Australopithecus deyiremeda

BRT-VP-3/1 (top) and BRT-VP-3/14 (bottom) shown in occlusion (Haile-Selassie et al., 2015).

Overview

Discovered in the Woranso–Mille study area, central Afar, Ethiopia in 2011 and officially named in 2015, Australopithecus deyiremeda is a lesser-known but scientifically significant hominin species that lived around 3.3 to 3.5 million years ago. The discovery of this species, based on limited fossil jaws and teeth, challenged long-standing assumptions that Australopithecus afarensis was the only hominin in East Africa during this time period (Haile-Selassie et al., 2015). Au. deyiremeda shows distinct anatomical differences which suggests that multiple hominin species may have coexisted and followed different evolutionary paths (Spoor et al., 2016). Its name, meaning "close relative" in the Afar language, reflects its position within the human family tree, and raises important questions about diversity, niche occupation, and locomotion in early hominins.

Holotype: BRT-VP-3/1

From Haile-Selassie et al., 2015

The fossil specimen is a partial left maxilla from a young adult individual, preserving a portion of the upper jaw with teeth from the lateral incisor through the second molar. The bone is well-preserved with minimal post-depositional damage and retains important anatomical features such as parts of the palate, nasal floor, zygomatic root, and anterior maxillary sinus. The dental arcade forms a broad parabola with a prominent anterior arch, and the teeth show a mix of light wear and developmental completeness, consistent with a young adult (Haile-Selassie et al., 2015). The morphology of the face and dentition exhibits a unique blend of traits seen in both Australopithecus and early Homo, such as a flat nasoalveolar clivus, low placement of the zygomatic root, and a relatively shallow, wide maxillary sinus. These features suggest mosaic evolution and have contributed to interpretations of this specimen as representing a distinct hominin taxon (Spoor et al., 2016; Melillo et al., 2021).

Paratype: BRT-VP-3/14

From Haile-Selassie et a., 2015

This specimen is an adult mandible which was found in three pieces, the left and right corpora and a fragment of the left ascending ramus. It includes the apical halves of both central incisors and the complete crowns of RP3 to RM3, though the left side is broken at the root level. The mandible is robust, and is notably broader for the given size. The dentition shows significant occlusal wear, with the anterior teeth minimally projected and the postcanines forming a tight parabola. The premolars are notably small, particularly in their mesiodistal dimensions. The molar row is nearly straight with a slight lateral concavity at M2–M3. The teeth are heavily worn, with the incisors being hypoplastic and the canines broken but with long roots visible in CT scans (Haile-Selassie et al., 2015 and 2016).

Foot elements from BRT-VP-2/73 (Haile-Selassie et al., 2012)

Possible Foot of Au. Deyiremeda: BRT-VP-2/73

The Burtele foot specimen exhibits a grasping hallux and other traits inconsistent with the derived, rigid-footed locomotion of Australopithecus afarensis. Because of this, researchers propose a null hypothesis that the Burtele foot belongs to Au. deyiremeda, the only other known hominin from the same time and region (Haile-Selassie et al., 2012 and 2015). This hypothesis cannot currently be rejected, though it raises intriguing questions. If Au. deyiremeda descended from Au. afarensis, its grasping foot would represent a reversal to arboreal traits. However, if its ancestry traces to a more primitive hominin like Ardipithecus ramidus, which had a similar foot, such a reversal wouldn’t be necessary—but this would require independently evolved dentognathic traits. Other possibilities remain, including that the Burtele foot might represent a late-surviving Ardipithecus or another unknown hominin (Haile-Selassie et al., 2012). Until cranial, dental, and foot remains are found in clear association, these hypotheses remain speculative.

Key Morphologies

Because of the limited fossils discovered and attributed to Au. deyiremeda, the defining traits are drawn directly from BRT-VP-3/1 and BRT-VP-3/14. The key morphological features drawn from these specimens include:

Craniofacial & Maxillary Traits (Haile-Selassie et al., 2015 and 2016; Hanegraef and Spoor, 2025):

Anteriorly placed zygomatic root, suggesting forward cheekbone placement.
More anterior incisive foramen compared to Au. afarensis and early Homo.
Flexed hard palate with limited overlap onto the nasoalveolar clivus.
Relatively small anterior dentition (notably small M1s), with thick enamel on M2.
Postincisive planum pronounced, similar to A.L. 400-1 (afarensis).

Mandibular Traits (Haile-Selassie et al., 2015 and 2016; Skinner et al., 2020):

Thick, laterally flattened corpus without the lateral hollow seen in Au. afarensis.
Ramus arises near P4, more anterior than in Au. afarensis.
Premolars are smaller than typical Au. afarensis specimens.
Three-rooted premolars and non-molarized P3 with a weak metaconid.
Canines are non-incisiform, relatively small but with long roots.

Despite mandibular robustness, dentition suggests a more gracile dietary adaptation, with smaller premolars and postcanine teeth that contrast with the robust appearance of the mandible itself.

