Short one today. See figure 1 to compare primitive and derived bird and pterosaur palates. Lots of convergence! In each clade, one an archosaur, the other a lepidosaur, former tooth-bearing bones create a solid palate, meeting each other at the midline, as the rostrum comes to a sharp point, and the vomers gradually disappear.
Note: these are cherry-picked taxa chosen for maximum disparity within their clade and maximum convergence between clades.
Earlier we looked at the evolution of pterosaur palates in an 8-part series, ending here. Links there will lead you to the first seven parts. The evolution of bird palates is in process.
Revised December 16, 2021 with revised scores and some new nestings.
Another several days and nights of more binge studytrying to figure out the topology of the crown birds recovers a slightly more parsimonious hypothesis of interrelationships in this subset of the large reptile tree (LRT, 1865+ taxa then, 2018 taxa now; Fig. 1). A few surprises were recovered (see below) and I’m starting to understand why paleontologists gave up studying phenomic traits in bird phylogeny and turned instead to genomic molecules for their cladograms. Earlier struggles with the clade of crown birds can be found here and here.
Problem number 1: Most birds more or less fuse the premaxilla, maxilla and nasal bones. Cornified tissues (a keratinous beak) sometimes covers the anterior rostrum further obscuring underlying sutures. The extent of the premaxilla vs maxilla varies greatly among birds. Sometimes the two are laminated one atop the other. My bird palate data needed a closer look. Many corrections were made based on comparative anatomy.
Problem number 2. Although the cladogram (Fig. 1) is fully resolved, the ‘backbone’ of the cladogram still needs to be further strengthened for higher Bootstrap/Jackknife scores. This is probably not the ‘most’ parsimonious tree possible, but a ‘more’ parsimonious tree than previous presentations.
Many surprises popped up, resolving several issues:
Surprise number 1: Mousebirds (Urocolius) + quetzals (Pharomachrus), neither of which have long legs, split off early from the rest of the Neognathae (non-ratites) along with tiny Cyrilavis and headless Palaeoglaux, both from the Eocene. Based on phylogenetic bracketing, I hope to find a long-legged mousebird ancestor someday.
Surprise number 2: The long-legged wading ibis (Threskiornis) now nests with the short-legged grackle (Quiscalus) and the colorful hoopoe (Upupa, Fig. 2). Other workers nested the ibis with pelicans and the hoopoe with either hornbills or kingfishers.
Surprise number 3: The trumpeter, Psophia, is related to the extant screamer (Chauna, Fig. 3), and both arise from more primitive scrubfowl (Megapodius).
Surprise number 4: Pigeons now arise from the corn crake (Crex) via the sand grouse (Pterocles). Derived taxa include increasingly more plant matter in their diet. Screamers (Fig. 3) are convergent herbivores, but will feed their young with small captured animals.
Surprise number 5: Long-legged cranes (Cicconia) are basal to short-legged grebes (Gavia).
NOT a surprise number 1: New World vultures (Vultur) now nest with the osprey (Pandion). These should have been nested together earlier.
Don’t be surprised to see future changes in the bird clade of the LRT. Based on past experience, the present cladogram (Fig. 1) still needs a bit of polishing. The weakness has never been in the LRT, only in my ability to process the subtle and sometimes barely visible data found in birds. Having a catalog of data for rapid and thorough comparative anatomy in the form of constantly updated images at ReptileEvolution.com has been the key to bringing this ongoing study more and more into focus. Apologies for earlier oversights. I’m learning as I go without much guidance, because there just isn’t that much guidance out there. And there’s lots of convergence.
Novas et al. 2021 update Ostrom’s 1976 study of the motion of the humerus on the shoulder girdle of Archaeopteryx, Cathartes (a New World vulture) and other dinosaurs based on the many more pertinent taxa described since 1976.
This is a laudable effort, but does not go far enough. Novas et al. do not mention the convergent appearance of bird-like shoulder girdles in bats and pterosaurs, both flapping vertebrates. Nor do they shed any new light on the evolution of the coracoid (see below) with regard to the flapping ability of birds. Without flapping, there is no flight in tetrapods.
