Weekly Spotlight: Varanops

31 03 2010

Good tidings and well-wishes!

‘What’s so interesting about the Permian?’ you may ask.

Though I have little interest in it’s famed climax, this remarkable 48-million-year-long stretch of time boasts some of the most diverse and unique critters known to science, including the heavily ornamented Estemmenosuchus, the mysterious Ophiacodon, and the eccentric little Platyhystrix.

One of my favorite ambassadors of the period, however, is the lizard-like pelycosaur Varanops brevirostris of the American southwest.

A sampler of pelycosaur diversity. From back to front: Cotylorhynchus, Ophiacodon, and Varanops

Varanops is, unsurprisingly, the name-bearing genus of the varanopidae family, which emerged during the early Permian. According to palaeos.com,

“Of all the pelycosaurs, the varanopseids in appearance most resemble large modern varanid (monitor) lizards. None developed the distinctive sail that distinguished many pelycosaur groups. All are of small to medium size (none more than about 1.5 meters), with slender, lightly built skulls and a slender, very typically lizard-like body, fairly slender limbs, and a long tail. In fact, we might say that the varanopseids were lizardlike in its general aspect, though this must not be taken as an indication of any close relationships with the lizards…

All varanopseids have specialized marginal dentition, and flattened curved teeth with anterior and posterior cutting edges. The skull, as mentioned above, is light, the temporal fenestra being enlarged and the lower jaw slender. The postcranial skeleton is also lightly built… The varanopseids were probably the most agile predators of their time. These successful animals outlasted all other carnivorous pelycosaurs as highly specialized lizard-like insectvores and small carnivores, and survived as late as the early late Permian (Capitanian epoch). The last forms were all small, and in the end they were probably out-competed by the… diapsids.”

Varanops skeletal reconstruction.

Despite their relatively early emergence, varanopseids are easily identified as pelycosaurs on the basis of their fairly narrow elongated skulls with relatively posterior eye sockets and no trace of an otic notch (which would have theoretically supported an eardrum), with the ear openings located just above the point of jaw articulation (note that the dentition of these animals extended unusually far back in their mouths). When combined with the cladistic makeup of the varanopidae, the stratigraphic location of Varanops and its kin suggests that these quirky little critters may have given rise to the ophiacodontids, edaphosaurs, sphenacodontids and, eventually, us.

Right, then: onto the featured beast itself. With regards to what makes Varanops anatomically unique, I’d encourage any interested party to take yet another glance at the palaeos.com entry on the subject for a full character list. (I will, howbeit, give mention to the curious fact that nearly all specimens of this genus that have been collected to date are juveniles and sub-adults). Nevertheless, I wanted to utilize this space for the purposes of discussing a fact which makes this genus paleontologically unique: its implications for the paleobiological study of fossilized dietary habits. The slight proportions of the creature’s limbs coupled with its tapering teeth (the former skeletal characteristic may also explain why, despite their longevity and wide global distribution, the varanopidae has treated us to surprisingly few remains) ensure that the constant comparison of varanopseids with modern varanids is likely spot-on regarding diet: these were almost certainly relatively nimble animals designed to predate upon small vertebrates, arthropods, and possibly fish.

However, it would appear that what Varanops was eating wasn’t as scientifically interesting as what was munching on it. In 2006, a relatively undamaged skeleton was unearthed southwest of Abilene, Texas which bore a series of bite marks on its shoulder girdle, upper arm, pelvic girdle, and hindlimb. Additionally, the animal’s ventral scales (which were likely the sole source of scalation on most pelycosaurs who were otherwise draped in naked skin as evidenced by various soft tissue remains) were ‘bunched together’ rather than ‘spread out’ as is usually the case, suggesting that the gut region of the deceased Varanops was probably raided by the perpetrator as well.

This is a truly significant find, for it documents the earliest known instance of tetrapod-on-tetrapod scavenging. Even more interestingly, the authors believe that given the fairly miniscule proportions of the dental markings, the casual diner in question was probably not an amniote at all, but rather a land-based dissorophoid amphibian. Hence, never let it be said that amphibians played no further significant role in their various ecosystems following the advent and domination of the sauropsids and synapsids.

May the fossil record continue to enchant us all!




7 responses

1 04 2010
Zach Miller

Caesids are considered a branch of “pelycosaurs” now? I mean, I know that term is paraphyletic anyway, but it’s surprising to see those tiny-headed fatties mentioned in the same breath as sail-backed Dimetrodon and Edaphosaurus.

1 04 2010

I hear you, Zach… phylogeny can be quite bizarre.

2 04 2010

The permian is probably my favorite part of the Paleozoic.

6 04 2010

Same here…it’s awesome!

6 04 2010
Andreas Johansson

I’ve long been annoyed the Permian and Carboniferous get so short shrift in most popular accounts of the history of life. Far too many books give the impression that Dimetrodon was about the only thing living between Acanthostega and the first dinosaurs.

6 04 2010

“Far too many books give the impression that Dimetrodon was about the only thing living between Acanthostega and the first dinosaurs.”

Alas, sad but true…

30 06 2010

Very nice item!
I’m craving for information on the dermal characteristics of early synapsids, i.p. eupelycosaurs (naked, scaled, scuted?). Does anyone have any references to scientific papers on this matter?

Thanks a bunch!


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: