According to Wikipedia, “Throughout the Cloverly Formation, Tenontosaurus is by far the most common vertebrate, five times more abundant than the next most common, the ankylosaurSauropelta.”
Tenontosaurus is one of the earliest taxa with a hyperelongated tail provided with the same tall neural spines and deep chevrons that characterize ornithopods. These, along with a longer length create what seems to be an oversize tail, which readily identifies Tenontosaurus. The hands retained dull claws on five short fingers. These would evolve to become flat hooves in Edmontosaurus. Manus digit 1 is retained in Tenontosaurus, then lost in Edmontosaurus. Pedal digit 1 is retained in Tenontosaurus, then lost in Edmontosaurus.
References Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Peabody Museum Bulletin 35:1–234.
This placement was a fait accompli. Rhynchosaurs are truly bizarre. Derived rhynchosaurs, like Teyumbaita and Hyperodapedon (Fig 1) push the definition of ‘bizarre’ to its limits. And they are two of a kind.
For the last eleven years, according to the large reptile tree (LRT, 2152 taxa, rhynchosaurs, azhendohsaurs and trilophosaurs were ALL descendants of sphenodonts (= rhynchocephalians). If it was going to change, it would have changed a long time ago. It has not changed in eleven years.
Decades ago, two experts cherry-picking traits created the current problem. Carroll (1988) revisiting Carroll (1977) reported, “It was long thought that rhynchosaurs were closely related to modern sphendontids on the basis of general similarities of the skull and dentition. The common presence of primitive features such as the lower temporal bar only points to their common origin among early diapsids. Although the dentition appears to be vaguely similar, it is fundamentally different.”
So what? All other traits are the same. Carroll was cherry-picking traits, otherwise known as “Pulling a Larry Martin.” Don’t do that. You’ll end up embarrassed.
“Sphenodontids have only a single row of acrodont teeth in the maxilla, but rhynchosaurs have multiple rows of teeth set in sockets. Sphenodontids have a second row of teeth in the palatine, but this bone is edentulous in the rhynchosaurs. What appear to be long premaxillary teeth in the rhynchosaurs are actually processes from the premaxillary bones. Sphenodontids have true premaxillary teeth.”
So what? That is evolution in progress. Carroll also made an easy mistake. The palatine in rhynchosaurs is not edentulous (Fig 2). It is toothy and anteriorly fused to the maxilla. That may be the cause of Carroll’s error in the years prior to software-assisted phylogenetic analysis.
The other expert making mistakes was textbook author Michael Benton. Benton (1983) reported, “Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”
Benton did not realize the lower temporal bar was derived in sphenodontians. Early lepidosaurs don’t have it. Acrodont teeth are also derived from socketed teeth, so all sphenodontids had to do was stop fusing their teeth to their skull in order to go back to the socketed teeth found in rhynchosaurs. Rhynchosaurs stop fusing their ankles and stop fusing their teeth to their jaws. That’s a reversal or two. Benton was also cherry-picking triats, aka “Pulling a Larry Martin.”
This was two years before Benton’s first venture into software assisted phylogenetic analysis.
Four years after receiving his PhD, at the innocent age of 29 Benton 1985 nested pterosaurs closer to lepidosaurs than to dinosaurs (Fig 3). That was never repeated again until Peters 2007. Benton 1985 also missed the more obvious connection of pterosaurs to Macrocnemus, Tanytrachelos and Tanystropheus recovered by Peters 2000, 2007. Again, too few traits and too few taxa were tested in Benton 1985.
Getting back to rhynchosaurs, note the proximity ofTrilophosaurus to rhynchosaurs and lepidosaurs in Benton’s first ever cladogram (Fig 3). The basic problem with Benton 1985 was the use of only 14 taxa. In 2011 the LRT resolved Benton’s issues with 200+ taxa, none of them suprageneric. Today, in 2022 the LRT affirms the proximity of trilophosaurs, rhynchosaurs and sphenodonts with 2152 taxa.
Here’s a solution: Build your own LRT with a wide gamut of taxa to find out for yourself whether or not rhynchosaurs and trilophosaurs nest with more primitive sphenodonts. If somehow they don’t, you better have a damn good selection of taxa more similar than sphendonts. So far, and I’ve looked at everything out there, I don’t think you’re going to find competing candidates, let alone another set of sisters.
References Benton M J 1983. The Triassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Phil. Trans. R. Soc. Lond. B 302, 605–717. Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164. Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359–396. Carroll RL 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Co. New York. Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4:e1778 Mantefeltro FC, Langer MC and Schultz CL 2010. Cranial anatomy of a new genus of hyperodapedontine rhynchosaur (Diapsida, Archosauromorpha) from the Upper Triassic of southern Brazil. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101: 27–52. Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336. Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27. Schultz CL, Langer MC and Montefeltro FC 2016. A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary. Paläontologische Zeitschrift. in press (3): 593–609.
