The humpback Diadectes

Diadectids and Diadectomorpha are basal lepidosauromorph reptiles once thought to be the closest anamniotes (amphibians) to amniotes. Wikipedia still promotes this antiquated hypothesis. Here (Fig. 1) you’ll see that Diadectes and Procolophon both evolved from a sister to Romeria primus as recovered by the large reptile tree.

Figure 1. The evolution of Diadectes and Procolophon from tiny Romeria primes to scale.

Figure 1. The evolution of Diadectes and Procolophon from tiny Romeria primus to scale. Cope’s Rule is in effect here as the derived taxa are indeed larger, even on the branch leading to Procolophon.

Today we’ll look at a humpback diadectid, Diadectes (formerly Diasparactus) zenos (UC679). You’ll note the neural spines are much larger than in sister taxa.

Figure 2. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens.

Figure 2. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens. Note the long neural spines. These were likely a hump support, not a finback, adding bulk to this already bulky reptile.

The high neural spines of D. zenos were robust, more like those of a bison, than a Dimetrodon. That’s why they may have supported fatty or meaty tissues, rather than a sail.

The skull of D. zenos is poorly known, but the palate is well exposed. The dorsal ribs are short, as is the tail. Note that the axis bone  (cervical #2) grows from D. zenos to D. sammiguelensis (Fig. 2).

Earlier we looked at a putative diadectid, Stephanospondylus, which is actually a diadectid mimic that was ancestral to turtles. It had no neural spines, and neither do turtles, because they don’t need back muscles when they have a shell.

The anterior dorsal ribs of D. zenos were the widest among diadectids. These helped support that large pectoral girdle.

Please contact the writer(s) of the Wikipedia article and encourage them to update their account of Diadectes. You can’t be derived from reptiles and still be a ‘reptile-like amphibian.’

References
Berman DS, Sumida SS and Martens T 1998. Diadectes (Diadectomorpha: Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67:53-93.
Case EC 1907. Restoration of Diadectes. The Journal of Geology 15(6):556–559.
Case EC 1910.“New or little known reptiles and amphibians from the Permian (?) of Texas”Bulletin of the American Museum of Natural History 28:136–181.
Case EC, Williston SW and Mehl MG 1913. Permo-Carboniferous Vertebrates from New Mexico. Carnegie Institution. 81 pp. online pdf
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).

Wiki/Diadectes

Ambedus – a basal diadectid(?) with a shallow dentary

Diadectids come in many sizes, all bulky. Wiki considers them to be anamniotes (pre-reptiles), the first herbivores among tetrapods and the first tetrapods to attain large size. These are all debatable.

Ambedus pusillus (Kissel and Reisz 2004) is from the Early Permian of Ohio. It was considered the most primitive diadectid and one of the smallest. Like larger taxa, it had labiolingually broad blunt teeth with a central cusp over many of them. This genus is represented by MCZ 9436 (Fig. 1).

Kissel (2010) wrote: “Diagnosis: A small diadectid distinguishable from other members of the group by: 1) a shallow dentary; 2) relatively high maxillary and mandibular tooth count; 3) lack of a labial parapet of dentary; 4) anterior teeth of maxilla and dentary conical, in contrast to the incisiform anterior teeth of other diadectids; and 5) shallow alveolar shelf, which suggests a relatively shallow tooth implantation.”

Figure 1. Ambedus pusillus compared to candidate sister taxa. The shallow mandible and small size of this adult does not match the deep mandible found in diadectids, but more closely matches millerettids, solenodonsaurs and chroniosuchids. The outgroup of all of these taxa is Romeria primes, which has a medium depth dentary.

Figure 1. Ambedus pusillus compared to candidate sister taxa. The shallow mandible and small size of this adult does not match the deep mandible found in diadectids, but more closely matches millerettids, solenodonsaurs and chroniosuchids. The outgroup of all of these taxa is Romeria primus, which has a medium depth dentary. The labiolingually wide teeth of Ambedus connect it to diadectids, but Kissel and Reisz should have compared it to these taxa, too. You can’t be sure of basal status without including several even more basal taxa in the outgroup. Is Ambedus really a diadectid or a millerettid or a romeriid with convergent teeth? Maybe the teeth appeared first. More data would help.

Not a juvenile
Kissel (2010) wrote, “the remains described herein as A. pusillus possess none of the features that typify known juvenile individuals of previously described diadectid taxa. All elements are therefore thought to represent those of adult individuals.”

