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TST: New Content, Stories, Read-Aloud

Latest 5

The 5 latest stories.

One-minute tidbits.

1.

A Science Story.

From History:
Subject: Mammal Evolution.

Last Non-Cynodont Therapsids.

~205 Million years ago

The last non-cynodont therapsids likely included late dicynodonts, such as Lisowicia bojani and related Late Triassic forms. Dicynodonts were herbivorous therapsids with beak-like mouths and, in many species, tusks. They belonged to the broader mammal-side branch, but they were not cynodonts and did not lead directly to mammals. Their disappearance near the end of the Triassic marked the fading of the older non-cynodont therapsid lines.

By the Late Triassic, around 210–201 million years ago, late dicynodonts lived in a world increasingly dominated by archosaurs: early dinosaurs, large predatory rauisuchian-like relatives of crocodiles, pterosaurs, croc-line reptiles, turtles, amphibians, and other surviving therapsids, including cynodonts. Their environments likely included seasonal floodplains, river systems, forested lowlands, and open patches of vegetation across Pangaea. In Europe, Lisowicia bojani lived in what is now Poland, in a dinosaur-age ecosystem where large herbivores and large predators were both becoming more prominent. Its discovery showed that at least some dicynodonts were still competing in the “large herbivore” role at the same time early sauropodomorph dinosaurs were expanding.

Dicynodonts were an older, highly successful branch of therapsids — mammal-side animals, but not cynodonts. Most were plant-eaters with heavy bodies, short tails, powerful jaws, and beak-like mouths; many had tusks, though Lisowicia itself appears to have lacked the classic long tusks and instead had a massive beaked skull. Lisowicia bojani was extraordinary: elephant-sized, late-surviving, and more upright-limbed than earlier dicynodonts, showing that this older therapsid branch was still evolving, not merely fading away. But they were not on the direct mammal path. Their disappearance near the end of the Triassic marks the fading of the non-cynodont therapsid world, while the cynodont branch continued toward mammaliaforms and mammals.

 


That Science Story, 

was first published on TST 36 minutes ago.
2.

A Science Story.

From History:
Subject: Mammal Evolution.

Last Non-Mammaliaform Cynodonts.

~125 Million years ago

The last non-mammaliaform cynodonts included the tritylodontids, an advanced family of herbivorous cynodonts. They were close to mammals and shared several mammal-like traits, but they remained outside Mammaliaformes. Their extinction around 125 million years ago marked the end of the non-mammaliaform cynodont line, while mammals—the surviving branch—continued on.

By the Early Cretaceous, around 125 million years ago, the world of the last tritylodontids was no longer the old synapsid world. It was a dinosaur-dominated landscape of warm seasonal forests, floodplains, lakeshores, and volcanic basins. Tritylodontids would have shared these environments with early birds, lizards, amphibians, turtles, pterosaurs, and dinosaurs such as small theropods and herbivorous ornithischians. In places like Early Cretaceous East Asia, the ecosystem also included mammaliaforms and true mammals that were becoming surprisingly diverse, so tritylodontids were not simply “waiting for mammals.” They were living beside them. The Cretaceous ran from about 145 to 66 million years ago, and early mammals and mammal-relatives had already diversified into many ecological roles well before the dinosaur extinction.

Tritylodontids were advanced herbivorous cynodont therapsids, close to mammals but usually placed outside Mammaliaformes. They had small-to-medium bodies, strong jaws, large cheek teeth with multiple cusps, and a well-developed secondary palate, all pointing to a specialized plant-eating lifestyle. Some later forms, such as Fossiomanus sinensis, even show digging adaptations, suggesting they could occupy burrows or fossorial niches. They were among the last non-mammaliaform therapsids, surviving long after true mammals had appeared. That makes them a wonderful “living fossil” style branch in the mammal-side story: not mammals, not primitive throwbacks, but late-surviving cousins carrying an older version of the mammal-line experiment into the age of dinosaurs.

