This is the "Fossil Friday" post #62. Expect this to be a somewhat regular feature of the website. We will post any fossil pictures you send in to [email protected]. Please include a short description or story. Check the #FossilFriday Twitter hash tag for contributions from around the world!
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This week we have a very special Mazon Creek fossil to share. This absolutely stunning specimen comes from ESCONI member George Witaszek. It's a Trigonocarpus sp. nucellus, which is the shell surrounding the megaspore. These fossils are rarely found in the Mazon Creek biota. Amazing find George... thanks for sharing!
To learn more, have a look at pages 233 - 235 in "A Comprehensive Guide to the Fossil Flora of Mazon Creek". Here is the description from Jack Wittry.
Trigonocarpus sp. Brongniart, 1825
epidermis and sarcotesta
DESCRIPTION: These seeds are large, radiospermic, and range from 7 mm to 6 cm in length. They are rounded at the base and taper gently from the middle toward the distal end where a small aperture may be found. In life, the seed was divided into layers. Starting from the outside toward the center are the epidermis, sarcotesta, sclerotesta, and endotesta (which surround the innermost nutshell-like nucellus layer), and are collectively known as the testa. The details of layer stuctures are known from permineralized examples, but they are difficult to deter mine in the authigenic cementation fossils found in the Mazon Creek area. The epidermis (see Fig. 1) is rarely found; it is generally seen free from the seed and appears as a distorted, tough, flat skin. Next is the sarcotesta (see Fig. 3), which quickly rots away and is seldom preserved. It was fleshy and sometimes grooved. Below this is the tough, fibrous, and, in some species, deeply grooved sclerotesta (see Figs. 4, 5). Below this layer is the most commonly found and recognizable part: the hard, shiny shell of the centermost female gametophyte called the nucellus (see Figs. 6 through 8). It often displays the three-part organization from which the seed gets its name.
REMARKS: Trigonocarpus is rare and the third most common seed taxon in the Mazon Creek flora. In North America, 43 species of Trigonocarpus have been described. When found as authigenic cementation fossils like those in concretions, they can display many different aspects, caused either by compression or desiccation, and depending on which layer of the seed is exposed. It is now believed that the species count is inflated and contains many synonymous names. From permineralized examples in coalball peels where complete seeds with better details can be observed, only 14 species have been described. Due to this fact, no attempt is made to describe species here.
