19 October 2025
Mammalian ancestors have been around for 320 to 315 million years, but the first true mammals evolved during the time of the dinosaurs in the Late Triassic. These early mammals were uniformly nocturnal and small, no larger than a house cat, and they were furry. What did they look like? A study in Science in March 2025 examined six fossils species and found they were not as colorful as modern mammals. All of them were dark gray.
Back in 2008 we learned that dinosaurs were colorful. Studies of melanosomes found within their fossils indicated they were not only colorful but sometimes brilliant.
Using the same technique on six Mesozoic mammal fossils, researchers led by Matthew Shawkey compared the fossil melanosomes to those of 116 current (extant) mammals and found that extant mammals have more fur colors while the Mesozoic mammals were all the same color.
The diagram below shows the dark gray color scores compared to extant mammals (** see complete caption at bottom). I have added a pink line to diagram B to point out the difference. Extant mammals on left have a wider range of color (below line) than the fossil mammals (above line).
It’s hard to imagine these ancient mammals until you see an illustration. I have cropped it into two parts. See the complete caption (**) for the entire Fig. 4 below.
- At top: Two fossil mammals that resembled flying squirrels. “The green eyes of Arboroharamiya fuscus are an artistic license of the tapetum lucidum, an intraocular reflecting structure that enhances visual sensitivity, indicating nocturnality.“
- Below: Three more mammals. (**) see the caption for details.
Modern mammals are more colorful because melanosomes have changed over millions of years. But the one dark color was just fine for early mammals. They needed nighttime camouflage to hide from many much larger predators.
Read about these ancient dark gray animals at Yahoo News.
The full study citation –> Mesozoic mammaliaforms illuminate the origins of pelage coloration. Science 387, 1193-1198(2025). DOI:10.1126/science.ads9734
(**) Complete caption for Fig. 4 Artistic reconstruction of pelage coloration of five Jurassic mammaliaforms. (Top to bottom) Arboroharamiya fuscus (CUGB-P1901), Vilevolodon diplomylos (SDUST-V0010), Megaconus mammaliaformis (PMOL-AM00007), and Docodontans (SDUST-V0006 & SDUST-V0007). The green eyes of A. fuscus are an artistic license of the tapetum lucidum, an intraocular reflecting structure that enhances visual sensitivity, indicating nocturnality. Eutherian SDUST-V0008 from the Lower Cretaceous is not included in this artistic reconstruction. CREDIT: Chuang Zhao and Ruoshuang Li.
(**) Complete caption for Fig. 3. Melanosome diversity and pelage coloration across extant mammals and Mesozoic mammaliaforms. (A) Scatterplot of individual melanosome measurements from 116 extant mammals and six fossils; dot color shows RGB values derived from spectral curves measured at specific hair locations. Extant hair melanosomes, n = 2615; A. fuscus, n = 760; M. mammaliaformis, n = 103; V. diplomylos, n = 395; docodontan SDUST-V0006, n = 289; docodontan SDUST-V0007, n = 407; eutherian SDUST-V0008, n = 205. (B) Width variation of melanosomes. (C) Length variation of melanosomes. (D) Measured reflectance spectra of selected extant mammals [Vulpes vulpes (orange), Ailurus fulgens (red), Cephalophus dorsalis (brown), Pelomys fallax (darker brown), and Mephitis mephitis (black)] and predicted reflectance curves for six Mesozoic mammaliaforms (browns), highlighting their constrained brown coloration and minimal variation. (E) Detailed view of the predicted reflectance curves for the six Mesozoic mammaliaforms.