Marria, A Neglected Fossil from the
Burgess
Shale
Larry Solomon, 2006
The Middle Cambrian (c.530 mya) fossils found by Charles D. Walcott in
1909 in the
Burgess Pass of British Columbia have received considerable attention
in the last two decades. Even in the popular press, books have been
published, such as The Burgess Shale
by Harry B. Whittington (1985), Wonderful
Life by Stephen Jay Gould (1989) and The Fossils of the Burgess Shale by
Briggs, Erwin, and Collier (1994). It is unusual for the popular
imagination to be captured by invertebrate fossil life -- usually such
interest is restricted to dinosaurs and humans.
There are several reasons that the fossils of the Burgess shale are so
unusual and important. Firstly, their age is significant, because the
Cambrian was for a long time believed to be the age when life first
appeared on Earth. That is no longer so, but the Cambrian era is still
considered seminal for the development of complex life forms,
especially the metazoans, and it is still considered the period in
which life "exploded" into a myriad of complex new forms. This
"explosion" is often called the "The Cambrian Explosion" (CE).
Nowadays, CE doesn't seem to receive the debate that it
once did and still warrants. It seems that science has tacitly accepted
it as though it is fact. However, I believe that CE is an illusion.
The sudden occurrence of fossils of great variety during this era are
almost exclusively fossils of the hard parts of marine animals --
shells mostly. Even in the earliest Cambrian, trilobites with a complex
eye and other complex body structures are common. These could not have
appeared without previous evolutionary forms, yet undiscovered. Hard
shells probably evolved during the Cambrian, thereby making their
fossilzation possible. Earlier life forms probably didn't have these
hard shells -- just soft parts, making fossilzation much more
improbable. Earlier fossils have been discovered recently, but they
seem to
have no links to much of the Burgess shale fauna. Some are just as
bizarre, e.g., the Vendian faunas, and the earliest are invariably very
much simpler, e.g., cyanobacteria. It is rare, but not impossible, for
soft parts to be preserved in the fossil record. That is one of the
reasons that the Burgess shale fossils are so important and unusual.
Cyanobacteria are mostly preserved in the form of stromatolites, hard
skeletons that bacteria built and lived in. For a long time
stromatolites were not considered life forms at all. Many experts
considered them to be rock forms that resembled life, but not really
life. Then living stromatolites were found off the west coast of
Australia, and elsewhere. They made exactly the same forms as the
fossils. So stromatolites are among the oldest and longest continuously
living life forms on the planet.
Another factor that makes the Burgess fossils important is their
extraordinary preservation. Very fine details, soft parts, and even
internal organs of these ancient animals are captured in the rock
matrices. Such detailed preservation is very rare. They are also
interesting because many of their forms are bizarre, or at least very
unusual, and in some cases, have defied classification into any of the
standard categories of life. We still don't know what some of them are,
where they fall in the line of evolution, or how they fit into
known biological categories. Some of the forms do not occur in
the surrounding ages of evolutionary history; i.e., they are unique and
don't seem to have any links to life before or after them. No one knows
where they came from or where they led. Not all of these forms are
unusual or bizarre, however. Some, however, do fall nicely into known
families, like
those of trilobites and sponges.
In 1931 Rudolf Ruedemann described a new Crustacean from the Burgess
shale that he named Marria Walcotti. Plate 5 showed Ruedemann's
reconstruction of this bizarre animal.
Plate 5 from the article by Ruedemann,
which follows.
Plate 4, from the article that is reproduced below, shows an
unretouched photograph of the actual fossil. The holotype and paratype,
which are in the USNM as No. 83485, may be the only specimens of this
strange creature. The locality from which it was collected is on Mount
Strephen, rather than from the Burgess pass. What I find as strange is
the absence of any mention of this specimen in subsequent publications
about the Burgess shale fossils.
From the article text reproduced below, Ruedemann wrote "There is no
fossil crustacean that can be directly compared with Marria walcotti. The only fossil
form that to our knowledge in a general way resembles it is the
grotesque Bostrichopus antiuus Goldfuss of the lower Carboniferous
(Culm) of Nassau, Germany." (see reproduction below, Figure 1.)
