[PaleoMammalogy • 2024] Dianoconodon youngi • Fossils document Evolutionary Changes of jaw joint to mammalian middle ear

 

Dianoconodon youngi 

Mao, C. Zhang, Ren, T. Wang, G. Wang, F. Zhang, Rich, Vickers-Rich & Meng, 2024

DOI: doi.org/10.1038/s41586-024-07235-0  

 Researchgate.net/publication/379540254

Reconstruction by Chuang Zhao

Abstract

The dual jaw joint of Morganucodon consists of the dentary–squamosal joint laterally and the articular–quadrate one medially. The articular–quadrate joint and its associated post-dentary bones constitute the precursor of the mammalian middle ear. Fossils documenting the transition from such a precursor to the mammalian middle ear are poor, resulting in inconsistent interpretations of this hallmark apparatus in the earliest stage of mammaliaform evolution. Here we report mandibular middle ears from two Jurassic mammaliaforms: a new morganucodontan-like species and a pseudotribosphenic shuotheriid species. The morganucodontan-like species shows many previously unknown post-dentary bone morphologies and exhibits features that suggest a loss of load-bearing function in its articular–quadrate joint. The middle ear of the shuotheriid approaches the mammalian condition in that it has features that are suitable for an exclusively auditory function, although the post-dentary bones are still attached to the dentary. With size reduction of the jaw-joint bones, the quadrate shifts medially at different degrees in relation to the articular in the two mammaliaforms. These changes provide evidence of a gradual loss of load-bearing function in the articular–quadrate jaw joint—a prerequisite for the detachment of the post-dentary bones from the dentary and the eventual breakdown of the Meckel’s cartilage during the evolution of mammaliaforms.

Reconstruction of the newly described species Dianoconodon youngi.

illustration by Chuang Zhao 

Mammaliaformes Rowe, 1988

Dianoconodon youngi gen. et. sp. nov.

Holotype. A complete skull with associated dentitions and partialpostcranial skeleton (IVPP V4257, Institute of Vertebrate Paleontologyand Paleoanthropology, Chinese Academy of Sciences, Beijing) (Figs. 1and 2; Methods and Extended Data Figs. 1–6).

Etymology. Dian, the short form (Chinese phonetic Pinyin) of Yunnan Province, where the Lufeng fossil site is located; konos, Greek ‘cone’ or ‘cusp’; odon, Greek ‘tooth’. The specific name honours C. C. Young, who initiated the study of mammaliamorphs in Lufeng.  

Mandibular middle ears and transformation of the articular-quadrate joints in mammaliaforms. 

Fangyuan Mao, Chi Zhang, Jicheng Ren, Tao Wang, Guofu Wang, Fakui Zhang, Thomas Rich, Patricia Vickers-Rich and Jin Meng. 2024. Fossils document Evolutionary Changes of jaw joint to mammalian middle ear. Nature. DOI: doi.org/10.1038/s41586-024-07235-0 [03 April 2024]

 Researchgate.net/publication/379540254_Fossils_document_evolutionary_changes_of_jaw_joint_to_mammalian_middle_ear

 

[PaleoMammalogy • 2024] Feredocodon chowi • Jurassic shuotheriids show earliest dental diversification of mammaliaforms