 


That Science Story, 

was first published on TST 36 minutes ago.
3.

A Science Story.

From History:
Subject: Mammal Evolution.

First Therapsids.

~272 Million years ago
A more upright posture.

Therapsids are the advanced synapsids that began tightening the mammal-side body plan. Their most visible shift was toward a more upright posture, with limbs moving farther under the body instead of sprawling far out to the sides. Alongside that came a more powerful skull, more specialized teeth, and signs of a more active lifestyle. They were not mammals yet, but this is where the old synapsid line began to look more focused, more predatory in some branches, more specialized in others, and more clearly aimed toward the later mammal story.

To set the stage, picture the first therapsids living during the Middle Permian, around 272 million years ago. This is when Pangaea dominated the planet. Their world was warmer, more seasonal, and often drier than the earlier Carboniferous coal forests. A more upright posture allowing for running on dry land had real advantages. Picture open floodplains, river channels, muddy basins, patchy wetlands, seed ferns, horsetails, early conifers, and broad stretches of exposed earth. This was a changing world: less swamp-jungle, more seasonal land. In that setting, faster, more active synapsids had room to rise.

Raranimus dashankouensis is a good example of one of the earliest therapsids. It is known from a partial skull from Middle Permian China, and a 2021 reassessment confirmed it as a basal member of Therapsida. A 2024 paper also notes that until a newer early-middle Permian gorgonopsian find, Raranimus was considered the oldest known unequivocal therapsid. It still carried older synapsid features, but its skull and teeth show the early therapsid direction: sharper jaws, predatory adaptations, and the beginning of the line that would eventually include cynodonts, mammaliaforms, and mammals.

 


That Science Story, 

was first published on TST 36 minutes ago.
4.

A Science Story.

From History:
Subject: Mammal Evolution.

Last Non-Mammal Mammaliaforms.

~66 Million years ago (tentative placeholder date)

The Avashishta bacharamensis is dated to about 72 to 66 million years ago. It is known from a single tooth from Late Cretaceous India, Avashishta may represent a late-surviving haramiyidan, a non-mammalian mammaliaform near the mammal line. Its classification is debated, so this is best marked as a tentative “possible last known” entry.

For sure, non-mammal mammaliaforms lived to about 150 million years ago. For example, the Late Jurassic docodont mammaliaform from Portugal. It had many mammal-like traits, including complex teeth and mammaliaform-style tooth replacement, but belonged to a side branch outside the living mammal line.

 


That Science Story, 

was first published on TST 36 minutes ago.
5.

A Science Story.

From History:
Subject: Mammal Evolution.

First Crown Mammals.

~165 Million years ago (+/- 5 million)

The small Jurassic ancestor shared by all living mammals.

Crown mammals first evolved by the Middle Jurassic, roughly 170–160 million years ago, as small mammal-line animals living in dinosaur-dominated ecosystems. The “first crown mammal” was not a known named fossil but is the last common ancestor of living monotremes and therians. This is the ancestor of monotremes, marsupials, and placentals. It lived in a warm Jurassic world of forests, floodplains, and lakeshores. Common plants were conifers, cycads, and ferns. Common animals were small reptiles, amphibians, and larger pterosaurs overhead. These early crown mammals were likely small, secretive, and mostly nocturnal or crepuscular, surviving in the shadows while their anatomy quietly crossed the threshold into the living mammal branch.

A useful early fossil anchor is Ambondro mahabo, from the Middle Jurassic of Madagascar, about 167 million years ago. It is known only from a fragmentary lower jaw with teeth, so it should not be presented as “the first crown mammal” with certainty. But it is important because it shows complex tribosphenic-style molars — teeth with cutting and crushing surfaces, a key feature associated with later marsupials and placentals, though its exact placement is debated. Britannica describes Ambondro as a shrewlike extinct mammal from Middle Jurassic Madagascar and the oldest known mammal with complex tribosphenic dentition.

 


That Science Story, 

was first published on TST 36 minutes ago.

The end.

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