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There are only a few known
placoderm localities in northern Arizona which produce sizable
and potentially identifyable fossils of these primitive Devonian
fish. While Mount Elden may be the most well known locality,
there are several others across the Mogollon Rim that produce
fish. These others include the Highway 87/East fork of the Verde
crossing, Horton Creek, and this one Stoyanow's Arthrodire Red
beds north of Payson.
Introduction
The earliest
known jawed armored fish in North America come from the Devonian.
These primitive fish, known as Placoderms occupied fresh, brackish
and marine environments during that time dominated by bottom
and mid level ecological niches. Placoderms were covered by dense
bony armored plates, articulated with joint lines to allow limited
movement. This dense covering allowed many of the species to
be preserved in the fossil record as collections of both articulated
and disarticulated plates, known informally as "Fish Plates"
amongst paleontologists. Recently, we rediscovered the long lost
Arthrodirian Sandstone named by Stoyanow in 1936, at a location
north of Payson and here we describe our initial exploration
of that locality.
Background
In the
late 1800's, Walcott discovered fish material, specifically placoderm
Bothriolepis in the Devonian Temple Butte Limestone in the Grand
Canyon. Fish plates were found at the East fork of the Verde
River north of Payson by Stoyanow in the 30's, which we have
found at the base of the Martin in that location sometimes pressed
into reworked Cambrian sandstone from the Tapeats Sandstone.
Placoderm material has also been collected at Mount Elden up
in Flagstaff at an isolated outcrop in a side canyon. More recently,
H. Johnson from NAU describes the material from both Mount Elden
and from a broad area east of our new find, including an appendage
of Bothriolepis. While her group
failed to find the long lost Arthrodireian Sandstone beds described
by Stoyanow, the fossil material which was in a limestone/dolomite
matrix is very similar to what was found at our locality.
Geology
See the
Devonian Martin formation , and its some of its fossils on this
web site. It is important to note that it is only the lower facies
of the Martin that is fish bearing. The middle and upper layers
are dominated by a rich invertebrate fauna of corals, brachs,
and stromatoporoids.
Discussion
One of
our primary goals in exploring this area was to locate Frasnian
aged trace fossils, and Holocene travertine fossils known to
occur here. We also kept a look out for the fish material, since
we were traversing the lowermost levels of the Martin, just adjacent
to the Precambrian granites. It was not without many hours of
searching the area on numerous expeditions that we discovered
the reddish Devonian sandstone beds, with the richest fish fossil
assemblage we had ever seen in the State of Arizona.
Outcrop
Description: The reddish-tan sandstone which in places grades
into a fine conglomerate is in a layer about 50 feet thick, extending
horizontally along a wash for about 1000 feet. Rubble and broken
slabs of the material wash downstream, often exposing large numbers
of fossil armor plates within, some boulders containing scores
of dermal plates ranging in size from 1 to upward of 20 cm. A
monotonous gray micrite and dolomite lies on both sides of the
red bed, and contains occasional bone material but little else.
Fossils
include an assortment of indeterminate body armor plates, including
ventral median plates, fin spines, large sections of articulated
skulls, and countless lateral plates.
Associated
fossils include large 2cm sized Paleophycus type trace fossils,
Chondrites and an occasional brachiopod mix with poor preservation.
Here is a photo
pictorial of the material we have recently collected at the Stoyanow
locality, in what appears to be two separate speices - one textured
and one smooth bodied. All are Placoderms, with the textured
speices most likely Bothriolepis sp. As the above image
indicates, we have found perhaps a half dozen complete or nearly
complete placoderm specimens from this site alone. More specimens
collected in future outings may help us identify more clearly
the fossil types and speices of what we are finding in this unique
world class site.
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Bothriolepis
Devonian Arthrodire
found in the Martin
Formation north of Payson
Textured dermal plates
White bone material still present in many specimens
Textured dermal plates
Smooth plates from second species
Textured dermal plates
Textured dermal plates
Many slabs were a jumble of separate dermal plates
Textured dermal plates
One of the thickest pieces of bone we found that day
Textured dermal plates
Enchinoderm test was with the fish material
Large unidentifed plate with bone material
Probable appendage of smooth bodied sp. (juviniles?)
Downslope a rich trace fossil assemblage was found
Textured dermal plates with bone
Large smooth plates with bone
Textured dermal plates with bone
Textured dermal plates with bone
This piece of bone is very peculiar, and might be a large appendage
Textured dermal plate
Textured dermal plates with bone
Our prize of the day - a nearly complete specimen!
Textured dermal plates with bone
Probable ventral median dermal plate
Another prize find, two views of a nearly complete placoderm
Second image with more shadow
Textured dermal plates with bone
Very clear deliniations in the dermal plate texture
This nearly complete fish has a perfect fin appendage! (above penny)
Textured dermal plates with bone
Most of the smooth bodied species, with central ridge
Textured dermal plates with bone