 Feredocodon chowi

Mao, Li, Wang, Zhang, Rich, Vickers-Rich & Meng, 2024

 DOI: doi.org/10.1038/s41586-024-07235-0 

  Researchgate.net/publication/379540347

illustration by Chuang Zhao

Abstract

Shuotheriids are Jurassic mammaliaforms that possess pseudotribosphenic teeth in which a pseudotalonid is anterior to the trigonid in the lower molar, contrasting with the tribosphenic pattern of therian mammals (placentals, marsupials and kin) in which the talonid is posterior to the trigonid. The origin of the pseudotribosphenic teeth remains unclear, obscuring our perception of shuotheriid affinities and the early evolution of mammaliaforms. Here we report a new Jurassic shuotheriid represented by two skeletal specimens. Their complete pseudotribosphenic dentitions allow reidentification of dental structures using serial homology and the tooth occlusal relationship. Contrary to the conventional view, our findings show that dental structures of shuotheriids can be homologized to those of docodontans and partly support homologous statements for some dental structures between docodontans and other mammaliaforms. The phylogenetic analysis based on new evidence removes shuotheriids from the tribosphenic ausktribosphenids (including monotremes) and clusters them with docodontans to form a new clade, Docodontiformes, that is characterized by pseudotribosphenic features. In the phylogeny, docodontiforms and ‘holotherians’ (Kuehneotherium, monotremes and therians) evolve independently from a Morganucodon-like ancestor with triconodont molars by labio-lingual widening their posterior teeth for more efficient food processing. The pseudotribosphenic pattern passed a cusp semitriangulation stage, whereas the tribosphenic pattern and its precursor went through a stage of cusp triangulation. The two different processes resulted in complex tooth structures and occlusal patterns that elucidate the earliest diversification of mammaliaforms.

 Feredocodon chowi 

illustration by Chuang Zhao

Mammaliaformes Rowe, 1988

Shuotheridia Chow and Rich, 1982

 Feredocodon chowi

 

Fangyuan Mao, Zhiyu Li, Zhili Wang, Chi Zhang, Thomas Rich, Patricia Vickers-Rich and Jin Meng. 2024. Jurassic shuotheriids show earliest dental diversification of mammaliaforms. Nature. 628; 569–575. DOI: doi.org/10.1038/s41586-024-07235-0 [03 April 2024] 

  Researchgate.net/publication/379540347_Jurassic_shuotheriids_show_earliest_dental_diversification_of_mammaliaforms

 

[PaleoMammalogy • 2026] Megacauda sungei • A Jurassic mammaliaform swimmer and transformation of the mammalian pharynx

 Megacauda sungei 

Y. Li, P. Li, Neander, Zhang, Zhou, Martin & Luo, 2026 

 

DOI: doi.org/10.1038/s41586-026-11107-0 

Abstract

The discovery of a well-preserved mammaliaform fossil from the Middle Jurassic period of China reveals evidence on the evolutionary transformation of the feeding apparatus and the ecological diversity of Mesozoic era mammals. Mammaliaforms are evolutionary predecessors to modern Mammalia, and their morphologies provide primary insights into the evolutionary origin of mammals. The rare preservation of a therian-like pharyngeal vault (throat passage) and hyoid skeletal anatomy (throat bones) in this mammaliaform suggests that critical soft-tissue anatomy for therian-like swallowing, drinking and suckling behaviours had evolved in the common ancestors of Docodonta and Mammalia, long before the rise of modern mammals. This fossil exhibits a wealth of features specialized for swimming, filling in a major gap of anatomical knowledge of pelvis and hindlimb for early mammals. It is characterized by highly distinctive canines and pseudo-carnassial sectorial teeth for a faunivorous diet. We interpret that this mammaliaform was semiaquatic, swimming and foraging in water, with a lifestyle analogous to the extant platypus. This species is the largest of Jurassic mammaliaforms. It expands the body size range of docodontans, and adds to a growing body of evidence that multiple docodontans exploited diverse niches with semiaquatic and other ecomorphotypes. Docodontans are an early example of replicated evolution of the semiaquatic and other ecomorphotypes in the Mesozoic ecosystem dominated by dinosaurs, long before the diversification of extant mammals.

Holotype main-part of Megacauda sungei (Docodonta, Mammaliaformes) (PMOL–AM00026A).

