[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 

  

 

[PaleoMammalogy • 2025] Nujalikodon cassiopeiae • The Oldest definitive docodontan from central East Greenland sheds light on the Origin of the Clade

  

Nujalikodon cassiopeiae 

Patrocínio, Panciroli, Rotatori, Mateus, Milàn, Clemmensen & Crespo, 2025

DOI: doi.org/10.1002/spp2.70022  

 facebook.com: Sofia Patrocinio

Artwork by Pedro Andrade

 

ABSTRACT

The first mammaliaforms emerged in the Late Triassic, but their exact origins remain unclear due to the scarcity of fossils from this period. One of the earliest diverging mammaliaform groups, the order Docodonta, became unusually ecomorphologically diverse compared with other early mammals, and this may be connected to the possession of complex molar cusp morphology. The specimen described here, found in the Rhætelv Formation of the Kap Stewart Group (Rhaetian–Sinemurian) of central East Greenland, provides novel information on docodontan origins and evolution, as well as key biogeographic insights into early mammal dispersal. Nujalikodon cassiopeiae gen. et sp. nov. is the first mammaliaform found in the Rhætelv Formation, and is likely to be Early Jurassic (Hettangian) in age. Comprising an incomplete dentary with a single preserved molar, it was visualized using micro-computed tomography; the molar bears similarities to the putative early docodontan Delsatia, and docodontan Dobunnodon. Phylogenetic analysis places Nujalikodon cassiopeiae as a basal member of Docodonta or a close sister taxon, making it one of the oldest definitive docodontans and pushing the origin of the group back to at least the Early Jurassic. It provides insights into the development of docodontan dental complexity, a key factor in their ecological diversification during the Middle to Late Jurassic. Its presence in Greenland supports the hypothesis that docodontans originated in the region now comprising Europe and Greenland before dispersing across the rest of Laurasia.

Keywords: mammal, molar complexity, Docodonta, Mesozoic, Rhætelv formation

Nujalikodon cassiopeiae gen. et sp. nov. 

Sofia Patrocínio, Elsa Panciroli, Filippo Maria Rotatori, Octavio Mateus, Jesper Milàn, Lars B. Clemmensen and Vicente D. Crespo. 2025. The Oldest definitive docodontan from central East Greenland sheds light on the Origin of the Clade. Papers in Palaeontology. DOI: doi.org/10.1002/spp2.70022 [13 June 2025]

 facebook.com/SofiaPatrocinio79/posts/9917085835043616

 facebook.com/61551425206601/posts/122179127444047506

#mammaliaformes #docodon #docodonta #nujalikodon #nujalikodoncassiopeiae #paleoart #rhaetelvformation #greenland #latetriassic #scientificillustration #paleoillustration

[PaleoMammalogy • 2025] Ravjaa ishiii • New Late Cretaceous zhelestid mammal (Eutheria: Zhelestidae) from the Bayanshiree Formation, Mongolia

Ravjaa ishiii 

Okoshi, Takasaki, Chiba, Natori, Saneyoshi, Takahashi, Kodaira, Hayashi, Ishigaki, Mainbayar & Tsogtbaatar, 2025

 DOI: doi.org/10.4202/app.01213.2024 

 x.com/_HETAKA

Numerous exquisitely preserved mammal fossils unearthed from Upper Cretaceous strata in the Gobi Desert of Mongolia have played a key role in understanding Mesozoic mammalian evolution. These splendid mammal fossils have been recovered mainly from the Baruungoyot and Djadokhta formations, but only two fragmentary remains of mammals have been collected from the underlying Bayanshiree Formation. Here we report a new species of Zhelestidae, Ravjaa ishiii gen. et sp. nov., based on a new mammal specimen recently discovered from the Bayanshiree Formation at the Bayan Shiree locality. The new specimen is represented by a well-preserved partial right dentary with the distal portion of an ultimate premolar and the first to the third molars. The gross observation and the phylogenetic analyses demonstrate zhelestid affinities: the subequally tall protoconid and metaconid, closely approximated hypoconulid and entoconid. Zhelestidae was widely distributed from Eurasia to North America in the Late Cretaceous but has not previously been recovered in the abundant Late Cretaceous mammalian fauna of Mongolia. This species represents the first zhelestid from the Mongolian Upper Cretaceous strata and contributes to further understanding of their paleobiogeographic and ecological insights.

Key words: Mammalia, Eutheria, Cretaceous, Bayanshiree Formation, Mongolia.

. Holotype of the zhelestid eutherian mammal Ravjaa ishiii gen. et sp. nov. (MPC-M 100s/001) from the Upper Cretaceous Bayanshiree Formation, Dornogovi, Mongolia.
Right mandible in labial (A), occlusal (B) and lingual (C) views.
Photographs (A1–C1) and 3D model (A2–C2) produced from a CT scan.

