Retzius periodicity in the Late Miocene hominoid Lufengpithecus lufengensis from Southwest China:
implications for dental development and life history
Rong Hu, Baopu Du & Lingxia Zhao 2023 JHE 181, 103400 short comm.
doi org/10.1016/j.jhevol.2023.103400 open access

Introd.
In enamel, there are short- & long-period lines: daily cross-striations & Retzius lines resp.
These lines have been used to ascertain aspects of dental development, e.g.
- enamel daily secretion rates,
- Retzius line periodicities,
- crown formation times,
these in turn have been used in
- comparing life history schedules,
- examining phylogenetic relationships among extant & extinct primate taxa.
Enamel periodicity corresponds to the nr of daily cross-striations between adjacent Retzius lines,
in many studies, it is a critical value for estimating crown fm time.
Bromage & Dean (1985) first estimated the crown fm time of the permanent incisors of Pliocene hominins,
Retzius line periodicity + counts of perikymata & estimates of cuspal enamel fm time have been used to estimate the overall crown fm time.
Crown fm times + estimates of crown initiation ages have also been used to estimate ages of death in fossil hominins.
Retzius periodicity for early hominins can contribute toward solving difficult taxonomic diagnoses of fossil materials (fragmentary dental remains).
Previous work has demonstrated
- significant differences in mean Retzius periodicities in diverse spp,
- a correlation between the mean Retzius periodicity & body mass + MR in hominoids:
Retzius periodicity is a key developmental variable, that can provide insights into fossil hominoid dental development, metabolic biology, taxonomy & phylogeny.
In 1975, the Miocene ape c 8 Ma Lu.lufengensis was discovered at the Shihuiba site, Lufeng County, Yunnan prov.,
1000s of additional fossils have been recovered, incl.5 skulls, >40 partial or complete mandibles, several limb bone fragments, >1000 teeth.
Lufengpith.scapula & clavicle morphology is similar to orangutans?
2 phalanges are strongly curved, with markings of powerful flexor tendons + clear indications of suspensory behaviors.
Femurs & MT-1s show a more hominoid-like morphology, indicating a more terrestrial adaptation. (?? hominoid-like=aquarboreal! --mv)
Molar enamel is +-thick, the cusps are short, the occlusal surface bears complex crenulations = highly similar to orang molars: frugivory?
Paleo-environmental analysis points to swamp/moist tropical forest conditions. (=aquarboreal aqua+arbor :-) --mv)
Dental & mandible metrics indicate a degree of sex.dimorphism.
Zhao cs suggest:
- Lu.lufengensis had rel.long crown fm times in the anterior teeth,
- its dental development, eruption sequence & age at M1 emergence are more similar to extant gr.apes >Hs,
- its teeth exhibited high frequencies of linear enamel hypoplasia,
- time intervals between adjacent linear enamel hypoplasia defects were estimated to range from 4.8 to 6.6 months (aver.6): cf seasonal variation in food & habitat?
Retzius periodicity is a key parameter in assessing dental development, but currently little is known about Retzius periodicity in Lu.lufengensis.
Data on Retzius periodicity are necessary to
- estimate crown fm times & dental development accurately,
- reconstruct the pace of life history of Lu.lufengensis. I
Here we collected 9 broken teeth of Lu.lufengensis, made histological longitudinal sections, observed growth lines, determined Retzius periodicity,
we compared the Retzius periodicity of Lu.lufengensis with the periodicities of extant primates, Hs, other fossil hominoids & hominins,
we also discuss the relevance of Retzius periodicity to dental development, body mass, life history, taxonomy & phylogeny.
....

Concl.
The present study shows: Retzius periodicity is 9 days in the 9 teeth of Lu.lufengensis:
is it more appropriate to use a periodicity of 9 days as an average in estimations of crown fm times & dental development for Lu.lufengensis when the true periodicity is not known.
In comparison to extant primates & fossil hominoids & hominins, the average Retzius periodicity of Lu.lufengensis is rel.long:
- longer >prosimians, monkeys & lesser apes,
- closer to living & fossil Pongo & G.gorilla >P.troglodytes & Hs,
- closer to the periodicities of Asian fossil gr.apes (with longer periodicities) >African & Eur.Miocene fossil apes & extinct hominins.
The diversity in Retzius periodicities (Miocene fossil apes, early fossil hominins, extant apes & Hs) suggests phylogenetic differences in dental development & bio-rhythm variation in hominoid evolution.

