Hominin Trackways in the Cretan Miocene?

Guest Blogger: Sarah Hlubik


An in-press paper, available in the Proceedings of the Geologists’ Association on Aug. 31, describes trackways dating to 5.7 mya on Crete (shown in this post’s lead image, from Gierlinski et al. [2017]). This places them just before the Messinian Salinity Crisis, when the Mediterranean dried up, global climates were nice and warm, and the planet really did belong to the apes. A potential hominin trackway (let’s be real, any trackway at all) from this time period is WAY COOL for a couple of reasons:

1. Tracks do not preserve very well. Ever go walking along the beach and look behind you to see your footprints washed away by the next wave? Yeah, me too. Most footprints made in the dirt, sand, or mud, are going to be washed away or destroyed by other individuals, or simply smoothed over because there is so much water in the sediment. For tracks to preserve, they have to dry out a bit, and then be covered pretty quickly by sediment that is a little different in texture or that won’t end up squishing together with the underlying layer. So tracks at all are always really cool, and offer a glimpse into environments and animal communities that we generally don’t see.

2. The Miocene gets called the Planet of the Apes because of the intense radiation of apes that happened during that time period (23-5.3 mya). We know some about the vast array of species that must have occupied the Old World at that time, but there is a lot we don’t know (again, see how to become a fossil), and what we don’t know may have been living on ancient Crete and walking, at least some of the time. Suspensory locomotion evolved sometime during this period (see Pierolapithecus, Dendropithecus, and Dryopithecus), and many later Miocene apes were highly orthograde (which just means they sat upright). Today, suspensory locomotors include gibbons and orangutans, and these (also orthograde) apes are able to walk on two legs over the ground, so it isn’t outside the realm of possibility that a highly orthograde ape had to move across a relatively open, albeit somewhat gooey, landscape and did so on two legs.

Cheezburger animals monkey trees jungle GIF

3. Footprints can tell us a lot about who made them, even if they can’t tell us definitively who made them. Footprints can give us clues about how many toes, or digits, are on a foot, whether the toes had nails, hooves, or claws, and the overall shape of the foot. We can determine the direction individuals were walking, and get a general idea of a minimum number of individuals within a group (to an extent –preserved footprints should represent individuals who are walking over the landscape at roughly the same time, but who can say if they were there together). In this case, the authors claim that the footprints show a foot that resembles ours with all the toes, even the big toe, together, but without claws or a defined arch. Because of this, the authors claim that an original (basal) member of the Hominini clade (our own branch of the family tree) made these tracks, and suggest that whatever it was eventually gave rise to whatever we are now.

I’m not convinced, but I am certainly intrigued. At 5.7 mya, it post-dates early potential basal members of our lineage (Sahelanthropus and Orrorin) residing in Central and Eastern Africa, where current evidence overwhelmingly supports hominin evolution in savannah environments. Crete is a long way from any of these places, even if the Mediterranean Sea wasn’t a factor, and there are no Miocene ape fossils found particularly close to the trackways site. That doesn’t mean these footprints don’t belong to Miocene apes, but it makes it harder to argue that it was definitely an ape and not, say, a bear. Especially given the vast array of apes inhabiting the Planet of the Apes, I don’t have a problem with the possibility that more than one Miocene ape stood up to get across a flat surface, but it would be nice to point to a fossil close by in time and space and say, ‘Hey, it’s probably that guy!’.

Gierliński, G.D., Niedźwiedzki, G., Lockley, M.G., Athanassiou, A., Fassoulas, C., Dubicka, Z., Boczarowski, A., Bennett, M.R. and Ahlberg, P.E. (2017). Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?. Proceedings of the Geologists’ Association.

Sarah Hlubik is a PhD candidate in the Department of Anthropology at Rutgers University. She works on early hominin control of fire at Koobi Fora, Kenya.

Anthro News

Big-headed babies and manspreading

August has arrived, the summer is winding down, and those anthropologists lucky enough to be off doing fieldwork have started to come home. A new academic year will begin soon and, with it, the official resumption of the Bones, Stones, and Monkeys journal club! I’m looking forward to getting some new, interesting discussion posts going, but for now, two more pieces of anthro news.

This week’s news comes from the world of #scicomm (aka, public science communication). Science communication/outreach is definitely picking up steam as a major movement lately (though it has always been important) and some excellent #scicomm is being done by anthropologists. We’re lucky enough to study something that people always seem to find interesting – themselves!

