TEXT OF TALK
[SLIDE 1] (Title)
[SLIDE 2] THE HYPERCALCIFIED
DEMOSPONGES ARE ALMOST THE ONLY
SPONGES TO SURVIVE THE END-PERMIAN
EXTINCTION. THEY MUST BE TELLING US
SOMETHING. [SLIDE 3] HERE IS A PLOT OF
THE NUMBER OF GENERA THAT CROSS
INTERPERIOD BOUNDARIES. THE DATA
ARE FROM THE 2004 REVISED PORIFERA
VOLUME OF THE TREATISE ON
INVERTEBRATE PALEONTOLOGY, EDITED
BY ROGER KAESLER.
YOU WILL SEE THAT 31 HYPERCALICIFIED
DEMOSPONGE GENERA SURVIVED THE
END-PERMIAN EXTINCTION. [SLIDE 4]
THEY WERE DISTRIBUTED AMONG 21
FAMILIES. THIS PLOT SHOWS ALSO THAT
THE NUMBER OF BOUNDARY-CROSSING
FAMILIES ACTUALLY PEAKED AT THIS
TIME. IN FACT THE PLOT AS A WHOLE
CAN BE VIEWED AS A MIRROR OF
HYPERCALCIFIED DEMOSPONGE
DIVERSITY.
THE DIFFERENCE BETWEEN
HYPERCALCIFIED DEMOSPONGES AND
THE REST OF THE DEMOSPONGES CAN BE
SEEN WHEN WE COMPARE THE TWO
GROUPS. [SLIDE 5] NO DEMOSPONGE
GENERA OTHER THAN THE
HYPERCALCIFIED ONES, SURVIVED THE
END-PERMIAN EXTINCTION. ONLY ONE
FAMILY DID SO [SLIDE 6]
WHEN WE LOOK AT OTHER CLASSES OF
SPONGES WE SEE A SIMILAR PATTERN: IN
THE CLASS HEXACTINELLIDA [SLIDE 7] NO
GENERA SURVIVED THE END-PERMIAN
EXTINCTION, AND [SLIDE 8] ONLY 2
FAMILIES DID SO. (A CONTRAST WITH
THE K/T BOUNDARY, BY THE WAY).
WITH THE CLASS CALCAREA
(INCLUDING THE RELATED PALEOZOIC
HETERACTINIDA) [SLIDE 9] 3 GENERA
SURVIVED THE END-PERMIAN
EXTINCTION, AND [SLIDE 10] 2 FAMILIES
DID SO. ONE CAN SEE THAT THE
CALCAREA PEAKED IN THE JURASSIC AND
CRETACEOUS.
WHAT I THINK THE HYPERCALCIFIED
DEMOSPONGES ARE TELLING US IS THAT
THE END-PERMIAN EXTINCTION WAS
CAUSED BY HYPOXIA, THE ATTENDANT
DISRUPTION OF THE FOOD-CHAIN, AND
THE ATTENMDANT HIGH ULTRAVIOLET
FLUX CAUSED BY LOSS OF THE OZONE
LAYER. [SLIDE 11]
WHY? IF THE HYPERCALCIFIED
DEMOSPONGES HAD SYMBIOTIC
CYANOBACTERIA, WHICH MANY LIVING
DEMOSPONGES HAVE, AND WHICH THE
HYPERCALCIFIED ONES ARE LIKELY TO
HAVE HAD AS AN AID IN SECRETING
THEIR EXOSKELETON, THEY WOULD ALSO
HAVE ENABLED THE HYPERCALCIFIED
SPONGES TO TIDE-OVER A PERIOD OF
HYPOXIA AND POOR FOOD SUPPLY. IN
ADDITION, THE EXISTING EXOSKELETON
OF THESE SPONGES WOULD HAVE
PROTECTED THEM FROM EXCESS
ULTRAVIOLET LIGHT. [SLIDE 12]
NOW WHAT DO THESE
HYPERCALCIFIED DEMOSPONGES LOOK
LIKE? [SLIDE 13] THEY GROW BY ADDING
MODULAR UNITS THAT ACQUIRE AN
EXTERNAL SKELETON OF (USUALLY)
ARAGONITE. ULTIMATELY THE SOFT
PARTS DISAPPEAR FROM OLDER UNITS,
WHICH BECOME SEALED-OFF INTERNALLY.
