Episode 456: The oldest diplodocoid and a new Egyptian titanosaur. Tharosaurus, a dicraeosaurid like Amargasaurus, is the oldest diplodocoid ever found; The new titanosaur, Igai, was described from Egypt; and we explore how cabinets of curiosity were the original natural history museums
News:
- There’s a new titanosaur, Igai semkhu source
- There’s a new dicraeosaurid sauropod, Tharosaurus indicus source
- The Ubirajara fossil was officially returned to Brazil in June source
- Gavin Leng, a fossil hunter known for discoveries such as Eotyrannus, recently passed away source
- If you’re in London, check out the Brick Dinos exhibit at the Horniman Museum & Gardens source
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The dinosaur of the day: Megapnosaurus
- Also includes Syntarsus and to some extent Coelophysis
- Mentioned Megapnosaurus/Syntarsus briefly in episode 426 (there’s a pair of them on display in a diorama at the Natural History Museum of Zimbabwe)
- Coelophysid theropod that lived in the Early Jurassic in what is now Africa and possibly the U.S.
- Looked like Coelophysis, had a long tail, walked on two legs, had short arms, and a long face
- Similar in size and shape to Coelophysis
- Small to medium sized
- Estimated to grow up to 7.2 ft (2.2 m) long and weigh up to 29 lb (13 kg)
- Lightly built and fast
- Had a large brain cavity, so probably intelligent especially compared to other dinosaurs
- Based on growth rings, lived on average seven years
- May have been nocturnal, based on scleral rings looking similar to modern nocturnal birds
- Had a “weak joint” in the jaw bones, which gave it a hooked premaxillary jaw (tip of the snout)
- Hypothesis then that it was a scavenger (couldn’t go after live prey)
- Name is still debated, as Megapnosaurus, Coelophysis or a new genera
- Genus name Megapnosaurus means “big dead lizard”
- Two species? Megapnosaurus rhodesiensis and Megapnosaurus kayentakatae
- Some paleontologists consider Megapnosaurus to be synonymous with Coelophysis, but this is still being debated
- Start with Megapnosaurus rhodesiensis
- Megapnosaurus rhodesiensis found in the Elliot Formation in South Africa and the Forest Sandstone Formation in Rhodesia (now known as Zimbabwe)
- Megapnosaurus rhodesiensis estimated to be up to 7.2 ft (2.2 m) long and weigh up to 29 lb (13 kg)
- Described as lean and long, with an s-shaped neck, long legs that looked like legs of birds like the secretary bird (which looks like it’s walking on stilts)
- Had shorter arms, with four fingers on each hand, and a long tail
- No evidence it had feathers, but often portrayed that way, because it looked so bird-like
- Fossils first found in 1963
- Holotype includes most of a well preserved skeleton (only missing skull and neck vertebrae)
- More fragments also found
- Several specimens found in 1985 in South Africa (Elliot Formation), and 26 specimens collected in Zimbabwe (Forest Sandstone Formation) in 1963, 1968, and 1972
- Elliot Formation probably an ancient flood plain. Other dinosaurs that lived around the same time and place include the sauropodomorphs Massospondylus and Ignavusaurus, also ornithischians like Lesothosaurus and Heterodontosaurus
- Forest Sandstone Formation had crocodiles, Massospondylus and indeterminate prosauropods
- In 1972, Raath found hundreds of bones from at least 26 individuals from different growth stages (included skulls and neck vertebrae, as well as gut contents)
- Raath described the fossils in his thesis in 1977 (fossils from that locality now at the Queen Victoria Museum in Australia)
- Healed fractures of the leg and feet found in Megapnosaurus rhodesiensis, and one specimen had signs in the sacral rib of fluctuating asymmetry, which may be from living in stressful conditions
- Possible they hunted in packs
- Possible sexual dimorphism, based on some individuals being robust with large limbs and large muscle attachments compared to more gracile individuals that are similar in size (and adults)
- Lots of variable growth, with some individuals being larger but younger/more immature than smaller, mature adults
