Varanopids: the need for a larger inclusion set

Varanopids (Fig. 1) are those vaguely monitor-like basal synapsids, that are the plain brown sparrows of the clade. Yet from them arise the spectacular pelycosaurs and the less spectacular, but no less important, basal diapsids, according to the large reptile tree.

Figure 1. Varanodon, Varanops and Varanosaurus, three varanopids to scale along with the non-varanopids, Archaeothyris, Apsisaurus, Ophiacodon, Secodontosaurus and Haptodus.

Figure 1. On the left, varanopids according to the large reptile tree: Elliotsmithia, Aerosaurus, Varanops and Varanodon. On the right, non-varanopids: Archaeothyris, Apsisaurus, Varanosaurus, Ophiacodon, Secodontosaurus and Haptodus. Secodontosaurus appears to be close to Varanosaurus. As much as Secodontosaurus looks like Varanosaurus, they are not related. But evidently the genetic material was present as this represents a reversal to earlier morphologies following Haptodus as a direct ancestor.

The problem among paleontologists has been and continues to be: they never add basal diapsids to their inclusion sets. So they don’t know this varanopid-diapsid relationship exists. In the large reptile tree, some varanopids nest within the clade synapsida. Others do not. They are basal to diapsids, so they are called proto-diapsids.

Here’s the breakdown among tested taxa. On the synapsid branch:

  1. Elliotsmithia, Aerosaurus, Varanodon and Varanops form a basal synapsid clade.
  2. Then Archaeothyris.
  3. Then Apsisaurus, Varanosaurus and Ophiacodon, followed by the sailbacks and therapsids.

On the other protodiapsid branch we find:

  1. Mycterosaurus, Heleosaurus, Aracheovenator and Mesenosaurus
  2. Milleropsis, Millerosaurus and Broomia.

Wiki divides Varanopids traditionally into:

  1. Varanopidae: Apsisaurus, Archaeovenator, Varanosaurus and others.
  2. Subfamily-Mycterosaurinae: Elliotsmithia, Heleosaurus, Mesenosaurus and Mycterosaurus
  3. Subfamily-Varanopinae: Aerosaurus, Varanodon, Varanops and others.

Tomorrow and the next day we’ll look at proto-synapsids and proto-diapsids to scale.

The Strange Case of Secodontosaurus

At first, you don’t believe what you’re seeing.
Secodontosaurus (Fig. 1, Cope 1880) looks like a varanopid skull grafted onto a sphenacodont body, complete with dorsal sail. And there’s a genetic reason for that. It’s not modular evolution, although it seems like it at first. It’s more like a reversal because there’s a long line of other taxa between Secodontosaurus and Varanosaurus. And they left their genetic markers too.

Figure 1. Secodontosaurus and its ancestors going back to Varanosaurus. Secodontosaurus is the only sphenacodont with a varanopid-like skull.

Figure 1. Secodontosaurus and its ancestors going back to Varanosaurus. Secodontosaurus is the only sphenacodont with a varanopid-like skull.

Varanosaurus and Secodontosaurus shared traits
Long low rostrum. Naris close to jaw rim. Strongly concave dorsally dentary.

Varanosaurus and Secodontosaurus differences
Quadratojugal greatly reduced in Secodontosaurus. Lacrimal does not contact the naris. Reflected lamina on angular. Loss of mandibular fenestra. Posteriorly shorter postorbital, not in contact with supratemporal.

And that’s just for starters on the skull alone. If anyone has good refs for the post-crania, I’ll complete a reconstruction.

There have been some additions and revisions to reptileevolution.com around the synapsids as I’ve added new taxa recently.

Thanks for all your support.

References
Cope ED 1880. Second contribution to the history of the Vertebrata of the Permian formation of Texas. Proceedings of the American Philosophical Society 19:38-58.

 

Anningia – still an enigma?

Updated February 23, 2015 with an updated reconstruction of Mycterosaurus.

Anningia megalops (Broom 1927, Middle Permian, Transvaal Museum N. 4024) is only known from a poorly preserved back half of a skull (Fig. 1). My introduction was through Romer and Price (1940, Fig. 1) as they associated it with sphenacodonts, like Dimetrodon. Later Reisz and Dilkes (1992) considered “available information insufficient to determine taxonomic position or phylogenetic relationships beyond the likelihood that it may be the remains of a pelycosaur.” 

