land

dwellers). It was assumed that by study-ing this fish, the physiology, behaviorand ecology of our remote ancestorswould become c1ear. As these aspects are

not available from the fossil record, this

discovery was of great scientitlc vaiue.

When taken in the context of the times,

when evolutionary thought was begln-ning to percolate thlough the public con-

sciousness, it was something of a symbolof the "new science." The discovery ofthe lish aroused a surprising amount ofpublic attention. It is the only survivingmember of a "fossil" grouP of lobe-finned fish, the coelacanths, that originat-ed in the Devonian period, some 360 mil-lion years ago. They were thought tohave become extinct in the Cretaceousperiod, some 80 million years ago. As isclear even from their silhouettes, themodern coelacanth does resemble its fos-

sil ancestors to a remarkable degree.

The coelacanth received rnedia attentiononce again with the identification of a new

population in Indonesia. On Sept. I 8,

199'7, an individual specimen was identi-fied in a fish market on the Indonesian is-

land of Sulawesi. As part of an interna-tional lesearch eftbrt, an expedition rvas

launched, and on July 30. 1998, a second

specimen was captured. The results of this

expedition were published in Nnture, and a

photograph of a coelacanth graced thc cov-

er. This revelation demonstt'ated that the

public's cut'iosity about the "living fossil"had not abated.

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58

Living Fossil/ r*m page s7

Preliminary examination of the secondspecimen suggests that there are slight dif-ferences between this example and the Co-moran specimens. In specimens from theComoros, the color ranges from steel-blue,when captured, to brown, when dead for a

period of time. The Indonesian type ap-pears brown, even when alive, and hasgold flecks over the dorsal surface of thefins and body. These are apparently a pris-matic effect of light reflecting off numer-ous denticles and scales. This raises theimportant possibility that, given the greatdistance between the Comoros and In-donesia, the two specimens were notstrays, but represent different populations.This view is supported by both the dis-tance involved between the two popula-tions and the direction and force of pre-vailing ocean currents.

Fossil EvidenceThe order Coelacanthformes was de-

fined on the basis of a specimen found inthe Permain Marl Slate of Durham andNorthumberland. Fossils include both salt-and freshwater forms through the Triassicperiod. There is a distinct bias towardadult specimens, and the record is incom-plete regarding the morphology and rela-tionships of Paleozoic coelacanths. One ofthe most interesting observations that havebeen made about the coelacanth is that, inspite of many derived features, it is not ob-viously adapted, on the basis of specialfeatures, to a particular lifestyle. No aspectof its morphology indicates specializationfor a particular kind of food. Despite thefact that they have inhabited fresh- andsaltwater environments, they do not showany clear structural changes. The fossilrecord shows that their dentition is rather

feeble, with few genera possessing spe-cialized teeth for predation or crushing.There is no evidence to suggest that loco-motor patterns have changed since the De-vonian. This stands in contrast to the Dip-nal (lunglishes). who show progressiveevolutionary change from the early Devon-ian to the appearance of modern forms inthe Tertiary.

RelationshipsAs is the case in the discipline of an-

thropology, any lineage connected to hu-man evolution is contentious. This trend isalso revealed in the group of "fishes" thatlead to tetrapods. It has been assumed thatmobile land animals arose fiom within thesarcopterygian clade. There are a numberof different ways of defining featuresthought to link "fish" with "early amphib-ians." Part of this problem lies in the diffi-culty of reconstructing amphibian relation-ships, and much of the argument hascentered around the internal structures ofthe snout. The order of features such as

scale type and the configuration of thejaws within this group are also open to in-terpretation. What follows is a summary ofthe important points.

During the Devonian, Ihe Sarcopterygii(lobe fins) were more important than theActinopterygii, although by the Mesozoicnearly all orders were extinct. This isprobably due to the intense pressure thegroup was facing from its progeny, thetetrapods in particular. The early amphib-ians may have had a taste tbr their "ances-tors." Of the living members of this group,the lungfish and the coelacanths, both oc-cupy limited environments. It is hardlysurprising that the fossil record does notrecord the coelacanths aftel the Creta-ceous. After this time they (or a small sur-viving population) may have moved to an

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The coelocanth is one of the orders of rhipidistians, which are believed by sonte to be directanc?.ttors of human beings.

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offshore habitat with little potential forfossilization.

