Something about Clepsydrops (Dimetrodon natalis)

Figure 1. Clepsydrops (Dimetrodon) natalis. Here we find the original reconstruction with a too large pelvis. Putting the loose elements on the old reconstruction gets us closer to reality. There's a scaled version over the scale bar compared to a full-size Dimetrodon.

Figure 1. Clepsydrops (Dimetrodon) natalis. Here we find the original reconstruction with a too large pelvis. Putting the loose elements on the old reconstruction gets us closer to reality. There’s a scaled version over the scale bar compared to  Dimetrodon grandis. Ghosted area represents a restoration.

We first met Dimetrodon natalis a few posts ago when Romer and Price presented it along with a selection of other Dimetrodon skulls. I don’t know much about Clepsydrops (Cope 1875), a name which seems to have gone out of favor, or to the back of the museum drawer. Romer and Price in their Review of the Pelycosauria (1940), considered it an ophiacodont, close to Varanosaurus, perhaps based on size, but this was before the skull became known. The femur is robust. The data is a little hard to read. In the old days they used to say “image at 1/4 size” rather than applying scale bars.

Shelton et al. 2103 reported, “The Briar Creek Bonebed (Artinskian, Nocona Formation) in Archer County is oneof the richest sources of Dimetrodon bones in the Lower Permian of Texas, USA. Based on size, a small (Dnatal is ), an intermediate (D. booneorum), and a large species (D. limbatus) have been described from this locality. It has been proposed that these traditionally recognised species represent an ontogenetic series of only one species.

… The external fundamental systems observed in the largest humerus and the two largest femora confirm that D. natal is is not the juvenile of a larger species. The presence of the EFS in the cortex of their long bones unquestionably indicates that  these animals had attained skeletal maturity. 

…The results thus partially refute Bakker’s (1982) hypothesis,that the bones of D. natalis, D. booneorum and D. limbatus only represent an ontogenetic series of a single species, which may in turn disprove the juvenile/adult habitat shift hypothe-sis. Juveniles and adults of D. natalis are found in the samebonebed. However, the findings are insufficient for fully test-ing the habitat shift hypothesis. The results support Brinkman(1988), as well as the morphological classification used by Romer & Price (1940).”

References
Bakker RT 1982. Juvenile–adult habitat shift in Permian fossil reptiles and  amphibians. Science 217: 53–55.
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, 172–80.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of American Special Papers 28, 538 pp.
Shelton CD, Sander PM, Stein K, Winkelhorst H 2013. Long bone histology indicates sympatric species of Dimetrodon (Lower Permian, Sphenacodontidae) Earth and Environmental Science Transactions of the Royal Society of Edinburgh 09/2012; 103(3-4). DOI:10.1017/S175569101300025X

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.

Baby Dimetrodon – Chimaeras and Fakes – Part 1

Many have seen this cast (fig. 1) entitled, “Baby (or Juvenile) Dimetrodon.” It’s a common piece of plaster merchandise sold at fossil fairs, etc.

Is it a complete fake?
The specimen has not been illustrated in the literature (that I know of), but it has been described (Sternberg 1942) and the description is a perfect match. Parts (Fig. 1 in gray) have been added to the cast to make it more interesting and complete. Sternberg (1942) reported the specimen was originally at the Walker Museum in Chicago, but in 1953 most Walker paleo exhibits, perhaps including this one, were moved to the Field Museum.

Figure 1.  Sternberg 1942 described this specimen he attributed to a baby or juvenile Dimetrodon. Parts added by artisans are in gray.

Figure 1. Sternberg 1942 described this specimen he attributed to a baby or juvenile Dimetrodon. Parts added by artisans are in gray.

On the plus side
One of the more complete Permian fossils is this baby/juvenile Dimetrodon (Sternberg 1942, Figs. 1, 2), less than a quarter the size of an adult with a much shorter sail and much longer legs. If this is a juvenile Dimetrodon, these proportions change allometrically during growth. The mandible was slightly shorter, compared to the adult, indicating the skull was likewise not larger relative to the body.