Short tooth roots
Kissel (2010) wrote, “The shallow alveolar shelf in Ambedus pusillus suggests that tooth implantation was not as deep as that in other diadectids. The shallow alveolar shelf of MCZ 9436 indicates that root length is less than crown height in Ambedus, as observed in the diadectomorphs Limnoscelis and Tseajaia.”

No dentine infolding
Kissel (2010) wrote, “In no specimen is it possible to determine if the marginal teeth of Ambedus exhibit infolding of the dentine, a feature present in all other diadectomorphs.”

No incisiform teeth
Kissel (2010) wrote, “The maxillary dentition of heretofore known diadectids consists of two incisiform teeth that are succeeded by a series of molariform cheek teeth. The maxillary dentition of Ambedus adheres to this general pattern, but the anteriormost teeth of MCZ 9436 are not incisiform.”

Unique tooth number
Kissel (2010) wrote, “MCZ 9438, a complete left dentary, possesses a complete tooth row, and a total of 22 teeth are present. Such a tooth count represents the greatest yet recorded for a diadectid, with the mandibular tooth counts of other diadectids including 14 to 18 for Diadectes, 15 for Diasparactus, 14 for Desmatodon and  17 for Orobates.”

Humerus not referred
Kissel (2010) also referred to MCZ 8667 an isolated humerus that was collected within the same vicinity as the maxillae and dentaries. Kissel wrote: “Because the humerus exhibits no features indicative of Diadectidae, it is not referred to Ambedus pusillus, and it is therefore not described herein.” 

Summary
What we learn from the above is Ambedus is not very much like other diadectids. One wonders then, is it something else? Related taxa with a shallow dentary and more teeth include Solenodonsaurus and the chroniosuchids, neither of which had diadectid teeth. Milleretta is also similar (Fig. 1). Not sure about the tooth shapes there. Then again there’s a third, perhaps more likely possibility based on tooth shape and number. Ambedus may be the romeriid root taxon for all three of these clades with a nod toward the diadectidae based on tooth shape. If so, that humerus may come back “into play.” Notably the manus of Romeria priimus is very slender and very un-diadectid-like. Not sure what the rest of it looks like. We’ll see if the humerus data helps answer those questions. Currently it’s on loan.

References
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Toronto: University of Toronto Press. pp. 185. online pdf
Kissel RA and Reisz RR 2004. Ambedus pusillus, new genus, new species, a small diadectid (Tetrapoda: Diadectomorpha) from the Lower Permian of Ohio, with a consideration of diadectomorph phylogeny. Annals of Carnegie Museum 73:197-212.

 

Julius Csotonyi book and preview

Julius Csotonyi is the latest and perhaps best dino illustrator I have seen. A rare combination of supreme talent and vivid imagination, the work of Julius Csotonyi just blows my mind. Here’s a link to a Wired preview of the book.

Figure 1. Click to link to book preview and Wired article online for Julius Csotonyi. Just fantastic!!

Figure 1. Click to link to book preview and Wired article online for Julius Csotonyi. Just fantastic!!

 

Pisanosaurus revisited

Updated March 14, 2015 with a new restoration of the Pisanosaurus pelvis.

Pisanosaurus (Casamiquela 1967,  Bonaparte 1976, Late Triassic) has been considered a basal ornithischian for over 50 years. With its beveled teeth creating one long occlusal surface and the hint of a missing predentary, it’s a cladistic lock. The pelvis has been problematic. It doesn’t really show any ornithischian traits — but then what is preserved is only the part that surrounds the acetabulum. The illustrated data with regard to in situ vertebrae vs. reconstructed vertebrae did not match with regard to number.  Casamiquela described lumbar and caudal vertebrae and no cervicals. Bonaparte described cervicals with a skull on one end (Fig. 1), but no lumbars or caudals.

The proximal outgroup is Daemonosaurus, known only from some long cervicals and a complete skull with long teeth. Prior to that, basal sauropodomorphs and eoraptorids were ancestral. Evidently, ornithischians had a late start.

I recently revised my own reconstruction (Fig. 1) after realizing what I thought were the traced and unlabeled “humerus and manus” near the front half of the skeleton, beneath the anterior dorsals, were actually the tibia and pedal elements, which were better illustrated elsewhere. Embarrassingly, some things just take time to sink in.

