Homo sp.

*Homo* sp. is an unnamed species of hominin that lived in Kenya and Ethiopia during the Early Pleistocene.

## History

LD 350-1 was discovered by Chalachew Seyoum in 2013, a team member from the Ledi-Geraru research area of Afar. The fossil was found in what was likely an ancient river bend where remains washed in and fossilized, making the hill particularly fossiliferous. The fossil was sticking out from the sediment, where researchers knew it was a hominin upon discovery. Instead of being a *Homo habilis*, it is likely to be a new species. However, it was not named because species based on jaws (eg. *Homo habilis* and *Homo heidelbergensis*) typically encounter taxonomic problems down the line. Instead, Villmoare et al. (2015) described it as *H.* sp. indet. while noting KNM-ER 5431 is likely of the same new species. When more remains are discovered, it is likely to be given a formal name as the earliest human species.

## Description

This species is represented by an adult left jawbone with a canine, both premolars and all three molars in place. It is in the range of small Praeanthropus afarensis specimens, but otherwise it seems to be transitional of *Australopithecus* and *Homo*. Mental foramina not on a depression, a symphyseal keel, a somewhat constant depth on the bone and several tooth crown traits align LD 350-1 closer to *Homo*. This confirms that apomorphic dental and mandibular anatomy diverges from *Australopithecus* early on. It lacks a chin like other plesiomorphic forms. KNM-ER 5431 represents a single individual with a mix of australopith and human features. The tooth cusps are similar to australopiths and the C7 cusps on the M1 and M2s are "intermediate" of *P. afarensis*, *A. africanus* and early *Homo*.

## Classification

*Homo* is thought to diverge 2.8-2.5 million years ago during climatic shifts. Because this time has a relatively poor fossil record, it is unknown if this is a casual factor. Strong dental divergence has been suggested to represent a shift in diet. KNM-ER 5431 consits of left and right premolars and the first two molars may be of the same species. This specimen is 2.7-3 million years old, fitting the time range of the LD 350-1. These specimens discredit the long-standing theory that *Praeanthropus garhi* was the ancestor of *Homo* 2.6 million years ago. *P. afarensis* has been suggested to be an ancestor of this species due to a being roughly contemporaneous, but it allies far from the split in phylogenetic analyses, with the most likely candidate being *Australopithecus africanus*.

## Paleobiology

### Technology

In 2019, the earliest of the Oldowan industry were discovered from Ledi-Geraru. They were 2.6 million years old and made by this species. The invention of the Oldowan, sharp-edged, may be tied to anatomical and behavioural changes in the genus *Homo*. However, it is impossible to tell if this technology emerged independently from this species or if simpler forms were generationally brought down from australopithecine ancestors and advanced with time. These tools are ~250,000 years earlier than the previous oldest Oldowan at Gona. These tools are flaked and discovered in situ at Bokol Dora 1, Ledi-Geraru fossil site. They align with the level in complexity seen in early *Homo*, though still primitive in comparison.

## Notable Specimens

* LD 350-1: A jaw fragment with teeth first described by Villmoare et al. (2015) from the Ledi-Geraru site. It bears transitional features that align more so with *Homo* than australopiths such as *A. africanus*.
* KNM-ER 5431?: Postcanine mandibular dentition, isolate left and right P3-M2 rows, that are similar to LD 350-1, and are often concluded to be from early *Homo*. They have been suggested to be from the same species. They were recovered from the 2.7-3 million year old Tulu Bor Member of Koobi Fora.

Remains from the same time frame with a similar description include:

* Usno Formation: Various teeth from the Usno Formation (many molars, premolars and an incisor) White Sands B2 and Brown Sands B2 were reported by Wood ad Leakey (2011) and discovered from 1968-1973. They were stated to be from *Australopithecus* sp. and Hominidae indet., noted to belong to a gracile australopithecine. In the same formation, various early *Homo* and *Homo habilis* teeth are documented. These layers correlate with a 2.6-1.8 million years span, with the formation totaling to ~2.97 million years.
* Shungura Formation: A set of postcanine dentition from members E-G of the Shangura Formation. The mandible Omo 75-14 is the best representative from here, having shared featured with LD 350-1 through a reduced M3 crown and C7 cusp on the M1. From members B-C, there are also teeth that are more derived than *Australopithecus* and typically associated from either that genus or *Homo*. Also from Shangura is the jaw Omo 75-146 and the skull Omo L 894-1. The skull is similar to *Australopithecus* by having a large postglenoidal process and different from *Homo habilis*, consists of 26 fragments, a downward-directing prearticular surface as in *Homo habilis*, massive teeth, a thin superciliary ridge, no taurodontism, signs of enhanced meat consumption and multiple pathologies.
* Sterkfontein: A collection of early *Homo* material that has had a complicated taxonomic history. A 2022 study analyzed teeth from this collection, finding the following (all ~3 mya old given redating) to be definite or tentative early *Homo*. These all have mixed morphology characteristic of Ledi-Geraru.
	+ Stw 668-9?: A right permanent maxillar M1 (668) without roots with mixed australopithecine morphology, and a large, complete manual phalanx of ray 2 of the left hand. They are the first set of hominid remains from Milner Hall, Sterkfontein. The phalanx has black staining.
	+ Sts 9: A right mandibular M1.
	+ SE 1508: Assigned as a paratype of the wastebasket taxon *Homo guatengensis*. It has an enamel-dentine junction that leads to assignment to *Homo*.
	+ Stw 80-1: Stw 80 is a badly crushed mandible that was assigned paratype of the wastebasket taxon *Homo guatengensis*. It is also known as *Homo ergaster*. It was discovered associated with "Acheulean" remains.