Click to enlarge. Figure 1. Baby Dimetrodon (above) compared to adult (below) to the same scale and to different scales. Note the smaller sail and longer legs and tail. Regressing the baby to egg size suggests the sail developed after hatching.

Figure 2. Click to enlarge. Figure 1. Baby Dimetrodon (above) compared to adult (below) to the same scale and to different scales. This is the first reconstruction of this specimen that I am aware of. Restored parts in light red. Note the smaller sail and longer legs and tail in the juvenile.  Regressing the baby to egg size suggests the sail developed after hatching. I’m curious about the rib length from front to back on the juvenile, different from the adult.

So, longer legs on a juvenile synapsid?
That’s not the pattern we see in mammals or Heleosaurus, a varanopid(?) protodiapsid in which adults have the longer legs. In Dimetrodon the juveniles didn’t have marginally longer legs. Juveniles had legs relatively twice as long as those on adults. Generally longer legs provide more speed to attack prey or avoid predators.

Is this really a baby Dimetrodon?
Or is it a different smaller species? Bakker(1982) suggested different habitats for Permian juveniles would help them avoid adult predation. Brinkman (1988)  cast doubt on Bakker’s idea by showing that the specimens found in floodplain and swamp sediments represented two different species, not adult and juvenile populations of the same species.

Do we need more tiny specimens and a few teenage specimens to help determine what the situation is here? Both sides make sense.

Sternberg (1942) wrote,
“The preservation of the bone is poor: It is probable that the bony elements were never well ossified.” He also wrote that three or four partial skeletons of Dimetrodon grandis were found in the same pocket, which lies in the breaks of Coffee Creek in Baylor County, Texas. If we assume those were adults, there goes Bakker’s and Brinkman’s hypotheses. Brinkman did not reference the Sternberg paper, but noted that poor ossification attended smaller Dimetrodon specimens.

Only parts are fake
Just because parts of this specimen have been added with restoration, doesn’t mean the rest of the skeleton is useless or should be labeled “a fake.” In this case, we should use what is real and avoid what is fake. The size and proportion relationships are still good data that make a good story.

References
Bakker RT 1982. Juvenile-Adult Habitat Shift in Permian Fossil Reptiles and Amphibians. Science 217 (4554): 53–55. doi:10.1126/science.217.4554.53.PMID 17739981.
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.
Sternberg CW 1942. The skeleton of an immature pelycosaur, Dimetrodon cf. grandis, from the Permian of Texas. Journal of Paleontology 16 (4): 485–486.

A paper written on fossil fakes is online here.

Stenocybus and Haptodus

In lateral view Stenocybus and Haptodus are close matches. Even so, the two are distinct taxa separated by others according to the large reptile tree now up to 315 taxa (not counting the therapsid or pterosaur trees). Stenocybus was twice as large, but this specimen of Haptodus was one of the smallest ones known.

Figure 1. Comparing the basal therapsid Stenocybus to the basal sphenacodont, Haptodus. The similarities are great here, but Stenocybus still nested closer to Ophiacodon.

Figure 1. Comparing the basal therapsid Stenocybus to the basal sphenacodont, Haptodus. The similarities are great here, but Stenocybus still nested closer to Ophiacodon.

Haptodus
The maxilla was shorter than the lacrimal in Haptodus. The teeth were smaller. The quadratojugal was not visible. The ascending process of the premaxilla was shorter.

Stenocybus
The skull was narrower in ventral view and the palate was smaller in Stenocybus. The palatal elements (other than the vomers) were largely behind all the teeth in Stenocybus. Haptodus represents the plesiomorphic condition. The pterygoid was smaller in Stenocybus as were the quadrates. The frontal and parietal was smaller producing a more visible lateral termporal fenestra in dorsal view. The canine tooth was more prominent and the maxilla housing its root was much deeper, overlapping the shrinking lacrimal. The septomaxilla shifted more toward the surface and the prefrontals formed larger ‘eyebrows.’

Of course Tetraceratops, the darling of traditional paleontologists, is not related and does not resemble these two enough to drag it away from a closer nesting with Tseajaia.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again. 