Megacauda sungei

Y. Li, P. Li, A. I. Neander, H. Zhang, C.-F. Zhou, T. Martin and Z.-X. Luo. 2026. A Jurassic mammaliaform swimmer and transformation of the mammalian pharynx. Nature. DOI: doi.org/10.1038/s41586-026-11107-0 [07 October 2026]

https://news.uchicago.edu/story/uchicago-scientists-reveal-jurassic-otter-could-chew-and-swallow-modern-mammals 

  

 

[Paleontology • 2026] Craniomandibular osteology of Dinodontosaurus isiyavamanda sp. nov. (Therapsida: Anomodontia) from the Manda Beds of Tanzania and new support for a younger age for the alleged oldest dinosaurs

 

Dinodontosaurus isiyavamanda

George, Escobar, Moody, Saanane, Day & Larkin, 2026

DOI: doi.org/10.1080/02724634.2026.2692542

Life reconstruction by Gabriel Ugueto

 

ABSTRACT 

Fossils from the Manda Beds of Tanzania have greatly informed on the diversity and evolution of Triassic tetrapods, including on what might be the oldest dinosaurs. Here, a new dicynodont taxon from the Manda Beds is described. It lacks key anatomical traits of known dicynodonts from the Manda Beds, as well as the Sino-African genus Shansiodon to which some of this material was previously referred. The new taxon is referred to the otherwise South American Dinodontosaurus based on the diagnostic presence of frontals with “tab-like” anterior processes and a combination of other traits seen in the genus. This Tanzanian material possesses a predominantly bulbous posterior/median palatal ridge of the premaxilla and a midline groove along the temporal bar, among other traits that are absent in the South American Dinodontosaurus material, indicating it represents a distinct species, here named Dinodontosaurus isiyavamanda sp. nov. Phylogenetic analyses conducted with Bayesian estimation and parsimony support the inclusion of this species in Dinodontosaurus. The unique palate of D. isiyavamanda is hypothesized to be related to resource partitioning, representing different adaptations for food processing than coeval dicynodonts. The presence of Dinodontosaurus suggests the mid-to-upper Lifua Member of the Manda Beds is equivalent to the Dinodontosaurus Assemblage Zone of Brazil and the Chañares Formation of Argentina. Consequently, the mid-to-upper Lifua Member, which includes what are possibly the oldest records of dinosaurs globally, can be confidently interpreted as late Ladinian to Carnian in age, supporting recent research questioning its equivalency with the Cynognathus Assemblage Zone of South Africa.

SYSTEMATIC PALEONTOLOGY

SYNAPSIDA Osborn, 1903

THERAPSIDA Broom, 1905

ANOMODONTIA Owen, 1860

DICYNODONTIA Owen, 1859

DICYNODONTOIDEA Olson, 1944

KANNEMEYERIIFORMES Maisch, 2001

DINODONTOSAURUS Romer, 1943

Diodontosaurus Tupí-Caldas, 1936 [nomen suppressum].

Chanaria Cox, 1968.

Type Species––Dinodontosaurus oliveirai Romer, 1943 (=Dicynodon tener Huene, 1935).

Diagnosis––Medium- to large-sized kannemeyeriiform (maximum skull length ca. 40 cm) with the following unique combination of character states: frontals with a “tab-like” median anterior process; postorbital bone with elongate, curved suborbital process; elongate caniniform process sharply offset from zygomatic arch; and hypertrophied tusks present in large individuals (taken from Kammerer & Ordoñez, 2021).

DINODONTOSAURUS ISIYAVAMANDA sp. nov.

Ruhuhuungualasaurus croucheri Larkin, 1994, p. 2.

Shansiodon sp. Surkov and Benton, 2004, p. 627.

Shansiodon sp. Surkov and Benton, 2008, p. 1126.