In their description of Shearsbyaspis Castiello and Brazeau 2018wrote: “Stem-group gnathostomes reveal the sequence of character acquisition in the origin of modern jawed vertebrates.
That’s a tautology (= saying of the same thing twice in different words). The problem is Castiello and Brazeau picked the wrong stem-group(s) not knowing the origin of jaws occurred twice in vertebrates (Figs 2, 3). Neither involved derived petalichthyids, like Shearsbyaspis.
“The petalichthyids are placoderm-grade stem-group gnathostomes known from both isolated skeletal material and rarer articulated specimens of one genus. They are of particular interest because of anatomical resemblances with osteostracans, the jawless sister group of jawed vertebrates.
The problem is Castiello and Brazeau did not realize the difference between ‘resemblance’ and homology. In the large reptile tree (LRT, 2150 taxa, subset Fig 2) petalichthyids are not related to osteostracans like Hemicyclaspis (Fig 3) with roots in the Early Cambrian taxon, Haikouichthys. Yes, our fish ancestors are that ancient.
Because of this, they [petalichthyids] have become central to debates on the relationships of placoderms and the primitive cranial architecture of gnathostomes.
This is incorrect due to taxon exclusion and reliance on out-dated university textbooks. Basal petalichthyids are central to relationships of placoderms because petalichthyids are basal to other placoderms (Fig 2), but Shearsbyaspis is a derived petalicthyid, going its own way, away from the lineage that developed placoderm jaws.
Moreover, petalichthyids have nothing whatsoever to do with the primitive cranial architecture of gnathostomes. Extant sturgeons (Fig 3) provide that data.
Castiello and Brazeau 2018wrote: However, among petalichthyids, only the braincase of Macropetalichthys has been studied in detail, and the diversity of neurocranial morphology in this group remains poorly documented. Using X-ray computed microtomography, we investigated the endocranial morphology of Shearsbyaspis oepikiYoung, a three-dimensionally preserved petalichthyid from the Early Devonian of Taemas-Wee Jasper, Australia.
Glad to see that Shearsbyaspis (Fig 1) is 3D, because Lunaspis (Fig 1) is not.
“We generated virtual reconstructions of the external endocranial surfaces, orbital walls and cranial endocavity, including canals for major nerves and blood vessels. The neurocranium of Shearsbyaspis resembles that of Macropetalichthys, particularly in the morphology of the brain cavity, nerves and blood vessels. Many characters, including the morphology of the pituitary vein canal and the course of the trigeminal nerve, recall the morphology of osteostracans. Additionally, the presence of a parasphenoid in Shearsbyaspis previously not known with confidence outside of arthrodires and osteichthyans) raises some questions about current proposals of placoderm paraphyly. Our detailed description of this specimen adds to the known morphological diversity of petalichthyids, and invites critical reappraisal of the phylogenetic relationships of placoderms.”
Accepting that invitation, the LRT presents that “critical reappraisal of the phylogenetic relationship of placoderms” in figure 2.
It’s so important to start and finish every project using a valid cladogram. Simply add taxa to bring your own cladogram up to date. Otherwise all your studies are going to be off the mark, with misunderstood conclusions due to taxon exclusion.
From the Bestwick et al 2022 abstract: “Here, we restore the skull morphology of Effigia, perform myological reconstructions, and apply finite element analysis to quantitavely investigate skull function. We infer that Effigia was a specialist herbivore that likely fed on softer plant material, a niche unique among the study taxa and potentially among contemporaneous Triassic herbivores.”
To their credit, the ten co-authors compared their poposaur, Effigia (Fig 1), to two convergent dinosaurs, Ornithomimus and Struthio, The authors also compared Effigia to Alligator in order “to assess the degree of functional convergence with the above named taxa.”
I guess one of the ten co-authors must have insisted on this based on a convergent ankle joint in Alligator (see below). Otherwise it is difficult to compare alligator to ostrich morphologies, diet, niche, locomotion, etc. Nevertheless, ten PhD co-authors thought this was a good idea.
To their discredit, the ten co-authors still believe in the invalid clade Pseudosuchia, which they define as archosaurs more closely related to crocodylians than to birds. In the LRT (subset Fig 3) all archosaurs more closely related to crocodylians than to birds are members of the Crocodylomorpha. That’s it. Full stop. Outgroup taxa to crocs + dinos (Fig 3) are not archosaurs, by definition. Since poposaurs occupy this node, they are not archosaurs.
Poposaurs in the large reptile tree (LRT, 2149 taxa, subset Fig 3) are shown below (Fig 4). Turfanosuchus nests as the most basal poposaur. Effigia nests as the most derived poposaur.