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Credner H 1888. Die Stegocephalen un d’Saurier aus dem Rothliegnden des Plauen’schen Grudes bei Dresden: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 40, p. 490-558.
Currie PJ 1977. A new Haptodontine Sphenacodont (Reptilia: Pelycosauria) from the Late Pennsylvanian of North America: Journal of Paleontology, v. 51, n. 5, p. 927-942.
Huene F von 1925. Ein neuer Pelycosaurier aus der unteren Permformaiton Sachens: Geologische und Palaeontologische Abhandlungen, Jena., v. 18, NF 14, p. 215-264.
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

wiki/Haptodus
wiki/Stenocybus

Assembling the Squamate Tree of Life – part 1

Some of the heaviest hitters in paleontology joined forces to produce a 300-page paper (including tons of photos and the data matrix) of squamate phylogeny, including several fossil taxa. Gauthier et al. (2012) takes the reader through the history of squamate studies, discusses some of long standing problems and some of the new molecular studies. 141 extant and 51 extinct species were included. The outgroup consisted of three Rhynchocephalians. 610 characters were tested. 112 trees were recovered, chiefly at the base of the Iguania. The homoplasy index was 0.82, so a great deal of homoplay was present. This was a huge study and powerful due to its size.

Happily most of the Gauthier (2012) tree echoed the results of prior trees and the large reptile tree. At the base of both: Huehuecuetzpalli followed by Iguania and Scleroglossa with the latter divided into Gekkota, Scincomorpha and Anguimorpha. Major differences include: 1) Mosasaurs and their kin at the base of the Scleroglossa. 2) Eichstattisaurus at the base of the Gekkota, 3) Amphisbaenia as the sister to a 4) monophyletic Serpentes (snakes). The large reptile tree found 1) mosasaurs to nest with varanids, 2) Eichstattisaurus to nest with basal snakes close to mosasaurs and their kin, far from the Gekkota, 3) amphisbaenids as sisters to skinks, 4) and diphyletic clades of snakes arising from sisters to Lanthanotus and Adriosaurus.

The Gauthier et al. 2012 family tree of the squamates

Figure 1. Click to enlarge. The Gauthier et al. 2012 family tree of the squamates, color added for large clades.

We’ll look at these differences point by point in coming blogs and attempt to dissect the differences and why they occurred.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3-308. online here.

Convergence at the Pelycosaur/Therapsid Transition

A good look at the base of the Therapsida (Fig. 1) reveals several interesting convergences (taxa that look alike superficially). Prior studies used shared traits between Dimetrodon in the Sphenacodontia and Eotitanosuchus in the Therapsida to support a link between sphenacodonts and basal therapsids, but that is not supported in the large reptile tree. Previously unnoticed, the sphenacodont, Haptodus, bears a superficial resemblance to a basal therapsid, Stenocybus, which may be a juvenile of a longer snouted form.

 

Figure 1. Click to enlarge. Basal Therapsida. Note superficial similarities between Haptodus and Stenocybus. Note superficial similarities between Dimetrodon and Eotitanosuchus.

Figure 1. Click to enlarge. Basal Therapsida. Note superficial similarities between Haptodus and Stenocybus. Note superficial similarities between Dimetrodon and Eotitanosuchus.

Dimetrodon and Eotitanosuchus
The  dorsally convex skull in Dimetrodon and Eotitanosuchus (Fig. 1) appears to be a shared trait, but it is convergent in the large reptile tree. Both share a deeply convex maxilla and similar proportions in the orbit vs. rostrum. Both share a posteriorly sloping cranium, broken by elevated lateral temporal fenestrae in Eotitanosuchus. The jawline was shallowest beneath the orbit in both taxa.

Haptodus and Stenocybus
The short rostrum/large orbit skull shapes of Haptodus and Stenocybus (Fig. 1) were arrived at via convergence, as are the relatively short canines and convex rostrum. A larger suite of traits and several intervening taxa separate these two. Now, Stenocybus was never allied with Haptodus in the literature. Stenocybus was previously allied with anteosaurid dinocephalians (stepped incisors a key trait), but here it nests more parsimoniously with hipposaurids.

The strength of the large reptile tree (lots of taxa, lots of traits) separates these convergent taxa. In a smaller study they would have nested closer together.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.