3. Characteristics
Oldest known craniates
Date back to the middle of Ordovician until the
end of Devonian
Entire body was covered with bony dermal
armour
Bony shield head covering
Lacked jaws
Most lacked paired fins
Mostly 2-3 cm long; a few reached up to 2 m long
Heterocercal tail
4. Probably were slow, bottom-dwelling animals
Have median fins located down the midline of
their backs
Gills were located in pouches
Cartilaginous internal skeletons
A paired of side flaps aid in steering
Mouth served to obtain oxygen and retain bits
of food and was permanently open
Gills were used exclusively for respiration
5. Used muscular gill pouch to pull in small and slow
moving prey
10. According to E.A. Stensiö – paleontologist at the
University of Stockholm
Head skeleton of cephalaspis (one species of
an ostracoderm) was more or less flattened
denticle-covered body shield with four
dorsal apertures
Two dorsal apertures accommodated a pair of
upward-staring eyes
One accommodated the median or pineal eye
Another accommodated a small, anterior opening
that was a single naris from which a
nasohypophyseal duct led to an olfactory sac and
beyond
13. The body shield turned along its lateral edges
Beneath the gills the body covering were tile
like scales
A small mouth that is lined by gills opens to
the oropharyngeal chamber is found between
the anterior edge of the shield and the scales
Curved row external gill slits extends from the
corners of the mouth to the caudal margin of
the head shield
14. Head contained an endoskeleton of endochondral
bone and considerable cartilage
16. Acanthodians?
Class of Extinct species
Share features with Bony and Cartilaginous
fishes
In form they resemble sharks, but their
epidermis was covered by tiny rhomboid platelets like
the scales of holosteans.
Oldest jawed fishes
Holosteans – Bony fishes (Gars, Bowfins)
19. Acanthodians
Acanthodians did have cartilaginous skeletons
But their fins are bony based with a dentine spine
Most Acanthodians have heterocercal caudal fins.
Silurian to Permian Period.
Marine/Freshwater
-Devonian Period: Freshwater species became dominant
21. Orders
Climatiiformes
had shoulder armor and many small sharp spines
Ischnacanthiformes
Had teeth fused to the jaw
Acanthodiformes
filter feeders, with no teeth in the jaw, but long gill rakers.
22. Spiny Sharks
they were superficially shark-shaped, with a streamlined body,
paired fins, and a strongly upturned tail; stout bony spines
supported all the fins except the tail - hence, "spiny sharks".
However, they were not sharks.
Skeleton consisted of bone and cartilage.
They had a large operculum.
23. Brief History
Despite being called "spiny sharks," acanthodians
predate sharks. They evolved in the sea at the
beginning of the Silurian Period, some 50 million
years before the first sharks appeared.
Later the acanthodians colonized fresh waters, and
thrived in the rivers and lakes during
the Devonian Period.
But the first bony fishes were already showing their
potential to dominate the waters of the world, and
their competition proved too much for the spiny
sharks, which died out in Permian times
(approximately 250 MYA).
24. Many paleonthologists consider that the
acanthodians were close to the ancestors of the bony
fishes. Although their interior skeletons were made
of cartilage, a bonelike material had developed in the
skins of these fishes, in the form of closely fitting
scales. Some scales were greatly enlarged and formed
a bony covering on top of the head and over the
lower shoulder girdle. Others developed a bony flap
over the gill openings analogous to the operculum in
later bony fishes.
26. TAXONOMY
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Placodermi
Order: Arthrodira
Order Antiarchi
Order Rhenanida
Order Petalichthyida
Order Acanthothoraci
Order Ptyctodontida
27. Placoderms
Greek word “tablet & skin” referring to
their heavy armoured bony plates
an extinct class of armored fishes
Placoderms evolved from agnathan
(jawless) fishes
Abundant in the fresh waters of the
Devonian era
First to evolve true jaws
First animals to exhibit internalize egg
fertilization
28. Distinct Characteristics
layer of segmented armor across the
head and thorax
2 paired fins
Depending on species, the remainder
of the body would be scaled or naked.
sharpened points of bone which
protrude from the head to grind their
food.
30. Order Arthrodira
Best known placoderms
A heavy dermal shield covered the head
and gill region and another covered much
of the trunk
2 shield meet in a movable joint
Remainder of the body: covered with
smaller bony scales or,in late species, was
naked.
2 pairs upper jaw tooth plates
31. shark-like bodies
Some very large – e.g. Dunkleosteus and
Gorgonichthys to 6 - 9 m
The gigantic
superpreditor Dunkleosteus
terrelli
33. Gorgonichthys sp.
Reconstruction
of placoderm
Gorgonichthys,
Cleveland Shale
- copyright
John Long,
Museum
Victoria
Gorgonichthys sp.
34. Order Antiarchi
Were small placoderms
reach a length of 15-20
feet but majority were
shorter
Exhibit atypical pectoral
fins & dorsal eyes
Have flattened ventral
surface
Suggested to be bottom Bothriolepis Canadensi
feeders
Have eyes on top of their
heads
Pectoral fins are enclosed
in bony appendages
35. Order Rhenanida
Characteristics of Rhenanids:
reduction of the thoracic
armour
Body is covered by small
tesserae (small square of
stones)
dorso-ventrally flattened shape
enlarged pectoral fins
known from marine
environments and probably
pursued a ray-like benthic
lifestyle
Rhenanida, Gemuendina sp.
36. Order Petalichthyida
Closely related to
arthrodires
Rarely exceeds a meter
They are freshwater bottom
dwellers
Unlike the Arthrodires, they
are bottom-feeding fish
Flattened fish with short
trunk and long, spine-like
plates.
The nostrils and the anterior
part of the head shield
around the orbits, is covered
by a number of tiny scales, Lunaspis sp.
as is the long trunk.
37. Order Acanthothoraci
Generalized by a stout
spine emanating from the
median dorsal plate
Some acanthothoracids
are similar to rays,
expanded pectoral fins
and flattened appearance
Long head shields, very
shortened trunk
Brindabellaspis stensioi
With eyes and nares
pointing upwards,
suggesting a bottom
dweller
38. Order Ptyctodontida
have enlongate bodies
whip-like tails
reduced head
thoracic armor
Exhibits sexual
dimorphism
males of one
ptyctodontid, Rhamphod Rhamphodopis
opis, have clasper-like
intromittent organs
similar to those found
sharks and their kins
39. SUMMARY
Order Arthrodira (Arthrodires)
– jointed neck
–movable joint between the head and the thoracic body
Order Antiarchi (Antiarchs)
– pectoral fins are enclosed in bony tubes (pectoral
appendages)
Order Rhenanida(Rhenanids)
– enlarged pectoral fins
– body covered by unfused scales
Order Petalichthyida (Petalichthyids)
– typified by their splayed (spread out) fins
Order Acanthothoraci
– spiny trunk
Order Ptyctodontida
– some species exhibit sexual dimorphism
– has beak-like mouth
40. Differences
Ostracoderms Acanthodians Placoderms
-oldest known -oldest jawed -First animals to
vertebrate fishes exhibit
-jawless fishes -their skeleton internalize egg
-lacked paired consist of bone fertilization
fins and cartilage -armored fishes
with jaws