Diagnosis––Can be distinguished from both Dinodontosaurus brevirostris and Dinodontosaurus tener by a premaxillary posterior/median palatal ridge that expands anteriorly into a wide, bulbous morphology (does not retain the ridge-like morphology throughout its length), and extends further anteriorly than the point of eruption of the tusks; a midline groove extending along the temporal bar from immediately posterior to the pineal foramen to the posterior end of the postparietal; and mandibular rami that diverge more laterally. Can be further distinguished from Dinodontosaurus brevirostris by the lack of a ridge along the anterior surface of the mandibular symphysis. Can be further distinguished from Dinodontosaurus tener by a wider interorbital region and snout, and a pineal foramen that is not completely anterior to the intertemporal bar (i.e., pineal foramen is at the same anteroposterior level as the anterior portion of the bar).

Etymology––From the Manda words ‘isi ya vamanda’ that translate to ‘country of the Wamanda.’ In reference to the Wamanda people, many of whom were crucial to the discovery of the holotype, but whose individual names were not documented and never credited.

two bulky Dinodontosaurus isiyavamanda walking through dense vegetation 

Life reconstruction by Gabriel Ugueto

Hady George, Juan A. Escobar, Edmund R.R. Moody, Charles B. Saanane, Michael O. Day and Nigel R. Larkin. 2026. Craniomandibular osteology of Dinodontosaurus isiyavamanda sp. nov. (Therapsida: Anomodontia) from the Manda Beds of Tanzania and new support for a younger age for the alleged oldest dinosaurs. Journal of Vertebrate Paleontology. e2692542. DOI: doi.org/10.1080/02724634.2026.2692542 [15 Sep 2026]

 

[Paleontology • 2024] Early–middle Permian Mediterranean gorgonopsian suggests an equatorial origin of therapsids

a gorgonopsian from the island of Mallorca, western Mediterranean

in Matamales-Andreu, Kammerer, Angielczyk, Simões, Mujal, Galobart et Fortuny, 2024.  

DOI: doi.org/10.1038/s41467-024-54425-5  

Reconstruction by Henry Sutherland Sharpe

Abstract

Therapsids were a dominant component of middle–late Permian terrestrial ecosystems worldwide, eventually giving rise to mammals during the early Mesozoic. However, little is currently known about the time and place of origin of Therapsida. Here we describe a definitive therapsid from the lower–?middle Permian palaeotropics, a partial skeleton of a gorgonopsian from the island of Mallorca, western Mediterranean. This specimen represents, to our knowledge, the oldest gorgonopsian record worldwide, and possibly the oldest known therapsid. Using emerging relaxed clock models, we provide a quantitative timeline for the origin and early diversification of therapsids, indicating a long ghost lineage leading to the evolutionary radiation of all major therapsid clades within less than 10 Myr, in the aftermath of Olson’s Extinction. Our findings place this unambiguous early therapsid in an ancient summer wet biome of equatorial Pangaea, thus suggesting that the group originated in tropical rather than temperate regions.

Systematic palaeontology

Synapsida Osborn, 190313

Therapsida Broom, 190514

Gorgonopsia Seeley, 189415

Gorgonopsia indet.

Most relevant elements of DA21/17-01-01 and silhouette showing their positions

 Life reconstruction of the gorgonopsian from Mallorca in a floodplain setting.

Reconstruction by Henry Sutherland Sharpe

 Rafel Matamales-Andreu, Christian F. Kammerer, Kenneth D. Angielczyk, Tiago R. Simões, Eudald Mujal, Àngel Galobart and Josep Fortuny. 2024. Early–middle Permian Mediterranean gorgonopsian suggests an equatorial origin of therapsids. Nature Communications. 15: 10346. DOI: doi.org/10.1038/s41467-024-54425-5  

[Paleontology • 2024] Jurassic Fossil Juvenile reveals prolonged Life History in early Mammals

in Panciroli, Benson, Fernandez, Fraser, Humpage, Luo, Newham et Walsh, 2024.

