Conceived and designed the experiments: CB LD. Analyzed the data: CB. Contributed reagents/materials/analysis tools: JN RB LD. Wrote the paper: CB JN RB.
The authors have declared that no competing interests exist.
The fossil record reveals surprising crocodile diversity in the Neogene of Africa, but relationships with their living relatives and the biogeographic origins of the modern African crocodylian fauna are poorly understood. A Plio-Pleistocene crocodile from Olduvai Gorge, Tanzania, represents a new extinct species and shows that high crocodylian diversity in Africa persisted after the Miocene. It had prominent triangular “horns” over the ears and a relatively deep snout, these resemble those of the recently extinct Malagasy crocodile
The holotype consists of a partial skull and skeleton and was collected on the surface between two tuffs dated to approximately 1.84 million years (Ma), in the same interval near the type localities for the hominids
The new crocodile species was the largest predator encountered by our ancestors at Olduvai Gorge, as indicated by hominid specimens preserving crocodile bite marks from these sites. The new species also reinforces the emerging view of high crocodylian diversity throughout the Neogene, and it represents one of the few extinct species referable to crown genus
Until recently, it was thought that the ancestors of modern African crocodiles would be found among Oligocene through Pliocene fossils found in Africa
Several questions remain. Fossil and molecular data suggest a Neogene divergence among living species of
One of these,
Some of these are from the Plio-Pleistocene deposits exposed in Beds I through IV at Olduvai Gorge, northern Tanzania. Bed I is the oldest level at Olduvai and is best known for key discoveries of extinct human species, including the holotypes of
A partial skull and skeleton collected in 2007 by the Olduvai Landscape Paleoanthropology Project prompted a reevaluation of crocodile remains from Olduvai Gorge. It reveals a deep-snouted, horned animal outwardly similar to a recently-extinct osteolaemine from Madagascar (
AMNH, American Museum of Natural History, New York; FMNH, Field Museum, Chicago; KNM, National Museums of Kenya, Nairobi; NHM, Natural History Museum, London; NNHM-OLD, National Natural History Museum, Arusha, Tanzania (Olduvai Collections); PNCZ, Parque Nacional Ciénaga de Zapata, Playa Larga, Matanzas, Cuba; USNM, U.S. National Museum of Natural History, Washington, DC.
4t, 4th trochanter of femur; an, angular; art, articular; asf, anterior sacral facet; bo, basioccipital; ccr, caviconchal recess; cor, coronoid; cqc, cranioquadrate canal; cr, recesses on caviconchal recess medial wall; d, dentary; dlc, deltoid crest; dp, diapophysis; dpc, deltopectoral crest; ect, ectopterygoid; emf, external mandibular fenestra; en, external naris; eoa, external otic aperture; ex, exoccipital; f, frontal; faa, articular foramen aereum; faq, quadrate foramen aereum; fioc, foramen intermedius oralis caudalis; fm, foramen magnum; gf, glenoid fossa of articular; gfs, scapular glenoid fossa; hyp, hypapophysis; ibc, constriction on psterior iliac blade; if, incisive foramen; itf, infratemporal fenestra; j, jugal; k, keel; l, lacrimal; lc, lacrimal crest; lcf, lateral carotid foramen; leu, lateral Eustachian foramen; lf, lingual foramen; lhc, lateral hemicondyle; lp, lateral lamina of articular on surangular; m.pfp, medial process, prefrontal pillar; m5, fifth maxillary tooth/alveolus; mg, Meckelian groove; mhc, quadrate medial hemicondyle; mjf, medial jugal foramen; msc, muscle attachment scar; mx, maxilla; n, nasal; o, orbit; oc, occipital condyle; op, odontoid process; p.m5, protuberance on dorsal surface of maxilla corresponding to 5th alveolus; pal, palatine; pf, prefrontal; pfp, prefrontal pillar; pmx, premaxilla; pnr, prenarial rostrum; po, postorbital; pob, postorbital bar; poz, postzygapophysis; prz, prezygapophysis; psf, preotic siphonial foramen; psf, posterior sacral facet; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangular; soc, supraoccipital; sof, suborbital fenestra; sp, splenial; sq, squamosal; stf, supratemporal fenestra; sym, symphysis; ta, posteriormost (terminal) alveolus; tp, transition point between dorsal surface of skull table and squamosal horn; vf, vagus foramen; xii, foramen for hypoglossal nerve (cranial nerve 12). Articulation surfaces for adjacent bone denoted with “s.” (e.g. articulation surface for the maxilla = s.mx).
