Giant Mesozoic flat heads: Siderops and Koolasuchus

Little Gerrothorax has a new giant sister, Siderops,
(Fig. 1) in the large reptile tree (LRT, 1440 taxa). This is a traditional nesting recovered by prior workers.

We’re still missing those poorly ossified fingers and toes.
Or did this clade have lobefins (Fig. 2)? Nothing past the wrist is known for any clade members (that I’ve seen). Could go either way with available data… so, don’t assume fingers and toes.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale. Are these lobefins or did they have feet? And look at the size of those palatal fangs!

Speaking of clades,
both Siderops and Gerrothorax are traditionally considered temnospondyls, which all have fingers and toes. Here they nest prior to traditional temnospondyls, closer to flathead lobefin tetrapods, like Tiktaalik, in the LRT (subset Fig. 2).

Figure 1. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Figure 2. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Siderops kehli (Warren and Hutchinson 1983; Early Jurassic, 180mya; skull 50cm long, overall 2.5m long) was traditionally considered a chigutisaurid temnospondyl or a brachyopoid. Here Siderops nests with the much smalller Gerrothorax. No branchials and scales were reported. The back of the skull and the extremities are unknown, so modifications were made to reflect that lack of data here.

Koolasuchus cleelandi was a late surviving Early Cretaceous giant from this clade, presently known from just a few bones, like the mandible (Fig. 2).

Tomorrow we’ll take a look
at several giant ‘amphibians’ (= anamniote tetrapods) all to scale.


References
Warren A and Hutchinson M 1983. The last labyrinthodont? A new brachyopoid (Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of Queensland, Australia. Philosophical Transactions of The Royal Society B Biological SciencesB 303:1–62.

wiki/Gerrothorax
wiki/Siderops

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Why do human males develop facial hair?

Distinct from other apes,
human males develop facial hair at puberty that creates a beard and mustache. Then many men shave it off. If you’ve ever wanted to know why, here are some recent hypotheses.

According to the BBC online, “beards probably evolved at least partly to help men boost their standing among other men.” because women are not more interested in men with beards. “To reproduce, it’s often not enough to simply be attractive. You also have to compete with the same sex for mating opportunities.”

“A man’s ability to grow a fulsome beard isn’t actually neatly linkedto his testosterone levels. “

“Both men and women perceive men with beards as olderstronger and more aggressive than others. And dominant men can get more mating opportunities by intimidating rivals to stand aside.”

Figure 1. Percent of body hair on males worldwide appease here in darker tones. Both equatorial and polar humans have less hair. Mediterranean and Scandinavian men have more hair covering their bodies.

Figure 1. Percent of body hair on males worldwide appease here in darker tones. Both equatorial and extreme polar humans have less hair. Mediterranean and Scandinavian men have more hair.

“Men on average also think their body should be more muscular than women report that they want, while women on average believe they need to be thinner and wear more make-up than men report that they want.”

“Make-up use, average body composition, and even the very ability to grow facial hair all differ enormously across the world – meaning we could get different results elsewhere.”

This BBC article originally appeared on The Conversation (links below).


References
Dixson A DSc, Dixson B and Anderson M 2005. Sexual Selection and the Evolution of Visually Conspicuous Sexually Dimorphic Traits in Male Monkeys, Apes, and Human Beings, Annual Review of Sex Research, 16:1, 1-19, DOI: 10.1080/10532528.2005.10559826

http://www.bbc.com
https://theconversation.com

Megapodius: basal to all living birds (except ratites)

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites).

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites). And it looks like a basal bird, not too this… not too that.

So far, with the present list of tested taxa,
this living bird (Fig. 1) is the seemingly unchanged descendant of all living birds, other than the ratites and kiwis, according to the large reptile tree (LRT, 1089 taxa). Megapodius demonstrates that early neognaths, like their sister paleognaths, were long-legged terrestrial omnivores, able to fly, but not very well, despite the large and subdivided breastbone (keeled sternum) and long locked-down coracoids.

Figure 1. More taxa, updated tree, new clade names.

