Ahvaytum bahndooiveche: A Sauropodomorph Dinosaur from the mid-late Carnian of Wyoming.

The Carnian (237 to 227 million years ago) is the first epoch of the Middle Triasssic, and is noted for the appearance and spread of the Dinosaurs and their close relatives, while other groups, such as the Rhynchosaurs, Dicynodonts, and Stereospondyl Amphibians, which had dominated Early and Middle Triassic assemblages, began to decline significantly. However, all known Carnian Dinosaurs to date come from the Southern Hemisphere, with the oldest known Dinosaur from the Northern Hemisphere, the Theropod Lepidus praecisio from the Otis Chalk of Texas, being at most 221 million years old.

Carnian-aged Dinosaurs are known from a number of Southern Hemisphere locations, including Brazil, Argentina, Zimbabwe, and India (today in the Northern Hemisphere, but during the Triassic in the Southern Hemisphere). All of these are from high latitude locations (i.e. they were from a long way from the equator), which has been suggested to indicate that a hostile climate probably stopped them from spreading into other areas, at least until the Carnian Pluvial episode, between 234 and 232 million years ago, during which the global climate shifted, becoming significantly more humid.

This has led palaeontologists to conclude that the first Dinosaurs appeared during the early Carnian (or possibly a little earlier) in the Southern Hemisphere. However, this hypothesis is based upon the absence of Dinosaur fossils from other areas, something which could equally be caused by poor sampling of early Carnian rocks from the Northern Hemisphere. This alternative merits serious consideration, as Carnian deposits are rare in the Northern Hemisphere, and often poorly dated. Furthermore, a number of rock formations in the Northern Hemisphere which have been dated to the early Carnian have produced trace fossils which are attributed to Dinosaurs, strongly indicating their presence in areas where body fossils have not been found.

In a paper published in the Zoological Journal of the Linnean Society on 8 January 2024, David Lovelace and Aaron Kufner of the Department of Geoscience and Geology Museum at the University of Wisconsin-Madison, Adam Fitch, also of the Geology Museum at the University of Wisconsin-Madison, Kristina Curry Rogers of the Biology and Geology departments at Macalester College, Mark Schmitz and Darin Schwartz of the Department of Geosciences at Boise State University, Amanda LeClair-Diaz and Lynette St.Clair of Fort Washakie Schools, Joshua Mann of the Eastern Shoshone Tribal Historic Preservation Office, and Reba Teran, a Shoshone Language Consultant  at Wind River Reservation, describe a Sauropodomorph Dinosaur, as  well as an indeterminate Silesaurid, from the mid-late Carnian Popo Agie Formation of Wyoming.

The Popo Agie Formation is a Carnian-aged deposit which outcrops across western Wyoming, western Colorado, and Utah. It was laid down in a series of lakes and rivers which are thought to have covered much of what is now the American Southwest at this time. Vertebrate fossils are rare in the Popo Agie Formation, though it has produced Metoposaurid Temnospondyls, Hyperodapedontine Rhynchosaurs, and Loricatan Archosaurs, and has two notable horizons with mass-death assemblages of Metoposaurid and Latiscopid Stereospondyls.

The fossils described by Lovelace et al. come from a site 1 km south of the confluence of the East Fork of the Wind River and Spear Creek called Garrett’s Surprise, in reference to its discoverer, Garrett Johnson, who found the site while working as an undergraduate field assistant on undergraduate field assistant. The discovery was surprising because the surrounding geology is dominated by the Eocene Wind River Formation, with the much older Popo Agie Formation exposed in an erosional gully. 

The Sauropodomorph Dinosaur is described from a single isolated left astragalus, with the proximal end of a left femur which shows o clear Saurischian affinities also referred to the same species. This femur fragment was found within 5 m of the original specimen, and both specimens are encrusted with a similar micritic carbonate. The new species is named Ahvaytum bahndooiveche, where 'Ahvaytum' means 'long ago' and 'bahndooiveche' means 'handsome young man', 'Salamander', or 'Dinosaur' in the Shoshone language.

Holotype left astragalus of Ahvaytum bahndooiveche. (UWGM 1975). 3D model in (A) medial, (B) lateral, (C) lateral transparent, (D) posterior transparent, (E) distal, (F) proximal, (I) anterior, and ( J) posterior orthographic views. Photographs in (G) proximal and (H) distal views. Abbreviations: amc, anteromedial corner; ap, ascending process of the astragalus; g, groove; f, foramen; ff, fibular facet; ldn, laterodistal notch (= lateroventral depression); mf, medial fossa; nf, non-articular fossa (= dorsal basin, = semi-elliptical fossa); p, platform; plp, posterolateral process; plr, posterolateral ridge; tf, tibial facet. Diagonal lines indicate broken surfaces. Arrows indicate anterior direction. Scale bar is 1 cm. Lovelace et al. (2025).