The ten authors are kidding themselves and short-changing their readers by excluding several poposaurs (listed above). In the LRT relationships are completely resolved by including taxa excluded by Bestwick et al. who borrowed an invalidated cladgoram from co-author Sterling Nesbitt 2011, who was working on his doctoral dissertation and publishing that as a paper eleven years ago.
Bestwick et al confessed, “The order in in which poposaurid bauplans were assembled and/or modified is currently unclear (referencing co-author Nesbitt 2011),”
That study by Sterling Nesbitt was shown to suffer from inaccurate scoring to such an extent that when rescored here the topology matched the LRT.
Bestwick et al concluded, “Effigia possesses an unusual mosaic of mechanical features that most likely restricted habitual feeding functions to the anterior portion of its jaws. A shearing motion between the anterior parts of the mandible and rostrum during orthal closure would generated the least stress under modeling conditions.”
“Shearing” is usually done with shears = scissors. Scissors require a tight rotating joint that permits cutting at the precise junction of two sharp surfaces brought into close contact. That’s not what we see here (Fig. 5). Instead the mandible is smaller than the rostrum making it extremely loose and mobile. Apparently this obvious key to the Effigia feeding apparatus was overlooked by all ten co-authors.
What is the tenth man rule? “The Tenth Man strategy essentially says that if nine people agree on a particular course, the tenth person must, in the context of this strategy, take a contrary approach so that all alternatives can be considered. In business, this process can help break “groupthink” and ensure that a business considers all options.”
Effigia okeeffeae (Nesbitt and Norell, 2006) Carnian, Late Triassic, ~210 mya, ~ 2 m in length, was originally considered an early theropod dinosaur by Colbert, who collected the specimen in the late 1940s but never removed it from its jacket. A reassessment by Nesbitt and Norell (2006) and Nesbitt (2007) nested Effigia among the poposaurid rauisuchians based largely on the ankle, which they reported articulated in a crocodile-normal configuration, with a morphology similar to Alligator.
Yes, poposaurids are rauisuchians. For the same reason: crocodylomorphs and dinosaurs (including birds) are rauisuchians. They are all descendants of rauisuchians in the LRT (Fig 3).
Relying on ankle joints is no longer a paleo fad. The LRT employs 236 multi-state characters and 2100 taxa to determine tree topology and interrelationships.
This is yet one more reason why you need to build your own LRT, so you. too, can use this powerful tool with authority. Then, when you test your own wide gamut of taxa, you’ll have the confidence that taxon exclusion will not be your problem.
References Bestwick J et al (9 co-authors) 2022. Cranial funtional morphology of the pseudosuchian Effigia and implications for its ecological role in the Triassic. AnatomyPubs. Special Issue Article. online 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
This icon of the Synapsida and Cynodontia took a surprisingly long time to come to the top of the pile. And since it is THE icon for these two clades, it’s no surprise where Cynognathus nests in the large reptile tree (LRT, 2149 taxa).
Cynognathus crateronotus (Seeley 1895, Wynd et al 2018, Middle Triassic, 1.2m snout-vent length) extended its range across South Pangaea. No complete skeletons are known, so a composite (= chimaera) is created (Fig 3) based on Thrinaxodon proportions. The secondary palate is complete.
Note the robust lumbar transverse processes on Cynognathus (Fig 2), a trait shared with Thrinaxodon (Fig 3). These appear to occur at the transition from lateral undulation-dominated locomotion (like a sprawling reptile), to less-undulating, limb-dominated, more erect locomotion (as in basal mammals).
Here’s a thought. This change in locomotion strategies could have occurred during a burrowing phase in which the narrow tunnel itself environmentally constrained locomotion from a wider sprawl to a narrower tucking in (adduction) of the limbs. Vertebrate burrows were present during the time of Cynognathus (Groenewald, Welman and MacEachern 2001) and Thrinaxodon fossils have been found within burrows.
Burrowing cynodonts laid eggs. At the origin of reptiles (= amniotes) the lumbar ribs became reduced, enabling gravid females to stretch their abdomens laterally while carrying the new larger amniotic eggs. In extant lepidosaurs gravid females distend the lower abdomen (Fig 4). So when Cynognathus started burrowing, perhaps these large, transverse lumbar processes somehow protected the lumber region of gravid females. Males had similar lumbar regions because they were also burrowing. Genders have not yet been identified in these basal cynodonts.
Predecessors did not have large lumbar extensions. Neither did successors. That’s all I’m basing this hypothesis on. It needs to be further developed.
One last little oddity about Cynognathus is in the palate (Fig 1). The anterior jugals curl medially isolating the ectopterygoid (orange) from the maxilla without a suborbital fenestra. I have not seen that in other tetrapods.