Novas et al. report, “The aim of the present paper is to emphasize the anatomical similarities of some key features of the pectoral girdle in basal paravians, basal avialans and extant flightless paleognaths. Specifically, comparisons are detailed with the Greater Rhea (Rhea americana), and we provide a brief description of its musculature with the goal of comparing it with the inferred musculature of basal paravians. With all this information at hand we briefly re-analyze here the “hypothetical stages” in the acquisition of bird flight as originally proposed by Ostrom.”
The authors cite Ostrom 1976 throughout the paper, but they mistakenly provide a reference for Vincent Ostrom 1976, who wrote about “The American Experiment in Constitutional Choice.” rather than John H Ostrom who wrote about “Archaeopteryx and the origin of birds.” The work was edited by JK O’Connor and reviewed by AWA Kellner and D Marjanovic´ after submission by the five co-authors.
Ostrom 1976 reported, “The question of the origin of birds can be equated with the origin of Archaeopteryx, the oldest known bird. The skeletal anatomy of Archaeopteryx is extraordinarily similar to that of contemporaneous and succeeding coelurosaurian dinosaurs. Rejection of these similarities as adaptive structures only (parallel or convergent similarities), and therefore of no phylogenetic importance, is here considered invalid.”
Earlier we looked at the importance of an elongate, locked-down coracoid in the acquisition of flapping in birds, pre-pterosaur fenestrasaurs (Cosesaurus) and bats (Fig. 2; lacking a coracoid bats substitute a structurally similar clavicle) here in 2012. Novas et al. mention ‘flapping flight‘ in their abstract, then only once more in their text as they discussed the “main adductor/ depressor of the humerus.”
Sometimes a focused study can be too focused. If you’re going to make a vigorous and valid hypothesis, don’t leave some of your horses in the barn.
References Novas FE, Motta MJ, Agnolín FL, Rozadilla S, Lo Coco GE and Brissón Egli F 2021. Comments on the Morphology of Basal Paravian Shoulder Girdle: New Data Based on Unenlagiid Theropods and Paleognath Birds. Front. Earth Sci. 9:662167. doi: 10.3389/feart.2021.662167 Ostrom JH 1969. Osteology of Deinonychus antirrhopus, an Unusual Theropod from the Lower Cretaceous of Montana. Peabody Mus. Bull. 30, 1–165. doi:10. 2307/j.ctvqc6gzx Ostrom JH 1974. The Pectoral Girdle and Forelimb Function of Deinonychus (Reptilia: Saurischia): a Correction. Postilla 165, 1–11. Ostrom JH 1976. Archaeopteryx and the origin of birds. Journal of the Linnean Society8(2):91–182,
Updated December 16, 2021 here in part 3, with more insights and changes to the bird cladogram.
Short one today after another weekend binge learning more about the birds in the large reptile tree (LRT, 1865+ taxa then, 2018+ taxa now; subset Fig. 1).
The present topology (Fig. 1) settles some earlier issues and brings forth an interesting not-quite-overlooked relationship between the prehistoric long-legged duck, Presbyornis (Fig. 2) and the giant extant shoebill stork, Balaeniceps (also iin Fig. 2) which nests with Scopus, the hamerkop.
Figure 2. The extant shoebill stork, Balaeniceps, is much larger than the early Eocene duck ancestor, Presbyornis, but shares similar proportions.
The long-legged, extant hamerkop (Scopus umbretta, Fig. 3) also nests close to African hornbills (Buceros) and South American toucans (Pteroglossus). That means it must have existed before the appearance of the South Atlantic and the splitting of those two contents, 100 mya, a topic we looked at earlier here.
The LRT is never done. And the LRT is never perfect. A review of purported sisters should demonstrate a gradual accumulation of derived traits. Today’s corrections improve on prior attempts toward that goal. There is no phenomic bird evolution textbook to learn bird evolution, so some things. like this, you have to learn for yourself.
Ahlberg 2018 wrote: “The hypothesis that tetrapods evolved from elpistostegids during the Frasnian, in a predominantly aquatic context, has been challenged by the discovery of Middle Devonian tetrapod trackways predating the earliest body fossils of both elpistostegids and tetrapods.”
