Three related taxa from the Middle Triassic, Sinosaurosphargis (Fig. 1, Li, Rieppel, Wu, Zhao and Wang 2011), Atopodentatus (Fig. 2, Cheng et al. 2014, Chun et al. 2016) and Largocephalosaurus (Fig. 3, Cheng et al. 2012, Li et al. 2013) appear to have five nares in the rostrum. Only the middle pair are the real nares, homologous with those of other tetrapods. Apparently some of these were overlooked by prior workers. So were some of the sutures.
Figure 1. Sinosaurophargis skull from Li et al. 2011. Colors added here. Five nares in black. Note the overlooked upper temporal fenestrae and postorbitals. Here a crack was identified as a naris. The lacrimal was originally missing. Here it forms the largest portion of the rostrum.
Figure 2. Atopodentatus skuill from Chun et al. 2016. Colors added here. Five nares blink in dark gray. The lacrimal (tan) contacts the naris.
Figure 3. Largocephalosaurus skull from Li et al. 2013. Colors added here. Five nares blink in dark gray. Here the external naris (en) was overlooked and similar cracks were misidentified as nares.
The current review of the MacClade file that built the large reptile tree (LRT, 2049 taxa) prompted reexamination of these three specimens. Turns out the diagrams provided by the authors did not have all the correct data when it came to identifying certain traits and errant scores resulted. If your cladogram is experiencing loss of resolution at certain nodes, go back and review the data. These three examples demonstrate published data sometimes require a review.
References Cheng L, Chen X-H, Zeng X-W and Ca Y-J 2012. A new eosauropterygian (Diapsida: Sauropterygia) from the Middle Triassic of Luoping, Yunnan Province. Journal of Earth Science 23 (1): 33-40. Cheng L, Chen XH,Shang QH and Wu XC 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaften. doi:10.1007/s00114-014-1148-4. Chun L, Rieppel O, Cheng L and Fraser NC 2016. The earliest herbivorous marine reptile and its remarkable jaw apparatus. Science Advances 06 May 2016: 2(5), e1501659 DOI: 10.1126/sciadv.1501659 Li C, Rieppel O, Wu X-C, Zhao L-J and Wang LT 2011. A new Triassic marine reptile from southwestern China. Journal of Vertebrate Paleontology 31 (2): 303-312. doi:10.1080/02724634.2011.550368. Li C, Jiang D-Y, Cheng L, Wu X-C and Rieppel O 2013. A new species of Largocephalosaurus (Diapsida:Saurosphargidae), with implications for the morphological diversity and phylogeny of the group.
Housekeeping in the LRT, plus a dash of DGS (Figs. 1, 2), shed new light on the skulls of two aquatic younginiforms, Claudiosaurus (Fig 1), and Atopodentatus (Fig. 2). These two now nest a little more closely to one another.
Figure 1. Claudiosaurus skeleton based on changes in January 2022. Click to enlarge. The nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.
Figure 2. Atopodentatus skull in situ. Colors added here. The nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.
While reviewing scores in the large reptile tree (LRT, 2049 taxa) apomorphies in the MacClade files have brought attention to hundreds of errors and just as many true apomorphies.
Claudiosaurus was added to the LRT more than ten years ago and several years before colors were applied to bones.
Atopodentatus was added more recently, before DGS colors became standardized. Several errors were noticed today as this taxon was compared to Claudiosaurus. This is only one example of hundreds reviewed recently.
Turns out in both taxa the nasals are narrow and parallel. The maxilla is much deeper. The quadratojugal is absent.
Every low-resolution node in the LRT had been under review over the past ten days or so. Corrections are a continuing process. This has been very rewarding with minor discoveries popping up several times a day.
As a result, the fish subset of the LRT is now fully resolved. So is the theropod-bird subset. The much larger mid-subset of the LRT has about 1300 taxa. Corrections have brought the number of most parsimonious trees down to 50 or so. That means only three or four small clades remain that lack full resolution. The most recent changes to the topology of the LRT involve only slight shifts to closely related taxa. No big shifts.