References Groenewald GH, Welman J and MacEachern JA 2001. Vertebrate burrow complexes from the Early Triassic Cynognathus Zone (Driekoppen Formation, Beaufort Group) of the Karoo Basin, South Africa- Palaios. Jenkins FA Jr 1967. The postcranial skeleton of African cynodonts. Peabody Museum of Natural History Yale University Bulletin 36. Seeley HG 1894. Researches on the structure, organisation, and classification of the fossil reptilia.-Part IX, Section 1. On the Therosuchia: Philosophical Transactions of the Royal Society of London, series B, v. 185, p. 987-1018. Seeley HG 1895. Researches on the Structure, Organization, and Classification of the Fossil Reptilia. Part IX, Section 5. On the Skeleton in New Cynodontia from the Karroo Rocks. Philosophical Transactions of the Royal Society of London B 186: 59-148.
From the Pradel et al 2009 abstract: “A new taxon, Ramirosuarezia boliviana n. gen., n. sp. is erected for a single, articulated jawed fish (gnathostome) skull from the Middle Devonian (Eifelian) Icla Formation of Bolivia. The specimen displays an elasmobranch-like braincase, but lacks unambiguous elasmobranch and even chondrichthyan characters, although its peculiar tooth-bearing ‘labial’ elements evoke certain stem-holocephalans”.
Don’t look for a character or two to clearly support affinities. That’s called “Pulling a Larry Martin”, one of the six most common problems in paleontology. Instead, build and run your own LRT. Use hundreds of characters and taxa to determine affinities without ambiguity.
From the Pradel et al 2009 abstract continued: “Its endoskeletal elements seem lined with either perichondral bone or non-prismatic calcified cartilage, but show no evidence of endochondral bone. Although devoid of large dermal bones and scales, R. boliviana shares with certain ‘ostracoderms’, placoderms and holocephalans the lack of an otico-occipital fissure, but lacks a hypophysial fenestra.”
Don’t look for a character or two to clearly support affinities, etc.
“Certain features (elongated braincase, ‘labial elements’, sharp denticles and teeth) are also suggestive of the equally enigmatic coeval stensioellids, once regarded as either primitive placoderms or stem holocephalans.”
Don’t look for a character or two to clearly support, etc.
” The jaws are armed with platelets that bear blunt to pointed and sharp teeth, in which synchrotron radiation microtomography yields evidence of a large pulp cavity, a possibly osteichthyan-like character. No character clearly supports affinities of R. boliviana to any of the currently known major gnathostome groups”.
Don’t look for a character pr two to clearly, etc.
“Tenuous hints suggest a relationship to the enigmatic fossil Zamponiopteron , from the Eifelian of Bolivia, known by peculiar calcified ‘fin plates’ and isolated shoulder girdles.”
Don’t look for a character or two to, etc.
From the Pradel et al Conclusion: “Although known from an almost complete, articulated skull, R. boliviana remains an enigmatic gnathostome, which allies some vague resemblances to chondrichthyans and placoderms, notably rhenanids and stensioellids (the latter being regarded as either primitive placoderms or stem holocephalans). Yet it is impossible to pinpoint any of these resemblances as an unambiguous derived character shared with these major gnathostome taxa.”
Build your own LRT and you will neverhave to announce another enigmatic taxon.
So… the first known sharks with teeth were the size of fat pencil. Maybe that’s why fish remains are so hard to find in the Cambrian, Ordovician and Silurian.
Colleagues, when composing your abstract and text, it’s not useful to tell us what your new fossil might be or could be based on this trait or another. Add your new taxon to your own wide gamut analysis and let hundreds of traits and hundreds of taxa tell you what your new taxon is without ambiguity. Otherwise, someday a nobody with his own LRT will do it for you.
References Pradel A, Maisey JG, Tafforeau P and Janvier P 2009. An enigmatic gnathostome vertebrate skull from the Middle Devonian of Bolivia. Acta Zoologica (Stockholm) 90 (Suppl. 1):123–133.
A goldfish-sized specimen of Incisoscutum ritchiei (Dennis and Miles 1981; Trinajstic et al 2022; Early Devonian) lacking the front half of the skull (MV P230859) was otherwise preserved with internal organs, revealed by µCT scans (Fig 1). Publicity (see below) was worldwide and focused on the heart.
I was more interested in the phylogeny of Incisoscutum. Unfortunately the lack of skull parts prevents entry into the large reptile tree (LRT, 2147 taxa, subset Fig 3). Even so, it appears to be generally close to the giant Heterosteus (Fig 2) among tested taxa.
