Field of Science

Aetosaurs: New Phylogenetic Analysis, New Taxon; and New Technique to Analyze Incongruent Character Datasets

My new paper in PeerJ features a new phylogenetic analysis of the Aetosauria (Archosauria: Pseudosuchia). I've added many new characters and feature all known valid aetosaur taxa. In the Supplemental Materials, each character is described and figured to clarify them for future use.

 

This paper also introduces a new aetosaur, Scutarx deltatylus, from the Chinle Formation of Arizona. To date I've collected four partial Scutarx skeletons, the first in 2002, from Petrified Forest National Park. The holotype specimen includes a partial skull, the first good aetosaur skull material collected from Arizona since the 1930s. In previous papers I have assigned all of these specimens to Calyptosuchus (Stagonolepis) wellesi; however, when I undertook a revision of that taxon I noted that my Petrified Forest specimens (all from the Sonsela Member of the Chinle Formation) all possessed raised triangular bosses on the posteromedial corner of the paramdian osteoderms.  These are not present in the type specimen from Texas, or from the large amount of material from the Placerias Quarry of Arizona. Interestingly the boss-bearing and non-boss-bearing specimens were separated stratigraphically. Presently the specimens from the Blue Mesa Member of Arizona and the Tecovas Formation of Texas are those that lack the boss (Calyptosuchus wellesi), and those from the Sonsela Member, and middle Cooper Canyon Formation are those that possess the boss (Scutarx deltatylus). The skull and ilium of Scutarx are also autapomorphic as discussed in the paper.


Finally I adapted the method to compute Partioned Bremer Support to look at the possibility of character conflict between anatomical partitions in aetosaurs. Essentially does the armor have a different phylogenetic signal than the rest of the skeleton. Bremer Support is used in all phylogenetic analyses to show branch support; however, what is generally not realized is that the individual support values of characters from each anatomical partition combine to total this number. But if these character sets actually support a different tree than the one recovered in the total character analysis, they will reduce the Bremer Support value (negative Bremer Support). Some character sets are ambivalent and actually provide no support to the branches.  This analytic tool allows you to look at your tree support node by node and see what character datasets support the topology.  This technique has been used since the late 1990s to compare molecular vs. morphological character sets, but this is the first time it has been employed to look at anatomical partitions in a purely morphological study.  


That said, I am a little disappointed with my final discussion section in the paper.  While I am excited about the potential for Partitioned Bremer Support, I still am learning all that it demonstrates, thus my discussion is not as strong as I would have liked. I hope that others will find it of interest and utility and that we can see if if it works for other taxonomic groups. 


Parker, W.G. 2016. Revised phylogenetic analysis of the Aetosauria (Archosauria: Pseudosuchia); assessing the effects of incongruent morphological character sets. PeerJ 4:e1583 https://doi.org/10.7717/peerj.1583

Abstract- Aetosauria is an early-diverging clade of pseudosuchians (crocodile-line archosaurs) that had a global distribution and high species diversity as a key component of various Late Triassic terrestrial faunas. It is one of only two Late Triassic clades of large herbivorous archosaurs, and thus served a critical ecological role. Nonetheless, aetosaur phylogenetic relationships are still poorly understood, owing to an overreliance on osteoderm characters, which are often poorly constructed and suspected to be highly homoplastic. A new phylogenetic analysis of the Aetosauria, comprising 27 taxa and 83 characters, includes more than 40 new characters that focus on better sampling the cranial and endoskeletal regions, and represents the most comprenhensive phylogeny of the clade to date. Parsimony analysis recovered three most parsimonious trees; the strict consensus of these trees finds an Aetosauria that is divided into two main clades: Desmatosuchia, which includes the Desmatosuchinae and the Stagonolepidinae, and Aetosaurinae, which includes the Typothoracinae. As defined Desmatosuchinae now contains Neoaetosauroides engaeus and several taxa that were previously referred to the genus Stagonolepis, and a new clade, Desmatosuchini, is erected for taxa more closely related to Desmatosuchus. Overall support for some clades is still weak, and Partitioned Bremer Support (PBS) is applied for the first time to a strictly morphological dataset demonstrating that this weak support is in part because of conflict in the phylogenetic signals of cranial versus postcranial characters. PBS helps identify homoplasy among characters from various body regions, presumably the result of convergent evolution within discrete anatomical modules. It is likely that at least some of this character conflict results from different body regions evolving at different rates, which may have been under different selective pressures.

