Coccocephalichthys enters the LRT

Updated September 1, 2021
with the shifting of taxa based on new skull identities, plus the addition of several more closely related taxa. See the large reptile tree for the latest updates, not always repaired here.

Coccocephalichthys wildi (originally Coccocephalus wildi Watson 1925; Whitley 1940; Poplin and Véran 1996; Late Carboniferous; Fig. 2) was originally considered a palaeoniscid, like Cheirolepis.

Figure 2. Coccocephalichthys (formerly Coccocephalus) is a Late Carboniferous transitional taxon

In the large reptile tree (LRT, 1569 taxa) Late Carboniferous Coccocephalichthys among the paleoniscids. Several bones are re-identified above based on tetrapod homologs.

Most of the time,
this is how the LRT grows, by adding new transitional taxon between two presently tested taxa. In this case, the transitional taxon neatly helps illustrate the evolution that occurred between the two extremes. Using tetrapod labels (Fig. 2) has proven to help us understand the identity of facial bones in these fish.

Using colors to identify bones
is something I started doing in the vampire pterosaur, Jeholopterus (see header above, far right) in 2003. I was wondering if someone could send me an earlier example of this graphic technique? Today it seems to be growing in popularity, especially so since there are no additional color charges for papers published online.

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References
Poplin C and Véran M 1996. A revision of the actinopterygian fish Coccocephalus wildifrom the Upper Carboniferous of Lancashire. In Milner, A. R. (ed.) Studies on Carboniferous and Permian vertebrates. Special Papers in Palaeontology 52: 7-29.
Watson DMS 1925. The structure of certain palæoniscids and the relationships of that group with other bony fish. Proceedings of the Zoological Society of London, 54: 815–870.
Whitley GP 1940. The Nomenclator Zoologicus and some new fish names. Australian Naturalist, 10:241–243.

wiki/Strunius
wiki/Thunnus
wiki/Cheirodus
wiki/Mimipiscis
wiki/Coccocephalichthys

Really, aren’t we ALL didelphids?

There has been a traditional disconnect
in mammalian paleontology regarding the two transitions between the egg-laying Prototheria, the pouched Metatheria,  and the pouch-less Eutheria. So far as I can tell, only the large reptile tree (LRT, 1334 taxa; Fig. 2) has documented how and which species form transitional links in this chain of mammal evolution (Fig. 1). At present, and for the foreseeable future, didelphids, like Didelphis (the Virginia opossum), Monodelphis (the gray short-tailed opossum) and Caluromys (the wooly opossum) occupy basal nodes at large radiations of metatherians and eutherians in the LRT…hence the title of this post.

Figure 1. A selection of basal mammal skulls leading to placentals. This is the ‘gradual accumulation of traits’ recovered by the LRT. A third of these are traditional didelphids. Or two-thirds of these are cladistic didelphids. And, if so, then we humans are also didelphids. Haplodectes (IVPP V5235) nests as the basal primate in the LRT.

Traditionally
Didelphidae has been a clade restricted to the opossums without any insight to their eventual descendants… the rest of the marsupials and us placentals. That’s why several mousy and not-so-mousy ‘possums have been added to the LRT recently, to more precisely recover evolutionary patterns in deep time. Amazing that our more or less direct ancestors are still with us today, sometimes hidden in Amazon forests, other times raiding our backyard trashcans and tentatively crossing our highways and byways.

Figure 1. Subset of the LRT focusing on basal Mammalia after the addition of several marsupials. Red taxa are represented by only a few bones, like mandibles with teeth. Note the proximity of traditional creodonts to the basal placental clade, Carnivora, basal members of which are small, arboreal and opossum-like.

A new taxon in the LRT is Thylophorops
considered by Goin et al. 2009 to be the largest didelphid. Unfortunately, in the LRT, Thylophorops does not nest with Didelphis, but with Oxyaena and Thylacinus (Fig. 2)… themselves descendants of Didelphis with cat-like and wolf-like traits respectively.

Wikipedia reports,
“Thylophorops species (as well as several other contemporary opossum genera) show a high degree of speciation towards carnivory compared to the still living didelphines. Their premolar and molar teeth were proportionally larger than those of living opossums and their grinding facets imply a more dedicated shearing action; these have been interpreted as “omnivory leading towards carnivory” in Goin et al. 2009.”

Figure 3. Crowned as the largest didelphid (by not much actually, but it is a juvenile) Thylophorops lorenzini nests between leopard-like Oxyaena and wolf-like Thylacinus in the LRT. All are shown to scale here.

