Ancestral hair – Fossil Friday

Fossil of Spinolestes

Fossil remain of the Spinolestes xenarthrosus

Here is the Spinolestes xenarthrosus, or the fur ball as it has been nicknamed by the media. But it does not do it justice because this early mammal is the oldest evidence for a lot of features. While it is hard to appreciate it in this photo, it contained one of the basic elements that constitute modern mammals, hairs. Indeed, its skin and fur closely resembles modern mammals, nothing out of the extraordinary if it wasn’t for the fact that is 125 Millions of years!
There are a couple details that are interesting here about his animal. The first is the growth of hair. In a lot of mammals, a primary hair first grows and is followed by smaller and thinner secondary hairs which can be observed under the microscope on Spinolestes‘ remains.
On his back, along his vertrebal column, scientist found spine-like hairs. Just like hedgehod have evolved their spines from hair-like structures that fuse together, it seems this early mammal had an ancestral form of it.
What is equally fascinating is that some patches of hairs were observed to be shorter and black at the tips, which was probably due to a fungal infection. This kind infection is also present in modern mammals.
And at last, they also found some remains of organs which, again, given how old it is remains an astounding fact.

Reconstruction of the Spinolestes xenarthrosus, drawing: Oscar Sanisidro

Consider the xenarthrosus’ age – 125 Millions years old – which means the hair micro-structures have managed to stay intact until now, if that’s not exceptional we don’t know what is! It also means that mammals have evolved with hair-like structures and other features under their skin. This makes sense given that mammals are warm blooded: it means they need a way to keep warm, and alternatively sweat glands are there to keep them from over-heating. All in all, this Spinolestes is an extraordinary finding for understanding how, we, mammals evolved. It’s just fascinating how that we end up finding that some of the basic constituents of what we are today were already there 125 Millions years ago.

Let’s explore the past, interrogate the present and dream the future.
Adrien for Sci&Fi, over and out!

Martin, T. et al. (2015). A Cretaceous eutriconodont and integument evolution in early mammals. Nature.
Science, Daily, 125-million-year-old mammal fossil reveals the early evolution of hair and spines.

Visual credits:
Figure 2 from the original article
Figure 1 from the original article
Oscar Sanisidro, Living reconstruction of the Cretaceous mammal Spinolestes xenarthrosus.

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