Dr Sangster 2022 redescribes one of the first known pterosaurs, Dimorphodon macronyx (Buckland 1829, Figs 1, 2) in a new monograph. I’m guessing this follows and is largely based on Sangster 2001, her ?unpublished dissertation titled “Anatomy, functional morphology and systematics of Dimorphodon”.
Wonder what’s new in the last 21 years? Or the last 93?
The abstract: “Dimorphodon macronyx (Buckland, 1829) is one of the earliest known Jurassic pterosaurs and the first English pterosaur to have been formally described; the original specimens from the London Natural History Museum have not been fully reviewed since Richard Owen’s monograph of 1870. This monograph provides a detailed, comparative osteological description and emended diagnosis of D. macronyx, based primarily on the four key London and British Geological Survey specimens, and supplemented by the other known skeletal material. Previously undescribed palatal bones uncovered in one of the Natural History Museum specimens (NHMUK 41212) in 2002 are also described and a tentative reconstruction of the palate presented. A short review of previous phylogenetic studies on the taxonomic status of D. macronyx is provided.”
The palate of NHMUK 41212 (Figs, 1, 3) was presented here in 2011.
From the University of Birmingham website: “Sarah completed her PhD on the Jurassic pterosaur Dimorphodon at the University of Cambridge in 2003.”
As you can see, sometimes publications can be painfully slow in academia, with her PhD awarded two years after the date of her dissertation and the monograph 21 years later.
References Buckland W 1829. Proceedings of the Geological Society London, 1: 127. Owen R 1859. On a new genus (Dimorphodon) of pterodactyle, with remarks on the geological distribution of flying reptiles.” Rep. Br. Ass. Advmnt Sci., 28 (1858): 97–103. Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233. Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44. Sangster S 2001. Anatomy, functional morphology and systematics of Dimorphodon. Strata 11: 87-88. Sangster S 2022. The osteology of Dimorphodon macronyx, a non-pterodactyloid pterosaur from the Lower Jurassic of Dorest, England. Monographs of the Palaeontological Society 175, 221 (661):1–48.
A few Middle Jurassic mammal teeth led Averianov et al. 2022 to describe those as early multituberculates. Averinov’s team, by default, relied on dental traits, which can become convergent in unrelated taxa. They also excluded pertinent taxa.
First, build your own wide gamut cladogram from more or less complete fossils, then insert dental taxa only where it is safe to do so.
Multituberculates are close to carpolestids, plesiadapiforms and rodents in the large reptile tree (LRT, 2119 taxa). The LRT tests taxa that other authors omit. The Averianov et al. abstract says nothing about the origin of this clade, described as, “the most diverse and abundant group of Mesozoic mammals.” Averinov saves his hypotheses on interrelationships for the text.
Averinov et al report, “In spite of the large fossil record for Multituberculata, their origin and phylogenetic relationships are still unclear, because of their distinctive morphology that is different from that of all other mammals.”
Different from all other mammals? No. That ‘distinctive morphology’ is focused only on the posterior jaw bones, which do not shrink during ontogeny as an embryo to become ear bones. This was a reversal due to neotony, enhancing the ability of the jaws to slide posteriorly, as we learned earlier here in 2019 and here in 2016. Multis are rodents. So are aye-ayes. So are plesiadapiformes.
Averianov et al report, “The most intriguing finding from the discovery of the new Middle Jurassic multituberculate material is the fact that multituberculates show affinities not with Haramiyida as a whole, but specifically with Euharamiyida.” The LRT tests two purported haramiyids. After testing Arboroharamiya (Fig 3) nests with Carpolestes, between rodents and multituberculates in the LRT. Haramiyavia (Fig 2) is a pre-mammal that nests with Brasilodon and Sinoconodon.
References Averianov A et al (8 co-authors) 2020. Multituberculate mammals from the Middle Jurassic of Western Siberia, Russia, and the origin of Multituberculata. Papers in Palaentology 7(2): DOI:10.1002/spp2.1317
The new basalmost member of the Crocodylomorpha, Lewisuchus(Fig 1), is also the proximal sister to the same basalmost member of the Dinosauria, Herrerasaurus. Phylogenetic miniaturization is still present at and near this node where taxa are small, fast, bipedal and likely transitioned to a warm-blooded metabolism.