“Here I present a new hypothesis based on an overview of the trace fossil and body fossil evidence. The trace fossils demonstrate that tetrapods were capable of performing subaerial lateral sequence walks before the end of the Middle Devonian. The derived morphological characters of elpistostegids and Devonian tetrapods are related to substrate locomotion, weight support and aerial vision, and thus to terrestrial competence, but the retention of lateral-line canals, gills and fin rays shows that they remained closely tied to the water.”
“Elpistostegids and tetrapods both evolved no later than the beginning of the Middle Devonian. The earliest tetrapod records come from inland river basins, sabkha plains and ephemeral coastal lakes that preserve few, if any, body fossils; contemporary elpistostegids occur in deltas and the lower reaches of permanent rivers where body fossils are preserved. During the Frasnian, elpistostegids disappear and these riverine-deltaic environments are colonised by tetrapods. This replacement has, in the past, been misinterpreted as the origin of tetrapods”.
Despitetheir important discoveries, Per Ahlberg and Jennifer Clack promoted the wrong taxa as basalmost tetrapods due to taxon exclusion.
In the LRT Acanthostega and Ichthyostega left no polydactyl descendants. Contra Ahlberg, polydactyly is not primitive, but highly derived in taxa heading back to a more aquatic existence.
Four fingers and five toes is the primitive number of digits. Small limbs sprouting from a long low torso with a short tail is primitive for tetrapods, matching outgroup panderichthyids and eplistostegids.
Originally misidentified as a placoderm, Brindabellaspis was an Early Devonian elpistostegid in the LRT. Unfortunately only the partial skull is known, so let’s keep looking in coeval strata for more basalmost tetrapods.
References Ahlberg PE 2018. Early Vertebrate evolution. Follow the footprints and mind the gaps: a new look at the origin of tetrapods. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 2018: 1–23.
Pritchard et al. 2021 took another look at one of the pseudo-rib gliders, Weigeilitsaurus jaekeil (originally Palaeochameleo jaekeli Weigelt 1930; Figs. 1, 2), an arboreal, crested, basal lepidosauriform (Fig. 4) from the Late Permian.
Unfortunately the authors did not increase the size of their way-too-short taxon list borrowed from an earlier study by two of the authors (Pritchard and Sues 2019, Fig. 5).
Pertinent taxa omitted from both studies include (also see Fig. 4):
and dozens of other basal reptile taxa that separate diapsid-grade lepiosauromorphs from diapsid-grade archosauromorphs, which Pritchard et al. were unable to do with their abbreviated taxon list
Sadly, and once again, this is what happens when paleontologists cherry-pick their taxon list rather than let a wide gamut cladogram, like the large reptile tree (LRT, 1865+ taxa) provide a list of taxa, neither too few nor too many, pertinent to the more focused study.
Pritchard et al. report, “Patagia that support a gliding membrane independently evolved several times in diapsid reptiles, with weigeltisaurids representing only the oldest known example of such a system. However, in all other cases the homologies of the bones supporting the patagium are well understood.”
Ironically, this is not well understood by Pritchard et al. Their basic misunderstanding is based on the following error: “The most common patagium supports represented in extinct reptiles are elongated dorsal ribs (e.g., Kuehneosauridae, Mecistotrachelos apreoros, Xianglong zhaoi) that extend laterally or posterolaterally from their articulations with trunk vertebrae.”
Note to Pritchard et al: Look more closely. And add taxa. Those are not long ribs on Icarosaurus (Fig. 3), Kuehneosaurus (Fig. 1) and Xianglong(Fig. 1). Those pseudo-ribs are dermal in origin, as in Weigeltisaurus and Coelurosauravus (Fig. 1). What the authors thought were elongate transverse processes are actually short ribs fused to each vertebrae, except anteriorly where the pattern is revealed.
No related taxa have elongate transverse processes. That’s what you learn from adding taxa in analysis. The gliding mechanisms on all the above taxa (Fig. 1) are all dermal in origin, as in Weigeltisaurus.