Of phylogenetic interest, the flatter, wider dorsal and ventral armor of Incisoscutum (Fig 1) and its reduced size, recalls the ancestral morphology of the older, jawless, finless taxon, Arandaspis, and kin. Perhaps this was an example of a reversal encouraged by phylogenetic miniaturization, so far preceding no known descendant taxa.
From the Trinajstic et al 2022 abstract: “The origin and early diversification of jawed vertebrates involved major changes to skeletal and soft anatomy.”
From the Trinajstic et al 2022 abstract: “Skeletal transformations can be examined directly by studying fossil stem gnathostomes; however, preservation of soft anatomy is rare. We describe the only known example of a three-dimensionally mineralized heart, thick-walled stomach, and bilobed liver from arthrodire placoderms, stem gnathostomes from the Late Devonian Gogo Formation in Western Australia.
Phylogenetic bracketing (Fig. 3) indicates this should be no surprise since plesiomorphic and extant lampreys have a two-chambered, S-shaped heart (Fig 4).
From the Trinajstic et al 2022 abstract: “The application of synchrotron and neutron microtomography to this material shows evidence of a flat S-shaped heart, which is well separated from the liver and other abdominal organs, and the absence of lungs. Arthrodires thus show the earliest phylogenetic evidence for repositioning of the gnathostome heart associated with the evolution of the complex neck region in jawed vertebrates.”
As above, whatever was complex in the neck region of placoderms has more to do with what plesiomorphic lampreys have in their neck region. The most primitive placoderms (Fig 3) were also jawless, later developing their own jaws by convergence with gnathostomes. What makes a placoderm a placoderm, according to the LRT, is the armor. Armor is otherwise missing in pre-gnathostomes with one exception by convergence: Osteostraci (e.g. Hemicyclaspis), Armore reappears by convergence in armored catfish (e.g. Hoplosternum).
On a side note: At long last, I am relieved to report that members of the tall, narrow-skulled Ptyctodontida have FINALLY shifted to the Placodermi in the LRT (Fig 3). This new nesting matches traditional results. The key insight was recognizing that ptyctodonts did not have a premaxilla, like bony fish do. Instead ptyctodont placoderms employ the nasal as a biting organ (Fig 5). As in other placoderms, there is no premaxilla and maxilla. Jaws developed in the Placodermi by convergence with gnathostomes, as documented earlier. Likely the nares and oral cavity were merged in ptyctodonts like Campbellodus (Fig 5). (Ventral/palatal data is needed).
Moreover, and just as confusing to the novice (= me when I first encountered this morphology), the bone that would otherwise be the frontal atop the orbit is instead the preorbital. The narrow frontal is here atypically anterior to the preorbital. Moreover, all the elongate separate cheekbones are derived from a single large jugal plate. There is no quadrate. All of this had to be learned from experience and exposure. Unfortunately, that took time, taxa, some restless nights and head-scratching.
This placoderm update is just the latest example of 200,000 similar corrections over the last eleven years. Each correction exemplifies the phrase, “lifelong learner”, striving to create a never perfect, but constantly improving and fully resolved LRT.
Tetrapod homologies are not traditionally applied to placoderm skulls, but they must applied to be scored in the LRT. At present an additional 9 steps are required to return ptyctodonts to their former node, documenting the level of convergence overcome by these latest identity and scoring changes. It’s easy if you do it right the first time with lots of taxa to start with, but that’s not how the LRT accumulated mass.
PS. Taxa in the Trinajstic et al cladogram and missing from the LRT include Latviacanthus ventspilsensis (Schultze and Zidek 1982, Fig 6), discovered in the by-products of a deep drill boring core in Latvia.
From the Schultz and Zidek 1082 abstract: “Latviacanthus ventspilsensis n.gen., n.sp. is described from a drilling core at Ventspils, Latvia, U.S.S.R. It is placed near Euthacanthus, Climatiidae, chiefly on the basis of similarities in the gill region (1 hyoid and 3 accessoric gill covers). Main features of Latviacanthus are: palatoquadrate and Meckel’s cartilage ossified as a single element each, multiple-cuspid teeth not fused to the jaws, slender pectoral spine, weakly developed dermal shoulder-girdle.”
References Dennis K and Miles RS 1981. A pachyosteomorph arthrodire from Gogo, Western Australia. Zoological Journal of the Linnean Society. 73 (3): 213–258. Schultze H-P and Zidek JN 2022. Ein primitiver acanthodier (pisces) aus dem unterdevon lettlands. Paläontologische Zeitschrift 56:95–105. Trinajstic et al (12 coauthors) 2022. Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte. Science 377, 1311 DOI: 10.1126/science.abf3289
Updated Septermber 21, 2022 with a lateral view of the right femur, broken more or less at mid shaft.