Figure 2. Pisanosaurus pelvis restored the Sereno way (on the right) and like Haya (on the left). Note the possible placement of the obturator foramen, a pubis trait on the alternate orientation. And note the tab-like shape of the pubic contribution of the pubis (compare to figure 1).

Figure 2. Pisanosaurus pelvis restored the Sereno way (on the right) and like Haya (on the left). Note the possible placement of the obturator foramen, a pubis trait on the alternate orientation. And note the tab-like shape of the pubic contribution of the pubis (compare to figure 1).

So here (Fig. 1) is Pisanosaurus revised. It has more neck verts (more than any other ornithischian) and no preserved forelimbs. The pelvis could be saurischian, like the neck vert number, as shown, or with the pubis retroverted or something in between.

Nesbitt (2011) and Brusatte et al. (2010) derived Pisanosaurus and its sister Heterodontosaurus from Lesothosaurus and kin and these from Lewisuchus, which also gave rise to silesaurids, sauropodomorphs and theropods. By contrast, in the large reptile tree, Lewisuchus and silesaurids are basal archosaurs, more primitive than crocs. Theropods were basal dinosaurs and ornithischians arrived late, which matches the chronology better. With that long cervical series and sauropod-ish pelvis of Pisanosaurus, that also makes more sense.

References
Bonaparte JF 1976. Pisanosaurus mertii Casamiquela and the origin of the Ornithischia. Journal of Palaeontology 50(5):808-820.
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Casamiquela RM 1967. Un nuevo dinosaurio ornitisquio triásico (Pisanosaurus mertii; Ornithopoda) de la Formación Ischigualasto, Argentina. Ameghiniana 4 (2): 47–64. translated to English here.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
wiki/Pisanosaurus

The deep mandible of Tseajaia

The original reconstruction of Tseajaia (Vaughn 1964, Moss 1972) has a problem (Fig. 1). The mandible is too deep to fit inside the jaws. But, no worries! It’s a quick fix.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

References
Vaughn PP 1964. Vertebrates from the Organ Rock Shale of the Cutler Group, Permian of Monument Valley and Vicinity, Utah and Arizona: Journal of Paleontology 38:567-583.
Moss JL 1972. The Morphology and phylogenetic relationship of the Lower Permian tetrapodTseajaia campi Vaughn (Amphibia: Seymouriamorpha): University of California Publications in Geological Sciences 98:1-72.

wiki/Tseajaia

New basal pterodactyloid(?) Kryptodrakon = Sericipterus, a dorygnathid

The big news this morning:
Andres, Clark and Xu (2014) have claimed to discover the earliest known pterodactyloid (Middle/Late Jurassic, Shishugou Formation in Xinjiang, China).They wrote: “We report here the earliest pterosaur with the diagnostic elongate metacarpus of the Pterodactyloidea, Kryptodrakon progenitor, gen. et sp. nov., from the terrestrial Middle-Upper Jurassic boundary of Northwest China. Phylogenetic analysis confirms this species as the basalmost pterodactyloid.”

Andres reported, “In paleontology, we love to find the earliest members of any group because we can look at them and figure out what they had that made the group so successful.” 

If it is one, it’s a big one!
Wingspan estimates are over a meter.

That big size is the red flag
Of course, this flies in the face of the large pterosaur tree, which recovered four origins for pterodactyloid-grade pterosaurs at about this same time, and they were all tiny. Andres, Clark and Xu did not include these tiny pterosaurs in their phylogenetic analysis.

Figure 1. The bits and pieces of Kryptodrakon assembled into a Pterodactylus bauplan, from Andres, Clark and Xu 2014.

Figure 1. The bits and pieces of Kryptodrakon assembled into a Pterodactylus bauplan, from Andres, Clark and Xu 2014.

It’s always difficult to reassemble bits and pieces,
but not impossible. Andres, Clark and Xu did that above (Fig. 1), using a small Pterodactylus as their bauplan or blueprint.

There’s an alternate bauplan available
and it’s also from the same Shishugou Formation. Sericipterus is a very large and gracile dorygnathid (Fig. 2). When you put the bones of Krypodrakon on top of the bauplan for Sericipterus you find a good match. 

Figure 2. The bone bits of Kryptodrakon placed on the bauplan of the giant dorygnathid, Sericipeterus, also from the Shishugou Formation. There's a good match here.

Figure 2. Here the bone bits of Kryptodrakon are placed on the bauplan of the giant dorygnathid, Sericipeterus, also from the Shishugou Formation. There’s a good match here. Perhaps Kryptodrakon is a junior synonym for Sericipterus, filling in some of its missing pieces.