DOI: 10.1038/s41586-024-07733-1 

 x.com/gsciencelady

Abstract

Living mammal groups exhibit rapid juvenile growth with a cessation of growth in adulthood. Understanding the emergence of this pattern in the earliest mammaliaforms (mammals and their closest extinct relatives) is hindered by a paucity of fossils representing juvenile individuals. We report exceptionally complete juvenile and adult specimens of the Middle Jurassic docodontan Krusatodon, providing anatomical data and insights into the life history of early diverging mammaliaforms. We used synchrotron X-ray micro-computed tomography imaging of cementum growth increments in the teeth to provide evidence of pace of life in a Mesozoic mammaliaform. The adult was about 7 years and the juvenile 7 to 24 months of age at death and in the process of replacing its deciduous dentition with its final, adult generation. When analysed against a dataset of life history parameters for extant mammals5, the relative sequence of adult tooth eruption was already established in Krusatodon and in the range observed in extant mammals but this development was prolonged, taking place during a longer period as part of a significantly longer maximum lifespan than extant mammals of comparable adult body mass (156 g or less). Our findings suggest that early diverging mammaliaforms did not experience the same life histories as extant small-bodied mammals and the fundamental shift to faster growth over a shorter lifespan may not have taken place in mammaliaforms until during or after the Middle Jurassic.

Krusatodon 

 

Elsa Panciroli, Roger B. J. Benson, Vincent Fernandez, Nicholas C. Fraser, Matt Humpage, Zhe-Xi Luo, Elis Newham and Stig Walsh. 2024. Jurassic Fossil Juvenile reveals prolonged Life History in early Mammals. Nature. DOI: doi.org/10.1038/s41586-024-07733-1

  x.com/gsciencelady/status/1816127777407385636

[Paleontology • 2024] Riojanodon nenoi • A New early-diverging probainognathian cynodont and A Revision of the Occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the Faunistic Composition of the latest Middle–?earliest Late Triassic Tarjadia Assemblage Zone

Riojanodon nenoi

 Martinelli, Ezcurra, Fiorelli, Escobar, Hechenleitner, von Baczko, Taborda & Desojo, 2024

 DOI: 10.1002/ar.25388  

twitter.com/AnatRecord

 

Abstract

The Chañares Formation (Ischigualasto-Villa Unión Basin) is worldwide known by its exquisitely preserved fossil record of latest Middle-to-early Late Triassic tetrapods, including erpetosuchids, “rauisuchians,” proterochampsids, gracilisuchids, dinosauromorphs, pterosauromorphs, kannemeyeriiform dicynodonts, and traversodontid, chiniquodontid and probainognathid cynodonts, coming from the Tarjadia (bottom) and Massetognathus-Chanaresuchus (top) Assemblage Zones of its lower member. Regarding cynodonts, most of its profuse knowledge comes from the traditional layers discovered by Alfred Romer and his team in the 1960s that are now enclosed in the Massetognathus-Chanaresuchus Assemblage Zone (AZ). In this contribution we focus our study on the probainognathian cynodonts discovered in levels of the Tarjadia Assemblage Zone. We describe a new chiniquodontid cynodont with transversely broad postcanine teeth (Riojanodon nenoi gen. et sp. nov.) which is related to the genus Aleodon. In addition, the specimen CRILAR-Pv 567 previously referred to cf. Aleodon is here described, compared, and included in a phylogenetic analysis. It is considered as an indeterminate Aleodontinae nov., a clade here proposed to included chiniquodontids with transversely broad upper and lower postcanines, by having a cuspidated sectorial labial margin and a lingual platform that is twice broader than a lingual cingulum. Cromptodon mamiferoides, from the Cerro de Las Cabras Formation (Cuyo Basin), was also included in the phylogenetic analysis and recovered as an Aleodontinae. The new cynodont and the record of Aleodontinae indet. reinforce the faunal differentiation between the Tarjadia and Massetognathus-Chanaresuchus Assemblage Zones, in the lower member of the Chañares Formation, and inform on the diverse chiniquodontid clade with both sectorial and transversely broad postcanine teeth.

Keywords: Chiniquodontidae, Cynodontia, Probainognathia, South America, taxonomy

 

Riojanodon nenoi gen. et sp. nov.