- Variable growth likely common in earlier dinosaurs but later lost (birds don’t do it), and may have helped early dinosaurs adapt to harsh environments
- Originally named Syntarsus rhodesiensis by Michael Raath in 1969 based on the Zimbabwe (Rhodesia) fossils
- But in 2001, found there was a beetle named Syntarsus asperulus
- Ivie and others renamed Syntarsus rhodesiensis to Megapnosaurus in 2001
- Some controversy here (will get into)
- In 2001, Michael Ivie and others named Megapnosaurus and combined Megapnosaurus rhodesiensis (named by Raath in 1969) and Megapnosaurus kayentakatae (named by Rowe in 1989)
- Syntarsus asperulus was a beetle, named in 1869 by Fairmaire (though two of the authors, including Ivie made it a junior synonym of Cerchanotus in 1990—but still, name had been already used)
- According to Ivie and others: “This turn of events requires a new name, and although S. rhodesiensis is described inside the cover of the 1996 volume 3 of the journal SYTNTARSUS as “a small carnivorous dinosaur,” and although as good and loyal phylogeneticists, we understand that it was not really on the lizard lineage, at the scale of an entomologist, it looks like a big dead lizard. So, in what may well be the first name for a dinosaur every proposed in an entomological journal, we propose the replacement name Megapnosaurus”
- “[…] this moniker seems highly appropriate for this animal”
- Debates on whether to lump Megapnosaurus into Coelophysis (and make Megapnosaurus rhodesiensis a junior synonym, to become Coelophysis rhodesiensis)
- Gregory Paul, Michael Raath, and others agree
- Talked about Coelophysis in episode 204
- A couple studies in 2018, by Barta and others and by Christopher Griffin, found enough differences to keep them separate
- Some examples: Megapnosaurus rhodesiensis doesn’t have a fifth hand bone (metacarpal) and Coelophysis bauri does
- Also differences in scars, grooves, and depressions on the humerus and femur (arm and leg bones)
- Now on to Megapnosaurus kayentakatae
- In 1989, Timothy Rowe described a second species of “Syntarsus”, as Syntarsus kayentakatae, based on a skull and parts of a skeleton
- Fossils found in the Kayenta Formation in Arizona, U.S. (Early Jurassic)
- Kayenta Formation had rivers, and rainy summers and dry winters
- Other dinosaurs from the Kayenta Formation include theropods like Dilophosaurus and Kayentavenator (which was originally thought to be Syntarsus kayentakatae/Megapnosaurus kayentakatae—but there are enough differences to be separate), the “Shake-N-Bake” theropod, an undescribed coelophysoid known from a partial skeleton found in 1978 (lots of small bones cemented together in a dense matrix because the fossils had washed down together), sauropodomorphs like Sarahsaurus and Anchisaurus, heterodontosaurs, and armored dinos like Scelidosaurus and Scutellosaurus
- Other animals that lived around the same time and place include sharks, fish, frogs, turtles, lizards, pterosaurs, mammals, crocodylomorphs, mussels, and snails
- Found at least 16 individuals of Syntarsus kayentakatae (fragmentary remains)
- Fossils found between 1977 and 1979
- Type specimen of Syntarsus kayentakatae is a fully mature, robust adult
- Holotype of Syntarsus kayentakatae was distorted (mostly left side preserved, because it rested on left side and was partially buried, but right side including the skull was exposed to water currents)
- Species name refers to Dr. Kathleen Smith, who has the nickname “Kayenta Kay” because of her work in the Kayenta Formation, which includes finding the type specimen of Megapnosaurus kayentakatae
- Megapnosaurus kayentakatae estimated to be up to 8.2 ft (2.5 m) long and weigh up to 66 lb (30 kg)
- One big difference between Megapnosaurus rhodesiensis and Megapnosaurus kayentakatae is that Megapnosaurus kayentakatae had two small crests on its head (similar to Dilophosaurus but smaller)
- Whether to use the name Megapnosaurus or Syntarsus depends on who you ask
