Loxolophus

Credit: Andrey Atuchin.

*Loxolophus* is an extinct genus of arctocyonid 'condylarth' that lived in Canada and the United States during the Paleocene.

## Description

*Loxolophodon* was about the size of a raccon.

## Classification

*Loxolophus* forms the subfamily Loxolophinae among other related genera in Arctocyonidae. It and *Arctocyon* are sister to the Pantodonta-Periptychidae clade, with all of Arctocyonidae recovered as polyphyletic. They find the following with discrete unconstrained trees:

## Notable Specimens

* PAL405161: A skull, mandible and partial right M2 collected in 1936 by Harold Shepherd from the Nacimiento Formation. Cope published this as *L. hyattianus*.
* AMNH 3121: A crushed maxillary fragment with LM1-3's.
* UW 26491: A right dentary fragment with P4, M2-3's and fragmented PX and M1's assigned *L. faulkneri*. It was discovered from UW V-91003 of the Ferris Formation.
* AMNH 3108: A partial skull assigned *L. priscus*, including LP3-M3's and a mandibular fragment with M1-M2's.
* AMNH 16343: A cranial and left dentary preserving P3-M3's, assigned *L. hyattianus*.

## Paleoecology

*Loxolophus* appears about 300,000 years after the Chicxulub impactor caused the K-PG mass extinction event which killed 3/4 of all life on earth, which occurred 66 million years ago. Animals like *Loxolophus* represent a time where earth's ecosystems were barren, so the survivers of the impact quickly evolved and became quite large. At Corral Bluffs, Colorado concretions containing turtles, crocodiles and early mammals (including *Loxolophus*) are found. Tyler Lyson et al. described this assemblage. They find the Corral Bluffs fauna increase in size over time, likely caused by the extinction of non-avian dinosaurs, climate change and botanical change. They also find an explosion in diversity over time, including changes in jaw morphology. More than 6000 fossil leaves and more than 37,000 fossil pollen grains were collected and analyzed, respectively. They link these to a mosaic of changes after the K-PG boundary that may have led to mammal diversification. When *Loxolophus* emerges, many walnuts begin to appear, which led to increased herbivorous mammal diversity. This likely indicates that they served as a primary food source for many species. Ian Miller calls this the "Pecan Pie World". Corral Bluffs represents one of the most complete and well-documented record of life's recovery after the Cretaceous boundary.

## Species

* *L. criswelli*
* *L. faulkneri*
* *L. grangeri*
* *L. hyattianus*
* *L. kimbetovius*
* *L. pentacus*
* *L. priscus*
* *L. schizophrenus*
* *L. spiekeri*
* *L. stenognathus*

## Synonyms

* *Paradoxodonta*
* *Deltatherium interruptum*
* *Protochriacus simplex*
* *Protochriacus priscus* (=*L. priscus*)
* *Protochriacus hyattianus* (=*L. hyattianus*)
* *Protogonodon stenognathus* (=*L. stenognathus*)
* *Protogonodon criswelli* (=*L. criswelli*)
* *Protogonodon grangeri* (=*L. grangeri*)
* *Protogonodon kimbetovius* (=*L. kimbetovius*)
* *Protogonodon pentacus* (=*L. pentacus*)
* *Protogonodon spiekeri* (=*L. spiekeri*)
* *Chriacus hyattianus* (=*L. hyattianus*)
* *Chriacus priscus* (=*L. priscus*)
* *Mioclaenus pentacus* (=*L. pentacus*)
* *Desmatoclaenus spiekeri* (=*L. spiekeri*)

## References

1. ↑ https://onlinelibrary.wiley.com/doi/10.1111/brv.12242
2. ↑ https://www.si.edu/object/nmnhpaleobiology\_3448164
3. ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=47791
4. ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=47789
5. ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=47795
6. ↑ https://www.researchgate.net/figure/Loxolophus-hyattianus-AMNH-16343-skull-lateral-a-ventral-b-and-dorsal-c-views\_fig4\_281592499
7. ↑ https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene\_extinction\_event
8. ↑ https://www.smithsonianmag.com/science-nature/fossil-site-reveals-how-mammals-thrived-after-death-of-dinosaurs-180973404/
9. ↑ https://www.nytimes.com/2019/10/24/science/fossils-mammals-dinosaurs-colorado.html
10. ↑ https://www.5280.com/2019/10/groundbreaking-dmns-discovery-reveals-what-happened-to-mammals-after-dinosaurs-went-extinct/