Figure 1. Anniningia megalops as illustrated by Romer and Price 1940 (below) and in two views from Reisz and Dilkes 1992 with elements colorized and hypothetical rostrum and jaws added.

Figure 1. Anniningia megalops as illustrated by Romer and Price 1940 (below) and in two views from Reisz and Dilkes 1992 with skull element shapes colorized and hypothetical rostrum and jaws added. Remember, the bones are largely missing here. These are impressions of the inner side of the bones.

Comparing Anningia to other candidate taxa brings a pretty close match to Archaeovenator (among tested taxa, Fig. 3), a much smaller and much earlier genus. Broom, Romer and Price and Reisz and Dilkes noted superficial similarities to Mycterosaurus (Fig. 2), which nests close toArchaeovenator, but closer to Heleosaurus.

Figure 2. Mycterosaurus based on Berman and Reisz 1982.

Figure 2. Mycterosaurus based on Berman and Reisz 1982.

The Middle Permian of Anningia (Tapinocephalus Zone) is later than typical pelycosaur strata in the Early Permian. Archaeovenator of the Late Carboniferous, preceded the Permian. Elliotsmithia, another basal pelycosaur, was also a relic taxon in the Middle Permian. So some of these taxa had a long run.

Broom identified a pre-parietal bone, a bone found otherwise only in gorgonopsians and anomodonts and so thought Anningia was a transitional taxon leading to these.

It’s a mess.
There has been extensive fracturing  and erosion of the skull surface of Anningia, which complicates interpretation. Only impressions of the skull roofing bones are preserved. Reisz and Dilkes found “no sutures to suggest the presence of a pre parietal bone.”

Reisz and Dilkes note: “All the osteological features noted above can be interpreted as primitive features for synapsids, and are consistent with placement of A. megalops within varanopseids. Unfortunately, these features are not diagnostic for varanopseids, but are also present in primitive ophiacodontids.”

Reisz and Dilkes report that most of the critical portions of the skull have been lost because most of the type material (left side of the skull) was destroyed when transverse sections were made of the braincase.

Figure 2. Archaeovenator, a smaller relative of Anningia, itself a synapsid outgroup to the Diapsida.

Figure 3. Archaeovenator, a smaller relative of Anningia, itself a synapsid outgroup to the Diapsida. If you think this is starting to look kind of like Petrolacosaurus, you’re right.

Romer and Price reported it had a very short face, even though “the snout has vanished, but the complete lower jaw is present.” Unfortunately that jaw is not shown in Reisz and Dilkes. They report, “Contrary to previous interpretations of this material, we feel that there is insufficient information to determine the length of the complete lower jaw. These earlier interpretations were made before the wide range of jaw proportions of Paleozoic synapsids was known.”

Anningia comes from the same horizon as Galesphyrus capensis (Fig. 4), which is skull-less but Romer and Price repeat Broom’s suggestion that it is of a size that could accommodate the Anningia skull.

No way.
The skull of Anningia is at least as long as the glenoid-acetabulum length. Just check out those scale bars, which are nearly identical in figures 1 and 3.

Figure 3. Galesphyrus, a basal protodiapsid from the same horizon as Anningia.

Figure 3. Galesphyrus, a basal probable diapsid (look at the long ulnare and very short pedal digit1) from the same horizon as Anningia. Unless this is a juvenile, the Anningia skull would never mate to this neck.

In the large reptile tree, protodiapsids nest with varanopids (and the entire synapsid clade), as an outgroup, so the paradigm of calling these reptiles varanopids is entirely reasonable — but they are on another branch, not the Varanops branch. This point is overlooked in smaller prior studies that ignore and exclude basal diapsids (because, after all… we’re not talking about diapsids when we talk about synapsids, are we? [sarcastic droll rise of one eyebrow].