Similar to and derived from Late Triassic Planocephalosaurus (Fig 1), the new Late Jurassic Opisthiamimus (Figs 1–4) might seem to be just another sphenodontid. That’s how it was portrayed in the paper and the press.
Only one small femur is partially preserved. This morphology would seem to be distinct from the traditional large, beefy hind limbs presented in the Julius Csotonyi freehand illustration (Fig 4) that publicized this discovery, but the living tuatara (Sphenodon. Fig 1b) has a similar slender femur.
After DGS tracing, (Fig 3) a reconstruction is presented for Opistthiamimus. This is no surprise. It completes a phylogenetic trend (Fig 1).
Opisthiamimus is known from four specimens that together create an almost complete specimen, according to the authors.
According to DeMar, Jones and Carrano 2022, “The postcranial skeleton of O. gregori exhibits characteristics typical of a terrestrial rhynchocephalian.”
From the DeMar et al. abstract: “We describe a new, small-bodied rhynchocephalian reptile, Opisthiamimus gregori gen. et sp. nov., from the Upper Jurassic Morrison Formation of Wyoming, USA. We used micro-computed tomography to examine its skeletal anatomy in detail and to develop a three-dimensional reconstruction of the skull.”
Sounds like they had every modern tool at hand – except they lacked their own independently created and scored LRT (Fig 5), built from their own post-cranial reconstruction (Fig 3) and compare that to related taxa (Fig 1).
From the DeMar et al. abstract: “Our phylogenetic analyses use a substantially updated data set of 118 characters and 46 taxa, and both maximum parsimony and Bayesian frameworks. Results place O. gregori inside Eusphenodontia but outside Neosphenodontia, and therefore in a key position for contributing to character polarity for more deeply nested clades such as Clevosauridae, Sphenodontidae and Pleurosauridae.” (See figure 6).
The LRT (Fig 5) is essentially similar, but includes a much wider gamut of taxa overlooked and excluded by DeMar et al. This is what happens in academia. Traditionally misunderstood clades remain perpetually misunderstood because that’s the way they are printed in outdated textbooks that support the education the PhDs provide to their tuition-paying students worldwide. PhDs and grad students think ‘the work’ is already done by competent authorities. That’s why they borrow published cladograms.
You, too, will see behind the curtain and understand the limits of a university education when you run your own experiments, score your own taxa and let PAUP tell you how a wide gamut of taxa interrelate.
From the DeMar et al. abstract: “We also erect Leptorhynchia taxon nov., composed primarily of aquatically adapted taxa (e.g. Pleurosaurus, Sapheosaurus), which is supported by both cranial and postcranial characters.” (see Figure 6).
By contrast, the LRT (Fig 5) employs twice as many traits and several times as many taxa, and it nests basal Pleurosaurus far from derived Sapheosaurus (Fig 5). So the LRT does not support DeMar et al’s new clade. More taxa added to DeMar’s cladogram will show it is not monophyletic because they omitted several pertinent taxa while adding unrelated taxa.
“Because O. gregori is not particularly closely related to the other named Morrison rhynchocephalians (e.g. Opisthias rarus), it increases both the alpha and beta taxonomic diversities within the formation.”
Unfortunately, the best Opisthias fossil(Fig 1) is so incomplete it cannot yet be tested here.
“Similarly, major differences in body size and inferred diet of the Morrison taxa imply considerable concomitant palaeoecological diversity just prior to a major global decline in rhynchocephalian diversity around the close of the Jurassic.”
When the authors talk about ‘major differences in body size‘ in Morrison taxa, reminds us there were giant sauropods there. The authors left that to our imagination. Or did they want to restrict out thoughts to the ‘palaeoecological diversity‘ of just the rhynchocephalians?
Remember, tuataras are found in burrows. Like the descendants of burrowing Thrinaxoon, rhynchocephalians were survivors.
The DeMar et al cladogram is traditional, which means it suffers from a wider gamut of taxon exclusion. It intends to lump and separate species when it really needs to lump and separate the entire clade from all other clades. Many clade members are omitted here (Fig 6) and this comes from following Benton’s Vertebrate Paleontology textbook and the professors that teach from it. Stop spinning around like a spider going down a flushing toilet. Build your own LRT before you write your next paper.
Wouldn’t you rather know exactly what you are writing about without relying on others? Start off with a valid, fully resolved wide-gamut cladogram of your own making based on DGS tracings and reconstructions.
Then you will never suffer from the top six problems in paleontology: Number one: taxon exclusion (= the streetlight effect). Number two: borrowing cladograms that exclude taxa. Number three: trusting genomic results. Number four: trusting textbooks and academic traditions. Number five: freehand reconstructions. Number six: “Pulling a Larry Martin” = focusing on one to a dozen traits, rather than a complete suite. Solution: Keep adding taxa to your own trait-based cladogram. Trace specimens with transparent colors and from those tracings create more accurate and verifiable reconstructions.