And suddenly that “long metacarpus” is not so long anymore. Notably, Sericipterus had gracile wing bones, and that proved confusing to Andres, Clark and Xu. “Thinner” can sometimes be confused with “longer” unless you know what the bauplan is.

But wait, there’s more.
Compare the metacarpus of Kryptodrakon with its dorsal rib and the metacarpus doesn’t look so long anymore. The same holds for the distal carpal, scapula, humerus and wing joint scraps. They’re all too big for that metacarpus to be “elongate.”

A more parsimonious solution
Kryptodrakon and Seripterus are both from the same formation. They are the same size, and their bones have the same shape (so far as can be told from available scraps). We also know from a larger phylogenetic analysis that includes tiny pterosaurs that basal pterodactyloid-grade pterosaurs were all tiny and Kryptodrakon was big.

Therefore,
the more parsimonious solution is to consider Kryptodrakon a junior synonym for Sericipterus, a giant dorygnathid, not a pterodactyloid.

One more thing
Andres, Clark and Xu were also the discoverers and authors of Sercipterus, the only other pterosaur found in the Shishugou Formation.

Sorry to throw cold water on this.
But testing for parsimony is good Science.

References
Andres B, Clark JM and Xu X 2010.A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs, Journal of Vertebrate Paleontology 30: (1) 163-187.
Andres B, Clark J and Xu X 2014. The Earliest Pterodactyloid and the Origin of the Group. Current Biology (advance online publication)
DOI: http://dx.doi.org/10.1016/j.cub.2014.03.030

Read more: Science_News

The manus of Effigia revisited

The manus of Effigia is tiny.

Figure 1. Effigia. Note the tiny hands.

Figure 1. Effigia. Note the tiny hands.

Really tiny.
Even so, it is one of the few manus examples from a wide range of post-Proterosuchus and pre-Herrerasaurus taxa. The Effigia manus (Figs. 1, 2) includes only 3 metacarpals and 2 phalanges, plus two carpals. Another metacarpal, one that looked like mc1 of Coelophysis and measuring 12×5.5 mm was described by Nesbitt (2007).

Not much to go on, but PILs and sister taxa (even distantly related) can help (Fig. 1) make the restoration — in this case two restorations: one if you switch the two longest metacarpals, one if you don’t. I think you should, to match another poposaurid manus, that of Poposaurus (Fig.1), which we looked at earlier here so metacarpals 1-3 align. In either case, tiny digit 5 appears to be missing, so the known digits are 2-4, not 3-5.

Figure 1. The manus of Effigia reconstructed. Metacarpal 1 was described with measurements. Here two possible hands can be restored, but only when one switches the longest metacarpals. That's the one I think will prevail.

Figure 1. The manus of Effigia reconstructed. Metacarpal 1 was described with measurements. Here two possible hands can be restored, but only when one switches the longest metacarpals. That’s the one I think will prevail.

From Nesbitt (2007):
“Portions of the right manus were recovered somewhat articulated with both the radius and the ulna. Metacarpals III, IV, and V were found articulated together and a potential metacarpal I and the carpals were found together nearby. Unfortunately, the identity of the two carpals cannot be determined with certainty. The proposed metacarpal I proximal portion is broken, shifted ventrally, and appressed against the shaft. Metacarpal I is estimated to have been 12 mm long and 5.5 mm wide. It has a dorsoventrally compressed shaft and the distal end is asymmetrical; only the medial side bears a rounded articular surface; the lateral side tapers to a sharp edge. The morphology is strongly reminiscent of metacarpal I of Coelophysis and other theropods. Metacarpal II was not preserved.

“A much more robust phalanx is also present and may belong with either metacarpal III or metacarpal I. This phalanx indicates that at least one of the digits was not as reduced as much as digit I.”

If you shift the two longest metacarpals and add appropriate phalanges that fit the few established PILs, then you get a very poposaur-ish manus. If you don’t, you get an odd sort of manus, very autapomorphic. The carpals were matched to those of aetosaurs, Lotosaurus and Herrerasaurus, the closest known sisters with known carpals. If tiny distal carpals were present, they were not recovered.

On a side note,
the manus of Lotosaurus is looking ‘funky’ when compared to other popoosaurs. If anyone has good data on that piece of anatomy, please send it.

References
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf
wiki/Effigia