Cranial Anatomy of the Aetosaur Paratypothorax andressorum

Schoch, R. R., and J. B. Desojo. 2016. Cranial anatomy of the aetosaur Paratypothorax andressorum Long & Ballew, 1985, from the Upper Triassic of Germany and its bearing on aetosaur phylogeny. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279(1):73-95. DOI: http://dx.doi.org/10.1127/njgpa/2016/0542
http://www.ingentaconnect.com/content/schweiz/njbgeol/2016/00000279/00000001/art00008


Abstract -
The large aetosaur Paratypothorax andressorum has so far been known only by its osteoderms. Here we describe for the first time the skull of a complete, articulated specimen of this taxon that was found in the type horizon at Murrhardt, southwestern Germany. Paratypothorax
andressorum has the following cranial autapomorphies: (1) upper jaw margin with deep notch between premaxilla and maxilla, (2) maxilla-lacrimal suture with finger-like projection, (3) upper
temporal fenestra triangular, and (4) first paramedian cervical osteoderms narrow and oval, much smaller than second row. Apart from these features, the skull of P. andressorum closely resembles that of the small aetosaur Aetosaurus ferratus known from the same horizons, despite major differences in the morphology of osteoderms. Both taxa share (1) the pointed, beak-shaped premaxilla which expands only gently anterior to the nasal, (2) maxilla and lacrimal excluding jugal
from margin of antorbital fenestra, (3) exclusion of squamosal from margin of infratemporal fenestra, and (4) posterior part of jugal not downturned. Phylogenetic analysis reveals poorly resolved relationships within Aetosauria, but exclusion of a problematic taxon Coahomasuchus results in a much better resolution, with Paratypothorax to nest with Rioarribasuchus, Tecovasuchus, Typothorax, and Redondasuchus within a monophyletic Typothoracinae. Interestingly, Aetosaurus and Stenomyti form successive sister taxa of this clade rather than fall within an aetosaurine grade of basal aetosaurs, as suggested by previous authors. The resemblance of Paratypothorax and Aetosaurus in many cranial features, their close relationship as suggested by the present analysis, and the immature state of all available Aetosaurus specimens suggest two new alternative hypotheses: (1) Aetosaurus is the juvenile of a close relative of Paratypothorax or (2) it is itself the juvenile of Paratypothorax.

Archosauromorph from the Middle Permian of South America

Martinelli, A. G., Francischini, H., Dentzien-Dias, P. C., Soares, M. B., and C. L. Schultz. 2016.
The oldest archosauromorph from South America: postcranial remains from the Guadalupian (mid-Permian) Rio do Rasto Formation (Paraná Basin), southern Brazil. Historical Biology.
DOI:10.1080/08912963.2015.1125897
http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1125897


Abstract -
In this contribution, we report a distal portion of a left humerus that likely belongs to an indeterminate basal archosauromorph from the Guadalupian (mid-Permian) Rio do Rastro Formation (Paraná Basin) of southern Brazil. A precise taxonomy of the fragmented and isolated humerus UFRGS-PV-0546-P is not warranted at generic nor familiar level but, likely, this specimen belongs to an Archosauromorpha due to the lack of both the entepicondylar and the ectepicondylar foramina. The narrow distal end of the humerus, the rounded radial and ulnar condyles, and the moderately developed supinator process with a shallow ectepicondylar groove (not notched) are features reminiscent of tanystropheids rather than that of other archosauromorphs. This material likely represents the first and oldest Permian archosauromorph from South America and indicates the presence of this lineage before the P/T boundary.

The Early Evolution of Rhynchosaurs

Congratulations to Max Langer for being honored with his own rhynchosaur genus.

Ezcurra, M. D., Montefeltro, F., and R. J. Butler. 2016. The Early Evolution of Rhynchosaurs. Frontiers in Ecology and Evolution 3:142. DOI: 10.3389/fevo.2015.00142. http://journal.frontiersin.org/article/10.3389/fevo.2015.00142/full