Figure 2. subset of the LRT focusing on birds and their ancestors

Megapodius freycinet (Gaimard 1823) is the extant dusky scrubfowl, one of the most primitive of living neognath birds. This one nests at the base of the hook-beak predatory birds, the most basal extant neognaths.

References
Gaimard JP 1823. Mémoire sur un nouveau genre de Gallinacés, establi sous le nom de Mégapode. Bulletin General et Universel des Annonces et de Nouvelles Scientifiques 2: 450-451.

https://www.gbif.org/species/2482114

 

 

Cope’s Rule vs. Phylogenetic Miniaturization

Getting bigger
Wikipedia reports, Cope’s rule, named after American paleontologist Edward Drinker Cope, postulates that population lineages tend to increase in body size over evolutionary time. It was never actually stated by Cope, although he favoured the occurrence of linear evolutionary trends.”

Getting smaller
On the other hand, there is no Wikipedia category for Phylogenetic Miniaturization, which postulates that population lineages tend to decrease in body size over evolutionary time.

Both have their time and place.
For instance, if you take a look at the large reptile tree (LRT, 1026 taxa) in the mammal subset you’ll find the following taxon pairs representing Cope’s Rule:

  1. Toxodon is a giant Dromiciops
  2. Panthera (lion) is a giant Procyon (raccoon)
  3. Homo (human) is a giant Ptilocercus (tree shrew)
  4. Physeter (sperm whale) is a giant Tenrec (tenrec)
  5. Balaenoptera (blue whale) is a giant Ocepeia
  6. Giraffa (giraffe) is a giant Cainotherium
  7. Elephas (elephant) is a giant Procavia (hyrax)
  8. Ceratotherium (rhino) is a giant Hyracodon
  9. Paraceratherium is a giant Mesohippus.
  10. And in pterosaurs…Pteranodon is a giant Germanodactylus
  11. Quetzalcoatlus is a giant TM10341

Note:
these are general trends, not always direct lineages. We’ll never find the exact ancestors of living or fossil taxa, though we can get very close! Employed taxa represent evolutionary stages, sets of derived characters mixed with some small or large number of autapomorphic traits not shared by the unknown common ancestor of the small and large taxon pairs.

Likewise
you’ll also find in the LRT the following taxon pairs representing examples of phylogenetic miniaturization, some from the large pterosaur tree:

  1. Gephyrostegus is a tiny Proterogyrinus
  2. Terrapene (box turtle) is a tiny Elginia
  3. Cosesaurus is a tiny Macrocnemus
  4. Hypuronector is a tiny Jesairosaurus
  5. Bellubrunnus is a tiny Campylognathoides
  6. TM 13104 is a tiny Scaphognathus
  7. Tetrapodophis is a tiny Adriosaurus
  8. Hadrocodium is a tiny Haldanodon.
  9. Elaschistosuchus is a tiny Proterosuchus
  10. Gracilisuchus is a tiny Vjushkovia.
  11. Archaeopteryx is a tiny Sinornithoides.

What goes down (gets smaller), usually goes up (gets bigger)
And sometimes what gets bigger gets smaller. Case in point: the Pygmy or Channel Islands mammoth.

Anything can happen at any time in evolution
given enough time. As noted earlier, phylogenetic miniaturization was present at the origin of several major clades of tetrapods and in clades of pterosaurs in particular. And this appears to occur during times of survival stress for several reasons. On the other hand, apparently it takes an epoch filled with plenty of food and other resources to produce giant animals. As you know, various parts of the Earth have created stress and bounty throughout its long prehistory.

Sperm whales have faces, too!

Figure 1. This image comes from a news story on whale strandings and the contents of their stomachs. But I see two distinct faces here, like humans, chimps and other mammals with distinctive coloration patterns and variations on morphology.

Figure 1. This image comes from a news story on whale strandings and the contents of their stomachs. But I see two distinct faces here, like humans, chimps and other mammals with distinctive coloration patterns and variations on morphology.