Lovelace et al. note that Western taxonomy has a history deeply rooted in colonialism, with taxa often given names that reflect geographic features, regions, or waterways named by colonizers who did not recognize or validate pre-existing Indigenous names. In recognition of this, the name 'Ahvaytum bahndooiveche' was chosen by a collaborative project involving the Fort Washakie Schools 7th grade cohort of 2022, along with educators, Eastern Shoshone Tribal Historic Preservation Office, and Tribal Elders.

A reconstruction of Ahvaytum bahndooiveche as a small Sauropodomoph Dinosaur, along with an audio-explanation of the origin of its name. Lovelace et al. (2025).

The specimens assigned to Ahvaytum bahndooiveche were recovered from the surface of the upper part of a sandstone layer within the Popo Agie known as the Purple Unit. Uranium/lead analysis of zircons from this layer have yielded ages of between 227.34 and 229.04 million years before the present, with the layer which produced Ahvaytum bahndooiveche no more than 228 million years old. This places the fossils in the early Carnian, only slightly after the Carnian Pluvial Event.  Zircon is a volcanic mineral that forms as liquid magma slowly cools to form solid rock. As zircon forms it can incorporate a variety of different elements into its crystal matrix, including uranium but not lead. This is useful as over time uranium decays to form lead, so any lead in a zircon mineral must be the result of the decay of uranium. Since the decay of uranium to lead occurs at a steady rate, it is possible to determine the age of zircons by measuring the ratio of uranium to lead within them.

Proximal end of a left femur UWGM 7549 (A)–(E) referred to Ahvaytum bahndooiveche. 3D model in (A) anteromedial, (B) posterolateral, (C) proximal, (D) anterolateral, and (E) posteromedial orthographic views. Abbreviations: alt, anterolateral tuber; amt, anteromedial tuber; ce, concave emargination; dlt, dorsolateral trochanter; ft, fossa trochanterica (= facies articularis antitrochanterica); gt, ‘greater trochanter’; pmt, posteromedial tuber; ve, ventral emargination. Arrows indicate anterior direction. Scale bar is 1 cm. Lovelace et al. (2025).

As well as the specimens assigned to Ahvaytum bahndooiveche, the Purple Unit yielded the distal end of a left humerus (UWGM 7550) and the proximal end of a right femur (UWGM 7407), which Lovelace et al. determined to belong to a Silesaurid Dinosauriform.

Photographs of Sulcimentisaurian Silesaurid elements from the Garrett’s Surprise locality. Distal end of a left humerus UWGM 7550 (A)–(E) in (A) anterior, (B) posterior, (C) medial, (D) lateral, (E) and distal views. Proximal end of a right femur UWGM 7407 (F)–(J) in (F) proximal, (G) anterolateral, (H) posteromedial, (I) posterolateral, and ( J) anteromedial views. Abbreviations: alt, anterolateral tuber; amt, anteromedial tuber; at, anterior trochanter; dlt, dorsolateral trochanter; ect, ectepicondyle; ent, entepicondyle; g, groove; gt, ‘greater trochanter;’ ipmt, incipient posteromedial tuber; n, notch; rc, radial condyle; uc, ulnar condyle. Arrows point in the anterior direction. Scale bar equals 1 cm. Lovelace et al. (2025).

Silosaurids have long been considered the sister group to the Dinosaurs. However, a number of recent phylogenetic analyses, including that of Lovelace et al. have been unable to demonstrate that they are a separate clade, less closely related to Saurischian Dinosaurs than Ornithopod Dinosaurs are. This raises the posibility that Silosaurids are Dinosaurs, either being an early diverging group of Ornithpods, a separate group more closely related to Saurischians, or a polyophyletic group, potentially including both plus some in the original Dinosaur-sister-group position (many Silosaurids are known from highly fragmentary remains, so this would not be surprising). If the Silodaurids are Dinosaurs, then they increase the age of the Dinosaurs as a group, as they are present in the Ladinian Epoch (between 241 and 237 million years ago), whereas the oldest known non-Silosaurid Dinosaur fossils all date from the Carnian. Either way, Silosaurids have previously only been known from Southern Hemisphere sights before the discovery of the Garrett's Surprise specimen.