THE HEYDAY OF HYPERCALCIFIED
DEMOSPONGES COINCIDED WITH A TIME
FROM CARBONIFEROUS THROUGH
JURASSIC DURING WHICH SEAWATER
CHEMISTRY [SLIDE 14] FAVORED THE
DEPOSITION OF ARAGONITE RATHER
THAN CALCITE. (NOTE THAT TIME IN THIS
SLIDE READS FROM RIGHT TO LEFT.) THIS
MAY HAVE HELPED THEM SURVIVE THE
END-PERMIAN EXTINCTION (THE CALCITESECRETING RUGOSE CORALS DID NOT)
BUT IT WAS NOT LIKELY TO HAVE BEEN
THE SOLE REASON FOR THEIR SURVIVAL.
[SLIDE 15] HERE IS WHAT SOME THAT
SURVIVED LOOKED LIKE:
[SLIDE 16] THIS IS GIRTYOCOELIA, IN
WHICH THE MODULES ARE IN A LINEAR
SERIES, AND [SLIDE 17] HERE IS
CYSTAULETES, IN WHICH THE MODULES
FORM A ROLLED-UP SHEET.
[SLIDE 18] ONE COMMON
HYPERCALCIFIED GENUS DID NOT
SURVIVE THE PERMIAN, NAMELY
GUADALUPIA [SLIDE 19] IN WHICH THE
MODULES FORM AN OPEN SHEET. IT MAY
NOT HAVE SURVIVED BECAUSE THE
UPPER SURFACE LACKED AN
EXOSKELETON TO SCREEN OUT
ULTRAVIOLET LIGHT.
THAT ATMOSPHERIC OXYGEN LEVELS
DECLINED ABRUPTLY AT THE END OF THE
PERMIAN, SEEMS WELL-ESTABLISHED BY
RECENT WORK [SLIDE 20]
DEMOSPONGES [SLIDE 21] ARE THE
ONLY METAZOA TODAY THAT HAVE
SYMBIOTIC CYANOBACTERIA.
[SLIDE 22] IF THE PERMIAN
HYPERCALCIFIED DEMOSPONGES HAD
SYMBIOTIC CYANOBACTERIA, THE
PHOTOSYNTHETIC OXYGEN PROIVIDED BY
THE CYANOBACTERIA COULD HAVE
ENABLED THEM TO SURVIVE ANOXIA.
IT WAS SUGGESTED LONG AGO BY
SARA AND VACELET IN 1973, THAT
HYPERCALCIFIED SPONGES MAY HAVE
HAD SYMBIOTIC CYANOBACTERIA TO
HELP THEM SECRETE THEIR CALCAREOUS
SKELETON.
[SLIDE 23] HERE IS THE EQUILIBRIUM
REACTION (TOP EQUATION) FOR THE
PRECIPITATION OF CALCIUM CARBONATE.
CARBON-DIOXIDE IS GIVEN OFF AS A BYPRODUCT. IF IT IS REMOVED FROM THE
REACTION SITE, AS IT WOULD BE BY THE
PROCESS OF PHOTOSYNTHESIS (BOTTOM
EQUATION), THE REACTION WOULD BE
DRIVEN TOWARD THE PRODUCTION OF
MORE CALCIUM CARBONATE.
OF COURSE PHOTOSYNTHESIS ALSO
PRODUCES OXYGEN ALONG WITH THE
CARBOHYDRATES, AND THIS COULD
BENEFIT A SPONGE UNDER HYPOXIC
CONDITIONS.
THE GOOD EFFECTS OF
CYANOBACTERIA DO NOT STOP HERE.
THEY ALSO COULD BE EATEN BY THE
SPONGE [SLIDE 24], ESPECIALLY HELPFUL
IN A FOOD-POOR HYPOXIC ENVIRONMENT.
SPONGES NORMALLY FEED ON
BACTERIA OF ALL SORTS, THAT ARE
TRAPPED BY THEIR COLLAR CELLS.
DIGESTION IN SPONGES IS
INTRACELLULAR, WHICH RESTRICTS
THEIR DIET TO SMALL ONE-CELLED
ORGANISMS, PRINCIPALLY BACTERIA. IF
THE BACTERIA WERE INTERNAL
SYMBIONTS, THE SPONGE WOULD HAVE A
PRIVATE CHICKEN-COOP FILLED WITH
CHICKENS, SO TO SPEAK.