A11 the lobe fins share comrnon muscu-

lar features, paired fins and particular fea-

tures ofthe skull. There are three principalsarcopterygian groups: the rhipidistians,coelacanths (Actinistia) and lungfish (Drp-

noi). Both fossil and modern lungfish are

known for their lack of teeth around the

margin of the mouth. They have a pair ofdentine-covered grinding plates in the

middle of the palate. The lungfish are to-

day represented by three genera from Aus-

tralia, Africa and South America, where

they inhabit smail pools. They can breathe

air when the water becomes stagnant or

dries up, and aestivate to wait for the pool

to enlarge with subsequent rain. They are

represented in the fossil record by burrows

from the Devonian and Triassic periods,

which indicate that they had adopted theirlifestyle in a niche of an extreme environ-ment since that time.

The rhipidistians are particularly inter-

esting, as they are thought to have given

rise to tetrapods, who replaced them in the

Carboniferous period. They have a num-

ber of important features that relate them

to early tetrapods. Not only do the lobe

fins foreshadow structures used for loco-

motion on land, but several species have

labyrynthodont teeth, made from the in-folding of enamel and dentine. This group

is paraphyletic, and includes three orders.

The order Osteolepiformes (Devonian toEarly Permian) had a long body with large

midline fins and a heterocercal tail. The

orcler Porolepiformes had large, rounded

scales, deeP, short bodies, and shortskulis. Panderichthyids are thin andstreamlined, with long snouts. It is thus

something of an oversimplification to sug-

gest that the coelacanth is a direct ances-

tor to humans. It is one of the orders ofrhipidistians to claim that distinction.

The coelacanths arose in the middle De-

vonian and are present in the fossil record

until the late Cretaceous' They have short

bodies and large dorsal, anal and paired

fins. The tail is complex, cornpared to the

rhipidistians', and is divided into threeparts. An interesting feature that is observ-

able in recently dead specimens is a par-

ticular structure in the skull, which seems

to have parallels in rhipidistians. Lotime'ria is the only living animai to have a

functional intracranial joint that separates

the nasal organs and eye from the ear and

brain. The function of this joint has been a

matter of conjecture. Some suggest thejoint was incapable of movement, whileothers note that the persistence of such a

feature suggests it has (and therefore may

have had in the past) functional signifi-cance. While specimens fixed in preserva-

tives were immobile, experiments in 1966

with a thawed specimen showed that thejoint significantly increases the angle ofthe gape and the power of the bite. The

Actinistia (coelacanths) include a numbercontinued on next Page

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Living Fossil/ from page 5e

of specialized fishes. While they are an

"evolutionary blind ailey" in that they have

not led to higher forms, the living coela-

canth differs far less from its fossil ances-

tors than the modern lungfish.

ReproductionThe fossit record does not often offer

clues as to how an organism reproduces.

Latimeria, however, offers important in-formation about the particulars of repro-

duction for their ancestors, if one can as-

sume that the modern coelacanth has

remained the same in this aspect as well as

others. In a number of fossil fish speci-

mens, it is unclear whether a fish is preg-

nant or giving birth or has in fact eaten a

small fish. A major problem in definingwhat mode of reproduction Latimeria luses

is that collection of isolated adults has not

easily yielded a pregnant female. Finally,tn 19'75, a French specimen, given to the

American Museum of Natural History,was identified as having eggs.

Dissections of a gravid female Latime'ria demonstrated that the animal is ovovi-

viparous. Smith (et al. 1975) and his col-

leigues found young with attached yolksacs still in the body of a female. Previous

observations had demonstrated that fe-males contain large shel1-less eggs that

were apparently unsuited to life outside

the female's body. Further' there are a

number of features that make it likely that

they were ovoviviParous:. Latimeria has high levels of urea to

maintain its blood near that of sea water.. There is no evidence that the oviduct

is capable of producing a bony she1l.

. Males possess a modified cloacal re-

gion that could be seen as an intromittentorgan for internal fertilization.

Only the right oviduct is functional inthis species, and five small young were re-

covered from dissections' They are not alarval form, and resemble the adults bar-

ring the yolk sac, which hangs below the

animal. The size of the young averaged

317.8 mm. It is still uncertain whether this

is a derived characteristic, or one that is

shared by other crossopterygians and early

tetrapods.

HabitatStudies in a submersible vehicle have

given new insights into the locomotion and

habitat of Latimeria. Almost all coela-canths have been caught from the east

coast of Grande Comore in the Western In-dian Ocean. Coelacanths are nocturnal,and during the day they gather in smal1

groups in caves between 180 and 210 me-

ters deep. They hunt at night for fish. Be-

low 220 meters, there are fewer caves, and

their prey fish are fewer. They do not often

rise to the surface because they are adapt-

ed to colder, more oxygen-rich waters. The

total population on the west coast of the is-

tand could be between 150 and 210 indi-viduals. Considering the number of indi-viduals per cave and the number of avail-

able caves, it is likely that there could be

no more than 370 to 520 coelacanths at

Grande Comore. From available evidence,

it seems that they produce few offspringbut have a long life span. About 1 percent

of the total population is caught per year.