Unfortunately
there is no reference in Goin et al. to either Oxyaena or Thylacinus. So… taxon exclusion is still an issue with the Goin et al. taxon list. Such problems are largely resolved in the LRT, which tests all possible candidates, and even dozens of fringe candidates that no one else considers, recovering a fully resolved tree based on traits and taxa that extend back to Devonian tetrapods, ultimately relating all descendants to one another.

References
Ameghino F 1908. Las formaciones sedimentarias de la región litoral de Mar del Plata y Chapadmalal part 2
Goin  FJ, Zimicz N, de los Reyes M, Soibelzon L 2009. A new large didelphid of the genus Thylophorops (Mammalia: Didelphimorphia: Didelphidae), from the late Tertiary of the Pampean Region (Argentina). Zootaxa. 2005: 35–46.

wiki/Thylophorops

 

Strange Bedfellows – Nesbitt (2011) – part 7 – Lewisuchus and the Origin of the Dinosauria

Sometimes we miss the big picture. 
Here then, for your approval and disapproval are comparisons between closest kin found by the Nesbitt (2011) tree versus those found by the large reptile tree.

The origin of the Archosauria and the Dinosauria is today’s topic.
The Archosauria in the large reptile tree includes crocs and dinos, nothing else, with Lewisuchus, Gracilisuchus and Turfanoschus at their common base. See it here.

Figure 1. The Nesbitt (2011) tree with the Archosauria highlighted in yellow and Lewisuchus in blue. Taxa not in the Archosauria, according to the large reptile tree, are highlighted in orange. The large reptile tree found a similar nesting for Lewisuchus, but with the addition of more taxa, more resolution nests just crocs (including early bipeds like Scleromochlus) with dinos (which also includes silesaurs and poposaurs. Rauisuchians nest further back, closer to Euparkeria and erythrosuchids.

In the Nesbitt (2011) tree (Fig. 1) the Archosauria also includes the rauisuchians, pterosaurs, lagerpetids, ornithosuchians, aetosaurs, poposaurs (allied with Qianosuchus and the basal rauisuchian, Arizonasaurus). I thought this may have been part of the problem (see below). Furthermore, Nesbitt (2011) did not include some of the basal crocs, like Pseudhesperosuchus, Decuriasuchus and Scleromochlus. He also did not include Vjushkovia, a basal rauisuchian close to the basal crocs and basal dinosaurs. Without these key basal taxa the derived taxa are further from one another, making it more difficult to assess the gradual accumulation of traits we’re all looking for.

So, why not eliminate some of the strange bedfellows?
If we remove Mesosuchus, the Pararchosauriforms, Vancleavea and pterosaurs, we’re left with pretty much the same tree (Fig. 2). This pruned tree is in closer agreement with the large reptile tree except at the base of the Archosauria, where the aforementioned missing taxa would have nested and perhaps shifted things around a bit. Who knows? As noted earlier, the addition of several Youngina brings resolution to this problem, but it was excluded by Nesbitt (2011).

CM73372
Since CM73372 appears at the base of the crocs, just beyond the standard rauisuchia, and was first labeled a juvenile Postosuchus, I’m keenly interested in seeing this, but so far have not. Requests have been sent. No replies yet. Any jpegs would be welcome.

Figure 2. The Nesbitt tree without Mesosuchus, pterosaurs, pararchosauriformes and Vancleavea, taxa that belong elsewhere according to the large reptile tree. It holds together pretty well. Here Marasuchus arises more or less directly from Euparkeria. Here Lewisuchus is not so far from Gracilisuchus and Turfanosuchus, matching the large reptile tree results, almost.

Bipeds Galore!
According to Nesbitt (2011) the origin of the dinosaurs is led by one one biped after another (not to mention the pterosaurs, which most paleontologists ironically refuse to grant basal bipedal status to, due to Late Jurassic and Cretaceous footprints of secondarily quadrupedal beachcombers).

Figure 3. Basal bipedal dinosauriformes, from Lagerpeton through Marasuchus, Lewisuchus, Asilisaurus, Sacisaurus and Silesaurus, according to Nesbitt (2011). It’s easy to see why what little is known of Lagerpeton was lumped with these taxa (much of it due to hopeful glee), but its feet and ankles give it away as a Tropidosuchus sister.

The Large Reptile Tree Recovered Another Solution
This image was first published 11 months ago on a pterosaur heresies blog about the origin of the Dinosauria. It’s still pretty fresh. Note the gradual accumulation of traits in sisters that look more like each other than any competing set of candidates.

