Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes

  title={Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes},
  author={Samuel P. Davis and John A. Finarelli and Michael I. Coates},
Acanthodians, an exclusively Palaeozoic group of fish, are central to a renewed debate on the origin of modern gnathostomes: jawed vertebrates comprising Chondrichthyes (sharks, rays and ratfish) and Osteichthyes (bony fishes and tetrapods). Acanthodian internal anatomy is primarily understood from Acanthodes bronni because it remains the only example preserved in substantial detail, central to which is an ostensibly osteichthyan braincase. For this reason, Acanthodes has become an… 

An early chondrichthyan and the evolutionary assembly of a shark body plan

Preliminary phylogenetic results highlight the likely convergent evolution of conventional chondrichthyan conditions among earliest members of this primary gnathostome division, while skeletal morphology points towards the likely suspension feeding habits of Gladbachus, suggesting a functional origin of the gill slit condition characteristic of the vast majority of living and fossil chondRichthyans.

Morphology and histology of acanthodian fin spines from the late Silurian Ramsasa E locality, Skane, Sweden

The results support the current hypothesis of gnathostome phylogeny, which places "acanthodians" on the chondrichthyan stem and emphasize the need for further study of vertebrate fin spines using 3D approaches.

A Palaeozoic shark with osteichthyan-like branchial arches

A 325 million year (Myr)-old Palaeozoic shark-like fossil is described that represents the earliest identified chondrichthyan in which the complete gill skeleton is three-dimensionally preserved in its natural position, and its visceral arch arrangement is remarkably osteichthyan-like, suggesting that this may represent the common ancestral condition for crown gnathostomes.

The characters of Palaeozoic jawed vertebrates

A clearly stated hierarchy of synapomorphies covering the jaw-bearing stem gnathostomes and osteichthyan and chondrichthyan stem groups is provided and a proposed synapomorphy scheme is used to evaluate the status of the problematic fossil groups Acanthodii and Placodermi.

Oldest Near-Complete Acanthodian: The First Vertebrate from the Silurian Bertie Formation Konservat-Lagerstätte, Ontario

The combination of features found in Nerepisacanthus supports the hypothesis that acanthodians could be a group, or even a clade, on the chondrichthyan stem.

A symmoriiform from the Late Devonian of Morocco demonstrates a derived jaw function in ancient chondrichthyans

A previously undescribed symmoriiform shark, Ferromirum oukherbouchi, from the Late Devonian of the Anti-Atlas is reported, in which the jaw articulation is specialized and drives mandibular rotation outward when the mouth opens, and inward upon closure.

Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome

A conjunction of well-developed cranial processes in Janusiscus helps unify the comparative anatomy of early jawed vertebrate neurocrania, clarifying primary homologies in ‘placoderms’, osteichthyans and chondrichthyans.

The early elasmobranch Phoebodus: phylogenetic relationships, ecomorphology and a new time-scale for shark evolution

The first skeletal remains of Phoebodus from the Famennian (Late Devonian) of the Maïder region of Morocco are reported, revealing an anguilliform body, specialized braincase, hyoid arch, elongate jaws and rostrum, complementing its characteristic dentition and ctenacanth fin spines preceding both dorsal fins.

A new osteichthyan from the late Silurian of Yunnan, China

A phylogenetic analysis resolves Sparalepis within a previously recovered cluster of stem-sarcopterygians including Guiyu, Psarolepis and Achoania, suggesting that the South China block may have been an early center of diversification for early gnathostomes, well before the advent of the Devonian “Age of Fishes”.

New cranial material of the acanthothoracid placoderm Palaeacanthaspis vasta from the Lower Devonian of Podolia – phylogenetic and taxonomic significance

The specimen, although incomplete, is very well preserved in three dimensions and allows a thorough description of its external morphology, which is compared to that of Romundina stellina and other well-known Acanthothoraci.



The braincase and jaws of a Devonian ‘acanthodian’ and modern gnathostome origins

The first-known braincase of an Early Devonian acanthodian is presented, andylogenetic analysis resolves Ptomacanthus as either the most basal chondrichthyan or as the sister group of all living gnathostomes, to provide a more detailed picture of the acquisition of early Gnathostome characters.

A primitive fossil fish sheds light on the origin of bony fishes

This first tentative reconstruction of a 400-million-year-old fossil fish from China is presented, which changes the polarity of many characters used at present in reconstructing osteichthyan inter-relationships and offers new insights into the origin and evolution of osteichthyans.


Abstract The braincase of an Upper Devonian shark (Cladodoides wildungensis) is investigated using high-resolution CT scanning, and its internal and external morphology is described from

The braincase of the chondrichthyan Doliodus from the Lower Devonian Campbellton Formation of New Brunswick, Canada

Doliodus has curious bar-like, paired subcranial ridges ending posteriorly at the hyomandibular articulation, adding circumstantial palaeontological support to the old proposal that parts of visceral arches may be incorporated into the gnathostome braincase, although it seems more plausible that they formed in the lateral margins of the embryonic parachordal or hypotic lamina.

The oldest articulated osteichthyan reveals mosaic gnathostome characters

The discovery of an exceptionally preserved primitive fish from the Ludlow of Yunnan, China, that represents the oldest near-complete gnathostome (jawed vertebrate) offers insights into the origin and early divergence of osteichthyans, and indicates that the minimum date for the actinopterygian–sarcoperygian split was no later than 419 million years ago.

The most primitive osteichthyan braincase?

The discovery of the oldest and most primitive actinopterygian-like osteichthyan braincase known is reported, from 400–million-year-old limestone in southeastern Australia, which provides an important and unique counterpart to the similarly aged and recently described Psarolepis from China and Vietnam.


This specimen is the first early osteichthyan to demonstrate the presence of an eyestalk, previously known only in placoderms and chondrichthyans.

The braincase of a primitive shark

Plesiomorphic conditions for chondrichthyan braincases are found to include the presence of a persistent otico-occipital fissure, projection of the median dorsal aorta anterior to the occipital level, and absence of suborbital shelves.

The postorbital palatoquadrate articulation in elasmobranchs

  • J. Maisey
  • Environmental Science
    Journal of morphology
  • 2008
The term archaeostylic (“ancient pillar”) is proposed here for the suspensorial arrangement in Paleozic sharks with a postorbital articulation on the ventrolateral part of the lateral commissure.

The oldest articulated chondrichthyan from the Early Devonian period

This specimen is the oldest shark showing the tooth families in situ, and preserves one of the oldest chondrichthyan braincases, and shows the presence of paired pectoral fin-spines, previously unknown in cartilaginous fishes.