Spanish fossils enter human ancestry fray.

Fossils found in a cave in northern Spain constitute a new species in the human evolutionary family that may represent the last common ancestor of Neandertals and modern humans, according to a new report.

The approximately 800,000-year-old Spanish hominid, dubbed Homo antecessor by its discoverers, originated more than 1 million years ago in eastern Africa, where it gave rise to H. sapiens, propose paleobiologist Jose Maria Bermudez de Castro of the National Museum of Natural Sciences in Madrid and his colleagues. In their view, H. antecessor later trekked to Europe, where it was ancestral to a German species known as H. heidelbergensis and to Neandertals.

"H. antecessor displays a unique combination of cranial, dental, and [lower jaw] traits that collectively is different from other known Homo fossils," the Spanish researchers report in the May 30 Science.

The identification of fossil hominid species and their evolutionary relationships to one another is a controversial endeavor. For instance, after initial reports of the finds in Spain's Atapuerca Mountains (SN: 8/12/95, p. 100), some investigators assigned them to H. heidelbergensis. Other scientists hold that the extent of anatomical variation in Homo specimens from that general time range precludes any species designations.

"The Atapuerca specimens were part of a movement of early hominids from Africa into southern Europe that probably began more than 1 million years ago," asserts anthropologist Erik Trinkaus of the University of New Mexico in Albuquerque. "But it's highly premature to assign them to a new species and call it ancestral to later hominid groups."

The Spanish researchers disagree. Their position hinges on an analysis of nearly 80 Atapuerca fossil teeth, jaws, and braincase fragments from at least six individuals. The fossils were excavated between 1994 and 1996.

A specimen containing much of the midface, including the nasal cavity and upper jaw, is larger than the corresponding region in modern humans but otherwise looks much the same, they note. In particular, the Atapuerca face is relatively flat, in H. sapiens fashion, without the jutting jaw of the Neandertal.

However, Bermudez de Castro and his coworkers align several anatomical traits of the braincase, lower jaw, and teeth with those of more primitive hominids--H. ergaster, which lived in eastern Africa close to 2 million years ago, and H. erectus, which other scientists have proposed as the original settler of Europe around 500,000 years ago.

The unusual mosaic of modern and primitive features on the Atapuerca fossils merits their inclusion in a new species, the Spanish investigators contend. The specimens are the oldest undisputed hominids in Europe and have played a major role in pushing back many estimates of that continent's initial settlement to 1 million or more years ago (SN: 1/4/97, p. 12).

The discovery of other ancient hominid sites in southern Europe will help to clarify the evolutionary standing of the Atapuerca individuals, holds archaeologist John J. Shea of the State University of New York at Stony Brook. For now, Shea finds it difficult to accept the Spanish finds as a separate species from H. heidelbergensis.