This is Mazon Monday post #17.
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Acanthodes sp.
There are a few types of fish known in the Mazon Creek biota. And while, the classification has changed since the creature corner article on fish, which appeared in March 1989. It's still interesting and instructive. Here is the text and a few drawings.
Fish
A recent discussion into the classification of Mazon Creek fishes proved so interesting it is hoped that you, the reader, might find it equally so. Mazon Creek strata is Middle Pennsylvanian (Westphalian D) in age. "Modern" fish had not yet appeared upon the scene. As an aid in keeping this article from becoming over long, species names will be omitted.
All fish are divided into two basic groups -jawless fishes and jawed fishes. Jawless fishes (hagfisties and lampreys) are placed in the Class Agnatha.
Agnatha found in the Mazon Creek biota consists of: Mazomyzon, Pipiscius and Gilpichthys.
Jawed fishes are placed in the Superclass Pisces-Gnathostomata. This grouping is then further divided into three classes:
- Chondrichthyes - cartilaginous fishes -sharks, rays, etc.
- Acanthodii - spiny sharks -a problematical group
- Osteichthyes - bony fish
The Chondrichthyans of the Mazon Creek biota are: Bandringa, Dabascacanthus, Similharriota, and 8 more common genera.
The Acanthodians of Mazon Creek are: Acanthodes and Gyracanthus.
Now to keep things interesting, the Class Osteichthyes is divided into two subclasses: Actinopterygii (ray-finned fishes) whose modern representatives, the teleosts, are the common fishes of today. The remaining bony fishes are placed in the Sarcopterygii (fleshy-finned fishes), a group heading for extinction, although their ancient representatives are considered to be the ancestors of land vertebrates.
The species of the Actinopterygii present in Mazon Creek concretions are: Chirodus, Elonichthys, Palaeoniscoids, Pyritocephalus, Palaeophichthys, Platysomus and Haplolepis.
The Subclass Sarcopterygii is divided into two component groups: Crossopterygii (\obe-finned fishes or coelacanths) which are the ancestors of tetrapods and the Dipnoi (lungfish) whose large scales are found at Mazon Creek/Pit 11.
The species of the Order Crossopterygii found in the Mazon Creek biota are: Megalichthys, Rhizodopsis and Rhabdoderma.
Lastly, the order Dipnoi: Conchopoma, Ctenodus and Megapleuron.
Concretions containing well-preserved fishes are uncommon -much sought after by the scientific community. Many of the genera mentioned above are "firsts" and have vastly expanded our knowledge of vertebrate evolution.
Lest you think the listing above is "set in stone", classification (taxonomy) is a rigorous discipline, not for the unwary. One's pronouncements often engender heated discussions. To quote an old poet:
"Who didst with Pitfall and with Gin
beset the road that I was in."
Or so it seems at times.
- Andrew A. Hay
The following two concretions are Esconichthys, sometimes referred to as the bladei. At times in the past, it was classified as a larval amphibian. Some now consider it as a larval fish. Although, it's classification is open to further research.
The next one is an awesome Rhabdoderma, which is a coelacanth. This specimen and its modeled likeness was provided by David Duck. Soft tissue is so seldom preserved in the fossil record, and that's what makes this specimen so special. If you look closely, you can see its eggsac preserved three dimensionally. The model reconstruction is to 1:1 scale. Dave has been constructing models for quite a while. They are very detailed. See this post for more information and a picture of his Acanthodes.