References
Berman DS and Reisz RR 1982. Restudy of Mycterosaurus longiceps (Reptilia, Pelycosauria) from the Lower Permian of Texas. Annals of Carnegie Museum 51, 423–453.
Broom R 1927. On a new type of mammal-like reptile from the South African Karroo beds (Anningia megalops). Proceedings of the Zoological Society of London 227-232.
Reisz RR and Dilkes DW 1992.
The taxonomic position of Anningia megalops, a small amniote from the Permian of South Africa. Canadian Journal of Earth Sciences 29: 1605-1608.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

New Elliotsmithia semi-skull

This doesn’t add a lot to what we knew of Elliotsmithia (Broom 1937), but it does provide a canine tooth, and an upturned mandible tip. The question is: is this also Elliotsmithia? Or something else?

Figure 1. The new specimen referred to Elliotsmithia. It's the same size and shares many traits. In the original Elliotsmithia (Fig. 2) the posterior teeth appear larger. The part and counterpart are overlaid here. I'm guessing that the anterior lower dentary is buried here. Otherwise there would be no room for the next erupting tooth to develop.

Figure 1. The new specimen referred to Elliotsmithia. It’s the same size and shares many traits. In the original Elliotsmithia (Fig. 2) the posterior teeth appear larger. The part and counterpart are overlaid here. I’m guessing that the anterior lower dentary is buried here. Otherwise there would be no room for the next erupting tooth to develop.

The type Elliotsmithia had giant serrated teeth and a forward leaning squamosal. Even so, this is a very close match in most respects.

Figure 2. The type of Elliotsmithia. Those are really big teeth beneath the orbit. The pineal is more centrally placed. And the jugal appears to lean in more.

Figure 2. The type of Elliotsmithia. Those are really big teeth beneath the orbit. The pineal is more centrally placed. And the jugal appears to lean in more.

Elliotsmithia nests at the base of the Synapsida in the large reptile tree. As such it represents the most primitive appearance of the lateral temporal fenestra, but not the earliest. Living among therapsids in the Middle Permian, it was a relic taxon, like the living Sphenodon.

References
Broom R 1937. A further contribution to our knowledge of the fossil reptiles of the Karroo. Proceedings of the Zoological Society, Series B 1937:299-318.
Modesto S, Sidor CA, Rubidge BS and Welman J. 2001. A second varanopseid skull from the Upper Permian of South Africa: implications for Late Permian ‘pelycosaur’ evolution. Lethaia 34: 249-259.

New Anti-PterosaurHeresies YouTube Video

As you all know,
I’m fine with criticism. It helps to fix errors and clear up concerns. I’m not fine with this 36-minute video on YouTube by someone disguised in sunglasses pseudo-named AronRa (Fig. 1). Details follow.

Figure 1. Pterosaurs are Terrible Lizards YouTube video. Click to play it.

Figure 1. Pterosaurs are Terrible Lizards YouTube video. Click to play it. It’s a history of paleontology until you get 32 minutes in. Then it turns libelous.

The caption for the video reads:
“Explaining how human preconceptions, agendas, and biases have negatively impacted the study of evolution and the classification of life forms. This is to illustrate why we have the peer review process.”

I was writing this while watching, so I’m speaking to AronRa directly in the text below, which now appears in his YouTube comments log.

>>

Not much on pterosaurs here until 32 minutes in, but a good history of paleontology.

Contra your comment, Sharovipteryx is a complete fossil  with soft impressions.

At 32 minutes in
I was surprised to see my name mentioned. And then the libel begins.

Contra your comment, I never said everyone who has ever studied pterosaurs is wrong. When something is wrong, I provide evidence for the fact. And I’m quite specific in my criticism and my praise.

Contra your statement, pterosaurs do not have all the characters of the clade Archosauria. That’s why no archosaurs have ever been put forth as pterosaur sisters. And no archosaur has anything approaching pterosaur traits like a long manual digit 4, a long pedal digit 5 and clavicles wrapped around their sternal complex. Just the opposite in fact.

Contra your comment, I never said pterosaurs were lizards from the order Squamata. They nest as lepidosaurs outside of the Squamata. Mark Witton also made the same mistake in his book.

Contra your comment, I never said pterosaurs descended from “lizards with fully avian, double-veined flight feathers.” If you google that phrase, it doesn’t come up. Even fragments of that phrase don’t come up.