Pritchard et al. report, “A rib-supported patagium is also present in the extant gliding iguanians of the genus Draco of southeast Asia.”
Dracodoes have elongate ribs (and no transverse processes). This is a basic difference from the Permian through Cretaceous gliders (Fig. 1). We call this convergence. The interrelated taxa in figure 1 with pseudo-ribs all present homology, not convergence. Look at all the traits from head to toe, not just one or two ‘special’ traits.
We looked at Coelurosauravus and the other pseudo-rib gliders earlier here in 2011. So this has been online for ten years.
Pritchard et al. did not do a superb job of describing their taxon in detail (Figs. 7–10) with many oversights and errors published. It seems they attempted to trace Photoshop images either with outlines or colors, but did not always do so well.
Digital Graphic Segregation (DGS) was used (Fig. 7 left) to find the pelvic and sacral elements only partially identified by Pritchard et al. 2021, who had firsthand access to the fossil. The reconstruction based on the tracing at left is closer to bone shapes found in sister taxa (Fig. 1).
If you’re going to build a cladogram, do yourself a favor. Add pertinent taxa. Look more closely at related taxa. Don’t blindly follow out-of-date traditions and myths based on short taxon lists. Study your cladogram. Sometimes it will tell you exactly where there are errors in scoring. The LRT is here for you, either to use or to act as a suggestion box.
References Pritchard AC, Sues H-D. 2019. Postcranial remains of Teraterpeton hrynewichorum (Reptilia: Archosauromorpha) and the mosaic evolution of the saurian postcranial skeleton. Journal of Systematic Palaeontology 17(20):1745–1765 DOI 10.1080/14772019.2018.1551249. Pritchard AC, Sues H-D, Scott D and Reisz RR 2021. Osteology, relationships and functional morphology of Weigeltisaurus jaekeli (Diapsida, Weigeltisauridae) based on a complete skeleton from the Upper Permian Kupferschiefer of Germany. PeerJ 9:e11413 DOI 10.7717/peerj.11413 Weigelt J 1930.Palaeochameleo jaekeli nov. gen., nov. sp., ein neuer Rhynchocephale aus dem Mansfelder Kupferschiefer. Leopoldina 6:625–642.
Rafting on broken limbs and floating brush mats (perhaps in the wake of a typhoon) is a popular and traditional explanation for how several vertebrate taxa appear today on the African island of Madagascar, once a central part of the supercontinent, Gondwana (Fig. 1). Rafting is invoked because tradition holds that native lemurs, hippos, elephant birds, tenrecs and others did not live in Madagascar prior to the split from the mainland, 120 mya (Aptian, late Early Cretaceous).
Furthermore, the K-T extinction event is thought to have destroyed all large vertebrates in Madagascar, requiring a reinsertion. This hypothesis is not supported by the LRT. Notably, the K-T impact crater is on the other side of the world, almost at the antipodes from Madagascar.
Nowadays Madagascar is separated from the African mainland by a minimum of 300 miles (500 km). It has remained that far apart at least since 66 mya (Maatrichtian, Latest Cretaceous, K-T event), even during the recent ice ages. The Mozambique channel is also very deep.
Looking back through 167 million years (Fig. 1) geologists tell us Madagascar separated from Africa long before it separated from India and the Seychelles. Today Madagascar has drifted a little closer to Africa than it was 100 million years ago.
Lemurs Basalmost primates, lemurs, are today found only on Madagascar after a world-wide distribution (counting adapids in that clade). Based on the presence of derived members of Glires in the Middle Jurassic, according to the large reptile tree (LRT, 1861+ taxa) lemurs must have also been widespread at that time (167 million years ago). That’s when Madagascar was tucked into the middle of Gondwana (Fig. 1), so lemurs are native to Madagascar. They evolved in isolation following the split of Madagascar from African 167 mya and the split from India about 80 million years ago. This evidence indicates a continuous endemic presence on Madagascar without the need for rafting after the K-T extinction event.