To obtain that goal, a few far-from-complete taxa have been removed and set aside as ‘red taxa’ in the LRT, in addition to the hundreds of corrections described above.
Thank you for your patience and readership. I learn as I go. There is no time crunch. This is not an expensive endeavor, but it is time-intensive. This online experiment has been ongoing for more than a decade. Lessons from more recent taxa have helped to shed light on earlier errors — once I reexamine them. Housekeeping provides that opportunity.
Thankfully this online experiment was never committed to print. Changes are inevitable. A great number have already been reported, each one with a time stamp. This could not have been done without a few centuries of workers finding and describing taxa. IMHO this experiment could not have been done earlier without today’s computer software, PDFs and lots of time without other responsibilities.
This funny meme popped up on Facebook recently. FB memes that involve both clade names and the large reptile tree (LRT) are so rare and esoteric that this may be the first and only time such a combination will ever appear. Unfortunately, the target audience for this meme didn’t get the joke until it was explained online (see below).
Figure 1. From the FB account of professor of geology and paleontology Donald Prothero. Image sent to him from fellow paleontologist, Daniel Chure, retired, Dinosaur National Monument.
The setup for this esoteric joke sent by retired paleontologist, Daniel Chure, had its genesis in Prothero et al. 2021, who wrote, “The name “Cetartiodactyla” was proposed in 1997 to reflect the molecular data that suggested that Cetacea is closely related to Artiodactyla. Since then, that taxon has spread in popularity, even outside the scientific literature. However, the implications of the name are confusing, because Cetacea and Artiodactyla are not sister-taxa.Instead, the evidence clearly shows that cetaceans are a group embedded within Artiodactyla, not a sister-taxon of equal rank.”
Adding a punchline of even more esoteric humor, when more taxa are added the traditional clade Cetacea ceases to be monophyletic and was never embedded within Artiodactyla. Ba-dum…chhhh.
References Prothero et al. (15 co-authors) 2021. On the Unnecessary and Misleading Taxon “Cetartiodactyla”. Journal of Mammalian Evolution. https://doi.org/10.1007/s10914-021-09572-7
This is where precision and comparative anatomy shed light on the disappearance of the naris in the long rostrum pterosaur, theCtenochasma specimen described by Jouve 2004. Here (Fig. 1) the image tells the story. Late Triassic Bergamodactylus is the most basal pterosaur in the LPT, but any similar pterosaur with a separate naris and antorbital fenestra (Fig. 2) would have been equally instructive.
Figure 1. Ctenochasma skull from Jouve 2004. Colors added here. The remains of the naris and other small fenestra are indicated by dark gray.
Remember, the ctenochasma clade and their enlarged teeth arise from a series of Dorygnathus taxa (Fig. 2) omitted from other analyses. Likewise, the azhdarchid clade and their long rostrum kin arise in the large pterosaur tree (LPT, 262 taxa) from a different series ofDorygnathus taxa (Fig. 2), likewise omitted from other analyses.
Figure 2. Evolution of the naris in pterosaurs from 2011. Click to enlarge.
We first looked at the evolution of the naris in pterosaurs about a decade ago (Fig. 2) here. Over that span of time no one else, and no one with a PhD, has included these pertinent taxa in their analyses. Nor have they included Cosesaurus and kin as outgroup taxa. The taxa are out there. Use them.
This is the state of the art in paleontology: taxon omission and suppression. Willful blindness. No one else wants to test the less popular taxa. That’s what the LRT and LPT do, test as many taxa as possible and more every week. That’s why these two cladograms recover novel hypotheses of interrelationships readily accessible to anyone on the planet who wants to understand the details of this science with more precision.
We, as paleontologists, need to test every relatively complete taxon. then add the less complete taxa. Mistakes, omissions and enigmas have lingered far too long. The answers to those long-standing problems are readily accessed by simply adding taxa (Fig. 2)… and sometimes taking a closer, more precise examination of other taxa (Fig. 1). It will help to color bones like a map of states or countries. Cartographers figured this out decades ago. Let’s catch up to them.