Paleoenvironment

The discovery of Australopithecus deyiremeda at Woranso-Mille, dated to between 3.3 and 3.5 million years ago, is particularly significant because it marks the first known instance of multiple hominin species coexisting within the same temporal and geographic range during the Pliocene (Haile-Selassie et al., 2015 and 2016). Faunal and geological data indicate that the Woranso-Mille region was a heterogeneous landscape composed of riparian woodlands, floodplain grasslands, denser woodlands, and open shrublands, nourished by a large permanent river that likely fed into a lake (Su and Haile-Selassie, 2022). This environmental mosaic likely supported a wide array of flora and fauna, providing the ecological flexibility necessary to sustain more than one hominin species through dietary and behavioral niche differentiation. The coexistence of Au. deyiremeda with other hominins such as Au. afarensis suggests that Woranso-Mille had a relatively high hominin carrying capacity, setting it apart from other contemporaneous sites where only a single hominin species is typically represented (Haile-Selassie et al., 2015; Su and Haile-Selassie, 2022). This challenges traditional linear models of hominin evolution and highlights the importance of habitat heterogeneity in promoting species diversity.

Location map for the Woranso-Mille site and particularly the Burtele locality (BRT) (Su and Haile-Selassie, 2022).

Size of circle for each water or vegetation element indicates its inferred proportion on the landscape relative to the other elements (Su and Haile-Selassie, 2022).

Cladogram placing Au. deyiremeda as a sister taxon to Au. afarensis (Haile-Selassie et al., 2015)

Phylogenetic Placement

A parsimony-based phylogenetic analysis was conducted using morphological character data compiled from prior studies and adjusted to reflect Au. deyiremeda's unique anatomy. Although limited fossil evidence prevented the formation of a single most-parsimonious tree, the majority of tree topologies placed Au. deyiremeda as a sister taxon to a clade containing Australopithecus africanus, Kenyanthropus platyops, Paranthropus, and Homo. This suggests Au. deyiremeda occupies a basal position relative to later hominins (Haile-Selassie et al., 2015 and 2016; Spoor et al., 2016).

Despite morphological overlap with Paranthropus (thick enamel and wide mandibles), Au. deyiremeda lacks key Paranthropus dental traits like molarized premolars and reduced incisors. Its primitive traits, such as a poorly developed P3 metaconid and primitive maxillary canine, also distinguish it from Homo. These findings support the view that Au. deyiremeda is more derived than Au. afarensis, possibly descended from it, and may represent an ancestral lineage to the Paranthropus/Homo clade, rather than being within it (Haile-Selassie et al., 2015).

References

Haile-Selassie, Yohannes, Beverly Z. Saylor, Alan Deino, Naomi E. Levin, Mulugeta Alene, and Bruce M. Latimer. “A New Hominin Foot from Ethiopia Shows Multiple Pliocene Bipedal Adaptations.” Nature 483, no. 7391 (March 2012): 565–69. https://doi.org/10.1038/nature10922.

Haile-Selassie, Yohannes, Luis Gibert, Stephanie M. Melillo, Timothy M. Ryan, Mulugeta Alene, Alan Deino, Naomi E. Levin, Gary Scott, and Beverly Z. Saylor. “New Species from Ethiopia Further Expands Middle Pliocene Hominin Diversity.” Nature 521, no. 7553 (May 27, 2015): 483–88. https://doi.org/10.1038/nature14448.

Haile-Selassie, Yohannes, Stephanie M. Melillo, Timothy M. Ryan, Naomi E. Levin, Beverly Z. Saylor, Alan Deino, Ronald Mundil, Gary Scott, Mulugeta Alene, and Luis Gibert. “Dentognathic Remains of Australopithecus Afarensis from Nefuraytu (Woranso-Mille, Ethiopia): Comparative Description, Geology, and Paleoecological Context.” Journal of Human Evolution 100 (November 2016): 35–53. https://doi.org/10.1016/j.jhevol.2016.08.003.

Hanegraef, Hester, and Fred Spoor. “Morphological Variation of the Australopithecus Afarensis Maxilla.” Journal of Human Evolution 201 (April 2025): 103651. https://doi.org/10.1016/j.jhevol.2025.103651.

Melillo, Stephanie M., Luis Gibert, Beverly Z. Saylor, Alan Deino, Mulugeta Alene, Timothy M. Ryan, and Yohannes Haile-Selassie. “New Pliocene Hominin Remains from the Leado Dido’a Area of Woranso-Mille, Ethiopia.” Journal of Human Evolution 153 (April 2021): 102956. https://doi.org/10.1016/j.jhevol.2021.102956.

Skinner, Matthew M., Meave G. Leakey, Louise N. Leakey, Fredrick K. Manthi, and Fred Spoor. “Hominin Dental Remains from the Pliocene Localities at Lomekwi, Kenya (1982–2009).” Journal of Human Evolution 145 (August 2020): 102820. https://doi.org/10.1016/j.jhevol.2020.102820.

Spoor, Fred, Meave G. Leakey, and Paul O’Higgins. “Middle Pliocene Hominin Diversity: Australopithecus Deyiremeda and Kenyanthropus Platyops.” Philosophical Transactions of the Royal Society B: Biological Sciences 371, no. 1698 (July 5, 2016): 20150231. https://doi.org/10.1098/rstb.2015.0231.

Su, Denise F., and Yohannes Haile-Selassie. “Mosaic Habitats at Woranso-Mille (Ethiopia) during the Pliocene and Implications for Australopithecus Paleoecology and Taxonomic Diversity.” Journal of Human Evolution 163 (February 2022): 103076. https://doi.org/10.1016/j.jhevol.2021.103076.

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