Tiny Paleocene Zanycteris, now a marsupial even smaller than Jurassic Hadrocodium
This set of traditional small limnocyonid hyaenodonts
(Fig 1) nest within the carnivorous marsupials in the LRT. Limnocyon, Thinocyon Hapalodectes (IVPP V5235), tiny Zanycteris and Hadrocodium are known for their small size and flat, wide skull. Post-crania is generally not known, especially for the smaller taxa.
Figure 1. Paleocene Zanycteris is even smaller than Jurassic Hadrocodium.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=163″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=558″ class=”size-full wp-image-85754″ src=”https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=584&h=1073″ alt=”Figure 1. Paleocene Zanycteris is even smaller than Jurassic Hadrocodium.” width=”584″ height=”1073″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=584&h=1073 584w, https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=82&h=150 82w, https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg?w=163&h=300 163w, https://pterosaurheresies.files.wordpress.com/2024/05/hadrocodium_color_bones.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Paleocene Zanycteris is even smaller than Jurassic Hadrocodium.
These taxa
also provide a sequence ripe for study in a striking case of phylogenetic miniaturization in the Jurassic through Paleocene. The larger Eocene taxa are more primitive in the LRT, which could mean the only fossils known are late survivors of earlier radiations.
Evidently, being tiny helped this clade survive the asteroid impact.
Figure 2. Limnocyon, Thinocyon and Zanycteris to scale and nearly full scale on 72 dpi monitors. The larger two are from the Eocene. Zanycteris is earlier, from the Paleocene. So is Hapalodectes.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=121″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=412″ class=”size-full wp-image-85764″ src=”https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=584&h=1451″ alt=”Figure 2. Limnocyon, Thinocyon and Zanycteris to scale and nearly full scale on 72 dpi monitors. The larger two are from the Eocene. Zanycteris is earlier, from the Paleocene. So is Hapalodectes.” width=”584″ height=”1451″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=584&h=1451 584w, https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=60&h=150 60w, https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg?w=121&h=300 121w, https://pterosaurheresies.files.wordpress.com/2024/05/limnocyon_verus588-1.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Limnocyon, Thinocyon and Zanycteris to scale and nearly full scale on 72 dpi monitors. The larger two are from the Eocene. Zanycteris is earlier, from the Paleocene. So is Hapalodectes.
Usually tiny taxa, like Zanycteris,
are found at the base of new clades. Since Early Cretaceous Vincelestes (Fig 3) is more or less a descendant closer to Thinocyon (Fig 1), then this small predator may have had similar tiny ancestors from the Late Jurassic.
Figure x. Vincelestes overall.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=584″ class=”size-full wp-image-27836″ src=”https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=584&h=237″ alt=”Figure x. Vincelestes overall.” width=”584″ height=”237″ srcset=”https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=584&h=237 584w, https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=150&h=61 150w, https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg?w=300&h=122 300w, https://pterosaurheresies.files.wordpress.com/2016/08/vincelestes-overall588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Vincelestes overall. Scale bar = 1cm, so this skeleton is about full size @ 72dpi.
Limnocyon verus
(Marsh 1872, Middle Eocene) is known from a complete skull and mandibles plus a few uncrushed post-cranial bones.
Thinocyon medius
(Marsh 1872, Matthew 1909, Morlo and Gunnell 2003, Middle Eocene) was traditionally considered a small limnocyonine hyaenodontid mammal, but here nests with Vincelestes among the creodont marsupials. According to Morlo and Gunnell: “Limnocyoninae are relatively small hyaenodontid creodonts characterized by reduction and loss of upper and lower third molars.”
Zanycteris paleocenus
(Matthew 1917, Buerger 2013, Crowell, Wible and Chester 2024; skull length <1cm, Paleocene 61-57my, AMNH 17180) is among the smallest of all mammals and nests with Limnocyon and Thinocyon in the LRT. It was originally described as a Paleocene bat, then an archaic primate, then ‘not a primate’.
This could change. Basal mammals greatly resemble one another. Add marsupial predators to your own LRT to confirm, modify or refute this apparently novel hypothesis of interrelationships.
References
Burger BJ 2013. A new species of the archaic primate Zanycteris from the late Paleocene of western Colorado and the phylogenetic position of the family Picrodontidae.PeerJ 1(1):e191
Crowell JW, Wible JR and Chester SGB 2024. Basicranial evidence suggests picrodontid mammals are not stem primates. Biology Letters 20: 20230335.
https://doi.org/10.1098/rsbl.2023.0335
Forasiepi AM and Carlini AA 2010. A new thylacosmilid (Mammalia, Metatheria, Sparassodonta) from the Miocene of Patagonia. Zootaxa. 2552, ss. 55–68, 2010 (Ing.)
Marsh OC 1872. Preliminary description of new Tertiary mammals. American Journal of Science and Art, 4: Part I: 122-128, Part 11-IV: 202-224.
Matthew WD 1909. The Carnivora and Insectivora of the Bridger Basin, middle Eocene. Memoires of the American Museum of Natural History, 9: 289-567.
Matthew WD 1917. A Paleocene bat. Bulletin of the American Museum of Natural History. 37, 569–571.
Morlo M and Gunnell GF 2003. Small limnocyonines (Hyaenodontidae, Mammalia) from the Bridgerian Middle Eocene of Wyoming: Thinocyon, Prolimnocyon, and Iridodon, new genus. Contributions from the Museum of Paleontology, The University of Michigan31(2):43–78.
wiki/Vincelestes
wiki/Thinocyon – not yet posted
wiki/Limnocyonidae
wiki/Zanycteris – not yet posted
Publicity
discovermagazine.com/the-sciences/a-tiny-extinct-mammal-has-just-lost-its-primate-identity
Source: https://pterosaurheresies.wordpress.com/2024/05/04/tiny-paleocene-zanycteris-now-a-marsupial-even-smaller-than-jurassic-hadrocodium/
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