 

Mammalia Linnaeus, 1758 

Theria Parker and Haswell, 1897 

Eutheria Gill, 1872 

Zhelestidae Nessov, 1985a 

Genus Ravjaa nov. 

 Etymology: Derived from the 5th Noyon Khutugt lama of the Gobi, Dulduityn Danzanravjaa, the famous Buddhist scholar who was deeply respected by people in the Dornogobi region, where this specimen was unearthed. Given that the genus name “Ravjaa” originates from the personal name of a male figure, it should be considered masculine. 

Ravjaa ishiii sp. nov. 

Etymology: In honor of Ken-ichi Ishii, the director of Hayashibara Museum of Natural Sciences, Okayama, Japan, for his leading role in the Japanese team of the Mongolia-Japan joint expedition, which tremendously contributes to Mongolian paleontology. Holotype: MPC-M 100s/001, partial right dentary with a distal portion of the ultimate premolar, damaged m1, and well-preserved m2–3. 

Type locality: Bayan Shiree, located approximately 25 km southwest of Dzüünbayan, Dornogovi, Mongolia. 

Type horizon: Cenomanian–Santonian, Upper Cretaceous, Bayanshiree Formation. 

Diagnosis.—A zhelestid eutherian that differs from all other zhelestids in: the faint coronoid crest of the dentary with the shallow masseteric fossa, the concave dorsal alveolar margin of the dentary, the complete absence of the labial mandibular foramen, and the significantly high m2 crown that reaches approximately 70% of the height of the horizontal ramus directly below it on labial view.

Tsukasa Okoshi, Ryuji Takasaki, Kentaro Chiba, Masahito Natori, Mototaka Saneyoshi, Akio Takahashi, Shota Kodaira, Shoji Hayashi, Shinobu Ishigaki, Buuvei Mainbayar, and Khishigjav Tsogtbaatar. 2025. New Late Cretaceous zhelestid mammal from the Bayanshiree Formation, Mongolia. Acta Palaeontologica Polonica. 70 (1); 193-203. DOI: doi.org/10.4202/app.01213.2024

  x.com/_HETAKA/status/1908317608535089216

[PaleoMammalogy • 2025] Down to Earth: Therian Mammals became more Terrestrial towards the End of the Cretaceous

 

Dryolestes, a Late Jurassic relative of the Cretaceous therians

in Janis, Martín-Serra, Theodor et Scott, 2025.  

DOI: doi.org/10.1111/pala.70004

 Artwork by James Brown.

Abstract

The end Cretaceous extinctions had a profound effect on mammalian diversity, especially on metatherians (marsupials and their extinct relatives). Could mammalian substrate preference have influenced differential survival patterns? The plant fossil record shows changing angiosperm leaf anatomy during the last ten million years of the Cretaceous that would have resulted in a greater richness of terrestrial understory habitats, and work by other researchers implies that terrestrial (vs arboreal) substrate preference promoted increased survival over the Cretaceous–Palaeogene boundary for both mammals and birds. Here we use fragmentary postcranial remains of Late Cretaceous mammals and show that, at least in the Western Interior of North America, therian mammals were becoming more terrestrial in their locomotor mode towards the end of the Cretaceous.

Keywords: Mesozoic mammal, postcranial anatomy, locomotor mode, Cretaceous habitat, end Cretaceous extinction

Dryolestes (left) and Haldanodon (right), two creatures from the Late Jurassic period,

Digital reconstruction by James Brown, in consultation Pamela G. Gill.

 Copyright Pamela G. Gill.

Dryolestes, a Late Jurassic relative of the Cretaceous therians.

 Artwork by James Brown. Pamela Gill

Christine M. Janis, Alberto Martín-Serra, Jessica M. Theodor and Craig S. Scott. 2025. Down to Earth: Therian Mammals became more Terrestrial towards the End of the Cretaceous. Palaeontology. DOI: doi.org/10.1111/pala.70004 [01 April 2025] 

Researchers unlock life secrets of Jurassic mammals using X-ray imaging

https://www.southampton.ac.uk/biosci/news/2024/08/researchers-unlock-life-secrets-of-jurassic-mammals-using-xray-imaging.page

[PaleoMammalogy • 2025] Mesozoic Mammaliaforms illuminate the Origins of Pelage Coloration

in Li, D’Alba, Debruyn, Dobson, Zhou, ... Shawkey, 2025. 