____

Interesting study.
There are numerous Mio-Pliocene pongid fossils, but for some obscure reason (read: afro+anthropocentric prejudices) many paleo-anthropologists still believe australopiths are closer relatives of us than of Pan or Gorilla
(this is impossible: Pliocene Homo was in S-Asia ->early-Pleist.Mojokerto Java, cf. our lack of African retroviral DNA).
The "humanlike" traits in australopiths are no "hominin" innovations, but were simply aquarboreal adaptations in Mio-Pliocene hominoids: vertical wading-climbing in swamp forests.

littor...@gmail.com wrote:

> Retzius periodicity in the Late Miocene hominoid Lufengpithecus lufengensis from Southwest China:
> implications for dental development and life history
> Rong Hu, Baopu Du & Lingxia Zhao 2023 JHE 181, 103400 short comm.
> doi org/10.1016/j.jhevol.2023.103400 open access

I don't have access to these finds, the equipment to date them and,
quite frankly, wouldn't have much interest in learning how. But, based
on what is available to us unwashed masses...

It's younger than bipedalism, so it's likely an inland population of
an Aquatic Ape or Littoral or Waterside group.

It's location is less than 2,000 miles from the equator, which is
kind of okay, because after Yellowstone kicked off about 8.7 million
years ago they couldn't survive just anywhere. Yellowstone would
have HEAVILY favored coastal populations, populations in the
southern hemisphere and anyway the closer to the equator the
better...

I went on a rant about all this here:

https://groups.google.com/g/sci.anthropology.paleo/c/U8UkauixRek/m/LjVojYTMCgAJ

So what you call "Aquaboreal" and I call "Vestigial traits (from
their Aquatic Ape ancestors) would, in my opinion, be indicative
of a migration from the coast.

JTEM's sin is consistency, the same forces at work throughout
our history:

Groups peeled off from the parent "Aquatic Ape" population,
followed freshwater sources & transitional wetlands inland
where they adapted to their new environment.

I think this process began almost immediately and didn't stop
until humans ran out space, as the Americas were inhabited
this way...

-- --

https://jtem.tumblr.com/post/721305588274987008

Op donderdag 29 juni 2023 om 15:11:20 UTC+2 schreef JTEM is so reasonable:

> > Retzius periodicity in the Late Miocene hominoid Lufengpithecus lufengensis from Southwest China:
> > implications for dental development and life history
> > Rong Hu, Baopu Du & Lingxia Zhao 2023 JHE 181, 103400 short comm.
> > doi org/10.1016/j.jhevol.2023.103400 open access

> I don't have access to these finds, the equipment to date them and,
> quite frankly, wouldn't have much interest in learning how. But, based
> on what is available to us unwashed masses...
> It's younger than bipedalism, so it's likely an inland population of
> an Aquatic Ape or Littoral or Waterside group.
> It's location is less than 2,000 miles from the equator, which is
> kind of okay, because after Yellowstone kicked off about 8.7 million
> years ago they couldn't survive just anywhere. Yellowstone would
> have HEAVILY favored coastal populations, populations in the
> southern hemisphere and anyway the closer to the equator the
> better... I went on a rant about all this here:
> https://groups.google.com/g/sci.anthropology.paleo/c/U8UkauixRek/m/LjVojYTMCgAJ

I don't understand your Yellowstone argument, JTEM, but my answer then, a bit shortened:
.... hylobatids: vertical, no tail, gestation "too"long for their size:
the hominoid LCA was already BP/orthograde/aquarboreal: broad sternum-thorax, dorsal scapulas, arm-hanging, less lumbar vertebras etc.:
India approached S-Asia c 30-25 Ma = island archipel fm + coastal forests:
some Catarrhini reached these islands -> Hominoidea: BP waders-climbers: centrally-placed lumbar spine = vertical etc.:
aquarboreal = aq.apes s.l.
India underneath S-Asia split Hominoidea c 20 Ma into great (W) & lesser (E) apes in coastal forests along the N-Tethys Ocean.
The Mesopotamian Seaway closure c 15 Ma split hominids-dryopiths (W->Tethys-Sea) & pongids-sivapiths (E->Ind.Ocean coastal forests)/
Trachilos BP footprints etc. Dryopiths along rivers inland etc.
Med.Sea hominids-dryopiths died out (Zanclean flood? cold?), but Red Sea hominids=HPG survived:
incipient N-EARS c 8 Ma got colonized by Gorilla (HP/G split) ->Orrorin, Ardip., Sahelanthr., Praeanthr.afar.->boisei.
When the Red Sea opened into the Gulf (Francesca Mansfield 5.33 Ma? Zanclean mega-flood): Pan went right, Homo went left:
--Australopith-Pan followed the E.Afr.coast->S.Africa->Au.africanus->robustus S-EARS (//Gorilla in N-EARS),
--Homo followed the S.Asian coast->Java etc.: H.erectus etc.=aq."ape"s.s.: pachyosteosclerosis=shallow-diving = aq.ape s.s.

In short:
-wading-climbing Mio-Pliocene Hominoidea, google "aquarboreal" = aq.ape s.l.
-wading-diving early-Pleist. H.erectus cs, google "pachyosteosclerosis" = aq.ape s.s.
-wading-walking late-Pleist.Homo, google "gondwanatalks verhaegen" my book.