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In addition, this published work and the nomenclatural acts it contains have been registered in ZooBank, the proposed online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix “
Clade names follow currently-used phylogenetic definitions
Eusuchia Huxley 1873
Crocodylia Gmelin 1789, sensu Benton and Clark 1988
Crocodylidae Cuvier 1807
urn:lsid:zoobank.org:act:052051B8-6503-42B3-8D7A-9E7E49578401
NNHM-OLD-1001, partial skull and skeleton (
Right premaxilla in medial (A), ventral (B), dorsal (C), and lateral (D) view; partial left squamosal in dorsal (F), posterior (G), and lateral (H) view; left lacrimal in dorsal view (J); frontal with adjoining parts of prefrontals in dorsal (K) and left lateral (L) view. Specimens are compared with Crocodylus niloticus (KNM OR44, E; AMNH 7136, right side reversed, I; KNM OR54, M). Scale = 1 cm.
A, partial left nasal, dorsal view; B, right quadratojugal, lateral view; C, right jugal, lateral view; D, left jugal, lateral view; E, left jugal, medial view; F, right otic region and quadrate ramus, lateral view; G, left quadrate ramus, dorsal view; H, left quadrate ramus, ventral view; I, left quadrate ramus and paroccipital process, posteromedial view; J, braincase, posterior view; K, right pterygoid wing, ventral view; L, left pterygoid wing, ventral view; M, right ectopterygoid, ventral view; N, left ectopterygoid, ventral view; O, right postdentary bones, lateral view; P, left quadrate, dorsal view; Q, left surangular, medial view; R, fragment of dentary; S, left surangular, lateral view. Scale = 5 cm.
A, atlas intercentrum, anterior view. B, axis centrum and odontoid process, right lateral view. C, cervical vertebra, right lateral view. D, dorsal osteoderm, posterior view. E, dorsal osteoderm, dorsal view. F, proximal half of left humerus, ventral view. G, left ilium, medial view. H, metapodial, dorsal view. Scale = 5 cm.
NHM R.5891, cranial and postcranial fragments; NHM R.5893, partial skull and skeleton (
KNM CROC K OLD 62: anterior end of rostrum, dorsal (A) and ventral (B) view; partial frontal with portions of prefrontals in dorsal (C) and anterior (D) view; right otic region and quadrate ramus, lateral view (E). KNM FLKNI: partial orbital region, dorsal view (F); left maxilla, ventral view (G); right maxilla, medial (H), lateral (I), ventral (J), and dorsal (K) view; right squamosal, posterior (L), dorsal (M), and lateral (N) view. NHM R.5893: orbital region, dorsal view (O); partial right maxilla, ventral view (P); partial right maxilla and ectopterygoid, ventral view (Q); partial palatines and pterygoids, ventral view ( R); partial right jugal, lateral (S) and medial (T) view. Scale = 5 cm.
Scale = 5 cm.
Crocodile Korongo (CROC K): OLD 62, partial skull (
Bell's Korongo (BKII) channel: OLD 1960, right postdentary elements of mandible (
Frida Leakey Korongo North I (FLKNI): cranial, mandibular, and postcranial material (
KNM BKII OLD 1960: left postdentary bones and posterior end of dentary, medial (A) and lateral (B) view; KNM FLKNI, dentaries and portion of right splenial, dorsal view (C); NHM R.5893, left dentary and splenial, medial (D) and lateral (E) view. Scale = 5 cm.