There are no pterosaurs in this transition. Pterosaurs nest elsewhere, with small, bipedal, flapping, lepidoaur, tanytropheid fenestrasaurs.
There are no lagerpetids in this transition. Lagerpetonnests elsewhere, with mid-sized, bipedal, running on two toes proterochampsids close to Tropidosuchus.
There are no silesaurids in this transition. Silesaurusnests within Poposauria, derived from Turfanosuchus in a differernt direction.
Archosauria is comprised of just Dinosauria and Crocodylomorpha. That’s all.
Ornithodira and Avemetatarsalia are junior synonym for Reptilia in the LRT because they each include dinos and pteros. Thesee appear on opposite sides of the first reptilian dichotomy in the Viséan (Early Carboniferous) documented here a decade ago and called ‘The Big Kahuna.‘ To replicate this tree topology workers are going to have to add taxa back to the late Devonian taxon, Tulerpeton.
Why did ‘Avemetatarsalia’ subsume the earlier ‘Ornithodira’? Because professor MJ Benton 1999 came up with ‘Avemetatarsalia’ in his Scleromochlus paper AND he writes university level vertebrate paleontology textbooks. Professors have to teach what’s in the textbook, even if it’s been invalid since Peters 2000. (That’s how paleontology works.)
The definition of Avemetatarsalia is “all archosaurs more closely related to birds than to crocodilians.” Benton thought tiny Scleromochlus was close to dinosaurs and pterosaurs. Ironically Scleromochlus is a basal bipedal crocodylomorph in the LRT (subset Fig 2). Taxon exclusion is the problem here. Workers have been unwilling to test taxa that have been in the literature for pterosaur origins for the last 22 years (e.g. Peters 2000). That’s why the LRT is here: to test taxa that have never been tested together and to present results without academic filters and interference.
Still waiting for one more PhD to run an analysis with a similar taxon list and their own character list to confirm, refute or correct the LRT or a subset of it. Other workers did this a few years ago with Chilesaurus and Diandongosuchus by ?convergence. The lack of curiosity and the unwillingness to test more pertinent taxa in the academic community is still puzzling. As this blogpost documents, cladograms are not set in stone, even if printed in expensive and venerated textbooks. New data from old taxa and new taxa can modify tree topologies. That’s a good thing, always.
References Benton MJ 1999.Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. pdf Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
At its best, science advances step by step. Today’s post is just one of those steps.
References Clark JM, Xu X, Forster CA and Wang Y 2004. A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodilian skull. Nature 430:1021-1024. Ruebenstahl AA et al. 2022. Anatomy and relationships of the early diverging Crocodylomorphs Junggarsuchus sloani and Dibothrosuchus elaphros. The Anatomical Record DOI: 10.1002/ar.24949
Longrich, Martill and Andres 2018 described several North African pteranodontid pterosaurs, some of which we looked at earlier here.
Tethydraco regalis is the last of these North African pterosaurs, known from a few long bones in at least two sizes (Fig 1). The proportions indicate a volant pterosaur, with a relatively shorter tibia than the UALVP specimen. There’s not a lot more that can be said given the few bones described.
References Longrich NR, Martil DM and Andres B 2018. Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary. PLoS Biol 16(3): e2001663. https://doi.org/10.1371/journal.pbio.2001663
Jung et al 2022 describe “a new pterosaur footprint assemblage from the Hwasun Seoyuri tracksite in the Upper Cretaceous Jangdong Formation of the Neungju Basin in Korea. The assemblage consists of many randomly oriented prints in remarkably high densities but represents a single ichnotaxon, Pteraichnus.” See figure 1.
Jung et al 2022 continue: “Individuals exhibit a large but continuous size range, some of which, with a wingspan estimated at 0.5 m, are among the smallest pterosaurs yet reported from the Upper Cretaceous, adding to other recent finds which contradict the idea that large and giant forms entirely dominated this interval.”
“Unusual features of the tracks, including relatively long, slender pedal digit impressions, do not match the pes of any known Cretaceous pterosaur, suggesting that the trackmakers are as yet unknown from the body fossil record.