Abstract -
The rhynchosaurian archosauromorphs are an important and diverse group of fossil tetrapods that first appeared during the Early Triassic and probably became extinct during the early Late Triassic (early Norian). Here, the early evolution of rhynchosaurs during the Early and early Middle Triassic (Induan-Anisian: 252.2-242 Mya) is reviewed based on new anatomical observations and their implications for the taxonomy, phylogenetic relationships and macroevolutionary history of the group. A quantitative phylogenetic analysis recovered a paraphyletic genus Rhynchosaurus, with “Rhynchosaurusbrodiei more closely related to hyperodapedontines than to Rhynchosaurus articeps. Therefore, a new genus is erected, resulting in the new combination Langeronyx brodiei. A body size analysis found two independent increases in size in the evolutionary history of rhynchosaurs, one among stenaulorhynchines and the other in the hyperodapedontine lineage. Maximum likelihood fitting of phenotypic evolution models to body size data found ambiguous results, with body size evolution potentially interpreted as fitting either a non-directional Brownian motion model or a stasis model. A Dispersal-Extinction Cladogenesis analysis reconstructed the areas that are now South Africa and Europe as the ancestral areas of Rhynchosauria and Rhynchosauridae, respectively. The reconstruction of dispersal events between geographic areas that are broadly separated paleolatitudinally implies that barriers to the dispersal of rhynchosaurs from either side of the paleo-Equator during the Middle Triassic were either absent or permeable.

Archosauriform Remains from Late Triassic of San Luis Province, Argentina

Gianechini, F. A., Codorniú, L., Arcucci, A. B., Elías, G. C., and D. Rivarola. 2015. Archosauriform remains from the Late Triassic of San Luis province, Argentina, Quebrada del Barro Formation, Marayes–El Carrizal Basin. Journal of South American Earth Sciences. DOI:10.1016/j.jsames.2015.12.012
http://www.sciencedirect.com/science/article/pii/S0895981115301073


Abstract-
Here we present archosauriform remains from ‘Abra de los Colorados’, a fossiliferous locality at Sierra de Guayaguas, NW San Luis Province. Two fossiliferous levels were identified in outcrops of the Quebrada del Barro Formation (Norian), which represent the southernmost outcrops of the Marayes–El Carrizal Basin. These levels are composed by massive muddy lithofacies, interpreted as floodplain deposits. The specimens consist of one incomplete maxilla (MIC-V718), one caudal vertebra (MIC-V719), one metatarsal (MIC-V720) and one indeterminate appendicular bone (MIC-V721). The materials can be assigned to Archosauriformes but the fragmentary nature and lack of unambiguous synapomorphies preclude a more precise taxomic assignment. The maxilla is remarkably large and robust and represents the posterior process. It preserved one partially erupted tooth with ziphodont morphology. This bone shows some anatomical traits and size match with ‘rauisuchians’ and theropods. MIC-V719 corresponds to a proximal caudal vertebra. It has a high centrum, a ventral longitudinal furrow, expanded articular processes for the chevrons, a posteriorly displaced diapophysis located below the level of the prezygapophyses, and short prezygapophyses. This vertebra would be from an indeterminate archosauriform. MIC-V720 presents a cylindrical diaphysis, with a well-developed distal trochlea, which present resemblances with metatarsals of theropods, pseudosuchians, and silesaurids, although the size matches better with theropods. MIC-V721 has a slender diaphysis and a convex triangular articular surface, and corresponds to an indeterminate archosauriform. Despite being fragmentary, these materials indicate the presence of a diverse archosauriforms association from Late Triassic beds of San Luis. Thus, they add to the faunal assemblage recently reported from this basin at San Juan Province, which is much rich and diverse than the coeval paleofauna well known from Los Colorados Formation in the Ischigualasto–Villa Union Basin.

Reanalysis of the Diapsid Reptile Elachistosuchus huenei from the Late Triassic of Germany

Sobral, G., Sues, H.-D., and J. Müller. 2015. Anatomy of the enigmatic reptile Elachistosuchus huenei Janensch, 1949 (Reptilia: Diapsida) from the Upper Triassic of Germany and its relevance for the origin of Sauria. PLoS ONE 10(9): e0135114. doi:10.1371/journal.pone.0135114

Abstract - The holotype and only known specimen of the enigmatic small reptile Elachistosuchus huenei Janensch, 1949 from the Upper Triassic (Norian) Arnstadt Formation of Saxony-Anhalt (Germany) is redescribed using μCT scans of the material. This re-examination revealed new information on the morphology of this taxon, including previously unknown parts of the skeleton such as the palate, braincase, and shoulder girdle. Elachistosuchus is diagnosed especially by the presence of the posterolateral process of the frontal, the extension of the maxillary tooth row to the posterior margin of the orbit, the free posterior process of the jugal, and the notched anterior margin of the interclavicle. Phylogenetic analyses using two recently published character-taxon matrices recovered conflicting results for the phylogenetic position of Elachistosuchus–either as an archosauromorph, as a lepidosauromorph or as a more basal, non-saurian diapsid. These different placements highlight the need of a thorough revision of critical taxa and new character sets used for inferring neodiapsid relationships.