A, KNM DK I B, left scapula, lateral view; B, NHM R.5894, ?nuchal osteoderm; C, KNM DK I B OLD 62 54, right humerus, ventral view; D, KNM FLKNI, right femur, ventral view. Scale = 5 cm.
Douglas Korongo, trench 1B (DK IB): scapula and humerus (OLD 62 54).
Plio-Pleistocene, Olduvai Gorge, northern Tanzania. The holotype was collected from the surface of Middle Bed I between Tuffs IB and IC, dated to 1.845+/−0.002 and 1.839+/−0.005 Ma, respectively
The premaxillae (
The right premaxilla of the holotype preserves three complete alveoli and the anterior margin of a fourth (
None of the preserved maxillae are complete. One partial left element (
An isolated right maxilla (KNM FLKNI,
Each nasal bears a short conical process extending into the narial aperture. The nasals flare posteriorly as they approach the posterior tips of the premaxillae, but the point at which their lateral margins adopt a parasagittal orientation is not preserved. They taper posteriorly where they pass adjacent to the lacrimals and prefrontals, forming short triangular processes separating the frontal from each prefrontal.
None is complete, but the preserved jugal fragments (
The lacrimal forms the anterior margin of the orbit. The outline is not completely preserved, but it extended further anteriorly than the prefrontal. An oval aperture on its posterior surface, within the orbital margin, indicates the posterior opening of the lacrimal duct. It connected with the jugal laterally.
The partial left lacrimal associated with the holotype (
The prefrontal forms the anteromedial margin of the orbit and extends anteriorly to form an acute process between the nasal and lacrimal. Based on NHM R5893 (
The dorsal surface of the frontal between the orbits is flat (
Those portions of the prefrontal and frontal bordering the orbit are sharply upturned (
The postorbital includes a broadly crescentic dorsal corpus and columnar descending process comprising the dorsal and, ventrally, the medial portion of the postorbital bar. In at least one specimen (e.g. NNHM-OLD-1001,
The squamosal forms the posterolateral margin of the supratemporal fenestra. The lateral and posterior margins of the fenestra are almost linear, intersecting at a nearly right angle (
The dorsolateral margin of the squamosal forms a prominent dorsal hornlike projection. This takes the form of a mediolaterally flattened lamina and is triangular in lateral view, with an apex dorsal to the otic aperture and posterolateral to the supratemporal fenestra. It arises abruptly from the dorsal surface of the skull table. The apex is sharp in the holotype, and the lateral squamosal groove is continuous with a sulcus on the lateral surface of the horn (
The parietal is incompletely known. Its articulation surface for the frontal is concave, and it did not contribute to the supratemporal fenestra. Whether its dorsal surface was flat is unknown, but it did not expand laterally as it approached the squamosal and, hence, did not contribute to the squamosal horn.
The quadratojugal lies between the jugal and quadrate. The ascending ramus is not completely preserved, but based on sutural surfaces on the quadrate and jugal, it formed nearly all of the posterior margin of the infratemporal fenestra, extending from just dorsal to the posteroventral corner to nearly to its dorsal apex; but whether it contacted the squamosal is unknown.
The anterior process of the palatine was broad and formed a U-shaped structure at its anteriormost extent at approximately the level of the seventh maxillary alveolus (
Based on NHM R5893 (
The pterygoids met the palatines along a linear sutural contact anterior to (and not intersecting) the internal choana (
Anteriorly, the quadrate forms the margin of the otic aperture and is pierced by a small circular preotic foramen (
Details of the lateral braincase wall, including morphology of the laterosphenoid and prootic, are not preserved. Based on sutural contacts on the ventral surface of the frontal, the laterosphenoid capitate processes were oriented anterolaterally.