This is incorrect. When the tracks were traced, PILs (Peters 2000a) added and traits run through analysis in the large pterosaur tree (LPT, 262 taxa) ichnite ‘e‘ (Fig 1) matched the pes of the embryo Pterodaustro (Fig 1) without decreasing resolution (= increasing MPTs).
Jung et al did not correctly trace the specimens. They did not add PILs. They did not run pedal scores through a phylogenetic analysis that included the embryo Pterodaustro. They did not include ‘The Catalog of Pterosaur Pedes for Trackmaker Identification‘ (Peters 2011) in their citation list. Rather they (and co-author David Unwin) followed Chris Bennett’s curse, “You will not be published and and if you are published you will not be cited.”
“The Hwasun pterosaur footprints appear to record gregarious behavior at the exact location by individuals of different ages, hinting at the possibility that pterosaurs gathered in mixed-age groups.”
Ichnos published ‘The Catalog of Pterosaur Pedes’ and the ‘Description of Interphalangeal Lines’ (= PILs) for a reason: to help workers identify pterosaur tracks. If you’re wondering why academic workers don’t use and cite these and other pertinent pterosaur papers click this link to the Timeline of Pterosaur Origin Studies.
Benton and Wu 2022 considered several factors affecting the return of life following the Permian – Triassic extinction event, (Fig 2) universally considered the worst extinction event of all time. Pertinent abbreviations include:
MMR – Mesozoic Marine Revolution, (= the increase in shell-crushing and boring predation starting in the Early Triassic.
One factor Benton and Wu omitted was the near complete absence of Permian marine vertebrates in the fossil record (Figs 1, 2). That’s 47 million years of virtually absent taxa.
According to Benton and Wu 2022, “Marine predatory vertebrates show spectacular and rapid diversifications in the Early and Middle Triassic, and new discoveries from China have confirmed their early start in the Triassic, but not in the Late Permian.”
Or was this a geological illusion? There was a new dawn for animals following the PTME. We know which clades survived. Where did the survivors find refuge? Unfortunately, this topic is rarely to never covered, perhaps because those rare refugia have never been discovered or described. Extinction events garner headlines and take the spotlight.
From another point of view that ‘spectacular and rapid diversification‘ in the Triassic was at least partly due to the current paucity of marine fossils in the Permian (Figs 1, 2) and a relative trove of marine fossils in the Early Triassic. Blank spaces (Fig 2) can still provide data based on phylogenetic bracketing with a large gamut cladogram, like the large reptile tree (LRT, 2119 taxa, subset Fig 3).
As an example: here (Fig 3) the currently unknown pre-Triassic ancestors of ichthyosaurs and thalattosaurs would have to have been coeval with known and related Early Permian mesosaurs. Unfortunately all we have are two Middle Triassic late-surviving basal pachypleurosaurs and pre-pachpleurosaurs, Honghesaurus and Anarosaurus. That’s too few. Way too few for 47 million years. Where are all the Early to Late Permian marine fossils?
One answer: The late-surviving representatives of missing Permian taxa are present in the Early and Middle Triassic according to the LRT. That’s a clue that primitive relatives of Early Triassic taxa were present in the Permian.
There are no large phylogenetic gaps in the LRT. It documents a continuous gradation phyogenetically, but not chronologically due to the patchy fossil record in general. That also means Benton’s and Wu’s “spectacular and rapid diversificaiton” might actually represent a chronological illusion. In other words, with phylogenetic bracketing the wealth of Early Triassic ichthyosaurs and pre-ichthyosaurs likely arose sometime during the Early Permian. So far we’ve only found late survivors in the geologically richer Early and Middle Triassic strata. If so marine predators, including ichthyosaurs, had a slower, steadier, more typical radiation and evolution.
We haven’t found many Permian marine vertebrate fossils yet. Perhaps they weren’t fossilized. Perhaps those strata are not present. Perhaps those strata await discovery buried under other sediments. At times like this it’s smart to remember, in general fossils from all eras are extremely rare and often restricted to tiny pin points on the Earth’s surface skipping large swathes of geological time. That’s just the way it is.
Overlooked by Wikipedia, Benton and Wu and saved ’til now, there are several Permian marine and semi-marine younginiforms known from the late Permian. These include Claudiosaurus. Adelosaurus (Fig 4) and related late survivors of a Carboniferous radiation. They likewise had larger, more derived Triassic ancestors, like Atopodentatus (Fig 4).