 

Agustín G. Martinelli, Martín D. Ezcurra, Lucas E. Fiorelli, Juan Escobar, E. Martín Hechenleitner, M. Belén von Baczko, Jeremías R. A. Taborda and Julia B. Desojo. 2024. A New early-diverging probainognathian cynodont and A Revision of the Occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the Faunistic Composition of the latest Middle–?earliest Late Triassic Tarjadia Assemblage Zone. The Anatomical Record.  DOI: 10.1002/ar.25388

  twitter.com/AnatRecord/status/1752663017978814877

[Paleontology • 2024] Paratraversodon franciscaensis • Skull Anatomy and Paleoneurology of A New traversodontid (Therapsida: Cynodontia) from the Middle-Late Triassic of Brazil

 

 Paratraversodon franciscaensis

Kerber, Roese-Miron, Medina, da Roberto-da-Silva, Cabreira & Pretto, 2024

DOI: 10.1002/ar.25385

 

Abstract

Traversodontidae, a clade of gomphodont cynodonts, thrived during the Middle and Late Triassic, displaying a wide geographical distribution. During fieldwork in 2009, a new specimen was discovered in Ladinian/early Carnian stratigraphic layers in southern Brazil. Here, we describe this specimen and propose a new taxon closely related to Traversodon stahleckeri (Traversodontinae) but displaying a unique combination of traits (e.g., presence of a poorly developed suborbital process, mesiodistal length of the paracanine fossa similar to the length of the canine, short diastema between the fourth incisor and the upper canine, and coronoid process not entirely covering the distalmost lower postcanine). Furthermore, the endocranial anatomy of the new taxon was examined. The reconstruction of the cranial endocast revealed paleoneurological features consistent with non-Gomphodontosuchinae traversodontids. These features include the presence of a pineal body (but the absence of an open parietal foramen). These recent findings contribute significantly to our understanding of the evolutionary history and cranial anatomy of Middle-Late Triassic traversodontids, shedding light on the diversity and adaptations of non-mammaliaform cynodonts.

Keywords: Dinodontosaurus Assemblage Zone, Ladinian/Carnian, phylogeny, Traversodontidae

 Paratraversodon franciscaensis

Leonardo Kerber, Lívia Roese-Miron, Thais G. M. Medina, Lúcio da Roberto-da-Silva, Sérgio F. Cabreira and Flávio A. Pretto. 2024. Skull Anatomy and Paleoneurology of A New traversodontid from the Middle-Late Triassic of Brazil. The Anatomical Record. DOI: 10.1002/ar.25385

[Paleontology • 2023] Santagnathus mariensis • Old Fossil findings in the Upper Triassic Rocks of southern Brazil improve Diversity of traversodontid Cynodonts (Therapsida: Cynodontia)

 Santagnathus mariensis

Schmitt, Martinelli, Kaiuca, Schultz & Soares, 2023

DOI: 10.1002/ar.25244 

 twitter.com/mauriciosaurus 

Abstract

In this contribution we describe a new genus and species of gomphodontosuchine cynodont from the Late Triassic Hyperodapedon Assemblage Zone (AZ) of the Santa Maria Supersequence of southern Brazil, based on material collected 20 years ago. The new taxon, Santagnathus mariensis gen. et sp. nov., is based on numerous cranial and postcranial remains, which altogether provide data on several parts of the skeleton. Santagnathus mariensis is closely related to Siriusgnathus niemeyerorum and Exaeretodon spp. and expands the knowledge about gomphodontosuchine cynodonts. Morphologically, the new species has a skull bauplan particularly similar to S. niemeyerorum and E. riograndensis, differing from them by a unique combination of traits such as three upper incisors, the absence of a descending process in the jugal, a more posterior position of the postorbital bar and a preorbital region larger than the temporal one. The new traversodontid was found associated with the rhynchosaur Hyperodapedon sp., corroborating the assignment of the cynodont fossils to the Hyperodapedon AZ. We also provide comments on the status of the Argentine traversodontid cynodont Proexaeretodon vincei, typically considered a junior synonym of Exaeretodon argentinus, and here accepted as a valid taxon.