Despite a change from traditional to mod-

ern fishing methods, the rate of capture

has remained stable until the last several

years.

Locomotion and FeedingOn a two-kilometer stretch of coastline

off Grande Comore, 40 dives were made at

30 different locations. About eight hours

of observation of six different individuals

demonstrated that Latimeria takes advan-

tage of the current to drift' The fins are

used to stabilize and correct minor varia-

tions of the current. Swimming behaviors

that are particular to the Lotimeria include

drifting with the belly facing the surface

and swimming backwards. They also per-

form a "head standing" maneuver for up to

two minutes. This vertical, head-down po-

sition has been observed in other drift-feeding fishes. It is likely that this position

is adopted for catching prey as it rises, and

is quiikly taken up with a minimum of ef-

fort.It appears that the fin structure is adapt-

ed for slow swimming and not suited foractive predation. It has been noted that the

alternating coordination of the paired fins

is a feature shared with only a few bottom-

living fish-including the lungfish-andthis suggests that this pattern of locomo-

tion may have similarities with tetrapod

movement pattems. Neuromuscular coor-

dination for alternating fin movements to

better stabilize the heavy body may have

facilitated the transition to locomotion on

1and.

Because understanding the locomotionof this species may have direct relevance

for the evolution of the tetrapods, it is a

topic that is unusually controversial. The

coilacanth is a slow swimmer, just as its

ancestors probably were. The majority ofits propulsive force is generated by the

second dorsal fin and the first anal fin. The

fish can flap them from side to side, but

can also compress water between them in

a pattem that is unique to Latimeria. Thisis the range of motion of the second dorsal

fin and its peduncle, moving like a ball-and-socket joint, impeded only by the

body.There is particular debate about the role

of the tail in propulsion. The animal is ca-

pable of "fast stafis" that are powered by

strong tail strokes and sinusoidai move-

menti of the body. These bursts of speed

are of short duration, and it is still notclear how long they can be sustained' The

fins of the caudal region undulate slightly,

and it has been postulated that the tail fins

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do not serve for locomotion, because the

entire caudal region may remain rigid'However, some researchers note that while

no active movement of the tail may have

been recorded, there is reason to suspect

that oor.rerful tail strokes are possible be-

.urse of abundant musculature. Whatever

the case, it seems that with such limited

observations of the swimming behavior of

Latimeria, this argument will remain

open.To date, there has been surprisingly

little attention devoted to the feeding be-

havior and prey choice of Latimeria' Itsstomach contents show that the majority

of prey items are from deep water' It*oold b" interesting to examine several

parameters of the prey, including the

maximrm and minimum size range ofthe orevl hor.r active rhe prey species are

tin ierms of speedt: and how many calo-

iies the food ipecies can be expected to

yie1d.

Prospects for the FutureDeipite the amount of interest shown

by botit the scientific community and the

slneral public. conserving this species

ir.r.n,r'.ontiderable difficulty Unlikemany terrestrial species, basic facts ofcoelacanth populations are unknown'Longevity, growth rates or age at maturity,

and -age ind sex ratios in populatio-ns have

not bEen accurately determined' Whiie itis clear that they have a limited range and

a smal1 population, there has been littlepubtic interest in a species that cannot be

easily seen. The region where they live is

not a toudst destination.Several recent articles have raised the

cry that coelacanth populations in the Co-

-b.ot *uy not be as stable as had once

been thought. While early surveys (1987-

1991) showed that there was a relatively

stable population of as many as 650 indi-viduali, surueys rn 1994 demonstrated that

there was perhaps a 30-percent decline in

numbers. This decline is not due to scien-

tific overfishing, but instead due to the is-

landers' search for Ruvettus pretiosus, the

oilfish, which occupies the same depths

and will take the same bait' While some

fishermen set any coelacanth they capture

free, many will kill the animal in an effort

to save tireir line and hook, which is a

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considerable expense'While the species has been listed as

Schedule I of the conservation charter

CITES since October 1989, there is littlehope of saving the species without public

interest. A project suggested by the World

Bank, involving the installation of cameras

in the caves the fish inhabit and moving

fisheries offshore, is in the proposal stage'

Without further conservation efforts, the

long-term survival of this species in the Co-

moios is questionable. As to the population

off the coast of north Sulawesi, we must

wait for further information to become

available. <P

March 2001n

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