Gazelle : The Palestinian Biological Bulletin (ISSN 0178 – 6288) . Number 127, July 2015, pp. 1-8. | Página 2

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During a Wooster Expedition in summer 2013, the Geologists Lizzie Reinthal and
Steph Bosch collected the above specimen from the Matmor Formation (Middle
Jurassic, Callovian) of southern Palestine. The Geology Professor Mark Wilson
from the College of Wooster, Ohio, United States of America, simply assumed it
was an ammonite, especially because they were anxious to find ammonites to
further reinforce their biostratigraphic framework. When he later tried to identify
it by searching through the Jurassic ammonite literature, he could find nothing
like it. Prof. M. Wilson then sent a photograph to his friend the Paleontology
Professor Zeev Lewy, a prominent ammonite expert recently retired from the
Geological Survey of Israel. His answer was a surprise: this fossil is the
Gastropod Snail Discohelix tunisiensis Cox, 1969 (Wilson, 2013).
How could this be a snail when it looks so much like a cool, multi-whorled
planispiral ammonite, complete with ribs? Well, it is not planispiral, if you look
at it again. Below you see the other side (adapical side) of the specimen, with its
slightly depressed center. Most ammonites don’t show such asymmetry. This
actually is a gastropod, and it represents an ancient group (the clade
Vetigastropoda) with primitive features reminiscent of Paleozoic marine snails
(Archaeogastropoda). It is not as much that the snail has converged on an
ammonite style of shell; it’s that the ammonites developed a similar shell much
later for entirely different reasons (swimming, for example). Discohelix was likely
an herbivore grazing in patchy coral reefs like it was represented in the Matmor
Formation. It has become a useful index fossil for the Jurassic of the Tethyan
Realm, although this is the first time it was found in Palestine (Wilson, 2013).
The Jurassic Matmor Formation is the name given to the thick 100 meter unit
that is exposed in HaMakhtesh HaGadol. The Matmor Formation contains fossils
from a Jurassic equatorial shallow marine environment. Bivalves, gastropods,
sponges, corals, echinoderms, and sclerobionts are present in the Matmor
Formation to various degrees (Wilson et al., 2010). The stratigraphy of the
Matmor Formation consists of alternating layers of limestone and marl (Hirsch
and Roded, 1996) (Wikipedia).
Matmor Stratigraphy
The Iraq Petroleum Company originally described the Jurassic sequence in
HaMakhtesh HaGadol (The Big Crater) of Palestine in the 1930s (Hudson, 1958).
These findings were later described and published by Blake in 1935. Shaw (1947)
published a limited summary of the stratigraphy. Hudson (1958) later subdivded
the rocks into the Callovian, Divesian, Argovian, Sequanim biostratigraphic
stages. In 1963, Goldberg subdivided the section into the Zohar, Kidod and Be'er
Sheva formations. Goldberg (1963) further divided the Zohar formation into the
Ziyya and Madsus members. In 1966, Mayac dated the Callovian and what
Gazelle : The Palestinian Biological Bulletin – Number 127 – July 2015