Keywords: Eucynodontia, Late Triassic, Santa Maria Supersequence, Traversodontidae

 Santagnathus mariensis gen. et sp. nov.

 

Maurício Rodrigo Schmitt, Agustín Guillermo Martinelli, João Felipe Leal Kaiuca, Cesar Leandro Schultz, Marina Bento Soares. 2023. Old Fossil findings in the Upper Triassic Rocks of southern Brazil improve Diversity of traversodontid Cynodonts (Therapsida, Cynodontia). The Anatomical Record. 

DOI: 10.1002/ar.25244

  twitter.com/mauriciosaurus/status/1663194122847412227

[Paleontology • 2022] Taphonomy of Drought afflicted Tetrapods in the Early Triassic Karoo Basin, South Africa

Mummified skin on spreadeagled Lystrosaurus 

in Smith, Botha & Viglietti, 2022. 

DOI: 10.1016/j.palaeo.2022.111207

Highlights: 

• Outcrop containing hundreds of Early Triassic tetrapod fossils interpreted as evidence of drought.

• Clusters of articulated skeletons interpreted as drought-induced aggregations.

• Mummified skin on spreadeagled Lystrosaurus suggest rapid desiccation after death by starvation.

• Bone histology confirms that all the Lystrosaurus were juveniles or early sub-adult.

• Bonebeds of juvenile Lystrosaurus are interpreted as sheet-washed behavioural aggregations.

Abstract

The sedimentology and taphonomy of in-situ fossils from earliest Triassic strata (Induan) in the southern Karoo Basin of South Africa is presented as evidence for episodes of drought-induced mass death of the resident tetrapods. Abundant skeletons are preserved in a 2 m-thick tabular silty-sandstone capping a multi-storeyed low-sinuosity channel sandstone interpreted as a wide shallow channel that became progressively abandoned, with more ephemeral flow regime than in the underlying channels and subjected to intermittent flows of low-density sediment-laden floodwaters. Stratigraphic and planimetric distribution of 170 in-situ tetrapod fossils shows several clusters of up to eight closely-spaced articulated Lystrosaurus skeletons preserved in prone and spread-eagled body position. These are interpreted as drought-stricken carcasses that collapsed and died of starvation in and alongside dried-up water sources. Two of the specimens display an unusual micritic envelope with a distinctive pustular texture interpreted as permineralised mummified skin indicative of rapid desiccation after death. Bonebeds of disarticulated bones of multiple juvenile Lystrosaurus occur in shallow depressions within the rubified mudstones. Layering of different skeletal elements suggests some hydraulic sorting but the initial aggregation was likely a behavioural response to drought. Osteohistology of spread-eagled Lystrosaurus (L. declivis and L. murrayi species) skeletons show that they represent early juvenile stage which is in accordance with previous findings that throughout Pangaea Early Triassic Lystrosaurus died relatively young due to environmental stressors. Our results support the hyperthermal hypothesis that ~252 Mya increased continental aridity, already a consequence of the coalescence of Pangaea, was critically intensified by volcanogenic greenhouse gasses from the Siberian traps. We propose that in the aftermath of the End-Permian mass extinction event, a succession of climatic drying episodes orchestrated a series of fully-functioning terrestrial ecosystems that were markedly different to those of the pre-extinction, and likely had a profound and lasting influence on the evolution of tetrapods.