Tenrecs are also native to Madagascar. Some traveled north with Pakistan and India, evolving to become pakicetids, archaeocetids and extant odontocetes. Like lemurs, tenrecs are Middle Jurassic at their genesis so Madagascar is their native home and K-T refugium. This evidence indicates a continuous endemic presence on Madagascar without the need for rafting after the K-T extinction event.
Malagasy hippos Dwarf hippos on Madagascar recently became extinct. In life they were nearly identical to extant hippos in Africa other than smaller in size, longer in legs and eyes not so elevated (Fig. 4). Pre-hippos (genus: Oecepeia, skull length: 9cm; Morocco, amphibiious) are known from the Paleocene (60mya). Fossils indicate a radiation of large hippos (Simbakubwa, Merycopotamus) occurred by the Miocene (23mya) in Africa and Asia respectively. So how far back do Malagasy hippos go? About 2000 years.
According to Wikipedia “The fossil record of the Malagasy hippopotamus is extensive. At least seven hippopotamus bones show unequivocal signs of butchery, suggesting that they survived until humans arrived on Madagascar. The evidence of humans butchering the hippos also suggests their extinction may have been due to humans.”
The first human migration to Madagascar occurred around 10 CE (in Roman times) arriving on outrigger canoes large enough to carry many people, their food, water and other necessities. Genetic tests and the language of the inhabitants both point to a mixture of East African + East Indian ancestry. Among their food stocks were baby hippos taken from East Africa and let go in Madagascar for future foodstocks. So hippos alone rafted to Madagascar, on outrigger canoes steered by modern humans. Over time smaller size was naturally selected on the island.
Madagascar and Seychelle Island giant tortoises The Aldabra giant tortoise from the Seychelle Islands (Aldabrachelys, Fig. 5) is a close relative to the Madagascar giant tortoise. These are basal to the extant alligator snapping turtle (Macrochelys) and the Late Cretaceous marine turtle Archelon in the LRT. This evidence indicates a continuous endemic presence of turtles on Madagascar and the Seychelles without the need for rafting after the K-T extinction event.
Elephant birds The LRT links Aepyornis, the recently extinct elephant bird (Fig. 6), with Struthio, the ostrich. Both have a last common ancestor in Patagopteryx (80mya). Highly derived flightless geese (Asterorinis) are known from the latest Cretaceous. That means the much more primitive ratites had a much more primitive, Jurassic genesis, long before Gondwana split apart. This evidence indicates a continuous presence for large ratites on Madagascar without rafting in or walking in on a land bridge later than the K-T boundary.
Plesiorycteropus, the pseudo ‘aardvark‘ This taxon is known from a few partial fossils known since Fihol 1895 and described in detail by MacPhee 1994 (Fig. 7). Unfortunately MacPhee excluded many key taxa while discussing comparative anatomy, but did make comparisons to Talpa, the mole. In the LRT Plesiorycteropus nested with two other Madagascar taxa, the mongooses Crypotproctaand Eupleurus, not far from Herpestes the Eqyptian mongoose, Late Eocene Prohesperocyon, the pre-mole (not the earliest canid) and Talpa the extant mole, all within a subclade of the Carnivora. This basal placental clade had roots in the Early Jurassic. This phylogenetic evidence indicates a continuous presence for mongooses on Madagascar without rafting in or walking in on a land bridge later than the K-T boundary.
According to Masters, de Wit and Asher 2006 “by 83 million years, all of the major components we recognize today were separated by tracts of water. Madagascar’s fossil record and estimates of the timing of the extant vertebrate radiations in Madagascar are not easily reconciled with this history of fragmentation. Fossil faunas that lived prior to approx. 65 million years had a cosmopolitan flavour, but this was lost after the Cretaceous-Tertiary boundary.”
“Phylogenetic reconstructions of most extant Malagasy vertebrate radiations indicate divergence times that postdate the End-Cretaceous (lemurs, tenrecs, cichlid fish) and even the Early Miocene (chameleons, carnivores, rodents).”