References Carroll RL 1985. A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontids. DeMar DG, Jones MEH and Carrano MT 2022. A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria). Journal of Systematic Palaeontology. 20 (1): 1–65. Fraser NC and Sues H-D 1997. In the Shadows of the Dinosaurs: early Mesozoic tetrapods. Cambridge University Press, 445 pp. Online book. Heckert AB 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U.S.A. New Mexico Museum of Natural History and Science Bulletin 27:1-170. Meyer H 1831. IV Neue Fossile Reptilien, aud der Ordnung der Saurier.
Today the picture tells the story. Hope you know your macropodids, potorids and interatheres (Fig 1). If not the links will help. The large reptile tree (LRT, 2147 taxa) separates the extinct, one-toed, short-faced Procoptodon from the extant, several-toed, long-face Macropus. These two terminal taxa appear to have had a convergent kangaroo morphology revealed only by adding taxa that are smaller, more primitive and not so kangaroo-like.
Macropus giganteus Shaw 1790, extant) is the eastern gray kangaroo. The forelimbs were elongated. The hind limbs even more so. The pedal digits were reduced, all but the second digit, which was robust. Kangaroos hop bipedally and rest tripodally with the tail. Note the pelvis is essentially vertical here and the proximal femur was lower than the distal femur. The canines were absent and a diastema separated the incisors from the molars, convergent with rodents and multituberculates. The lower incisors were elongated and procumbent.
Procoptodon goliah (Owen 1873, extant, 2m tall; Pleistocene) is the extinct short-face kangaroo. The skull was very much like that of its ancestor, Interatherium.
References Owen R 1873.Procoptodon goliah, Owen. Proceedings of the Royal Society of London 21, 387. Shaw G 1790.Macropus giganteus. Nat. Miscell. plate 33 and text. kangaroo online pdf
Chinese paleontologists, Gao et al. 2009, accepted an invitation to visit North Korea to describe a small anurognathid (unnamed, unnumbered, Figs 1–3) from “The Lower Cretaceous Sinuiju Series of the Jasong Supergroup.” Not sure what I’m missing here, but in the text Gao et al report, “and now the new fossil discovery from North Korea may well provide the evidence for a geologically younger range extension of the family into the Upper Cretaceous.” And “In general, several bird fossils from the Sinuiju Series, North Korea, document the occurrence of confuciusornithid and enantiornithine birds in the Upper Cretaceous of the Korean Peninsula, and may include some other forms that have not been previously recognized in the fossil record.”
These could be editing mistakes as the title of this paper reports, “Early Cretaceous.”
Gao et al. reported, an approximate length of this pterosaur at 25cm. Here it has a snout-vent length of 12cm. Gao estimated the wingspan at 80cm. Here it measures only 56cm (f the scale bar is correct). Gao reported, “The skull is bilaterally compressed, but the postcranial skeleton is dorso-ventrally compressed as preserved.” Actually the skull was disc-shaped in vivo (Fig 3) and was also dorso-ventrally compressed during fossilization. The rest of the description is more or less trouble-free.
The free fingers and one foot are off the matrix. The skull (Fig 2) is difficult, but not impossible to reconstruct. The crushed skull elements match those seen in related anurognathids, not the Bennett 2007 monstrosity with giant eyeballs and an abbreviated rostrum that has grown beyond mythology to become widely accepted tradition. No related taxa have giant eyeballs close to the anterior margin.
The shorter than wide skull of this specimen (Fig 3) makes this anurognathid distinct. Relatives (Figs 4, 5) had relatively larger and longer skulls.
Coming only six years after Jeholopterus, Gao et al 2009 reported, “Compared to Jeholopterus from China, the immediate differences that can be recognized in the Korean form are: ten rib-bearing trunk vertebrae (vs. 12-13); synsacrum formed by fusion of at least seven sacral vertebrae (vs. by three); scapula and coracoid roughly equal in length (vs. coracoid about half length of the scapula); and greater elongation of the ulna/radius segment to twice the length of the humerus. Although it can be recognized as a member in the family Anurognathidae, the taxonomy of this Korean pterosaur at the generic and species level cannot be determined before a thorough study of the available specimens.”
Workers seem to have ignored this North Korean pterosaur, perhaps because it is curated above the 38th parallel. I first learned about this specimen a few days ago via a David Hone podcast on anurognathids from 6.21.22. However, take Hone’s exposition and ‘facts’ with a grain of salt. He has a pretty dismal track record of portraying invalidated myth as fact. See below for more examples.