The supraoccipital is likewise poorly known. Based on the holotype (
The exoccipital formed the posterior portion of the paroccipital process, narrowing laterally from the post-temporal fenestra (
The basisphenoid is unknown, but based on sutural surfaces on the basioccipital of NNHM-OLD-1001and KNM FLKNI, it would have formed an anteroposteriorly thin sheet ventral to the basioccipital. This sheet would have had a dorsoventrally short exposure on the posterior occipital surface based on the minimal distance between the ventral margins of the basioccipital and pterygoid (
The basioccipital bears a robust spherical occipital condyle projecting from a main body (
No complete dentaries are preserved, but based on preserved specimens (
The splenials do not meet at the midline. Its anteriormost extent is ventral to the slender Meckelian groove on the dentary at approximately the level of the sixth dentary alveolus (
One left (KNM BK II OLD 1960,
The angular has a broadly convex ventral surface. Its medial lamina forms the posteroventral and part of the dorsal margin of the caudal foramen intermandibularis oralis. Its lateral surface is smooth and unpitted where it forms the ventrolateral portion of the retroarticular process. Most preserved specimens (e.g. NNHM-OLD-1001,
The surangular (
The descending ramus of the articular is triangular in cross-section, tapering to a rounded apex ventrally (
All associated teeth are conical and bear unserrated mesiodistal carinae.
Associated postcranial material is consistent with homologues in living species of
The heuristic searches recovered 426 equally optimal trees (length = 225, CI excluding uninformative characters = 0.493, RI = 0.717). Strict and Adams consensus trees of these results (
Adams consensus of 426 equally optimal trees (length = 225, CI excluding uninformative characters = 0.493, RI = 0.717). Dashed lines indicate lost resolution in a strict consensus of the same trees. O = Osteolaeminae, M = Mekosuchinae, T = Tomistominae. Heavy branches indicate living lineages.
If the relationships among outgroup taxa are not constrained to reflect more inclusive analyses of Crocodylia (i.e. forcing
Placements of
A close relationship between
The medial wall of the caviconchal recess – a large pneumatic feature in the maxilla dorsomedial to the toothrow – is perforated with a linear array of blind pits in
An isolated ilium associated with the
Derived states typically found in osteolaemines are absent from
Cranial ornamentation features that diagnose
These ornamental features are sufficient to distinguish
Posterodorsal squamosal horns characterize the Cuban (
A, AMNH 3101,
Although not as prominent, dorsally expanded squamosals are sometimes found in very large specimens of most other living species of
A few extinct crocodylians also bear squamosal horns similar to those of
Another crocodylid with squamosal horns is
One character might suggest monophyly of extant
All images from right side of skull in ventral view. A, NHM R.5893,
But further examination of
Even fewer specimens of
We have no complete skulls for
Nevertheless, differentiation of isolated fragments of
Preliminary analyses of the phylogeny of Neogene African crocodiles suggested that
That the features distinguishing
Fossil bones of at least two hominid individuals from Olduvai Gorge bear tooth marks characteristic of crocodile feeding
The FLK 22 and FLK NN 3 sites formed in close proximity (<50 m) to wetland settings from which crocodile body and trace fossils are documented
Predation risk from crocodiles likely impacted the foraging and land use behavior of hominids at Olduvai and at other tropical and sub-tropical near-wetland sites. Crocodiles were the largest predators encountered by hominids and are commonly found in the lake and river basins that also preserve fossil hominids in East Africa and elsewhere
List of characters and character matrix used in this analysis.
(0.06 MB DOC)
M. Norell, C. Raxworthy, M. Kearney, A. Milner, C. McCarthy, A. Wynn, R. Soberón, R. Ramos, and E. Mbua permitted access to collections. Reviews by J. A. Alcover and M. Delfino prompted improvements to the paper, and we thank them. We are grateful to the Tanzania Commission for Science and Technology, the Antiquities Department of the Ministry of Natural Resources and Tourism, and the Ngorongoro Conservation Area Authority for permission to conduct the research that produced the new fossils reported here. We thank the Olduvai Landscape Paleoanthropology Project for field support during our work at Olduvai Gorge, and the National Natural History Museum, Arusha, Tanzania, for cooperation during the curation and study of NNHM-OLD-1001. Logistical support was provided by Joe's Place I.C.