DOI: doi.org/10.1126/science.ads9734 

Artwork by Chuang ZHAO

Abstract

Pelage coloration, which serves numerous functions, is crucial to the evolution of behavior, physiology, and habitat preferences of mammals. However, little is known about the coloration of Mesozoic mammaliaforms that coevolved with dinosaurs. In this study, we used a dataset of melanosome (melanin-containing organelle) morphology and quantitatively measured hair colors from 116 extant mammals to reliably reconstruct the coloration of six Mesozoic mammaliaforms, including a previously undescribed euharamiyidan. Unlike the highly diverse melanosomes discovered in feathered dinosaurs, hairs in six mammaliaforms of different lineages and diverse ecomorphotypes showed uniform melanosome geometry, corresponding to dark-brown coloration consistent with crypsis and nocturnality. Our results suggest that the melanosome variation and color expansion seen in extant mammals may have occurred during their rapid radiation and diversification after the Cretaceous-Paleogene extinction.

Ruoshuang Li, Liliana D’Alba, Gerben Debruyn, Jessica L. Dobson, Chang-Fu Zhou, ..., and Matthew D. Shawkey. 2025. Mesozoic Mammaliaforms illuminate the Origins of Pelage Coloration. Science. 387(6739); 1193-1198.  DOI: doi.org/10.1126/science.ads9734 

https://www.cugb.edu.cn/jdxw/47835.jhtml 

Editor’s summary: In the past decade or so, the identification of melanosomes in some dinosaur feathers and skin has led to the suggestion that many bore bright and complex coloration. Less work has been done to explore the coloration of early mammals. Li et al. looked at melanosome patterns in multiple species of Mesozoic mammals and compared these with those seen in more than 100 species of extant mammals. There was little color variation, and the animals were entirely dark in color. The authors argue that this was likely due to the animals’ nocturnal nature, and that brighter and more varied colors in mammals may have arisen after the extinction of dinosaurs at the end of the Cretaceous period. —Sacha Vignieri

  

[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

[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 • 2019] The Postcranial Anatomy of Brasilodon quadrangularis and the Acquisition of Mammaliaform Traits Among Non-mammaliaform Cynodonts

Brasilodon quadrangularis 

Bonaparte, Martinelli, Schultz & Rubert, 2003

 from the Riograndia Assemblage Zone of the Candelária Sequence, Santa Maria Supersequence (Brazil).

  Illustration: Jorge Blanco. 

in Guignard, Martinelli & Soares, 2019. 

 DOI: 10.1371/journal.pone.0216672

Abstract

Brasilodon quadrangularis (Cynodontia, Probainognathia) is an iconic non-mammaliaform cynodont from the Late Triassic of Brazil (Riograndia Assemblage Zone, Candelária Sequence), being considered as the sister taxon of Mammaliaformes. Although its phylogenetic position is very important, several aspects of its postcranial anatomy remain unclear or unstudied. Here, we present a detailed description of the postcranial elements referred to Brasilodon, including previously mentioned specimens and new ones, which add relevant information about its postcranial morphology and provide a new insight into the anatomical transition between advanced non-mammaliaform cynodonts and early mammaliaforms. Functional and ecological implications are also investigated, based on the postcranial morphology and muscular reconstructions. The postcranium of Brasilodon differs from most non-mammaliaform cynodonts and presents similarities with tritylodontids, early mammaliaforms and extant therians, such as a ventrally oriented scapular glenoid facet, a distinct and ossified greater humeral tubercle, lack of ectepicondylar foramen, olecranon process, hemispherical humeral and femoral heads and a prominent intertrochanteric crest. The humeral torsion, the length of the deltopectoral crest, the large bicipital groove and the well-developed lesser tubercle, indicate that the forelimb of Brasilodon was hold in a semi-sprawling position, with well-developed adductor muscles to maintain the body off the ground. The short femoral neck and the strong medial projection of the femoral head indicate the femur was held in a more erect posture than in basal non-mammaliaform cynodonts. The anterodorsally projected iliac blade with reduced postacetabular process, reduction of the anterior part of the pubis, medially located lesser trochanter indicate a basically mammalian pattern of pelvic musculature, able to swing the femur in a nearly parasagittal plane.

Fig 13. Paleoartistic reconstruction of Brasilodon quadrangularis (left) and Riograndia guaibensis (right), two abundant probainognathian cynodonts from the Riograndia Assemblage Zone of the Candelária Sequence, Santa Maria Supersequence (Brazil), which exhibits different morphologies in skull, dentition and locomotor apparatus.

 Illustration: Jorge Blanco.

Conclusion: 

The postcranium of Brasilodon quadrangularis differs from other non-mammaliaform cynodonts and is similar to early mammaliaforms and extant therians (e.g., hemispherical humeral and femoral head, distinct greater tubercle of the humerus, circular acetabulum, salient intertrochanteric crest of the femur). The morphology of the ulnar condyle of the humerus and olecranon process of the ulna suggests more abilities for extension and flexion of the elbow, a necessary component for a parasagittal locomotion. However, the humeral torsion, the length of the deltopectoral crest, the large bicipital groove and the well-developed lesser tubercle, indicate that the forelimb of B. quadrangularis was hold in a semi-sprawling position, with well-developed adductor muscles to maintain the body off the ground. The short femoral neck and the strong medial projection of the femoral head indicate the femur was held in a more erect posture than in basal non-mammaliaform cynodonts. The anterodorsally projected iliac blade with reduced postacetabular process, enlarged obturator foramen, reduction of the anterior part of the pubis, prominent and distinctive greater trochanter, medially located lesser trochanter, narrow intertrochanteric fossa represent a further continuation of trends that indicates a basically mammalian pattern of pelvic musculature, able to swing the femur in a nearly parasagittal plane.