Finally, Lovelace et al. describe a partial foot print from the upper Jelm Formation at Red Wall in Natrona County, Wyoming. This is small, roughly 8.0 x 5.6 cm, and comprises a partial hindlimb print with digits II–IV, with a very faint associated possibly forelimb trace. The pes digits are relatively straight, long, and slender with small acuminate claw impressions. Pads are observable, but not sharply defined. Lovelace et al. consider that this could be assigned to either of the ichnogenera Atreipus or Grallator. The trace is preserved on a slab which has fallen from the Red Wall (a cliff), but can confidently be sourced to a section 1-2 m thick, about 15 m beneath the top of the Jelm Formation, which stratigraphically underlies the Popo Agie Formation. 

UWGM 7435 (left) is an isolated slab containing a single tridactyl pes and possible manus impression attributed to an Atreipus–Grallator plexus tracemaker from the upper Jelm Formation, Natrona County, Wyoming, USA. (A) Digital surface-depth map (right) produced in METASHAPE (v.2.0.3; Agisoft) from surface light-scans demonstrates the depth and toe pad delineations of pes (p) digits II–IV. The manus impression may be present (m?); other than a very slight depression there are no morphological features to confidently identify it as such. Scale bar is in 1-cm increments. Lovelace et al. (2025).

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Musankwa sanyatiensis: A new species of Massopodan Sauropodomorph from the Late Triassic of Zimbabwe.

The Upper Karoo Group deposits of South Africa and Lesotho have produced numerous Late Jurassic and Early Jurassic Dinosaur fossils, contributing considerably to our understanding of the early evolution of the group. Deposits of similar ages are known from across much of Southern and East Africa, although these have been less thoroughly explored by Palaeontologists. Such deposits are present in the Kalahari Karoo Basin of Botswana (where no identifiable Vertebrate remains have been found), Waterberg-Erongo region of Namibia (from which a partial skeleton attributed to the Prosauropod Massospondylus sp. has been described), and the Mana Pools Basin of Zambia (which have yielded a single partial Sauropodomorph). 

In Zimbabwe, Upper Karoo Group sediments are found in the Tuli, Mana Pools, Cabora Bassa, and Mid-Zambezi basins, all of which have yielded Dinosaur fossils. These deposits are capped off by flood basalts, of equivalent ag to the Drakensburg Group, which can be dated to between approximately 176 and 186 million years ago, giving a minimum age to any fossils found in the deposits below. As in other areas of Southern Africa, the most abundant Dinosaurs are Protosauropods, with most specimens assigned to Massospondylus sp., although none of the Zimbabwean material has been compared in any detail to the South African type material. This means that the presence of the taxon in Zimbabwe cannot actually be confirmed, which is important as it has been used as a major piece of evidence in the comparative dating of the two areas. Other Zimbabwean Protosauropods have been assigned to Euskelosaurus (though this is now considered dubious), Vulcanodon karibaensis, and Mbiresaurus raathi, both of which are only known from Zimbabwe. A number of Early Theropod skeletons have also been described from Zimbabwe, all of which have been assigned to the Coelophysoid 'Syntarsus' rhodesiensis.

In a paper published in the journal Acta Palaeontologica Polonica on 30 May 2024, Paul Barrett of the Fossil Reptiles, Amphibians and Birds Section at the Natural History Museum, and the Evolutionary Studies Institute at the University of the Witwatersrand, Kimberley Chapelle of the Department of Anatomical Sciences at Stony Brook University, and the  Evolutionary Studies Institute at the University of the Witwatersrand, Lara Sciscio of the Jurassica Museum, Timothy Broderick of Harare, Michel Zondo of the Natural History Museum of Zimbabwe, Darlington Munyikwa of National Museums and Monuments of Zimbabwe, and Jonah Choiniere, again of the Evolutionary Studies Institute at the University of the Witwatersrand, Johannesburg, describe a new species of Sauropodomorph Dinosaur from the Pebbly Arkose Formation of Spurwing Island on Lake Kariba, Zimbabwe.

The new species is named Musankwa sanyatiensis, where 'Musankwa' is the name of the houseboat used in two expeditions to Lake Kariba in 2017-18, and means 'boy close to marriage' in the Tchitonga language of the BaTonga people, who inhabited the land flooded by Lake Kariba following the construction of the Kariba Dam, and 'sanyatiensis' means 'from Sanyati' in reference to the Sanyati River Basin, which was flooded by the formation of Lake Kariba, which Spurwing Island was once part of.