> So what you call "Aquaboreal" and I call "Vestigial traits (from
> their Aquatic Ape ancestors) would, in my opinion, be indicative
> of a migration from the coast.
> JTEM's sin is consistency, the same forces at work throughout
> our history:
> Groups peeled off from the parent "Aquatic Ape" population,
> followed freshwater sources & transitional wetlands inland
> where they adapted to their new environment.

OK, but apparently early-Pleist."archaic"Homo became *more*aquatic: + diving:
-pachyosteosclerosis leaves 0 doubt
-shell engravings, google "Joordens Munro"
-Mojokerto SE.Asia, later Flores far oversea
-fossilizations amid shellfish
-larger brain: DHA? cf.sea-mammals
-no Pliocene Afr.retroviral DNA
-etc.:
only *incredible*imbeciles believe that pachyosteosclerotic H.erectus ran after antelopes... :-DDD

> I think this process began almost immediately and didn't stop
> until humans ran out space, as the Americas were inhabited
> this way...

Yes, but we have to discern schematically 2 different phases:
wading-climbing hominoids
-> wading-diving H.erectus cs

littor...@gmail.com wrote:

> I don't understand your Yellowstone argument

If Yellowstone touches off tomorrow it would (conservatively
estimated) release the energy equivalent of about 100,000
nuclear weapons. It would plunge the entire globe into a
"Volcanic Winter" as all that ash/smoke AND ESPECIALLY
THE SULFUR fill our atmosphere. Temperatures would
plummet.

The eruption of some 8.7 million years ago would have
been larger.

It would have been on the order of the Toba eruption, which
was maybe 74k years ago.

The Younger Dryas Cooling lasted for over a thousand
years. The Yellowstone Eruption would have taken at least
that long to clear out of our skies.

The northern hemisphere takes the brunt. Yes, even if the
eruption happens in the southern hemisphere. It's just the
way the earth ends up distributing things.

The equator is probably the best place to be, as that is
where most of the energy of the sun falls.

The coast is vastly more survivable than inland. The sea
is a great moderator of climate. It takes a lot of energy
to heat up the water, so it's cooler, and the sea is holding
so much energy (if it weren't it would be ice, not liquid)
that it makes the climate a little warmer, when it gets
cold.

This is how heat works: It from from warm to cold. So
if the sea is colder than the air, it absorbs energy. If the
sea is warmer than the air, it releases energy.

Yes. For real: Water is an actual battery, storing energy!

So when Yellowstone exploded 8.7 million years ago,
conditions favored equatorial coastal populations, and
actively selected AGAINST inland groups.

Get into the center of continents and that's where you're
coldest...

This isn't a one-time deal. It's the reason why we say "Out
of Africa."

Toba exploded like 74k years ago. Africa was the best
place to be. Sundaland would have been good but it was
Ground Zero for Toba, so that nixed that.

We're talking like 250x the Krakatoa eruption...

Toba would have virtually wiped out any inland groups
of Neanderthals. Or Denisovans, etc.

I've argued that Hss -- the population or "ethnicity" that
we call modern humans -- were sexually selected, likely
matriarcal.

Why?

Because there was more than one African population!

So the sexually selected group, with a Quantity over
Quality reproductive strategy won. They could bounce
back FIRST and fill the vacuum left by Toba. And because
they were sexually selected they were more attractive,
displayed more neonatal traits... like hairlessness.

There's even one study that says penis size correlates
to this!

Google: Penis size and r/K selection

It raised quite a fuss. And it's all so very, Very, VERY not
allowed to be spoken of...

This would have sped the demise of the Neanderthals,
as the males would have preferred mating with Hss
females... unless they were gay. In which case they
would have preferred Neanderthal females.

(Not as much sexual dimorphism there)

I always speculated that Neanderthals were patriarchal,
and monogamous but not in a way that we think of as
monogamous. It was more a case of sperm competition,
where Neanderthals had a lot less than Hss, they weren't
sexually selected. They were probably closer to
Gorillas: One male and a troupe of females.

Polygamy is actually a much better model here,
evolutionarily speaking, than is monogamy. This is
because a male could switch to another female while
the first is breast feeding. It allows for the maximum
child-rearing time and commitment.

Many ancient cultures -- i.e. the ones that are old but
not so old that we can't know about them -- had
prohibitions against sex with a nursing women. This
made sense, at if a women had a second baby while
still nursing the first, one or both of those babies
was in trouble.

Plus the more time and attention you can give a
child, the more successful it's going to grow up to
be: Safety. Learning. nutrition.

> OK, but apparently early-Pleist."archaic"Homo became *more*aquatic: + diving:

You say "More Aquatic" I say "Less infused with the
DNA from inland-adapted populations."

We split clean into Homo & Pan about 3.7 million
years ago, population wise (not necessarily two
full blown species), but the same dynamics that
lead to African apes in the first place would have
continued, so it wouldn't be until erectus and the
chromosome fusion when what we think of as
"Humans" arose.

-- --

https://jtem.tumblr.com/post/721305588274987008