Gorilla skull compared

Today’s blog is essentially a silent movie.
Just sit back and compare these two skulls: Gorilla gorilla vs. Homo sapiens. Note the differences AND the similarities.

Figure 1. Gorilla skull with DGS colors applied to distinguish the bones. Compare to Homo sapiens in figure 2.

Figure 1. Gorilla skull with DGS colors applied to distinguish the bones. Compare to Homo sapiens in figure 2.

Figure 2. Labeled skull bones in Homo sapiens.

Figure 2. Labeled skull bones in Homo sapiens.

Some subtle points you may have missed:

  1. Human upper canines are not behind the lower canines
  2. Human incisors are larger than the canines
  3. The pterygoid is visible through the orbit
  4. The rims and ridges around the temporal opening in Gorilla are anchors for jaw muscles, all reduced in Homo.
  5. The bridge of the nose in Homo is lacking in Gorilla
  6. Perhaps I missed a few you’ll notice…
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Olympian Michael Phelps and the aquatic ape hypothesis

According to Wikipedia (abridged)
“The aquatic ape hypothesis (AAH) is the idea that the ancestors of modern humans were more aquatic. The hypothesis in its present form was proposed in 1960 by Alister Hardy. Though ignored or derided by the majority of workers, a few suggest in the last five million years humans became dependent on essential fatty acids and iodine, which are found in abundance in sea resources. Efficient function of the human brain requires these nutrients. The “aquatic ape” proposal is more popular with the lay public than with scientists.”

FIgure 1. Michael Phelps, gold medal winner in Olympic swimming, compared to Ardipithecus skeleton.

FIgure 1. GIF movie of Michael Phelps, gold medal winner in Olympic swimming, compared to Ardipithecus skeleton, not to scale.

We don’t have the nasal bones
for Ardipithecus. So it is possible that they were not flat, but arched, as in humans. And in humans, the ventral opening of the nostrils prevents water from entering the air passage whenever underwater.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo. We don’t have the nasal bones for Ardipithecus (in gray), so they could have arched to create a protruding nose with ventral nostrils.

Hardy argued aquatic adaptations in humans include:

  1. lack of body hair
  2. subcutaneous fat (but captive apes have levels similar to humans.
  3. location of the trachea in the throat rather than the nasal cavity
  4. the human propensity for front-facing copulation
  5. tears and eccrine sweating
  6. bipedalism as an aid to wading
  7. tool use evolved out of the use of rocks to crack open shellfish
  8. selection for wading, swimming and diving in procurement of aquatic food distinct from the jungle niche leading to chimps.

So what does Olympian Michael Phillips have to do with Ardipithecus?

  1. Both have a wider ‘wingspan’ than height.
  2. Both have a long trunk and relatively short legs.

Admittedly,
this is just ‘cocktail-chatter,’ and will probably always be ‘cocktail-chatter.’

FIgure 2. Primate cladogram with the addition of Pan, Gorilla, Ardipithecus and Indri. The topology of the LRT did not change with these additions.

FIgure 2. Primate cladogram with the addition of Aegyptopithecus, Pan, Gorilla, Ardipithecus and Indri. The topology of the LRT did not change with these additions.

The addition of the five primates, Indri, Aegyptopithecus, Pan, Gorilla and Ardipithecus to the large reptile tree (LRT, 1172 taxa, subset Fig. 2) recovers nothing controversial and does not change the LRT topology of the primates.

References
Hardy A 1960. Was Man More Aquatic in the Past? New Scientist 7(174):642–645.

wiki/Aquatic_ape_hypothesis

Proconsul, Pan and Homo: face changes

Just some musings today
over chimps and humans (Fig. 1) and some other higher primate skulls (Figs. 2, 3). Chimps have not yet made it into the large reptile tree (LRT, 1068 taxa), but they will someday.

The tradition is
to consider chimps (genus: Pan) the starting point in human (genus: Homo) evolution and to make comparisons between the two. Once again, taxon exclusion becomes a problem.

The actual starting point
is closer to an extinct ancestor of both, Proconsul (aka: Dryopithecus; Hopwood 1933; 18–14mya; Figs. 2, 3) a genus that resembled a chimp, but did not knuckle-walk (Fig. 3) and lacked brow ridges, both traits retained by Homo.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. See text for details.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. Pupils are aligned. Everything else morphs. See text for details.

 

Question #1 today is…
What changes can we see in the face of a human compared to a chimpanzee?

