Well, here are the relevant portions of the statute:
§ 365.012. Illegal Dumping; Criminal Penalties
(a) A person commits an offense if the person disposes or allows or permits the disposal of litter or other solid waste at a place that is not an approved solid waste site, including a place on or within 300 feet of a public highway, on a right-of-way, on other public or private property, or into inland or coastal water of the state.
. . .
(d) An offense under this section is a Class C misdemeanor if the litter or other solid waste to which the offense applies weighs five pounds or less or has a volume of five gallons or less.
(e) An offense under this section is a Class B misdemeanor if the litter or other solid waste to which the offense applies weighs more than five pounds but less than 500 pounds or has a volume of more than five gallons but less than 100 cubic feet.
. . .
An offense under this section may be prosecuted without alleging or proving any culpable mental state, unless the offense is a state jail felony.
Looks like you're guilty of violating the statute. You can try to plead down to class C misdemeanor, or raise a defense of necessity. In order to have a succesful defense you'd have to show all of the following:
- Leaving the dog on the road caused danger to yourself or others
- You had no adequate alternative (e.g. calling 911)
- Harm caused by your actions was less than harm avoided by leaving the dog
- You didn't create the initial situation