Figure 4. The heretical model of dinosaur origins (Peters 2007). Here basal rauisuchians gave rise to smaller bipedal crocs and dinos, which later diversified. There’s Lewisuchus at #4, just in front of tiny Scleromochlus.

There’s more about the origin of dinosaurs here. Seems Lewisuchus was not far from the origin of the Dinosauria, and may be the best candidate, but it also may be a deadend. More bipedal crocs will help us figure this out.

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
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.

Tijubina – A New Tritosaur Sister to Huehuecuetzpalli

Tijubina pontei (Bonfim and Marques 1997) was a tiny Early Cretaceous lizard from the Crato Formation (late Aptian) of northeast Brazil. In a recent redescription Simões (2012) reported Tijubina lacked the posteroventral and posterodorsal processes of the dentary and the tibial/fibular length equaled the femoral length. Its posterior dentary teeth were robust, cylindrically based, unsculptured and bore no cuspids. Simoes (2012) nested Tijubina in a basal position among the Squamata. Reynoso (1998) reported a similar nesting for Huehuecuetzpalli. Neither considered the possibility that both specimens nested in a third squamate clade, the Tritosauria, outside of the Iguania + Scleroglossa.

Figure 1. The skull of Tijubina reconstructed (left) and in situ dorsal view, skull roof missing (right). Click for more info. Some skull parts identified here are disputed by Simoes (pers comm).

Late Survivors
Both Huehuecuetzpalli and Tijubina were late survivors of a 130 million year earlier Late Permian radiation of lizards. Tijubina is distinguished by its teeth, which are larger posteriorly and shaped like cylinders instead of sharp points. Tijubina was about half the size of its Huehuecuetzpalli.

Figure 2. Tijubina in situ, nearly full size on a 72dpi screen. Click to enlarge.

Not a Juvenile
Simoes (2012) described Tijubina as immature due to a imcompletely calcified joints, a wide open sternal fontanelle (hole), unfused pectoral and pelvic elements. Adult tritosaur lizard sisters are likewise incompletely calcified. Unlike Huehuecuetzpalli, and despite its smaller size, the carpal elements of Tijubina were well ossified. The lack of dorsal and ventral processes of the posterior dentary are traits shared with Huehuecuetzpalli.

Figure 2. Manus of Tijubina identifying carpal elements. Metacarpal 4 is largely beneath mc5. Here the two centrale are ossified along with the other carpal elements and present. The carpus is unossified in adult Huehuecuetzpalli.

The carpus is not ossified in Huehuecuetzpalli, but it is well ossified in the much smaller Tijubina and both centrale are present. Earlier I wondered if the pteroid and preaxial carpal were migrating at the evolutionary stage represented by Huehuecuetzpalli because the carpus was poorly ossified. That would have been an ideal time to do it! Here Tijubina may have been a sister Huehuecuetzpalli, but the latter was closer to fenestrasaurs including pterosaurs.

 

Figure 3. The pelvis and possible prepubis and Tijubina. Is this the origin of the prepubis? Or just a splinter or two of bone in the position of the prepubis. I can’t tell for sure. Phylogenetically Tijubina was scored without a prepubis and pteroid.

Cosesaurus through pterosaurs all have a prepubis, a new bone extending beyond the ventral margin of the pubis. So the prepubis appeared some time prior to Cosesaurus. It may or may not be present in Langobardisaurus. It is not present in Huehuecuetzpalli. A possible prepubis may be present in Tijubina (Fig. 3). On the other hand, that little fleck of bone(s) may just be a splinter from the damaged pubis. No problem either way.

A Long Tibia
Since the tibia was subequal to the femur, Tijubina was likely a sprinter and a possible occasional biped, like many living lizards with similar proportions. Such traits and behaviors likely led to the development of a prepubis in sister taxa.

Figure 4. Pes of Tijubina. PILs added.

Pes
The pes of Tijubina had tendril-like toes, indicating an arboreal lifestyle. Like Huehuecuetzpalli and Cosesaurus the proximal phalanges of digit 5 were long. The tarsals were not coossified, a trait typical of many (but not all) tritosaurs. Fenestrasaurs (including pterosaurs) did not ossify two distal tarsals. Drepanosaurs and all living lizards co-ossified the proximal tarsals.

Summary
Tijubina was a late-surviving representative of the Tritosauria, a clade of lizards that ultimately gave rise to tanystropheids, drepanosaurs and pterosaurs. The cylindrical teeth were autapomorphies not found in other clade members. The tiny size and crushed nature of the specimen prevent confirmation of several possible fenestrasaur-like traits.

