Week Of Wonders: Anthracosaurus

15 12 2009

Good tidings and well wishes!

I realize that it’s been well over a month since my last ‘Weekly’ Wonders installment. So, to compensate for this regrettable trend of inactivity, I’ve decided to initiate a ‘week of wonders’: every day of this work-week will feature a brand new article of ‘Weekly Wonders’ design. Suggestions for specific critters to be highlighted will be considered.

I’ve said it before, and I’ll readily say it again: amphibians have had a fascinating, though somewhat under-studied, evolutionary history which has produced a series of genuine odd-balls that have, for innumerable generations, inspired the emergence of nearly every emotion imaginable, including awe, confusion, and even fear. The sight of the latter feeling in this context may seem incredibly odd, for when one grows up in the company of Kermit the frog and “The Wind in the Willows”, imagining a terrifying amphibian suddenly becomes a tall order.

But in spite of our synthetic biases, a number of prehistoric amphibians (including everyone’s favorite (‘flat frogs’) were in fact equipped with truly ferocious-looking dental arrangements. But arguably no amphibian of any era displays a more intimidating set of chompers than Anthracosaurus russeli: a massive, eel-like predator of the Carboniferous.

Anthracosaurus cranial reconstruction.

Anthracosaurus, incredibly enough, hails from the anthracosauria order the members of which, according to Jennifer A. Clack in her book “Gaining Ground: The Origin And Evolution Of Tetrapods”,:

“are characterized by contact between the tabular and parietal bones in the skull table in combination with the presence of an intertemporal (a primitive character), a closed palate with small or no vacuities [(‘holes’)]in the midline, and often a skull table that is separated from the cheek plates by a noninterdigitating suture. [(connection points between bones that don’t interlock like clasped hands)].

Anthracosaurus skull reconstruction (the largest image is in aerial view)

Additionally, the anthracosauria is  an incredibly diverse group, containing the problematic seymouriamorpha, the intriguing diadectamorpha (which produced some of the planet’s earliest known terrestrial herbivorous vertebrates), the bizarre  gephyrostegida, and the generally ferocious-looking members of the embolomeri. Anthracosaurus itself is allied with the latter group, which largely consisted of crocodile-like piscivores whose remains have been unearthed in both the U.K. and eastern U.S. and sports such genera as Pholiderpeton, and Archeria.

In the “Catalogue Of The Fossil Reptilia And Amphibia In The British Museum (Natural History)“, describes Anthracosaurus itself as follows (never let it be said that these animals had a shortage of teeth!):

“Skull broadly triangular with large postero-lateral expansions [(‘widened ridgstemming from the skull’s rear and sides’)]… orbits very small, subtriangular, approximated, and situated in the hinder third of the skull…. Premaxillary and maxillary teeth few, unequal, and forming an irregular series; one large palatine tusk near the posterior nares [(‘the rear of the nasal openings’)], and the others further back; mandibular teeth irregular [(‘the teeth on the lower jaw are relatively uneven in size and shape’)]; pterygoids apparently carrying a number of denticles. Crowns of teeth ridged, conical, with a transversely oval section at the base, and laterally compressed [(‘flattened from side to side’)] and curved near the summit… Cranial sculpture pitted and very sparsely distributed. Intercentra apparently absent in vertebral column.”

The legendary evolutionary biologist and anatomist Thomas “Darwin’s Bulldog” Huxley first described Anthracosaurus in 1863, giving it the Greek name of ‘coal lizard’ after its geological affiliations.

May the fossil record continue to enchant us all!

UPDATE: For a brief discussion of the relationship that exists between paleo-amphibians and modern amniotes, please check the comments section.




3 responses

16 12 2009

Using the term amphibian as a synonym for stem-tetrapod or non-amniote tetrapod is perfectly legitimate, but it might be slightly confusing to the layman, because it suggests a close relation to modern lissamphibians, which isn’t always there. Reptilomorphs like anthracosaurs or seymouriamorphs are probably closer to us than they are to a frog or even to a temnospondyl – Marjanovic might correct me if I am wrong.

> which produced the planet’s earliest known terrestrial herbivores

The planet’s earliest known vertebrate terrestrial herbivores*, maybe, or at least among the earliest – AFAIK, *Diadectes* is early Permian, while *Edaphosaurus* may extend back to the earliest Permian. Call me a synapsid chauvinist if you want to :).

*I guess at least some of the Carboniferous insects and other terrestrial arthropods must have been herbivorous, even if the majority of them were either predators or were eating fungi and detritus

16 12 2009

> *Edaphosaurus* may extend back to the earliest Permian

Or even the latest Carboniferous.

16 12 2009

Thanks for the insight and corrections, Johannes! I’ve updated the post accordingly.

Note: “which produced the planet’s earliest known terrestrial herbivores” was supposed to say “which produced the planet’s earliest known terrestrial vertebrate herbivores”. My bad. 😛

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