Later, he states:
"The great age of the form and the fact
that a similar development of the antennae (at least of the second
pair) takes place in at
least two orders of the Branchiopoda, namely, the Phyllopoda and the
Cladocera, as well as in the next order, the Copepoda, make it
probable a priori that the species represents a generalized type, not
directly referable to any of the recent orders of crustaceans.
Positive determination of its relationship is prevented by the fact
that
the mandibles and maxillae remain unknown and that the
subdivisions of the body can not be definitely made out."
Perhaps someone can shed some light on the apparent
enigmatic disappearance of this fossil from the records. For those who
are curious, I would like to offer a few pictures of recent animals
that seem to me to bear some resemblance. These are all Copepods from
Ernst Haeckel's Kunstformen der Natur
(1904)..
- Calanus pavo (Dana)
- Clytemnestra scutellata
(Dana)
- Oncaea venusta (Philippi)
- Cryptopontius thorelli
(Giesbrecht)
- Acontiophorus scutatus
(Brady)
- Corycaeus cenustus
(Dana)
- Sapphirina darwinii
(Haeckel)
- Augaptilus filigerus
(Giesbrecht)
The following
article
is reproduced from From the Proceedings of the United States
Museum, Vol 79, Art 27
Smithsonian Institution, United States National Museum, Washington,
D.C., 1931
SOME NEW MIDDLE CAMBRIAN FOSSILS FROM BRITISH COLUMBIA
By RUDOLF
RUEDEMANN
New York State Museum, Albany, N. Y. 1931
The Middle Cambrian faunas of British Columbia, particularly
the marvelous assemblage of organisms from the Burgess Pass, dis-
covered by Dr. Charles D. Walcott in 1910 and studied by him
throughout the remainder of his life, continue to afford most inter-
esting subjects for research. A small group of these fossils from
the Burgess shale and the Stephen formation was sent me some time
ago by the authorities of the United States National Museum for
further study. In their general appearance they suggest graptolites,
and as such had been laid aside for future study by Doctor Walcott.
Upon close study, however, they have proved to be an unusually
interesting and at the same time difficult assemblage of fossils, none
of which belong to true graptolites. It is with the full realization
of the tentative nature of the determinations that the following
results of my studies are published.
Plate 4
PROCEEDINGS OF THE NATIONAL
MUSEUM VOL. 79
CRUSTACEA
MARRIA WALCOTTI, new genus and species
PLATES 4-5
Two specimens (from the famous fossil bed on Mount Stephen,
Loc. 14s), when seen with the naked eye are amazingly suggestive
of a graptolite such as Nemagraptus
gracilis. They were laid aside
by Doctor Walcott with the other supposedly Cambrian graptolites.
After the study of these two specimens on which the following
description and discussion are based, further search yielded five
more incomplete ones, most of which had been regarded as frag-
ments of the sponge Pirania
muricata Walcott.1
When the specimen selected as the holotype was studied
under
the microscope it lost its graptolitic aspect and revealed itself
as
the segmented body of a crustacean with large regularly jointed
arms, each joint of which gives rise to a side branch. In other
words, it is a bizarre crustacean, its immense swimming feet
serving
to distinguish it from all other Cambrian crustacean genera.
Inasmuch as Marrella may become a synonym, if
my subsequent
contentions are sustained, and thus nullify the compliment that
Doctor Walcott wished to pay his friend Prof. John E. Marr, of
St. Johns College, Cambridge University, I am calling this new
crustacean Marria in order to perpetuate the compliment.
Description.—Body
small (7.5 mm. long and 3.5 mm. wide in com-
pressed condition), elliptical in outline, with truncated front.
Cara-
pace of head (or cephalothorax ?) of subquadrangular outline
(about
3.25 mm. long and 3.5 mm. wide) occupying half of the body.
Postcephalic portion (either thorax + abdomen or abdomen only)
consisting of seven (or possibly eight) simple segments, the
first of
which is 0.7 mm. long, the others decreasing slightly in length
as
well as regularly in width. There is no trace of a telson or of
caudal
styles. The frontal portion of the supposed head possesses a sub-
triangular depression, the base of which is in front. Near the
apex
is a small tubercle with a central depression, strongly
suggesting the
presence of an eye. Since the surfaces of the head and segments
show
no sculpture, they were apparently smooth. On the head, to the
left
and right and behind the eye, are several irregular nodes, which
may
be incidental to the preservation. There is also a pair of black
spots
or minute tubercles on either side of the eye. A distinct
tubular de-
pression, suggesting the alimentary canal, begins behind the eye,
where it is somewhat wider, and extends backward to the first
segment.