First up, Dr. Julienne Rutherford (U. Illinois – Chicago) gave a public radio interview about how modern birth practices might affect human evolution. The overarching question this type of research is trying to answer is, essentially, how does culture interact with and shape biological evolution. Humans babies have relatively large heads compared to those of most other primate babies, which tends to make giving birth difficult. We’ve gotten around the complications of this issue culturally via C-section, but before surgical interventions were possible the size of a baby’s head was a serious selective pressure on birth canal size – too large a head could mean death for both mother and infant. With that pressure removed, Dr. Rutherford suggested that we could potentially see even more variation in female pelvis/birth canal size and somewhat bigger-headed (though not super genius) babies as a result. I’d be curious to see estimates of how long it might take for infant head size/female pelvis size and shape to decouple, given that there has been some cool previous research on how these two things are linked.

Next up, Dr. Caroline VanSickle threw down about “manspreading.” Spoiler alert – it’s a cultural phenomenon, not a biological one. Basically, an emeritus kinesiology professor suggested in an interview that manspreading is the result of sexual dimorphism (sex-related differences in appearance/shape/size) between the male and female pelvis. Specifically, the narrow pelvis of men causes their hip joints to pinch when their knees are together – an issue that is allegedly alleviated by manspreading. Dr. VanSickle shoots this down as not being a biological reality. Behavior isn’t determined by one’s skeleton, which changes during life depending on what you do with it. We call this Wolff’s Law (and I’m probably biased in my enthusiasm for her invocation for it – my entire dissertation was on Wolff’s Law and the pelvis). In addition to being able to shape your skeleton with your behavior, she also mentions research showing that manspreading does not occur in all cultures or with the same frequency between cultures. Personal bias aside, Dr. VanSickle’s case against biological determinism as an excuse for rude behavior was nicely made, so let’s all just keep our knees to ourselves on public transportation, okay?

That’s all I’ve got today from the world of anthro news! The Leakey Foundation tweeted today that they have “exciting fossil news to share tomorrow,” so stay tuned!

Disclaimer: I know Caroline (as I’ve said before, the pelvis world is small). She’s still right. 

Further Reading
Fischer, B., & Mitteroecker, P. (2015). Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma. Proceedings of the National Academy of Sciences112(18), 5655-5660.

Academic Family Trees

You may have noticed from literally all of the preceding posts that evolutionary anthropologists are into family trees. Who is related to what and how? Is Homo naledi the weird cousin at the family reunion or your great-great-great-great-grandhominin? The interest doesn’t stop at the relationships between fossil taxa; anthropologists are also into their own family trees – their academic family trees, that is.

A couple of years ago, some anthropologists from the University of Texas started the Academic Phylogeny of Physical Anthropology (physanthphylogeny.org) with the goal of tracing advisor-advisee relationships in our field. The tree now includes 2036 people (including me!) from 163 institutions and goes back to some of anthropology’s biggest names, like Louis Leakey, Earnest Hooton, and Franz Boas, to name a few. (Hooton has the most descendants, by far.)

But some of the folks on the tree also have some more unusual “ancestors” – people who weren’t anthropologists at all (like Nobel Prize winning biologist Nikolaas Tinbergen). I’m one of those people; my earliest ancestor to make it onto the tree is Dr. Glenn Jepsen, the first person to be appointed Sinclair Professor of Vertebrate Paleontology at Princeton University. He also served as the Curator of Vertebrate Paleontology and the Director of Princeton’s natural history museum. He worked on Paleocene/Eocene fossil mammals from South Dakota and Wyoming, including preparing and describing the earliest known definitive fossil bat Icaronycteris index.

icaronycteris index
Icaronycteris index Jepsen, 1966 – From the Yale Peabody Museum of Natural History Collections website

That is one good-looking fossil bat. Anyway, what got me started writing this post is that, when I’m not shouting into the internet science void, I work as a collections technician at the New Jersey State Museum under the Curator of Natural History – who actually knew Jepsen! As Jepsen ran Princeton’s (now defunct) natural history museum and it was right down the road from the NJSM, there was naturally communication back and forth between Jepsen and various museum-affiliated people, some of which is still stored at the NJSM. Earlier this week, I found this amusing letter to him in a drawer of old correspondence:

Jepsen letter snip

“…and even the physical anthropologists,” indeed! Apparently we’re a tough crowd. Guess some things don’t change!

