Bottosaurus

Bottosaurus harlani was a broad-snouted alligatoroid from eastern North America, known from material spanning the latest Cretaceous and Paleocene. Its large, rounded rear teeth set it apart from long-snouted fish-catching forms, but the best evidence is more varied than the teeth alone. A specimen from the Rowan Fossil Quarry in New Jersey preserves posterior skull bones and parts of the skeleton. Bottosaurus is included in the ancient crocodylomorph catalogue.

The genus is relevant to the early history of caimans. A 2018 description of specimen NJSM 11265 added features of the skull table and postcranial skeleton, while a later study named another Bottosaurus species from the Paleocene of Texas. Those finds make the history richer, but they also require species to be kept separate: the Texas animal is not simply an older or younger individual of B. harlani.

Quick facts

From isolated crushing teeth to a better sample

The name Bottosaurus harlani dates to the nineteenth century and was based on fossils from New Jersey. For a long time, the conspicuous blunt teeth carried much of the identification. That is a weak basis on its own because rounded, thick crowns evolved in several alligatoroid lineages that processed resistant food.

NJSM 11265, collected at Rowan Fossil Quarry in Mantua Township, New Jersey, changed the anatomical picture. Adam Cossette and Christopher Brochu described it in 2018 as the most complete individual attributable to B. harlani. It preserves a partial skull with posterior regions not previously described for the species, along with limbs, girdle elements, vertebrae and osteoderms. The parts improve comparisons, although they do not constitute a single complete skeleton.

The locality records a Cretaceous–Paleogene transition. A second species named from the lower Paleocene Black Peaks Formation of Texas, in a 2020 paper published in 2021, shows that broad-snouted caimanines were also present farther south. Its distinct species status and anatomy should not be folded into the New Jersey species when describing either one.

A skull built for a varied bite

Bottosaurus harlani had a relatively short, broad muzzle. The rear teeth are low-crowned and rounded, with a substantial surface that could crush rather than merely pierce. This is direct evidence for dental form and a reasonable basis for inferring resistance to compressive loading. Shells, hard-bodied invertebrates or small vertebrate bones are possible targets, but the fossil has no gut contents that identify them.

The anterior teeth could still grasp prey, so a crushing function at the back of the jaw need not mean a diet limited to molluscs. Nor does tooth shape tell us how much plant material was eaten or whether feeding changed with age. It indicates what the jaw could do more reliably than what an individual chose to eat.

What the skull table says about relatives

Cossette and Brochu noted a nearly straight frontoparietal suture between the supratemporal openings, a feature used in support of caimanine affinity. Their analyses placed B. harlani near living dwarf caimans in several optimal trees, but the exact branching order varied. Later datasets have also recovered early fossil caimanines in different positions. The cautious label is an alligatoroid with a proposed caimanine relationship, rather than an unquestioned member of the modern caiman crown group.

A phylogenetic placement is not a direct record of ancestry. Similar skull features may be inherited from a common ancestor, retained from a deeper one, or affected by convergence. The fossils establish an early North American alligatoroid radiation; they do not alone pinpoint when alligators and caimans split or show that the living species descend from this genus.

Across an extinction boundary

Late Cretaceous and Paleocene occurrences make Bottosaurus part of a small set of crocodilian lineages whose records approach or cross the K–Pg boundary. That temporal pattern is significant, but it must be interpreted at the scale the fossils support. A taxonomic record before and after the boundary does not demonstrate uninterrupted local survival, an unchanged population or a single mechanism of resilience.

Reconstruction can confidently show a broad head, blunt rear teeth and the general osteoderm-covered body typical of crocodilians. Precise length, colour, hunting behaviour and preferred habitat are less constrained. More associated skeletons and a better resolved species-level chronology would sharpen both its ecology and its place in early caiman history.