  1. Forehead present (housing more cerebral frontal matter)
  2. Longer and protruding nose with ventral nostrils (better for underwater)
  3. Shorter nose-to-lip distance with philtrum (medial furrow)
  4. Chin boss (deeper in adults)
  5. Internal lip tissue externalized
  6. Shorter muzzle
  7. Thicker, less patchy and eternally growing cranial hair (+ beard on males)
  8. The rest of the face (and most of the body) hairless
  9. Smaller iris vs. sclera (whites of the eyes)
  10. Smaller ears
  11. Fewer wrinkles on breeding adults and babies
  12. Brow ridges absent, replaced by decorative eyebrows
  13. Maturity does not include a change of face color
  14. Not visible: smaller canines
  15. Lower cheekbones (jugal, zygomatic arch) relative to tooth row

It looks like the ears are lower in humans, but relative to the eyes and nose, they are not.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Question #2 today is…
What changes can we see in the face of a chimp (Pan) compared to Proconsul?

  1. Loss of forehead in Pan compared to Proconsul
  2. Nose unknown in Pronsul, but bones are shorter and flatter in Pan
  3. Longer nose-to-lip distance in Pan
  4. Chin, absent, as in Proconsul
  5. Internal lip tissue unknown in Proconsul
  6. Muzzle the same in Pan, less above, but more below the nose
  7. Hair unknown in Pan
  8. Skin unknown in Pan
  9. Eyes unknown in Proconsul, but note their relatively higher placement in Pan
  10. Ears unknown in Proconsul
  11. Wrinkles unknown in Proconsul
  12. Brow ridges present in Pan, absent in Pronsul
  13. Skin color unknown in Proconsul
  14. Canines slightly larger in Pan
  15. Higher jugal relative relative to tooth row (= taller premaxilla and maxilla) and coronoid process of mandible
Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles.

Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles

And then there’s one more transitional taxon
Ardipithecus (Fig. 4) nesting somewhere between Proconsul and Homo

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

In Ardipithecus,
compared to Proconsul, we find larger eyes, a larger, lower nose, smaller canines, and an overall shorter/wider face… and a pelvis more appropriate for an upright stance, freeing the long arms to do something else, like carrying everything from infants to water to weapons to belongings. This is where we lost our hair, became long distance runners, developed sweat glands, and became wanderers.

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

 

 

References
Hopwood AT 1933a. Miocene primates from British East Africa. Annals and Magazine of Natural History (Series 10), 11, 96-98.
Hopwood AT 1933b. Miocene primates from Kenya. Journal of the Linnean Society of London. Zoology 38:437–464.

https://en.wikipedia.org/wiki/Proconsul

 

Where does Rooneyia nest on the primate cladogram?

Rooneyia viejaensis (Kirk et al. 2014; Late Eocene, 40 mya; Fig. 2) is a basal primate known from a nearly complete skull. Everyone agrees on that. Where Rooneyia nests within the Primates is the point of contention.

FIgure 1. Subset of the LRT focusing on the primate/bat clade. Rooneyia nests between lemurs and higher primates.

FIgure 1. Subset of the LRT focusing on the primate/bat clade. Rooneyia nests between lemurs and higher primates.

Kirk et al. 2014 report: 
“Rooneyia viejaensis is a North American Eocene primate of uncertain phylogenetic affinities. Although the external cranial anatomy of Rooneyia is well studied, various authors have suggested that Rooneyia is a stem haplorhine, stem strepsirrhine, stem tarsiiform, or stem anthropoid.”

The large reptile tree (LRT, 1051 taxa) nests Rooneyia between lemur-like Notharctus and all higher primates, including tarsiers like Tarsius and Darwinius. Granted there are not very many primates on the LRT. Nevertheless, those are the current results. So the LRT indicates or suggests that Rooneyia is a stem hapolorhine, stem strerpsirrhine, stem trasiiform AND stem anthropoid. I’ll have to add more taxa in these clades to make a more precise recovery.

Figure 1. Rooneyia images from Digimorph.org and used with permission. White background and overlying DGS colors added here. The basal tree shrew/primate, Ptilocercus, is shown to scale.

Figure 2. Rooneyia images from Digimorph.org and used with permission. White background and overlying DGS colors added here. The basal tree shrew/primate, Ptilocercus, is shown to scale. The postorbital bar and canine depth on Rooneyia are imagined. Does not color help one understand the bones so much better and more quickly?

References
Kirk EC, Daghighi P, Macrini TE, Bhullar B-AS and Rowe TB 2014. Cranial anatomy of the Duchesnean primate Rooneyia viejaensis: new insights from high resolution computed tomography. Journal of Human Evolution, 74, 82-95). online here.