Huehuecuetzpalli, Tijubina, Cosesaurus and Macrocnemus are basal tritosaurs.

References
Bonfim Júnior DC and Marques RB 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia – Formação Santana, Aptiano da Bacia do Araripe. Anuário do Instituto do Geociencias 20:233-240
Bonfim-Júnior F de C and Rocha-Barbosa O 2006. A Paleoautoecologia de Tijubina pontei Bonfim-Júnior & Marques, 1997 (Lepidosauria, Squamata Basal da Formação Santana, Aptiano da Bacia do Araripe, Cretáceo Inferior do Nordeste do Brasil). Anuário do Instituto de Geociências – UFRJ ISSN 0101-9759 Vol. 29 – 2 / 2006 p. 54-65.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Simões TR 2012. Redescription of Tijubina pontei, an early cretaceous lizard (Reptilia; Squamata) from the crato formation of Brazil. An Acad Bras Cienc. Feb 2, 2012. pii: S0001-37652012005000001. [Epub ahead of print].

Another Really Tiny Pterosaur: BMNH 42736

The smallest known pterosaur B St 1967 I 276 (No. 6 of Wellnhofer 1970 ) was discussed earlier. Today we get to meet maybe the second smallest pterosaur, Pterodactylus meyeri BMNH 42736 (Munster 1842, Fig. 1) is the same size as No. 6, but had several distinct traits (Fig. 2). I ran across the BMNH specimen in Unwin’s (2006) The Pterosaurs From Deep Time book on page 151. Dr. Unwin considered the specimen a “flapling” (= newly hatched pterosaur able to fly) with a wingspan of 17 cm, so that is the reconstructed scale (Fig. 3).

The Value of a Reconstruction
It’s a shame that modern workers don’t produce reconstructions of crushed pterosaurs anymore. There is so much to see (Figs. 2, 3), especially when one compares similar specimens. Many traits would go unnoticed if left crushed.

Figure 1. One of the world's smallest pterosaurs, traced from Unwin (2006, p. 151). The feet of the "flapling" were not articulated and a certain amount of guesswork was applied to the idenfication of the pedal elements and their reconstruction. Note how the left radius and ulna are parallel to and beneath the elongated right scapula. The right coracoid is largely beneath the right humerus. The left hand and proximal wing finger are beneath the right hand. Soft tissue stains are highlighted in orange. The wing had a narrow chord at the elbow. Colorizing the bones is a result of employing DGS, digital graphic segregation.

Phylogenetic Nesting
Here the “flapling” nested between No. 6 and No. 12, two other tiny ornithocephalians (and former Pterodactylus) outside of the Pterodactylus lineage, at the base of the Germanodactylus clade. Conveniently (for those looking for transitional taxa) No. 6 was smaller and No. 12 was larger than the BMNH “flapling.”

Distinct from No. 6, the “flapling” had a deeper skull, more and smaller dorsal vertebrae and ribs, a longer scapula (almost touched the pelvis), a deeper and more fully fused pelvis and a larger sternal complex than either of its sisters. Considering the reconstructed differences in quadrate elevation, jugal shape and pelvis dimensions (Fig. 2), you might think the “flapling” would have nested further apart from No. 6 and No. 12. These distinctions suggest that the “flapling” may have been at  the base of its own clade of currently unknown descendants.

Figure 2. The tiniest pterosaurs. On the left, Unwin's "flapling" Pterodactylus meyeri BMNH 42736. On the right, B St 1967 I 276, No. 6, the former sole owner of the title.

Juvie or Adult?
If the BMNH tiny pterosaur was indeed a juvenile of a larger more established taxon, which one did it match up to? And if so, why did it nest with other tiny pterosaurs? No. The BMNH specimen was an adult. The many autapomorphies (= differences) in the “flapling” also follow a larger trend seen in other tiny pterosaurs: morphological innovation.

Figure 3. Full scale image of ginkgo leaf and the two smallest pterosaurs to scale on a 72 dpi screen. Yes, these are tiny, but just look at the size of a hatchling on the far right, no bigger than a small fly.

Special Premaxillary Teeth
In the BMNH “flapling” we see more substantial anteriorly-directed medial teeth forming the tip of the premaxilla. Those two teeth evolve to become one in the rostral tip of Germanodactylus. That tooth is the only one retained in so-called “toothless” pterosaurs like Pteranodon and Nyctosaurus that have sharply tipped jaws.