The Dicynodon-Lystrosaurus Assemblage Zone Boundary May Not Approximate the Marine-Defined Permo-Triassic Extinction Event

Wow, well this should definitely generate some discussion and a bit of research.... 

Gastaldo, R. A., Kamo, S. L., Neveling, J., Geissman, J. W., Bamford, M., and C. V. Looy. 2015 Is the vertebrate-defined Permian-Triassic boundary in the Karoo Basin, South Africa, the terrestrial expression of the end-Permian marine event? Geology (Advanced Online). doi: 10.1130/G37040.1

Abstract: The end-Permian extinction records the greatest ecological catastrophe in Earth history. The vertebrate fossil record in the Karoo Basin, South Africa, has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems, recently claimed to be in synchrony with the marine crisis. Workers assumed that systematic turnover at the Dicynodon assemblage zone boundary, followed by the appearance of new taxa directly above the base of the Lystrosaurus assemblage zone, is the continental expression of the end-Permian event and recovery. To test this hypothesis, we present the first highprecision age on strata close to the inferred Permian-Triassic boundary. A U-Pb isotope dilution–thermal ionization mass spectrometry zircon age of 253.48 ± 0.15 Ma (early Changhsingian) is from a silicified ash layer ~60 m below the current vertebrate-defined boundary at Old Lootsberg Pass (southern South Africa). This section yields newly discovered plants and vertebrates, and is dominated by a normal polarity signature. Our collective data suggest that the Dicynodon-Lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported, and older than the marine extinction event. Therefore, the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end-Permian mass extinction. The actual Permian-Triassic boundary in the Karoo Basin is either higher in the Katberg Formation or is not preserved. The currently accepted model of the terrestrial ecosystem response to the crisis, both in this basin and its extension globally, requires reevaluation.

So Long Paleorhinus and Pseudopalatinae

Long needed redescription of the type material of the phytosaur Parasuchus hislopi from India and a revision of the non-mystriosuchin parasuchid phytosaurs. It will take me awhile to abandon the name Pseudopalatinae. 

Kammerer, C. F., Butler, R. J., Bandyopadhyay, S., and M. R. Stocker. 2015. Relationships of the Indian phytosaur Parasuchus hislopi Lydekker, 1885. Papers in Paleontology (early online). 

Abstract:
The neotype skull of the Indian phytosaur Parasuchus hislopi Lydekker, 1885 (ISI R42) is re-evaluated and compared with the type material of other basal phytosaurs. Parasuchus hislopi is extremely similar to species previously placed in Paleorhinus (P. bransoni and P. angustifrons), sharing with them such characters as a series of nodes on the lateral surface of the jugal, paired ridges on the squamosal and a frontal depression. Parasuchus hislopi represents a valid species: it can be distinguished from P. bransoni by a relatively low narial eminence and P. angustifrons by the absence of paired nasal depressions. Inclusion of Parasuchus hislopi in a phylogenetic analysis of phytosaurs recovers it in a well-supported clade with P. bransoni and P. angustifrons. Parasuchus is considered the senior synonym of Paleorhinus and Arganarhinus. Parasuchus (here considered to include P. hislopi, P. angustifrons, P. bransoni and P. magnoculus) has a broad circum-Pangaean distribution, with species occurring in the south-western United States, Morocco, central Europe and India. Phytosaur higher-level taxonomy is also revised: Parasuchidae is redefined to include ‘Paleorhinus-grade’ phytosaurs and the later-diverging Mystriosuchinae (the group formerly known as Phytosauridae), and Pseudopalatinae is renamed Mystriosuchini for reason of priority.