Purgatorius: What is it?

Wikipedia reports: 
“For many years, there has been a large debate as to whether Purgatorius is a primitive member of the Primates or a basal member of the Plesiadapiforms.” Here (Fig. 1) taxa from the Plesiadapiformes have giant procumbent (rat-like) incisors followed by a long diastema, followed by flat molars…completely UNLIKE Purgatorius. So what were they thinking?

Halliday et al. 2015
nested Purgatorius outside crown group placentals with Protunugulatum (Fig 1). That seems reasonable, though it is twice the size. However, the large reptile tree (LRT, 1044 taxa) was not able to replicate most of the Halliday team’s cladogram, which nested hyraxes with elephant shrews…and horses… and that clade with pre-odontocetes and an early artiodactyl. It just gets worse after that. Protunugulatum was originally allied with condylarths, large plant-eating mammals. Halliday et al. nested it outside the placentals. Wible et al. 2007 nested it with whales + artiodactyls (a clade not validated by the LRT).

Purgatorius is another one of those fossils
known from an incompleted mandible with teeth and little else. Based on a lack of other bones, this is the sort of fossil the LRT cannot successfully resolve and it does not make it onto the list. So we go to plan #2: visual comparisons.

Figure 1. Purgatorius compared to other basal and often Paleocene mammals.

Figure 1. Purgatorius compared to other basal and often Paleocene mammals. Given these choices, Purgatorius looks more like Palaechthon, the basal dermopteran, than any other taxa in the LRT. Taxa in yellow nest together in the LRT with primates. Taxa in pink nest with rats and rabbits. Maelestes is a basal tenrec.

Rat-sized Purgatorius unio
(Valen and Sloan 1965; Latest Cretaceous/Earliest Paleocene) gained some early notoriety as the earliest known primate. Ankle bones found in association with Purgatorius, but not articulation, show signs of being flexible like those of primates (Kaplan 2012).

I can describe Purgatorius in the simplest of terms
based on comparisons to related basal mammal taxa (Fig. 1) and without describing any molar cusps (except one).

  1. small in overall size (skull < 2cm in length)
  2. robust mandible with convex dorsal and ventral rims and straight in occlusal view
  3. incisors likely procumbent, but not large
  4. canine tiny
  5. three robust premolars and three robust molars with one very tall cusp
  6. Premolar #3 taller than other teeth

Based on a visual comparison
of candidate taxa (Fig. 1), Purgatorius looks more like Protungulatum and even more like Palaechthon. The latter nests with flying lemurs like Cynocephalus. So we’re close to the base of primates, but closer to their cousins, and far from plesiadapiformes.

Best I can do for now…

References
Halliday TJD, Upchurch P and Goswami A 2015. Resolving the relationships of Paleocene placental mammals Biological Reviews. | doi = 10.1111/brv.12242
Kaplan M 2012. Primates were always tree-dwellers. Nature. doi:10.1038/nature.2012.11423
Van Valen L and Sloan R 1965. The earliest primates. Science. 150(3697): 743–745.
Wible JR, Rougier GW, Novacek MJ and Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.” Nature volume 447: 1003-1006

wiki/Purgatorius

Goodbye Scrotifera. Goodbye Euarchontaglires. Goodbye Scandentia. etc. etc.

Earlier the large reptile tree
found that several former clades, like Parareptilia, PterodactyloideaCetacea, Testudinata (Chelonia) Notoungulata, Pseudosuchia, Ornithodira and Pinnipedia were not monophyletic… and that list keeps growing.

The large reptile tree (LRT, 1044 taxa) does not replicate the following mammalian clades:

  1. Scandentia – tree shrews: yes, closely related, but at the bases of different clades.
  2. Euarchontaglires – rodents, rabbits, tree shrews, flying lemurs and primates,  (Fig. 1)
  3. Euarchonta – tree shrews, flying lemurs, primates and plesiadapiformes.
  4. Glires – rodents, rabbits
  5. Scrotifera – Eulipotyphla (see below), bats, pangolins, Carnivora, Euungulata (including whales)
  6. Eulipotyphla – hedgehogs, shrews, solenodons, moles (moles are Carnivora))
  7. Euungulata – perissodactyls, artiodactyls (including whales)
  8. Tenrecidae – tenrecs, some are closer to shrews, others closer to odontocetes
  9. Macroscelidea – elephant shrews, some are closer to tenrecs
  10. Primates – Plesiadapiformes and extant primates, including Daubentonia (the aye-aye. No giant anterior dentary teeth in valid primates.
  11. there are a few more I’m overlooking. I’ll add them as they come to me.
Figure 1. Glires and Euarchonta are two clades within the Mammalia in the LRT.