Bigger Eggs?
A deeper pubis and pelvis in the BMNH specimen could have produced a larger egg. A stronger sternal complex and longer scapula could have made the “flapling” a more powerful flyer.

Soft Tissue Preservation
Despite a flipped mandible and poorly preserved feet, the “flapling” is otherwise well preserved and largely articulated. A soft tissue stain can be seen (overprinted in Fig. 1) that demonstrates a narrow chord at the elbow wing membrane construction.

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
Meyer H von 1842. Notes on labyrinthodonts and fossil reptiles, including a description of Belodon plieningeri, new gen. and sp. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie 1842, pp. 301-304.
Unwin D M 2006. The Pterosaurs From Deep Time. 347 pp. New York, Pi Press.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

Bat Origins and DNA

Updated September 30, 2016 with the addition of taxa to the LRT and new data on Protictis.

Where DO Bats Nest? The Question Returns.
A renowned (unnamed) professor interested in the origin of bats questioned my morphological nesting of bats with Ptilocercus and Nandinia (among living taxa) and Palaechthon (among fossil taxa). The professor sent me a pdf of Meredith et al. (2011), the most recent DNA tree to lump and split living mammals, as his best hypothesis on bat origins.

Figure 1. Bats and their sisters according to Meredith et al. 2011.

Mammal Diversification
Meredith et al. (2011) sought diversification patterns and times in mammals. They constructed a molecular supermatrix for mammalian families and analyzed these data with likelihood-based methods and relaxed molecular clocks. Their results came in traditionally, with Monotremata, Marsupialia and Placentalia at the base. The latter was divided into Xenartha + Afrotheria and all other placentals, which were divided into Laurasiatheria and Euarchontoglires.

DNA Results for Bats
Lots of bats were tested and they all lumped together in a single clade subdivided into three with fruit bats (Fig. 1 in orange) separating two microbat clades (in blue and green). Bats appeared as the unresolved sisters to Carnivora and Artiodactylia. Basal insectivores (not shown hre) nested as outgroup taxa to this super clade.

That’s an overly general nesting for bats that doesn’t provide much insight. On the other hand, I wasn’t surprised to see bats nesting so close to basal carnivores, like Nandinia and the vivverids, because the morphological results recovered the same relationship. I was surprised to bats nesting close to rhinos and camels.  :-) Pangolins are indeed close to bats, so we agree here (Fig. 2).

Figure 2. Bat origins cladogram. Here Onychonycteris and Pteropus represent bats.

DNA Results for Flying Lemurs
The base of the Euarchontoglires (Meredith et al. 2011, not shown in Fig. 1) included tree shrews and demopterans. I wasn’t surprised to see rabbits nesting close to Tupaia, the common tree shrew, because the morphological results recovered the same relationship. I also wasn’t surprised to see Ptilocercus, the pen-tailed tree shrew, nesting close to the flying lemurs, because the morphological results recovered the same relationship. Note these taxa didn’t nest with bats in the DNA study, but they did all nest at or near their unresolved common base.

Figure 2. Known bat ancestors to scale. Click to enlarge.

Morphological Results
The Meredith et al. (2011) results do not match the morphological evidence, which derives both bats and flying lemurs from a sister to Ptilocercus, a Paleocene pro primate and Chriacus, all close to basal carnivorans like Nandinia. Nandinia is a living carnivore that sometimes drops from trees and has an omniovorous diet. Chriacus was a long-legged tree-dwelling omnivore. Phylogenetic bracketing indicates that post-cranial characters were something like Chriacus and/or Ptilocercus. Ptilocercus is a flying lemur ancestor, but shares with bats several characters including flat ribs, a high floating scapula, wide cervicals, a rotating carpus and metatarsal + phalanx ratio similarities.

The question is…
why don’t the DNA results more closely match the morphological results, and vice versa?

DNA results cannot include fossil taxa. With bats evolving prior to the Eocene (52 mya), fossil taxa are necessary in any study on bat evolution.

The DNA of modern tree shrews and bats, etc. is not the same as the DNA of Paleocene tree shrews and bats, etc.

The Meredith et al. (2011) evidence indicates that DNA results for large clades of mammals  cannot resolve large clades. DNA and amino acid results do not agree with one another in the case of large reptile clades and the same is true in large mammal clades. DNA and amino acids apparently become more useful the more closely taxa are related. The resolution is very high, for instance, in human DNA, which is why it can be used in criminal investigations.