(A) Map showing the geographic setting of the Mid-Zambezi Basin in northwest Zimbabwe. (B) Position of Spurwing Island relative to the Zimbabwean (southern) shoreline of Lake Kariba. (C) Spurwing Island; arrow indicates the fossil locality at the Spurwing East Palaeosol site. (D) =Sedimentology of the Spurwing East Palaeosol site. (E) Articulated hind limb of Musankwa sanyatiensis (NHMZ 2521) as discovered in situ. (F) Evidence of bioturbation in the form of invertebrate traces (e.g., Taenidium isp. with menisci highlighted by red mudstone). (G) Associated sediments of the fossil site: pedogenically-modified fines with desiccation cracks, carbonate nodules, and colour mottling. Abbreviations: f, fine; m, medium; vf, very fine. Barrett et al. (2024).

The species is described from a single partial right hind limb, consisting of a complete femur, tibia, and astragalus, with associated indeterminate bone fragments, discovered by Paul Barret during an expedition to the southern shore of Lake Kariba in March 2018. At the time of its discovery it was weathering out of the rock, with the preserved elements still in an articulated state. The whole specimen is heavily sun-cracked and weathered, with poor surface preservation that mightreflect a long period of surface exposure prior to collection,- as well as pre-burial damage. Following collection the limb was placed in the collection of the Natural History Museum of Zimbabwe, and given the specimen number NHMZ 2521.

Right hind limb of the sauropodomorph dinosaur Musankwa sanyatiensis (NHMZ 2521) from the Pebbly Arkose Formation (Norian, Upper Triassic) of Spurwing Island, Zimbabwe. (A) Right femur in posterior (A₁), lateral (A₂), anterior (A₃), medial (A₄), proximal (A₅), and distal (A₆) views. (B) Right tibia with conjoined astragalus in anterior (B₁), lateral (B₂), posterior (B₃), medial (B₄), and proximal (B₅) views. Barret et al. (2024).

Specimen NHMZ 2521 shows no unique features not seen in other Protosaurpods, which is unsurprising given the limited nature of the material available, but does show a sufficiently unique combination of features that Barrett et al. feel comfortable in describing it as a new species and genus. A phylogenetic analysis recovered Musankwa sanyatiensis as the earliest-branching member of the Massopoda, a paraphyletic 'grade' which gave rise to the Sauropods (the Massopoda is considered paraphyletic because all members of the group are descended from a single common ancestor, but not all descendents of that ancestor are considered to be members of that group). However, Barret et al. note that the phylogeny of the Massapoda is poorly resolved, and prone to changing each time a new specimen is found, due to the fragmentary nature of many of the specimens from which species assigned to the group have been described.

Time-scaled reduced strict consensus of over 10 000 maximum parsimony phylogenetic treess with lengths of 1669 steps resulting from inclusion of Musankwa sanyatiensis. Barrett et al. (2024).

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A small-sized Sauropodomorph Dinosaur from the Early Jurassic of South Africa.

The Sauropodomorph Dinosaurs include the largest land Animals every known to have lived on Earth, with some species producing individuals which exceeded 90 tons in mass. However, they were not always this large, with the earliest known Sauropodomorphs being bipedal omnivores which lived in the Carnian (Earliest Triassic, 233-231 million years ago), and had body masses of less than 15 kg. By the Early Jurassic, the group had achieved a global distribution, and included both bipedal and quadrupedal forms, with many species exceeding 10 tons in mass. This increase in body mass is remarkable, and therefore has attracted considerable interest among scientists. The favoured explanation is that ecological circumstances created a cascade of evolutionary pressures which favoured larger Sauropodomorph species. By the Early Jurassic small (less than one ton) Sauropodomorphs are rare, although they do persist across most of the globe until the Pliensbachian (192.9-184.2 million years ago). It is possible that smaller Sauropodomorphs were at a disadvantage due to the large number of competing groups occupying this niche in the Triassic and Early Jurassic, which included Gomphodont Cynodonts, Ornithischian Dinosaurs, herbivorous Crocodyliforms, and secondarily herbivorous Theropods. However, modern Mammal-dominated ecosystems commonly host a wide range of herbivore species, which range in size from about 10 g to about 7 tons, with the largest number of different species in the smaller and middle parts of this range, which suggests that the driving pressure which created large Sauropodomorphs is unlikely to have been as simple as this model suggests.