If I’ve missed any taxa that need to be tested, please send a few at a time.
References Jouve S 2004. Description of the skull of a Ctenochasma (Pterosauria) from the latest Jurassic of eastern France, with a taxonomic revision of European Tithonian Pterodactyloidea. Journal of Vertebrate Paleontology, 24(3):542-554.
Chiappe and Dyke 2006 reported, “A burst of discoveries of Cretaceous birds over the last two decades has revealed a hitherto unexpected diversity; since the early 1990s, the number of new species described has more than tripled those known for much of the last two centuries. This rapid increase in discoveries has not only filled much of the anatomical and temporal gaps that existed previously, but has also made the study of early birds one of the most dynamic fields of vertebrate paleontology.”
Historically, Chiappe and Dyke reported, “The work of Walker and Ostrom provided new impetus for the re-examination of the origin of birds, with the emergence of the crocodylomorph and theropod hypotheses as a possible alternative to the archosauromorph ideas that had prevailed for much of the 20th Century.”
I remember those days, as many of you do, too. These were the coolest and most confusing hypotheses circulating during the pre-software, pre-China days of the 1990s. That’s when even Larry Martin was “Pulling a Larry Martin” by focusing on only the braincase, only the ankle, etc. instead of comparing every trait in toto with a wide gamut of taxa using software like MacClade and PAUP. A few days ago we looked at mistaken efforts to make the early archosauriform, Euparkeria, a bird ancestor candidate. That was very typical of that era.
Historically, Chiappe and Dyke reported, “For almost a century, knowledge of the Mesozoic avifauna was greatly limited to just the Late Jurassic Archaeopteryx and a series of fossils from the Late Cretaceous Pierre Seaway of North America,” (= Hesperornis and Ichthyornis).
Those three bird taxa should have been enough, but note even in 2006 these two PhDs mentioned only one of the ten Solnhohfen birds. So their lament about the paucity of fossil bird fossils in 2006 was exaggerated and self-inflicted.
Chiappe and Dyke reported, “some of these have been used to erect new species, albeit not very convincingly.”
Not convincingly? Take your opinion out of the equation. Let the software tell you how taxa are related to one another. Add the taxa. Score the traits. Run the analysis. Report the results. In Chiappe and Dyke’s only cladogram a paltry 18 taxa were tested. Archaeopteryx is a single taxon. Sadly, so is the taxon: ‘modern birds’.
Figure 2. Rahonavis nests with Jianchangosaurus in the LRT.
Chiappe and Dyke briefly discussed the Late Cretaceous Madagascar ‘bird’ Rahonavis (Fig. 1), noting how primitive it was, especially for such a late taxon. They did not realize in 2006 that Rahonavis was not a bird, and not even related to birds. Today it nests as a small therizinosaur close to Early Cretaceous Jianchangosaurus(Fig. 1, Pu et al. 2013) in the large reptile tree (LRT, 2050+ taxa). Not sure where it would have nested in 2006, but adding taxa might have been helpful. Don’t assume Rahonavis is a bird. Or even a theropod. Run the analysis.
Chiappe and Dyke reported on the traits of Archaeopteryx (but which one of the ten specimens?). The problem with doing this is the tendency to seek and report on ‘important’ or ‘key’ traits when what separate one taxon from another might just be the fusion of two skull bones in one and the lack thereof in the other. Or something even less obvious.
The authors compared Rahonavis to Archaeopteryx, noting the former was more ‘derived’ in certain traits. Apparently the authors were blind to convergence, something the LRT tends to weed out by comparing hundreds of traits over a wide gamut of taxa, not just two. In other words, their methods were not adequate back in 2006. It’s better to compare traits AFTER a valid phylogenetic context has been established by unbiased software. Just deliver the cold hard facts. The authors concluded, “Nonetheless, the precise evolutionary relationships of Rahonavis remain unclear.”
Since the LRT tests all competing taxa, relationships are precise and clear. With every additional taxon, relationships become more and more precise and clear. In this case, Rahonavis was not a bird. So irrelevant taxa were added to their taxon list. Who knows how that screwed things up.