On the Other Hand
In fossil evidence you can point to a long list or suite of homologous morphologies, from tooth cusps to phalanx ratios. DNA results cannot provides these details. Morphology will always trump DNA, especially when bats nest with camels in DNA studies. DNA can only be verified with morphological evidence. DNA results can guide our efforts but the bottom line is morphology. The Meredith et al. (2011) study was unable to provide a specific sister taxon to bats. The morphological study provided Chriacus. When closer sisters are discovered, they will be reported.

Dermopterans and Bats
Flying lemurs nested close to bats and bat babys have short fingers like those of flying lemurs. Problem is: Ptilocercus, which comes between the two, has no extradermal membranes or webbed fingers and its limbs are not elongated. I have no answers for that other than both bats and flying lemurs are about 60 million years old and likely had a common long-limbed ancestor with extradermal membranes in a sister to Ptilocercus. Or bats and flying lemurs both developed extradermal membranes by convergence. Or Ptilocercus lost its ancestral long limbs and membranes.

Can we trust results?
In science we don’t trust anything. Not DNA. Not morphology. Everything is tentative and provisional.

 

References
Meredith RW et al. 2011. Impacts of the Cretaceous Terrestrial Revolution and KPg Extinction on Mammal Diversification. Science 334:521-524.

Eichstättisaurus. Not a Gekkotan. A Snake Ancestor.

Eichstaettisaurus and its sister, Ardeosaurus, were two small lizards found in Solnhofen limestones from the late Jurassic period, approximately 150 mya. Originally (Meyer 1860) and subsequently (Mateer 1982) these two were considered basal gekkotans, relatives of the living gecko, Gekko. Not much attention has been paid to either one. Both are typicall preserved complete and articulated, sometimes with some scalation and soft tissue preservation.

Figure 1. Eichstattisaurus and Ardeosaurus. Two Jurassic lizards in the lineage of snakes.

New Nesting
After entering the characters of both lizards, I was surprised to see that they nested not with Gekko, but with Adriosaurus, a hyper-elongated lizard with tiny limbs and a long neck, and Pachyrhachis, a basal snake with tiny hind limbs. This nesting, ancestral to snakes, has been largely overlooked by prior studies. I missed it too. The relationships is not obvious at first glance. I just finally got around to studying these two, fully expecting them to nest with Gekko.

Characters shared by members of this clade with Adriosaurus and Pachyrhachis include the orbit shape, the quadrate shape, supraoccipital fusion, converging temples, ectopterygoid shape, the absence of the retroarticular process, and the metatarsus configuration, among dozens of other traits that are shared with larger clades and by convergence with other reptilian clades.

The slender and elongated premaxillary ascending process was overlooked by Mateer (1982). If anyone has a palate view of either taxon, I’d like to see it.

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
Mateer NJ 1982. Osteology of the Jurassic Lizard Ardeosaurus brevipes (Meyer). Palaeontology 25(3):461-469. online pdf
Meyer H von 1860. Zur Fauna der Vorwelt. Reptilien aus dem lithographischen Schiefer des Jura in Deutschland mit Franchreich. Frankfurt-am-Main.

wiki/Ardeosaurus

The Campylognathoides / Rhamphorhynchus Transition

The phylogenetic nestings of Campylognathoides and Rhamphorhynchus are today’s topics.

Unwin 2003
Dr. David Unwin nested Campylognathoides with Eudimorphodon. Rhamphorhynchus nested with Dorygnathus and together these two nested with Scaphognathus and Sordes.

Kellner 2003
Dr. Alexander Kellner also nested Campylognathoides with Eudimorphodon but nested Rhamphorhynchus alone at the base of all pterodactyloid-grade pterosaurs. Dorygnathus, Scaphognathus and Sordes all nested at more basal positions.

Andres et al. 1010
Dr. Brian Andres et al. nested Campylognathoides between Dimorphodon and Scaphognathus (and kin) + Sordes (and pterodactyloids + anurognathids). Rhamphorhynchus nested with Cacibupteryx between several dorygnathids including Dorygnathus and Angustinaripterus.

Figure 1. The Campylognathoidea.

The Present Tree
The present large tree, several times larger than any prior tree, and the first and only one to employ more than one specimen from several genera, nested the several species of Rhamphorhynchus following the several species of Campylognathoides and this clade was derived from Eudimorphodon cromptonellus and Eudimorphodon ranzii. 