According to David Hone in this video: 1.Baby anurognathids had a giant head, adults did not. This is incorrect. All pterosaurs grow isometrically as shown by Pterodaustro, Zhejiangopterus and all embryos. 2. Baby anurognathids had giant eyes, adults did not. Incorrect. This myth is based on the mistakes of Bennett 2007 who confused a maxilla with a sclerotic ring. See figure 7. 3.We have very few adult anurognathids. Most are juveniles. Incorrect. See #1 above and figure 5 above. 4.Pedal digit 5 was incorporated into the uropatagium. Incorrect (see figure 4). We have pterosaur tracks with this long fifth digit impressing the matrix. This traditional error is based on the mistakes of Unwin and Bakhurina 1994 who studied Sordes. 5. Wings were deep and broad. No membranes extend beyond the knee as mistakenly shown above. This is also due to mistakes made in Unwin and Bakhurina 1994. Instead all pterosaur membranes were stretched between the wing tip and elbow. This facilitated folding and tucking the wing finger inside the elbow. AND matches all fossils, contra Elgin, Hone and Frey 2011. 6.Anurognathids were basal pterosaurs, we just haven’t found them yet in the Triassic. Incorrect, but Triassic precursors, like Preondactylus, are known. Hone has been historically loathe to add fenestrasaur outgroups to pterosaur analyses especially when creating supertrees, He is known to delete taxa that don’t agree with his or his mentor, professor Mike Benton’s, preconceptions. Anurognathids are derived from dimorphodontids in the LPT. 7.We don’t really know where they sit in the pterosaur tree. Yes we do. Click here to see where they sit in the LPT. Hone and Benton 2009 deleted pterosaur ancestors recovered after three analyses by Peters 2000. 8.Some anurognathids had thumbs. None did. The three free fingers often and typically rotate axially because the deep axis of the claws are pushed down to the bedding plane during crushing. Ironically, finger 3 did have a more flexible ball and socket joint enabling posterior orientation while making manus prints. This is rather common. 9. Hone is into ‘believing‘ or ‘not believing.’ This is unscientific thinking. He should be testing for facts. There should be no belief in science, nor trust, nor friendship, nor alliance, nor bias. 10.Anurognathids lived in tree hollows. None have ever been associated with fossil timber. 11. Here is how Dr. Hone described the skull of the anurognathid Cascocauda (Yang, Benton, Hone, Xu, McNamara and Jiang 2022, Fig 7): The skull is just smooshed. Its just bone bits. Its really quite wide and it’s not very long. It’s got quite a big head, and yeah, I’m running out of bones after that.“
In the video Hone described the North Korean specimen (Figs 1–3) as “famously inaccessible”, then described the ‘bad‘ photo of a ‘bad’ specimen, ‘scanned badly from the original print’, and the ‘damn skeleton is complete’.
Thanks, Dr. Hone, for both alerting me to this taxon while dismissing it. I love such challenges. After a few hours of work I found it is not all that ‘bad’. This specimen comes after a long line of related taxa that all have a similar morphology. I’m trying to help fellow workers by publishing these tracings and reconstructions to confirm, refute or modify… or in your case, to help you get over your refusal to trace the specimen with precision. This is the anurognathid Bauplan.
Unprofessional labeling (e.g. ‘bad’) and name-calling is never appropriate in science. Others may confuse your dismissive words and actions with elitism and/or a lack of self-confidence in taking on the most important and challenging opportunities of your chosen profession. Your students pay their tuition to learn from, and be inspired by your leadership.
Dr. Hone, you need no longer confess to ‘running out of bones after that,’ or describing the skull as ‘smooshed.’ Next time, don’t give up… give it a go! Try tracing the specimen using the DGS method of coloring bones. It’s easy. More and more of our colleagues are doing this now. It only takes time and patience. Use these figures as a guide. Let me know of any errors.
I know you don’t like to be challenged or corrected. However, it’s OK to make mistakes. It’s all part of the scientific process.
It would be better for you to learn something that you can teach (which is how you make your living), than to give up and walk away just because something appears to be too difficult or corrections come from someone you don’t like. If I can figure this out, you can, too. You have been granted a PhD. That means you have the training and wherewithal.
Now try your hand at some precision work (don’t pass this off to a grad student) so you can turn around your (so far) dismal track record. You are more than a decade in, but you’re still a young man. It’s not too late for you. Discard your preconceptions. Start from scratch if you have to. Understand the data as is.
References Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398. Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145 Gao K-Q 2009. Early Cretaceous birds and pterosaurs from the Snuiju Series, and geographic extension of the Jehol Biota into the Korean Peninsula. J. Paleont. Soc. Korea 25(1:57-61. Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336. Unwin DM and Bakhurina NN 1994.Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.