In a paper published in the journal Royal Society Open Science on 14 June 2023, Kimberley Chapelle of the Division of Paleontology at the American Museum of Natural History, and the Evolutionary Studies Institute at the University of the Witwatersrand, Jennifer Botha, also of the Evolutionary Studies Institute, and of the Centre of Excellence in Palaeosciences at the University of the Witwatersrand, and Jonah Choiniere, again of the Evolutionary Studies Institute at the University of the Witwatersrand, describe the left humerus of an exceptionally small Sauropodomorph Dinosaur from the Early Jurassic Elliot Formation of Free State in South Africa.

The specimen, BP/1/4732, described by Chapelle et al. was collected by palaeontogist James Kitching in 1978, from an outcrop in what was then Bethlehem District in Orange Free State, and is now Thabo Mofutsanyana District in Free State Province. Its form suggests that it came from a bipedal Sauropodomorph, and sufficiently from any other described Sauropodomorph humerus to establish that it comes from a previously unknown species within the Massopoda, although the humeri of Sauropodomorphs are insufficiently distinctive to classify it further.

Left humeral morphology of BP/1/4732. (a) BP/1/4732 in anterior view. (b) BP/1/4732 in posterior view. (c) BP/1/4732 in medial view. (d) BP/1/4732 in lateral view. Abbreviations: b, boss; cuf, cuboid fossa; dpc, deltopectoral crest; entc, entepicondyle; hh, humeral head; oc, olecranon fossa; rc, radial condyle; it, internal tuberosity; uc, ulnar condyle. Chapelle et al. (2023).

A section taken through the cortex revealed large medullary cavity is surrounded by a relatively narrow, compact cortex. The cortex shows a number of lines of arrested growth, seasonal pauses in growth associated with a season which did not favour growing, such as a winter or dry season, similar to the rings seen in trees. It is not possible to estimate the age of the specimen, as the innermost portion of the cortex has been secondarily remodelled, but there are eleven tightly-packed lines in the outer part of the cortex, which is a strong indicator that growth had stopped by the time the specimen died; i.e. it was an adult. 

Sauropodomorph humerus BP/1/4732. (a) Overall transverse section showing a few trabeculae within the medullary cavity. (b) Overall cortex showing resorption cavities that extend into the mid-cortex. (c) Secondary osteons within the inner and mid-cortex. (d) Woven-parallel complex interrupted by LAGs. (e) Same as (d) in cross-polarized light. (f ) High magnification of the EFS. (g) Mid-cortical LAGs and EFS in cross-polarized light. (h) Cortex showing the EFS (bracket) in polarized light. Arrowheads indicate LAGs. Abbreviations: MC, medullary cavity; PFB, parallel-fibred bone; RC, resorption cavity; SO, secondary osteon; WPC, woven-parallel complex. Scale bars (a) 1000 µm, (b), (g), (h) 500 µm, (c)–(f) 100 µm. Chapelle et al. (2023).

The midshaft circumference of the humerus has previously been shown to be strongly tied to overall bodymass in bipedal Sauropodomorph Dinosaurs. BP/1/4732 has a humeral midshaft circumference of 66 mm, smaller than the same measurement for any other Early Jurassic bipedal Sauropodomorph, and which Chapelle et al. calculate would indicate a living Animal with a mass of about 73.35 kg. 

This makes BP/1/4732 the smallest-known post-Triassic Sauropodomorph, with the second smallest being Ngwevu intloko, another Early Jurassic Massospondan from South Africa, with a predicted mass of 107.91 kg, based upon a single specimen which, importantly, isn't considered to have been fully grown at the time of death. BP/1/4732 therefore significantly increases the known size range of Early Jurassic Sauropodomorphs, with sizes now ranging from tens of kilograms to tens of tons. Notably, this is less than the size range of modern Mammals, a group which includes many species with masses below 10 kg, although some non-Sauropodomorph Dinosaurs from the period, such as the Ornithischians Heterodontosaurus tucki and Lesothosaurus diagnosticus did weigh less than 10 kg.

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Tuebingosaurus maierfritzorum: A new species of Massopodan Sauropodomorph Dinosaur from the Palaeontological Collection of the University of Tübingen.

The Palaeontological Collection of the University of Tübingen contains one of the largest assemblages of Sauropodomorph Dinosaurs in Europe, but also one of the least studied. Much of this material was collected from sites around Tübingen, Aixheim and Löwenstein in the nineteenth and early twentieth centuries and classified under the genus Plateosaurus. 