No Consensus
It is apparent that no one here agrees with each other, but some share certain elements. Importantly no prior trees nested Rhamphorhynchus with Campylognathoides. This is likely due to the choice of which specimen was used in analysis. The variety within each genus is substantial and certain Rhamphorhynchus specimens do indeed converge with certain Dorygnathus specimens. The large study promoted here used several specimens in order to alleviate this problem. However, what we’re most interested in today is the Campylognathoides to Rhamphorhynchus transition.

Figure 1. The size reduction at the Campylognathoides to Rhamphorhynchus transition. From left to right: CM 11424, the Pittsburgh specimen of Campylognathoides, St/Ei 8209 Rhamphorhynchus intermedius, and the BMM specimen of Rhamphorhynchus.

Our Transitional Players
The most derived Campylognathoides is the Pittsburgh specimen CM 11424, specimen C3 in the Wild (1975 catalog) from the Early Jurassic. The most basal Rhamphorhynchus is R. intermedius (Koh 1937) , St/Ei 8209, No. 28 in the Wellnhofer 1975 catalog from the Late Jurassic. Not surprisingly, the latter looks like a smaller version of the former and had plenty of time to evolve from it. We know of no Campys in the Late Jurassic and no Rhamphs in the Early Jurassic.

A juvenile?
R. intermedius was considered a juvenile Rhamphorhychus by Bennett (1995), who used long bone measurements rather than a phylogenetic analysis. R. intermedius was larger than its phylogenetic successors, like R. longicaudus, but smaller than derived Rhamphorhynchus species, like R. longiceps. The phylogenetic size decrease between the specimens was due to serial precocious maturity and serial smaller egg size, as in several other pterosaur lineages.

Differences
Distinct from the C. liasicus, the skull of R. intermedius was relatively larger with a smaller naris and antorbital fenestra. Only one maxillary tooth was enlarged to fang status and like the premaxillary teeth, it was procumbent. The mandible was robust and convex dorsally. Several anterior dentary teeth also leaned anteriorly. The cervicals were slightly longer. The dorsal series was slightly shorter. The scapula and coracoid were not fused. This lack of fusion is not a sign of maturity, but follows phylogenetic lines. The deltopectoral crest was narrower. The ulna + radius was longer. The three distal wing phalanges were shorter and gracile. The  prepubis perforation is expanded beyond the leading edge leaving an anterior process and a ventral process above and below the former perforation. The hind limbs were among the shortest among pterosaurs. The pedal digits were shorter than the metatarsals and digit V was longer than in Campylognathoides.

Size Reduction
In pterosaurs phylogenetic size reduction appears to mimic juvenile characters. But we already know that pterosaur hatchlings were nearly identical to adults. That means the phylogenetic changes precede that hatchling stage and move back into the embryonic stage. Smaller pterosaur adults matured more rapidly than larger pterosaur adults. Smaller pterosaur eggs were ready to hatch sooner than larger pterosaur eggs. These changes produced the smaller wings, tail and legs seen in R. intermedius.

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
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Koh TP 1937. Unterscuchungen über die Gattung Ramphorhynchus. – Neues Jahrbuch Mineralogie, Geologie und Palaeontologie, Beilage-Band 77: 455-506.
Padian K 2009. The Early Jurassic Pterosaur Dorygnathus banthenis (Theodori, 1830) and The Early Jurassic Pterosaur Campylognathoides Strand, 1928, Special Papers in Paleontology 80, Blackwell ISBN 9781405192248
Plieninger F 1907. Die Pterosaurier der Juraformation Schwabens. Paläontographica 53: 209-313 & pls 14–19.
Quenstedt FA 1858. Über Pterodactylus liasicus. Jahresheft des Vereins für Vaterlundische Naturkunde in Württemberg 14: 299-310.
Wellnhofer P 1974. Campylognathoides liasicus (Quenstedt), an upper Liassic pterosaur from Holzmaden – the Pittsburgh specimen. Annals of the Carnegie Museum, Pittsburgh, 45: 5-34.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33.Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

wiki/Campylognathoides

wiki/Rhamphorhynchus

Youngina, Youngoides and the Younginiformes

There are several skulls and fewer post-crania attributed to Youngina and Youngoides, originally by R. Broom (1914), but CE Gow (1975) and others (see below) also made contributions.

The big question is: are the skulls crushed into a variety of shapes? Or do the variety of shapes reflect important morphologies that separate the various specimens into various clades? If you have any Youngina/Youngoides skull photos, please send them!!

The other question is: do some specimens harbor an antorbital fenestra?

Here’s why I wonder:

Figure 1. Youngina BPI 375. Is this a nascent antorbital fenestra?

And Here’s Another One:

Figure 2. Youngina AMNH 5561. Is this a nascent antorbital fenestra?