Then Chiappe and Dyke discussed the ‘lacustrine cornucopia’ of feathered fossils then coming out of Early Cretaceous China. They reported, “The exquisite and numerous fossils recovered from these and other Early Cretaceous localities in China include more than a dozen species breaching the enormous evolutionary gap between Archaeopteryx and modern birds.”
Ironically, if Chiappe and Dyke had only tested the ten Solnhofen birds as individual taxa that ‘enormous evolutionary gap’ would have become greatly reduced as demonstrated by the bird subset of the LRT (Fig. 2). In 2020, with many more taxa employed, the number of nodes between the London specimen of Archaeopteryx and crown birds is reduced to six. Not so enormous after all.
Figure 3. Subset of the LRT focusing on basal birds. Blue taxa are all Solnhofen birds (= traditional Archaeopteryx). Sulcavis and the el Montsec bird are highlighted in yellow.
Chiappe and Dyke discuss a turkey-sized bird from the Early Cretaceous, Jeholornis (Fig. 4), which nests in the LRT as a scansoriopterygid descendant of the Munich specimen of ‘Archaeopteryx‘, a relatively primitive Solnhofen bird. The authors discuss the various traits, all of which must be considered in toto, not piecemeal.
Figure 4. Jeholornis prima is longer and larger than J. curvipes.
References Chiappe LM and Dyke GJ 2006. The early evolutiionary history of birds. J. Paleont. Soc. Korea 22(1):133-151
Chrioxiphia caudata (Shaw and Nodder 1793; 15cm) is the blue manakin, native to the Amazon. Many of the skull bones are fused. Phylogenetically (Fig. 2) manakins and their relatives are neotonous descendants of larger, long-legged ancestors like the South American seriema (Cariama) and its sister the flamingo (Phoenicopterus).
Figure 1. Chrioxiphia, the blue manakin of the Amazon, nests with cuckoos worldwide.
Jungle-dwelling Chrioxiphia is related to jungle-dwelling Menura (the lyrebird) from Australia and jungle-dwelling Musophaga from Africa, these showy, colorful birds probably split phylogenetically prior to the Early Cretaceous appearance of the Atlantic Ocean. Few cuculids are long distance flyers. The showy birds in this clade prefer their jungles to crossing oceans.
Figure 2. Subset of the LRT focusing on the Cuculidae (flamingos to cuckoos)
In the LRT giant lightless South American terror birds are more closely related to African secretary birds (Sagittarius). Traditionally Cariama has been cherry-picked for that role, but Cariama is closer to flamingos and lyrebirds (Fig. 2). According to results recovered by the LRT the phylogenetic split of secretary birds from terror birds must have also occurred before the appearance of the Atlantic Ocean. So in the Early Cretaceous of South America we should expect to find secretary bird bones someday. The value of this hypothesis, like any hypothesis, can be measured by its predictive value. Let’s see what happens.
References Shaw GK and Nodder F 1793. The Naturalist’s Miscellany 1789–1813.
From the Wang, Zhou and Sullivan 2016 abstract: “A fish-eating enantiornithine bird with a gastric pellet composed of fish bones has recently been reported from the Lower Cretaceous Jiufotang Formation of Liaoning Province, northeastern China.”
The bird (Fig. 1) is the size of a sparrow and the size of the related bird, Sulcavis. The fish it could eat would have been really tiny, even for a table top aquarium.
“Along with other discoveries, this specimen reveals that distinct features of modern avian digestive system were well established in those early birds. On the basis of a detailed anatomical study presented here, we show that this fish-eating enantiornithine bird represents a new taxon, Piscivorenantiornis inusitatus, gen. et sp. nov. The well-preserved elements of the skull, neck, sternum, and pelvis further enrich our understanding of the morphological diversity in early enantiornithines. Most notably, the cranial articular facet of the caudal cervical vertebra is dorsoventrally concave and mediolaterally convex, a feature otherwise unknown among other birds and with unclear functional significance.”