The genus Plateosaurus was once used to classify almost all non-Sauropod Sauropodomorph Dinosaurs, and by the mid twentieth century contained over 20 species, of which only four are considered valid today. Unfortunately, while it is now recognised that the non-Sauropod Sauropodomorph Dinosaurs are a more diverse group than once understood, and that understanding this diversity is the key to understanding the emergence of the true Sauropods, one of the most remarkable groups of organisms ever to appear on Earth, several rival schemes for the classification of this group have appeared, hampering this understanding.

In a paper published in the journal Vertebrate Zoology on 8 September 2022, Omar Rafael Regalado Fernández of the Fachbereich Geowissenschaften an der Universität Tübingen, and Ingmar Werneburg, also of the Fachbereich Geowissenschaften an der Universität Tübingen, and of the Senckenberg Centre for Human Evolution and Palaeoenvironment an der Universität Tübingen, describe a new species of Sauropodomorph Dinosaur from the Palaeontological Collection of the University of Tübingen, based upon a specimen, GPIT-PV-30787, collected from Lower Dinosaur Bed at Obere Mühle in 1932.

The complex nature of Sauropodomorph Dinosaur taxonomy meant that Regalado Fernández and Werneburg were obliged to carry out multiple phylogenetic analyses in order to try to accommodate specimen GPIT-PV-30787 into the competing phylogenies for the group. Fortunately, these produced reasonably consistent results, with the specimen being found to be closely related to Schleitheimia schutzi, making it a Massopodan Sauropodomorph, close to the origin of the true Sauropods.

Based upon this information, Regalado Fernández and Werneburg describe specimen GPIT-PV-30787 as the holotype of a new species, giving it the name Tuebingosaurus maierfritzorum, where 'Tuebingosaurus' refers to Tübingen and 'maierfritzorum' honours Wolfgang Maier, professor of evolutionary zoology in Tübingen from 1987 to 2007, and Uwe Fritz, former editor-in-chief of the journal Vertebrate Zoology.

Specimen GPIT-PV-30787 comprises a complete pelvis (three sacral vertebrae, two ilia, two pubes, two ischia), five anterior caudal vertebrae, four chevrons, left femur, left tibia, left and right fibulae, left astragalus, left calcaneum, metatarsal I, and pedal fingers 3 and 4.

Reconstruction of Tuebingosaurus maierfritzorum, as a quadruped Dinosaur, using the outline of Riojasaurus as a base, next to the silhouette of Friedrich von Huene. The drawing of the bones is based on and modified from the original illustrations of specimen 'GPIT IV' (the name originally ascribed to GPIT-PV-30787) by von Huene. The right fibula is marked in grey as it was found nearby with similar measurements to the left fibula and has been assumed to be part of the same individual. Regalado Fernández & Werneburg (2022).

Regalado Fernández and Werneburg's phylogeny suggests that Tuebingosaurus maierfritzorum is a Massopodan, making it the earliest member of the group known from the Upper Triassic Trossingen Beds. Despite this taxonomic placement, Tuebingosaurus maierfritzorum still shares a number of features more generally associated with Plateosaurian Sauropodomorphs, most notably a heel-like projection in the posterior part of the ischiadic peduncle of the ilium and a straight lateral margin in metatarsal II, features which led to the assumption that this was a specimen of Plateosaurus. 

This presence of Plateosaurian-like features in early Massopodan Dinosaurs is unlikely to be unique to Tuebingosaurus maierfritzorum, and re-examination of other historic specimens at Tübingen and other palaeontological collections may provide more examples, helping to unravel the origins of the Sauropods.

Reconstruction of the last moments in the life of Tuebingosaurus maierfritzorum (collection number of the painting: GPIT-PV-41827). The cortical bone on the left side of the fossil is fractured into flakes, which can be explained if the carcass was exposed over a long time on the mud, two to four years, before being buried – in the reconstruction, the Animal will fall to its right body side. The reconstruction shows the animal sinking in a mud trap, attacked by a Rauisuchian, Teratosaurus, which has also been found in the Trossingen Formation in Baden-Württemberg. In the background, a herd of Plateosaurus trossingensis runs away from the scene. The flora in the swamp is reconstructed based on fossils from the Germanic basin, with shoots of Horsetails and Ferns covering the swamp and a forest comprising Cycads (Taeniopteris), Lycophytes (Lepacyclotes) and Coniferous Plants (Brachyphyllum). Regalado Fernández & Werneburg (2022).