I provide photographic evidence, as in your Sharovipteryx example, so the evidence and interpretation can be tested by others. That’s good Science. The fact that no one else has repeated the experiment with an alternate interpretation does not give you the right to say “no one else has seen what Peters sees.” Everyone traces complex fossils and publishes their observations and interpretations! That’s standard practice. Moreover, I support my tracings with reconstructions taken directly from the digital tracings and all the bones fit into standard patterns of construction. So the fault is your believing what one person says, versus what another person can show. 

Contra your comment, I never said that Longisquama had feathers.

I did say Longisquama was a glider, but with pterosaur-like membranes (which you show after making the comment), not with feathers.

You say none of my observations of Longisquama’s hind quarters are evidently true. That’s because no one else has put in the effort. It’s as simple as that. Note that even without the parts I have added, Longisquama still nests between long-legged sister taxa with attenuated tails, uropatagia, a sternal complex, an antorbital fenestra and other traits shown in my drawing. So using phylogenetic bracketing would get you pretty much the same reconstruction. That’s called “multiple lines of evidence.”

Contra your assertions and the stories you have heard, I have traveled to museums around the world to see fossils with my own eyes, just like the other paleontologists. I have also been published in peer-review journals including Science, Nature, the Journal of Vertebrate Paleontology, Historical Biology and others, just like other paleontologists.

You put in a lot of effort to create your video, but to what end? If you have any specific questions or need any clarification on any issue, please bring them to me and either I will set you straight, or you will set me straight.

For you to say my work is “wrong, and remarkably wrong” after planting so many lies, doesn’t make you look good. And supporting the work of Darren Naish (at Tetrapod Zoology) who used discarded ideas and the work of other artists to mock my work shows you’re not very careful about how you weigh truth versus fiction.

You picked on two traditionally controversial taxa of the 500 or so I have covered. If you have better interpretations, let’s talk about them. 

Blackwashing always backfires.

>>>

Here’s a short addition.

AronRa is a creationist debunker. His website is here. So why would he be trying to debunk a site  >devoted< to evolution?

I don’t know.

Sphenacodonts to scale

Yesterday we looked at ophiacodonts from Romer and Price (1940) and showed them to scale. Today we’ll do the same with sphenacodonts (Figs.1,2).

Figure 1. Sphenacodont pelycosaur skulls from Romer and Price 1940.

Figure 1. Click to enlarge. Sphenacodont pelycosaur skulls from Romer and Price 1940. Notice how similar the skull of sail-less Sphenacodon is to that of Dimetrodon. Little Anningia was shown to be undiagnosable by Reisz 1992. D. natal is is evidently the baby Dimetrodon. If so most of the skull is imaginary here.

It’s a different picture, isn’t it, when scale is applied to illustrations.

Figure 2. Click to enlarge. Sphenacodont skulls to scale. Figure 2. Click to enlarge. Sphenacodont skulls to scale.

Figure 2. Click to enlarge. Sphenacodont skulls to scale.

Paleontologist Alfred Romer erected the species Dimetrodon natalis in 1936, previously described as Clepsydrops natalisD. natalis was the smallest known species of Dimetrodon at that time, and was found alongside remains of the larger-bodied D. limbatus. Sternberg (1942) didn’t mention it in his description of an “immature Dimetrodon cf. grandis,” which is a different and smaller specimen, the baby Dimetrodon found here.

Secodontosaurus is the oddball here, but the postcrania is indistinguishable from Dimetrodon. More on that one later.

References
Brinkman D 1988. 
Size-independent criteria for estimating relative age in Ophiacodon and Dimetrodon (Reptilia, Pelycosauria) from the Admiral and lower Belle Plains formations of west-central Texas. Journal of Vertebrate Paleontology 8 (2): 172–180.
Reisz RR, Dilkes DW 1992. The taxonomic position of Anningia megalops, a small amniote from the Permian of South Africa. Canadian Journal of Earth Sciences, 1992, 29(7):1605-1608.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.
Sternberg CW 1942. The skeleton of an immature pelycosaur, Dimetrodon cf. grandis, from the Permian of Texas. Journal of Paleontology 16 (4): 485–486.