“Most biogeographic explanations of these groups rely, therefore, on Simpson’s model of sweepstakes dispersal [Simpson 1940, 1951], but there are significant problems in applying the model to migrations from Africa to Madagascar, although its application is not so intractable between India and Madagascar. Alternative migration routes for consideration lie:
along the suite of fracture zones between Antarctica and Africa/Madagascar (known as the Antarctic-Africa Corridor), which may have been exposed episodically above sea level;
along a series of submerged basaltic ridges/plateaus with known or suspected continental crust between Antarctica and Africa/Madagascar/India flanking the Antarctic-Africa Corridor (e.g. the Madagascar Ridge, Mozambique Ridge, Conrad Plateau, Gunnerus Ridge);
between Africa and Madagascar along the Davie Ridge (parts of which are known to have been exposed episodically above sea level);
along the Deccan hotspot corridor between India and greater Africa.” (Fig. 8).
Masters, de Wit and Asher 2006 report the traditional story, “The fossil records of the living mammalian orders begin at or shortly after the Cretaceous-Tertiary boundary [Alroy, 1999]. Hence the composition of Madagascar’s End-Cretaceous fauna is an important starting point for reconstructions of its biodiversity.”
As Masters, de Wit and Asher note, tradition holds that there is no continuity between pre K-T boundary Madagascar fauna and post K-T fauna but remains are extremely rare. Only one pre-K-T mammal, the derived paedothere marsupial Adalatherium, has been described.
By contrast, the LRT indicates that endemic Madagascar birds and mammals survived the K-T extinction event on the other side of the world.
Masters, de Wit and Asher continue, “The lack of close relationships between the Upper Cretaceous fossils and the extant Malagasy vertebrates has led researchers to conclude that the basal stocks of the modern taxa must have arrived later by waif dispersal.”
According to the LRT, only the hippos rafted over, carried by First Century humans hoping to have hippo burgers in the years ahead. The rest of the taxa were Jurassic basal placentals and basal crown birds that survived the K-T extinction event on their island home close to the antipodes of the K-T crater. Fossils of these K-T survivors might show up someday on Madagascar, but for now the LRT provides the first phylogenetic and chronological evidence against the widely believed rafting hypothesis for most Madagascar vertebrates. If not, please provide a citation for that earlier hypothesis so I can promote it here.
PS What about those Late Cretaceous dinosaurs? They all became extinct. Yes, they did and had a long time to do so if the K-T extinction event did not kill them.
References Filhol H. 1894. Observations concernant quelques mammiferes fossiles nouveaux de Quercy. Ann. Sci. Nat., Zool. Paleontol. (7e ser.) 16: 129-150. Masters JC, de Wit MJ and Asher RJ 2006. Reconciling the Origins of Africa, India and Madagascar with Vertebrate Dispersal Scenarios. Folia Primatol 2006;77:399–418. MacPhee RDE 1994. Morphology, Adaptations, and Relationships of Plesiorycteropus, and a Diagnosis of a New Order of Eutherian Mammals.” Bulletin of the American Museum of Natural History, 220 (1994): 1-214. Reeves C 2014. The position of Madagascar within Gondwana and its movements during Gondwana dispersal. Journal of African Earth Sciences 94(2014):45–57. Simpson GG 1940. Mammals and land bridges. Journal of the Washington Academy of Sciences 30:137–163. Simpson GG 1951. Probabilities of dispersal in geologic time. Bulletin of the American Museum of Natural History 99: 163–176.
Summary for those in a hurry: The Brockllehurst et al. 2021 cladogram (Fig. 1) shuffles various pre-mammal and mammal taxa together almost randomly due to taxon exclusion. So this paper is working from an invalid phylogeny where some placentals are considered ‘mammaliaforms’ and one monotreme is considered a ‘placental’, etc. etc.
From the Brockllehurst et al. 2021 abstract: “We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms.”
“Our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors.”
The authors say it was beast vs. beast… …not so much daylight dinos vs. daylight beasts, the traditional hypothesis. Traditionally mammals were were thought to have been forced to go nocturnal and arboreal to avoid getting eaten by dino predators. Instead the authors report the “The release of this constraint occurred later than the extinction of the dinosaurs.” The keywords, ‘nocturnal’ and ‘diurnal’ are not found in the text.