Benton and Wu 2022 cited Sanders et al. 2021 who reported on a giant ichthyosaur, Cymbospondylus youngorum (Fig 5). The authors reported, “The animal existed at most 8 million years after the emergence of the first ichthyosaurs, suggesting a much more rapid size expansion that may have been fueled by processes after the Permian mass extinction.” Benton and Wu considered this “a prime example of an ‘early burst’ radiation.“
That’s only 3 million years past the Early Triassic or 35 milllion years past the Early Permian, when pre-ichthyosaurs had their roots. How fast ichthyosaurs evolved is left up to the vagaries of the poor Permian marine fossil record vs the rich Triassic marine fossil record known to geology at present.
On land, Benton and Wu remind us, “the Triassic was marked by a posture shift from sprawling to erect, and a shift in physiology to warm-bloodedness, with insulating skin coverings of hair and feathers.”
The authors consider the origin of hair in Permian synapsids as “an insulating pelage”. Before hair can act as insulation it must be thick enough covering a broad enough area. So the genesis of sparse and individual hairs (Fig 6) must have had some other use that enhanced survival. Perhaps the burrowing naked mole rat, Heterocephalus, can give us some insight into the origin of individual hairs first appearing in burrowing cynodonts, retained in mole rats by either a deep time reversal or neotony from ‘hairless’ newborns, or both as ontogeny recapitulates phylogeny. Yes, this is what some cynodont skin looked like.
Benton and Wu report, “Pterosaurs, the sister group of dinosaurs, also have dermal insulating structures commonly called pycnofibres.”
Benton and Wu continue, “even if researchers balk at calling pycnofibres feathers, it does not change the fact that insulating dermal structures appeared in the first dinosaurs and the first pterosaurs, and the shared ancestry of these two clades is dated to the Early or early Middle Triassic.”
Fact? Insulating dermal structures appeared in the first dinos and pteros? Yes, for pterosaur ancestors like Cosesaurus in the Middle Triassic. No, for dinosaurs like Herrerasaurus, also in the Middle Triassic. Benton has a long history of omitting taxa related to pterosaurs recovered by Peters 2000a, b. Paleo academics at large (any exceptions?) continue to do the same.
References Benton MJ and Wu F 2022. Triassic Revolution, Frontiers in Earth Science (2022). DOI: 10.3389/feart.2022.899541 Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41. Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336. Sanders et al. (6 co-authors) 2021. Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans. Science374 (6575): DOI: 10.1126/science.abf5787
A while back, paleontologist Greg Paul let me know about his new Princeton Field Guide in prep, this one about pterosaurs (Fig 1). Paul is widely acknowledged as the early leader in creating reconstructions of dinosaurs and other animals by strictly adhering to their skeletal traits and proportions.
Paul’s newst Field Guide was published June 7, 2022 with little fanfare. I only heard about it yesterday via an off-hand blogpost comment that did not mention the book or author by name. Knowing what was in the pipeline, a keyword search was enough to find the book online. Barnes and Noble, Amazon, even Target all advertise it.
From the publisher’s description: “Once seen by some as evolutionary dead-enders, pterosaurs were vigorous winged reptiles capable of thriving in an array of habitats and climates, including polar winters. The Princeton Field Guide to Pterosaurs transforms our understanding of these great Mesozoic archosaurs of the air. This incredible guide covers 115 pterosaur species and features stunning illustrations of pterosaurs ranging in size from swallows to small sailplanes, some with enormous, bizarre head crests and elongated beaks. It discusses the history of pterosaurs through 160 million years of the Mesozoic—including their anatomy, physiology, locomotion, reproduction, growth, and extinction—and even gives a taste of what it might be like to travel back to the Mesozoic. This one-of-a-kind guide also challenges the common image of big pterosaurs as ultralights that only soared, showing how these spectacular creatures could be powerful flappers as heavy as bears.”
This field guide features 115 different kinds of pterosaurs as skeletal drawings and full-color life studies. It covers pterosaur biology and the colorful history of pterosaur paleontology. Surprisingly I am listed in the ‘Acknowledgments’ section.