At the Base of the Archosauriformes
These two Youngina specimens nest at the base of the Archosauriformes in the midst of several other younginiforms. Do those little skull breaks/indentations represent antorbital fenestra? Good question. The answer is, it really doesn’t matter in phylogenetic analysis because predecessors in the protorosauria do not have an antorbital fenestra and successors in the archosauriformes do. Not all Youngina had or have to have an antorbital fenestra. These things tend to come and go, especially when they first appear.

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
Broom R 1914. A new thecodont reptile. Proceedings of the Zoological Society of London, 1914:1072-1077.
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis(Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3):online PDF
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.
Reisz RR, Modesto SP and Scot DMT 2011. A new Early Permian reptile and its significance in early diapsid evolution. Proceedings of the Royal Society, London B
doi:10.1098/rspb.2011.0439

From Whence Arrived the Aetosaurs?

Few paleontologists have ventured to guess, or determine through analysis, from whence arrived the aetosaurs. They don’t look much like any other archosauriforms. They seem to appear as sideshows in various analyses. Notably the latest analyses find no consensus. Nesbitt (2011) nested aetosaurs with Revueltosaurus. Outgroup taxa included Turfanosuchus and Gracilisuchus. Brusatte et al. (2010) nested Aetosauria with Gracilisuchus, Erpetosuchus and Crocodylomorpha. The Phytosauria was the outgroup.

“From whence arrived the praying mantis?” — Ogden Nash

Here aetosaurs nested with Ticinosuchus, a basal rauisuchian with a small head, short rostrum,  a reduced lateral temporal fenestra, a large mandibular fenestra, an upturned toothless dentary tip, a toothless premaxilla, a smaller pectoral girdle and scutes both above and below its tail. The hands and feet are also close matches. Ticinosuchus was also a sister to Qianosuchus and Yarasuchus, the long-necked rauisuchians sharing a dorsal naris with the basal rauisuchian, Vjushkovia and aetosaurs. It helped, of course, to actually reconstruct the skull of Ticinosuchus. It’s more aetosaur-like than previously thought. The size reduction between Ticinosuchus and Aetosaurus, the most primitive aetosaur, parallels other size reductions prior to major morphological changes in basal reptiles, mammals and birds. Chronologically the Late Triassic aetosaurs succeeded the Middle Triassic Ticinosuchus.

Figure 1. Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

Little Aetosaurus
As we’re finding over and over again, whenever a major clade is introduced, its basal member is small. Aetosaurus is less than a third the size of its phylogenetic predecessor, Ticinosuchus, but the skull length is more than half that of Ticinosuchus. The development of more extensive armor and an herbivorous dentition coincides with this size reduction. The only catch is, Aetosaurus is not the earliest known aetosaur. Perhaps it was a late survivor. All other aetosaurs, including earlier specimens, were larger with a more extensive armor coating and an expanded gut for plant digestion.

Figure 2. Aetosauroides.

Aetosauroides
Aetosauroides scagliai (Casamiquela 1960) Late Triassic (~210 mya) was a transitional taxon between Aetosaurus and Ticinosuchus. It had unconstricted tooth crowns, postnarial contact between the premaxilla and nasal, and a ventral margin of the dentary without a sharp inflexion. The teeth were primitive. I do not know the size of the skull. It was described as “large.”

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
Desojo JB and Ezcurra M.D 2011. A reappraisal of the taxonomic status of Aetosauroides(Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31(3):596-609. doi:10.1080/02724634.2011.572936
Fraas O 1877. Aetosaurus ferratus Fr. Die gepanzerte Vogel-Echse aus dem Stubensandstein bei Stuttgar. Festshrift zur Feier des vierhundertjährigen Jubiläums der Eberhard-Karls-Universät zu Tübingen, Wurttembergische naturwissenschaftliche jahreshefte 33 (3): 1–22.
Krebs B 1965. Ticinosuchus ferox nov. gen. nov. sp. Ein neuer Pseudosuchier aus der Trias des Monte San Giorgio. Schweizerische Palaontologische Abhandlungen 81:1-140.
Lautenschlager S and Desojo JB 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First DOI: 10.1007/s12542-011-0105-1
Schoch R 2007. Osteology of the small archosaur Aetosaurus from the Upper Triassic of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlung. 246/1:.1–35. DOI: 10.1127/0077-7749/2007/0246-0001
Walker AD 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transactions of the Royal Society B 244:103-204.

wiki/Aetosaur
wiki/Stagonolepis