## Paleoecology

LD 350-1 lived in a drier, more open environment than *P. afarensis*. Abundant grazing animals suggest that it was likely similar to modern African open grasslands like the Serengeti or the Kalahari. However, the presence of *Deinotherium bozasi*, a browser that was one of the last of the genus, may indicate gallery forests and *Hippopotamus afarensis*, fish and crocodiles indicate bodies of water such as lakes and rivers. This would make the environment a mosaic of open grassland, shrubland, gallery forest and likes/rivers. A faunal turnover occurs 2.8-2.6 million years ago at Ledi-Geraru, which corresponds with increased aridity and explosive diversity in grazers. Climatic and vegetation shifts were posited to have happened based on "extensive volcanism", which would change the composition of sedimentary basins. This site represents key data for the history of this region at this time. It has been suggested that increasing aridity between the Gurumaha and Lee Adoyta fault blocks expanded grasslands and influenced populations at Ledi-Geraru.

## Gallery

### Possible Specimens

Omo L 894-1.Omo 75-14.Omo 75-146.Stw 80 (left and right) and SK 15 (middle).Stw 668 (right) and 669 (left).SKK X 21204.
## References

1. ↑ https://doi.org/10.1007%2F978-1-4020-9980-9\_2
2. ↑ Otto Schoetensack: *Der Unterkiefer des Homo Heidelbergensis aus den Sanden von Mauer bei Heidelberg. Ein Beitrag zur Paläontologie des Menschen.* Leipzig, 1908, Verlag von Wilhelm Engelmann
3. ↑ https://www.csmonitor.com/Science/2015/0305/Ethiopia-fossil-could-be-from-oldest-known-human-species
4. ↑ https://prehistorian.wordpress.com/2015/03/05/the-ld-350-1-jawbone/
5. ↑ 5.0 5.1 5.2 5.3 https://doi.org/10.1126%2Fscience.aaa1343
6. ↑ https://doi.org/10.1016%2Fj.cub.2015.04.009
7. ↑ https://www.science.org/doi/10.1126/science.aaa1343
8. ↑ https://onlinelibrary.wiley.com/doi/full/10.1002/ajpa.23387
9. ↑ Leakey R. E., Walker A. C., Further hominids from the Plio-Pleistocene of Koobi Fora, Kenya. *Am. J. Phys. Anthropol.* ***67***, 135–163 (1985).
10. ↑ https://onlinelibrary.wiley.com/doi/abs/10.1002/evan.20335
11. ↑ https://paleobiodb.org/classic/basicCollectionSearch?collection\_no=21632&is\_real\_user=
12. ↑ https://paleobiodb.org/classic/basicCollectionSearch?collection\_no=22003&is\_real\_user=
13. ↑ https://paleobiodb.org/classic/basicCollectionSearch?collection\_no=21555&is\_real\_user=
14. ↑ https://pubmed.ncbi.nlm.nih.gov/4817659/
15. ↑ https://antropogenez.ru/location/60/
16. ↑ https://www.pnas.org/doi/full/10.1073/pnas.2123516119
17. ↑ https://pnas.org/doi/full/10.1073/pnas.2111212119
18. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0047248415003139
19. ↑ https://www.researchgate.net/publication/340365141\_The\_dental\_proteome\_of\_Homo\_antecessor
20. ↑ https://www.cambridge.org/core/books/abs/african-genesis/brief-review-of-history-and-results-of-40-years-of-sterkfontein-excavations/6089970204C3FFE9E642D54881428156
21. ↑ https://books.google.ca/books?vid=ISBN9789400759190&redir\_esc=y
22. ↑ https://paleobiodb.org/classic/displayCollResults?taxon\_no=157873&max\_interval=Pliocene&min\_interval\_no=Pleistocene&country=Ethiopia&is\_real\_user=1&basic=yes&type=view&match\_subgenera=1
23. ↑ Pickford, Martin; Pourabrishami, Zeinolabedin (2013). "Deciphering Dinotheriensande deinotheriid diversity". *Palaeobiodiversity and Palaeoenvironments*. **93**: 121–150.
24. ↑ https://paleobiodb.org/classic/displayCollResults?taxon\_no=170143&max\_interval=Pliocene&country=Ethiopia&is\_real\_user=1&basic=yes&type=view&match\_subgenera=1
25. ↑ https://doi.org/10.1126%2Fscience.aaa1415
26. ↑ https://paleoanthropology.org/ojs/index.php/paleo/article/view/1022/985