A New Lagerpetid Dinosauromorph from the Late Triassic of Argentina

Martínez, R. N., Apaldetti, C., Correa, G. A., and D. Abelín. 2015. A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina. Ameghiniana (future issue) doi:10.5710/AMGH.21.06.2015.2894

Abstract:
The early evolution of Ornithodira, the clade that includes pterosaurs and dinosaurs, is poorly known. Until a decade ago, the basal radiation of Dinosauromorpha, the clade including dinosaurs and birds, was poorly understood because of a scarce of fossil record, which was restricted to specimens known of the Ladinian Chañares Formation from Argentina. In the last years the discovery of several non-dinosaurian dinosauromorphs dramatically expanded this record and also demonstrated that this group—previously restricted to the Middle Triassic—persisted at least well into the Norian. Although Norian non-dinosaurian dinosauromorphs have been reported from several places around the world, the only known Norian non-dinosauriform dinosauromorphs—Dromomeron romeri and Dromomeron gregorii—come from North America. We report here the first record from the Southern Hemisphere of a non-dinosauriform dinosauromorph, Dromomeron gigas sp. nov., from the Norian Quebrada del Barro Formation, northwestern Argentina. A phylogenetic analysis recovers Dromomeron gigas nested into the monophyletic group Lagerpetidae, and as the sister taxon to Dromomeron romeri. The inclusion of D. gigas within Lagerpetidae suggests that body size increased in this lineage over time, as was previously demonstrated for Dinosauriformes as a whole, and that lagerpetids reached a larger size than previously thought. Finally, the new finding provides novel information on the basal radiation of Dinosauromorpha constituting the first record of a Norian association of dinosaurs with non-dinosauriform dinosauromorphs outside North America.

Evidence of Interaction between Two Late Triassic Apex Predators

I've been away for a bit, but am interested in trying to get back into the swing of things here so please bear with me.  This is a paper from late last year that I haven't mentioned before.

Drumheller, S. K., M. R. Stocker, and S. J. Nesbitt. 2014. Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America. Naturwissenschaften 101:975-987. DOI 10.1007/s00114-014-1238-3

Rather than get into the details here I'll send you to this podcast which does a great job featuring the significance of this study.

Systematics of Putative Euparkeriids from the Triassic of China

Sookias, R. B., Sullivan, C., Liu, J., and R. J. Butler. 2014. Systematics of putative euparkeriids (Diapsida: Archosauriformes) from the Triassic of China. PeerJ 2:e658 doi:http://dx.doi.org/10.7717/peerj.658

Abstract - The South African species Euparkeria capensis is of great importance for understanding the early radiation of archosauromorphs (including archosaurs) following the Permo–Triassic mass extinction, as most phylogenetic analyses place it as the sister taxon to crown group Archosauria within the clade Archosauriformes. Although a number of species from Lower–Middle Triassic deposits worldwide have been referred to the putative clade Euparkeriidae, the monophyly of Euparkeriidae is controversial and has yet to be demonstrated by quantitative phylogenetic analysis. Three Chinese taxa have been recently suggested to be euparkeriids: Halazhaisuchus qiaoensis, ‘Turfanosuchus shageduensis’, and Wangisuchus tzeyii, all three of which were collected from the Middle Triassic Ermaying Formation of northern China. Here, we reassess the taxonomy and systematics of these taxa. We regard Wangisuchus tzeyii as a nomen dubium, because the holotype is undiagnostic and there is no convincing evidence that the previously referred additional specimens represent the same taxon as the holotype. We also regard ‘Turfanosuchus shageduensis’ as a nomen dubium as we are unable to identify any diagnostic features. We refer the holotype to Archosauriformes, and more tentatively to Euparkeriidae. Halazhaisuchus qiaoensis and the holotype of 'Turfanosuchus shageduensis’ are resolved as sister taxa in a phylogenetic analysis, and are in turn the sister taxon to Euparkeria capensis, forming a monophyletic Euparkeriidae that is the sister to Archosauria+Phytosauria. This is the first quantitative phylogenetic analysis to recover a non-monospecific, monophyletic Euparkeriidae, but euparkeriid monophyly is only weakly supported and will require additional examination. Given their similar sizes, stratigraphic positions and phylogenetic placement, the holotype of ‘Turfanosuchus shageduensis’ may represent a second individual of Halazhaisuchus qiaoensis, but no apomorphies or unique character combination can be
identified to unambiguously unite the two. Our results have important implications for understanding the species richness and palaeobiogeographical distribution of early archosauriforms.

Silesaurid-Herrerasaurid-Neotheropod Assemblage from the Late Triassic of Poland

This is currently free from the Palaeontology Online website.