The authors appear to have done their due dilligence except when it came to their cladogram. They report, “Four matrices, which between them contain the largest available sample of taxa across a broad range of Mesozoic mammaliaform clades, were chosen to compare patterns between Mesozoic crown therians, stem therians and nontheriimorph mammaliaforms.” So they trusted both the taxon lists and the observations of others rather than creating their own cladogram and taxon list using their own observations. Notably, no prior workers include members of Glires in their studies of Mesozoic mammals, so multituberculates don’t have the opportunity to nest within Glires, as they do in the large reptile tree (LRT, 1861+ taxa, subsets Figs. 3 and 4).
Brocklehurst et al. use only fossil taxa in their cladogram (Fig. 1). The LRT employs extant and extinct taxa. Extant taxa are not only good attractive elements for extinct taxa (keeping workers on a solid footing), but extant taxa also fill in many gaps in the fossil record (Fig. 2). As an example, tree shrews are rare as fossils, but living tree shrews are basal taxa in several placental clades in the LRT. That means there must have been tree shrews in the Jurassic (Fig. 2), but you would not know that based on the fossil record.
From the Discussion: “Our findings suggest that Mesozoic crown-group therians were substantially more constrained than other mammaliaforms, occupying only a small portion of the total mammaliaform character state space. We show that relaxation of this constraint played a central role in the Cenozoic radiation of placental mammals, but that this did not occur until after the Danian, during the second half of the Paleocene, several million years after the extinction of non-avian dinosaurs.”
The authors’ conclusions rely on a scrambled cladogram (Fig. 1). Unscramble that cladogram and redo the charts. Brocklehurt et al. correctly nested only one of 15 placentals taxa, three of 14 marsupial taxa and 2 of 13 monotremes (which they label Australosphenida). A valid phylogenetic context is essential before you lift a finger on any other aspect of your paleo studies.
Workers should not put their trust in small taxon lists created by others. Neither should they put their trust in results recovered by the LRT. Rather they should use extinct and extant taxa perhaps suggested by the LRT and other sources to create their own cladograms that they can then use for the rest of their careers. Avoid tooth-only taxa until your cladogram is on a rock-solid footing, then slowly add tooth-only taxa.
References Brocklehurst N, Panciroli E, Benevento GL and Benson RBJ 2021. Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals. Current Biology (2021), https://doi.org/10.1016/j.cub.2021.04.044
One new taxon, the giant flightless goose, Cnemiornis (Figs. 1, 2), and an old taxon with a new nesting, the Cretaceous enigma bird, Asteriornis (Field et al. 2020, Fig. 3), were recovered after a four-day binge review of theropods and birds in the large reptile tree (LRT 1861+ taxa; subset Fig. 4). Other changes are reviewed below. Low scores in your phylogenetic analysis = trouble.
You might remember, we looked at Asteriornis, the so-called ‘super chicken, a year ago here (now updated).
Cnemiornis calcitrans (Owen 1866; recently extinct; 1 m tall) is the New Zealand goose, a very large and flightless goose with reduced forelimbs, reduced sternum and not much webbing between the toes. The neck is longer than in Anser and pedal digit 1 is absent. So is the radius (Fig. 1). Compare the skull of Cnemiornis (Fig. 2) to that of the Cretaceous bird, Asteriornis (Fig 3).
Asteriornis maastrichtensis (Field et al. 2020; latest Cretaceous, 66 mya; NHMM 2013 008) was originally considered basal to chickens and geese, but here nests as a sister to the giant filghtless goose, Cnemiornis, a highly derived, rather than basal, bird. The authors reported, “The fossil represents one of the only well-supported crown birds from the Mesozoic era.” Note the fused lacrimal + prefrontal, the robust postfrontal + postorbital that together separate the orbit from the antorbital fenestra and temporal fenestrae. Now these two openings almost connect with one another as in Cnemiornis, a rare trait in other birds and tetrapods in general.