Humans have distinct faces.
So do chimps, dogs, cows, other mammals and animals in general. We just have to see two in close proximity (as in Fig. 1) to notice the slight variation that Nature puts on pod mates and/or family members. This minor variation, of course, is the engine by which large variation can add up in isolation to produce new species, whether larger or smaller, more robust or more gracile, shorter, longer, with longer or shorter limbs, longer or shorter faces. The variations are endless, but patterns can be gleaned in phylogenetic analysis.

Look closely
and you’ll see the profile of these two beached whales are slightly different, the flippers are slightly different, to say nothing of the variations on the white patches and scars that they are partly born with and then develop during their lifespan as white scars.

Just think,
this odontocete is derived from swimming tenrecs, derived from basal placentals, derived cynondonts, etc. etc. all due to subtle variations in family members like you see here, over vast stretches of time and millions of generations.

Trimerorhachis and kin to scale

Updated April 23 with a revision to the tabulars of Panderichthys. Thanks DM! My bad. 

Yesterday we took a revisionary look at Trimerorhachis insignis (Cope 1878, Case 1935, Schoch 2013; Early Permian; 1m in length; Fig. 1). Today we take a quick peek at the taxa that surround it in the large reptile tree (LRT, 980 taxa, Fig. 1) all presented to scale. Several of these interrelationships have gone previously unrecognized. Hopefully seeing related taxa together will help one focus on their similarities and differences.

Figure 1. Trimerorhachis and kin to scale. Here are Panderichthys, Tiktaalik, Ossinodus, Dvinosaurus, Acanthostega, Batrachosuchus and Gerrothorax. Maybe those tabular horns on Acanthostega are really supratemporal horns, based on comparisons to related taxa.

Figure 1. Trimerorhachis and kin to scale. Here are Panderichthys, Tiktaalik, Ossinodus, Dvinosaurus, Acanthostega, Batrachosuchus and Gerrothorax. Maybe those tabular horns on Acanthostega are really supratemporal horns, based on comparisons to related taxa.

And once again
phylogenetic miniaturization appears at the base of a tetrapod clade. Note: the small size of Trimerorhachis (Fig. 1) may be due to the tens of millions of years that separate it in the Early Permian from its initial radiation in the Late Devonian, at which time similar specimens might have been larger. Provisionallly, we have to go with available evidence.

We start with…

Panderichthys rhombolepis (Gross 1941; Frasnian, Late Devonian, 380 mya; 90-130cm long; Fig. 1). Distinct from basal taxa, like Osteolepis, Pandericthys had a wide low skull, a wide low torso, a short tail and five digits (or metacarpals). No interfrontal was present. The orbits were further back and higher on the skull. Dorsal ribs, a pelvis and large bones within the four limbs were present.

Tiktaalik roseae (Daeschler, Shubin and Jenkins 2006; Late Devonian, 375mya: Fig. 1) nests between Pandericthys and Trimerorhachis in the LRT. Distinct from Panderichthys the opercular bones were absent and the orbits were even further back on the skull.

Ossinodus pueri (Warren and Turner 2004; Viséan, Lower Carboniferous; Fig. 1) was orignally considered close to Whatcheeria. Here it nests between Trimerorhachis and Acanthostega. The presence of an intertemporal appears likely. Distinct from Acanthostega, the skull is flatter, the naris is larger. Distinct from sister taxa, the maxilla is deep and houses twin canine fangs. A third fang arises from the palatine.

Acanthostega gunnari (Jarvik 1952; Clack 2006; Famennian, Late Devonian, 365mya; 60cm in length; Fig. 1) was an early tetrapod documenting the transition from fins to fingers and toes. Based on its size and placement, the nearly circular bone surrounding the otic notch is here identified as a supratemporal, not a tabular, which appears to be lost or a vestige fused to the supratemporal. This taxon is derived from a sister to Ossinodus and appears to have been an evolutionary dead end.