[SLIDE 25] HERE IS VERONGIA (OR
APLYSINA) (PAINTED FROM LIFE, AT THE
NEW YORK AQUARIUM, BY A FRIEND OF
MINE), SEVERAL SPECIES OF WHICH HAVE
SYMBIOTIC BACTERIA, SOMETIMES
CONSTITUTING AS MUCH AS 40% OF
THEIR VOLUME.
[SLIDE 26] HERE IS A
PHOTOMICROGRAPH OF VERONGIA
AEROPHOBA SHOWING SYMBIOTIC
CYANOBACTERIA (THE SMALL ROUND
BODIES) SURROUNDED BY AMOEBOCYTES
OF THE SPONGE.
AT BOTTOM CENTER, A
CYANOBACTERIUM IS BEING INGESTED BY
THE AMOEBOCYTE. ABOVE IT ARE
SEVERAL FOOD-VACUOLES CONTAINING
CYANOBACTERIA IN VARIOUS STAGES OF
DIGESTION --- ENDING UP AS A FINE
POWDER.
ANOTHER REASON FOR
HYPERCALCIFIED SPONGES SURVIVING A
HYPOXIC EVENT MAY HAVE BEEN THEIR
THICK EXOSKELETON. BERKNER AND
MARSHALL, MANY YEARS AGO,
SUGGESTED THAT EXOSKELETONS
EVOLVED TO PROTECT AGAINST
ULTRAVIOLET RADIATION AT A TIME OF
LOW OXYGEN AND THE CONSEQUENT
ABSENCE OF AN OZONE-LAYER TO
SCREEN OUT ULTRAVIOLET. A UV-PEAK
MAY HAVE ACCOMPANIED THE ENDPERMIAN ANOXIC EVENT.
AS FOR THE CAUSE OF END-PERMIAN
HYPOXIA, THE SIBERIAN FLOOD-BASALTS,
DATED RADIOMETRICALLY AT 251
MILLION YEARS B.P., HAVE OFTEN BEEN
CITED AS A SOURCE OF METHANE AND
CARBON-DIOXIDE THAT WOULD HAVE
REDUCED ATMOSPHERIC OXYGEN.
[SLIDE 27] THE RECENT DISCOVERY IN
ANTARCTICA BY VON FRESE AND POTTS
(2006) OF A PROBABLE IMPACT
STRUCTURE 300 KM IN DIAMETER
(ALMOST TWICE THE SIZE OF CHICXULUB)
ROUGHLY ANTIPODAL TO THE SIBERIAN
BASALTS [SLIDE 28] PROVIDES A
POSSIBLE DOUBLE SOURCE OF CO2 AND
CH4.
THE ANTIPODAL RELATION OF MAJOR
IMPACT STRUCTURES TO AREAS OF
FRACTURED CRUST AND VOLCANISM IS
WELL-ESTABLISHED.
[SLIDE 29] THIS SHOWS THE RELATION
OF MERCURY’S CALORIS BASIN TO THE
ANTIPODAL AREA OF FRACTURED CRUST.
[SLIDE 30] ON MARS, THE LARGEST
IMPACT BASINS ARE ROUGHLY
ANTIPODAL TO THE MAJOR VOLCANIC
AREAS: THE DEEP HELLAS BASIN IS
ANTIPODAL TO MOUNT OLYMPUS (THE
LARGEST MARTIAN VOLCANO), THE
ARGYRE BASIN (ROUGHLY) TO ELYSIUM
MONS, AND THE ISIDIS BASIN TO NOCTIS
LABYRINTHUS AND THE THARSIS BULGE.
[SLIDE 31] IF THE ANTARCTIC
IMPACTOR WAS A KUIPER BELT OBJECT,
LIKE THIS MOON OF SATURN (PHOEBE),
MADE OF CO2 (AND PERHAPS CH4) ICE, IT
WOULD ADD EVEN MORE OF THESE GASES
TO THE ATMOSPHERE.
(Note added November 20, 2006 and revised December 4,
2006) The Hypercalcified Demosponges discussed in the
present paper are those having Sphinctozoan and Inozoan
morphology (see Finks and Rigby, 2004, pp. 585-594, for a
discussion of morphologies and relationships) because they are
the only ones for which recent comprehensive data on generic
ranges are available, that is, those dealt with in the 2004 Porifera
Volume 3 of the Treatise on Invertebrate Paleontology. In more
than two-thirds (147 genera) of the 210 Hypercalcified
Demosponge genera dealt with there, growth is modular, and the
outer surface of each module is heavily calcified; this is called
“Sphinctozoan morphology.” The interior of each module may be
completely unskeletalized, or it may contain partitions, or it may
be filled with a skeleton of branching solid fibers or hollow tubes.