Contra the conclusion of Field et al. 2020, the presence of highly derived Asteriornis in latest Cretaceous strata indicates that all taxa that phylogenetically precede it had Cretaceous roots. At present this is only confirmed by the presence of 80-million-year-old Patagopteryx, an ostrich ancestor. Other Cretaceous crown birds will surely follow.
Other changes to the theropod subset of the LRT include:
The long-beaked hamerkop (Scopus) moves to long-beaked barbets, toucans (Pteroglossus) and hornbills on one node and on the other node. Given that Cretaceous Asterornis now nests with geese, it’s time to start looking for hamerkops earlier in the Cretaceous.
Of course, none of the above hypothetical interrelationships match genomic testing, which readers should be discouraged from ever using in deep time studies. Why? Because they lead to false positives. Using traits, as in the LRT, let’s you see, trait-by-trait how taxa slowly evolved via microevolution. With the present housekeeping based on new taxa and fresh looks at old taxa, the evolution from one taxa to another looks better. Not perfect. Never perfect. Just better.
Sharp-eyed readers will note the deletion of all Bootstrap/Jackknife scores in the LRT and its subsets from now on. A kind reader noted such scores are impossible given the size of the LRT, overlooking the note that all such scores are based on smaller overlapping subsets due to limitations in computing power. That excuse is no longer needed with the deletion of all Bootstrap/ Jackknife scores from public view. The reader was right. Such scores are not appropriate for the LRT because they misinform. I will continue to use Bootstrap scores in my studies because they indicate strong and weak nodes in fully resolved subsets of the LRT. PAUP usually needs three extra steps to get scores over 50. Scores under 50, despite being fully resolved, usually means some sort of problem in my experience. Just getting a fully resolved subset is only the first step. Behind the scenes it won’t be the only step.
References Field DJ, Benito J, Chen A, Jagt JWM and Ksepka DT 2020. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579:397–401. Owen R 1866. XI. On Dinornis (Part X.): containing a Description of part of the Skeleton of a flightless Bird indicative of a New Genus and Species (Cnemiornis calcitrans, Ow.) Journal of Zoology 1866 The Zoological Society of London. Padian K 2020. Poultry through time. Nature online
Bindellin et al. 2021 bring us four new specimens of the the Middle Triassic ichthyosaur, Besanosaurus (Fig. 1), a taxon previously added to the large reptile tree (LRT, 1845 taxa) based on crushed data. The new 3D data it welcome! Only a few scores changed and they do not change the prior nesting of Besanosaurus in the LRT.
Even so, the Bindellin et al. cladogram (Fig. 2) bears little resemblance to the LRT (subset Fig. 3). They do start similarly.
Good to see Wumengosaurusat the base of the ichthyosaur tree here (Fig. 2). This confirms the LRT nesting from many years ago. Thalattosuchia and Mesosauria should also be included as outgroup clades. Sclerocormus + Cartorhynchusare ichthyosaur-mimic basal pachypleurosaurs closer to Qianxisaurus.
Cherry-picking included taxa too often leads to problems. Let your software and your wide gamut taxon list tell you which taxa should be included in focused studies, not the other way around.
Besanosaurus leptorhyncus (Dal Sasso and Pinna 1996; Bindellin G et al. 2021; Middle Triassic, Ladinian, up to 6m in length) is one of the largest ichthyosaurs known. The 4m long female included four embryos. Besanosaurus was derived from a sister to Chaohusaurus with a longer rostrum, longer flippers and an overall larger size. The scapula was larger and disc-shaped. Large hyoid bones (in gray) anchored the tongue and could have expanded the throat.
References Bindellin G et al. 2021. Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano Formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications. PeerJ 9:e11179 DOI 10.7717/peerj.11179 Dal Sasso C and Pinna G 1996. Besanosaurus leptorhynchus n. gen. n. sp., a new shastasaurid ichthyosaur from the Middle Triassic of Besano (Lombardy, N. Italy). Paleontologia Lombarda, Nuova serie 4:1-23. Young CC and Dong Z 1972. On the Triassic aquatic reptiles of China. Memoires of the Nanjing Institute of Geology and Paleontology 9: 1–34.