This is Mazon Monday post #167. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
-----------------------------------------------------
An early reconstruction of P. longissima
Phlegethontia longissima is a leg-less animal, often incorrectly called an amphibian. It is a vertebrate, which is classified as an aistopod from the Carboniferous and Permian periods. It has been found in Europe and North America. As with any Mazon Creek vertebrate, it is very rare. Some even consider it one of the Holy Grail fossils of Mazon Creek.
P. longissima is referred to as Phlegethontia mazonense and Aornerpeton mazonense in older literature, but those names are now classified as synonyms.
Figure 146.1, Phlegethontia longissima; modified after Shabica and Hay (1997). Top: left lateral view reconstruction. Bottom left to right: skull reconstruction: dorsal, ventral, and right lateral views, respectively. Scale bars = 2 mm.
It was first described as Dolichosoma longissima by Antonin Fritsch in 1875. Fritsch was a Czech paleontologist, biologist, and geologist. He is known for his contributions to the Permo-Carboniferous ecosystems. He also named a few animals which were once thought to be dinosaurs (Albisaurus albinus and Ponerosteus exogyrarum) and the only pterosaur known from the Czech Republic - Cretornis hlavaci.
P. longissima appears on page 146 of "The Fossil Fauna of Mazon Creek" by Jack Wittry.
Phlegethontia longissima Fritsch, 1875
Phlegethontia longissima is a limbless animal and a member of a group of snake-like amphibians that inhabited the Mississippian to Permian swamps of Europe and North America. The length of a complete animal is from 8 to almost 20 cm. The skull has a long snout with jaws containing sharp recurved teeth. The skeleton contains between 200 and 210 vertebrae. Ribs of Aïstopoda (Greek for not-visible feet) are very unusual among the tetrapods. Indirect evidence of a shoulder girdle in some specimens has been detected. This indicates the ancestors of these animals may once have had limbs. The features of this animal are those of a terrestrial predator that likely fed upon active prey. It is believed they moved by undulating their bodies, much like most modern snakes.
This specialized, legless, snake-like amphibian might, at first glance, be mistaken for some type of fossilized leaf or stem material. Closer examination will reveal numerous ribs and a flat amphibian-like skull. P. longissima was first described in 1875 based on a partial skeleton from the Czech Republic. Later, similar fossils were found and described in the Mazon Creek Biota and given the name Aornerpeton mazonense. This name is no longer used, and now has the status of a junior synonym.
The "Richardson's Guide to the Fossil Fauna of Mazon Creek" discusses P. longissima on page 261.
Order Aïstopoda Aornerpeton (Phlegethontia) mazonense (Gregory) Figures 19.12-19.14
Locality. Mazon Creek, near Morris, Grundy County, and Braidwood, Will County. Horizon. Francis Creek Shale, Carbondale Formation, Desmoinesian.
Aornerpeton mazonense, represented by five specimens, is the second most common amphibian encountered at Mazon Creek. These limbless, snakelike amphibians have highly specialized skulls that are lanceolate in dorsal view. The fused frontals and parietals form the dermal skull roof above the large orbital and temporal fenestrae. A sclerotic ring surrounds each eye. There are no interpterygoid vacuities. The braincase bears large ventrolaterally directed fenestrae ovales.
The lower jaw articulates with the quadrate anterior to the posterior margin of the occiput. Each long and slender mandible apparently consists of only two elements, the dentary and a posterior element (McGinnis, 1967). A pair of delicate, roughly sickle-shaped hyoids can also be preserved.
Approximately 90 precaudal and 50 caudal vertebrae are known in one specimen of A. mazonense (McGinnis, 1967). The holospondylous vertebrae are characterized by low neural spines, moderately well developed transverse processes, and large intravertebral foramina for the spinal nerves.
The ribs are long and very thin and may possess up to two stiletto-like costal processes that emanate from the proximal end of the shaft (Lund, 1978). The processes form an overlap- ping pattern between adjacent ribs. The unicipital ribs appear to attach only to the transverse process. Aornerpeton mazonense lacks any trace of either pectoral or pelvic girdles and limbs.
The ventral surface of the body is clad in a series of delicate needlelike gastralia (ventral scales). Individual scales are only about 1.2 mm long and 0.03 mm in diameter (Gregory, 1948). The overall pattern is en chevron. One specimen of A. mazonense appears to retain what Lund (1978) interprets as a pigment pattern consisting of dark transverse bars and spots distributed over the head, neck, and throat region. These markings may correspond to cryptic or disruptive coloration comparable to that seen on many diurnal predacious snakes (Lund, 1978).
George Langford describes P. longissima as Phlegethontia mazonense in his second book, "".
Figure 220. Phlegethontia mazonensis. This second specimen was found in the Wilmington area by Mr. and Mrs. (Priscilla) William D. Turnbull in 1953, along with the holotype of Turnbullia priscillae (see Figures 157, 158). It is the first and only amphibian found in the Wilmington area, and oddly enough it was found on the Turnbulls' first visit there. It was a 300,000-to-1 shot. Mr. J. C. Carr, of Morris, Illinois, lifelong collector at Mazon Creek, figured that his chance of finding an amphibian was about 300,000 to one. He never found one. For my companions and myself in the Wilmington area, the chance was less than one in 500,000. We split more than that number of concretions and found no amphibian.
At first glance, this specimen might be mistaken for a long Lepidophyllum leaf, but if examined closely, it will be seen to have many ribs; also a skull, which might be mistaken for a leaf scale attachment. The specimen is described and figured by the Turnbulls (1955). It is number PR281, Chicago Natural History Museum.
Figure 221. Phlegethontia mazonensis, drawing of the second specimen.
Specimens
From "The Fossil Fauna of Mazon Creek"
From George's Basement