Figure 1. Piscivorenantiornis inusitatus in situ from Wang, Zhou and Sullivan 2016 and semi-reconstructed here. Scaled to 0.8x life size. This is a sparrow-sized specimen. So the fish it could eat had to be tiny. Note the small manus, the double-hump ilium.
Piscivorenantiornis inusitatus (Wang, Zhou, Sullivan 2016, Early Cretaceous, 18 cm long est) was a sparrow-sized (Sulcavis-sized) fish-eating bird, preserved with a gastric pellet. Only parts of this disarticulated skeleton can be reconstructed. Note the double-hump ilium and relatively short manus vs ulna. These traits nest Piscivorenantiornis between Sulcavis and Sinornis.
References Wang M, Zhou Z and Sullivan C 2016. A fish-eating enantiornithine bird fromthe Early Cretaceous of China provides evidence of modern avian digestive features. Current Biology 26:1170–1176.
In their description of a new Early Cretaceous birds ‘without teeth’, Zhou and Li 2010 traced Zhongjianornis and did a great job on the skeleton overall (Fig. 1).
Figure 1. Zhongjianornis in situ from Zhou and Li 2010.
The Zhongjianornis skull was another matter as the authors made several errors (Fig. 2). They just did not put in the effort to pull out details, but were content to trace broad areas.
Figure 2. Zhongjianornis skull from Zhou and Li 2010, plus their tracing (gray diagram). Colors and reconstruction added here. The reconstruction is the puzzle you put together based on the color tracings. If all the pieces fit, that’s a good sign, but mistakes are still possible.
Here, without looking at the fossil first-hand, and only using DGS methods to trace their published photo, a more accurate identification of skull parts is offered. The skull parts can be moved (as they are without the unconscious bias of freehand) to a reconstruction of the skull that not only fits together like the puzzle it is, but also matches patterns and shapes in closely related taxa, in this case, Confuciusornis (Fig. 4). Only the beak is relatively longer.
Figure 3. Confuciusornis skull traced and reconstructed. Compare to Zhongjianornis in figure 2.
Zhongjianornis yangi (Zhou and Li 2010; Early Cretaceous, IVPP V15900, pigeon-sized, scale bar on skull image is 1cm) nests with Confuciusornis in the LRT, but has a longer beak, shorter hands and smaller sternum. Pedal digit 4 is as long as 3. The present tracing is more precise than the original. Confuciusornithids had only 8 cervicals, one less than most coeval birds.
Zhou and Li reported in their abstract: “The new taxon is characterized by possessing the following combination of features: upper and lower jaws toothless, snout pointed, humerus with large and robust deltopectoral crest, second phalanx of the major manual digit longer than the first phalanx, unguals of the alular and major digits of similar length and significantly shorter than the corresponding penultimate phalanges, tibiotarsus slender and more than twice the length of the tarsometatarsus, and metatarsal IV longer than the other metatarsals.”
Several of these traits are common to Confuciusornis. The short metatarsus relative to the tibia is not found in related taxa. Zhou and Li’s own tracing indicates mt 4 = mt3 and digits 3 and 4 extend subequally measured from the tarsus (Fig. 1).
“Phylogenetic analysis indicates that Zhongjianornis is phylogenetically basal to Confuciusornis and the dominant Mesozoic avian groups, Enantiornithes and Ornithurae, and therefore provides significant new information regarding the diversification of birds in the Early Cretaceous.”
By contrast, in the LRT (Fig. 3) Zhongianornis nests with the GMV-2132 specimen of Confuciusornis and these two nest with MBAv1168 specimen, so Zhongianornis is not basal to the genus, but perhaps congeneric. Confuciusornithids are derived members of a larger clade that nests basal to Enantiornithes and Ornithurae in the LRT, agreeing with Zhou and Li.
“It also represents the most basal bird that completely lacks teeth,”
Not the most basal bird in the LRT where it shares that credit (Fig. 2) See above.
“suggesting that tooth loss was more common than expected in early avian evolution and that the avian beak appeared independently in several avian lineages, most probably as a response to selective pressure for weight reduction.”