In a smaller number of genera (63 genera), this last type of
structure constitutes the entire skeleton, with the surface of the
sponge variably covered with a discontinuous calcified outer
layer; this non-modular (or single-module) structure is called
“Inozoan morphology.” Hypercalcified Demosponges of
Stromatoporoid and Chaetetid (including Favositid)
morphologies, formerly considered Cnidaria, were not dealt with
in Porifera Volume 3, and are not dealt with in this paper. They
are at present under revision(?). They peaked in the Paleozoic,
and survived to the present-day in strongly-reduced diversity. It
is not clear to what extent they were affected by the endPermian extinction event. These morphologies lack a
hypercalcified (i.e., solidly-covered) upper surface. It is possible
that, as largely reefal forms, they were affected by an increased
ultraviolet flux accompanying the end-Permian extinction event,
as suggested above for the Sphinctozoan Guadalupia, and that
rare deeper-water species carried them on into post-Paleozoic
times. The five genera of Inozoan morphology that survived the
end-Permian extinction (the other 26 surviving genera were
Sphinctozoans) also would have lacked a covered upper surface,
but this surface was rather narrow in the case of these genera,
and they could also have lived in deeper water. H. D. Holland
(personal communication) called my attention at the Meeting to
the fact that seawater is an efficient screen against ultraviolet
light at any but the most shallow depths. It may be of interest in
this connection, that 40% (26 out of 65) of the Permian
Sphinctozoan genera survived the end-Permian extinction, but
only 12.2% (5 out of 41) of the Permian Inozoa did so. Total
percentage of Permian Hypercalcified Demosponge survivors ( 31
out of 106) is 29.3%. In terms of diversity, the total number of
Inozoan Demosponge genera living in the Permian was 41, and
the total number of them living in the Triassic was only 21, a
diversity decrease of 50%; on the other hand, the total number of
Sphinctozoan Demosponge genera living in the Permian was 65
or 66, and the total number of them living in the Triassic was 76,
a diversity increase of 15%. The only other genera of sponges to
survive from Permian to Triassic are three genera of
Hypercalcified Calcarea, two with Inozoan morphology and one
with Sphinctozoan morphology. No genera of purely siliceous
sponges, i.e., the non-hypercalcified Demospongea (42 Permian
genera) and the Hexactinellida (11 Permian genera), survived the
Permian. Of course it should be noted that failure of genera to
survive a Period boundary can be due to evolution into new
genera, rather than extinction of populations. If diversity within
a group of related genera decreases across a Period boundary,
extinction of populations has to be involved. If diversity
increases, evolution is certainly involved, although extinction of
populations may also be involved, with new species replacing
them. In the case of the non-hypercalcified Demosponges, there
are only 9 Triassic genera, a decrease in diversity of 81%. In the
case of the Hexactinellida, there are 30 Triassic genera, an
increase in diversity of 173%. As for the Calcarea/Heteractinida,
there are no non-hypercalcified Calcarea in either period, there is
one genus in each period for the sphinctozoan hypercalcified
Calcarea, 2 Permian and 5 Triassic genera for the inozoan
hypercalcified Calcarea, and 2 Permian and no post-Paleozoic
genera of Heteractinida. At the Family level the picture is
perhaps clearer. Except for the 20 Families of Hypercalcified
Demosponges (counting only families actually present in both
periods: 15 Sphinctozoan and 6 Inozoan) that pass the PermoTriassic boundary, only one or two Families do so for each of the
other Classes (and none at all for the Heteractinida). However,
Family-level diversity shows little change across this boundary;
the respective values are Sphinctozoan Demosponges (19/22),
Inozoan Demosponges (8/6), non-hypercalcified Demosponges
(13/9), Hexactinellida (10/10), Sphinctozoan Calcarea (1/1),
Inozoan Calcarea (1/2), Heteractinida (1/0). In the case of all but
the Hypercalcified Demosponges, many new families developed
in the Triassic to replace those lost (or evolved out of?) at the
end of the Permian.