Niedźwiedzki, G., Brusatte, S. L., Sulej, T., and R. J. Butler. 2014. Basal dinosauriform and theropod dinosaurs from the mid–late Norian (Late Triassic) of Poland: implications for Triassic dinosaur evolution and distribution. Palaeontology 57(6): 1121–1142 DOI: 10.1111/pala.12107
 
Abstract - The rise of dinosaurs during the Triassic is a widely studied evolutionary radiation, but there are still many unanswered questions about early dinosaur evolution and biogeography that are hampered by an unevenly sampled Late Triassic fossil record. Although very common in western North America and parts of South America, dinosaur (and more basal dinosauriform) remains are relatively rare in the Upper Triassic deposits of Europe, making any new discoveries critically important. One of the most diverse dinosauriform assemblages from Europe comes from the Poręba site in Poland, a recently described locality with exposures of the Zbąszynek Beds, which have a palynomorph assemblage characteristic for the mid–late Norian in the biostratigraphic schemes of the Germanic Basin. Using a synapomorphy-based approach, we evaluate several isolated dinosauriform specimens from Poręba. This assemblage includes a silesaurid, a herrerasaurid and remains of another type of theropod (potentially a neotheropod). The Poręba herrerasaurid is the first record of this rare group of primitive dinosaurs from Europe and one of the youngest records worldwide, whereas the silesaurid is the youngest record of a silesaurid from Europe. These findings indicate that silesaurids persisted alongside true dinosaurs into the mid–late Norian of Europe and that silesaurid–herrerasaurid–neotheropod assemblages (which are also known from the Norian of North America, at low latitudes) were more widespread geographically and latitudinally than previously thought. Silesaurid–herrerasaurid–neotheropod assemblages may have been a common ecological structuring of dinosaurs during their early evolution, and their widespread distribution may indicate weak palaeolatitudinal controls on early dinosaur biogeography during the latest Triassic.

Dr. Ruth L. Elder - July 22, 1954 – Nov. 4, 2014

Dr. Ruth L. (Jessie) Elder passed away earlier this month at the age of 60.  Dr. Elder is best known in the vertebrate paleontology community for her work on the Triassic vertebrate fauna from the Dockum Group near Otis Chalk, Texas. The purported rhynchosaurian Otischalkia elderae is named in her honor.

Dr. Elder's obituary can be viewed here.

Garjainia madiba, a new Erythrosuchid Archosauriform from the Early Triassic of South Africa

Gower, D. J., Hancox, P. J., Botha-Brink, J., Sennikov, A. G., and R. J. Butler. 2014. A New Species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa. PLoS ONE 9(11): e111154. doi:10.1371/journal.pone.0111154

Abstract -
A new species of the erythrosuchid archosauriform reptile Garjainia Ochev, 1958 is described on the basis of disarticulated but abundant and well-preserved cranial and postcranial material from the late Early Triassic (late Olenekian) Subzone A of the Cynognathus Assemblage Zone of the Burgersdorp Formation (Beaufort Group) of the Karoo Basin of South Africa. The new species, G. madiba, differs from its unique congener, G. prima from the late Olenekian of European
Russia, most notably in having large bony bosses on the lateral surfaces of the jugals and postorbitals. The new species also has more teeth and a proportionately longer postacetabular process of the ilium than G. prima. Analysis of G. madiba bone histology reveals thick compact cortices comprised of highly vascularized, rapidly forming fibro-lamellar bone tissue, similar to Erythrosuchus africanus from Subzone B of the Cynognathus Assemblage Zone. The most notable differences between the two taxa are the predominance of a radiating vascular network and presence of annuli in the limb bones of G. madiba. These features indicate rapid growth rates, consistent with data for many other Triassic archosauriforms, but also a high degree of developmental plasticity as growth remained flexible. The diagnoses of Garjainia and of Erythrosuchidae are addressed and revised. Garjainia madiba is the geologically oldest erythrosuchid known from the Southern Hemisphere, and demonstrates that erythrosuchids achieved a cosmopolitan biogeographical distribution by the end of the Early Triassic, within five million years of the end-Permian mass extinction event. It provides new insights into the diversity of the Subzone A vertebrate assemblage, which partially fills a major gap between classic ‘faunal’ assemblages from the older Lystrosaurus Assemblage Zone (earliest Triassic) and the younger Subzone B of the Cynognathus Assemblage Zone (early Middle Triassic).

Garjainia madiba reconstruction by Mark Witton