Let’s look inside the first few pages… The Preface Paul is an engaging writer who draws the reader in with his literary conceit as a ‘mysterious time traveler’ both ‘startled’ and ‘delighted’. Paul described the ‘surreal’ variety in head crests.
Unfortunately Paul errs and promotes myth 1. when he describes Quetzalcoatlus (Fig 2) as, ‘the largest flying creature possible.’ 2. when he calls pterosaurs distant archosaur relatives of birds. 3. when he reports, “Remaining frustratingly unresolved are the origins of pterosaurs.”
History of discovery and research section Paul’s account is accurate and reminds one of how few and far between pterosaur papers appeared prior to the 1970s. This is when Paul estimated mass for Quetzalcoatlus (Fig 2). He reports, “My calculation that the biggest pterosaurs must have weighed much more than the biggest living ground birds (Paul 1991, 2002) was initially controversial, but it has since become widely accepted.”
If I’m not mistaken, this was Paul’s last contribution to pterosaur research. He has not participated in any phylogenetic studies, nor is he a co-author on any discoveries. Let me know if this is an error and I will correct it.
History of discovery and research section continued. “And the old classic Pteranodon underwent a notable revision with the realization that it had a major overbite, with the lower beak markedly shorter than the upper.”
The is true, but only for some Pteranodon species (Fig 3), not all. Paul should have known this before writing his book.
Paul continues his history of discovery and research. “What has not yet shown up is fossils of protopterosaurs because suitable fine-grained lake or lagoon bottom deposits… are not known”
This is incorrect. We have pterosaur ancestors back to Cambrian worms in the large reptile tree (LRT, 2119 taxa). Proximal Middle Triassic ancestors include Cosesaurus(Fig 4, Peters 2000). Relatives of the fenestrasaur radiation include Sharovipteryx and Longisquama(Fig 4). Each of these are found in such fine-grained sediments that jellyfish, insects and soft tissue are preserved or molded. Paul should have known this before writing his book.
Unfortunately Paul has never constructed a phylogenetic analysis. Like Paul, I was once a paleo artist, but I learned that a phylogenetic analysis answers so many questions and resolves every enigma with authority. No more wondering.
Paul continues his history of discovery and research. “The evolution of human understanding of pterosaurs has not undergone as dramatic a transformation as has our view of dinosaurs over the last quarter millennium.”
This is incorrect as figure 4 shows. Paul should have known this before writing his book.
Paul 2022 – What is a pterosaur? Paul relies on ‘the great majority of researchers’ who also throw up their hands in frustration, not willing to examine the taxa in figure 3. This is a surprising action given Paul’s earlier fame at breaking with consensus based on his own research. Instead here Paul relies on the literature. He writes, “There has been considerable speculation as to which archosaurs the pterosaurs are most closely related to.”
This is the problem. Pterosaurs are not and have never been archosaurs. So let’s stop looking there and look elsewhere (Fig 4). Like Witton before him, Paul should have known what pterosaurs were before writing his book. Presently Paul is 22 years behind the times (Peters 2000) and promoting invalid myths.
“Pterosaurs had a simple dinosaur-type ankle.”
Never, ever rely on a single character to define a clade. That’s called ‘Pulling a Larry Martin.” Pterosaurs developed this ankle-type by convergence. The old ankle fetish among paleontologists goes back several decades and is now rarely brought up. Why focus on the ankle when pterosaurs have a giant finger four? Where else do we find finger four larger than three or five? Not in archosaurs. See figure 3 where each taxon in turn share a longer suite of traits with pterosaurs including a longer finger four.
Paul describes the extreme elongation of ‘an outer finger’, apparently unable to determine if it is the fourth following the three free fingers, all bearing the typical reptile/lepidosaur number of phalanges. Paul reports, “The chest features a large sternal plate…lacking the deep bony keel. There is no wishbone furcular“. (= conjoined clavicles).
The pterosaur sternal complex is actually composed of co-ossified clavicles, a single sternum overlapping an interclavicle (Fig 5). We’ve known that since Wild 1993. Archosaurs don’t have interclavicles. Lepidosaurs do. Paul fails to mention the strap-like scapula and locked-down stem-like coracoid that indicates bipedality and flapping, as in birds. Paul should have known this before writing his book.