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Sauropodomorph Dinosaur eggs from the Early Jurassic of South Africa, China, and Argentina.

The Amniotes, Vertebrate animals in which the egg and developing embryo are contained within a watertight membrane (the amnion), and which are therefore capable of laying their eggs out of water, first appeared during the Carboniferous Period, around 312 million years ago. However, while the adult forms of these animals are numerous in the fossil record from the Permian onwards, their eggs no not become numerous as fossils until the Middle Jurassic, from which point forward numerous eggs of Crocodiles, Birds, non-Avian Dinosaurs, Pterosaurs, Lizards, and Turtles, are known. The earliest known Amniote eggs date from the Early Jurassic Sinemurian Epoch (195-192 million years ago), when the eggs of three different Sauropodomorph Dinosaur species are known, from South Africa, China, and Argentina, though only one of these has previously been formally described, due to the poor preservation of many of the specimens.

In a paper published in the journal Scientific Reports on 14 March 2019, Koen Stein of Earth System Science at the Vrije Universiteit Brussel, and the Directorate of Earth and History of Life at the Royal Belgian Institute of Natural Sciences, Edina Prondvai of Evolutionary Morphology of Vertebrates at Ghent University, and the Lendület Dinosaur Research Group at Eötvös Loránd University, Timothy Huang of the International Center of Future Science, and Dinosaur Evolution Research Center at Jilin University, and the National Chung Hsing University, Jean-Marc Baele of the Department of Geology and Applied Geology at the University of Mons, Martin Sander of the Steinmann Institute of Geology, Mineralogy, and Paleontology at the University of Bonn, and the Natural History Museum of Los Angeles County, and Robert Reisz, also of the International Center of Future Science, and Dinosaur Evolution Research Center at Jilin University, the National Chung Hsing University, and the Department of Biology at the University of Toronto Mississauga, provide descriptions of all three Sinemurian Sauropodomorph egg types, and discuss the implications of these for our wider understanding of egg evolution in Dinosaurs.

The eggs of Lufengosaurus are found in the Lufeng Formation of Yunnan Province; these have been briefly described previously as part of a study of the neonate Dinosaurs found within them. The calcareous layer of shells of Lufengosaurus are extremely thin, ranging from 60-90 μm in thickness, and made up of wedge-and-crown shaped units similar to those seen in the eggs of modern Crocodiles. These units are radial in nature and made of calcite, with interlocking crystals, and are imbedded in a phosphorous-rich fibrous layer thought to represent the original eggshell membrane. This is topped by an even thinner (about 10 μm) crystalline phosphatic layer, which has a scalloped appearance, with low pits and ridges that do not appear to directly corelate with the borders of the units in the calcareous layer. These irregularities may relate to the ornamentation seen in later Dinosaur eggs, but they are so small in scale as to make them effectively invisible to the naked eye, making their purpose unclear. Pores in the eggshell are hard to define, they appear to be quite sparse in distribution, but their actual density could not be established.

(a) Section through nugget containing numerous Lufengosaurus eggshell fragments (plane polarized light). (b), close-up (plane polarized light) of a Lufengosaurus eggshell fragment, showing calcite crystals of the mammillary layer radiating from an organic core embedded in the eggshell membrane. (c) As in (b) under cross polarized light, highlighting the calcite crystals of a mammillary cone. (d) Different cross polarized light view with lambda waveplate. (e) Line drawing of (d). (f) Lufengosaurus cathodoluminescence view with 880 nm filter. Scale bars, (a) 1 mm, (b)–(f) 50 μm Abbreviations: cl, calcareous layer; em, eggshell membrane; ps, pore space; su, shell unit. Stein et al. (2019). 

Eggs attributed to the Sauropodomorph Dinosaur Massospondylus are known from a number of locations in South Africa. These eggs have a slightly thicker shell than those of Lufengosaurus, in the range of 80-100 μm, but have a similar structure, with radially arranged calcite crystals arising from a phosphorous rich membrane, and an outer layer which is rugged with tubercles and depressions. Pores are again sparse.

(i) Massospondylus eggshell fragment (ppl), showing wedges in the calcareous layer, and a homogenous eggshell membrane. (j), Line drawing of (i). (k) Massospondylus cathodoluminescence view with 880 nm filter. Scale bars, (i), (j) 100 μm, (k) 50 μm. Abbreviations: cl, calcareous layer; em, eggshell membrane. Stein et al. (2019).