The most important feature of this
organism is the presence of
the two pairs of immense swimming appendages, both of which
proceed from the anterolateral corners of the head. Both are
funda-
mentally biramous, dividing into two principal branches, which in
turn send out a series of secondary, filamentous branches bearing
setae on one side. The first pair, which is the shorter, is
directed
forward, the second sideways. Only one of the first pair (on the
right side) of swimming appendages is preserved. The protopodite
is short and stocky. One of the branches (exopodite) has only the
base preserved; the other branch (endopodite) bears four or five
(one displaced) long, flexuous, secondary branches and shows the
base of a fifth or sixth. The series of secondary branches on the
exopodite from the four bases shown on the stump in front of the
head, as drawn in the restoration (pl. 5), are conjectural. We can
not determine whether this first pair of appendages represents the
first pair of antennae or the second; if the latter, the first
pair of
antennae may have been small or very tenuous.
The second pair of swimming appendages
is by far the larger
of the two and may either represent the second pair of antennae
or
may correspond to the mandibular foot of the nauplius. (See under
-Relationships.) The protopodite is again short and powerful and
appears to consist of two joints. The forward division of the
foot,
which we take to be the exopodite, is extended horizontally and
reaches a length of 20 mm.; the number of its joints can not be
defi-
nitely established. On one side it bears 7 to 11 thin flexuous
sub-
branches (exites) and on the other about 6, which branch off
nearer
the base. The posterior division of the swimming foot, according
to
our view the endopodite, curves backward nearly parallel to the
body, giving off about 10 slender, thin endites, about 14 mm.
long,
on the outer side of the branch, and terminates in a similar but
shorter (9.5 mm.) endite.
All the exites and endites are provided
with short setae on one
side. These, however, may be only the bases of longer bristles,
since
there is one fragment that retains long stiff setae on the
portion of
the swimming appendage preserved.
On the left side are three simple legs,
two of which undoubtedly
proceed from the underside of the head, and the third (not drawn
on
restoration) appears to do so. On the right side are the bases
of what appear to have been abdominal feet, the stumpy second,
however, being doubtful. There is no evidence of a biramous
struc-
ture or of gills, the exopodites apparently alone protruding
beyond
the body.
Occurrence.—Middle
Cambrian, Stephen formation (Loc. 14s),
Mount Stephen, British Columbia.
Holotype and
paratypes.—U.S.N.M. No. 83485.
Relationships of
Marria.—There is no fossil crustacean that can be
directly compared with Marria
walcotti. The only fossil form that
to our knowledge in a general way resembles it is the grotesque
Bostrichopus antiquus Goldfuss
of the lower Carboniferous (Culm.)
of Nassau, Germany. (See fig. 1.) The one specimen known to
have been found is preserved in the Bonn collection. Good figures
are given in part 1 of Roemer's Lethaea geognostica (1876), pi. 38,
figs. l0a-b, and recently (1929) Steinmann has redescribed it, giving
a restoration. According to Goldfuss's figure this minute crustacean
is surrounded by a corona of 60 extremely thin, flexuous, filamen-
tous appendages, radiating from three (or four?) short basic ap-
pendages, located behind the head. Steinmann reconstructs the
form as having the filamentous feet distributed evenly in pairs on
the segments of the body and concludes that the species belongs to
an entirely extinct class of crustaceans. Even though the swimming
feet have a similar structure, our species is still different in the
form
of the body, especially of the head, which bears two large eyes in
Bostrichopus.
The outstanding characters of Marria are the very simple body
and the enormous development of the antennae (see postea), which
indicates an extreme adaptation of an otherwise primitive form.
The great age of the form and the fact
that a similar development
of the antennae (at least of the second pair) takes place in at
least
two, orders of the Branchiopoda, namely, the Phyllopoda and the
Cladocera, as well as in the next order, the Copepoda, make it
proba-
ble a priori that the species represents a generalized type, not
directly referable to any of the recent orders of crustaceans.