Although fossorial or semifossorial habits appear to have been common in derived non-mammaliaform probainognathians (i.e., Riograndia, Irajatherium and Kayentatherium), the postcranial study of B. quadrangularis shows more generalized adaptations and highlights that distinctive ecological strategies (Fig 13) were developed among small-sized non-mammaliaform cynodonts.

 Morgan L. Guignard, Agustin G. Martinelli and Marina B. Soares. 2019. The Postcranial Anatomy of Brasilodon quadrangularis and the Acquisition of Mammaliaform Traits Among Non-mammaliaform Cynodonts.  PLoS ONE. 14(5): e0216672. DOI: 10.1371/journal.pone.0216672

[PaleoMammalogy • 2018] Cifelliodon wahkarmoosuch • Late-surviving Stem Mammal Links the Lowermost Cretaceous of North America and Gondwana

 Cifelliodon wahkarmoosuch 

Huttenlocker, Grossnickle, Kirkland, Schultz  & Luo, 2018

  DOI:  10.1038/s41586-018-0126-y

 Illustration: Jorge A. Gonzalez  nature.com

Abstract

Haramiyida was a successful clade of mammaliaforms, spanning the Late Triassic period to at least the Late Jurassic period, but their fossils are scant outside Eurasia and Cretaceous records are controversial. Here we report, to our knowledge, the first cranium of a large haramiyidan from the basal Cretaceous of North America. This cranium possesses an amalgam of stem mammaliaform plesiomorphies and crown mammalian apomorphies. Moreover, it shows dental traits that are diagnostic of isolated teeth of supposed multituberculate affinities from the Cretaceous of Morocco, which have been assigned to the enigmatic ‘Hahnodontidae’. Exceptional preservation of this specimen also provides insights into the evolution of the ancestral mammalian brain. We demonstrate the haramiyidan affinities of Gondwanan hahnodontid teeth, removing them from multituberculates, and suggest that hahnodontid mammaliaforms had a much wider, possibly Pangaean distribution during the Jurassic–Cretaceous transition.

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew to be about the size of a small hare.

 Illustration: Jorge A. Gonzalez

Mammaliaformes sensu Rowe (1986) 

Haramiyida Hahn, Sigogneau-Russell and Wouters (1989) 

Hahnodontidae Sigogneau-Russell (1991) 

Cifelliodon gen. nov.

Cifelliodon wahkarmoosuch sp. nov.  

Etymology. Cifelli’s tooth (Latin: -odon) of the Yellow Cat (Ute language: yellow, wahkar; cat, moosuch). Genus name honours Richard Cifelli for his contributions to Cretaceous mammal research in the American West.

Holotype. An exceptionally preserved skull, UMNH VP 16771 (Natural History Museum of Utah, Vertebrate Paleontology Collection).

Locality and horizon. The holotype is from the ‘Andrew’s Site’ quarry in the Lower Cretaceous Yellow Cat Member, Cedar Mountain Formation, Grand County, Utah, USA15. Radiometric dating places the age between approximately 139 and 124 million years old.

Diagnosis. Medium-to-large Mesozoic mammaliaform with broad, shallow skull and rostrum and a reduced marginal tooth count; dental formula: I2:C1:PC4; ultimate upper molars with high anterobuccal cusp and low, broad posterolingual cusp connected by a low ridge; septomaxilla absent; incisive foramina enlarged and positioned posteriorly on palate behind the level of the last (posterior) incisor pair; massive pterygoid transverse process that extends far ventral to the palatal surface; attenuated lacrimal anterior process with limited nasolacrimal contact; prominent sagittal crest; extensive occipital exposure of parietal and postparietal; plesiomorphic retention of a tabular bone; differs from Hahnodon in its larger size and higher aspect ratio of the rear molar in occlusal view (slightly more triangular than oval, with posterior apex).

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew to be about the size of a small hare.

 Illustration: Jorge A. Gonzalez 

Adam K. Huttenlocker, David M. Grossnickle, James I. Kirkland, Julia A. Schultz and Zhe-Xi Luo. 2018. Late-surviving Stem Mammal Links the Lowermost Cretaceous of North America and Gondwana. Nature.  DOI:  10.1038/s41586-018-0126-y

A 3D view of early mammals   nature.com/articles/d41586-018-05134-9

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