Paul mentions the prepubis, but fails to note its significance or distribution (Fig 4). He also notes the long slender ilium, but fails to note its significance or distribution (Fig 4). Paul reports, “the foot was plantigrade.” Sometimes that was so. Other times, no (Peters 2011). Paul reports, “pterosaur eggs were soft-shelled”, but he fails to note that significance. Lepidosaurs have similar soft shells and the mother keeps them within her body longer, sometimes until just prior to hatching. Paul should have known this before writing his book.
Moving into phylogeny again, Paul writes, “There does not seem to be a great division within the Pterosauria in which two or more distinct groups split apart soon after the initial appearance of the group.”
This is wrong. According to the large pterosaur tree (LPT, 262 taxa) that phylogenetic split occurred in the Late Triassic when Preondactylus (Fig 7) became the last common ancestor of the fragile-skulled, dimorphodontid-anurognathid clade of insect-eaters. On the other branch, Eudimorphodon (Fig 7) was the last common ancestor of all other pterosaurs, the robust-skulled fish-eaters. A phylogenetic analysis would have been helpful here, rather than relying on a vague notion from the extremely flawed (due to taxon exclusion) literature. That way Paul would have been able to tell his readers that the pterodactyloid grade appeared five times by convergence (4x according to Peters 2007. A 5th was recently added). Here again, Paul should have known this before writing his book.
Paul mistakenly writes, “No known pterosaur was flightless.”
Gee, I wish Greg had touched base while writing his book just once so I could have suggested new directions and help him avoid omissions. Then I could have earned that Acknowledgements mention. As is, this book comes as a disappointing rehash of old and discredited pterosaur myths. Missing here is the spirit and drive of the brilliant, young Greg Paul, the one we leaned from so many decades ago, the one who saw things precisely, sometimes differently than “the great majority of researchers” he now leans on.
References Paul GS 2022. The Princeton Field Guide to Pterosaurs. Princeton Field Guides. Online. Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41. Peters D 2000b. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336. Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301. Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27. Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330. Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification Ichnos 18(2):114-141.http://dx.doi.org/10.1080/10420940.2011.573605 Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.
Gai et al. 2022 discuss their views on the origin of the vertebrate spiracular region in Shuyu (Gai et al 2011, Middle Silurian; Fig 1), atiny galeaspid lacking a spiracle (Fig 2) in a clade lacking spiracles (Fig 3).
Galeaspids were the only vertebrates to migrate their primitive immobile oral cavity to the dorsal skull (Figs 1, 3). Ecollogically galeaspids appear to have been flattened, sit-and-wait filter feeders, hiding while buried in sandy sediments with only their dorsal surface and oral cavity exposed.
Note: There is no galeaspid named Galeaspis. That’s a trilobite.
Also note: Paleo fish workers don’t yet understand there were two origins for jaws in vertebrates. Galeaspids were not in the gnathostome lineage. Rather their proximal outgroup taxon, Drepanaspis (Fig 3), was also basal to placoderms. Note the gradual migration of the terminal oral cavity to the dorsal surface. Primitive galeaspids retain a transverse oral cavity and lateral eyes. Derived galeaspids developed skull processes, migrated the eyes dorsally and the oral cavity evolved to become circular, then slit-shaped at right angles to the original orientation. Very strange.
Also note: Despite their bony and immobile head plates, galeapids were not related to osteostracans, like the pre-sturgeon, Hemicyclaspis (Fig 4 frame 4). Lampreys, osteostracans and sturgeons all retained a ventral oral opening.
Gai et all 2011 dismiss the hypothesis that osteostracans were the closest jawless relative of the gnathostomes because, “their massive, mineralized braincase has a median nasohypophyseal organ resembling the condition in lampreys.”
By contrast, descendants of lampreys (Pteromyzon) in the large reptile tree (LRT, 2119 taxa, subset Fig 6) split into two clades: 1) hard-headed arandaspids, galeaspids and placoderms; and 2) soft-headed Jamoytius, Birkeria, Haikouichthys, hard-headed Hemicyclaspis, semi-hard-headed Thelodus, hard-headed sturgeons and gnathostomes. Both clades evolved their own jaw. Past efforts at describing or discovering the evolution of jaws have failed due to not recognizing the dual and convergent genesis of jaws that comes from adding taxa.