Posi-
tive determination of its relationship is prevented by the fact
that
the mandibles and maxillae remain unknown and that the subdivi-
sions of the body can not be definitely made out. How uncertain
are
the determinations of Cambrian crustaceans from incomplete re-
mains is clearly evidenced by the fact that Walcott's
determinations
of the Burgess shale crustaceans were challenged by Fedotov (1925)
and Fedotov's in turn by Henricksen (1928).
Other important characters of Marria
are the immense develop-
ment of two swimming arms (first and second pair of antennae, see
postea), the large unsegmented head with carapace (possibly cephalo-
thorax) bearing a single eye, five pairs (or less) of legs, a simple
abdomen, consisting of about seven segments, and the absence of a
telson.
It is customary to refer the earlier Paleozoic
crustaceans to the
suborder Phyllopoda of the order Branchiopoda, because these are
the oldest and most primitive crustaceans. [The recent genus Apus,
or Lepidurus, has been traced
to the Permian (Ruedemann, 1922).]
There is indeed a close resemblance to the family Limnadiidae of the
Phyllopoda—particularly to Limnetis
in the biramous, strongly
developed second antennae, the single (not bivalved) carapace, the
fused compound eyes in the middle of the head, and the small num-
ber of thoracic feet. Although a telson is present in Limnetis, in
L. brachyura it is so small
that this species appears but little differ-
ent from our specimens in this respect. The body of the Limnadi-
idae is, however, laterally compressed and the carapace covers most
of it.
According to common consensus of opinion the Limnadiidae lean
toward the second suborder of the Branchiopoda, the Cladocera.
Marria also has important characters in common with Cladocera,
namely, the strong development of the biramous second antennae
into principal organs of locomotion, the fused compound eyes, and
the short body with a small number of thoracic limbs. Though the
Cladocera have a telson, it is variable in size and in some species
much reduced. The carapace is likewise variable, for while it is
most frequently a bivalve shell inclosing the whole postcephalic
region of the body, it may be reduced to a mere brood pouch, as in
Leptodora. The segmentation of the body is little pronounced, if
not obscure, the thorax bearing as many pairs of limbs as there
are
segments; the abdomen having but three segments, bearing no limbs,
but with a telson. The head in the Cladocera, however, is always
bent downward so that the first pair of antennae and the median
eye
are on the ventral side.
It will be seen that our form, though
not directly referable to the
Cladocera, agrees well with that order in the development of the
second antennae, the carapace (aside from its common bivalve form
in the Cladocera), the fused eyes, the small number of segments,
and
thoracic limbs. It would seem to differ in not possessing the
down-
ward bend of the head or a telson.
Our species also invites comparison with the
second order of
crustaceans, the Copepoda, in regard to the possible retention of
the
single nauplius eye, the strongly developed biramous second pair
of
antennae, and the possible absence of a carapace. The Copepoda
differ from Marria in having five pairs of biramous feet, the first of
which is attached to the cephalothorax and the others to the thoracic
somites. On the other hand, the strong development of plumed
hairs in the pelagic forms may well be duplicated in Mama. Some
of the members of the family Peltiidae of the suborder Podoplea
have even flattened bodies, somewhat like isopods and probably
Marria.
Finally, the close resemblance of our form to
the nauplius of
many crustaceans, among them even the Cirripedia and Malaco-
straca, is undoubtedly most striking. These bear not only a single
eye but also two pairs of large biramous swimming legs, formed by
the second pair of antennae and the mandibles. These biramous
limbs, as, for example, in the nauplius of Lepas (see fig. 2), bear a
large number of long spines, which in turn are set with stiff setae,
the whole producing an organ strangely resembling that of Marria
in which the spines are further developed into jointed secondary
branches (endites and exites). As we can not be certain that thft
two pairs of swimming limbs of Marria
represent the first and
second pairs of antennae, it is possible to assume that they may be
the second antennae and mandibles and that we see in the nauplius,
and still more so in the following protozoaean larva of the Eucarida,
a recapitulation of an ancestral Marria. We can visualize our species
making its way through the water in a jerky or saltatory and more
or less irregular manner, like most of the crustaceans that have large
biramous swimming legs and short bodies.
As none of the crustaceans here used for comparison,
except the
nauplius and protozoaean stages of later crustaceans, possesses a
like development of the two large biramous swimming limbs, it
appears necessary to consider Marria not only as a member of a
new family, the Marriocaridae, but even of a distinct suborder of
the Entomostraca, the Marriocarida.
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