- In 2000, Alex Downs compared Coelophysis bauri and Syntarsus rhodesiensis and found them to be so similar that Syntarsus was a junior synonym to Coelophysis (only had minor details in the neck length and other small differences)
- In 2004 Anthea Bristowe and Michael Raath synonymized Coelophysis and Syntarsus as well, based on work on a partially disarticulated skull of a juvenile Syntarsus specimen
- Said “that the recently proposed facetious replacement name for Syntarsus (Megapnosaurus) should not stand”
- Found only minor differences and said that could be because they lived at different times (Coelophysis in Late Triassic and Syntarsus in Early Jurassic)
- In 2017, Daniel Barta and others found differences in the hands of Coelophysis bauri and Megapnosaurus rhodesiensis (fifth metacarpal)
- In 2018 Christopher Griffin found Megapnosaurus to be valid (enough differences between the two, including that there were some characters that varied as Megapnosaurus grew that weren’t found in Coelophysis, like scar on the humerus, and depressions on the femur)
- Though, did so most of the features that changed while growing (during ontogeny) were the same, and they were similar in size once fully grown
- In 2020 Adam Marsh and Timothy Rowe kept the name Syntarsus rhodesiensis instead of using Megapnosaurus or Coelophysis “because the systematic relationships of these animals within Coelophysoidea is in flux”
- In 2021 Ezcurra and others found that Syntarsus kayentakatae was not closely related to Coelophysis bauri or Megapnosaurus rhodesiensis
- In 2022 Skye McDavid and Jeb Bugos found Megapnosaurus rhodesiensis to be the valid name
- Controversy on the name change to Megapnosaurus and whether how it was changed was valid (some sources said whether it was ethically done)
- According to McDavid and Bugos, “If a taxonomic name is invalid (preoccupied or incorrectly formulated), then it is considered ethical to contact its original describer or describers to inform them of the problem so that they can correct their own error. If the original describer or describers are unreachable (for example if they are deceased or do not respond to correspondence) then the person who learns of the error will typically publish a correction. Ivie attempted to contact Raath but never received a reply. He and coauthors proceeded with publication of the replacement name after two years, and after being (incorrectly) told by dinosaur paleontologist John “Jack” Horner that Raath was deceased. (Michael Ivie, pers. comm.)”
- Also said, “The genus Megapnosaurus is here considered to be likely distinct from Coelophysis, but in need of further research”
- Found Megapnosaurus rhodesiensis to be correct, for now, but said it could possibly be a junior synonym and “usage of the name Megapnosaurus rhodesiensis is recommended. Usage of the name Coelophysis rhodesiensis is neither recommended nor discouraged. Usage of the name Syntarsus rhodesiensis is discouraged.”
- Also found that Syntarsus kayentakatae is most likely its own genus, and recommend it be provisionally referred to as ‘Megapnosaurus’ kayentakatae, “with quotation marks indicating a problematic genus assignment, until a new genus is formally described for this species”
- Other fossils found that may be Megapnosaurus or used to be Megapnosaurus/Syntarsus
- Darlington Munyikwa and Michael Raath described part of a Megapnosaurus/Syntarsus snout found in the Elliot Formation in South Africa (this is now known as Dracovenator)
- Several coelophysoid bones found in Mexico from the Early Jurassic were described as “Syntarsus” “mexicanum” but they weren’t properly described and are probably from an indeterminate coelophysoid
- Scientists referred a theropod specimen from Wales to Syntarsus sp. But in 2021 that was later named Pendraig (talked about in ep 360)
- In 2004, Randall Irmis reported fossils of Megapnosaurus found in Lufeng Formation, China, Early Jurassic (two specimens found). Would mean Megapnosaurus was also in Asia
Fun Fact:
Dicraeosaurids are not unique for their bifurcated neural spines (like those on Amargasaurus), even we have them!
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