Trimerorhachis insignis (Cope 1878, Case 1935, Schoch 2013; Early Permian; 1m in length; Fig. 1) was considered a temnospondyl close to Dvinosaurus, but here nests as a late surviving basal tetrapod from the Late Devonian fin to finger transition. It is close to Ossinodus and still basal to Dvinosaurus (Fig. 1) and the plagiosaurs. As a late survivor, Trimerorhachis evolved certain traits found in other more derived tetrapods by convergence, like a longer femur and open palate. The presence of a branchial apparatus indicates that Trimerorhachis had gills in life. Dorsally Trimerorhachis was covered with elongated scales, similar to fish scales.

Dvinosaurus primus (Amalitzky 1921; Late Permian; PIN2005/35; Fig. 1) Dvinosauria traditionally include Neldasaurus among tested taxa. Here Dvinosaurus nests basal to plagiosaurs like Batrachosuchus and Gerrothorax and was derived from a sister to Trimerorhachis.

Batrachosuchus browni (Broom 1903; Early Triassic, 250 mya; Fig. 1) nests with Gerrothorax, but does not have quite so wide a skull.

Gerrothorax pulcherrimus (Nilsson 1934, Jenkins et al. 2008; Late Triassic; Fig. 1) was originally considered a plagiosaurine temnospondyl. Here it nests with the Trimerorhachis clade some of which  share a lack of a supratemporal-tabular rim, straight lateral ribs and other traits.

This clade of flathead basal tetrapods
is convergent with the flat-headed Spathicephalus and Metoposaurus clades and several others.

References
Berman DS and Reisz RR 1980. A new species of Trimerorhachis (Amphibia, Temnospondyli) from the Lower Permian Abo Formation of New Mexico, with discussion of Permian faunal distributions in that state. Annals of the Carnegie Museum. 49: 455–485.
Broom R 1903. On a new Stegocephalian (Batrachosuchus browni) from the Karroo Beds of Aliwal North, South Africa. Geological Magazine, New Series, Decade IV 10(11):499-501
Case EC 1935. 
Description of a collection of associated skeletons of Trimerorhachis. University of Michigan Contributions from the Museum of Paleontology. 4 (13): 227–274.
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Clack JA 2009. The fin to limb transition: new data, interpretations, and hypotheses from paleontology and developmental biology. Annual Review of Earth and Planetary Sciences. 37: 163–179.
Coates MI 2014. The Devonian tetrapod Acanthostega gunnari Jarvik: Postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution. Earth and Environmental Science Transactions of the Royal Society of Edinburgh.
Coates MI and Clack JA 1990. Polydactly in the earliest known tetrapod limbs. Nature 347: 66-69.
Colbert EH 1955. Scales in the Permian amphibian. American Museum Novitates. 1740: 1–17.
Daeschler EB, Shubin NH and Jenkins FA, Jr 2006. A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature. 440 (7085): 757–763.
Gross W 1941. Über den Unterkiefer einiger devonischer Crossopterygier (About the lower jaw of some Devonian crossopterygians), Abhandlungen der preußischen Akademie der Wissenschaften Jahrgang.
Jarvik E 1952. On the fish-like tail in the ichtyhyostegid stegocephalians. Meddelelser om Grønland 114: 1–90.
Jenkins FA Jr, Shubin NH, Gates SM and Warren A 2008. Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a reassessment of head lifting in temnospondyl feeding. Journal of Vertebrate Paleontology. 28 (4): 935–950.
Nilsson T 1934. Vorläufige mitteilung über einen Stegocephalenfund aus dem Rhät Schonens. Geologiska Föreningens I Stockholm Förehandlingar 56:428-442.
Olson EC 1979. Aspects of the biology of Trimerorhachis (Amphibia: Temnospondyli). Journal of Paleontology. 53 (1): 1–17.
Pawley K 2007. The postcranial skeleton of Trimerorhachis insignis Cope, 1878 (Temnospondyli: Trimerorhachidae): a plesiomorphic temnospondyl from the Lower Permian of North America. Journal of Paleontology. 81 (5):
Warren A and Turner S 2004. The first stem tetrapod from the Lower Carboniferous of Gondwana. Palaeontology 47(1):151-184.
Williston SW 1915. 
Trimerorhachis, a Permian temnospondyl amphibian. The Journal of Geology. 23 (3): 246–255.
Williston SW 1916. The skeleton of Trimerorhachis. The Journal of Geology. 24 (3): 291–297.