Figure 1. Glires and Euarchonta are two clades within the Mammalia in the LRT.

Let’s focus on Plesiadapiformes
Bloch et al. 2007 found plesiadapiforms (Plesiadapis, Carpolestes and kin) more closely related to primates than to any other group. They did not test against rodents and multituberculates. The LRT does not replicate these results, but finds plesiadapiforms more closely related to multituberculates and rodents when included.

According to Bloch & Boyer 2002
“Plesiadapiforms share some traits with living primates, including long fingers well designed for grasping, and other features of the skeleton that are related to arboreality.” That’s fine, but there are other taxa in the tree topology with long fingers, too.

Paromomyidae
Krause 1991 reports, “Paromomyids …have long been regarded by most workers as members of the Plesiadapiformes.” Again, the LRT does not support this, but nests Paromomyids, like Ignacius (Fig. 2), with rodents, like Mus and Paramys. Paromomyids have squared off and flat molars, but Paromomys does not.

Figure 2. The skull of Ignacius nests with other rodents, not plesiadapiformes.

Figure 2. The skull of Ignacius nests with other rodents, not plesiadapiformes. Ironically it is closer to the squirrel-like Paramys than to Paromomys.

Beard 1990 thought paromomyids,
as plesiadapiforms, where close to colugos or “flying lemurs”. The LRT (Fig. 1) does not support this relationship. Rather paromomyids, like Ignacius, were squirrel-like, able to scamper both in the trees and on the ground. Ignacius graybullianus (USNM 421608, Fig. 1) is a new taxon that nests as a basal rodent in the LRT.

Figure 3. Ignacius clarkforkensis known parts.

Figure 3. Ignacius clarkforkensis known parts.

Remmber, no primates 
have giant anterior dentary teeth. The aye-aye, Daubentonia, has such teeth, but the LRT finds it nests with Plesiadapis and multituberculates and rodents, not primates. Yes, plesiadapiformes and Ignacius had long limbs, big brains and binocular vision, but by convergence with primates.

References
Beard KC 1990. 
Gliding Behavior and palaeoecology of the alleged primate family Paromomyidae (Mammalia, Dermoptera). Nature 345, 340-341.
Bloch J, Silcox MT, et al. 2007.
New Paleocene skeletons and the relationship of plesiadapiforms to crown-clade primates.  Proceedings of the National Academy of Science 104, 1159-1164.
Kay RF, Thewissen JG and Yoder, AD 1992. Cranial anatomy of Ignacius graybullianus and the affinities of the Plesiadapiformes. American Journal of Physical Anthropology. 89 (4): 477–498. doi:10.1002/ajpa.1330890409.
Krause DW 1984. Mammal Evolution in the Paleocene: Beginning of an Era. In: Gingerich, P. D. & Badgley, C. E. (eds.): Mammals: notes for a short course. Univ. of Tennessee, Department of Geological Sciences.
Krause DW 1991. Were paromomyids gliders? Maybe, maybe not. Journal of human evolution 21:177-188.

In honor of Mother’s Day…

We have a pregnant
plesiosaur (Fig. 1; O’Keefe and Chiappe 2011; LACM 129639; Late Cretaceous, 78 mya)…

Figure 1 Pregnant Polycotylus (LACM 129639) from O'Keefe and Chiappe 2011.

Figure 1 Pregnant Polycotylus (LACM 129639) from O’Keefe and Chiappe 2011.

and a pregnant primate (Fig. 2) very dear to my heart.

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet).

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet) and about three years ago.

Being a mom goes way, way back
In our lineage, first cells stuck together, flagella out (Fig. 3). Then four cells stuck together. Then eight. Ultimately hundreds stuck together creating a sphere, or blastula. And little blastulas formed inside until they were large enough to break free.

Figure 3. Blastula from the book, "From the Beginning" by Peters 1991.

Figure 3. Blastula from the book, “From the Beginning” by Peters 1991.

Plesiosaurs and primates capable of understanding prehistory
followed shortly thereafter. The basics of being a mother haven’t really changed much in the last few billion years.

References
O’Keefe FR and Chiappe LM 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science. 333 (6044): 870–873. doi:10.1126/science.1205689.
Peters D 1991. From the beginning – the story of human evolution. Little Brown. 128 pp. Online here.

wiki/Polycotylus