The spiracle is a small opening in the temple region of rays (Fig 2), sawfish and other flattened, bottom-dwelling, cartilaginous fish. With the ventral mouth buried in silty sediment the spiracle serves as an alternate water intake for respiration. It is also the ear hole in tetrapods. Traditionally the spiracle is homologous with the first gill opening in lamprey-grade and higher chordates (Fig 1). The spiracle is lost in hammerhead sharks and many bony fish (Fig 4). Galeaspids and kin (Figs 1, 4) do not have a spiracle. Their first gill chamber (Fig 1) is not different from the other gill chambers.
From the Gai et al 2022 abstract “The spiracular region, comprising the hyomandibular pouch together with the mandibular and hyoid arches, has a complex evolutionary history”.
Perhaps more complex than Gai et al realize due to their not recognizing the dual origin of jaws (placoderms and gnathostomes by convergence) in vertebrates (Fig 1). Adding taxa resolves this issue.
From the abstract “Here we present the first confirmed example of a complete spiracular gill in any vertebrate, in the galeaspid (jawless stem gnathostome) Shuyu. Comparisons with two other groups of jawless stem gnathostomes, osteostracans and heterostracans, indicate that they also probably possessed full-sized spiracular gills and that this condition may thus be primitive for the gnathostome stem group”.
No. Gnathostomes (= Chondrosteus (Fig 4) and descendants) developed jaws apart from placoderms. Shuyu is not a stem gnathostome. Sturgeons are pre-gnathostomes.
“This contrasts with the living jawless cyclostomes, in which the mandibular and hyoid arches are strongly modified and the hyomandibular pouch is lost in the adult”.
Living lampreys are 500 million years away from that last common ancestor that ultimately split into the placoderm and gnathostome clades. So living lampreys can be highly modified from their Cambrian ancestors.
“On the basis of these findings we present an overview of spiracular evolution among vertebrates.” [See figure 4 frame 1.]
Gai et al. almost have a valid phylogenetic topology (Fig 4). It is missing just a few elements. Do not proceed on your own studies without a valid cladogram. Otherwise all your subsequent hypotheses are prone to crack and possibly crumble.
Gai et al. 2022 report, “Our new evidence indicates that the so-called interbranchial ridges of galeaspids are actually the dorsal portion of branchial arches. They are incorporated into the neurocranium to form a massive skull as assumed in osteostracans by Stensiö.
By contrast, in the LRT (subset Fig 6) these two bone-headed fish clades (galeaspids and osteostracans) are not related. This is yet another example of convergence not recognized by the authors. Don’t make the same mistake. Create your own LRT so you, too, will have a panoramic view of all vertebrates. Don’t focus too much on one clade or another. You’ll miss something by convergence on the outskirts and the LRT will catch it.
“Compared to osteostracans, the entire branchial apparatus in Shuyu retains a general vertebrate condition, thus, it is easy to identify the mandibular and hyoid arches according to their topological position and nerve innervation.”
Shuyu nests close to the base of the Vertebrata in the LRT. So it should retain a general condition.
Gai et al. 2022 introduced a well-known acanthodian in their cladogram (Fig 4), Cheiracanthus (Egerton 1861, Middle Devonian, Fig 5), not previously tested in the LRT. Here Cheiracanthus is traced, scored and nested with Homalacnathus at the base of the acanthodians, which is at the base of the clade the ultimately produced lobe-fin fish and tetrapods. So it’s a human ancestor, but not a tuna ancestor.
This appears to be a novel hypothesis of interrelationships. If not, please provide a citation so I can promote it here.
PS What drives the stream of water carrying food and oxygen in a galeaspid? The mouth doesn’t move and it is not pointed anteriorly. The gills don’t move within the solid skull. The soft tissue atrium must be able to shrink and expand like a bellows within the solid skull. The galeaspid skull is open ventrally to permit the expansion of this gular sac (Fig 7, 8). It does not include an open mouth and gill slits, as in unrelated, but often convergent osteostracans.