 

wiki/Ossinodus
wiki/Acanthostega
wiki/Tiktaalik
wiki/Panderichthys
wiki/Trimerorhachis
wiki/Gerrothorax
wiki/Batrachosuchus

Taxa closest to the human lineage in the LRT

The large reptile tree is capable of providing a list of taxa closest to the lineage of any included taxon. And it is updated all the time…

For instance,
in the lineage of humans (Homo sapiens) the following taxa are closest to that main line. Read this list with the understanding that taxa closest to the main line have often evolved traits that we infer (from phylogenetic bracketing) were not present in the actual hypothetical ancestor. The chance of finding the actual ancestors in the fossil record are vanishingly small, so we do the best we can with what specimens we have. Also note that the rare appearance of key fossils may be tens to hundreds of millions of years after their likely first appearance in this lineage. Thus the the chronological order may not match the phylogenetic order, but it does provide a ‘window’ to that first appearance.

  1. Ichthyostegabasal tetrapod  365 mya
  2. Pederpes 350 mya
  3. Proterogyrinus 322 mya
  4. Seymouria 275 mya
  5. Utegenia – also basal to frogs 300 mya
  6. Silvanerpetonproximal to the basalmost reptile 335 mya
  7. Gephyrostegus bohemicusbasalmost reptile/amniote 310 mya
  8. Eldeceeonbasalmost archosauromorph 335 mya
  9. Romeriscus 306 mya
  10. Solenodonsaurus also basal to chroniosuchids 290 mya
  11. Casineria – 335 mya
  12. Brouffia 310 mya
  13. Coelostegus  310 mya
  14. Protorothyris MCZ 1532 290 mya
  15. Protorothyris CM 8617 290 mya
  16. Protorothyris MCA 2149 290 mya
  17. Vaughnictis – last common ancestor of mammals and dinosaurs 290 mya
  18. Apsisaurus –  basalmost synapsid 295 mya
  19. Varanosaurus FMNH PR 1760 280 mya
  20. Varanosaurus BSPHM 1891 XV20 280 mya
  21. Archaeothyris 306 mya
  22. Ophiacodon 290 mya
  23. Haptodus – also basal to pelycosaurs 305 mya
  24. Stenocybus – also basal to anomodontids 295 mya
  25. Cutleria basalmost therapsid 295 mya
  26. Hipposaurusbasalmost kynodont 260 mya
  27. Ictidorhinus 260 mya
  28. Biarmosuchus 260 mya
  29. Eotitanosuchus 260 mya
  30. Lycosuchus 260 mya
  31. Procynosuchusbasalmost cynodont 250 mya
  32. Thrinaxodon 245 mya
  33. Probainognathus 230 mya
  34. Haldanodon 145 mya
  35. Pachygenelus 195 mya
  36. Sinoconodonbasalmost mammal, also basal to living monotremes 195 mya
  37. Megazostrodon 200 mya
  38. Juramaia 160 mya
  39. Cronopio 98 mya
  40. Didelphisbasalmost metatherian extant
  41. Thylacinus – basal to many living marsupials recently extinct
  42. Monodelphisbasalmost eutherian extant
  43. Eomaia 125 mya
  44. Nandinia – also basal to carnivores extant
  45. Ptilocercus – basalmost primate/dermpteran/bat extant
  46. Notharctus – also basal to lemurs 54 mya
  47. Aegyptopithecus* 33 mya
  48. Proconsulbasalmost anthropoid 18 mya
  49. Ardipithecus* basalmost hominid 5 mya
  50. Australopithecus* 3 mya
  51. Homo sapiens extant

* not yet listed in the LRT, but documented at ReptileEvolution.com

With the recent addition of certain stem mammals,
like Haldanodon and Liaconodon, this list expands upon and refines the list that first appeared in Peters 1991. Each of the names links to further information. There is also a video that includes most of these taxa here on YouTube.com.

References
Peters D 1991. From the Beginning, the Story of Human Evolution. online PDF.