This is a common trope, or recurrent theme that might be a myth. Think about it. Which would weigh more: a set of small teeth or a swallowed mouse? If herbivorous, substitute a pile of seeds or a drink of water.
“Finally, the presence of a significantly enlarged humeral deltopectoral crest suggests that Zhongjianornis shares with other basal birds such as Jeholornis, Sapeornis and Confuciusornis a distinctive mode of adaptation for flight contrasting with that seen in more advanced birds, which instead possess an elongated sternum and a prominent keel.”
Note thatJeholornis, Sapeornis and Confuciusornis are members of related clades in the LRT (Fig. 2).
Figure 3. Subset of the LRT focusing on basal birds. Blue taxa are all Solnhofen birds (= traditional Archaeopteryx). Note: Archaeopteryx (Wellnhoferia) grandis) nests at the base of the Confuciusornis clade.
Members of the Confuciusornis clade were not restricted to China. A basal member, Archaeopteryx (= Wellnhoferia) grandis (Fig. 4) is from the Late Jurassic of the Solnhofen Formation. Whenever taxa are added, unexpected interrelationships tend to appear.
Figure 4. Confuciusornithiformes to scale. Note the lack of a pygostyle in the majority of taxa.
Recent housekeeping on the bird and fish subsets of the LRT resulted in several details and scores. Corrections were made. Now each of those subsets is completely resolved. Based on the number of taxa, it still takes a few minutes for the software to crunch the numbers on my old IBook that still runs System 9, but a single tree was recovered. PAUP can only handle a maximum of 1500 taxa, which is the reason for the splitting up of the 2052 taxa into three overlapping MacClade files.
Your cladogram can be your best friend. If it is not fully resolved, those poorly resolved nodes are telling you where some of the mistakes are. The DGS method of coloring digital images of bones mentally simplifies comparative anatomy. It is also helpful to have all the data digitized or online for ready and rapid access on a pair of monitors. Gone are the days of rifling through a file cabinet full of photocopies, thank goodness.
I’m not saying the scoring is perfect now. It never is. I am saying the scoring is much improved at the nodes that needed it.
References Zhou Z and Li FZZ 2010. A new Lower Cretaceous bird from Chna and tooth reduction in early avian evolution. Proceedings of the Royal Society B 277:219–227.
Evidently the Madagascar tenrec issue is still not resolved. Wikipedia reports Setifer. the greater hedgehog tenrec. is not close to hedghogs. The author of that Wiki page considers Setifer a tenrec.
By contrast the large reptile tree (LRT, 2042+ taxa) recovers Setifer with hedgehogs like Echinops, not with Tenrec and Hemicentetes. So, we need to do a little updating in the literature based on traits, not genomics.
The problem goes back to geographic viruses affecting genes in geographic areas (think Afrotheria). Both Setifer and Tenrec live in close contact on Madagascar, apart from European hedgehogs. Their genes were affected by the same viruses. Similarly the dissimilar aye-aye (Daubentonia) and lemur (Lemur), both from Madagascar, share enough genes to fool genomicists. These genes are also due to endemic viruses. Don’t trust genes in deep time studies. Trust skeletons and PAUP.
Figure 1. Setifer, the hedgehog ‘tenrec’ museum mount. Closer to hedgehogs, not close to tenrecs.
Figure 2. Setifer skeleton from Mivart 1871. Colors added here. Look at those lower incisors.
Setifer setosus (von Schreber 1778, Madagascar; 18.5cm) is the extant greater hedgehog tenrec. It nests with hedgehogs in the LRT, not with tenrecs, based on skeletal data. Note the digitigrade digits. The molars are premolarized as in archaeocete whales by convergence. Note the lateral incisors erupting deep on the anterior face of the dentary.
References Mivart St G J 1871. The genesis of species. Macmillan and Co. London and New York. von Schreber JCD 1778. Die Saugethiere in Abbildungen nach Natur mit Beschreibungen. Erlangen. 1774- 1855, 1789. Theil 1-17 suppl, vol 1-5.