Added the morning after publication: Rhegmaspis (Figs. 7, 8) is a streamlined galeaspid. Nochelaspis and Platylomaspis (Fig 8) are large galeaspids often reconstructed with ventral oral and gill openings, like osteostracans. I don’t see those traits here (Fig 8). Rather the ventral portion appears to have been soft tissue, a gular sac that expanded and contracted to drive inhalation and exhalation along with water borne tiny food particles. In other words these are the only fish with a mouth on top of the skull. Nares are not present, but a pineal opening often is present. All this points to a lifestyle not of predation, but of sit-and-wait filtration.
References Egerton P de MG 1861. British fossils, pp 51-75 in Huxley TH (ed), Preliminary Essay Upon the Systematic Arrangement of the Fishes of the Devonian Epoch, Figures and Descriptions Illustrative of British Organic Remains. Memoirs of the Geological Survey, U.K, (Decade 10). Gai Z et al 2011. Fossil jawless fish from China foreshadows early jawed vertebrate anatomy. Nature 476:324–327. Gai Z. Zi M. Ahlberg PE and Donoghue PCJ 2022. The Evolution of the Spiracular Region From Jawless Fishes to Tetrapods. Font. Ecol. Evol., 19 May 2022 | https://doi.org/10.3389/fevo.2022.887172
Harris et al 2000 described and named a “leaf-toothed crocodile,” Phyllodontosuchus lufengensis (Sinermurian, Early Jurassic China, 200mya, BVP568-L12, Fig 1), based on the middle and posterior teeth. The anterior teeth remained recurved and sharp. The tiny skull is 7cm (less than 3 inches) long. The authors considered this taxon a sphenosuchian crocodylomorph without conducting an analysis.
After analysis in the LRT (subset Fig 3), Phyllodontosuchus nests elsewhere, apart from Sphenosuchus and kin.
Harris et al reported, “Unfortunately, much of the detail in the only known skull of Phyllodontosuchus is not discernable due o nuances of preservation, including similarity of the bone to the surrounding matrix. Nevertheless, enough detail is preserved to permit diagnosis.”
Harris et al thought the premaxilla was not preserved.
Colors helped to identify the premaxilla here (yellow Fig 1). The naris is terminal and breaks the jawline, as in equally tiny Coloradisuchus (Fig 2). That can be confusing.
Harris et al thought “no sutures are discernable in any fragment”.
Maybe they should have colored the bones between the sutures using DGS (Fig 1).
Harris et al thought “Crushing has apparently filled in the supratemporal fenestrae, and their outlines are likewise indeterminate.”
Digital graphic segregation (Fig 1) was able to discern these structures.
The authors focused their attention on the teeth, comparing them to herbivorous dinosaurs and other archosauriforms. Harris et al more or less correctly concluded the specimen “shows more similarities with the basal Crocodylomorpha (Sphenosuchia) than any other.”
After reconstruction and analysis in the large reptile tree (LRT, 2118 taxa) Early Jurassic Phyllodontosuchus nested with Late Triassic Coloradisuchus (Fig 2), a taxon not described until Martinez, Alcober and Pol 2017. These taxa nest between Gracilisuchus and Scleromochlus + Saltopus + Lagosuchus as basal bipedal members of the Crocodylomorpha. The latter two taxa are known from post-crania only, which don’t resolve with skull-only taxa Phyllodontosuchus and Coloradisuchus. In order for complete resolution in the LRT either the skull-only or the skull-less taxa must be left out.
Unfortunately the tiny, bipedal crocodylomorphs, Gracilisuchus, Scleromochlus, Saltopus and Lagosuchus are not often, if ever, included in other crocodylomorph studies. The LRT, which tests taxa together that have never been tested together, indicates that traditional omission needs to change. Simply add these taxa (and more) to your croc studies to see for yourself how well they fit in. Then let us know what you get.
PS Martinez, Alcober and Pol 2017 mistakenly considered Coloradisuchus“a new protosuchid crocodiliform.” Unfortunately, Phyllodontosuchus, Gracilisuchus, Scleromochlus, Saltoposuchus and Lagosuchus were not mentioned in the text. Protosuchus nests elsewhere in the LRT.
References Harris JD et al 2000. A new and unusual sphenosuchian (Archosauria: Crocodylomorpha) from the Lower Jurassic Lufeng Formation, People’s Republic of China. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 215(1): 47–68. Martinez RN, Alcober OA and Pol D 2017. A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1491047.