Shells assigned to the Sauropodomorph Mussaurus are known from the Laguna Colorada Formation of Argentina, again associated with embryo material but never before formally described. These shells are not well preserved, but the one examined appeared to follow the same pattern as the other two species, with a thick (150-180 μm) phosphatic layer interpreted as a membrane, with sparse preserved calcite crystals apparently radiating from growth points.

(g) Mussaurus eggshell, showing thick eggshell membrane, and distorted calcareous layer. (h) Line drawing of (g). Scale bars 100 μm. Abbreviations: cw, crystal wedges of calcareous layer; em, eggshell membrane. Stein et al. (2019). 

Fragments of all three Sauropodomorph egg types retain their curvature, suggesting that the shells had a rigid structure, though all three have very thin mineralised shells. This contrasts with later Dinosaur eggs, which are widespread from the Middle Jurassic onwards, which all have thicker shells (as do modern Birds). This is particularly curious as the later eggs come from a wide variety of Dinosaur species, including Theropods, Ornithischians, and Sauropods (which were presumably more closely related to the Early Jurassic Sauropodomorphs than they were to the other two groups). However, beyond the differences in thickness, all these Dinosaur eggs are essentially similar in structure, with shells made up of interlocking calcite crystals which radiate from points of growth on the underlying membrane.

Eggshell membrane and porosity in Massospondylus eggs. (a) Nest of Massospondylus eggs with preserved embryos. Note the presence of numerous cracks in the eggs, likely caused by postmortem crushing of the thin but hard eggshell. Eggshell membrane is exposed in egg number 4, just beneath the skull, and in egg number 7, just beneath the right scapula. (b) CT scan of a complete egg in a, showing the eggshell (es) and the detached preserved eggshell membrane (em). (c) Outer surface SEM image of a Massospondylus eggshell fragment showing rare small and irregularly shaped pores occurring in random patterns (red arrows). (d) Enlarged view of boxed area in (c). Stein et al. (2019).

Mineralised Crocodile eggs also become widespread in the Middle Jurassic; these are similar in nature to Dinosaur eggs in their mineralogy, but their structure is somewhat different, which suggests they may have a common mineralised ancestry, but that it was long before the appearance of their eggs in the fossil record. Turtle eggs appear at about the same time, but are aragonitic in structure, and Turtles are generally thought to have evolved mineralised eggs separately.

Since strongly mineralised eggs have a good preservational potential, Stein et al. suggest that the absence of such eggs in the fossil record before the Middle Jurassic probably suggests that they were not being produced. This raises the question of why several different Archosauromorph lineages should suddenly start to produce mineralised eggs in a very short period, all over the world. Stein et al. reason that mineralised eggs have a structural and protective benefit that would have been just as useful before the Middle Jurassic as it was after, and that therefore some ecological constraint must have prevented them from doing so up until this point.

Reconstruction of a basal Sauropodomorph egg showing detail of the eggshell. Eggshell units (esu) form the calcareous layer (cl) and are embedded with organic cores in the eggshell membrane (em). Stein et al. (2019).

Stein et al. theorise that the most likely explanation for this may have been atmospheric oxygen levels. The Earth’s atmosphere is thought to have contained about 32-33% oxygen during the Carboniferous, with oxygen levels falling steadily during the Permian and Triassic, eventually falling to around 15% in the Early Jurassic, then rising to around 20% in the Middle Jurassic, a level which has remained more-or-less constant till today. Modern Archosaurs are known to produce weakly mineralised eggs if they are suffering from oxygen starvation, which suggests that high levels of oxygen are needed for mineralised egg production, with the possibility that oxygen levels in the Triassic and Early Jurassic were too low for mineralised egg production, but that once sufficient oxygen became available, multiple Archosauromorph lineages quickly developed the ability to produce such eggs.

Ancestral state reconstruction of calcareous layer thickness to egg mass ratios. Note that the root was set to represent the hypothesized ancestral flexible shelled condition. Nodes represent (a), Archosauromorpha, (b), Archosauria (c), Ornithodira, (d), Dinosauria, (e), Birds. Note the independent acquisitions of thick eggshell in Choristoderes (represented by Hyphalosaurus), Chelonians, Crocodiles, Pterosaurs and several Dinosaur clades, as well as reversals in Chelonians. From the Sinemurian (199 million years ago) onwards, eggshells (e.g. Testudoflexoolithus and Lourinhanosaurus) show a significant calcareous layer thickness increase corresponding with atmospheric oxygen increase. Stein et al. (2019).

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