Thanks for reading! (And definitely check out physanthphylogeny.org)

BS&M Does Homo naledi

On May 9th, Lee Berger and colleagues published three new papers on Homo naledi, the most recent South African hominin fossil find to make media waves. The original H. naledi fossil material was discovered in 2013 by two cavers working with Berger; it comes from the Dinaledi Chamber of the Rising Star cave system, from which it takes its species name (Berger et al. 2015). The first H. naledi discovery was remarkable because there are at least 15 individuals (from juveniles to adults of both sexes) represented in the assemblage and there are often multiple copies of each skeletal element present, which allows paleoanthropologists to look at variation within the species, and to see how it grew and developed. In total, there are about 1550 hominin bones and teeth in the assemblage – the largest single species assemblage found anywhere in Africa (Berger et al. 2015).

The three new articles covered the discovery of additional skeletal material (Hawks et al. 2017) and the age of the fossils (which had been a major source of speculation) (Dirks et al. 2017), and proposed a hypothesis for understanding Pleistocene hominin diversity in subequatorial Africa as part of a larger mammalian biogeographic pattern (Berger et al. 2017).

The new fossil material comes from a second chamber within the Rising Star system, the Lesedi Chamber, and represents at least three individuals (though in actuality the material likely comes from more than three individuals, based on where the bones were recovered from within the Chamber). The most spectacular of these remains is a relatively complete skull with associated skeletal material; the researchers have named this individual Neo. The new material looks a lot like the previously discovered H. naledi bones and teeth, and also includes both adult and juvenile material. The major thing that differentiates the Lesedi Chamber finds from the Dinaledi Chamber finds is that the Lesedi Chamber also contains animal skeletal material (Hawks et al. 2017).

The paper on the age of the fossils used several different methods (including dating geological features of the cave itself as well as directly dating some of the fossil teeth) to produce an age range for the material of 236,000-335,000 years old (Dirks et al. 2017). This means that the material is later Middle Pleistocene in age, much younger than would have been predicted based on looking at features of the skull and skeleton (like brain size).

In a previous paper, Hawks and Berger (2016) discussed what three different hypothesized ages (including a scenario that does match the new date) for the original H. naledi material would mean for its place in human evolution, and they follow up on this in the third new paper – now that we have a date, what does it mean? The date is younger than the first appearance of Homo erectus around 1.8 million years ago. As H. erectus is generally thought to be part of the lineage that is directly ancestral to us, this would seem to preclude H. naledi as a member of our direct line, unless it represents a sister group to our species that preserves a lot of the primitive morphology of a shared ancestor. This interpretation bumps H. erectus to a side branch of our family tree. A different type of analysis of the features of various species of Homo suggests instead a more bushy view of earliest Homo – whatever that ancestor was split into a number of species, each having only some of the ancestor’s features. What we can say is that H. naledi is likely only part of a branch that originated earlier in time, with the authors going so far as to suggest that we might already have fossils from earlier on this branch that we have not recognized due to their fragmentary nature (Berger et al. 2017).

Regardless of where Homo naledi ends up on our family tree, it’s still an incredible discovery that contributes to our understanding of the human fossil record. It provides a window into a time period in our history from which we don’t have great data and underscores two important ideas: first, that for most of our evolutionary history, Homo sapiens was not the only hominin species on the planet; and second, that there are still spectacular fossils waiting to be discovered.

Continue reading “BS&M Does Homo naledi”

Welcome to BS&M

Hello! Welcome to the Bones, Stones, and Monkeys (BS&M) journal club blog. Every Friday, graduate students (and sometimes faculty) from the evolutionary side of the Department of Anthropology at Rutgers University meet up to discuss a newly published paper in the field of biological/evolutionary anthropology. While BS&M has been around for a while, we recently decided to start this digital experiment as an exercise in science communication.

What you can expect from us here is a mostly jargon-free summary of whatever paper(s) struck our fancy that week, along with some sort of commentary. Right now, we’re trying out various written formats (partial transcripts, interesting insights/questions, etc), but we have some designs on turning our anthropological shenanigans into a podcast (because, somehow, the hilarity of shouting that Homo naledi are mole people! just doesn’t come across in writing).

Hopefully you’ll enjoy our little experiment! You can also find us on Facebook at the Center for Human Evolutionary Studies at Rutgers University or on Twitter @CHES_Rutgers.