Keywords: Early Triassic, Katberg Formation, Lystrosaurus, Drought accumulations, Bonebeds, Mummified skin

Roger M.H. Smith, Jennifer Botha and Pia A. Viglietti. 2022. Taphonomy of Drought afflicted Tetrapods in the Early Triassic Karoo Basin, South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology. In Press, 111207. DOI: 10.1016/j.palaeo.2022.111207 

[PaleoMammalogy • 2021] Mammaliaform Extinctions as A Driver of the Morphological Radiation of Cenozoic Mammals

 large Gobiconodon outcompeted the ancestors of modern mammals in the time of dinosaurs.

in Brocklehurst, Panciroli, Benevento & Benson, 2021. 

 DOI: 10.1016/j.cub.2021.04.044

 twitter.com/palaeo_neil 

Illustration: Corbin Rainbolt.  twitter.com/CorbinRainbolt

Highlights

• The therian mammal radiation is usually associated with extinctions among dinosaurs

• Mesozoic therians show greater morphological constraint than their close relatives

• The release of this constraint occurred later than the extinction of the dinosaurs

• The therian radiation was in part driven by extinctions among other mammaliaforms

Summary

Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species. The Cenozoic radiation of placental mammals, the foundational example of this concept, gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs. However, study of this and other radiations has focused on variation in evolutionary rates, leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized. We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. 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. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, 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. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.

Keywords: adaptive radiation, constraint, mammal, Mesozoic, K/Pg mass extinction

Early lineages of mammal like this large Gobiconodon from Mongolia outcompeted the ancestors of modern mammals in the time of dinosaurs.

Illustration: Corbin Rainbolt.

 twitter.com/CorbinRainbolt

 

Neil Brocklehurst, Elsa Panciroli, Gemma Louise Benevento and Roger B.J. Benson. 2021. Mammaliaform Extinctions as A Driver of the Morphological Radiation of Cenozoic Mammals. Current Biology. DOI: 10.1016/j.cub.2021.04.044

 twitter.com/palaeo_neil/status/1394303018565255172

In brief: Brocklehurst et al. report that Mesozoic therians evolved under greater morphological constraint than contemporary mammaliaforms. This constraint was released later than the extinction of non-avian dinosaurs, including in therians less than 100 g. They suggest the therian radiation was in part driven by extinctions among non-therian mammaliaforms.

Mammals in the time of dinosaurs held each other back

  eurekalert.org/pub_releases/2021-05/uoo-mit051721.php

 twitter.com/CorbinRainbolt/status/1394313394178727940

[Paleontology • 2021] Niche Partitioning shaped Herbivore Macroevolution through the early Mesozoic

in Singh, Elsler, Stubbs, ... et Benton, 2021. 

DOI: 10.1038/s41467-021-23169-x  

twitter.com/PalaeoSingh 

Abstract

The Triassic (252–201 Ma) marks a major punctuation in Earth history, when ecosystems rebuilt themselves following the devastating Permian-Triassic mass extinction. Herbivory evolved independently several times as ecosystems comprising diverse assemblages of therapsids, parareptiles and archosauromorphs rose and fell, leading to a world dominated by dinosaurs. It was assumed that dinosaurs prevailed either through long-term competitive replacement of the incumbent clades or rapidly and opportunistically following one or more extinction events. Here we use functional morphology and ecology to explore herbivore morphospace through the Triassic and Early Jurassic. We identify five main herbivore guilds (ingestion generalists, prehension specialists, durophagous specialists, shearing pulpers, and heavy oral processors), and find that herbivore clades generally avoided competition by almost exclusively occupying different guilds. Major ecosystem remodelling was triggered multiple times by external environmental challenges, and previously dominant herbivores were marginalised by newly emerging forms. Dinosaur dominance was a mix of opportunity following disaster, combined with competitive advantage in their new world.

 

Suresh A. Singh, Armin Elsler, Thomas L. Stubbs, Russell Bond, Emily J. Rayfield and Michael J. Benton. 2021. Niche Partitioning shaped Herbivore Macroevolution through the early Mesozoic. Nature Communications. 12: 2796. DOI: 10.1038/s41467-021-23169-x

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