After 22 years professor Michael Benton once again returns his attention to the pre-sauropod, Thecodontosaurus antiquus (Fig. 1), one of the first dinosaurs described (Riley and Stutchberry 1836, Morris 1843).
Figure 1. Thecodontosaurus traced from Benton et al. 2000 and filled in here. the tail is unknown.
Benton et al. 2000 described the anatomy (Fig. 1) and systematics (Fig. 2) of Thecodontosaurus.
Ballell, Rayfield and Benton 2022 described the myology (muscle attachment points) of Thecodontosaurus.
Thecodontosaurus was found in Bristol, England, so these University of Bristol researchers (Ballell, Rayfield and Benton 2022) and the original discoverers and describers (Riley and Stutchberry 1836, Morris 1843 did not have to travel far.
Figure 2. Cladograms from Benton et al. 2000 (above) and Ballell, Rayfield and Benton 2022 (below) both featuring Thecodontosaurus. Only a few taxa are tested in both studies. Color added to the top graphic. Bone shapes removed from the bottom graphic.
Benton et al. 2000 wrote: “Although much of the original topotype material found in the 1830s in Bristol, England, has now been lost, some 245 specimens remain A cladistic analysis indicates that Prosauropoda is probably a clade, rather than a series of outgroups to Sauropoda, but support for this conclusion is weak.”
Their 2000 and 2022 cladograms are both shown here (Fig. 2). Some taxa were omitted from the earlier study, according to the 2022 cladogram. Others were added.
Ballell, Rayfield and Benton 2022 wrote: “The skeletal anatomy and arrangement of forelimb muscles indicate that elbow flexors and extensors were well-developed in Thecodontosaurus, and the range of motion at the shoulder would have been limited, suggesting that the forelimbs were not used in habitual locomotion but in manipulation, as in other early sauropodomorphs.”
The general proportions of Thecodontosaurus present a bipedal configuration. Moreover, quadrupedal dinosaurs are rare in the Late Triassic (Fig. 4).
Figure 3. Subset of the LRT focusing on phytodinosauria. Here Ornithischia is a clade within Sauropodomorpha and within Phytodinosauria. Pampadromaeus is a last common ancestor for both clades.
At some point sauropods reverted to a quadrupedal configuration. The question is: did that reversion happen just once? Or several different times by convergence?
According to the LRT all basal phytodinosaur taxa (Fig. 4), other than Saturnalia (Fig. 4), had a bipedal configuration with short forelimbs or hands inappropriate for placing on the ground. By contrast, in the LRT Early Jurassic Yizhousaurus nests basal to the large quadrupedal sauropods. The Yizhoursaurus hand had robust short fingers with flat unguals. These are traits expected if bearing weight. Yizhousaurus is another close relative to the Thecodontosaurus clade with the present short list of tested taxa. Given the present taxon list, quadrupedalism in sauropomorphs appeared twice.
Figure 4. Phytodinosaur taxa from the LRT to scale. Colors match those in figure 3. It is worthwhile noting the comings and goings of a short vs long neck. All but one or two are in the same size range here.
Ballell, Rayfield and Benton examined every muscle scar on every bone of Thecodontosaurus to conclude that it was bipedal. That’s excellent, but it is something that was described and illustrated 22 years earlier by Benton et al. 2000.
Recent publicity (see below) makes news of bipedalism in Thecodontosaurus by comparing it to more popularly known giant quadrupedal sauropods. Readers, if you want to grab headlines, follow this example. Ballell, Rayfield and Benton know how to do it, and so should you.
References Ballell A, Rayfield EJ and Benton MJ 2022. Walking with early dinosaurs: appendicular myology of the Late Triassic sauropodomorph Thecodontosaurus antiquus, Royal Society Open Science (2022). DOI: 10.1098/rsos.211356 Benton MJ, Ruul L, Storrs GW and Galton PM 2000. Anatomy and systematics of the prosauropod dinosaur Thecodontosaurus antiquus from the Upper Triassic of Southwest England. Journal of Vertebrate Paleontology 20(1):77–108. Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp. Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.
The Pterosaur Heresies 